Table of Content
Volume 30 Issue 1
30 January 2006

Research Articles
VARIATIONS IN GRASSLAND VEGETATION COVER IN RELATION TO CLIMATIC FACTORS ON THE TIBETAN PLATEAU
YANG Yuan-He, PIAO Shi-Long
Chin J Plan Ecolo. 2006, 30 (1):  1-8.  doi:10.17521/cjpe.2006.0001
Abstract ( 4780 )   PDF (616KB) ( 1939 )
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To advance our understanding of the effects of climate change on grass land ecosystems, we used a time series (1982-1999) data set of the Normalized Difference Vegetation Index (NDVI) together with historical climate data to analyze interannual variations in grassland vegetation cover and explore the relationships between NDVI and climatic factors on the grasslands of the Tibetan Plateau. The NDVI increased significantly by a ratio of 0.41% a-1 and a magnitude of 0.001 0 a-1 during the growing season (p=0.015). An increase in NDVI during the growing season resulted from both the advanced growing season and accelerated vegetation activity. The largest NDVI increase was in the spring with a ratio of 0.92% a-1 and a magnitude of 0.001 4 a-1. The NDVI increase in the summer was a secondary contributor to the NDVI increase during the growing season with a ratio of 0.37% a-1 and a magnitude of 0.0010 a-1. In the spring, the NDVI increased significantly in the alpine grasslands (alpine meadow and alpine steppe) and temperate steppe (p<0.01; p= 0.001; p=0.002). During the summer, a significant NDVI increase was found in alpine meadows (p=0.027). However, the NDVI increase in alpine and temperate steppe was not significant (p=0.1 06; p=0.087). In the autumn, no significant increase was found in the three gras slands (p=0.585; p=0.461; p=0.143). In the spring, the NDVI increase in three grasslands was corresponded to an increase in temperature. In the summer, the NDVI was related to temperature and sensitive to precipit ation in the spring in the alpine grasslands (alpine meadow and alpine steppe). However, no significant statistical relationship was found between NDVI and climatic factors in temperate steppe. Significant lagged correlations between precipitation and NDVI were found for alpine grasslands (alpine meadow, alpine steppe).

INFLUENCE OF LONG_TERM RICE_DUCK FARMING SYSTEMS ON THE COMPOSITION AND DIVERSITY OF WEED COMMUNITIES IN PADDY FIELDS
WEI Shou-Hui, QIANG Sheng, MA Bo, WEI Ji-Guang, CHEN Jian-Wei, WU Jian-Qiang, XIE Tong-Zhou, SHEN Xiao-Kun
Chin J Plan Ecolo. 2006, 30 (1):  9-16.  doi:10.17521/cjpe.2006.0002
Abstract ( 3220 )   PDF (706KB) ( 1256 )
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Weed infestation is a major threat to rice production, and herbicides have been used extensively to control weeds in paddy fields. However, increasing environmental pressures against herbicide use have led farmers to consider alter native approaches to weed control and more emphases have been placed on the development of ecologically sound weed management strategies. Ducks can be used to control weeds, and rice_duck farming systems, which integrate raising ducks into rice cultivation methods, provide an innovative approach to weed management. Field studies were conducted during 2000-2003 in Danyang, Jiangsu Province, to evaluate the long_term influence of rice_duck farming systems on the structure and dynamics of weed communities in paddy fields, including effects on the populati on density, species richness, species diversity, community evenness and the similarity of weed communities across years. The results showed that under long_term rice_duck farming systems, the density of paddy weeds decreased annually and the trend was best fit by the model, y=k+a•ebx, where the parameter b indica ted the rate of decrease of different weed populations. Of the six main weed species in paddy fields, the population density of  Fimbristylis miliaceae, Lindernia procumbens, and Ludwigia prostrata decreased rapidly, followed by slower decreases in Monochoria vaginalis, Cyperus difformis, and Echinochloa crusgalli . Rice _duck farming decreased the species richness and species diversity in paddy fields, and increased the evenness of weed communities. Compared to weed communities before the introduction of ducks, Sorensen's similarity indices of weed communities in paddy fields decreased every year, revealing that the structure of weed community was changed substantially. Rice_duck farming provided a more diver sified environment for weed growth and seed storage, which greatly limited weed infestation in paddy fields. Consecutive surveys showed that rice_duck farming was an effective control of paddy weeds with more than a 99% overall reduction by the end of the fourth year. Rice_duck farming is an effective and ecologically_ based weed management strategy that has significant economic and ecological benefits.

ACCESSIBILITY ANALYSIS OF URBAN GREEN SPACE IN JINAN
YIN Hai-Wei, KONG Fan-Hua
Chin J Plan Ecolo. 2006, 30 (1):  17-24.  doi:10.17521/cjpe.2006.0003
Abstract ( 3408 )   PDF (610KB) ( 1270 )
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Urban green space is viewed as the last remnant of the nature in urban areas, and usually performs important ecological and socio_economic functions. In addition to protecting biodiversity, absorbing pollutants, and mitigating urban heat island, green spaces also can provide many social benefits such as amenity_recreation venues. Urban green spaces can usually play an important integrative social role if adequately designed and enhance urban livability from a social development perspective. There has been a surge in the concept of “eco_city", “garden city" and “sustainable city", and urban green spaces have become an important indicator of a city's character. Concomitantly, a series of evaluation systems were applied. However, most of these indictor systems lacked any social indicators about societal equity of urban green space. In this research, a quantitative method based on landscape accessibility of green space was put forward to improve the indictor systems. Jinan was chosen as our case study. The basic landscape data were obtained from SPOT satellite images in the years of 1989, 1996 and 2004, and an urban green space map, aroad network map and a watershed map were produced using remote sensing (RS) and geographic information system (GIS). Based on the concept and pri nciple of landscape accessibility, a cost weighted distance analysis (in “Spati al Analyst" module of ARCMAP) was conducted to analyze the accessibility of urban green spaces, public parks and plaza_green space. Finally, the influencing factors for the spatio_temporal change of accessibility were explained in detail. The results showed: 1) The methods used in this research were able to evalua te the distribution pattern and rationality of urban green space. 2) A comparison of urban green space accessibility across the three years indicated a significant overall increase. 3) The spatial pattern of accessibility also changed but still had high degrees of un_equilibrium and un_rationalization. 4) The main reas ons for improved accessibility were increased urban green space area and patch numbers, a more balanced distribution pattern, and the gradually perfected road network. 5) Accessibility was an important indicator to weight the social equity of urban green space, which is an indicator of the satisfaction to all inhabitants. Accessibility is a necessary supplement to the indictor system presently used to evaluate eco_city. Recommendations for urban green space planning were put forth for government officials and planners to help optimize urban green space patterns in Jinan.

LEAF PHENOLOGY OF WOODY SPECIES IN DECIDUOUS BROAD_LEAVED OAK FORESTS IN NANJING AREA, EAST CHINA
ZHU Xu-Bin, SUN Shu-Cun
Chin J Plan Ecolo. 2006, 30 (1):  25-32.  doi:10.17521/cjpe.2006.0004
Abstract ( 2869 )   PDF (643KB) ( 750 )
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Leaf phenology has long been thought to evolve to maximize plant carbon gains, and it reflects plant life history strategies for exploiting resources. Extending leaf life span is of great importance for some species of temperate deciduous forests to gain enough carbon needed for plant survival and persistence , because their growing seasons are repeatedly interrupted by cold winters. Leaf life span can be extended by early leafing, late shedding, or both. To examine which approach was employed to maximize leaf longevity, the phenology of leaf emergence and abscission was investigated for species of two deciduous broad_leave d oak forests in Nanjing area, East China, and the relationships between leaf phenological parameters were analyzed.  The timing of leaf emergence differed greatly among species. The earlier the species leafed out, the earlier the species ended the process of leaf emergence; th eearlier a species leaf began to abscise its leaves, the longer it took to end the process of leaf abscission. Consequently, the leaf abscission for all species was completed within a narrow time period although the start of leaf abscission differed greatly among species. Both correlation analysis and regression analysis indicated close relationships between leaf longevity and the timing of leaf emergence and abscission, in which a longer leaf life span was related to early leafing and late shedding. The timing of leaf emergence seems more important for plant carbon gain than the timing of leaf abscission, assuming that early leafing has advantages over late shedding for carbon gain for the woody species living in the study region. No significant relationship was found between the timing of leaf emergence and leaf abscission indicating that long leaf longevity could be achieved by either early leaf emergence or late leaf abscission. Early leafing is not necessarily correlated to late shedding for the study species.

DISTRIBUTION OF ELEMENTS ALONG THE LENGTH OF DIFFERENT_AGED NEEDLES OF PINUS MASSONIANA AT DINGHUSHAN
KUANG Yuan-Wen, WEN Da-Zhi, ZHOU Guo-Yi, ZHANG De-Qiang
Chin J Plan Ecolo. 2006, 30 (1):  33-39.  doi:10.17521/cjpe.2006.0005
Abstract ( 2681 )   PDF (616KB) ( 819 )
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Chemical analysis of plant tissues, such as in pine trees, is a frequently used method to evaluate the changes of forest health caused by air pollution . Pine needles also have been used widely as bioindicators of atmospheric pollution due to their wide distribution and easy identification. However, the results of whole needle analysis may ignore differences in elemental concentrations in particular needle parts. To date, only limited research has described the concen trations of different elements in various parts of needles injured by pollutants.  Masson pine (Pinus massoniana) is a pioneer species widely spread throughout Southern China. Six separate trees were selected from Dinghushan, Guangdong Province and cut down. The healthy looking current year (C) and previous year (C+1) needles were separated from branches at the upper, middle and lower crown. The needles were cut into three sections, defined as tip section (T), middle section (M) and base section (B), proportional to the needle length. The sheath (S) of each needle_age group also was collected. All parts of the different_aged needles were dried and ground for chemical analysis of the elements, total S, total P, K, Mg, Na, Ca , Al, Mn, Zn, Cu, Fe, Pb, Cr, Cd and Ni. The Ca/Al ratios of each needle compone nt were calculated.  The mean concentrations of the elements in the C+1 needles were higher than in t he C needles, except for total S, total P, K and Cd which were not significantly different, whereas the Ca/Al ratios were lower. The elements were unevenly distributed along the length of the needles. The total S, Na, Ca, Al and Mn did not show significant differences among the different needle sections whereas K, Mg, Zn, Fe , Cr, Ni and the Ca/Al ratios differed statistically among the different sections of the C and C+1 needles. The total P, Cu, Cd and Pb were significantly different among the sections in the C+1 needles only. The element patterns along the needles were mainly caused by air pollution. The needles were under Al stress as determined by the Al concentrations and Al/Ca ratios, especially in the base section. Values of Al and/or Ca/Al ratios in the base of the needle potentially can be used as an early diagnostic index of Al toxicity. Concentrations of Cu and Pb in the area were far above background values for Masson Pine needles implying that excessive heavy metals might damage the needles. Concentrations of Fe, Cu, Pb, Zn, Cd, Ni and Cr in the needle sheath were significantly higher than in the other three sections of the needle suggesting that the needle sheath might be a better bioindicator of those elements than other needle parts. The results of this study and the techniques employed constitute a new contribution to the development of biogeochemical methods for environmental monitoring. These methods may be of value for follow up studies aimed at the assessment of municipal and industrial pollution.

COMPARATIVE STUDIES OF PHOTOSYNTHETIC CHARACTERISTICS IN TYPICAL ALPINE PLANTS OF THE QINGHAI_TIBET PLATEAU
SHI Sheng-Bo, LI Hui-Mei, WANG Xue-Ying, YUE Xiang-Guo, XU Wen-Hua, CHEN Gui-Chen
Chin J Plan Ecolo. 2006, 30 (1):  40-46.  doi:10.17521/cjpe.2006.0006
Abstract ( 3728 )   PDF (657KB) ( 1336 )
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The photosynthetic characteristics of three medicinal alpine plants, Rheum tanguticum, Anisodus tanguticus and Gentiana straminea, were studied and compared to a low land species, Isatis indigotica. The response of net photo synthesis rate (Pn) to intercellular CO2 concentrations (Ci) and photon flux density (PFD) was determined using a LI_6400 photosynthesis system. The photosynthetic pigments and UV_B_absorbing compounds also were determined in the four species in order to evaluate differences in their photosynthetic characteristics. The results indicated that the three alpine plants had relatively low photosynthetic quantum yields (AQY) as compared to the low land species of I. indigotica, and AQY, carboxylation efficiency (CE) and photorespiratory rate (Rp) were the lowest in R. tanguticum. However, Pn did not respond strongly to changes in PFD, which may be due to the high concentration of phot osynthetic pigments and UV_B_absorbing compounds in the leaves. Similar to R. tanguticum, the alpine plant G. straminea also had higher contents of UV_B _absorbing compounds, chlorophyll and carotenoids, but its Rp was higher and Pn was limited by stomatal conductance in response to PFD and Pn was lower. The photosynthetic characteristics of the alpine species, A. tanguticus, was similar to the low land species, I. indigotica, both of which had a high AQY and CE. These results indicated that although there were some differences among the three alpine species, no corresponding characteristics appeared in photosynthetic advancements. The response of Pn to Ci exhibited Pi regeneration limitations after reaching full CO2 saturation. The changes of Rp in the four species were similar to that of maximum Pn in photosynthetic Ci response.

EFFECTS OF ENHANCED UV_B RADIATION ON WATER USE EFFICIENCY, STOMATAL CONDUCTANCE, LEAF NITROGEN CONTENT AND MORPHOLOGICAL CHARACTERISTICS OF SPIRAEA PUBESCENS IN A WARM_TEMPERATE DECIDUOUS BROAD_LEAF FOREST
CHEN Lan, ZHANG Shou-Ren
Chin J Plan Ecolo. 2006, 30 (1):  47-56.  doi:10.17521/cjpe.2006.0007
Abstract ( 2791 )   PDF (885KB) ( 773 )
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Spiraea pubescens, a common shrub in the warm_temperate deciduous forest zone, is distributed in the Dongling Mountain area of Beijing, was exposed to ambient and enhanced ultraviolet_B (UV_B, 280－320 nm) radiation by artificially supplying a daily dose of 9.4 kJ•m-2 for three growing seasons, a level that simulated a 17% depletion in stratospheric ozone. The objective of this study was to explore the effects of long_term UV_B enhancement on stomatal conductance, leaf tissueδ13C, leaf water content, and leaf area. Particular att ention was paid to the effects of UV_B radiation on water use efficiency (WUE) and leaf total nitrogen content. Enhanced UV_B radiation significantly reduced leaf area (50.1%) but increased leaf total nitrogen content (102%). These changes were as sociated with a decrease in stomatal conductance (16.1%) and intercellular CO2 concentration/air CO2 concentration (Ci/Ca) (4.0%), and an increase in leaf tissueδ13C (20.5‰), leaf water content (3.1%), specific leaf weight (SLW) (5.2%), and WUE (4.1%). The effects of UV_B on the plant were greatly affected by the water content of the deep soil (30-40 cm). During the dry season, differences in the stomatal conductance,δ13C, and WUE between the control and UV_B treated shrubs were very small, whereas differences became much greater when soil water stress disappeared. Furthermore, the effects of UV_B became much less significant as the treatment period progressed over the three growing seasons. Correlation analysis showed that enhanced UV_B radiation decreased the strength of the correlation between soil water content and leaf water content,δ13C, Ci/Ca, stomatal conductance, with the exception of WUE that had a significant correlation coefficient with soil water content. These results suggest that WUE would become more sensitive to soil water variation due to UV_B radiation. Based on this experiment, it was found that enhanced UV_B radiation had much more significant effects on morphological traits and growth of S. pubescens than hydro_physiological characteristics. 

CONTRASTING WATER USE STRATEGY OF CO_OCCURRING PINUS_ QUERCUS TREES IN THREE GORGES RESERVOIR
SUN Shuang-Feng, HUANG Jian-Hui, LIN Guang-Hui, HAN Xing-Guo
Chin J Plan Ecolo. 2006, 30 (1):  57-63.  doi:10.17521/cjpe.2006.0008
Abstract ( 3673 )   PDF (635KB) ( 1072 )
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With the rise of water level, the construction of the Three_Gorges Dam may have significant impacts on plant carbon_water relation and ecosystem prope rties in this region. To understand how the plants in this region adapt to the c hanges in water environments, we measured gas exchange, water potential andδ13C of sapling and mature trees of three co_occurring coniferous and dec iduous spec ies: Pinus massoniana, Quercus variabilis and Q. aliena, all are dominant tree species in this region. The two deciduous broad_leaf trees (Q. variabilis and Q. aliena) exhibited higher photosynthetic (Pn) and stomatal conduc tance (Gs) than the evergreen conifer species (P. massoniana). The pre dawn water potential (ψpd) of P. massoniana was lower than that of the two broad_leaf species. Intrinsic water use efficiency (WUEi, Pn/Gs) of P. massoniana was higher than those of Q. variabilis and Q. aliena. However, the differences in carbon isotope ratio (δ13C) of leaves among species, which gives integrative information of WUE in growing seas on period, were not statistically significant. We also compared eco_physiologica l parameters between saplings and mature trees of these three species. The Pn and Gs values of the mature trees were significantly lower than t hose of the saplings. The mature trees showed lower ψpd value, but the difference between the mature trees and the saplings was not statistically significant. However, the WUEi values of all mature trees were significantly higher than those of the saplings. The δ13C values of mature trees showed more positive than those of corresponding saplings, indicating also higher WUE in the mature trees. From these results, we concluded that 1) P. massoniana showed different wa ter use strategies from two Quercus trees species, and 2) the mature trees of these three dominant tree species showed lower photosynthetic rate but higher WUE than those of their corresponding saplings.

LEAF_SCALE DROUGHT RESISTANCE AND TOLERANCE OF THREE PLANT SPECIES IN A SEMI_ARID ENVIRONMENT: APPLICATION AND COMPARISON OF TWO STOMATAL CONDUCTANCE MODELS
LIU Ying-Hui, GAO Qiong, JIA Hai-Kun
Chin J Plan Ecolo. 2006, 30 (1):  64-70.  doi:10.17521/cjpe.2006.0009
Abstract ( 2872 )   PDF (457KB) ( 840 )
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We measured diurnal gas exchange properties of three major species in a semi_arid site, and two stomatal conductance models were then applied to the data. The result indicated that the BBL model and the Gao model could explain on a verage 77.6% and 59.3% of variation in the observed stomatal conductance, respectively. Sensitivity analysis of the models indicated that the BBL model tended to give higher predictions of stomatal conductance than the Gao model. Both models showed similar responses to changes in vapor pressure. The sharp contrast between the two models, however, was that the Gao model responded to changes in soil water stress to different extents. The BBL model coupled with the TJ photosynthesis model was indifferent to increases of soil water stresses, which contradicts concurrent understanding and observations about plant physiology in arid and semiarid regions. Thus the BBL model, even though it provided better explanations of the variations in field stomata data, may not be appropriate for experimental data analysis and ecosystem simulation applications. The analysis using the Gao model indicated that Populus simonii was the least tolerant and resistant to water stresses among the three species studied. Pinus tabulaeformis had both high tolrance and resistance, but stomatal conductance of the pine tree was the least insensitive to changes in soil water stresses. Hence this pine tree may not be good for water conservation under extremely dry conditions. Caragana intermedi a, however, had both larger drought tolerance and larger sensitivity to incremen tal soil water stresses, and thus can provide large stomatal conductance for photosynthesis when soil water stress was low, but reduce water consumption under severe water stresses by decreasing stomatal conductance with increasing soil water stress.

EFFECTS OF NITROGEN ON GRAIN YIELD AND QUALITY IN WHEAT GROWN UNDER DROUGHT OR WATERLOGGING STRESS FROM ANTHESIS TO MATURITY
FAN Xue-Mei, JIANG Dong, DAI Ting-Bo, JING Qi, CAO Wei-Xing
Chin J Plan Ecolo. 2006, 30 (1):  71-77.  doi:10.17521/cjpe.2006.0010
Abstract ( 2918 )   PDF (532KB) ( 967 )
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Soil water stress is a major ecological factor which limits grain quality formation in wheat. Previous studies have mainly focused on the effects of drought or waterlogging and the interactive effects of nitrogen availability and drought on grain quality, while little information is available on nitrogen supply under waterlogging conditions on grain quality. Therefore, the effects of nitrogen levels on grain yield and quality of two different wheat varieties that differ in grain protein content were compared under drought and waterlogging conditions in a pool culture experiment. Three water treatments, waterlogging, drought (45%-50% of field capacity) and moderate water supply (corresponding to 7 0%-80% of field capacity), were maintained from anthesis to maturity. Under each water treatment, two nitrogen levels, 120 and 240 kg•hm-2, were implemented. Both drought and waterlogging significantly reduced 1 000_kernel weight, grain number perear and grain yield in wheat, compared with moderate water supply (CK). Under CK and drought, nitrogen increased grain yield but reduced yield under water logging. Compared with CK, drought increased the contents of protein, dry gluten and wet gluten, SDS_sedimentation volume and falling number, while waterlogging reduced the contents of grain protein, dry and wet gluten. Under the same water treatment, nitrogen increased the protein content, ratio of glutenin to gliadin, amylopectin content and ratio of amylopectin and amylose. Significant interactions between water and nitrogen on glutelin content, amylose content and falling number in the two different wheat varieties were observed. In addition, significant interactions between water and nitrogen on kernel number per spike, contents of albumin and globulin, ratio of glutenin to gliadin, amylopectin content, ratio of amylopectin and amylose and dry gluten in Xuzhou 26' were observed, but no differences in the Yangmai 9' were found. Significant interactions on 1 000 _ker nel weight, total starch content and gluten index in Yangmai 9' were observed, while no differences in Xuzhou 26' were found. The effects of water and nitrogen on grain yield and quality varied with different wheat cultivars. These results established the relationship between wheat grain quality with nitrogen under drought or waterlogging conditions. The results of this study offer insights into techniques for resisting stress and regulating high quality wheat under different ecological conditions.

RICE NITROGEN NUTRITION DIAGNOSIS USING CONTINUUM_REMOVED REFLECTANCE
ZHANG Jin-Heng
Chin J Plan Ecolo. 2006, 30 (1):  78-82.  doi:10.17521/cjpe.2006.0011
Abstract ( 2424 )   PDF (432KB) ( 874 )
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A new method was developed for estimating the nitrogen nutrition of rice using continuum_removed reflectance. The most upper fully expanded leaves and the third fully expanded leaves were sampled during their important growth stages (tiller stage, booting stage and heading stage), and their concentrations of nitrogen and their reflectance measured. The value of the continuum_removed reflectance (550-750 nm) decreased as the nitrogen levels increased. Several properties of the continuum_removed reflectance spectra of fresh rice leaves were calcu lated, including the continuum_removed reflectance value, the minimum of the continuum_removed absorption features, symmetry, total area of absorption peak and left area of the absorption peak. High correlations were found between the spectral properties of the continuum_removed reflectance and leaf nitrogen concentrat ions. Stepwise multiple linear regression was used to select parameters that were most highly correlated with the nitrogen concentration of the leaf samples. Results of this research showed that total area of absorption peak was the best predictor of nitrogen levels in the third fully expanded leaves throughout theird ifferent growth stages (tiller, booting and heading stage). However, for the most upper fully expanded leaves, the significant model parameters included in the model were not always consistent. The basis for this method for diagnosing rice nitrogen nutrition on fresh leaves is not very clearly understood, but this research has demonstrated that continuum_removed reflectance is a feasible method.

ALLOCATION OF PRECIPITATION IN A SUB_ALPINE DARK CONIFEROUS FOREST OF WESTERN SICHUAN USING STABLE OXYGEN ISOTOPES
XU Qing, LIU Shi-Rong, AN Shu-Qing, JIANG You-Xu, WANG Zhong-Sheng, LIU Jing-Tao
Chin J Plan Ecolo. 2006, 30 (1):  83-89.  doi:10.17521/cjpe.2006.0012
Abstract ( 2784 )   PDF (680KB) ( 729 )
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The stable oxygen isotope, δ18O, is a very useful tracer tool to study the impacts of forests on the water cycle. The Wolong Natural Reserve is a key conservation area focusing on the protection of Panda, rare animals and alpine ecosystems. The Wolong Natural Reserve is located in the Mingjiang River headwaters and plays an important role in the conservation of soil and water in this watershed as wel l as the upper reaches of the Yangtze River. Although much research has been conducted on the water cycle, including changes in precipitation intensity, rainfall frequency, runoff dynamics and subsurface flow, little has been devoted to understanding rainfall water allocation in sub_alpine dark coniferous forests. Using a stable oxygen isotope technique, we studied changes in precipitation, throughfall and soilwater flow over time under different rainfall intensities in three plots in a sub_alpine dark conifer forest. The results showed that 1) there were no significant differences between rainfall δ18O and daily precipitation (r=0.612, p≥0.05, n=20). There was a significant linear relationship between the rainfall δ18O and throughfall δ18O defined by the following equations for the three plots: plot A:  y1=0 .970 6 x1 - 2.254 2, R12=0.796 2, p<0.05, F=42.97; plot B: y 2=0.997 6 x2 -1.632 1, R22=0.729 7, p<0.05, F=29.60; plo t C: y3=0.920 3 x3 - 2.728 9, R32=0.729 7, p<0.05, F=26. 47. 2) The δ18O exceeded 0 when precipitation ≥ 3.20 mm, and the maximum δ18O value occurred when precipitation was 12.65 mm due to the interactions between canopy evaporation and precipitat ion. 3) There was l imited soil water flow when rainfall intensity, daily precipitation or rainfall continuity was low resulting in a slow response of the precipitation δ18O signature on soil water. When soil water flow was strong and continuous, the precipita tions δ18O signature showed up rapidly in the soil water flow. The δ18O of soil water showed the same rise and fall patterns o f the rainfall δ1 8O when precipitation was less than 10 mm, but with 4_day time lag. When precipitation was b etween 10 mm to 20 mm, the time lag in the increase in the soil water δ18O occurred 2-3 days after raining, and, when precipitation was from 20 mm to 30 mm, the time lag was only 1-2 days after the rain fall event. The well_developed sub_ alp ine dark coniferous forest could effectively regulate rainfall by delaying the time, and rainfall became part of the subsurface water flow that helping to prevent downs tream flooding. There were no significant differences in the δ18 O between rainf all and throughfall (p=0.491>0.05), but there were a signficant differences between throughfall and soil water δ18O (p=0.025<0.05). T hese results suggest that soil water flow was not directly supplied by the current rainfall event but was supplemented by a pre_rainfall event.

NITRIFICATION AND DENITRIFICATION IN SUBALPINE CONIFEROUS FORESTS OF DIFFERENT RESTORATION STAGES IN WESTERN SICHUAN, CHINA
LIU Yi, CHEN Jin-Song, LIU Qing, WU Yan
Chin J Plan Ecolo. 2006, 30 (1):  90-96.  doi:10.17521/cjpe.2006.0013
Abstract ( 2706 )   PDF (631KB) ( 960 )
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Nitrification is biological conversion of organic or inorganic nitrogen compounds from a reduced a more oxidized state. Denitrification is generally referred as the microbial reduction of nitrate to nitrite and further gaseous forms of nitric oxide, nitrous oxide and molecular nitrogen. They are functionally interconnected processes in the soil nitrogen cycle that are involved in the control of long_term nitrogen losses in ecosystems through nitrate leaching and gaseous N losses. In order to better understand how nitrification and denitrification change during the process of ecosystem restoration and how they are affected by various controlling factors, gross nitrification rates and denitrification rates were determined using the barometric process separation (BaPS) technique in subalpine coniferous forests of different restoration stages. The results showed that the forest restoration stage had no significant effect on gross nitrification and denitrification rates (One_way ANOVA, p<0.05). There were no significant differences in the temperature coefficient (Q10) for gross nitrification rate among all forest types (One_way ANOVA, p<0.05). Gross nitrificati on rates were positively related to water content (p<0.05) but not to soil pH, organic matter, total nitrogen, or C/N ratios. Denitrification rates in all forest soils were low and not closely related to the water content, the pH value, organic matter, or total nitrogen. Nevertheless, we found that C/N ratios obviously affected denitrification rates (p<0.05). Results from this research suggest that gross nitrification is more responsible for the nitrogen loss from soils as compared with denitrification.

SOIL RESPIRATION IN A TROPICAL SEASONAL RAIN FOREST AND RUBBER PLANTATION IN XISHUANGBANNA, YUNNAN, SW CHINA
FANG Qiu-Lan, SHA Li-Qing
Chin J Plan Ecolo. 2006, 30 (1):  97-103.  doi:10.17521/cjpe.2006.0014
Abstract ( 3530 )   PDF (696KB) ( 1026 )
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Xishuangbanna is the most northerly situated tropical rain forest in the world and, as aresult, has remarkable seasonal climate variations, which is different from tropical rain forests in other regions. In Xishuangbanna, the canopy of rubber plantations, Hevea brasiliensis, often form a single layer structure that is different from the multi_layer canopy of tropical seasonal rain forests. The objectives of this study were as the following: 1) to compare the soil respiration characteristics of a rubber plantation and a natural tropical seasonal rainforest using the alkaline absorption technique; 2) to measure seasonal changes in air temperature, soil temperature at 5 cm depth, soil water content and soil respiration rates in two communities; and 3) to evaluate the relationships between soil respiration rates and soil temperature, air temperature, and soil water content. Measurements of soil respiration rates were carried out for one year in a tropical seasonal rain forest in a Nature Reserve (21°57′ N, 101°12′ E) and a rubber plantation (21°56′ N, 101°15′ E). The two sites are about 5 km away near the Xishuangbanna Tropical Botanical Garden in Xishuangbanna, Yunnan. The results showed that there was remarkable seasonal changes in the soil respiration rates in both the tropical seasonal rain forest and rubber plantation with changes in soil temperature at 5 cm depth, air temperature and soil water conte nt. Soil respiration rates of the tropical seasonal rain forest and rubber plant ation were greatest in October (9.24 and 11.06 kg CO2•m-2•d-1, respectively), and lowest in February (4.71 and 5.13 kg CO2•m-2 •d-1, respectively). Soil respiration rates in May, June, July, August, Septemb er and October were higher than those in November, December, January, February, March and April. Soil respiration rates in the rubber plantation were significantly higher than that of the tropical seasonal rain forest (p<0.01). There was a significant correlation between soil respiration rates and soil temperature at 5 cm depth, air temperature, and the correlation between soil respiration rate and soil temperature (r2= 0.87 and r2=0.82, respectively) was higher than that between soil respiration rate and air temperature (r2=0.80 and r2= 0.72, respectively) (p<0.01) for the forest and plantation. There was a significant (p <0.01) correlation between soil respiration rates and soil water content in the forest and plantation (r2= 0.73 and r2= 0.63, respectively). The annual CO2 efflux from the tropical seasonal rain forest and rubber plantation were 2.64 and 2.8 0kg CO2•m-2•a-1, respectively. The Q10 values of the tr opical s easonal rain forest and rubber plantation were 2.16 and 2.18, respectively. The Q10 value of the tropical seasonal rain forest measured by the alkalin e absorpti on method in our study was slightly higher than values measured using the staticopaque chamber and gas chromatography techniques. The Q10 values of the seasonal tropical rain forest and rubber plantation in Xishuangbanna are higher than those reported in other tropical regions.

EFFECT OF SHADING ON THE SENESCENCE OF FINE ROOTS OF FRAXINUS MANDSHURICA SEEDLINGS
XU Wen-Jing, WANG Zheng-Quan, FAN Zhi-Qiang, SUN Hai-Long, JIA Shu-Xia, WU Chu
Chin J Plan Ecolo. 2006, 30 (1):  104-111.  doi:10.17521/cjpe.2006.0015
Abstract ( 2630 )   PDF (717KB) ( 994 )
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Fine root production and mortality play essential roles in carbon allocation and nutrient cycling in forest ecosystems. Despite the ecological importance of fine root turnover and the tremendous research effort on this subject, our knowledge of fine root mortality is still limited because little is understood on processes of fine root senescence. The most important function of fine roots is nutrient and water acquisition from the soil. Thus, to perform this function , carbohydrates fixed in leaves must be transported belowground to build the root system and support their functions, such as root elongation, nutrient and water uptake, and support microbes in the rhizosphere. More recently, studies on root longevity and root orders have found that first_order roots at the distal end of a root system are thinner in diameter and shorter in life_span than higher or der roots. Also, fine root mortality was caused mainly by exhaustion of carbohyd rates, suggesting that carbon allocation to fine roots may be an important factor affecting the senescence and mortality of fine roots. The objective of this study was to answer the following two questions: how does senescence of fine roots with different orders responds to reduced C allocation and what is the sequence of senescence from first_order to higher order roots? This study was conducted in greenhouse on the campus of Northeast Forestry University during growing season from April to October in 2004 using Fraxinus mands hurica seedlings as experimental materials. Three one_year_old F. mandshurica seedlings were planted in each of 30 pots with crop soil in April 2004. At the end of June, two light treatments were carried out. Seedlings in 15 pots were grown under natural sunlight (1 000 µ mol•m-2•s-1) used as controls, and the other 15 pots were completely shaded. After treatments for 30, 60 and 120 d, roots in five pots were carefully excavated, washed and separated into root tips, first_order, second_order and third_order roots. Four physiological indices (i.e. root vigor, concentrations of soluble sugars and soluble proteins, and membrane permeability) were analyzed from the root samples of diff erent orders for assessing the degree of fine root senescence.  The results showed that there was reduced C allocation to the fine roots in the shading treatment that induced reduced root vigor, decreased concentrations of soluble sugars and soluble proteins, and increased membrane permeability, compared with controls. After the 60 and 120 d of shading, root vigor reduced 50% and 95%, soluble sugar concentrations decreased about 74% and 73%, and soluble proteins reduced 5% and 30%, respectively, but membrane permeability increased one_fold after 120 d. These results suggest that reduced C allocation to fine roots caused by leaf shading has great impacts on the physiological functions of fine roots and stimulated root senescence. Root senescence differed significantly among root order: root tips exhibited senescence followed by the first_ and second_order roots, and the third_order roots had the least amount of senescence. As the physiological functions of the fine roots changed, coloration of the roots also changed with the root tips being a dark brown, and the first_, second_ and third_order roots becoming increasing lighter in color. These results indicat that fine roots senesce in sequence explaining why fine roots of the first_order at the distal ends of a root system have a short life_span and rapid turnover.

EFFECT OF ROOT_ZONE HYPOXIA STRESS ON GROWTH AND RESPIRATORY METABOLISM PATHWAY OF MUSKMELON SEEDLING ROOTS
SUN Yan-Jun, GUO Shi-Rong, HU Xiao-Hui, GAO Hong-Bo
Chin J Plan Ecolo. 2006, 30 (1):  112-117.  doi:10.17521/cjpe.2006.0016
Abstract ( 2187 )   PDF (552KB) ( 908 )
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In this paper, two muskmelon cultivars, Xiyu 1' with low hypoxia_resistance and Dongfangxingguang' with high hypoxia_resistance, were used to study the changes in the activities in PDC, ADH, LDH and MDH under hypoxia stress. (DO at 2±0.20 mg•L-1). When seedlings grew to 3rd euphylla, they were cultured in a Hoagland nutrient solution and divided into two sets. One set of seedlings was exposed to normal dissolved oxygen levels (DO) using vigorous aeration to main tain DO levels at 8.0-8.5 mg•L-1, and the other set was treated with hypoxia stress using a DO analyzer (QUANTUM_25) to keep levels at 2.0±0.2 mg•L-1. The results showed that seedling growth of both cultivars were significantly inhibited and the root activity increased under hypoxic conditions. The PDC activity i n roots of both seedlings increased significantly under hypoxia stress, but there were no obvious differences between the two cultivars. The MDH activity in roots of both seedlings decreased significantly under hypoxia stress and the decrease of activity of Xiyu 1' was much more than that of Dengfangxingguang'. The activities of ADH and LDH of both seedlings increased significantly under hypoxia stress. The increase in the activity of ADH in Dongfangxingguang' was more than that of Xiyu 1', while the increase of the activity of LDH in Xiyu 1' was more than that of Dongfangxingguang'. The results suggested that Dongfangxinggua ng' could maintain high levels of aerobic respiration, and ethanol fermentation was the primary pathway of anaerobic respiration under hypoxic stress whereas lactate fermentation was the leading pathway of anaerobic respiration under hyp oxia stress in Xiyu 1'.

EFFECT OF EXOGENOUS SPERMIDINE ON POLYAMINE CONTENT AND ANTIOXIDANT ENZYME ACTIVITIES IN ROOTS OF CUCUMBER SEEDLINGS UNDER ROOT_ZONE HYPOXIA STRESS
LI Jing, HU Xiao-Hui, GUO Shi-Rong, WANG Su-Ping, WANG Ming-Hua
Chin J Plan Ecolo. 2006, 30 (1):  118-123.  doi:10.17521/cjpe.2006.0017
Abstract ( 2433 )   PDF (487KB) ( 952 )
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Polyamines (PAs) have long been recognized to be linked with growth, differentiation, plant senescence and defense reactions of plants to various environmental stresses. However, little is known about their physiological relevance in plants subjected to hypoxia stress. In the present experiment, the effects of exogenous spermidine on polyamine content and antioxidant enzyme activities in seedlings of two cucumber cultivars (Cucumis sativus cv. Zhongnong No.8 and cv. Lübachun No.4) with different resistances to hypoxia stress were investigated. The results showed that under hypoxia treatment, the contents of putrescine (Put), spermidine (Spd), and spermine (Spm) in roots of seedlings of two cucumber cultivars increased significantly in the early period of treatment and then decreased in the later period. Over the entire treatment period, concentrations of PAs were significantly higher than those in the control. Activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) over the treatment period followed the same pattern as PAs. The fresh weight and dry weight of the two cucumber cultivar seedlings were significantly lower than the controls. Exogenous Spd treatment increased the contents of Spd and Spm in roots while decreased the Put content when compared to the hypoxia treatment, enhanced the activities of the antioxidant enzymes, and the fresh and dry weight of seedlings were similar to the controls. Under the same treatment, the activities of the antioxidant enzymes in the roots of the hypoxia_resistant cultivar (cv. Lübachun No.4) were higher than in the hypoxia_sensitive cultivar (cv. Zhongnong No.8). These results indicated that exogenous Spd can change the contents of PAs in the roots of both cucumber cultivars under hypoxia stress, and higher levels of Spd and Spm in roots can enhance both the activities of antioxidant enzymes and the growth of cucumber cultivar seedlings.

TOXIC EFFECTS OF POTASSIUM CHLORATE ON PEANUT GROWTH
LI Hua-Shou, ZHANG Xiu-Yu, ZENG Xiang You, NIE Cheng-Rong
Chin J Plan Ecolo. 2006, 30 (1):  124-131.  doi:10.17521/cjpe.2006.0018
Abstract ( 3161 )   PDF (761KB) ( 1167 )
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Chlorates are a group of oxidizers with strong toxic effects that can cause significant damage to plants. However, chlorates have been used as a non_selective herbicide, defoliant and desiccant. It was found that potassium chlorate can induce flowering in longan (Dimocarpus longan). It has been widely used in longan orchards in recent years, especially in north Thailand and south China, but research has shown that potassium chlorate is toxic to organisms. It can also contaminate soil and water. The aim of this study was to determine the effects of potassium chlorate stress on the growth and physiological response of peanut (Arachis hypogaea). The main method used to induce flower initiation in longan for off_season production is the application of potassium chlorate under the tree canopy. Most research efforts have been devoted to determining the optimum time and amount of application. Little is known about the phytotoxic effects of potassium chlorate on peanut plants, which usually is planted within longan orchards. In this paper, the effects of potassium chlorate on the growth of peanut plants were studied. Usin g the soil culture method, six potassium chlorate treatments were used to assess its effects on seed germination, chlorophyll content, levels of electrolytic leakage (EL), membrane permeability (MP), and activities of nitrate reductase (NR) and catalase (CAT) in peanut seedling leaves, as well as the biomass and number of Rhizobium,  and the transpiration and photosynthetic rates in mature peanut plants. The results showed that: when the concentration of potassium chlorate was higher than 50 mg•L-1, the germination rates of peanut seeds and root lengths were greatly reduced, while the amount of electrolytic leakage and the activity of CAT were increased significantly. When the concentration of potassium chlorate was higher than 50 mg•kg-1 in soil, its phytotoxic effects resulted in a significant increase in MP in seedling leaves, and a decrease in NR, chlorophyll, biomass and the number of Rhizobium, and a reduction in transpiration and photosyn thesis. It can be concluded that soil concentrations of potassium chlorate higher than 50 mg•kg-1 would have a significantly negative effect on the growth of peanut plants.

THE EFFECT OF NUTRIENT SUPPLY ON SEXUAL AND ASEXUAL REPRODUCTION OF THREE SPECIES OF GLOBBA
GAO Xiu-Xia, CHEN Jin, ZHOU Hui-Ping, BAI Zhi-Lin
Chin J Plan Ecolo. 2006, 30 (1):  132-139.  doi:10.17521/cjpe.2006.0019
Abstract ( 2534 )   PDF (662KB) ( 908 )
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Among the three Globba species in this study, Globba barthei and G. schomburgkii propagated only by bulbils and with no seed set while G. racemosa propagated by both seeds and bulbils under natural conditions. The aim of this study was to understand the effect of nutrition supply on the relative levels of sexual and asexual reproduction of these three species in both natural and artificial conditions and to determine whether there is compensatory mechanism that enhances sexual reproduction when asexual reproduction is constrained and vise versa. For G. barthei and G. schomburgkii, young seedlings propagated by bulbils were planted in flowerpots (30 cm in diameter) and placed under a rain and insect proof greenhouse in XTBG. The soil medium in the flowerpots was composed of forest soil (2), coarse sand (2), peat (2) and scattered brick (1). Treatments in the experiment included: 1) high_level fertilizer supply consisted of 150 ml per pot of a 5% mixed fertilizer (N∶P∶K=15∶15∶15) once every two weeks; 2) high_level fertilizer supply (same as treatment (1)) plus removal of flowers buds everyday; 3) high_level fertilizer supply (same as treatment (1)) plus removal of bulbils once a week; 4) low_level fertilizer supply (only water supplied) 5) low_level fertilizer plus removal of flower buds everyday; 6) low_level fertilizer plus removal of bulbils once a week. The results showed that 1) high_level fertilizer supply significantly increased bulbil dry weight ((1.11±0.10) g vs. （3.08±0.69）g, p=0.010 7), bulbil number ((30.58±2.92) vs. (74. 74±9.73), p=0.000 4), bulbil size ((10.5±1.48) mg vs. (53.50±11.42) mg , p=0.001 5) and vegetative organ dry weight ((3.99±0.23) g vs. (9.67±1. 17) g, p=0.000 2) of G. barthei and the bulbil number ((51.74±3.64) vs. (108.71±21.52)，p=0.018 1) of G. schomburgkii; 2) different levels of fertilizer supply did not significantly affect the flower number of the two species (p>0.05); 3) removing bulbils or flowers had no significant effect on the number of flowers or the bulbils in the current year (p>0.05). For G. racemosa,  we collected 30 individuals from six native populations through out Yunnan Province and measured the biomass and size of sexual and asexual organs of each individual. Meanwhile, we collected three soil samples from each of the six populations and analyzed the physical and chemical characteristics of the soil samples. The bulbil size, bulbil number, bulbil dry weight, fruit dry weight, seed number and vegetative organ dry weight among the six populations varied significantly (p<0.001). Bulbil number was positively correlated to vegetative organ dry weight (r=0.901, p<0.05), bulbil dry weight was positively correlated to bulbil size (r=0.849, p<0.05). Fruit dry weight was positively correlated to seed number(r=0.998; p<0.05). A principal component analysis on soil factors of the six populations indicated that the three principal factors could explain 50.58%, 1820% and 11.88% of the total variation. Total nitrogen, available nitrogen and soil organic matter wese the main factors of the first principal component, and the loading values were 0.959, 0.885 and 0.821, respectively. Available phosphorous was the main factor for the second factor with a loading value of 0.824. Vegetative organ dry weight had a significant positive relationship with available phosphorous (r=0.906, p<0.01), bulbil size was positively related to total nitrogen (r=0.798, p<0.05), available nitrogen (r=0.78 0, p<0.05) and soil organic matter(r=0.821, p<0.05). Fruit dry weight and seed number were not significantly correlated to any soil factors. As a whole, the asexual organs of the three Globba plants were more sensitive to different levels of nutrient supply whereas the sexual organs did not show any significant response. Compensatory mechanisms between sexual and asexual reproduction were not detected in these three species.

A PRELIMINARY STUDY ON THE STRESS RESISTANCE OF RHIZOBIA ISOLATED FROM AMMOPIPTANTHUS MONGOLICUS
HE Heng-Bin, JIA Kun-Feng, JIA Gui-Xia, DING Qiong
Chin J Plan Ecolo. 2006, 30 (1):  140-146.  doi:10.17521/cjpe.2006.0020
Abstract ( 2609 )   PDF (621KB) ( 763 )
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Ammopiptanthus mongolicus is an endangered evergreen broad_leaf species in the northwest desert zone of China. Shapotou, Alashanzuoqi, Dengkou and Wulatehouqi were defined as research regions based on soil, water and other ecological factors. Nodules of A. mongolicus were collected during the last twenty_ days of April, which was the flowering period of the host, and their characteristics were studied. The resistance of rhizobia isolated from A. mongolicus also was studied in relation to environmental factors of the distribution areas. Seventeen rhizobia strains were isolated from A. mongolicus. It was found that nodules had various attachment modes, sizes, shapes and colors, which were related to differences of their environment, of which water may be the most important determinant. Several biochemical characteristics were determined, including resistance to salt, acid_alkali, temperature variation and intrinsic antibiotics. The results indicated that 64.7% strains could tolerate NaCl stress at 3% concentration , 94.1% strains could grow at a range of pH from 5-11, and all strains could grow after being exposed to 60 ℃ for 10 min. Differences in resistance to different intrinsic antibiotics existed among strain ZW4, and Wh41 had high a resistance to different intrinsic antibiotics. Rhizobia strains from Dengkou had higher resis tance to acid_alkali conditions and temperature. These results indicated that rhizobia strains isolated from A. mongolicus were highly resistant to stresses . However, there were differences among strains in their resistance to stresses, which might be related to adaptations of rhizobia to the diverse landscapes indiff erent regions. Resistances of rhizobia strains isolated from accompanying plants , for example, Caragana corshinskii, Caragana intermedia and Oxytropis aci phylla, also were studied, and the results indicated that they also were highly resistant to stresses similar to the rhizobia strains isolated from A. mongolicus. These results indicated that the symbiosis between rhizobia and legumes was influenced by their environment. The high resistance of A. mongolicus may be relate d to the high resistance of its rhizobia, and that the symbiotic relation was beneficial to the development and maintenance of its community in diverse landscapes.

SUBPOPULATION GENETIC STRUCTURE IN A PANMICTIC POPULATION AS REVEALED BY MOLECULAR MARKERS: A CASE STUDY OF CASTANEA SEQUINII USING SSR MARKERS
WANG Ying, KANG Ming, HUANG Hong-Wen
Chin J Plan Ecolo. 2006, 30 (1):  147-156.  doi:10.17521/cjpe.2006.0021
Abstract ( 2739 )   PDF (767KB) ( 846 )
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Castanea squinii, an endemic tree widely distributed in China, has great value both for chestnut breeding and in natural forest ecosystems. The spatial genetic structure within and among populations is an important part of the evolutionary and ecological genetic dynamics of natural populations and can provide insights into effective conservation of genetic resources. In the present study, the spatial genetic structure of a natural population of C. sequinii in the Dabie Mountain region, including three subpopulations, was investigated using SSR markers. Nine prescreened SSR loci generated 29-33 alleles and were used for spatial autocorrelation analysis. Based on Moran's I coefficient, a panmictic population of C. sequinii was revealed that lacked spatial genetic structure in the Dabie Mountain region. These results suggested that high pollen flow among subpopulations counteracted genetic drift or genetic differentiation and played an important role in maintaining a random and panmictic population structure in t he region. However, spatial genetic structure was detected in the geographic ra nge of each subpopulation's scale (0.228 km) indicating that spatial genetic structure occurred at a fine scale within each subpopulation. All three subpopulations showed significant fine_scale structure. The genetic variation was not randomly distributed within 61 m in each subpopulation (Moran's I positive valu es). However, although Moran's I values varied among the different subpopulations, Moran's I in all the three subpopulations reached the expected values with an increase in distance suggesting a general patchy distribution in the subpopulations. The fine_scale structure seemed to be influenced by restricted seed dispersal and microenvironment selection. These results have important implications for understanding the evolutionary history and ecological process of natural populati ons of C. squinii and provide baseline data for formulating conservation strategies of Castanea species.

GENETIC DIVERSITY IN FRAGMENTED POPULATIONS OF BERCHEMIELLA WILSONII VAR. PUBIPETIOLATA, AN ENDANGERED PLANT ENDEMIC TO EASTERN CHINA
XU Feng-Hua, KANG Ming, HUANG Hong-Wen, JIANG Ming-Xi
Chin J Plan Ecolo. 2006, 30 (1):  157-164.  doi:10.17521/cjpe.2006.0022
Abstract ( 2348 )   PDF (684KB) ( 933 )
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Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered tree species with a narrow distribution in fragmented habitat patches in Tianmu Mountain, Zhejiang Province and Dabie Mountain, Anhui Province, east of China. The habitat has been severely disturbed because of agricultural practices by local residents. Over the past several decades, there has been a decrease in the population number and size. Information on genetic variation and structure is critical for developing successful conservation strategies for this species . The amplified fragment length polymorphisms (AFLPs) were used to evaluate the genetic diversity and population structure of four extant populations of B. wilsonii var. pubipetiolata. A total of 122 unambiguous bands were gene rated using eight primer combinations of which 45 (36.9%) were polymorphic across all individuals. In comparison with other endangered woody plants, B. wilsonii var. pubipetiolata has similar genetic diversity at the population level (Pp=2 6.4%, Hep=0.162 8) and species level (Ps=36.9%, Hes=0.202 4). A relatively high value of FST (0.193 9) indicated significant genetic differentiation among populations. Analysis of molecular variance (AMOVA) further revealed that 24.88% of the AFLP variation resided between geographic domes (Zhejiang and Anhui Province), 14.71% among populations and 60.42% within populations. The results of this study suggest that habitat fragmentation and reduction of population size caused by anthropogenic activities have caused genetic erosion and population differentiation in B. wilsonii var. pubipetiolata, which poses a potential threat to the long_term survivability of this species. Genetic information obtained in the present study provides useful baseline data for formulating conservation strategies. Conservation management should include both in situ conservation and ex situ conservation programs and need to be well designed. An ex situ conservation strategy for extensive sampling of all extant populations to maximize genomic representation of the species is recommended. 

ALLOZYME VARIATION IN 10 NATURAL POPULATIONS OF PICEA ASPERATA
LUO Jian-Xun, GU Wan-Chun, CHEN Shao-Yu
Chin J Plan Ecolo. 2006, 30 (1):  165-173.  doi:10.17521/cjpe.2006.0023
Abstract ( 2769 )   PDF (716KB) ( 749 )
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Picea asperata is an important tree for the production of pulp wood and timber and a prime reforestation species in western China. P. asperata occurs in the alpine and canyon regions of northwestern Sichuan Province and sout heastern Gansu Province (100°-105° E, 30°-35° N), which are important water self_restraint regions. The genetic diversity of ten populations of P. asperata  in the western part of China was assessed using allozyme analysis by horizontal sliceable starch gel electrophoresis. Seventeen loci (27 alleles) of 8 enzyme systems demonstrated relatively low levels (mean He=0.096) of genetic variation within populations with values of PP=29.41% - 41.18%, AP=1.4 - 1.6 and Hep= 0.06 - 0.131; at the species level, the genetic diversity of P. asperata ( Ps=4 1.18%, As=1.2, Hes=0.138) was lower than the mean value of long_ lived woody angiosperm species (Ps=59.5%, As=2.10, Hes=0.183 ). Genetic diversity is generally the result of long_term evolution. The low level of genetic variation present in P. asperata populations may be due to severe contractions in the area of distribution and population size during the last glacial period. Wrights F statistics analysis indicated that Fis, a measure of deviation from random mating within the 10 populations, was 0.005 suggesting deviation from Hardy_Weinberg equilibrium and a slight (homozygosity) excess in some populations. The higher level of differentiation (Fst=0.311) among populations than those of other long_lived woody plants may have resulted from factors such as habitat fragmentation, introgression from another species, variation in environmental conditions and differing selection pressure. Low level of gene flow (Nm=0.553 9), low level of inbreeding (mean Fis=0.005), and high level of outbreeding (Fis=0.005) could be caused by environmental deterioration and human disturbance, including over_harvesting. There were significantly negative correlations between Fdh_2_B gene and ecological gradient value (r=0.661 1*), as well as between expected heterozygosity (He) and longitude (r=0.683*). It was worth noting that the 10 populations harbored the majority of alleles and had higher genetic diversity suggesting that these populations in particular should be conserved in situ and form population used for tree improvement.

ASEXUAL AND SEXUAL REPRODUCTIVE STRATEGIES IN CLONAL PLANTS
ZHANG Yu-Fen, ZHANG Da-Yong
Chin J Plan Ecolo. 2006, 30 (1):  174-183.  doi:10.17521/cjpe.2006.0024
Abstract ( 3469 )   PDF (765KB) ( 1330 )
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Most plants can reproduce both sexually and vegetatively, and the balance between the two reproductive modes may vary widely between and within species. Extensive clonal growth may affect the evolution of life history traits in many ways. First, in some clonal species, sexual reproduction and recruitment are very low and drop to nil in extreme cases. Variation in sexual reproduction may strongly influence the adaptation to local environments and the evolution of the geographic range. Second, clonal growth can increase floral display, and thus pollinator attraction, while it may impose serious constraints and evolutionary challenges on plants through geitonogamy that may strongly influence pollen dispersal. Geitonogamous pollination can bring a fitness cost for the female and male function in both self_compatible and self_incompatible species. Some co_evoluti onary interactions, therefore, may exist between the spatial structure and the mating behavior of clonal plants. Finally, a trade_off may exist between sexual reproduction and clonal growth. Resource allocation towards the two reproductive modes may depend on environmental conditions, competitive dominance, life span and genetic factors. If different reproductive modes are the adaptive strategies for plants in different environments, we can predict that most of the resources should be allocated towards sexual reproduction in habitats with fluctuating environmental conditions and strong competition, while clonal growth should be dominant in stable habitats. Yet we know little about the consequences of natural selection on the two reproductive modes and the underlying ecological and/or genetic factors that control the balance of the two reproductive modes. It is still unclear whether clonal growth unidirectionally determines sexual reproductive processes or whether the selection pressures arising from sexual reproductive proce sses leads to clonality. Few studies have investigated the reproductive strategies of clonal plants simultaneously both from sexual and asexual perspectives. 

A DISCUSSION ON PLANT DIVERSITY OF TROPICAL MONTANE RAIN FORESTS IN XISHUANGBANNA, YUNNAN
ZHU Hua
Chin J Plan Ecolo. 2006, 30 (1):  184-186.  doi:10.17521/cjpe.2006.0025
Abstract ( 2372 )   PDF (345KB) ( 965 )
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This paper discusses the results of a previously published paper on the plant diversity of the tropical montane rain forests in Xishuangbanna, which was based on six sampling plots. The six plots are from quite different habitats at different altitudes and with conspicuously different physiognomic, floristic and species richness characteristics and actually represent different classificat ion types of vegetation. Based on the vegetation classification of Yunnan sugges ted by Wu (1987), plots I and II, which are dominated by Millettia leptobotrya  (Papilionaceae), could represent a secondary tropical seasonal rain forest in the region. Plots V and VI, which are dominated by species of Lauraceae and Fagaceae, could represent the so_called monsoon evergreen broad_leaved forest, while plots III and IV, which are in the upper montane cloudy zone with dense epiphytic moss plants on the trees, could be a type similar to the mossy evergreen broad_l eaved forest. Some other problems in the data analysis and comparisons of biodiversity among the different forest types in the paper also are discussed. However, the results presented in the paper did reveal some characteristics of plant species diversity along altitudinal gradients in tropical montane forests in Xishuangbanna, but the data could not be used for explaining plant diversity of the particular vegetation type of the tropical montane rain forest in Xishuangbanna , Southern Yunnan.

THREATENED THE NATURAL ECOSYSTEMS IN BEIJING
Chin J Plan Ecolo. 2006, 30 (1):  190-190.
Abstract ( 1325 )   PDF (31KB) ( 809 )
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