Aims Karst forest occurs with limestone soil and humid climate. China's southern karst region is subtropical and centered in Guizhou Province. Precipitation is high and unequally distributed seasonally. Soil drought is frequent as a result of climatic and edaphic factors. Our objectives were to enhance understanding of karst forest ecology and methods of controlling loss of soil and water as a means of managing karst desertification.

Methods For five years, we observed karst natural forest and secondary natural forest in 20 m×20 m plots and analyzed major precipitation ions by ion chromatography. Main indicators were analyzed by Forest Soil Analyzed Methods and observed by Meteorological Observational at Ground Standards.

Important findings Rankings of annual precipitation value regularity were openland > outside karst forest > inside karst forest > under tree and herbaceous layer > runoff at surface and in 90 cm soil > stemflow, and transpiration at forestland and another > total interception in arbuscular and herbaceous layer > total interception in arboreal layer. Annual dynamics of these variables were higher in summer and lower in winter. Maximum water holding capacity ranked soil layer>vegetation, and that in arboreal layer > litter layer > tree layer > herbaceous layer. Ion contents in precipitation had obvious month regularity and decreased in spring and increased in autumn and were high in winter and low in summer. Along precipitation flows (outside forest → in forest → surface runoff → runoff in soil → stream), eight ions were divided into three types: a sustainable rich type included Ca²⁺ and Mg²⁺; a surface rich type included K⁺, Na⁺, Cl^-, \mathrm{N} {\mathrm{O}}_3^{-} and \mathrm{N} {\mathrm{H}}_4^{+} ; and another type included \mathrm{S} {\mathrm{O}}_4^{2-} . Ions input by precipitation, output by runoff and retained in karst natural forest were higher than that in karst secondary natural forest.

Aims As a primary limiting factor affecting survival and growth of plants, moisture has important effects on above- and below-ground morphological characteristics. We studied root distribution characteristics in the Tarim Desert Highway Protection Forest to provide suggestions for water management.

Methods We excavated soil to study root distribution in Haloxylon ammodendron seedlings grown with different amounts of irrigation (35, 24.5 and 14 kg·ind. plant^-1·once^-1) in the Taklimakan Desert.

Important findings With less irrigation, the distribution of root biomass shifted to greater depth. Underground biomass had a significantly negative logarithmic relationship with soil depth under different irrigation amounts. Maximum horizontal spread of roots was twice that of vertical root spread, and horizontal distribution of root biomass was consistent under all irrigation amounts. The vertical distribution of absorptive roots was nearly consistent with vertical changes of soil moisture; all had a unimodal curve, but peak values of absorptive roots biomass were in different soil layers with different irrigation amounts. With smaller amounts of irrigation, absorptive roots were concentrated in deeper soil layers. Root length, root surface area and root volume all exhibited a unimodal curve under different irrigation amounts; the less irrigation, the deeper the peak values. Root-shoot ratios and proportion of vertical root depth and plant height increased as irrigation amounts decreased.

Aims This study was designed to analyze the partitioning of night sap flow in Acacia mangium and its implication for estimating whole-tree transpiration.

Methods Analyses were performed on the partitioning of night sap flow into refilling of internal water storage and transpiration in A. mangium. Sap flow of trees was monitored continuously with Granier's sensors for estimating whole-tree transpiration. Night sap flow data were used to calculate trunk water recharge. Possible night transpiration and stomatal conductance at leaf level in the canopy were measured with a Li-6400 photosynthesis measuring system.

Important findings Vapor pressure deficit (VPD) and wind speed (V) could not fully explain sap flow in A. mangium at night (night leaf transpiration and stomatal conductance were weak). Therefore, night sap flow of mature A. mangium trees was mainly associated with water recharge in the trunk. No significant change in night water recharge of the trunk was found at both seasonal and inter-annual scales. Morphological features of trees including diameter at the breast height (DBH), tree height, and canopy size could explain variances of night water recharge. Furthermore, the error caused by night water recharge on whole-tree transpiration was negligible. The mechanisms and ecological implications of night sap flow partitioning of A. mangium deserve further investigation.

Aims Net primary production (NPP) is plant community production and is the basis of matter and energy cycles of ecosystems. The aim of this study is to accurately simulate NPP on the watershed scale in an area of desertification using simulated results of accumulated soil water replenishment and net radiation.

Methods Using a digital elevation model (DEM) at 30 m×30 m spatial resolution, accumulated soil water replenishment was simulated by using the distributed dynamic model of soil water, and net radiation was simulated by using the Penman-Monteith formula. TheNPP model was developed based on NPP data, accumulated soil water replenishment and net radiation. NPP was accurately simulated for the Kaokaolaigou watershed of the sandy desertification area in eastern Erdos Plateau by inputting the simulated results of the accumulated soil water replenishment and net radiation into the NPP model. We tested the simulated NPP results.

Important findings The test of the simulated NPP results shows that the correlation level between measured and simulated values is 0.05 for the fixed dunes, semi-fixed dunes and sample line 2 and simulated and measured values are in close agreement. The range of relative error between simulated and measured values is 3.22%-6.27%, and the range of skewness between simulated and measured values is from -12.84% to 4.43%. Results show that NPP is different on different slopes and aspects. The NPP decreased from 233.39 to 112.91 g DW·m^-2·a^-1 when the slope increased from 0° to 20°, the maximumNPP of 283.21 g DW·m^-2·a^-1 occurred on flatland and the minimum NPP of 101.68 g DW·m^-2·a^-1 occurred on the south aspect. In conclusion, the NPP model can be used to simulate the distribution of NPP. This research method may allow precise simulation of NPP on a watershed scale.

Water uptake is generally accepted as the most important function of plant roots, while the fact that roots can also release water to soil and its ecological consequences and significance to ecosystem function are not well understood. Studies in the past 20 years confirmed the existence of hydraulic redistribution (HR), which describes the passive movement of water from moist soil to dry soil via roots when transpiration ceases (usually at night). The direction of HR can be upward, downward or lateral in soil along water potential gradients. Because this newly recognized small cycle of soil-root-soil exists within the Soil-Plant-Atmosphere Continuum (SPAC), the mechanism of dynamic movement and storage in the soil-root system has interested many functional ecologists. Continuous measurement of soil water potentials or contents and root sap flow and the use of stable isotopes techniques have been extensively used in HR research. HR acts as a good feedback mechanism between plant water status and soil water dynamics. When deep soil water is plentiful, HR could enhance the efficiency of water uptake via roots, helping plants to make full use of water to improve transpiration and photosynthesis rates and hence maintain physiological function and hydraulic conductivity of the SPAC system. When rainfall comes after the dry season, more precipitation could be transferred to deep soil as an effective storage because of HR, thus increasing availability of rainfall to plant growth. HR was significant for water flux in some ecosystems, for example arid-semiarid sandlands and grasslands, as well as seasonal dry forests. Experiments on HR in Chinese ecosystems are expected or are already underway. On the other hand, integrating HR into ecosystem and hydrology models to study the water relationships between neighboring plants and predict the dynamics of ecosystems with HR is also important. The implications of HR to designing agro-forestry, vegetation recovery, calculating ecological water demand and water conservation in agriculture also deserve more attention.

Long-distance water transport in plants is an important issue in plant physiology and eco-physiology. The recent development of the Xylem Pressure Probe for direct measurement of pressure in individual xylem elements of intact, transpiring plants elicited challenges to the long-standing, widely accepted Cohesion-Tension (C-T) Theory. These challenges instigated debate in the field of plant physiology over mechanisms of long-distance water transport. The challengers and proponents of the C-T theory mutually criticized the Pressure Bomb and the Xylem Pressure Probe technology, and they debated over all three elements of C-T theory (high tension in xylem units; pressure gradients over tree height; the continuous water column in xylem vessels) by reviewing literature and providing physical bases. The debate has cooled down. As a result, the C-T theory has not been discredited while the raised questions in the debate remain mainly unanswered and call for future researches.

Aims Our objective is to assess the impacts of topography, a main source of spatial and temporal environmental heterogeneity, on the dynamics of mountain forest communities.

Methods We sampled a 200 m×100 m plot of mixed evergreen broad-leaved and deciduous forest at Mt. Dalaoling in the Three Gorges Region of China using a 10 m×10 m grid. We measured the topography and set up a digitalized elevation model with resolution of 1∶500. We then took tree ring samples of 16 common tree species, fitted species specific diameter-age models and estimated community age in each of the 200 grids. Multivariate linear regression and ANOVA were applied to analyze the relationship between community age and habitat variables.

Important findings Power model successfully describes the quantitative relationship between DBH and age in all species. Community ages of the grids range from 14 to 179 years old, with a mean of 95 years old. The oldest individuals in the grids include 24 tree species, but the top 5 species make up the oldest individuals in 68.5% of the grids. Significant correlations exist between estimated community age and stream impact index, position, slope, sum of basal area of disturbed trees, and growth rate index, implying that soil erosion critically impacts community development, although species-specific potential age is a constraint of community age. We suggest that topography impacts on community age by controlling the spatial pattern of disturbance regime (by surface erosion), and habitat choice of species with diversified ecological strategies. However, our quantitative estimate of community age has considerable uncertainty due to the complexity of the object studied and the method applied.

Aims Prediction of potential distribution of tree species and their responses to climate change is an increasingly important field of global change. Larix are important tree species in northeastern China. In this study we predict the potential distribution of three Larix species based on “climatic-topographic" relationships. Our aims are to determine: 1) the dominant factors that control the distributions of the three Larix species and 2) the sensitivities of the species to climate change.

Methods Spatial overlap analysis was used to sample the distribution information of the three Larix species and corresponding environmental factors. A logistic regression model was used to explore the quantitative relationships between environmental factors and Larix species. A map calculator method was used to transform the results of the logistic regression model to a prediction map in ArcGIS. Three indices (sensitivity, specificity and percentage of correctness) were used to assess the prediction accuracy of the logistic regression models. Five temperature change scenarios (+1 ℃, +2 ℃, +3 ℃, +4 ℃, and +5 ℃) and six precipitation change scenarios (-30%, -20%, -10%, +10%, +20%, and +30%) were used to explore the impacts of climate change on the distributions of the three Larix and the sensitivities of the species to climate factors.

Important findings Mean annual temperature, annual precipitation and elevation were found to be dominant factors controlling the distributions of the Larix species. The sensitivity of the species changed from 61% to 88%, the specificity changed from 80% to 99.8% and the percentage of correctness changed from 80% to 99.8%. Larix gmelinii decreases by 12% and L. olgensis var. changpaiensis and L. principis-rupprechtii increase by 23% and 500%, respectively, with the temperature increase 1 ℃. L. olgensis var. changpaiensis increases by 64% and L. gmelinii and L. principis-rupprecntii decrease by 12.5% and 15%, respectively, with the precipitation increasing 10%. With climate change to “warm and dry" (+5 ℃, -30%), L. gmelinii shifts northwestward by about 100 km, L. olgensis var. changpaiensis expands northwestward by about 100 km and L. principis-rupprecntii expands northeastward by about 800 km. With climate change to “warm and wet" (+5 ℃, +30%), L. gmelinii shifts northwestward by about 400 km, L. olgensis var. changpaiensis expands northwestward by about 550 km and L. principis-rupprecntii expands northeastward by about 320 km. All three species are sensitive to climate change; therefore, future climate change in northeastern China may greatly impact their distributions.

Aims Amaranthus retroflexus is the most harmful, widely distributed invasive species in its genus. Our objective was to determine its potential worldwide distribution and compare that with its present distribution.

Methods We selected 28 environmental factors including climatic, topographic and soil factors as GIS layers and determined their quantitative relationship with the actual global distribution of the species, based on 4 207 herbarium records. Principal component analysis (PCA) was used to select the environmental factors influencing the distribution of the species. Based on these results, we estimated the central and maximum potential distribution of A. retroflexus and compared them to its actual geographical distribution.

Important findings Fourteen environmental factors importantly affected the distribution of A. retroflexus. The central potential distribution range was southern New Zealand, southeastern Australia, some areas in northern South America, northwestern and southeastern North America, most of Europe and southeastern China. The maximum potential distribution range was southcentral South America, most of North America, some areas in northern Africa, most of Europe, some areas in southern and northern Australia and most of Asia including most of China except Tibet, Qinghai Province, Xinjiang and western Sichuan Province. The potential central distribution of the species matched its actual distribution, whereas the potential maximum distribution was much larger.

Aims There are problems with estimating vegetation cover using remotely sensed data. Many models have been developed by regression of field data and remotely sensed data, but this simple scale transformation often results in large errors. Our objective was to combine field data and multi-scale remotely sensed data to estimate vegetation cover for a typical temperate steppe of North China.

Methods Within our research area, we selected 49 sample fields from areas with high, medium and low vegetation cover and sampled each using 1 m plots nested within larger plots. We vertically photographed each 1 m sample plot with a digital camera positioned at 2 m height. We estimated vegetation cover in each image. Using these data and data obtained through ASTER and MODIS images, we developed a two-stage experiential model of vegetation cover based on the bottom-up method.

Important findings We accurately estimated vegetation cover of typical temperate steppe of North China at a regional scale based on our two-stage model using field data and ASTER and MODIS images. Using a series of MODIS images, it would be possible to estimate vegetation cover of typical steppe across China.

Aims NDVI is extensively used as an important index in evaluating vegetation growth and dynamics, including inter-annual dynamics; however, research on the relationship between inter-annual vegetation dynamics and land use is largely lacking. This study was conducted in the Jinghe watershed to determine inter-annual NDVI dynamics in different land use types.

Methods MODIS data were used to calculate NDVI time serial values from 2001 to 2004. Correlation coefficient (r) and t-test were used to test the consistency in six temporal intervals including one-, two- and three-year scales of four land use types: cropland, forest, shrub and grassland. We calculated the percent area to quantify the spatial extent of significant inter-annual NDVI variation.

Important findings The four land use types had similar NDVI dynamics in all temporal scales. Differences were significant in 2001-2003 and 2001-2004. Cropland and grassland were generally less consistent than forest and shrub in six temporal intervals, especially in 2001-2002, which may be the result of the policy of returning farmland to forest and grassland. Annual NDVI tended to increase over time in the four land use types, suggesting vegetation in this area was gradually restored. Grassland had the greatest percent of area with significantly increasing NDVI, followed by cropland, shrub and forest.

Aims Alpine timberlines are ecotones highly sensitive to disturbances and environmental changes that have become a major focus of global climate change research. Sabina saltuaria is an endemic timberline tree in the Qinghai-Tibetan Plateau. It occurs mainly on south-facing slopes and may be useful in ecological restoration of the high-altitude ecosystem. Understanding its ecological characteristics is necessary for understanding its adaptation strategies, as well as the causes and dynamics of timberline patterns in the region.

Methods We established one 0.42 hm² sample plot at timberline >4 390 m on the south-facing slope of Baima Snow Mountain, Northwest Yunnan Province. We recorded height, DBH (diameter at breast height) or diameter at base for seedlings and saplings, and location of each individual. We used a compass and electronic distance-measuring tool to record the location of each individual. We analyzed the size and DBH structure, time-specific life table, survivorship rate, mortality and hazard rate, spatial point pattern of individuals in each age-class and the co-relationships between different age classes.

Important findings Few seedlings occur at timberline in the area of our field survey (about 17 ind·hm^-2, only 1/6 and 1/14 of that of saplings and trees, respectively). Densities declined from trees to saplings to seedlings, and the number of individuals decreased gradually with greater DBH. The survivorship curve was between Deevy type Ⅱ and Ⅲ. The mortality rate curve was similar to the hazard rate curve; both exhibited a peak of mortality at 6-9 cm DBH). Spatial point pattern analysis indicated that most individuals of different age classes had a clumped distribution at different scales (the older the trees, the more aggregative the distribution pattern); however, seedlings had a random distribution at the scale of <14 m. Also the relationships among individuals in different age classes were all significantly correlated with each other. The associations were more significant between seedlings and trees.

Aims The Huanglong Valley of Sichuan is rich in orchid species, with >30 species in 19 genera, and some orchids dominate the herbaceous layer. However, little is known about their interspecific relationships. Our aim was to investigate how the orchid species interact with each other and with other species.

Methods We sampled 6 621 m×1 m releves in the orchid communities in Huanglong Valley, selected 24 dominant species according to importance values and studied interspecific associations and correlations by usingχ²-tests and Spearman rank correlations.

Important findings Results of χ²-tests of species associations and Spearman rank correlations were consistent and indicated two groups of dominant species. One group, including Cypripedium bardolphianum, C. flavum, C. tibeticum, Orchis diantha, O. chusua and Calanthe delavayi, is mostly distributed where both light and shade are provided by tree overstories. The other group, including Tipularia szechuanica, Malaxis monophyllos, Corallorhiza trifida, Goodyera repens, Calypso bulbosa, Platanthera minutiflora and Listera smithii, is mostly distributed in shade. Non-orchid species, Arctous rube, Gentiana scabra, Pedicularis davidii, Elymus nutans and Pinguicula alpine, which are mostly distributed in open areas, are significantly positively correlated with orchid species of the first group, but mostly negatively correlated with the second group. In contrast, Clintonia udensis, Pedicularis humilis and Carex lehmanii, which are mostly distributed in shaded environmental conditions, have reverse correlations with the two orchid groups. Polygonum macrophyllum, Pyrola calliantha and the orchid Oreorchis nana show no obvious correlations with either of the orchid groups. Our findings indicate that the interspecific interactions of orchid species of Huanglong Valley are complex and the orchid species may have differentiated with regard to the resource use. Reproductive facilitation may play an important role for orchid species diversity in this area.

Aims The issue of rationally classifying plant species into plant functional types at different scales has been a major challenge in ecosystem sciences, especially ecosystem simulation. A typical steppe in Inner Mongolia of China was chosen for study. We asked: 1) Can plant species be classified into several plant functional groups according to their ecophysiological characteristics of stomatal conductance and net photosynthesis? 2) Are there common ecophysiological traits of each plant functional group? 3) What are the advantages and disadvantages of this classification method in ecological modeling?

Methods Diurnal stomatal conductance and net photosynthetic rate of nine plant species were measured in the field during May, July, and late August 2005. Ecophysiological characteristics of these species were quantified by applying models of stomatal conductance and net photosynthesis to the field data. The models were fitted to the data to obtain model parameters for each species. The analysis showed that the model explained up to 55.87% and 78.19% of the variation in the stomatal conductance and net photosynthetic rate, respectively. Cluster analysis was then applied to identify plant functional types on the basis of the model parameters, which are regarded as ecophysiological traits of plant species.

Important findings Nine plant species were classified into three plant functional groups: 1) highly drought-resistant plants with moderate photosynthetic efficiencies, including Stipa krylovii, Heteropappus altaicus, Artemisia frigida, Convolvulus ammannii and Caragana microphylla; 2) medium drought-resistant plants with high photosynthetic efficiencies, including Leymus chinensis, Achnatherum splendens and Iris lacteal; 3) low drought-resistant plants with low photosynthetic efficiencies, including Phlomis mongolica. This study suggests that plant species in natural ecosystems can be classified into several plant functional groups using our methods. Therefore, the complexity of ecological models and calculation times can be reduced by substituting plant functional groups for individual species. Our approach can be an effective way to quantitatively distinguish plant traits, thus contributing to scaling up of ecosystem simulation.

Aims Spring ephemerals characterized by very short-term growth rhythm and specific biological traits in the Junggar Desert of China play an important role in succession of the desert plant community, maintenance of the desert biological diversity and conservation of water and soil in desert. The main aim of the present study was to address: 1) the photosynthetic characteristics and the biomass allocation traits of spring ephemerals and 2) the relationship between these traits and unique growth pattern of these spring ephemerals.

Methods In vivo photosynthetic traits of 16 spring ephemerals at their growth stages were measured by an open gas-exchange measurement system (Li-6400) and biomass allocation patterns were measured in seven species.

Important findings Maximum net photosynthesis rate (P_nmax),maximum transpiration rate (T_rmax) and water use efficiency (WUE) of 16 species were 8.07~35.96 μmol CO₂·m^-2·s^-1, 3.16~29.64 mmol H₂O·m^-2·s^-1 and 0.54~ 4.26 μmol CO₂·mmol^-1H₂O, respectively. P_nmax was positively correlated with maximum stomatal conductance, the correlation coefficient was 0.77 (p<0.05) and the slope in the linear region was 26.36 μmol·mmol^-1. Based on analysis for the response of P_n to internal CO₂ concentration and to photosynthetic photon flux density, apparent CO₂ compensation point are in the range of 4 to 5 Pa (ambient air temperature of 28~30 ℃ during the measurement), apparent carboxylation efficiency ranged from 0.64 to 1.86 μmol CO₂·m^-2·s^-1·Pa^-1, and apparent quantum yield ranged from 0.05 to 0.06. Biomass allocation data analysis showed that individual biomass of spring ephemerals were very low (0.05~0.39 g). Total leaf area ranged from 3.24 to 51.40 cm², leaf mass per unit leaf area ranged from 0.40 to 0.77 g·m^-2, root/total biomass ratio was 5.72%~19.43%, and leaf area ratio was 2.92~9.00 m²·kg^-1. The percentage of total biomass allocated to roots was positively correlated with WUE for the seven investigated species (r=0.93, p<0.01). Results indicate that the species investigated are typical C₃ plants. These spring ephemerals are characterized by higher P_n, T_r and lower WUE in comparison with other desert species. The unique biomass allocation of low root/aboveground biomass ratio, higher leaf area ratio, higher leaf mass per unit leaf area, and photosynthetic traits are involved in the physiological mechanisms that contributed to the rapid growth of desert spring ephemerals.

Aims Our objective was to develop a new method for simultaneously measuring evapotranspiration and CO₂ absorption in plant communities using the LI-6262 CO₂/H₂O analyzer for regional integration of water and CO₂ dynamics.

Methods We measured evapotranspiration and CO₂ absorption of some plant communities in the typical steppe of the Xilin River Basin, China.

Important findings Our method enabled us to concurrently measure evapotranspiration, photosynthesis and respiration, the important ecological processes of communities and therefore obtain a series of valuable measurements of community characteristics. Our method is precise, the instruments are easily portable, and the method is adaptable for plant communities of steppe, sand lands and wetlands. The method has important practical value for study of the impacts of global change on ecological functions of steppe.

Aims Accurate simulation of green area index is critical for reliable prediction of crop growth and yield using a crop growth model. Our study was undertaken to develop a process-based simulation model for predicting dynamic green area index, including leaf area index (LAI) and pod area index (PAI), in winter rapeseed (Brassica napus).

Methods Leaf area expansion was simulated through the relationship between LAI and source- or sink-limited dry matter. Daily leaf expansion rate increased in an S-shaped growth curve under source limitation, as influenced by temperature, water and nitrogen levels. Under the sink limitation, leaf area expansion was quantified on the basis of specific leaf area. Pod area was calculated from specific pod area and pod dry matter. The specific leaf area and specific pod area were determined from physiological development time and genotype. We calibrated and validated the model using experimental data from different varieties, sowing dates and nitrogen fertilization rates.

Important findings Root mean square error (RMSE) values of LAI were 11.15%, 15.57% and 16.87% at three N levels, and the average RMSE value of PAI in two varieties was 12.92%. Plotting the 1∶1 relationship between the simulated and observed values inLAI and PAI growth dynamics indicated a good fit. Our model of green area index in winter rapeseed shows a high accuracy and applicability under different conditions.

Aims It is very important to develop a nondestructive method for estimating nitrogen status and growth characters in cotton. We carried out two experiments to investigate the quantitative relationship between leaf nitrogen concentration and the canopy hyperspectral parameter in cotton.

Methods Based on the canopy hyperspectral reflectance and derived hyperspectral parameter, we investigated the quantitative relationship between leaf nitrogen concentration and canopy reflectance spectra in different cotton cultivars under different N rates and put forward the sensitive parameters and monitoring equations for leaf nitrogen concentration. Experiment 1 was conducted with two cultivars (‘Sumian 12’ and ‘Zhongmian 29’) and four N application levels (0, 150, 300 and 450 kg·hm^-2) in 2004. Experiment 2 included two cultivars (‘Kemian 1’ and ‘Meimian 33B’) with three nitrogen levels (0, 240 and 480 kg·hm^-2) in 2005.

Important findings Leaf nitrogen concentration and canopy hyperspectral reflectance significantly changed with levels of nitrogen fertilization. The sensitive bands of leaf nitrogen concentration were 600-700 nm of visible light and 750-900 nm of near infrared light, and the quantitative relationships between leaf nitrogen concentration and ratio vegetation index (RVI) [average (760-850), 700] of canopy were significant with an average R² of 0.70 in four cultivars. An integrated regression equation could be used for describing the dynamic change pattern of leaf nitrogen concentration with hyperspectral parameters in different varieties, growing stages and nitrogen levels in cotton. These results provide a technical approach for monitoring plant nitrogen status and guiding precision nitrogen management in cotton production.

Aims The aim was to reveal the effects of flooding on photosynthesis and growth of the riparian plant Salix variegata for revegetation of riparian areas in Three Gorges Reservoir Region.

Methods Four flooding treatments were applied to the plants: no flooding, belowground submergence and whole plant submergence to water depths of 0.5 and 2 m. Net photosynthetic rate, apparent quantum yield, carboxylation efficiency, intercellular CO₂ concentration and maximal photochemical efficiency of PSII (F_v/F_m) were determined at 0, 40, 60 and 90 d. The numbers of adventitious roots were determined at 6, 15, 25 and 32 d. Increase of stem length, increase of number of shoots, number of newly grown leaves on stem, number of shed leaves on stem, increase of root biomass and increase of plant biomass were determined at 10, 20, 40, 60 and 90 d.

Important findings Control and belowground-submerged plants maintained high net photosynthetic rate, apparent quantum yield and carboxylation efficiency during inundation. At 40 d, the net photosynthetic rate of S. variegata was significantly higher than that in the waterlogging-tolerant species S. babylonica (p<0.05). At 60 and 90 d, the photosynthetic capacity andF_v/F_m of wholly submerged plants decreased significantly as compared with that of the control and belowground-submerged plants (p<0.05), but the plants could still maintain high photosynthetic capacity. At 40, 60 and 90 d, the intercellular CO₂ concentration of wholly submerged plants was higher than that of the control and belowground-submerged plants. At 32 d, many adventitious roots were developed in belowground-submerged plants, while the wholly submerged plants had few adventitious roots. The belowground-submerged plants had greater increase in stem length, number of shoots, and newly generated leaves on stem, root biomass and total plant biomass than wholly submerged plants. During the flooding period, the stem length, number of shoots, and newly generated leaves on stem, root biomass and total plant biomass of wholly submerged plants increased, and the number of shed leaves of wholly submerged plants was higher than that of the control and belowground-submerged plants. At 90 d, all belowground-submerged and wholly submerged S. variegata were alive. Therefore, S. variegata has high photosynthetic capacity and growth adaptability over inundation of 90 d and is a promising species for revegetation of the riparian zone in the Three Gorges Reservoir Region.

Aims We investigated aerenchyma formation in stems of riparian plants Arundinella anomala and Salix variegata as affected by addition of ethylene and α-naphthalene acetic acid (α-NAA) under non-flooded conditions in order to ascertain whether phytohormone ethylene and auxin are direct stimuli for aerenchyma formation in flooded plants.

Methods Our experiment included treatments of ethylene (0, 250, 500 mg·L^-1), α-NAA (0, 50, 100 mg·L^-1) and joint addition of ethylene and α-NAA (250 mg·L^-1+50 mg·L^-1) for A. anomala and S. variegata plants. Five days following hormone additions, we obtained transverse sections of mid-stems of A. anomala and S. variegata and analyzed aerenchyma formation using E80i Nikon microscope, ACT-2U and Simple PCI software.

Important findings Aerenchyma formation was enhanced when plants were irrigated with either ethylene or α-NAA. Moreover, aerenchyma formation increased with hormone concentration. Aerenchyma formation was enhanced when plants were irrigated with a mixture of ethylene (250 mg·L^-1) and α-NAA (50 mg·L^-1), but it did not differ from aerenchyma formation induced by either ethylene addition of 250 mg·L^-1 or α-NAA addition of 50 mg·L^-1. Our work demonstrates that, in flooded environments, the aerenchyma formation in plant stems is directly related to increases of ethylene and auxin, and flooding may not be the direct stimulus for the formation of aerenchyma.

Aims Ectomycorrhiza (ECM) was generally considered to have a positive impact on the host plant exposed in contaminated soil and could enhance heavy metal tolerance. However, most researches have focused on single-ECM seedlings in experimental conditions, and the effects of mixed-ECM on the host are inadequately studied. Because woody plants are usually inoculated by mixed-ECM in natural conditions, it is essential to study the differences between single- and mixed-ECM inoculations, especially the dissimilar effects on heavy metal tolerance, which can help us better understand the mechanism of ectomycorrhiza.

Methods After a 4-week growth period, Pinus tabulaeformis seedlings inoculated by Boletus edulis and Xerocomus chrysenteron and the uninoculated control were planted in Cu and Cd contaminated soil. We measured growth and element accumulation 12 weeks later.

Important findings Compared with the uninoculated control, ECM inoculation not only enhanced the host's growth and biomass, but also reduced the concentration of heavy metals and their transportation from root to shoot. Seedlings inoculated by mixed-ECM strains had higher heavy metal tolerance than those inoculated by single-ECM strain. This advantage was especially remarkable at higher concentration. Results showed that in 3 mg·kg^-1 Cd contaminated soil, Cd concentrations in the shoot and root of mixed-ECM seedlings were only 59.1% and 70.7% of the control, 11.3% and 18.1% lower than single-ECM ones. However, the dry weights of mixed-ECM seedlings' shoot and root were 1.14 and 1.20 times than the control vs. 1.18 and 1.17 times for single-ECM. In 400 mg·kg^-1 Cu contaminated soil, the dry weights of mixed-ECM seedlings' shoot and root were 1.01 and 1.09 times than the control, while the Cu concentrations in the shoot and root of mixed-ECM seedlings were only 61.8% and 79.6% of the control, 0.7% and 3.8% lower than single-ECM seedlings.

Aims Some species-specific secondary metabolites are key players in the interaction between plants and their environment. An ecotype of wild soybean (Glycine soja), naturally growing in saline soil of Yellow River delta in Shandong Province of China, shows substantial genetically determined salt-resistance, and its isoflavone content is higher than that in many cultivated soybeans. Our objective was to investigate the relationship between isoflavone and saline condition in Glycine soja through experimentation.

Methods The ecotype of wild soybean mentioned above and a variety (Huiming Soybean) of cultivated soybean (Glycine max) from same area were cultivated under saline condition. We determined the isoflavone contents in their leaves, roots and seeds, phenylalanine ammonia lyase activities and phenylalanine contents in their leaves, the number of nodules and nitrogen-fixing enzyme activities in their roots.

Important findings Isoflavone anabolism in the wild soybean was promoted by salt while it was inhibited in the cultivated soybean. The higher isoflavones contents of the wild soybean were significantly associated with the higher activities and efficiency of nitrogen fixation in its roots. Results suggested that isoflavones, secondary metabolites of the wild soybean, played an important role in the wild soybean adapting to the saline environment. Underlying processes require further investigation.

Aims Salinity is a serious abiotic stress that adversely affects rice productivity and quality. Proper regulation of ion flux is necessary for cells to keep concentrations of toxic ions low and to accumulate essential ions. The purpose of our experiment is to detect differences in the physiological response and absorption and distribution of Na⁺ and K⁺ among rice seedlings tolerant or sensitive to salt stress.

Methods Seedlings of three salt-tolerant varieties (‘AB52’, ‘02402’ and ‘02435’) and a sensitive variety (‘Nipponbare’) were grown under different salt stresses (fresh water, 5 000 and 8 000 mg·L^-1 NaCl). We recorded agricultural traits and measured Na⁺ and K⁺ contents with ICP.

Important findings Seedling length, green leaf area, dry weight and moisture content of green leaves declined under salt stress, while moisture content of stems and sheaths increased. Plant growth and leaf damage of salt-tolerant varieties were less than that of the salt-sensitive variety when they were grown under 5 000 mg·L^-1 NaCl for 10 d. However, differences among varieties grown under 8 000 mg·L^-1 NaCl were small. Under salt stress, rice seedling absorbed Na⁺ from roots and discharged K⁺. There was a regular range of Na⁺ and K⁺ in seedlings. The Na⁺ concentration in different organs ranged from low to high. Generally, younger green leaves contained less Na⁺ than dried leaves under normal condition, and still had low Na⁺ and high K⁺ concentrations under salt stress. The Na⁺ concentration in green leaves of the salt-sensitive variety was the highest under 5 000 mg·L^-1 NaCl; however, the salt-tolerant varieties reached the highest Na⁺ level under 8 000 mg·L^-1 NaCl. It seems a major character of salt tolerance mechanism in rice seedling that the confine distribution area of Na⁺ in shoots maintaining green leaves a homeostasis of Na⁺, K⁺ with higher K⁺/Na⁺ ratio by selective transportation K⁺ from stems and sheathes to green leaves and roots, and interception Na⁺ in stems and sheathes. The result that K⁺ concentration in stems and sheathes of the salt-tolerant varieties were higher than that of the sensitive variety suggests that it could cause less Na⁺ concentration and maintain higher K⁺/Na⁺ ratio in green leaves. Therefore, K⁺/Na⁺ ratio in green leaves could be an index for evaluating salt tolerance.

Aims Ethylene accumulation and oxidative stress are two common responses of plants to environmental stresses; however, little is known about their relationships. Our objective was to investigate the role of reactive oxygen species (ROS) in ethylene synthesis induced by UV-B radiation (280-320 nm) in leaves of maize (Zea mays).

Methods Lamps were suspended above and perpendicular to the plastic trays and filtered with 0.13-mm thick cellulose diacetate (transmission down to 290 nm) for UV-B irradiance. The desired UV-B irradiation was obtained by changing the distance between the lamps and the plastic trays. The levels of UV-B irradiation were 4.8 kJ·m^-2·d^-1.

Important findings UV-B radiation led to the generation of ROS and ethylene. The accumulation of ethylene induced by UV-B was not only inhibited by the scavengers of ROS, but also by aminoxyacetic acid (AOA) and 2-aminoethoxyvinlglycine (AVG), which are specific inhibitors of ethylene synthesis. The inhibition effect of ROS scavengers on UV-B-induced ethylene production was reversed by $\text{O}_{2}^{{\bar{.}}}$ donors. Results indicated that the increase in ethylene production may not be the cause of the increase in ROS production under UV-B stress. In contrast, the increase of ROS led to the accumulation of ethylene. Results suggested that ROS are involved in UV-B stress-induced ethylene accumulation. The accumulation of UV-B-induced ethylene was not affected by DPI, an inhibitor of NADPH oxidase and CAT, a specific scavenger of H₂O₂. Results suggested that the effect of H₂O₂ on UV-B-induced ethylene production in leaves of maize seedlings can be excluded, $\text{O}_{2}^{{\bar{.}}}$ plays an important role in UV-B-induced ethylene synthesis in leaves of maize seedlings and $\text{O}_{2}^{{\bar{.}}}$ serves as a potential mediator of ethylene production that the plant can sense the UV-B stress. The related ROS are not from plasma membrane NADPH oxidase. The source of ROS contributing to ethylene accumulation under UV-B stress is unknown.

Aims Elucidation of the molecular mechanism of local adaptation to changing environments represents a central goal in evolutionary biology and ecology. Formation of adaptive populations probably involves activation or repression of pre-existing tolerant genes by transcription factors (TFs) and retrotransposons under stress. Research in this area can lead toward to a unified theory of evolution.

Methods The consensus sequence of drought responsive element binding protein (DREB) from the wild soybean (Glycine soja) in Yellow River delta has been cloned, sequenced, and called GsDREB1. An integrase gene of Gypsy-like retrotransposon called GsINT was also cloned from G. soja. Southern hybridization indicated that GsINT consisted of multiple copies and showed restriction fragment length polymorphism among individuals in salinity populations. From both sequences of GsINT and GsDREB1, other pairs of primers were designed for amplification of 5'upstream of GsDREB1 in order to see if partial sequence of GsINT was inserted. Results indicated multiple copies of space sequence between INT and DREB and its diversity among individuals of plants within each population. Gene cloning and sequencing of amplified products showed possible existence of GsINT sequence in 5' upstream of GsDREB1.

Important findings Results led to a hypothesis on the origin of tolerant populations, i.e., a molecular mechanism on adaptive evolution of plants. In normal conditions, plant populations mainly contain non-tolerant individuals. Under stress conditions, retrotransposons increase their frequency of transposition. Most mutants are neutral without phenotypical change. Few insertions located into 5' upstream of transcriptional factors will change intensity of TFs' expression. Then a series of pre-existed stress responsive genes controlled by TFs will simultaneously change their rates of gene expression, resulting in formation of more tolerant or sensitive individuals. Individuals with high stress tolerance may appear by accumulation of several tolerant inserts step by step. As a result of complicated interaction among genes, plants with different levels of stress tolerance occur quickly under stress. By means of natural selection, stress-sensitive plants are lost under stress conditions; however, stress itself continuously creates new sensitive individuals. Few of them with a short life cycle may survive by using a short period time of weakened stress. This hypothesis explains that tolerant populations quickly form because transposition frequency under stress becomes very high. It also explains why tolerant populations contain higher genetic diversity and why a few stress-sensitive individuals exist under stress conditions.

Aims Energy flow characteristics of alley cropping have been rarely studied, although alley cropping is common in Sichuan in order to control soil erosion and promote productivity. Our aims are to understand growth pattern and production mechanization of crops, determine effects of hedgerows on main crops in order to realize positive interactions, promote the level and structure of energy inputs, optimize and establish an environment-friendly farming system and realize sustainable agriculture on hillsides.

Methods We recorded labor input, fertilizer, pesticides, farming activities and leaf fall on the soil surface in trial plots for two years. After harvesting, we separated plant parts to determine economic yield and biological yield, calculated energy of the different parts according to a conversion ratio of energy and studied energy structure and energy efficiency of alley cropping by statistical analysis.

Important findings In comparison with the traditional agricultural system on hillsides, there were differences between hedgerows and crop in shape and spatial distribution of crown and roots, such that light, heat, water and soil were utilized continuously in time and in space, resulting in enhanced efficiency of light utilization, efficiency of input labor energy utilization and total output energy per unit area on steeper hillsides. Moreover, input of inorganic energy of alley cropping was reduced significantly and use of chemical fertilizer and pesticide could be reduced, resulting in environmental protection. Quantity and structure change of output and input energy of alley cropping was affected mainly by the type of hedgerow subsystem. Total energy input (including organic energy) of hedgerow system with fruit trees was increased, which was useful for improving input energy structure and ecosystem and enhancing intensive agricultural development. A hedgerow system of shrubs and herbs could reduce input labor energy, decreasing input energy and input energy consumption greatly and resulting in increased efficiency of input labor energy utilization and biomass and energy output/input ratio of the main crops. Alley cropping conserved water and soil, thereby playing an important role in agricultural reform in the vast mountainous and hilly area of Sichuan.

Aims The interaction between Ficus species and their pollinating wasps (Agaonidae) is a striking example of a mutualism. Figs are also exploited by chalcidoid wasps that develop within the figs but do not transfer pollen. F. racemosa, a common species in the Xishuangbanna tropical area, is monoecious, and there are five species of non-pollinating fig wasps that coexist with the fig-pollinating Ceratosolen fusciceps inside the syconium. These non-pollinating fig wasps oviposit from outside the fig wall using long ovipositors to reach the ovules inside during different phases of syconium development. We studied the effect of the non-pollinating wasps on mutualism, in order to determine the relationship between the time and the distribution of female flowers, and to understand how non-pollinating species coexist with the mutualistic species.

Methods We isolated syconia at different phases, using bags in order to prevent non-pollinating wasps from ovipositing on the fig wall. We brought the syconia into the laboratory when the figs were mature and let the pollinating and non-pollinating fig wasps leave the syconia in the isolation bags. We then counted the number of seeds and pollinating fig wasps and compared differences in numbers with independent-samples t-test.

Important findings During the prefemale phase, before the pollinating fig wasp enters the fig cavity, Platyneura testace, Apocrypta sp. and P. mayri oviposit on the fig wall. These non-pollinators significantly affect the mutualism, especially the product of the pollinating fig wasp. During the interfloral phase, when the pollinating fig wasp has entered the fig cavity, P. mayri, A. westwoodi and P. agraensis oviposit on the fig wall. Although these non-pollinators reduce the number of seeds and fig-pollinating wasps, they do not significantly affect the fig-wasp mutualism. P. mayri is a gallmaker that oviposits during prefemale and interfloral phases. It affects the reproduction of fig-pollinating wasps during prefemale phase, but mainly affects seed production during the interfloral phase. Apocrypta sp. and A. westwoodi do not parasitize C. fusciceps but P. testacea and P. mayri. So the number of pollinating wasps and non-pollinating wasps remains balanced, and this is favorable for stability of the fig-pollinating wasp mutualism.

Aims Beta diversity is the variation in species composition among sites in a geographic region. Beta diversity is a key concept for understanding the functioning of ecosystems, for the conservation of biodiversity, and for ecosystem management. This paper describes how to analyze it from community composition and associated environmental and spatial data tables.

Methods Beta diversity can be studied by computing diversity indices for each site and testing hypotheses about the factors that may explain the variation among sites. Or, one can carry out a direct analysis of the community composition data table over the study sites, as a function of sets of environmental and spatial variables. These analyses are carried out by the statistical method of partitioning the variation of the diversity indices or the community composition data table with respect to environmental and spatial variables. Variation partitioning is briefly described in this paper.

Important findings Variation partitioning is a method of choice for the interpretation of beta diversity using tables of environmental and spatial variables. Beta diversity is an interesting “currency" for ecologists to compare either different sampling areas, or different ecological communities co-occurring in an area. Partitioning must be based upon unbiased estimates of the variation of the community composition data table that is explained by the various tables of explanatory variables. The adjusted coefficient of determination provides such an unbiased estimate in both multiple regression and canonical redundancy analysis. After partitioning, one can test the significance of the fractions of interest and plot maps of the fitted values corresponding to these fractions.

Development of modern plant ecophysiology is synchronous with progress in instrumentation, with higher quality instruments becoming more portable, capable and automatic. The progress of instrumentation and its important effects on the development of ecophysiology of photosynthesis are described, and problems with controlled experiments and pseudo-replication in experimental design are discussed.