An ecological regionalization system was developed for the arid lands of northwestern China based on ecological and environmental factors, including climate, large-scale terrain features, landform, geology, vegetation, and soils, in combination with characteristics of social and economic development. The region was stratified into discrete geographical units of uniformity at three levels: Level I, the ecodomain, was based on climate and large-scale terrain features with consideration of the role of higher levels of regionalization and industrial development; Level II, the ecoregion, was based primarily on secondary landform, topography and large-scale vegetation types; and, Level III, the ecodistrict, was based on differences in local vegetation due to differences in geology and soils, as well as its eco-productive paradigm and potential future development. Based on this three-class system, we defined three ecodomains, 23 ecoregions and 80 ecodistricts. An ecoregional map of northwestern arid lands of China was drawn at 1∶1 million scale using GIS. The goals of the ecological regionalization classification were not only to develop a unique system of arid land ecological classification, but also to supervise local development and land use management to promote sustainable development of arid lands in northwestern China.

In this paper, the principles and methodologies for developing data set of land cover characteristics for the Northeast China transect (NECT) are discussed. Data set was developed using multi-temporal NOAA/AVHRR NDVI images with 1-km spatial resolution. Elevation, climate, soil, vegetation, land use, land resource, ecoregions, political boundaries, economic data, and social data were included as data layers, and all data layers were standardized and then integrated by digitization, spatial interpolation, geometrical registration, and projection transformation. Using this data set, several land use characteristics were mapped and analyzed. 1) Land cover mapping: multi-temporal NOAA/AVHRR NDVI images with 1-km spatial resolution were adopted to classify the land cover map of NECT. The first classification included 8 land cover types, forest, grassland, desert, shrub, cropland, mixed type, building area and water bodies. There were 12 land cover types in the second classification. Classification accuracy was 81.61% determined by ground truthing. The land cover patterns reflected the integrated physical geographical characteristics of NECT. 2) Land cover parameters were calculated using multi-temporal remotely sensed reflectance data that included annual NDVI maximum (NDVI max ), seasonal NDVI amplitude (x am ) and annual NDVI standard deviation (x′ s). Strong inter-annual and seasonal changes in vegetation growth for different land cover types were apparent. NDVI max, x am and x′ s showed an increasing trend with an increase in annual average temperatures for meadow steppe, typical steppe and desert steppe. 3) Two methods were used to evaluate seasonal changes in the length of the growing seasons over time. The length of the growing seasons of the meadow steppe and typical steppe lengthened by (9±2) days and (11±3) days, respectively, from 1983 to 1999. Similar change was not detected for the desert steppe. These results are in accordance with field records. This data set is a foundation for future research on land cover characteristics and their changes along the NECT. It also is an important contribution to international research on large-scale gradients as well as to global change research based upon the NECT.

Topography is a primary factor that creates microenvironmental heterogeneity in a landscape. In previous studies, topographic factors, such as slope and aspect, were measured as discrete data and had limited use in analyses. In this paper, a digital elevation model (DEM) was used to analyze the influence of topographic heterogeneity on the distribution patterns of woody plants at the community level by calculating digital topographic values and creating a digital description of the landform. The establishment of a DEM can be generalized in three steps: 1) gathering the topographic data; 2) data adjustment & interpolation; and 3) displaying the data. To illustrate this process, a DEM was built based on a 0.96 hm 2 permanent forest plot in the Shennongjia area (31°19′4″ N, 110°29′44″ E). The forest was dominated by Fagus engleriana and Cyclobalanopsis oxyodon. Topographic data were gathered when the plot was established. A total of 425 sample points were mapped by elevation. An inverse distance weighted method was used to interpolate data between points. Using Arcview GIS software, the slope and aspect of all 425 points within the plot were calculated. The slope varied from 18.2 to 74.6 degrees in the 0.96 hm 2 plot. The precision of the DEM was 0.4 m. Using the DEM, the slope and aspect of every point within the permanent plot were calculated and these topographic factors were then used to analyze species distribution patterns. Twenty-four species were chosen to calculate their correlations with slope, aspect and position. The positive and negative correlations with the slope, aspect and position were 7, 7, 6, 3, and 8, 5 respectively. One problem of using a DEM at small scales is related to the difficulties associated with the collection of the original data. Under the forest canopy, it was difficult to gather topographic data using GPS, remote pictures or other automated tools. To achieve the required precision, all topographic data were acquired using a compass, which limited the scale at which the analysis could be conducted. Although improvements are needed in this method, the DEM provided a lot of information and was a convenient method for analyzing species distributions in relation to topographic factors. Because remote sensing cannot provide a detailed description of species distributions within forest communities, such research should be combined with the establishment of permanent plots.

Micrometeorological measurements depend on knowing the spatial resolution of the heterogeneous surface, defined as the source area. Based on 2002-2003 flux data at the Mid-Subtropical forest area (Qianyanzhou Station), the flux source area was examined using the FSAM analytical model. Evidence suggested that the source area changed with measurement height, time and atmospheric stability, i.e., under the same conditions, a higher measurement and more stable atmospheric layer created a larger flux source area and farther minimum horizontal distance (a) away from the tower. Seasonal variation of wind direction influenced the distribution direction of the area. A higher measurement height and more stable atmospheric layer caused a stronger pertinence of d/Z 0 and S v/u *, which was independent of wind direction. Because of the big fetch, the measurements were representative of the specific characteristics of the instrument location, i.e., the surface of the underlying forest. Moreover, plotting the wind direction and flux data (including the CO 2 flux, the sensible heat flux and the latent heat flux) on a synchronous basis indicated that when the Z/L data satisfy the model requirements, the flux data almost converge at the same wind direction. The results were obtained under conditions of horizontally homogeneous turbulence, which meets the basic need of the model. In Qianyanzhou Station, the FSAM model can only simulate the flux source area under conditions of day-and-night stable atmospheric layer and inactive turbulence. Future work needs to study the turbulent characteristics within and above the forest and improve the model so that it can be applied more widely in the station.

Dinghushan biosphere reserve (112°30′39″-112°33′41″ E, 23°09′21″-23°11′30″ N) is located in central Guangdong Province in southern China, about 84 km from Guangzhou city, with an area of 1 156 hm 2. Due to its location on the tropic of cancer, the forest vegetation is very rich and dominated by monsoon evergreen broad-leaved forests. The dominant forest types in the Dinghushan biosphere reserve are Pinus massoniana forests (PF), mixed Pinus massoniana/broad-leaved forests (PBF), and monsoon evergreen broad-leaved forests (MBF), which form a natural successional sequence. The aim of this paper was to quantify the magnitude and annual variation of water yields in the Dinghushan Nature Reserve in the three forest types, which would be used for estimating carbon outputs in streamflow, and to discuss how hydrological processes vary at different successional stages of forest development. Climatic data were obtained from weather stations located at the Dinghushan Forest Ecosystem Research Station, Chinese Ecosystem Research Network (CERN). Runoff was monitored at three landscape levels. The first level was the entire eastern watershed. The second level referred to small catchments within the larger watershed that were dominated by the different forest types, i.e., a PF catchment, a PBF catchment, and a MBF catchment. The third level referred to three surface runoff plots placed within each of the three catchments. Stream runoff in the eastern watershed and the three smaller catchments was monitored continuously year a round by measurement weirs with streamflow recorders. The ephemeral surface runoff from the nine surface runoff plots was collected in separate plastic tanks and the water level of each tank was recorded automatically following every precipitation event. The subsurface water table depth was recorded manually at 5-day intervals in wells located in the valley of the eastern watershed at elevations of 20-30 m. Soil water content has been measured monthly using neutron probes since 1983. Soil water content was measured at 10-15 places in each of the three catchments and distributed across the elevational gradient. At each point, the water content was monitored at three soil depths, 0-15, 15-30 and 30-45 cm. Throughfall was collected at four sites in each catchment using cross-shaped troughs with a horizontal area of 2.25 m 2, and was measured using a fluviograph (Zhou, 1997). Thirty trees adjacent to each throughfall site that represented the range of species and size of trees in each catchment were selected and stemflow monitored (Gash et al. 1978). Stemflow was collected in an open PVC tube wrapped around the stem of each tree that led to a tipping bucket rain gauge. Throughfall and stemflow were monitored from April 1999 to April 2000, during which time there were 61 rain events. Leaf area index and canopy cover were measured at 10 sampling sites within each catchment four times each year using a CI-110 digital plant canopy imager (CID, Inc. Vancouver). The water yield in the eastern watershed of Dinghushan biosphere reserve was 66.5% of its rainfall with the maximum outflow occurring about one day after a rain event. The subsurface water table averaged 2.22 m below the soil surface, with the deepest water levels at 2.84 m and highest at 1.14 m depth. The annual average position was 2.38, 2.27, 2.08, 2.13 and 2.11 m deep in the years 1999, 2000, 2001, 2002 and 2003, respectively. The depth of the water table in the eastern watershed was correlated with rainfall events that occurred 16 days previously. There was an abating tendency of soil water content for all the three forest communities. The tendency was statistically significant for MBF (p<0.01) and PBF (p<0.05), whereas no statistically significant effect for the PF was found. The relationship between the amount of throughfall and precipitation was linear for the three different forest communities at different successional stages, but the correlation decreased from MBF, PBF uo PF. The ratio of throughfall to precipitation also decreased with successional stage of the forest, from 83.4%, 68.3% to 59.9% for the PF, PBF and MBF, respectively. The relationship of stem flow with DBH was controlled by the effects of the whole forest community instead of a single species. The canopy structure of the forest community played a key role in the redistribution of precipitation. The canopy interception rate in the MBF was 83.3% in February when total precipitation was 28.7 mm, but was only 18.9% when precipitation was 297.8 mm in June. The canopy interception rate increased in the three forest types from PF, PBF to MBF.

The monsoon evergreen broad-leaved forest (MEBF) in Dinghushan Biosphere Reserve, Guangdong Province, China, is considered climax forest vegetation in this climatic zone. Studies of its ecological processes, including the hydrology and inorganic solution chemistry, are important for understanding ecosystem function and to direct ecological restoration efforts in this region. In order to understand the response of nutrient cycles to environmental impacts and characterize the nutrient element cycles in this ecosystem, water samples of precipitation, throughfall, soil water at 30 and 80 cm depth and runoff in MEBF were collected weekly and the concentrations of eight inorganic elements measured from February 2001 to March 2002. The elements Al 3+, Mn 2+, Sr 2+ and Pb 2+ were measured by ICP (ps-1000AT, USA), Ca 2+ and Mg 2+ were analyzed using Atomic Absorption Spectrometer, and K + and Na + were determined using Flame Atomic Absorption Spectrometer. The results showed that the average concentration of Al 3+ in throughfall (0.393 3 mg·L -1 ) was slightly higher than that in precipitation (0.329 mg·L -1 ). The average concentrations of Al 3+ soil solutions were much higher than in precipitation and were about 4.7 times and 3.8 times higher in soil water collected at 30 cm depth and runoff, respectively. Al 3+ in runoff was derived primarily from soil leaching. Average concentrations of Mn 2+, K + and Mg 2+ were lowest in precipitation and Sr 2+ and Ca 2+ concentrations were lowest in runoff. The average concentrations of Mn 2+, Sr 2+, K +, Mg 2+ and Ca 2+ in throughfall were much higher than in precipitation as a result of strong interactions with the tree canopy. The average concentration of Pb 2+ in precipitation was as high as 0.062 mg·L -1, indicating some Pb 2+ pollution, and it was about 5 times and 10 times higher than that in throughfall and runoff, respectively. This indicated that the Pb 2+ in precipitation could be largely absorbed by the tree canopy and soil. The average concentration of Na + gradually increased as it passed through the ecosystem from precipitation (0.320 2 mg·L -1 ) to throughfall (0.524 7 mg·L -1 ), soil water at 30 cm (0.627 3 mg·L -1 ) and 80 cm (0.639 1 mg·L -1 ) depth and finally as runoff (0.629 6 mg·L -1 ). Coefficients of variation of the elemental concentrations in the different solutions ranged from 51.1% and 236.7%. The average concentrations of those elements in precipitation, throughfall, soil water at 30 and 80 cm depth were higher during the dry season than during wet season, but their concentrations in runoff during the dry season were lower than or close to that during the wet season. The element Mg had the highest element-couple correlation as compared to all other elements. The greatest element-couple correlations were found in throughfall. Correlations among other elements were highly variable. The results show that element nutrient cycles in this forest ecosystem are stable even though under environmental stress.

Based on data obtained from field investigations, this paper aims to analyze the inter-specific relationships of desert riparian forest plant communities, assess the influence of different quadrat sizes on inter-specific associations, discuss what is an appropriate quadrat size for best results, and present the relationships among populations in desert riparian forests in the middle and lower reaches of the Tarim River using Fisher's exact test. The results showed that 16 species noted in 21 sampling sites formed the principal community of the desert riparian forest. The vertical structure of the forest consisted of a tree layer, shrub layer and herb layer. It was found that 4 sampling sites had 3 layers, 10 had 2 layers and 7 had 1 layer. There were 120 species pairs formed by 16 species in 210 quadrats among which 17 species pairs showed significant and very significant inter-specific associations, accounting for 14.2% of total species pairs. Thirteen species pairs were positively correlated and four species pairs were negatively correlated. The size of the quadrat influenced the inter-specific associations among species pairs, but the most suitable quadrat size varied among species and sampling sites. A quadrat from 8 m×8 m to 30 m×30 m may be the most suitable size for analysis of inter-specific associations of desert riparian forest communities in Tarim River basin. Different species pairs had different minimum quadrat sizes. There was spatial variance in the interaction between different populations of the desert riparian forest. Different patterns and relationships of inter-specific associations were found as the size of the quadrat increased. Generally, four types of changes in species associations were observed with changing quadrat size. For the first type, the correlative significance of species pairs changed from high to low and then to high as the quadrat size changed from the minimum size of 2 m×2 m to the maximum size of 32 m×64 m. These species pairs accounted for 17.6% of the total species pairs. In the second type of variation, the correlative significance of species pairs changed from low to high and then to low with an increase in quadrat size. These species pairs accounted for 41.2% of the total. For the third type, the significant and very significant inter-specific associations occurred in quadrats that ranged in size from 8 m×16 m to 32 m×64 m. The correlative significance of species pairs changed from low to high, and if the quadrat size continued to increase, new relationships would emerge. These species pairs accounted for 29.4% of the total. For the forth type, the significant and very significant inter-specific associations changed from low to high and then from low to high again as the quadrat size continued to increase. These species pairs accounted for 11.8% of the total. Species associations among shrub-herb and herb-herb pairs were more numerous in 17 inter-specific associations, accounting for 76.5% of the total. Species associations between Populus euphratica and arbor and shrub-shrub were distributed independently of each other. Even if inter-specific associations among species-pairs appeared, they were usually negative correlations. Most species-pairs, which were between arbor and herb-shrub and herb-herb, typically had positive correlations.

The analyses of spatial distribution patterns of plant populations are useful for understanding pattern types and intra/inter-specific relationships. One of the most frequently employed methods in detecting spatial distribution patterns of populations is the nearest neighbor analysis proposed by Clark and Evans in 1954. This method has been highly successful for analyzing spatial patterns at a single scale but is rarely used for analyzing distribution patterns at multiple scales. We present the extended nearest neighbor analysis (ENNA) in this paper to solve the scale-dependent problem associated with the traditional method of nearest neighbor analysis. The Clark-Evans index was modified by using a distance scale parameter d (m), described in the following equation: CE (d) =r dA /r dE = (1N d∑N di=1r di ) / (0.5A d/N d+0.051 4P d/N d+0.041P d/N d 3/2 ). Accordingly, the equation for testing the calculated CE index values against the significant deviation from 1 was changed into u (d) = (r dA -r dE ) /σ d, where the parameters, r dA, r dE, N d, r di, A d, P d, σ d, refer to the mean distance between an individual and its nearest neighbor (m), the expected mean distance of the individuals of a population randomly scattered (m), the number of individuals in the current sample plot, distance between individual i and its nearest neighbor (m), surface of the current sample plot (m 2), circumference of the current sample plot (m), and the standard deviation, respectively. The procedure of scaling transformation in this approach was similar to that of the sandbox experiment in fractal theory, and the rule for detecting the pattern type was the same as that in the traditional nearest neighbor analysis. The traditional nearest neighbor analysis is a special case for the extended nearest neighbor analysis in which the minimum value of the distance scale parameter (d) is used. An example using the data from a needle and broad-leaved mixed forest community at Heishiding Nature Reserve, Guangdong Province was presented to explain the procedure. Five typical plant populations of this community, Pinus massoniana, Symplocos laurina, Castanopsis nigrescens, Itea chinensis and Rhodomyrtus tomentosa, were chosen for the multi-scale analysis of spatial distribution patterns. The results showed that spatial patterns of all five populations were scale-dependent with varying degrees of intensity. The Pinus massoniana population was randomly distributed at most scales examined, which may have been caused by the random self-thinning process in the population. The population of Itea chinensis was clumped at all scales examined. A simulation with the aid of geographic information system (GIS) also revealed that the distribution patterns of Symplocos laurina, Castanopsis nigrescens, Itea chinensis and Rhodomyrtus tomentosa were mainly clumped or random with an increase of distance scale. These results demonstrated that the ENNA method presented in this paper could be used for multi-scale analysis of spatial distribution patterns of plant populations that could not be solved using the traditional nearest neighbor analysis.

Ever since Darwin, competition has been considered to be one of the major forces that shape the morphology and life history of plants and affect the structure and dynamics of plant communities. Competition among plants occurs when resource availability falls below the sum requirement of the community needed for optimal growth. Competition includes intraspecific and interspecific competition for both aboveground and belowground resources and takes place over different spatial and temporal scales. Although many researchers have determined the zone of competition according to their past experiences, it is important to define the zone of influence by using a competition index (CI) that includes all competitors and sources of competition for scarce resources. Phenotypic plasticity is thought to be an adaptive trait evolved in plants growing in spatially or temporally heterogeneous environments. Plasticity of growth and morphology in response to different levels of light, nutrient and water availability in herb plant species has been extensively documented. However, very few studies have addressed phenotypic responses to neighborhood competition in hardwood plants, especially concerning morphology. Larix chinensis is an endemic species in China distributed only in the alpine and sub-alpine belt of the Qinling Mountains. It is also an endangered species listed in the Chinese Plant Red Data Book. It is a dominant species at altitudes of 2 560-3 500 m with special functions that maintains the ecological balance at timberline. In order to define the zone of competition, intraspecific and interspecific competition in L. chinensis communities were investigated using a method that gradually increases the zone of interaction and Zhang's competition index model for individual trees. Data for this study were collected in the Taibai Mountain Natural Reserve of Shaanxi Province in China. Ten 40 m 2-plots were investigated, and every plot was stem-mapped, and species, DBH, total height, and crown length were recorded for each tree that had a diameter of at least 5 cm at breast height. In order to study neighborhood competition effects, morphological characteristics, such as the branching angle, total branch-number, current-year branch length, average branch length, and living branch number of the main stem in different strata were investigated for L. chinensis under different levels of neighborhood competition intensity. The results showed that as a tree increased in size and the distance between plants increased that intraspecific competition intensity decreased due to self-thinning. L. chinensis is the dominant tree in the community, and the few other species tree species in the forest community are all much smaller than L. chinensis. As a result, intraspecific competition was more intense than interspecific competition. The order of competition intensity was: L. chinensis-L. chinensis >Abies fargesii-L. chinensis > Betula platyphylla-L. chinensis > other species-L. chinensis. The relationship between competition intensity and growth of the tree of interest closely followed the following equation: CI×AD -B. The change in competition intensity is very small when the diameter of the objective tree reaches 35 cm. The model can simulate and predict intraspecific and interspecific competition efficiently. The morphology of L. chinensis, such as the branching angle, total branch-number, current-year branch length, average branch length, and living branch number of main stem, was modified in response to different intensities of neighborhood competition. The study provides a new approach to ascertain the zone of competition among trees for studying plant competition. L. chinensis can improve its capacity to intercept light and adapt to different levels of neighborhood competition through morphological changes.

Abies chensiensis is an endangered tree that occurs primarily in the Qinling Mountain of China and is distributed across a wide range of elevations extending from 1 350 m to 2 500 m. The objectives of our study were: i) to investigate the fruiting and basic characteristics of the cones and the seeds; and ii) to determine how the characteristics of the cones and seeds of Abies chensiensis vary with elevation. Cones of Abies chensiensis were collected from trees in a high elevation and low elevation population. Through field investigations, laboratorial experiments and comparisons with other Abies, it was found that the cones and seeds of Abies chensiensis were bigger than other Abies species and had more seeds per cone but fewer full developed seeds per cone. Also, it was found that only 12.03 percent of the seeds were fully developed under natural conditions; this percentage increased to 21.6% after hand selecting seeds and to 38.1% after machine selection. Other seeds were empty, rigid or worm infested. At higher elevation, the percentage of adult trees that fruited and the number of cones produced per tree was reduced. The mean percentage of fruiting trees was 55% across sites; however, at low elevation, 76% of the trees fruited whereas only 34% fruited at high elevation. The mean number of cones per tree was 113. About 64.5 percent of fruiting trees produced no more than 100 cones with half of them producing 50 to 100 cones. Also, 16.1 percent of the fruiting trees produced from 100 to 200 cones and 19.4 percent produced over 200 cones. Trees with more than 200 cones all grew at low elevations; at high elevation, most trees produced less than 50 cones. Further analyses indicated significant differences in the characteristics of cones and seeds between the two elevations. Most traits were higher at low elevation sites than at higher elevations. From these analyses, we conclude that the reproductive potential of Abies chensiensis was greater at low elevation than at high elevation, most likely due to more suitable climatic conditions, more fertile soils and less steep topography at low elevation.

Berchemiella wilsonii var. pubipetiolata is a local endemic species distributed discontinuously throughout the Mt. Dabieshan region of the Anhui Province and Mt. Qingliangfeng region of Zhejiang Province, eastern China. Because of the human impacts on natural ecosystems, it is under the threat of extinction and has been ranked as an endangered species. In this study, we assessed the community status of B. wilsonii var. pubipetiolata as a basis for its conservation. Based on 2×2 contingency tables, the interspecific correlation of B. wilsonii var. pubipetiolata in the tree layers and shrub layers with other species analyzed in four different communities were studied by using χ 2 tests and association coefficients (AC). The results indicated that the interspecific correlations of B. wilsonii var. pubipetiolata to other species were very similar in each of the four sites. The value of AC between most species and B. wilsonii var. pubipetiolata ranged from -0.2 to 0.2, which indicated that there was no relationship between B. wilsonii var. pubipetiolata and other species. The χ 2 analysis indicated that either no species or only one species in a community had a significant relationship with B. wilsonii var. pubipetiolata. There were no significant relationships between the dominant species and B. wilsonii var. pubipetiolata in any of the communities. All of the above results imply that B. wilsonii var. pubipetiolata was distributed independently or had random occurrence in the different communitiesindicating that it is an incidental or rare species. This case study highlights the importance of having a good understanding of the ecological characteristics of uncommon plants as a basis for making decisions regarding their conservation.

By combining root auger and image analysis methods for root sampling and measurement, this study investigated the dynamic characteristics of cotton plant root growth and the spatial distribution of root length, diameter and area. The experiment was conducted during 2001 and 2002 at an experiment station located in Anyang city, Henan Province. A root performance experiment of different genotypes was conducted in 2001 using 4 cotton cultivars: middle season hybrid `CRI29' with Bt, middle season variety `CRI35' without Bt, middle season variety `CRI32' with Bt and early season variety `CRI37' with Bt. Plant density was 60 000 plants per hectare. In 2002, the American middle season variety `33B' with Bt was included and measured in 40 cm×40 cm×100 cm deep soil pits. The soil was loam. Climate data from a nearby weather station were used to calculate the cotton physiological development time (PDT). Computation of PDT also integrated thermal effectiveness, photoperiod effectiveness, genetic effectiveness and its interactions. Root samples were collected at four distances from the cotton row: 0, 15, 25 and 35 cm. Root samples were collected from 40 cm×40 cm×100 cm deep soil pits and sampled every 10 cm from 0 to 100 cm soil depth at each location. The roots were sampled using a root auger that had a volume of 316.73 cm 3. The roots were washed form the soil core with all cotton roots collected in the samples. Cleaned roots were scanned to a black and white image at a resolution of 200 dpi. DT-SCAN software was used to calculate root length, root diameter and root surface area. Compared to the ruler measurement method to estimate root length density (RLD), the image analysis method using DT-SCAN for estimating RLD gave similar results (R 2=0.899, n=1 318). The results indicated that the RLD of cotton averaged 1.21-1.27 mm·cm -3 during flowering and boll stage, 1.04-1.12 mm·cm -3 after boll opening, and 0.76 mm·cm -3 during the harvest period. Root diameter was significantly different among genotypes (p=0.022), with the thickest root diameter of 0.52 mm in an insect resistant hybrid cultivar and the thinnest root diameter of 0.36 mm in the early maturation cultivar. Root diameters were not significantly different between soil layers but were significantly thinner with increasing distance from the cotton row. Because of the significant differences observed in root length and diameter among soil layers, distance from plant and genotypes, we developed a root area index (RAI) that has similar biological meaning as the leaf area index. The RAI and LAI were exponentially related (R 2 = 0.799). The dynamic time course of RAI fit a logistic growth pattern (R 2=0.849) with physiological development time (PDT) when the PDT was smaller than 40, and exhibited a linear decreasing pattern (R 2=0.570-0.895) when PDT was greater than 40. The highest RAI calculated was in the insect-resistant hybrid cultivar and the lowest in early maturation cultivar. The vertical and temporal changes in RAI were as follows: RAI was the greatest in the topsoil layer (0-30 cm) before flowering, in the mid soil layer (40-60 cm) during flowering and boll stage, and in the deep layer (70-100 cm) and at locations away from the cotton row after boll opening.

The reproductive success (Ovule fertilization and the pollen dispersal) of animal-pollinated plants is dependent upon floral visitors and their visiting behavior. The visitor and their behavior are primarily determined by the rewards offered by the plant, mainly nectar secretion and its components. In this study, we linked the floral visitors and their visiting behavior with the fruit and seed siring on a flexistylous ginger, Alpinia blepharocalyx, in Caiyanghe Provincial Natural Reserve (22°30′ N, 101°22′ E), southwest China. The study was carried out from March 16 to April 28,2003. We established 9 plots within 3 noncontiguous patches of a large population of A. blepharocalyx and measured nectar volume and concentration, recorded floral visitor species and their behavior, recorded fruit set and seed production, and measured the effects of a nectar robber, the striped squirrel (Tamiops swinhoei) on reproductive success. Nectar was measured 6 times a day; a micro-capillary tube was used to collect nectar secretions and a refractometer used to analyze sugar concentrations. Visiting frequency and duration were recorded every 2 hours from 7∶30-19∶00 during the entire flowering season. Seventeen species of floral visitors were recorded during the observation period, 8 species of which were pollinators. Of these, Bombus eximius and Bombus richardis were the most effective pollinators due to higher visiting frequencies and apparent well-suited body sizes. The nectar secretion patterns of two phenotypes were opposite: anaflexistylous flower secreted more nectar in the afternoon than that in the morning whereas the cataflexistylous flower showed the reverse pattern. The sugar concentration of both phenotypes declined during the anthesis period from 07∶30 to 20∶00. The visiting frequencies of pollinators were higher in the afternoon than in the morning. Pollinators spent a longer time at the flower during a single visit before 10∶30 A.M. when the visiting frequency was low, but shortened the duration of a visit when the visiting frequencie increased after 11∶30 A.M. The fruit set ratio of A. blepharocalyx was not significantly different between nectar robbed and non-robbed plots, but seed production was greater in the non-robbed plants.

Atmospheric CO 2 concentrations are expected to double around the middle part of the 21 st century. Plant growth might be favored by CO 2 enrichment, but water limitation is a common stress for plant growth and productivity. At present, only a few studies have looked at the combined effects of CO 2 enrichment and drought on plant ecophysiology. This experiment was conducted to investigate the responses of two dominant desert shrubs, Caragana intermedia and Hedysarum mongolicum, in western China to the interaction of doubled CO 2 levels and soil drought in large environmental growth chambers (19 m 2). In this paper, we employed different methods, including allometry and carbon isotope discrimination, to examine the effects of water availability on carbon allocation and stable carbon isotope composition (δ 13 C) of the two desert shrubs under two CO 2 concentrations. The objectives included the following: 1) to investigate the effects of soil drought and CO 2 enrichment on plant biomass and δ 13 C; 2) to investigate the effects of soil drought and CO 2 enrichment on the allocation of dry matter and carbohydrates; and 3) to elucidate the adaptive strategies of C. intermedia and H. mongolicum to soil drought under doubled atmospheric CO 2 concentrations. Compared to ambient CO 2 concentrations, doubled CO 2 concentrations did not improve the leaf water status, but soil drought significantly reduced the leaf relative water content (RWC). Doubled CO 2 concentrations enhanced plant growth under well-watered conditions but increased root growth under drought conditions resulting in an increase in root to shoot ratios. Soil drought significantly reduced plant biomass and increased root to shoot ratios, especially for H. mongolicum. The δ 13 C values were reduced at doubled CO 2 concentrations but increased under drought conditions. By plotting the leaf δ 13 C values against the root δ 13 C values, it was possible to assess carbon allocation and incorporation into roots in relation to present biomass. There was a significant and linear relationship between leaf δ 13 C and root δ 13 C values, and the slope of H. mongolicum was greater than that of C. intermedia indicated a higher plasticity in the ability to change carbon allocation patterns. This resulted in higher root to shoot ratios in H. mongolicum under drought conditions. The results indicated that both C. intermedia and H. mongolicum had a higher tolerance to severe water deficits under doubled CO 2 conditions. Decreases in precipitation might accompany with future increases in atmospheric CO 2 concentrations in the region dominated by these two species, suggesting that distribution ranges of C. intermedia and H. mongolicum might be constrained. Our results suggest that H. mongolicum has a higher tolerance to environmental stress than C. intermedia. Future work should emphasize how to enhance the drought tolerance of plants in semiarid region under conditions of CO 2 enrichment.

Increases in the world population combined with accelerated rates of industrialization has led to increases in green-house gases in the atmosphere, particularly CO₂ concentrations, resulting in an increase in global temperatures. Water use efficiency (WUE) is a measure of a plant’s performance growing under different environmental conditions, and is an important index that reflects a plant’s ability to adapt to climate change. Carbon isotopes provide a long-term, integrative measure of WUE with high δ¹³C indicating high WUE. Stable carbon isotopes have become an important technique in ecophysiology studies in recent years for analyzing the long-term WUE of plants growing in different habits and to study the response of plant to different environmental variables, such as light intensity, precipitation, temperature, CO₂, and mineral nutrient availability. The Loess Plateau is a critical ecosystem in China but suffers from serious soil erosion problems. Water is the most important limiting environmental factor in this region and research on plant WUE responses to climate change is of particular relevance. However, only a few studies have examined foliar δ ¹³C value in response to climate change in this ecosystem. Four C₃ plants that are typical of the Loess Plateau were chosen as materials: Quercus liaotungensis, a tree, and three species of shrubs, Ostryopsis davidiana, Zizyphus jujuba var. spinosa and Sophora viciifolia. Dry leaves were collected from herbarium specimens collected over a 70 year period from the 1930’s to 2002. A total of 25 samples from about 160 plant specimens were analyzed that were collected from the hilly and gully region of the Plateau ranging from the northern Tongchuan to the southern Yanan. The carbon isotope composition (δ¹³C) of leaves was analyzed using a MAT-251 mass-spectra photometer. The results showed that the variation in the δ ¹³C values differed among the species tested: :Ostryopsis davidiana (-25.05‰ to -29.75‰) > Quercus liaotungensis (-25.51‰ to -29.20‰) > Sophora viciifolia (-25.12‰ to -28.80‰) > Zizyphus jujuba var. spinosa (-26.69‰ to -28.69‰). The mean δ13C value of four plants was -27.04‰ ranging from -25.05‰ to -29.75‰. Comparing the mean δ¹³C value among four species in the age of 30, 50, 70, 80 and the year 2002 indicated that the following order of Sophora viciifolia (-26.54‰) > Ostryopsis davidiana (-26.99‰) > Quercus liaotungensis (-27.14‰) > Zizyphus jujuba var. spinosa (-27.49‰) is obtained. A decrease in the foliar δ¹³C value with time was found in all four species, indicating that the WUE of the four species all declined over time. However, the decrease in foliar δ ¹³C values varied among the four species with significant decreases measured in two species, Sophora viciifolia and Quercus liaotungensis, a strong but not significant decrease in the leaves of Ostryopsis davidiana, and only a slight decrease in Zizyphus jujuba var. spinosa. The decrease in the δ ¹³C values in the four species were: 14.65‰, 14.46‰, 11.99‰ and 2.44‰, respectively. It was shown that different species have different sensitivities to climate change, and Zizyphus jujuba var. spinosa was the most drought-tolerant of the four species with a high WUE.

The ability for vegetation and soil organic matter (SOM) to sequester atmospheric CO 2 has received a lot of attention recently. Two management options being considered for enhancing C sequestration from the atmosphere include tropical forest conservation and establishment of plantations; however, there is still considerable debate regarding the appropriateness of using plantations and the sequestration potential of tropical plantations. There are 1.3×10 5 hm 2 of rubber trees (Hevea brasiliensis) plantations in Xishuangbanna, southwest China, which account for approximately 14% of the forest lands in this region. In this study, eleven plantations of different ages were selected to investigate C sequestration in the vegetation and soils following the establishment of rubber tree plantations on former arable lands. The results indicated that the average biomass growth rates of the rubber trees, calculated according to two different biomass growth equations, were 10.2×10 3 and 9.4×10 3 kg t·hm -2 ·a -1. Soil C stocks in the top 40 cm and 1 m of soil increased at rates of 0.61×10 3 and 0.72×10 3 kg t C·hm -2 ·a -1, respectively. In total, C sequestration was approximately 5.82×10 3 to 5.42×10 3 kg t C·hm -2 ·a -1 in the vegetation and soil as calculated by the two biomass growth models. When comparing the two models, our results showed that the biomass calculated based on the equation of Tanget al.was higher than that based on the equation of Brown, especially in young- and middle-aged rubber tree plantations.

Different methods of pasture management have been adopted in individualized pastures of northwestern Sichuan, one of the most important pastoral areas in China. In this paper, common analytical chemistry and barometric process separation methods were used to determine soil N and C pools, denitrification rates, gross nitrification rates, and N 2O and CO 2 flux rates of pastures under different management methods, including natural pasture, fenced pasture, tilled pasture and artificial pasture. The results indicated that SOM (Soil organic matter) and total N in soils of the study area were 101.8 and 5.1 g·kg -1, respectively, which were notably lower than 181.3 and 7.4 g·kg -1 of other typical sub-alpine soils. In contrast to common belief, the content of NO 3 --N was three-to-eleven times higher than that of NH 4 +-N, which was probably caused by the anthropogenic disturbance. There was a significant effect of different methods of pasture management to N and C pools, N transformation rates and soil respiration. After fence, SOM and total N increased notably. For example, fenced pasture was 61% and 58% and tilled pasture was 46% and 51% higher than natural pasture in these two respects, respectively. Accordingly, N transformation rates and soil respiration rates accelerated a lot, especially in soils of tilled pasture. For example, in soils of tilled pasture gross nitrification and N 2O flux rate were 5.1 times and 2.4 times that of natural pasture. Thus, although tillage in spring might help to enhanced crop yields (or pasturage), it also runs a great ecological risk including increased emissions of CO 2 and N 2O to the atmosphere and leaching of NO 3 - to ground water. This research also found that the gross nitrification rates were 20-93 times higher than net nitrification rates, and thus net nitrification rates do not provide valuable information on the dynamic character of soil nitrification in this high-altitude region.

Leymus chinensis, a rhizomatous graminoid, is a dominant species in the grasslands of northern China. The characteristics of L. chinensis populations have been well documented in many research papers. Because of overgrazing, grasslands of northern China have become degraded since the 1980s. As a result, the density and biomass of L. chinensis populations have decreased significantly. Fertilization is a common technique for management of pastures in many countries; however, it is not widely used in the grasslands of China. Nitrogen is an important driver of community succession in grassland ecosystems, but the response of L. chinensis populations to nitrogen additions in typical steppe, a semiarid area of northern China, remains unclear. We conducted a sequential nitrogen addition experiment in a lightly degraded grassland plot that was fenced in 1999. Nitrogen (NH 4NO 3) was applied on July 5 for two years at application rates of: 0, 1.75, 5.25, 10.5, 17.5, and 28 g N·m -2, respectively. There were 9 replicate 5 m×5 m plots of each of the six treatments with each plot spaced 1 m apart. A completely randomized design was used for this experiment. Before the experiment, soil samples were collected and dry bulk density, pH, soil nitrogen and soil carbon were analyzed. After two years of nitrogen fertilization, we measured the density, height, aboveground biomass and belowground biomass of L. chinensis in each plot. The results showed that L. chinensis population characteristics were highly responsive to nitrogen additions. With an increase in nitrogen application rates, the density, height, aboveground biomass, belowground biomass and total biomass of L. chinensis increased significantly whereas the ratio of aboveground biomass/belowground biomass decreased. The allocation of biomass among plant parts was significantly affected by nitrogen additions: the proportion of biomass allocated to rhizomes decreased remarkably with increasing nitrogen rates whereas that allocated to leaves and roots increased significantly. The relative biomass and relative density of L. chinensis also increased with increasing nitrogen additions. In summary, adding nitrogen to lightly degraded grassland not only increased the density and biomass of L. chinensis population but changed the resource partitioning among plant parts as well.

The ability to non-destructively monitor crop water status by remote sensing is of significant importance for optimizing of crop irrigation systems and precision farming. In order to develop quantitative models for monitoring rice water status by canopy reflectance spectra, an investigation was conducted to study the relationship between canopy reflectance characteristics and plant water status under different water and nitrogen levels with different pot and pool experiments. The results showed that the crop spectral reflectance decreased in the visible wavelength regions and short-wave infrared (SWIR) (1 400-1 700 nm) regions with increasing water supply, because absorption of visible light (450-700 nm) by leaf chlorophyll was aggravated whereas the spectral reflectance in the near infrared (NIR) (750-950 nm) wavelength regions increased. A high reflectance spectra flat roof formed which remained throughout the entire growth period. Under different water regimes, canopy reflectance showed similar patterns of change. Under the same water supply, the canopy spectral reflectance in the visible wavelength and SWIR regions was lower under high nitrogen supply than under low nitrogen supply rates but showed an opposite pattern in the NIR wavelength regions. Canopy reflectance in single bands is often subject to interference by biomass, background and so on, but the ratio of two bands can alleviate interference due to topography and enlarge the difference of spectral reflectance between vegetation types thus improving the precision of estimates by spectral reflectance. Consequently, in order to eliminate some of the interferences for distinguishing leaf and canopy structure and establish the best predictive model for assessing leaf water content, all regressions between ratio indices, normalized difference indices and leaf and plant water content were conducted. The results indicated that there was a linear relationship between the vegetation index ratio (R 810 /R 460 ) and canopy leaf water content and plant water content after jointing stage regardless of leaf nitrogen levels, with an RMSE of 0.93 and 1.50, respectively, for model testing. It is concluded that the vegetation index ratio of R 810 /R 460 can be used to monitor leaf water content and plant water content at different growth stages of rice.

Zea mays cv. Luyu 14' was used to study the effects of Ca 2+ on stomatal conductance, net photosynthetic rates, Mehler reactions and the activities of the antioxidant enzymes, SOD and APX, under NaCl stress. Additions of 2-16 mmol·L -1 Ca 2+ suppressed stomatal conductance of maize leaves under normal growing conditions but significantly increased stomatal conductance under NaCl stress. Mehler reaction dependent electron transport rate was increased by the addition of 2-8 mmol·L -1 Ca 2+ both in controls and in the NaCl stressed maize leaves; however, the extent of the increase was greater in salt stressed maize leaves. The total electron transport rate was reduced in controls but increased in NaCl stressed maize leaves by the addition of 2-8 mmol·L -1 Ca 2+. The addition of 8 mmol·L -1 Ca 2+ significantly increased the activities of SOD and APX with the extent of the increase greater in APX than SOD. In conclusion, addition of Ca 2+ alleviated inhibition induced by NaCl stress in maize leaves, which was associated with the promotion of photosynthesis, the enhancement of Mehler reaction, and the activities of antioxidant enzymes. The enhanced Mehler reaction could not only consume excess excitation energy to avoid over reduction of the electron chain of photosynthesis but also promoted xanthophyll cycle dependent thermal dissipation by forming a transthylakoid membrane pH gradient (ΔpH) to efficiently protect maize leaves against photodamage under salt stress. Also, the active oxygen produced via the Mehler reaction was scavenged by the enhanced anti-oxidative enzymes.

Alpine environments are characterized by rapid changes in climate, and leaves of alpine plants are routinely exposed to high light intensities at low temperatures. The fact that there seems to be no impairment of photosynthesis by high light and low temperatures under field conditions indicates a very well regulated system of carbohydrate turnover together with a functional system of antioxidants. To study the mechanisms of adaptation of alpine plants, we investigated the antioxidative defense capacity in leaves of two alpine plants, Rhodiola quadrifida and R. gelida. Field investigations were carried out on the slopes of Tianshan Mountain near the Tianshan Glacier NO. 1. Along this slope, R. quadrifida was found between 3 500 and 3 805 m and R. gelida was found between 3 805 and 4 010 m. The two species coexisted at 3 805 m. Plant specimens used in this experiment were collected at 50 m intervals from 3 610 to 3 900 m. Our results showed that the malondialdehyde (MDA) content in leaves of R. gelida was significantly greater than that in R. quadrifida, suggesting that R. gelida might suffer more serious oxidative stress compared to R. quadrifida. The fact that R. gelida can survive and maintain normal metabolism at high elevations suggests that it might be an adaptive mechanisms to endure serious oxidative stress in this harsh environment. The increase in the activities of antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) as well as the contents of reduced glutathione (GSH) and ascorbic acid (AsA), in the leaves of R. gelida suggested a combined and balanced enhancement of antioxidants to improve stress resistance in alpine plant leaves. Among all the antioxidative enzymes examined, peroxidase (POD) was quite distinct from others. Activity of POD was below the limits of detection in leaves of R. quadrifida collected from elevations lower than 3 805 m, but enhanced activity was observed in leaves of R. gelida as altitude increased implying that POD might play an important role in plant adaptation to alpine environments. Given the inverse relationship between growth rate and peroxidase activity demonstrated in many plant developmental systems, in-depth studies on the role of peroxidases in adaptation of R. gelida to high altitudes are warranted.

Cloning of cytosolic (GS1) cDNA and chloroplast glutamine synthetase (GS2) cDNA from Pisum satium was carried out previously in our laboratory. To identify the functions of the GS genes, we first constructed a plant expression vector, p2GS, harboring two different isoenzymes, GS1 and GS2 cDNAs, under the control of two constitutive promoters of rice, Actin1 (Act1) and maize Ubiquitin (Ubi) genes. Then, using an Agrobacterium tumefaciens-mediated transformation method, we introduced GS1 and GS2 genes into wheat (Triticum aestivum) plants, producing 2GS-transgenic wheat plants using immature embryos as the explants. Presence of the transgenes GS1 and GS2 in wheat plants was confirmed by PCR and Southern blot hybridization analyses. Forty-one independent transgenic wheat plants with tolerance to an herbicide (Phosphinothricin, PPT) were generated. Results from Basta tests showed that the 2GS-transgenic wheat plants were endowed with herbicide-tolerant properties. Almost all of the transgenic plants were normal in morphology, and seed production was similar to that of the control wheat plants. Our study suggest that PPT resistance is conferred by effective expression of glutamine synthetases in transformed wheat plants, and glutamine synthetase genes can serve as a selective marker gene of wheat transformation system in our study.