Aims There are two hypotheses on the mechanism of functional diversity driving ecosystem processes: one is the mass ratio hypothesis based on dominant species, and the other is the diversity hypothesis based on ecological niche. Both hypotheses have been supported by different studies, but their applicability and universality are still controversial. Our objective was to clarify whether the explanatory ability of these two hypotheses to productivity is influenced by the existence of intensive environmental filtering, which was flooding in this study.
Methods Three meadow communities and three marsh communities were studied over two years in the Momoge National Nature Reserve in western Jilin Province. The aboveground biomass, species diversity (species richness and Shannon-Weaver index), functional diversity (community weighted mean and Rao’s quadratic entropy), and several environmental factors were compared among different communities. The functional diversity was calculated for seven plant traits. The relationship between diversity index and aboveground biomass was explored by simple linear regression analysis and multiple linear regression analysis with stepwise method.
Important findings Both Rao’s quadratic entropy and community weighted mean could explain more variation in community productivity than species diversity. Furthermore, both mass ratio hypothesis and diversity hypothesis supported the diversity-productivity relationship. However, the mass ratio hypothesis may play a relatively greater role than the diversity hypothesis, indicating that the ecosystem function mainly depended on the functional traits of dominant species. Intensive environment filtering in terms of flooding affected the diversity-productivity relationship. The mass ratio hypothesis based on community weighted mean explained more variation of the productivity in meadow communities without flooding filtering, while diversity hypothesis based on Rao’s quadratic entropy explained more variation of the productivity in marsh communities with flooding filtering.

Aims The objective of this study was to determine whether fertilization and clipping would affect species diversity, productivity, and the relationship between species diversity and productivity in a subalpine meadow of China.
Methods The experiment was set up as a randomized block design consisting of three levels of fertilization and three intensities of clipping with eight replications, using quadrat size of 0.5 × 0.5 m². The aboveground biomass and species diversity were measured within each quadrat. The relationship between species diversity and productivity were tested by plotting aboveground biomass against species diversity based on linear and non-linear regressions by treatments.
Important findings Fertilization and clipping had significant effects on aboveground biomass; community biomass increased with the level of fertilization but decreased with the clipping intensity. Both fertilization and clipping had no apparent effects on species diversity. The relationships between aboveground biomass and species diversity occurred as monotonic, quadratic, or non-correlated depending on fertilization and clipping treatments, meaning that the relationship between species diversity and productivity is not always isotropic and changes with conditions of fertility and level of biomass removal in the community. Thus, productivity is unlikely related to species diversity under conditions of varying fertilization regimes and clipping treatments.

Aims Water is the most constraining factor for implementing the “Grain for Green” project in arid and semiarid steppe regions of China. Our objective was to determine how vegetation and water budget would change following restoration in semiarid grasslands.
Methods Field experiments were conducted in the Farmland and Grassland Ecosystem Observation Station of Beijing Normal University during the growing seasons between 2008 and 2009 in Taibus Banner, located in a typical agro-pastoral zone in Inner Mongolia, northern China. Vegetation composition was studied in six plots representing the natural grasslands (consisting of three separate plots at three sites) and the restored grasslands with two, four and eight years of history, respectively. Three Bowen ratio towers were set up to collect the local meteorological data and to estimate evapotranspiration in each plot. Soil water content was measured using the gravimetric method and soil evaporation was determined by micro-lysimeters with a volume of 200 cm^-3 each.
Important findings In the restored grassland plots, plant community coverage increased but the number of species decreased with time of restoration, and the dominant species were gradually transformed from the annual xeric herbs into perennial xerophytic herbs. Plant transpiration, with maximum values of 4.5 to 5.8 mm·d^-1, consumed most of the water in the restored grasslands, and longer the restoration higher the rate of evapotranspiration. Soil water in the restored grassland plots was 0.09 m³·m^-3 in average, compared with 0.06 m³·m^-3 in the natural grassland plots. The soil water content was found to be greatest at 20 cm depth in the natural grassland plots; whereas it was found to be greatest at 60 cm depth, and decreased with time of restoration, in the restored grassland plots. The water budget was balanced at an annual scale in the restored grassland plots because the evapotranspiration was lower than precipitation, while in the growing season of an extreme dry year when annual precipitation was only 174 mm, the evapotranspiration exceeded the precipitation. In conclusion, our results suggest that restored grasslands are able to use more water for establishing vegetation and increase water use efficiency with time of restoration, but the decreasing trend of soil water content should be paid more attention and monitored more comprehensively.

Aims Adaptation of plants to their habitats through phenotypic plasticity in which they trade off various kinds of functional traits is an important ecological strategy. Whereas plant functional traits and its effects on grassland ecosystem functioning have received much attention, the importance of grazing effects on functional traits is poorly understood. This study, therefore, aimed to analyze the responding model of Leymus chinensis functional traits to long-term grazing in semi-arid grassland.
Methods The study was conducted in a field experiment involving treatments with various grazing and enclosure schemes in Nei Mongol. We compared the effects of long-term enclosure, short-term enclosure (SE), moderate grazing (MG), and heavy grazing on plant functional traits in L. chinensis. Partial Least Squares Regression was used to analyze the contributions of controlling factors on changes in biomass in response to grazing.
Important findings The size of L. chinensis became smaller in plots subject to long-term grazing compared with in the plots of enclosures. It had a significant conservative property of plant dwarf which can be found in the SE plot. Interestingly, the variability increased significantly with the increasing of plasticity index of different functional traits. Also, some functional traits, such as aboveground biomass, plant height, mean leaf length etc., were sensitive traits to grazing. However, other indicators, such as leaf numbers, stem diameter, mean leaf width etc., which were inert functional traits. Stem length, plant height and other traits were main factors which cased the decreasing of L. chinensis aboveground biomass. On the whole, phenotypic change is an important adaptive strategy of L. chinensis to long term grazing.

Aims Trade-offs are the basis of the theory on plant life-history strategies, and the trade-off between flower size and flower number is an important determinant of flower biomass allocation. Our objective was to study the changes in the relationship between flower size and flower number in Stellera chamaejasme populations with elevation in Northwest China.
Methods The study site was located in a degraded alpine grassland on the northern slope in Qilian Mountains, Gansu Province, China. Survey and sampling were carried out at four elevations at intervals of 100 m from 2700 m to 3000 m; a GPS was used to determine the elevation. Community traits were investigated and 45 individuals of S. chamaejasme were collected randomly at each elevation. The samples were cleaned and divided into different organs, and their biomass were then measured after being dried at 80 °C in an oven.
Important findings With increasing elevation, the height, density, and aboveground biomass of the plant communities displayed a pattern of initial increase and then followed by a subsequent decline; the flower biomass in S. chamaejasme increased with increasing elevation, while the flower numbers decreased. The flower size was negatively correlated with the flower number, but the relationship varied along the elevation gradient; there was a highly significant negative correlation (p < 0.01) between the flower size and the flower number at elevations 2700, 2900, and 3000 m, whereas the correlation only reached a significant level (p < 0.05) at the elevation of 2800 m, indicating that there is a trade-off between the flower size and flower number. The elevation of 2800 m appeared to be a switching point where the S. chamaejasme individuals with more but smaller flowers at the lower elevations were transformed into ones with fewer but bigger flowers with increasing elevation. Consequently, a change in the reproductive strategy with a trade-off between flower size and flower number ensures successful reproduction of the S. chamaejasme populations in adverse environments.

Aims Flower symmetry is closely related to pollination system and variations in flower traits are under the selection role of pollinators. Berg predicted that flower size varies much less in bilateral species than in radial species because of the stable and/or directional selection by pollinators, and that it should also show lower variability than vegetative organs which have relatively higher sensitivity to environments. We examined these so-called Berg’s hypotheses in an alpine meadow.
Methods By measuring the traits of flowers and leaves in 50 flowering plants in an alpine meadow in the eastern Qinghai-Xizang Plateau, we compared the coefficients of variations (CV) in flower size and leaf size between 31 radial and 19 bilateral species and also performed phylogenetically independent comparisons.
Important findings Our results were not completely consistent with the Berg’s hypotheses. The CV of flower size was significantly smaller than that of leaf size in both radial and bilateral species as predicted by Berg, indicating that pollinator-mediated stabilizing selection would benefit flower stability. But the CV of flower size did not differ between the bilateral and the radial species, which is inconsistent with the Berg’s hypothesis even if we controlled confounding effects of phylogenetic relatedness. The role of pollinators in alpine ecosystem where bumble bees and flies predominate is likely more affected by local climatic environments, which leads to considerable variability in the selection of pollinators on flowers.

Aims For sustainably managing the subalpine grassland of western Sichuan, a post-fire recovery in diversity and intensity of soil microbial function was studied.
Methods The activities of seven soil enzymes, including β-glucosidase, acid phosphatase, alkaline phosphatase, urease, sucrase, protease, catalase, and fluorescein diacetate hydrolase, were measured on soil samples collected from burned and unburned sites in the study area following a wildfire on 5 December 2010. The diversity and intensity of soil microbial function were estimated by the methods of Bending and Perucci.
Important findings In this study, we found that the activities of the seven soil enzymes in the 0-5 cm soil layer were all increased significantly by the fire, but the responses to fire and soil depth varied among different soil enzymes. The alkaline phosphatase appeared to be a good indicator of the short-term responses in the diversity and intensity of soil microbial function to fire in this area. On the whole, although fire enhanced the surface soil microbial function to some extent, the diversity and intensity of soil microbial function were not significantly affected by the fire in the 0-20 cm soil layer. Future research on the functional stability of soil microbial community could better reveal the underlying mechanisms of the impact of disturbance on soil microbial biodiversity.

Aims Pinus massoniana is the major plantation tree species in the low hilly lands of the upper Yangtze river valley for commercial purpose. The large areas of plantations have caused serious ecological problems such as biodiversity decline and soil degradation. Our objectives were to study the dynamics of species composition and plant diversity in forest gaps, to test the hypothesis that forest gaps facilitate the regeneration and plant diversity in P. massoniana plantations, and to determine the size of forest gaps that harbors the most complex compositional structure and the greatest plant diversity.
Methods We selected 39-year-old P. massoniana plantations with seven different gap sizes in the study, and used combination of systematic and representative sampling approaches. In the spring, summer, and autumn of 2013, sampling plots of the dimension 5 m × 5 m were laid out in the center of the forest gaps and under the canopy, and plants within each plot were surveyed for determination of their diversity and compositional structure.
Important findings The understory of P. massoniana plantations were dominated by phanerophyte plants, followed by hemicryptophytes, geophytes, and therophyte plants. The phanerophyte plants were more abundant under the canopy than in forest gaps. The large gaps had more phanerophyte plants, while the geophytes and therophyte plants were less frequent under the canopy than in the small gaps. The species richness and diversity were significantly lower under the canopy than in the large forest gaps. Moreover, species richness, dominance, and diversity differed significantly among the forest gaps of different sizes. Seasonally, the highest diversity occurred in summer, followed by autumn, with the spring having the lowest diversity. The greatest diversity was found in the forest gaps of the size 1225-1600 m², which could be the optimal gap size for facilitating plant diversity and regeneration of vegetation in P. massoniana plantations.

Aims The objectives of this study were to investigate the effects of disturbance through wind erosion and sand burial on water relations and photosynthesis in Alhagi sparsifolia, and to determine the best habitat for the growth of A. sparsifolia in the southern edge of the Taklimakan Desert.
Methods We set up five treatments, including wind erosion depth of 10 cm, wind erosion depth of 5 cm, control, sand burial depth of 10 cm, and sand burial depth of 30 cm. Measurements were made on the concentration of photosynthetic pigments, chlorophyll fluorescence parameters, leaf water potential, and leaf water content in A. sparsifolia under different treatments on a sunny day.
Important findings Leaf water potential and leaf water content in A. sparsifolia m significantly decreased following the wind erosion treatments, thereby causing a reduction in the stomatal conductance, which in turn resulted in declining photosynthetic rate and transpiration rate. The water use efficiency in plants under the wind erosion treatments was lower than that under the sand burial condition, especially in the treatment of wind erosion depth of 10 cm. In addition, leaf water potential and leaf water content in A. sparsifolia were higher in the sand burial treatments than in the wind erosion treatments, which were associated with higher values of stomatal conductance, photosynthetic rate, transpiration rate, and water use efficiency. The maximum photochemical efficiency (F_v/F_m) in A. sparsifolia was suppressed under the wind erosion treatments, indicating increased stress suffered by the plants. However, A. sparsifolia may resist the adverse effects of wind erosion through increases in the number of active reaction centers and photochemical efficiency. The F_v/F_m in A. sparsifolia was higher under the sand burial treatments, indicating that the stress of A. sparsifolia suffered was alleviated. The absorption of light quantum yield and energy used for the photochemical reaction in the reaction center decreased increasing sand burial depth. This might be a survival strategy that A. sparsifolia adopted in response to the severe wind-blown sand environment. Compared with those in the treatments of wind erosion depth of 5 cm and sand burial depth of 10 cm, the growth of A. sparsifolia plants was significantly inhibited in the treatment of wind erosion depth of 10 cm, and significantly enhanced in the treatment of sand burial depth of 30 cm.

Aims Our main purposes were to determine the effects of Vigna radiata, a nitrogen fixing plant, on growth, water balance and gas exchange of the intercropping Juglans regia seedlings and to investigate the hydraulic mechanism involved in photosynthesis and growth.
Methods We measured growth, hydraulic characteristics, and rate of gas exchange in J. regia seedlings, and analyzed the effects of the intercropping nitrogen fixing V. radiata on xylem anatomic structure, water balance and photosynthetic characteristics of J. regia seedlings under conditions of nitrogen deprivation and enrichment.
Important findings Under conditions of nitrogen deficiency, the nitrogen fixing V. radiata facilitated the growth of the intercropping J. regia seedlings by improving xylem development, water transport and hydraulic characteristics in high transpiration demand. However, with nitrogen addition, the occurrence of V. radiata inhibited the growth of J. regia seedlings, likely by competing for water and other elements.

Aims We studied the effects of the methyl viologen (MV) in the culture medium on the antioxidant enzyme system in Salvia miltiorrhiza cells and investigated changes in the contents of H₂O₂, malonaldehyde (MDA), glutathione (GSH), and antioxidant enzyme. The differential expressions of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were discussed. Our objective was to explore if the MV could significantly affect the antioxidant system in the cultured S. miltiorrhiza cells.
Methods We treated the S. miltiorrhiza cells in suspension cultures with MV as an elicitor on the accumulation of H₂O₂, and used the diuron (DCMU) as an electron transporting antagonist. The biosynthesis of H₂O₂, MDA, and GSH, and the activities of SOD, CAT, and POD were determined by ultraviolet spectrophotometry. The specific isoenzymes bands of SOD, CAT, and POD were examined by acrylamide gel electrophoresis technique.
Important findings We found that MV significantly increased the accumulation of H₂O₂, MDA, and GSH, along with increased activities of CAT and POD as well as enhanced expressions and increased number of isoenzymes bands of CAT and POD; whereas DCMU inhibited the effects of MV. Results in this study suggest that MV could significantly enhance H₂O₂ accumulation in chloroplasts and regulate the antioxidant system in S. miltiorrhiza cells in suspension cultures, in order to maintain normal physiological conditions.

Aims For adoption and localization of the high precision rice growth model ORYZA2000, the model parameters were calibrated and high-temperature sensitivity analysis was performed based on observed data for five rice varieties at nine experimental stations and daily meteorological data in Jiangsu Province.
Methods The latest version of ORYZA2000 (V2.13) was used in this study. The model parameters were calibrated using the observed data for three rice varieties at five experimental stations, and then the aboveground biomass, leaf area index, and final yield were estimated for two other rice varieties at four experimental stations for model validation; a t-test was performed for quality evaluation. By using the validated model and raising the temperature at different time periods, a simulation of high temperature impact on rice biomass and yield was carried out. The simulation results were compared with the observational data from the greenhouse experiments assessing the high temperature responses of the rice varieties studied.
Important findings The results show that after calibration, the model parameters reliably simulated the dynamics of biomass accumulation and leaf area index development in the rice varieties studied; the simulated values are consistent with the observed values. The total biomass, panicle biomass, and final yield decreased by 12%-25% compared to the control (CK) when the growth temperature was raised to 35 °C for 3, 5 and 7 consecutive days from booting to flowering stages. Those values decreased by 18%-31% when the temperature was raised to 38 °C and by 20%-38% when the temperature was raised to 41 °C over the same periods. In general, the magnitudes of decline in the growth of rice varieties from model simulations were comparable with controlled laboratory observations. ORYZA2000 model could be applied to predict rice response to temperature increase on the basis of crop parameter calibrations.