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Table of Content
    Volume 28 Issue 5
    30 September 2004
    Research Articles
    XU Zai-Fu, ZHU Hua, WANG Ying-Xiang, YANG Lan, LIU Hong-Mao, YANG Da-Rong, YANG Da-Tong
    Chin J Plan Ecolo. 2004, 28 (5):  585-593.  doi:10.17521/cjpe.2004.0078
    Abstract ( 2982 )   PDF (388KB) ( 1628 )   Save
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    Three fragments of tropical rainforest in Xishuangbanna, southern Yunnan and within the Lower-Lancang/Upper-Mekong River basin, were sampled to investigate species diversity patterns based on comparisons with a contiguous tropical rainforest. Compared with the contiguous forest, the fragments were lower in plant abundance, species diversity indicies, a lower percentage of mega-phaenerophytes, meso-phaenerophytes, chamaephytes and epiphytes, but had a higher percentage of liana, micro-phaenerophytes and mini-phaenerophytes. The floristic composition was also different in the fragments with a greater percentage of pan-tropical and tropical Asia to tropical Africa elements increased, whereas the percentage of regional or local elements decreased. Meanwhile, tree species in the upper canopy layer were more stable than that in the lower layers of the fragmented forest. The animal species diversity and evenness were higher in the contiguous forest than in the fragmented forests, which apparently were due to better habitat size and quality. The relationship between changes in the microclimate of the forest fragments and species changes were also considered. The interior forest of the fragmented forests transformed from a wet-cool to dry-warm microclimate, called the internal effect, and was found to be an important mechanisms accounted for observed species changes.

    LEI Bo, BAO Wei-Kai, JIA Yu
    Chin J Plan Ecolo. 2004, 28 (5):  594-600.  doi:10.17521/cjpe.2004.0079
    Abstract ( 3090 )   PDF (276KB) ( 1523 )   Save
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    Bryophytes on the ground under six types of artificial forests, Picea balfouriana forest (P), Pinus tabulaeformis forest (Y), Pinus armandii forest (H), Larix kaempferi forest (L), Picea balfouriana-Pinus tabulaeformis forest (P-Y) and Pinus tabulaeformis-Pinus armandii forest (Y-H), were investigated in the upper Minjiang River in order to understand the bryophyte composition and synusia structure of these different forest types. In the 19 bryophyte species identified, only 13, 10, 7, 11, 9 and 10 species were present in the P, L, H, Y-H, Y and P-H forests, respectively. Four mosses, Brachythecium glaciale, Thuidium cymbifolium, Entodon concinnus and Eurhynchium savatieri, were common in all six plantations. Another three mosses, Entodon macropodus, Mnium spinosum and Polytrichum formosum, occurred only in the Picea balfouriana forest. The highest frequency of bryophyte occurrence was under the P forest (90%) and the lowest frequency under the H forest (17.65%). Thuidium cymbifolium had the highest frequency (60%) of all species under the P forest, and the second was Brachythecium glaciale (50%). The predominant species, based on the importance value, was Thuidium cymbifolium under the P forest and Brachythecium glaciale, occurred under the other five plantations, which indicated that Brachythecium glaciale was the most common moss species in the study area. In all forests, the P forest had the highest bryophyte diversity (Shannon-Wiener index, species richness index) and the H forest had the lowest diversity. The lowest Simpson index was calculated for the H forest and the highest one for the P forest. The highest similarity index (Sorensen similarity) occurred between the H and Y forests (0.89) and the lowest similarity index between the P and H forests (0.40). The greatest percent coverage (17.79%±1.67%), shoot density ((3 807.11±412.90) shoots•m-2) and thickness ((19.89±1.69) mm) of bryophytes occurred under the P forest, and the lowest values (0.41%±1.49%, (27.99±367.95) shoots•m-2, and (1.80±1.51) mm, respectively) under the H forest. For the Y, L, Y-H and P-H forests, ground bryophyte cover was 5.20%±1.58%, 2.44%±1.58%. 2.73%±1.61%, and 2.71%±1.61%, respectively, shoot density was (623.08±391.71), (566.13±391.71), (253.38±398.41), and (188.69±398.41) shoots•m-2, respectively, and average bryophyte thickness was (9.60±1.61), (14.93±1.61), (9.59±1.63), and (6.69±1.63) mm, respectively. No statistical differences (p<0.05) were found in any of these measures among the Y, L, Y-H and P-H forests. The low bryophyte diversity and limited structure development (density, coverage, thickness) found under all six plantations indicate that, in general, these are poorly developed bryophyte communities. Our results show that the best bryophyte community have developed under the spruce forest with a relatively open canopy and low tree density. Our results suggest that tree thinning or canopy pruning would be an effective measure for improving bryophyte development under dense forests.
    XU Chi, LIU Mao-Song, ZHANG Ming-Juan, LU Xiao-Zhen, WANG Lei, LIU Zhi-Bin
    Chin J Plan Ecolo. 2004, 28 (5):  601-608.  doi:10.17521/cjpe.2004.0080
    Abstract ( 3008 )   PDF (372KB) ( 1476 )   Save
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    We studied 50 years of change in the species composition, abundance, frequency, importance value, population structure and species diversity of secondary subtropical forests in Nanjing Spirit Valley by comparing data collected along the same belt transects in 1951, 1981 and 2002. In general, the amount of stumpage was relatively steady over time, but the spatial heterogeneity increased. The number of under-story seedlings, saplings and shrubs changed significantly, increased from 4 712 in 1951 to 44 130 in 1981, and then decreased to 7 372 in 2002. Both species richness and dominance changed greatly. The number of species decreased from 75 in 1951 to 50 in 1981 and increased to 73 in 2002. The species diversity indices varied but there was no obvious increase or decrease over time. During over 50 years of secondary succession, the dominant species in the masson pine forest, Pinus massoniana, declined over time because of poor regeneration. It was first replaced by intolerant broad-leaved species, such as Pistacia chinensis and Liquidambar formosana, which were then replaced by relatively tolerant species, such as Quercus variabilis. Some evergreen species invaded successfully and were increasing in dominance. Artificial coniferous forests succeeded to coniferous and deciduous mixed forests, then to deciduous forests, and gradually to zonal vegetation —— deciduous and evergreen broad-leaved mixed forests. Communities on good sites were found to have faster successional rates of change.

    HOU Ji-Hua, HUANG Jian-Hui, MA Ke-Ping
    Chin J Plan Ecolo. 2004, 28 (5):  609-615.  doi:10.17521/cjpe.2004.0081
    Abstract ( 2196 )   PDF (337KB) ( 1207 )   Save
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    The population dynamics of major species in a Quercus liaotungensis forest in the Dongling Mountain region, northern China was described based on data from a permanent plot (30 m×40 m) collected over an 11-year period. The age of this forest is about 80 years. The total density of all trees >2 m in height decreased from 1 658 trees•hm-2 (1991), to 1 442 trees•hm-2 (1997) and to 1 400 trees•hm-2 (2002). This decrease in density was mainly due to the death of Q. liaotungensis individuals, which accounted for ca. 75.88%, 72.82% and 67.86% of total density in 1991, 1997 and 2002, respectively. The total basal area increased from 23.48 m2•hm-2 to 27.38 m2•hm-2 over the 11 years, reflecting the growth of surviving individuals. Despite a lack of saplings and new recruits, the Q. liaotungensis had an abundant population of adult trees and exhibited a unimodal size distribution in all three investigations (1991, 1997 and 2002) with no significant differences between them. The patterns of growth, mortality and competition in the Q. liaotungensis population were investigated for individuals>2 m in height, based on the diffusion model. The mortality rate curve, M(t,x), was inverse J-shaped and decreased significantly with DBH up to 10 cm, indicating size-dependent mortality. The mean value of absolute growth rates, G(t,x), was linearly correlated with DBH. The analysis of coefficients in the model and concave relationship of G(t,x) - D(t, x) in Q. liaotungensis population suggested asymmetric intraspecific competition, mainly for the limited light resource due to the relatively high density of the forest. Asymmetric competition might act as a structuring force to maintain the stability of Q. liaotungensis populations and community dynamics.
    HE Zhi-Bin, ZHAO Wen-Zhi, CHANG Xue-Li
    Chin J Plan Ecolo. 2004, 28 (5):  616-622.  doi:10.17521/cjpe.2004.0082
    Abstract ( 2902 )   PDF (297KB) ( 1461 )   Save
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    The modifiable areal unit problem has significant implications for ecological research that involves the use of spatial data. The objective of the present study was to discuss the scale effect and zoning effect by investigating and analyzing the spatial heterogeneity of vegetation communities in the transitional zone between oasis and deserts. Geostatistical techniques were used to evaluate the spatial characteristics of plant communities. The spatial structures of different plant populations were characterized using exponential model variogram parameters, including nugget (C0), range (A0) and sill (C0+C). Two methods were employed to determine the scale effect of spatial heterogeneity: 1) a constant plot area (10 m×10 m) and the sampling area expanded to analyze spatial heterogeneity of plant populations; 2) the plot area was changed for maintaining a constant sampling area to analyze spatial heterogeneity. In addition, the plots at the scale of 500 m×500 m were clustered into nested units of different shapes and directions (10 m×200 m, 20 m×100 m, 40 m×50 m, 50 m×40 m, 100 m×20 m and 200 m×10 m) and analyzed at a resolution of 10 m×10 m to examine the zoning effect. The results showed that the spatial heterogeneity of plant populations in the transitional zone between oasis and desert were influenced significantly by scale and zoning approach. Using sensitivity analysis, we were able to obtain a suitable sampling area and zoning approach to weaken the scale and zoning effects. The scale at which different parameters were sensitive was variable. For example, C0 and C0+C were relatively sensitive at small scales, A0 was affected significantly by changes at larger scales, and C0 and A0 were relatively sensitive to different zoning approaches. In order to gain more representative vegetation information of spatial heterogeneity, the sampling area should be more than 200 m×200 m for Nitraria sphaerocarpa populations, 100 m×100 m for Reaumuria soongorica populations, and a plot area of 20 m×20 m to 30 m×30 m should be feasible.
    YANG Jing-Cheng, HUANG Jian-Hui, PAN Qing-Min, HAN Xing-Guo
    Chin J Plan Ecolo. 2004, 28 (5):  623-629.  doi:10.17521/cjpe.2004.0083
    Abstract ( 2751 )   PDF (320KB) ( 878 )   Save
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    Previous studies have suggested that land use changes affect not only the content of soil organic matter (SOM), but also the chemical composition of SOM. The objective of this study was to confirm this finding at a site in tropical China. To understand the effect of land use changes on the quantity and quality of SOM, spectroscopic characteristics of humic acids from the topsoil (0-5 cm and 5-20 cm) and subsoil (20-40 cm) from a secondary tropical forest, a cropland, and a rubber tree plantation were investigated in Xishuangbanna, southwest China. The cropland had been cultivated for six years following the clearing of a secondary forest, and the 3-year old rubber tree plantation had been established on land that had been cultivated for 3 years following clearing of a secondary forest. Humic acids were extracted using an alkaline solution (0.1 M NaOH), and the extractions analyzed using Ultraviolet-visible spectroscopy (UV-VIS) and Fourier-Transform infrared spectroscopy (FT-IR). Six years after the conversion of secondary forest to cropland, SOM content in the 0-5 cm and 5-20 cm topsoil samples were reduced by 33.6% and 23.7%, respectively. Conversion of secondary forests to rubber tree plantations also greatly reduced SOM content by 28.6% in the top horizon (0-5 cm) and 27.6% at 5-20 cm depth. Comparison of UV-VIS spectra showed that E4/E6 ratios of humic acids from 0-5 cm and 5-20 cm depths in the secondary forest were higher than in the cropland and the rubber tree plantation soils, which indicated that the proportion of aromaticity in humic acids in the secondary forest was lower than the other two ecosystems. FT-IR spectra also indicated that land use change influenced the chemical composition of SOM. The proportion of carboxylic and phenolic groups in the humic acid was higher and the aliphatic and aromatic groups and polysaccharide-like substances were lower in the secondary forest than in the soils from the cropland and rubber tree plantation.

    YANG Jian-Wei, LIANG Zong-Suo, HAN Rui-Lian
    Chin J Plan Ecolo. 2004, 28 (5):  630-636.  doi:10.17521/cjpe.2004.0084
    Abstract ( 2852 )   PDF (358KB) ( 1941 )   Save
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    We studied water consumption and water use characteristics of poplar under three different soil water regimes: adequate soil water, medium drought, and severe drought conditions, which were about 70%, 55% and 40% of field capacity. The results showed that water potential, water content, photosynthesis rate, water use efficiency of leaves, and plant growth rates decreased significantly with decreases in soil water content. At levels of adequate soil water content and medium drought, fast growth and biomass accumulation of poplar occurred during May and June, whereas this occurred during May only under severe drought conditions. Total water consumption and biomass growth were greatest under adequate soil water conditions, decreased under medium drought, and was lowest under severe drought conditions. Total water use efficiency was highest under medium drought conditions and lowest under severe drought. Patterns of water consumption on a daily rate, every 10 days, and monthly rates were different under the three soil water treatments. For all three treatments, the highest monthly water consumption occurred in July and then June. The highest water consumption over a ten-day period was in the second ten days of July, the first ten days of July, and the last ten days of June for the three treatments, respectively. The highest water consumption day of the medium and severe drought treatments occurred one or two months earlier than the adequate soil water treatment. The time of day when the greatest water consumption occurred changed throughout the life span of the poplar and under the differnt soil water treatments.From our results, we conclude that poplar does not have characteristics of drought resistance plants; hence, we do not recommend that this species is planted over a wider range in the loess plateau.

    WANG Hua-Tian, MA Lü-Yi, XU Jun-Liang
    Chin J Plan Ecolo. 2004, 28 (5):  637-643.  doi:10.17521/cjpe.2004.0085
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    Spatial and temporal variations of the soil-plant-atmosphere-continuum (SPAC) water potential gradient and sapwood flow velocity in Pinus tabulaeformis and related factors were measured using a thermal dissipation probe (TDP) and micro-weather station that kept a continuous record of solar radiation, air temperature, air humidity, wind speed and wind direction, rainfall, and soil temperature at the teaching and researching station of Beijing Forestry University in West Mountains of Beijing in April 15-24, 2001. The results showed that soil humidity declined in the top layer soil and declined only to a small extent in the deep layer soil. Following a simulated rain event of 47.77 mm, surface soil water potential increased abruptly and water potential in the mid-layer soil increased after 2 days later but decreased and approached that of the control gradually due to wood evapotranspiration. Compared to the large water fluctuation in the surface and mid-layer soil, diurnal water potential in deep soil had stable daily fluctuations. The water potential of the SPAC elements decreased gradually from the soil to air. The soil-leaf-air water potential gradient of the rain treatment increased to 1∶15∶90 as compared to 1∶5∶30 of the control. Water potential differences of the leaf-soil, air-leaf and air-soil also increased after watering. The daily water potential of the SPAC elements declined gradually after a long drought period and declined in the following order: air>leaf>soil. The lowest daily leaf water potential occurred at 14∶00 pm, 4 hours earlier than the soil. The lowest air water potential occurred at the same time. Air temperature was the dominant environmental factor affecting air and soil water potential, and relative humidity of the atmosphere and soil moisture were the most important factors affecting leaf water potential. There were significant correlations between the surface soil and leaf water potentials the surface soil and air water potentials both for the treatment and control. Daily sapwood flow velocity (SFV) fluctuated in accordance with variations in the water potential of the SPAC elements and meteorological factors. Significant correlations were found between SFupper and 50 cm deep soil water potential, wind speed, solar radiation intensity, air humidity and air temperature, SFlower and soil temperature between 10-50 cm, wind speed, air humidity and air temperature for control, SFupper and wind speed, solar radiation intensity, air humidity and air temperature, SFlower and soil temperature between 10-50 cm for watering treatment. Correlation coefficients between SFV and the water potential of the different SPAC elements decreased with watering.
    LI Xiang-Yi, ZHANG Xi-Ming, HE Xing-Yuan, ZENG Fan-Jiang, THOMAS F. M., FOETZKI A.
    Chin J Plan Ecolo. 2004, 28 (5):  644-650.  doi:10.17521/cjpe.2004.0086
    Abstract ( 2701 )   PDF (374KB) ( 1492 )   Save
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    The southern rim of the Taklimakan Desert is the most arid region in central of Asia where mean annual precipitation is less than 40 mm and the potential evaporation is about 2 600 mm. The Qira (Cele) oasis is located in this region, and the perennial tree, Tamarix ramosissima is the dominant and most important indigenous species that grows along the margins of the Qira oasis. Besides sheltering the oasis against wind blown sand, this species is used by local people as construction material for houses and fences and as a fuel source. In view of large population increases in Qira, the maintenance of the vegetation belt by T. ramosissima is of high ecological and economical importance. Generally, water is the limiting factor that restricts vegetation regeneration and restoration in desert areas, and investigations into the water relations of plants can provide valuable information on the capability of plants to cope with the harsh conditions. Moreover, it can also provide information on how to restore and regenerate vegetation in the arid lands surrounding the oases. Therefore, the objectives of our investigation were as follows: 1) To assess the status of drought stress in T. ramosissima during the growing season; 2) To assess the importance of physiological and morphological features in acclimatization and adaptation to this extreme environment; and 3) To investigate the response of the water status in T. ramosissima to a single irrigation event in the summer that imitated natural flooding. In order to achieve these goals, water-relation parameters of twigs were derived from pressure-volume curves (PV curves) measured each month from April to October using a pressure chamber. In addition, the daily course of twig water potentials, including predawn potentials, were measured using a pressure chamber. The effect of flooding on soil water content was monitored using Time Domain Reflectometry (TDR) with sensors at five different soil depths. An automatic weather station was installed and climatic variables were recoreded continuously. The results showed that T. ramosissima was able to balance water deficits that developed during the day and maintained nearly constant and rather high predawn water potentials during the growing season. Except for one measurement, the water and osmotic potentials decreased only moderately during the growing season, and this seemed to be an endogenous process that was not caused by drought stress. T. ramosissima did not show any physiological adaptations to drought stress; the rapid decreases in osmotic potential and increased apoplastic water, incipient plasmolysis at relatively high water content and very small differences in osmotic potential are not characteristic drought responses. T. ramosissima depends on having a constant water supply to cope with the extremely high water pressure deficits and the relatively high evaporative demand of its environment which it obtains by maintaining contanct with deep water sources through the production of an extensive root system. Hence, a single artificial flooding event had no effect on plant water relations. Since T. ramosissima depends on ground water availability, the long-term survival of this species at the Qira oasis will require that the ground water table is maintained at a depth that can be accessed by the roots of T. ramosissima. The water and osmotic potentials of T. ramosissima were higher than those of typical desert plants and were more similar to mesophytic plants. The primary mechanism of T. ramosissima to cope with arid environments is through drought avoidance.

    YANG Qi-He, GE Xue-Jun, YE Wan-Hui, DENG Xiong, LIAO Fu-Lin
    Chin J Plan Ecolo. 2004, 28 (5):  651-656.  doi:10.17521/cjpe.2004.0087
    Abstract ( 3304 )   PDF (269KB) ( 1679 )   Save
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    The rare and endangered plant, Ammopiptanthus nanus is the only evergreen broad leaved plant in Xinjiang listed as a Category 1 National Protected Plant. It is a xerophytic relict species of the subtropical evergreen forests of the Tertiary and found only in the arid Tarim Basin. Previous studies have examined the anatomical characteristics and drought-resistant mechanisms of this species. In this paper, we examined seed characteristics, including germination in relation to temperature and various light regimes duration of storage, seedling emergence and survival rate in relation to soil moisture content (MC) and seeding soil depth, and effects of a fungicide treatment. Our results showed that Ammopiptanthus nanus seeds were dispersed only short distance from the parent plants due to their morphological characteristics and high predation rates. the seed germination rate reached 38% in seeds stored for 60 d at ambient temperature (AT) of 18 - 32 ℃. The dried and ripened seeds of this plant often had impermeable seed-coats, and only 33.33% of the dried seeds with 7.68% MC absorbed water and swelled up after soaking for 90 h at 30 ℃. Seed germination did not require illumination. Germination percentage (GP) was above 80% when seeds were incubated for 9 d at 15 ℃, 20 ℃, 25 ℃ , 30 ℃, 20/30 ℃ and AT, and seeds germinated most quickly at 30 ℃. The seedling emergence rates were greater than 75% when seeds were buried in 1-2 cm depth below the surface of sandy soil. Seedling emergence rates decreased with increasing soil depth and were less than 20% at 6 cm soil depth. The most suitable MC of sandy soil for seedling emergence was 19.35%-28.75%; when soil MC was above 32.43% or below 3.85%, few seedlings emerged. After seed storage for 210 d at 10 ℃ and 5 ℃, MC of 19.36%, 10.64% and 7.68% had no significant effect on GP, but GP decreased significantly at AT and 35 ℃. The decreasing GP rate had a significantly positive correlation with seed MC or storing temperature. When sowing seeds and nursing seedlings in soils of 7.41%, 13.79% and 28.75% MC, the seedling mortality rates were 77.49%, 81.25% and 89.49% respectively. When seeds were treated with triadimefon, mortality rates were still as high as 50.27%, 69.53% and 76.03% in the three soil MC treatments, respectively. The seedling mortality rate had significant positive correlation with sandy soil MC.

    WU Jian-Guo, ZHANG Xiao-Quan, XU De-Ying
    Chin J Plan Ecolo. 2004, 28 (5):  657-664.  doi:10.17521/cjpe.2004.0088
    Abstract ( 2790 )   PDF (284KB) ( 1639 )   Save
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    Soil carbon is a large component of the global carbon cycle, and the influence of land-use changes on soil carbon pools can significantly affect atmospheric CO2 concentrations. Labile soil organic carbon (LSC) is the fraction of soil organic matter that is most sensitive to changes in land-use. Over the last several centuries, extensive areas of native vegetation in the Liupan Mountain Forest Zone have been converted to croplands and rangelands and, in last several decades, some of these former croplands and rangelands have returned to forests. The impacts of these land-use changes on soil organic carbon (SOC) are unclear. In order to assess the impacts of land-use change on LSC, we compared the LSC concentrations in adjacent plots of secondary forest (i.e. dominated by Quercus liaotungensis, Populus davidiana, or brushwood), cropland, rangeland, and 13, 18, and 25-year old larch (Larix principis-rupprechtii) plantations that were planted on former croplands and rangelands. All plots were the same elevation, exposure and soil type. The LSC concentrations were determined using a KMnO4 (333 mmol•L-1) oxidation technique. It was found that the mean content of LSC in 0-110 cm deep soil layer was 60% lower under cropland (0.605 gC•kg-1) and 36% lower in rangeland (0.973 gC•kg-1) than under the secondary forest (1.612, 1.68 and 1.325 gC•kg-1 for the brushwood, Populus davidiana and Quercus liaotungensis forests, respectively). LSC was 129% and 29% higher under the plantations (1.127, 1.520 and 1.523 gC•kg-1 for the 13, 18 and 25-year old Larix principis-rupprechtii plantations, respectively) than under the cropland and rangeland respectively. The change of LSC content with soil depth was greater under the secondary forest and plantation than under the cropland or rangeland. The difference of LSC content between secondary forest and rangeland or cropland was greater in the 0-70 cm depth than in the 70-90 cm deep soil layer, whereas differences in LSC content between the plantations and rangeland or cropland was greater in the 0-50 cm than 50-110 cm soil layer. The mean fraction of LSC in the 0-110 cm soil layer was 11% lower under cropland (0.087) and 4% lower under rangeland (0.094) than under the secondary forest (0.098, 0.099 and 0.099 for brushwood, Populus davidiana and Quercus liaotungensis forests, respectively). The mean LSC fraction was 13.3% and 5.3% higher under the plantations (0.103%, 0.093% and 0.101% for the 13, 18 and 25-year old Larix principis-rupprechtii plantations, respectively) than under the cropland and rangeland, respectively. The change in the LSC fraction with soil depth under cropland was greater than for all other land use types. The difference in the LSC fraction between secondary forests and rangeland or cropland was greater in the 0-20 cm and 70-110 cm than the 20-70 cm soil layer, whereas the difference in the LSC fraction between the plantation and rangeland or cropland was greater in the 0-110 cm soil layer. In general, the differences in LSC among the different land use types and changes with depth were greater for the content of LSC than the LSC fraction. Differences in LSC among the different land use types are attributed to differences in the inputs, stabilization and quality of soil organic matter, and the distribution of roots among the different land uses. The results of this study indicate that the LSC content and fraction will decline if natural secondary forest are converted to cropland or rangeland but will increase with afforestation of croplands or rangelands. In addition, the distribution of the content or fraction of LSC within the soil profile will change with changes in land use, but the change in the LSC fraction is smaller than the chaoge of the LSC content.

    PAN Qing-Min, BAI Yong-Fei, HAN Xing-Guo, YANG Jing-Cheng
    Chin J Plan Ecolo. 2004, 28 (5):  665-671.  doi:10.17521/cjpe.2004.0089
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    An important grassland ecosystem management strategy is the application of nitrogen fertilizer; however, the fate of applied nitrogen is highly correlated with risks and benefits associated with the fertilization of grasslands. The fate of nitrogen tracers applied to a typical Inner Mongolia steppe ecosystem has not been studied previously. We examined the fate of 15N-labelled fertilizer in a Leymus chinensis site at the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. The results showed that after one growing season an average of 31.61% (range from 25.33% to 38.65%) of the applied 15N was recovered in the plant pool. 15N recovered by aboveground and belowground organs significantly increased with increasing nitrogen rates suggesting that nitrogen fertilizer significantly affected the recovery of 15N by plants. About 2.92% (range from 2.58% to 3.16%) of the applied 15N was recovered in the litter, with the percent 15N in the belowground litter significantly higher than in the aboveground litter pool. About 36.16% of the labelled nitrogen was retained in the soil pool, mostly in the 0-40 cm soil layer. 15N retained by the soil increased significantly with increases in the nitrogen application rate. The loss of 15N was about 21.77%-43.38% of the labelled nitrogen. Risk/benefit analysis showed that, under the climatic and soil conditions prevailing during this experiment, fertilizer application rates of 5.25 g N•m-2 and 28 g N•m-2 were associated with high risk/benefit ratios, whereas the 17.5 g N•m-2 fertilizer treatment achieved the lowest risk/benefit ratio among the nitrogen rate treatments. These results provide a reference for future grassland ecosystem management strategies.

    YANG Tie-Zhao, YIN Quan-Yu, DING Yong-Le, ZHANG Yu-Mei
    Chin J Plan Ecolo. 2004, 28 (5):  672-679.  doi:10.17521/cjpe.2004.0090
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    Changes in stoma density and stomatal conductance of 10 tobacco (Nicotiana tabacum) genotypes and its relationships to weather-fleck caused by ozone were studied in controlled field experiments in 2001 and 2002. Under controlled growing conditions in 2002, changes in the activities of 3 antioxidant enzymes in leaves of 5 genotypes were analyzed in relation to the degree of ozone injury following a combined treatment of ozone and low temperatures (10 ℃). The results showed that there were significant differences in leaf resistance to ozone injury among genotypes. Stoma density and stomatal conductance on the lower epidermis of tobacco leaves were related to weather-flecks caused by ozone. The lower leaves on the plants were especially sensitive to ozone injury. Correlation coefficients between stoma density and weather-flecks and between stomatal conductance and weather-flecks were 0.65 -0.68 and 0.80-0.87, respectively. Therefore, it is proposed that stoma density and stomatal conductance of the lower leaves on tobacco plant be used as a selection marker for disease-resistance breeding. The results of controlled experiments showed that ozone combined with low temperatures of 10 ℃ induced weather-flecks in leaves of 5 flue-cured tobacco genotypes. The activity of SOD increased in ozone-injured leaves and increasing SOD activity was negatively correlated to the weather-fleck index. Activity of CAT was slightly enhanced but activity of POD decreased remarkably. Activity of antioxidant enzymes was low and hence weather-fleck injury was great in tobacco genotypes with little resistance to ozone, whereas when the activity of antioxidant enzymes was high in genotypes, there was strong resistance to ozone injury. The results indicated that ozone combined with low temperatures of 10 ℃ markedly affected active oxygen-scavenging systems in tobacco leaves caused by an imbalance in activities of 3 antioxidant enzymes. Sharp decreases in POD activity might be one of the major reasons why leaves were injured by ozone, whereas increases in the activities both of SOD and CAT helped to protect against ozone injury.

    FAN Xue-Mei, JIANG Dong, DAI Ting-Bo, JING Qi, CAO Wei-Xing
    Chin J Plan Ecolo. 2004, 28 (5):  680-685.  doi:10.17521/cjpe.2004.0091
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    Drought occurs frequently in northern and waterlogging is common in southern China during the grain filling period and can sometimes last throughout the entire wheat growing season. Depending on the duration of soil drought or waterlogging, the quality of grain formation in wheat can be significantly affected. Previous studies have focused on effects of either drought or waterlogging on grain quality. Therefore, the present experiment was conducted to investigate the simultaneous effects of both soil drought and waterlogging treatments after anthesis on the quality of grain in two wheat genotypes, ‘Xuzhou 26’ and ‘Yangmai 9’, which differ in grain protein content. Three water treatments were utilized from anthesis to maturity: drought (45% to 50% field capacity), waterlogging and moderate soil water status (70% to 80% field capacity). Compared to controls, both waterlogging and drought treatments reduced grain yields and protein yields. The post-anthesis drought increased the protein content of gliadin, whereas waterlogging reduced the accumulation of protein in the grain. Total starch and amylose content in the grain were the highest under waterlogging treatments while the amylopectin content was the highest with CK. Drought increased the content of wet and dry gluten, SDS-sedimentation volume and falling number, whereas waterlogging reduced processing quality of the wheat grain. Drought and waterlogging had different effects on grain protein content, starch content and composition, and flour quality, and thus had different impacts on the quality of wheat. For the strong-gluten wheat cultivar ‘Xuzhou 26’, moderate soil water deficit improved grain quality, whereas for weak-gluten wheat ‘Yangmai 9’, relatively high soil water content favored the quality of grain produced. These results contribute to our understanding of the mechanisms that control the quality of wheat grain produced under soil water stress (drought and waterlogging) and provide a theoretical basis for the production of high quality and high yield wheat.

    XU Fu-Xian, ZHENG Jia-Kui, ZHU Yong-Chuan, WANG Gui-Xiong, Yang Da-Jin, LIU Kang
    Chin J Plan Ecolo. 2004, 28 (5):  686-691.  doi:10.17521/cjpe.2004.0092
    Abstract ( 2390 )   PDF (213KB) ( 1253 )   Save
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    In the eastern and southern districts of Sichuan Province, grain yields of hybrid midseason-rice varieties have been increased, but its grain quality remains very poor. In particular, the head rice percentage is low and chalkiness is high due to high air temperatures that occur 0 to 20 days after full heading. Although many studies have examined the effects of cultivation factors on grain quality, few improvements in grain quality have been made in these special districts. This paper explores the effect of super sparse cultivation on head rice recovery and chalkiness in hybrid rice varieties and provides a theoretical and practical basis for the cultivation of high quality rice. The experimental design consisted of three hybrid rice varieties (‘II you 7’,‘Shanyou 63’ and ‘Xiangyou 2’) planted at six different densities, where the hill was removed at full heading and N applied on different days after full heading in a randomized block design with 3~4 replications. Using analysis of variance and correlation analysis, the results indicated that there were highly significant negative correlations between planting density and the percentage of head milled rice and highly significantly positive correlations between plant seedling density and the chalky percent. When super sparse cultivation was at 7.51×104 hill•hm-2 with 150-210 kg N•hm-2, the grain yield was equal to CK (21.64×104 hill per hm2 with 150 kg N•hm-2), but the percentage of head milled rice increased by 15.69% to 22.92%, and the chalky percent decreased by 16.34% to 21.22%. The increase in grain quality in super sparse cultivation was due to an increase in the number of spikelets per panicle, a decrease in the weight of leaf per grain at full heading, and reduced grain filling rate; hence, the percentage of head milled rice and chalkiness were improved. Additionally, the seed setting rate and the percentage of head milled rice in super sparse cultivation were increased by applying N 20 days after full heading.

    L Chao-Qun, SUN Shu-Cun
    Chin J Plant Ecol. 2004, 28 (5):  692-703.  doi:10.17521/cjpe.2004.0093
    Abstract ( 2918 )   PDF (380KB) ( 2866 )   Save
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    Terrestrial ecosystems are a large carbon density and play an important role in the global carbon budget and mitigating global warming by carbon sequestration. To encourage additional carbon sequestration and storage in global vegetation and soils, we need to be clear about the distribution patterns of carbon density and the factors that influence these patterns. Therefore, the characteristics of the distribution patterns of carbon density in terrestrial ecosystems of the world and China are reviewed in this paper. At the global scale, the distribution of carbon in vegetation corresponds with the spatial pattern of biomass and generally decreases from low-latitude to high-latitude with the exception of boreal forests. In contrast, soil organic pools of carbon increase along the same gradient. The largest stores of carbon in biomass are in tropical and boreal forests, and the largest stores of soil carbon are in the high latitude ecosystems (boreal forest and tundra). Total carbon density of both vegetation and soils are highest in tropical and boreal forests. In the tropics more carbon is stored in vegetation than in soils, while in the boreal region far more carbon is stored in the soils. At the regional scale, these patterns might vary due to differences in climate, topography and human influence among regions. Several major factors, including climatic conditions, soil nutrients, biodiversity, climate and atmospheric CO2 changes, land use and cover changes, all contribute to the storage and maintenance of carbon. For example, carbon density will be high in regions where temperature and precipitation are favorable for abundant plant growth. The enhanced carbon sequestered in response to elevated levels of CO2 or nitrogen, or their combination, is less in species-poor than in species-rich regions. In a word, they can raise the carbon density in terrestrial ecosystems by directly or indirectly accelerating net primary production, or constraining respiration and decomposition. However, in spite of its great significance for explaining the present distribution patterns of carbon pools and estimating future changes, the mechanisms by which these processes occur are not fully understood. It is critical that we strengthen our research effort in this area of study. Although a great deal of effort has been put into the carbon density researches, there still remains much uncertainty regarding data collection, mechanistic explanations, and model construction in the relevant studies. In the future, we should establish a standardized and unified system to estimate carbon density, produce more accurate and useful models, and perform integrated studies at multi-scales and multi-resolutions levels.
    MEI Li, WANG Zheng-Quan, CHENG Yun-Huan, Guo Da-Li
    Chin J Plant Ecol. 2004, 28 (5):  704-710.  doi:10.17521/cjpe.2004.0094
    Abstract ( 2830 )   PDF (289KB) ( 2495 )   Save
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    Fine root is a critical determinant of root turnover and therefore carbon (C) and nutrient flow in terrestrial ecosystems. Despite the ecological importance of fine root longevity and the tremendous research efforts devoted to it,the understanding of fine root longevity and turnover is still rudimentary. This article reviews some of the most important factors that control fine root longevity,including carbon allocation,fine root structure,soil nitrogen (N) and water availability,soil temperature,and soil biota in forest ecosystems,with the purpose of providing a brief summary of recent advances in fine root longevity research and to point out the gaps of understanding and directions for future root longevity research in China.The most important function of fine roots is resource acquisition from the soil. To perform this function,C fixed in leaves must be used to build the fine root biomass and to supply energy needed for root growth,resource uptake,and maintenance of the fine roots. Consequently,C availability to roots may exert strong control over root longevity,and the interactions between C source (leaves) and C sink (roots) has been postulated as a mechanism through which root longevity may be explained. However,due to the lack of experimental evidence,the mechanisms by which C is allocated to roots and how C availability in roots controls root longevity remains poorly understood. Detailed studies on C allocation and utilization in processes such as root growth and root respiration (in growth and maintenance) are needed.In addition to physiological controls of root longevity (e.g.,C availability),structural characteristics of root systems also have a strong influence over root longevity. Recent studies showed that both root diameter and branching order were important regulators having shorter lifespans and turn over more rapidly than larger diameter,higher order roots. These findings are likely to contribute greatly to a more accurate quantification and prediction of C and nutrient flow via root turnover. The efficiency model,which suggests that the mortality of fine roots may occur when the C costs of plant roots exceed the benefits (e.g.,nutrient acquisition) they provide,also has been invoked to explain root mortality and longevity. This model necessitates that root longevity is closely related to resource availability in the soil. Some evidence suggests that roots in resource rich sites live longer,while others suggest the opposite. Much of the controversy may result from different methods used in estimating fine root longevity and turnover,and differences in C sink-source relationships among different species,stand development,as well as the length of the experiments in which the influence of resource levels on root longevity are tested. Climatic factors also influence root longevity. Fine root longevity appears to be the longest in cold environments with marked seasonal variations in seasonal environments. However,most recent evidence suggests that root longevity may be more dependent on root structure than on root environment,with first order roots having similar longevity regardless of differences in species and the root environment.Finally,ecosystem-scale processes,such as environmental stresses and pathogen and herbivory pressure,may also influence root longevity. Drought and high temperatures may shorten root longevity. However,because soil moisture,temperature,leaf C fixation,and soil resource availability are tightly linked,independent tests of moisture and temperature influences on root longevity are difficult to conduct. Evaluating the regulation of herbivores and pathogens on root longevity is also difficult,in part because little quantitative information is available on the populations of root pathogens and herbivores in different ecosystems and the responses of root systems to different levels of pathogen and herbivory pressure. In sum,root longevity is a critical but difficult research subject. There are many opportunities as well as challenges for future root longevity research in China,of which we list only a few: 1) C allocation and C utilization in fine roots may be a primary mechanism controlling root longevity,but,to understand this mechanism fully,the methods for accurately estimating C allocation and utilization in roots of different structural and functional characteristics must be developed first;2) Root longevity is clearly related to soil resource availability (e.g. N and moisture) and environmental factors (e.g.,soil temperature and moisture),and further studies on the impact of these factors on the longevity of individual roots and root systems as a whole may prove fruitful. Studies in this area should be large-scale and long-term to encompass large environmental variability frequently observed in natural ecosystems and to provide relevant information for a better understanding of the belowground

    YIN Chun-Ying, PENG You-Hong, LUO Jian-Xun, LI Chun-Yang
    Chin J Plant Ecol. 2004, 28 (5):  711-722.  doi:10.17521/cjpe.2004.0095
    Abstract ( 2300 )   PDF (472KB) ( 2337 )   Save
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    Conservation of biodiversity is a major issue of concern within the international community, and genetic diversity, the basis of species diversity and ecosystem diversity, is an important research area. Populus is planted widely throughout the world, and understanding its genetic diversity is critical for both theory and application. To date, the genetic diversity of Populus has been studied at different levels of organization: phenotype, chromosome, protein and DNA. 1) Phenotype diversity. Studying the morphology or phenotypic diversity of trees is the easiest and oldest method to measure genetic diversity. Phenotypic diversity is expressed in the size of the population, morphology, phenology, wood properties and tolerance to biotic or abiotic stress. 2) Chromosome polymorphism. Chromosomes are the carriers of genes, and their variation must lead to the variation of biological organisms and thus play an important role in evolution. Diversity of chromosomes includes both the number and structure variation. For Populus, the natural triploidy is found in P. tomentosa, P. bolleana, and the tri/aneuploid hybrid is found in the lager population of P. trichocarpa×P. deltoides hybrids, but chromosome structure variation is not found. 3) Protein polymorphism. Most studies focus on the isozyme. The method of isozyme e1ectrophoresis, a popular method for examining genetic diversity, is used to examine the genetic diversity of Populus and the characters or differentiation of clones or varieties. 4) DNA polymorphism. Genetic messages result from the sequencing of DNA, so analyzing DNA directly is the best method for studying genetic diversity. The DNA molecular markers, RFLP, RAPD, AFLP and SSR, have been applied to the study of Populus. Based on the objectives of a study, different types of plant DNA (nDNA, cpDNA and mtDNA) are used. Using molecular markers, the origins and evolution of Populus have been studied. This paper reviewed the progress in research on the genetic diversity of Populus. The results show that the genetic diversity in sections, populations and clones of Populus is high and related to its origins, large number of species and broad global distribution. Because genetic diversity controls evolution rates of biological adaptation and is the basis of breeding and conservation biodiversity, we suggest research in the following areas: 1) combine the study of population genetic structure and differentiation with studies of the conservation and utilization of Populus; 2) construct the gene pool of Populus; 3) develop breeds of fast-growing and stress tolerant Populus.

    YANG Juan, LIU Li-Juan, GE Jian-Ping, DING Yi, TAN Ying-Chun
    Chin J Plant Ecol. 2004, 28 (5):  723-726.  doi:10.17521/cjpe.2004.0096
    Abstract ( 2627 )   PDF (173KB) ( 1250 )   Save
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    Canopy gap disturbances are important processes that maintain forest structure and diversity. We investigated the distribution and characteristics of canopy gaps in Wolong Nature Reserve around Wuyipeng, Sichuan. The results showed that small-scale gaps were the predominant types of disturbance. The average gap density was 12.5 km-1. The distribution pattern of gaps was aggregated on south facing slopes and was approximately homogeneous on north facing slopes. Conifer trees were the primary gap-makers in this forest that was dominated by Abies faxoniana, Tsuga chinensis, Betula utilis, both in abundance and diameter rank. The decay class distribution of gap-makers indicated that the mode of gap formation and gap-maker species changed with age of the forest; the contribution of conifer species to gap formation decreased with time and broadleaf species increased. Moreover, the proportion of gaps caused by cutting and tree falls decreased while the proportion caused by standing dead and broken trunks increased. Association analysis of the mode of gap formation showed that there were significant negative associations between trees that were cut and tree falls and between snapped trunks and tree falls. Association coefficients for trees that were cut were relatively high with all other modes of gap formation, but there were no other significant associations between other modes of gap formation.

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