Fine root life-span and turnover play an important role in carbon allocation and nutrient cycling in forest ecosystems because of high levels of fine root production and consequent mortality and decomposition. Fine roots typically are defined as having the following characteristics: less than 1 or 2 mm in diameter; short life-span; and greater efficiency in accessing belowground resources than large diameter roots. However, when categorizing roots by diameter size, the position of an individual root on the complex lateral branching pattern has often been ignored, and our knowledge about relationships between branching order and root function is limited. More recently, studies on root order have found that first-order fine roots at the distal end of a root system, which has the primary function of nutrient uptake rather than storage and transport, are thinner in root diameter and have higher tissue nitrogen (N) concentrations, higher maintenance respiration rates, and lower total nonstructural carbohydrate (TNC) concentrations. Thus, the smaller diameter roots have a shorter life-span in contrast to higher order roots (which are coarser roots with larger diameter). Although either approach (diameter or root order) is reasonable to use in fine root studies, estimates of fine root life-span or turnover are much more variable when using root diameters because of the large variation in diameter sizes. The objectives of this study were (1) to examine variations of fine root diameter and diameter range (minimum-maximum) as a function of branching order from first order to fifth order; and (2) to determine the relationship between fine root diameter and root branching order and soil resource availability using two tree species, Manchurian ash (Fraxinus mandshurica) and Dahurian larch (Larix gmelinii).
This research was conducted in Maoershan Forest Research Station (45°21'-45°25'N, 127°30'-127°34' E) owned by Northeast Forestry University in Harbin, Heilongjiang, China. Both ash and larch forests were planted in 1986. In each plantation, we established three 20 m×30 m plots at an elevation of 506 m. On May 15, July 15 and September 15 of 2003, three small intact segments of the fine root system were excavated carefully at a random location in each plot. Soil blocks (20 cm×20 cm×10 cm) were excavated from the sties at depth of 0~10 cm and 11~20 cm. All intact root segments were collected from each block. Once excavated, the intact segments were put into plastic bags with ice and stored at a temperature of 0~2 ℃. In the laboratory, each individual root was dissected by branching order beginning with the distal end of the root system (labeled as the first-order) increasing sequentially with each branch from the first to higher order roots. After the dissection, length, diameter and dry weight of a given order were determined.
The results showed that mean diameters of fine roots were significantly different (p<0.001) among orders with the diameter increasing regularly from first-order to fifth-order branches in both species. The mean diameter of first-order roots was 0.26 mm for ash and 0.34 mm for larch, and fifth-order roots had average diameters of 1.54 mm and 1.70 mm for ash and larch, respectively. If fine roots were defined as having a diameter less than 1-2 mm, five orders of ash and four orders of larch would be defined as being fine roots. If the diameter of fine roots was defined as being smaller than 0.5 mm, the first three orders of ash roots and the first two orders of larch roots would be included in the fine root population. Within the same root order, there was variation within fine root diameters and there were differences between the two species. The diameter ranges of the fine roots from first order to fifth order were 0.15-0.58, 0.18-0.70, 0.26-1.05, 0.36-1.43, and 0.71-2.96 mm for ash, and 0.17-0.76, 0.23-1.02, 0.26-1.10, 0.38-1.77, and 0.84-2.80 mm for larch. The mean coefficient of variation in first-order roots was less than 10%, second- and third-order was 10%-20%, fourth- and fifth-order was 20%-30%. Thus variation in root diameter also increased with increasing root order.
These results suggest that “fine roots”, which are traditionally defined as an arbitrary diameter class (i.e., <2 mm in diameter), may be too large a size class when compared to the finest roots. The finest roots have much shorter life-spans than larger diameter roots; however, the larger roots are still considered a component of the fine root system. Root order also is important to root life-span, because variation in diameters among roots within the same order is large and diameters varied from <0.2 mm, to 0.2-0.5 mm and to >0.5 mm even in the first-order roots. Differences in the life-span between root diameter and root order affect estimates of root turnover. Therefore, based on this study, both diameter and order should be considered when estimating fine root life-span and turnover.

Most desert soil management decisions are based on quantitative measurements of the biomass of the dominant plant species. The biomass of the dominant plant species in a typical oasis-desert ecotone (ODE) of Minqin was measured in 82 plots (10 m×10 m). The results showed that the distribution and total cover was approximately 16.12%. Above- and below-ground biomass of five dominant desert species (Nitraria tangutorum, Calligonuum mongolicum, Haloxylon ammodendron, Agriophyllum squarrosum and Halogeton arachnoideu) was measured by excavation. Linear regressions were used to analyze the relationships among all the biomass components for each plant (fresh and dry weight of above- and below-ground biomass) and the basal diameter, total height and canopy cover. Best fit models were constructed for each species using 80% of the data. Our results showed that basal diameter (excluding N. tangutorum) and canopy cover were the best predictors of biomass for all five desert plant species. A validation test using the other 20% of the data not used for estimating the regression equations indicated that these equations made accurate predictions of desert plant species biomass.

To assess the effects of the Indo monsoon on litterfall dynamics and changes of litterfall along altitudinal gradients in the tropical rain forests of southwestern China, eight plots were chosen along three elevational gradients of 600, 1 100 and 1 600 m in Xishuangbanna, China. We examined the relationship between litterfall dynamics and climate, and their changes with increasing altitude. On three gradients, average annual temperature was 22.1, 20.1 and 16.6 ℃ respectively, with a mean lapse rate of -0.005 3 ℃ m^-1. With increasing altitude, annual average rainfall increased (1 532, 1 659 and 2 011 mm, respectively), while in the dry season they were similar (282-295 mm); evaporation changed slightly (1 369, 1 374 and 1 330 mm, respectively); annual average relative humidity decreased (86%, 81% and 84%, respectively) and was much more pronounced in the late dry season; and soil water content increased significantly. Litterfall production of tropical seasonal rain forest (1 072 to 1 285 g·m^-2·a^-1) was higher than in the tropical montane rain forest (718 to 1 014 g·m^-2·a^-1). Both litterfall production and CV of annual litterfall processes had a significant and negative linear relationship with altitude. Litterfall production had a significant and positive linear relationship with temperature and was inversely related to rainfall. Peak litterfall during the dry season was influenced by relative air humidity and soil water content. Peak litterfall occurred earlier in the dry season at altitudes of 1 100 to 1 720 m due to decreasing humidity with altitude whereas at higher sites (1 820 m), increasing soil moisture levels delayed the litterfall peak. Our results suggested that 1) litterfall production of the tropical seasonal rain forest coincided with those of moist tropical rain forests in Southeast Asia; 2) water stress in the dry season changed with altitude and determined the timing of peak litterfall; and 3) with increasing altitude, there was a transition from seasonality to stability in annual litterfall process.

Altitudinal gradients incorporate multiple resource gradients which vary continuously in different fashions. Studies of mountain floristic patterns along altitudinal gradients has revealed regular patterns of the flora along environmental gradients, changing trends in biodiversity along altitudinal gradients as well as a better understanding of biological fitness. To explore the floristic compositional characteristics and the ecological significance of floristic patterns along altitudinal gradients in the China National Natural Reserve of Dawei Mountain in southeast Yunnan, the flora was quantified along two transects, one on the southwest slope and the other on the northeast slope of the reserve, including a vertical vegetation transect. Further investigations were conducted on the flora of Dawei Mountain which have ever been accounted for in the literature, such as Flora of Yunnan, The Seed Plant in Yunnan and so on. The structural characteristics of the flora and the altitudinal distribution patterns of its floristic components were analyzed. Systematic cluster analysis was applied to the data to determine how composition changed with changes in altitude and climate. The conclusions can be summarized as follows: 1) There was a strong boundary that differentiated tropical floristic elements from evergreen broad-leaved forests at an altitude of approximately 1 500 m; 2) Cluster analysis showed that humid rain forests occurred below 700 m a.s.l, mountain rain forests were between 700 m and 1 500 m, monsoon evergreen broad-leaved forests were between 1 300 m and 1 800 m, and the mountain mossy evergreen broad-leaved forest occurred above 1 800 m a.s.l. Non-representative mountain mossy dwarf forests (above 2 100 m) in the area are distributed on windward slopes and barren land on the mountain slopes.

Using non-brown fractal model, this study was tailored to quantify and compare the variations of species richness of trees, shrubs, herbs and total plants along altitudinal gradients and characterize the dominating ecological processes that determined the variations.
Two transects were sampled far away from any anthropogenic disturbances along the shady slopes of the Dongling Mountains, Beijing, China. Both transects were continuous and 2 m wide, and every individual tree and shrub was recorded in each transect. Discrete quadrats of 1 m×1 m were located along transect A and B for estimation of herb species richness along the altitudinal gradients. The bevel interval between the quadrats was 10 m and 25 m, respectively. In the present study, transect A and B were combined into one transect AB, and 40 m was selected as optimal quadrat length along the altitudinal gradients for measuring plant species richness patterns. Species richness in each quadrat was calculated by a program written in Matlab 6.0.
Firstly, direct gradient analysis was used to describe the overall trends in species richness of trees, shrubs, herbs and total plants with changes in altitude, and the non-brown fractal model was used to more accurately detect their variations at various scales along the gradient. The model assumed that each class of ecological processes affecting the distribution of a variable could be represented by an independent spatial random function. Generally, ecological phenomena were determined not by a single ecological process but by multiple ones. These processes acted on ecological patterns at their own spatial scales. In the non-brown fractal model, the spatial random functions were nested within a larger range of spatial scales. The relative contribution of spatial random functions to the spatial variation of a variable was indicated by a weighting parameter that had to be greater than or equal to zero.
In this paper, we reached the following results and conclusions. Firstly, the direct gradient method described the general trends of trees, shrubs, herbs and total plants along the altitudinal gradient but was unable to provide more detail about altitudinal variations of species richness. The non-brown fractal model uncovered altitudinal variations in species richness of trees, shrubs and herbs at various scales and related them to ecological processes. The sharp changes in the double-log variograms suggested that the non-brown fractal model was advisable for characterizing the altitudinal patterns in species richness of trees, shrubs and herbs at various scales but not appropriate for explaining the variation of total plant species richness, because there was no obvious sharp change in its double-log variogram. Secondly, for trees, the double-log variogram was divided into two scale ranges (0-245 m and 245-570 m), with a fractal dimension of 1.83 and 1.10, respectively, implying that changes in tree species richness was nearly random at small scales (0-245 m) and nearly linear at large scales (245-570 m) along the altitudinal gradients. This suggested that altitudinal variations in tree species richness were dominated by short-range processes at small scales and by long-range processes at large scales. Thirdly, for shrubs and herbs, the double-log variograms exhibited three sections (0-101 m, 125-298 m and 325-570 m), and the fractal dimensions were 1.78 and 1.97, 1.56 and 1.43, and 1.08 and 1.25, respectively. The results indicated that, like trees, species richness of shrubs and herbs were distributed randomly at small scales and changed in a more linear fashion at large scales although variations in herb species richness was less heterogeneous than shrub species richness at large scales. These results also indicated that species richness of shrubs and herbs changed approximately like brown movement at middle scales. The results also suggested that altitudinal variations in species richness of shrubs and herbs were dominated by three ecological processes, short-range ecological processes at small scales, long-rang ecological processes at large scales, and brown fractal processes at middle scales. Interestingly, comparisons of the variations in species richness of shrubs and herbs found that shrubs and herbs presented the same scale ranges in spatial variation in species richness buu displayed contrary trends in species richness along the altitudinal gradient, i.e. shrub species richness decreased with increasing elevation whereas herb species richness peaked at mid-high elevation. These patterns suggest that although the scales at which the main processes affected patterns in species richness were the same, the processes were completely different, or the processes were similar but the responses of shrubs and herbs to the ecological processes were different. Finally, total plant species richness did not show any obvious pattern along the altitude gradient and maintained a constant fractal dimension across all scales, perhaps because the processes defining the patterns of total plant species richness had similar weights and acted over closely related scales.

With an increase in vegetation coverage, there can be a decrease in soil water content due to uptake and evapotranspiration by the vegetation. At high planting densities, poor growth and even mortality has occurred due to the decrease in soil water content. Hence, a better understanding of the relationship between soil water content and the density of plants is important for designing effective restoration projects. To study these relationships, we developed a soil water dynamic simulation model of a Caragana intermedia woodland under different slope gradients and slope aspect in the Huangfuchuan watershed conditions based on previous studies and field experiments. The model took into account soil characteristics, precipitation infiltration, vegetation transpiration, and soil evaporation. Daily changes in soil water content, transpiration, and evaporation of Caragana intermedia woodlands with different vegetation coverage, slope gradient, and slope aspect was simulated from 1971 to 2000. Through model simulations, we determined the functional relationships among soil water content, plant coverage and slope as well as the optimal plant density on flat slopes. With further simulations, we determined the effects of slope gradient and slope aspect on soil water content. When slope gradient was less than 10 degrees, the optimal planting density was sensitive to slope gradient. In the range of 10 and 30 degrees, planting density was not sensitive to slope gradient. Therefore, when reconstructing vegetation, it is important to consider planting densities on the hillsides with slope gradients less than 10 degrees.

Crop growth simulation models have extensive application in crop growth monitoring, yield forecasting and utilization of enviromental resources. However, problems arise when scaling crop simulation models from the field to regional scales, especially in acquiring initial conditions and parameters for the model. Fortunately, satellite remote sensing has the potential to improve some of the model parameterization for monitoring crop growth at regional scales. Thus, there is interest in developing an approach and methodology for incorporating remotely-sensed information with crop growth simulation models.
In this paper, the crop model WOFOST (World food study) was adapted for simulating growth of winter wheat by using field experimental data from North China, and the radiative transfer model SAIL-PROSPECT was adapted by adjusting the sensitivity of its parameters. The two models were then coupled using LAI to simulate the vegetation indices SAVI. Finally, WOFOST was re-initialed by minimizing differences between SAVI_s simulated by coupling the model and SAVI_m synthesized from MODIS remote sensed data using an optimization software program (FSEOPT). The results were validated by using field experimental data (including leaf area index, dry weight of leaves, stems and storage organs) in Zhengzhou, Henan Province, Tai'an, Shandong Province, and Gucheng, Hebei Province, and some MODIS data during the growing season of winter wheat from 2001 to 2003.
The main results in this study were as follows: (1) Differences between the simulated mature date, after re-initializing the emergence date using remote sensing data and simulated values, with the actual ermergence date was within 2 days, and simulated LAI and gross above-ground dry matter weight were 3-8 percent of actual values; (2) By re-initializing biomass weight in the turn-green stage, relative errors of the simulated LAI and gross above-ground dry matter weight were within 16% at key development stages, and simulated LAI and storage organ weight were closer to measured values during the entire growing period; (3) Appropriate remote sensing data during the period from the turn-green stage to earing stage was more critical for improving crop modeling when biomass in the turn-green stage was adjusted.
We presented a novel method for validating and adjusting crop models to regional scales. Optimization of the crop simulation model by dynamical adjustment of the initial variables and parameters based on remote sensing data produced highly satisfactory results. This research provides a basis for optimizing crop models by using remotely sensed data at regional scales. However, errors in the simulation results due to uncertainty of remote sensing data and SAIL-PROSPECT parameters still exist and further study is needed.

Based on non-supervised classification methods, multi-temporal images, such as NOAA-AVHRR, SPOT-VEGETATION and MODIS series data, have been used to map regional, continental or global land cover patterns. Because of limitations of the classification method and spatial resolution of images, traditional non-supervised classification often results in many errors in the transition zones in which the spatial distribution of vegetation show segmental patterns. This problem can decrease the integral accuracy of the classification to a certain extent.
In this paper, a new method, the topographical restrictive features, is presented to classify remotely sensed images using the Jinhe watershed in the Loess plateau as a case study. First, 25 relatively independent classes were obtained using the non-supervised classification method with multi-temporal NDVI data derived from the first two bands of MODIS data. Every cell with 500 m spatial resolution of the classification determined by the non-supervised method was divided into 25 homogenous cells with 100 m spatial resolution. Then, topographical features were defined. Information about aspect, slope, elevation, river net structure, and vegetation regional characteristics, derived from 1:250 000 geographical spatial data, ETM+ image and yield data, were used to construct topographical restrictive features. Finally, the classification of every sub-cell was tested using the restrictive features and some cells were reclassified while maintaining their original classification. After the secondary classification, all cells were labeled by land cover type according to the land cover classification system, which was defined previously on the base of the IGBP land cover classification system and UMD system.
Using this new method, the accuracy of the land cover classification increased from 71.88%, in traditional non-supervised classification method, to 84.09%. In particular, the accuracy of cropland and urban type classification improved. The method of cell sub-division avoids the shortcomings of traditional classification methods owing to the coarse resolution of the image processing, and makes it more highly probable that land cover types are homogenous within cells. The introduction of topographical restrictive features decreases uncertainty of traditional fuzzy classification and provides more precise distinctive features to classify the fuzzy zone, and thus improves the accuracy of classification.

Mapping and quantifying land use and land cover changes are important for evaluating recent changes in the regional and global environment and for simulating future changes under different climate change and human land use scenarios. The normalized difference vegetation index (NDVI) and surface temperature (T_s) are two important parameters used to describe the characteristics of land cover. The NDVI-T_s feature space combines these two parameters into one variable. By and large, T_s/NDVI is synchronized to the growing season of vegetation so it can approximate the different phases and status of vegetation growth. Compared to NDVI and T_s, NDVI-T_s contains more land cover information and should be more suitable for characterizing the distribution of vegetation or land cover.
The aim of this paper was to discuss the feasibility of using the NDVI-T_s feature space to better characterize the current distribution and changes in vegetation and land cover in China. We used several classification methods, including Principal Component Analysis (PCA), unsupervised classification and post-classification sustained based on digital elevation models (DEM). The results indicated that T_s/NDVI was highly sensitive and could discriminate different vegetation cover categories in China at large-scales. The accuracy of vegetation classification based on T_s/NDVI was 72.0%, a 3.3% improvement in accuracy as compared to NDVI images, using unsupervised classification, and the Kappa value increased 0.020 2. Moreover, because of the simplexity of remote sensing information, the classification based on seasonal T_s/NDVI data could not avoid completely the mixed classification phenomena. It was necessary to add other information, reflecting vegetation characteristic and its environment to implement post-classification, such as DEM.
When the inversing accuracy of T_s improved, T_s/NDVI data can precisely describe the status of vegetation or land cover in China and improve monitoring of land use changes. This technique has great research potential and practical value.

Dissolved organic carbon is an important component of the carbon balance of terrestrial ecosystems and source of energy, carbon, and nutrient transfer from terrestrial to aquatic ecosystems. Land use changes caused by human activities have had major impacts on terrestrial ecosystem carbon cycles, including impacts of soil DOC dynamics. Hence, it is important to understand the impacts of land use changes on DOC for assessing the impacts of land use change on the carbon cycle. Over the last several centuries, extensive areas of native vegetation in the Liupan Mountain Forest Zone have been replaced by croplands or rangelands, whereas in recent decades former arable lands and rangelands have been afforested. However, the impacts of these land-use changes on the terrestrial ecosystem carbon cycle are unclear, especially on the soil DOC dynamics. In order to assess the impacts of land-use changes on soil DOC dynamics, we measured the concentrations of DOC in precipitation, subsurface water, soil leachate, detrital leachate solutions, throughfall, and water percolating through the soil in plots with the same elevation, exposure, and soil types but with different vegetation types. A natural secondary forest dominated by Querces liaotungensis, Populus davidiana, or brushwood, a cropland and rangeland derived from destruction of the natural secondary forests, and a 13, 18 and 25 year old larch plantation, Larix principis-rupprechtii, afforested on former croplands or rangelands were studied.
Our results showed that concentrations of DOC in precipitation and subsurface water from May to October was 0.80 -1.60 mg·L^-1 and 2.43-7.66 mg·L^-1, respectively. From September to October, the concentration of DOC in throughfall was 1.78-15.20 mg·L^-1 which was higher under natural forests or plantations than in croplands or rangelands and positively correlated with annual production of aboveground detritus (p=0.05). The concentration of DOC in detrital leachate solutions, derived from detritus submerged in water for 24 h, was 12.30-64.79 mg·L^-1 and its fraction was not more than 1%. The concentration of detrital DOC was 400% and 153% higher under natural forests than cropland and rangeland, respectively, and 194% and 50% higher under plantation than cropland and rangeland, respectively. Its fraction was 79% and 98% higher in the cropland and rangeland than the natural forest, respectively, and 180% and 210% higher in the cropland and rangeland than the plantation, respectively. The concentration of DOC in detrital leachate was positively correlated with aboveground detrital carbon storage of leaf, branch, humus and litter (p=0.05, n=184). The concentration of DOC in soil solutions in the 0-20 cm deep soil layer was 7.88-88.44 mg·L^-1 and its fraction was not more than 1%. The concentration of soil solution DOC was higher under the natural secondary forest or the plantation than cropland or rangeland, and its fraction was lower under natural forest than cropland or rangeland but higher under the plantation than natural secondary forests. The difference of the soil solution DOC concentration or fraction between the natural secondary forest or plantation and rangeland or cropland was greater at 0-10 cm soil depth than 10-20 cm soil layer. The change of this DOC concentration with soil depth was greater under the natural secondary forest or plantation than cropland or rangeland. The concentration of this DOC was positively correlated with detrital carbon storage and soil water content (p=0.05), and soil water content was the main factor that influenced the concentration of DOC in soil solutions. The concentration of DOC in soil percolation water was 5.76-58.84 mg·L^-1 which was higher under the natural forest or plantation than cropland or rangeland. The difference in this DOC concentration between the natural secondary forest or plantation and rangeland or cropland was greater in the 0-10 cm than 10-40 cm soil layer. The change of this DOC concentration with soil depth was greater under the natural secondary forest or plantation than cropland or rangeland. These differences were ascribed to the differences in vegetation and soil properties that resulted from changes in land use and their consequent impacts on hydrological processes. The results of this study indicate that changes in land use have large impacts on terrestrial DOC concentrations.

Phenological characteristics and patterns of biomass allocation were studied in four ephemeral species of Trigonella (T. cancellata, T. arcuata, T. monantha and T. orthoceras) from the Zhungaer desert. The results showed that germination strategies were diverse among species. Seed germination occurred in the spring, summer and autumn in all four species, but was most prevalent in the spring and autumn. The germination time of seeds was very closely related to environmental factors, such as temperature and precipitation. There were no obvious interspecific differences in germination time. Plant growth was quick and the life cycle short in all four species. The fruits maturate before the arrival of the arid summer season. All four species are monocarpic, and their life-history strategy can be described as that of escaping aridity. The reproductive yield of plants germinated in the spring and autumn was maximized by an instantaneous switch from vegetative growth to reproductive growth after a short period of vegetative growth. The four species allocate a high proportion of carbon to reproductive output and was 62.3%, 51.9%, 54.3% and 58.3% for the four species, and the absolute measures of reproductive output were size-dependent. The reproductive output increased with plant size, with the r-value 0.989, 0.935, 0.720 and 0.924 in all the four species (p<0.001). There were significant differences in the size (p<0.01) and the reproductive output (p<0.05,p<0.01) among plants that germinated in different seasons. The plants that germinated in the spring were smaller and their reproductive output lower than those hat germinated in the autumn, but the difference in the proportion of reproductive allocation was not significant (p>0.05). These results indicate that differences in reproductive output can be explained by size differences in plants from different germination times. Finally, we discussed the life-history strategies of the four ephemeral species and analyzed their differences based on individual size, survival ability and reproductive output of plants germinated during different season, and their adaptation strategies to the arid environment of the Zhungaer desert.

Characteristics of the leaf epidermis of 8 species in the genus Caragana, which grow from the east to the west on the Ordos Plateau, were studied by observation through a light microscope (LM) and a scanning electron microscope (SEM). The study showed that the leaf epidermal cells were usually irregular or polygonal shaped, and the type of stomatal apparatus was mainly anomocytic. The stomatal density and the stomatal index of the xero-mesophytic C. purdomii were higher than these of the seven other xerophilous species (C. opulens, C. intermedia, C. korshinskii, C. roborovskyi, C. stenophylla, C. tibetica and C. brachypoda). Comparisons within species showed that C. intermedia, C. stenophylla, and C. tibetica had higher stomatal density when growing in heavier drought areas, whereas C. korshinskii had lower stomatal density; C. stenophylla and C. tibetica had a higher stomatal index whereas C. intermedia and C. korshinskii had a lower stomatal index. The leaf epidermis of C. intermedia, C. korshinskii, C. tibetica and C. roborovsky had a dense trichome, which was an adaptive characteristic caused by the droughty environment. The leaf epidermis of xerophytic species had a higher plasticity than that of mesophytic species. The plasticity index of C. stenophylla and C. tibetica, which are the dominant species in semi-deserts, was the highest among the 8 species. Observation using SEM revealed that there were two types of stomas: stomas located below the epidermal cells and stomas located on the same level with epidermal cells. It also revealed that there was cuticle and wax on the leaf epidermis, and that the trichome on the leaf epidermis was a single cell hair.

The model of West, Brown and Enquist shows that total hydraulic resistance in trees can be independent of path length provided that vascular conduits taper upward sufficiently. This model contradicts the hydraulic limitation hypothesis on tree height growth. To test the validity of this model, we investigated axial and radial changes in xylem anatomical characteristics of six evergreen broadleaved tree species in a subtropical forest in Yunnan. The six species studied included Castanopsis wattii, Lithocarpus chintungensis, L. xylocarpus, Cyclobalanopsis stewardiana, Schima noronhae, and Hartia sinensis. The first four species are from the Fagaceae and the other two species are from Theaceae. Fourteen trees (15-25 m) were sampled from the six species. Sapwood cores were taken from each tree at intervals of 1 m along the trunk to study the axial variation in xylem anatomy. Stem cross sections were collected at three heights from the four Fagaceae species to characterize radial variation. Transverse sections of 50-80 μm thickness were made using a sliding microtome. Our analysis of transverse microscopic sections showed that the conduit lumen diameters increased from the top to the base of the crown in all trees and to the base of the bole in four trees. Conduit lumen diameter was approximately constant from the crown base to the tree base in the remaining trees. Vessel density increased with height, especially within the crown. The lumen/total sapwood area ratio was constant along the trunk in four of the twelve trees and decreased from the base of the crown to its top in most of the remaining trees. The theoretical specific hydraulic conductivity decreased substantially from the base of the crown to its top and was constant below the crown base in most trees. Conduit lumen diameters increased linearly for the first 20 - 40 years of cambial age and then stabilized in most of the eight trees of Fagaceae. There was no difference in conduit lumen diameter produced by the same aged cambium at different aboveground heights. Our results suggested that axial and radial trends in conduit lumen diameter of the six evergreen broadleaved species were consistent with partial buffering of hydraulic resistance from path length effects. The uniform size of conduit lumens below the crown base contradicted the critical assumption of constant conduit taper along the trunk in the model of WBE.

Dipterocarps dominate the canopy of tropical rainforest of Southeast Asia. They are not only the world's main source of hardwood timber, but their canopy leaves are main organs for global carbon sequestration. Due to anthropogenic activities, many species of dipterocarps are threatened. Because of this situation, ex-situ conservation efforts were employed to conserve the genetic resources of several dipterocarps.
In this study, four dipterocarp species, Dipterocarpus retusus, Hopea hainanensis, Parashorea chinensis (emergent tree species in the rainforest) and Vatica xishuangbannaensis, were selected as study species that had been transplanted in 1981 to an ex-situ dipterocarp conservation forest in Xishuangbanna Tropical Botanical Garden. We measured the diurnal changes in photosynthetic rates, parameters of chlorophyll fluorescence, and morphological traits of their canopy leaves at 15-21 m height during the rainy season of 2004. The results indicated that the maximum photosynthetic rates (P_max) per unit leaf area (7.5 to 18.1 μmol·m ^-2·s^-1) and mass (89.08 to 150.82 nmol·g^-1 DW·s^-1), dark respiration rates (R_d), light saturation point (LSP), light compensation point (LCP) and leaf morphological traits differed significantly among species. Photosynthesis in the four species was depressed at midday. The results revealed that stomatal closure induced by high leaf-to-air vapor pressure deficit (LAVPD) led to photosynthetic depression at midday. Quantum yields of photosystem II (Φ_PSⅡ) in four dipterocarp species decreased significantly at midday, indicating that photoinhibition occurred. However, their PSⅡ values recovered to the early morning value by sunset, indicating that photoinhibition was reversible. The nonphotochemical quenching rate (NPQ) increased significantly in D. retusus, H. hainanensis and V. xishuangbannaensis, indicating that NPQ was used mainly to dissipate excess light energy absorbed by PSⅡ. At midday, the electron transport rate (ETR) in P. chinensis was maintained at high levels, while its photosynthetic rate decreased, suggesting that a large proportion of electrons were allocated to photorespiration. Thus photorespiration was the main mechanism protecting the photosynthetic apparatuses of P. chinensis during the midday photosynthesis depression. Other parameters, such as leaf area, size and density of stomata, and total chlorophyll content, also were measured at the same time. There was a general ranking of P_max in the following order from highest to lowest: D. retusus, P. chinensis, H. hainanensi, V. xishuangbannaensis. Based on the diurnal changes in chlorophyll fluorescence, both leaf stomatal limitations and non-stomatal effects played an important role to prevent photodamage during the midday depression of photosynthesis brought by the high irradiances, high air temperature, low humidity, and so on. The high midday leaf water potential of the four species showed that water limitations had no influence on photosynthetic rates.

Pistachio (Pistacia vera) is one of the most important dried fruit trees in the world and is mainly cultivated in Xinjiang, China. However, soil salinization is one of the main limiting factors for its promising potential of development. In this experiment, the effects of NaCl stress on physiological and biochemical characteristics were investigated in seedlings of two cultivars of Pistacia vera, `Changguo' and `Kerman'. Seedlings were grown in pots and treated with four NaCl concentrations: 50, 150, 250 and 500 mmol·L^-1. The membrane permeability, malondialdehyde content (MDA), superoxide dismutase (SOD) activity, catalase (CAT) activity and peroxidase (POD) activity in the leaves of these two cultivars were measured and compared after 5, 10 and 20 days of NaCl treatments.
The experimental results showed that the membrane permeability and MDA content in both cultivars increased considerably with the increasing NaCl stress, which aggravated the degree of membrane lipid peroxidation and injured the membrane stability. The membrane permeability and MDA content in the `Changguo' cultivar increased more quickly than the `Kerman' cultivar and thus experienced greater damage at higher NaCl concentrations. The activities of SOD, CAT and POD had similar trends for both cultivars, first increasing with NaCl concentrations up to 250 mmol·L^-1 and then decreasing at the highest NaCl stress of 500 mmol·L^-1. The coordinated changes of activities among the antioxidant enzymes of SOD, POD and CAT could scavenge active oxygen and maintain a balance of active oxygen accumulation in cells to protect membrane structure. The results also showed that the damage by NaCl stress to the membrane structure and function for both cultivars were mitigated considerably 20 days after the treatments were initiated. There were significant correlations among the membrane permeability, MDA content and the activity of SOD in both cultivars, which implied that the membrane permeability in the plant cells had a close relation with MDA content and oxygen free radical content, as well as the activity of antioxidant enzymes. Together, these results indicated that the `Kerman' cultivar has higher antioxidant levels and greater salt-tolerance than the `Changguo' cultivar of Pistachio.

Pollutions of agricultural land by heavy metals impose a more and more serious risk to environmental and human health in recent years. Heavy metal pollutants may enter the human food chain through agricultural products and groundwater from the polluted soils. Progress has been made on phytoremediation, a safe and inexpensive approach to remove contaminants from soil and water using plants, in the past decade. However, in most cases, agricultural land in China can not afford to grow phytoremediator plants instead of growing crops to be economically sustainable. Therefore, new and effective methods to decrease the risk of heavy metal pollution in crops and to clean the contaminated soils are urgently needed. If we can find crop germplasms (including species and varieties) which sequester heavy metals in their edible parts, such as fruits of vegetables or grain of cereals, at low enough level for safe consumption, then we can grow these selected species or varieties in the lands contaminated or potentially contaminated by heavy metals. If we can find crop germplasms sequester low concentrations of heavy metals in their edible parts and high content of the metals in their inedible parts, then we can use these selected species or varieties for soil remediation. In this study, the feasibility of the method is assessed by analyzing Pb contents in edible and inedible parts of 25 varieties of Zea mays grown under Pb contaminated soils. The soil concentrations of Pb were 595.55 mg·kg^-1 in the high Pb-stress group and 195.55 mg·kg^-1 in the control group.
The results showed that the Pb concentrations in different tissues were in the order of root>shoot≌leaf >grain. Compared with the control, the Pb concentrations in root, shoot and leaf were greatly increased under the highly Pb- stressed condition, while the increments of Pb concentration in grain were relatively lower. Under the high Pb-stress, the grain Pb concentrations of 12 varieties exceeded the National Sanitation Standard of China (NSSC) and were inedible. This indicates that there is a high Pb pollution risk forZea mays grown on Pb polluted sites. Although 22 of the 25 tested varieties had harvest loss under the highly stressed condition, ranging from 0.86%-38.7% of the grain biomass acquired at the control, the average harvest loss of all tested varieties was only 12.6%, which is usually imperceptible in normal farming practices. Therefore the risk of Pb pollution in Zea mays products can not be promptly notified and prevented based on the outcome of the harvest. However, we did find 13 varieties of 25 tested varieties had grain Pb concentration lower than the NSSC. It is, therefore, possible to reduce the pollution risk if these favorable varieties are used for Zea mays production in Pb polluted or potentially polluted agricultural lands.
Pb concentrations in vegetative tissues (root, stem and leaf) were significantly correlated with each other, while Pb concentrations of each vegetative tissues were not significantly correlated with that of grain. Among the 25 tested varieties, some varieties had Pb concentrations in grain lower than (No.1-3 and No.6) or slightly above (No.4) the NSSC level, while their Pb concentrations in the vegetative tissues were among the highest. When excluding these varieties, correlations between the Pb concentrations of grain and those of vegetative tissues of the rest of the tested varieties became highly significant. In addition, variety No.1 had the lowest harvest loss under high Pb-stress, and the highest Pb sequestration in vegetative tissues (51.69 mg·plant^-1, 12 times as much as in the control). The similar features were also observed in varieties No.2, No.3 and No.6, which sequestered 36-42 mg·Pb plant^-1 under high Pb-stress. We recommend these varieties of Zea mays to be used for bioremediation of Pb contaminated soil and crop production at the same time.

Nearly half the irrigated fields in the world are becoming saline and alkaline. Soil salinization is becoming a serious problem in China, especially in the seashore plain of north China where there is a highly developed industrial and agricultural economy and a huge population. With the high speed of industrial development and rapidly increasing population, groundwater overuse is leading to an influx of seawater and further expediting salinization of freshwater resources and soil. Lack of freshwater is a main factor restricting social and economic development in the seashore plain of north China.
Irrigation of crops with diluted seawater has been proposed as a way to conserve freshwater supplies. This experiment was conducted to study the characteristics and effects of irrigation with diluted seawater on a salt tolerant economic plant and provide recommendations for saline water irrigation in these drought/semi-drought seashore areas. `Oleic sunflower G101' (Helianthus annuus), a salt-tolerant economic plant, was irrigated with different proportions of diluted seawater in the Laizhou, Shandong Province, where seawater intrusion is a very serious problem. The effects of irrigation with diluted seawater on various growth indices, the accumulation and distribution of ions in the plant, and total yields of `G101' planted under local rainfall conditions were investigated during two growing seasons, 2002 (drought year) and 2003 (wet year). The sunflower was irrigated twice during the growing season, one at early bud and the other at early florescence. The results showed that 1) In both the drought year (2002) and the wet year (2003), a 40% seawater irrigation solution was a safe dilution ensuring economic yields for the 100 day growth period of `G101'. During the drought year, `G101' seed yields decreased significantly when irrigated with 40% seawater or greater, while there were no differences in seed yields in the wet year when irrigated with 40% or 60% seawater. Thus, irrigation with a 40% seawater solution was economically feasible. 2) During the drought year, most growth indices of oleic sunflowers when treated with 20% seawater were not significantly different with that irrigated with freshwater (p=0.95), except for stem thickness and disc fresh weight during early florescence. However, in the wet year, all measured growth indices were not significantly different from the freshwater treatment when treated with up to 40% seawater (p=0.95). 3) When irrigated with 0-40% seawater, Ca²⁺ and Mg²⁺ homeostasis was maintained in the leaves and root K⁺ selective ion transport to the disc was strong. Accumulation of Na⁺ was mainly in the root and stem, while Na⁺ concentrations in the leaves and disc were lower. Chloride content was the greatest in the stem as compared to other parts of the oleic sunflowers.

The biological sciences developed very fast during the 20th century and have become increasingly sophisticated and predictive. Along with this trend, areas of research also have become increasingly specialized and fragmented. However, this fragmentation and specialization risks overlooking the most inherent biological characteristics of living organisms. One can ask if the living organisms on the earth have unified and essential characteristics that can connect the disparate disciplines and levels of biological study from molecular structure of genes to ecosystem dynamics. By exploring this question, a new science, ecological stoichiometry, has been developed over the past two decades. Ecological stoichiometry is a study of the mass balance of multiple chemical elements in living systems; it analyzes the constraints and consequences of these mass balances during ecological interactions. All biological entities on the earth have a specific elemental composition and specific elemental requirements, which influence their interactions with other organisms and their abiotic environment in predictable ways. Ecological stoichiometry has been incorporated successfully into many levels of biology from molecular, cellular, organismal and population to ecosystem and globe. At present, the principles of ecological stoichiometry have been broadly applied to research on population dynamics, trophic dynamics, microbial nutrition, host-pathogen interactions, symbiosis, comparative ecosystem analysis, and consumer-driven nutrient cycling. This paper reviews the concepts, research history, principles, and applications of ecological stoichiometry and points out future research hotspots in this dynamic field of study with an aim to promote this discipline of research in China.

Small-scale spatial structure of plant species is important in plant ecology as it affects the dynamics of plant populations, communities and ecosystem processes. Plants interact primarily with their immediate neighbors, and the view of the community as seen by an individual plant can be quite different from processes averaged over large spatial scales. Many processes influence the formation and dynamics of small-scale spatial structures of plant species, and local spatial structure in turn has an effect on the vital processes of plant growth, birth and death. This paper summarizes developments in this area of research based on the extensive literature on small-scale spatial structure of plant species to help direct further research efforts. Firstly, this paper introduces six factors that lead to the formation of small-scale spatial structure of plant species, including 1) habitat spatial heterogeneity, 2) dispersal of propagules, 3) interactions between plants, 4) effects of the biological environment (animals and microbes), 5) effects of exoteric disturbances, and 6) the integrated effects of many factors. The significance and effects of small-scale spatial structure on studies of biological diversity, plant population genetics and restoration ecology are then examined. Finally, several questions were raised and a list of suggested areas of future research on this topic were presented that included: 1) Information on small-scale spatial structure should be integrated into vegetation dynamics at large scales; 2) Either biologically or ecologically, the research about small-scale spatial structure of vegetation should focus on plants, make certain the adequate scale and adopt correct spatial statistical methods; 3) The practical implications of small-scale spatial structure for degraded ecosystems should be highly taken into account; 4) Integration of whole community characteristics should begin with local patterns on small scales; and 5) Small-scale spatial structure should be combined with traditional mean-field theory in order to deeply explore plant community dynamics.

Eupatorium adenophorum, native to Mexico and Costa Rica of Central America, is a worldwide noxious invasive weed. It occurs throughout many terrestrial areas of the world and is especially rampant in Southeast Asia, Hawaii (U.S.), New Zealand, Australia, and the Pacific Islands. Since its invasion to China from the boundaries of Vietnam and Burma, the speed of its spread has been faster than anticipated, particularly in the southern and southwestern parts of the country. Presently, E. adenophorum can be found in Chongqing, Yunnan, Sichuan, Guizhou, Tibet, Guangxi, Taiwan and Hubei Provinces. A rough estimate of the annual spreading rate of E. adenophorum is about 10-60 km from south to north and from west to east in China. It is considered a threat to local economy and biodiversity. As a result, an increasing number of Chinese scientists have become interested in studying this species and much progress in understanding the biology and ecology of this species has been made to date. In particular, much is known about the underlying mechanisms of its invasion biology.
This paper reviews some of the hot research topics of this invasive species in China, including its distribution, predicting its potential distribution, the mechanisms underlying its invasion and spread, and methods for control and elimination. The distribution of this invasive plant in China has been mapped and its potential distribution has been predicted using a computer model based on climatic factors.
Among current research efforts, understanding the mechanisms underlying its invasion and spread is one of the hottest topics. Recent research also has studied the patterns of genetic variation within populations of the invasive weed, novel biochemical mechanisms of interspecies interactions, biological characteristics of the invasive species that explain its highly successful spread, e.g., small seed size, persistent soil seed bank, high offspring production, potential long-distance dispersal of propagules, vegetative reproduction, relatively high CO₂ fixation capacity, shade tolerance, high adaptive ability, and tight link of life-history traits with climatic rhythm.
Although much progress in understanding the biology and ecology of this species has been achieved, there have been no dramatic breakthroughs on how to control E. adenophorum so far. At present, control methods of E. adenophorum are divided into three general categories: manual, chemical and biological control. Biological control is considered the most promising sustainable control strategy for this weed. Several natural enemies and pathogens have been reported that might be able to control the reproduction of this weed, such as Procecidochares utilǐs, Cercospora eupatorii and Alternaria alternata.
The current status of research on the invasive species, E. adenophorum, was reviewed in this paper. Five areas of future research have been proposed: 1) modeling long-distance seed dispersal; 2) allelopathic mechanisms of invasion; 3) ecophysiological adaptations of the invasive species; 4) breeding system of the invasive species; and 5) effective biological control of the invasive species, especially the potential role of genetically engineered fungi.

Macadamia integrifolia originated from Australia where it grows in the rainforests of the eastern coastal areas of the Northern Rivers district of New South Wales and South-East Queensland. The Macadamia tree belongs to Proteaceae. The Macadamia was in fact the only native Australian plant ever developed to a commercial food crop. Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with the roots of approximately 90% of terrestrial plant species. These fungi are an important component of ecosystems, and the diversity of the AMF could largely influence plant biodiversity, ecosystem variability and productivity.
We examined the role of M. integrifolia root exudates in stimulating the germination and growth of AMF. In September 2003, 100 g of M. integrifolia roots were sampled, dried and crushed. The roots were then extracted for two hours in a 70% methanol solution, stirred in 80 ℃ water and filtered. The extract was diluted to 20%, 40%, 60%, 80% and 100% with methanol. The AMF cultures were sterilized, and the spores of Gornas mosseae and Gigaspora margarita were inoculated and cultured at 25 ℃ in the dark for 20 days. The number of spores that germinated was counted and the length of the mycelium measured.
When the concentration of the extract was diluted by 60% methanol, spore germination of Gornas mosseae and Gigaspora margarita reached maximum levels of 81.7% and 76.0%, respectively. At higher extract dilution levels, spore germination decreased, and at 100% dilution, spore germination was lower than 65%. The mycelium reached maximum lengths when the extract was diluted by 60%. The length of Gornas mosseae was 31.2 mm and Gigaspora margarita was 28.0 mm. Mycelium growth declined when the extract dilution increased, especially at 100% dilution. At lower dilutions of 20%, the growth of Gornas mosseae appeared to be stimulated but no effect on Gigaspora margarita growth was observed. At the zero percent dilution, the promotion of mycelium growth was not observed. The concentration of flavones in the extract was the greatest in the 60% methanol dilution (19.26%) but was lower at lower dilutions and only 2.56% in the zero percent dilution. Flavone concentrations also decreased at higher dilutions and the content of flavones was lower than 80% at 100% dilution. There were significant positive correlations (correlation coefficient > 0.95) between the concentration of flavones in the extract and spore germination and mycelium growth of AMF.