Aims The decomposition of plant litter is a complex process mediated by biotic and abiotic factors. However, litter decomposition and its controlling factors are still controversial and unclear in arid and semi-arid ecosystems. In arid lands, precipitation has inconsistent effects on litter decomposition and nitrogen dynamics. Our objectives were to: (1) examine litter decomposition and nitrogen dynamics in litter with water additions at different seasons and (2) determine the factors critical to surface litter decomposition in arid lands.
Methods We used the litter-bag method to investigate leaf decomposition of Eremurus inderiensis and Erodium oxyrrhynchum and stem decomposition of Erodium oxyrrhynchum and Seriphidium santolinum in China’s Gurbantunggut Desert. We placed litterbags filled with those litters on soil surface in October 2009. We added snow from December to March of the next year and water from June to August. Litterbags were collected in April, July and October of 2010 and in April and July of 2011. Mass loss, carbon, nitrogen and phosphorus content, and decomposition rates of litter were analyzed at each decomposition stage. In addition, soil water content at 0-10 cm soil depth was measured at 10-day intervals from April to November.
Important findings The mass loss of different litters fit the exponential decay model (R²> 0.90). After 637 days of decomposition, no significant differences were observed among natural precipitation, snow addition and water addition treatments, and the mass remaining for leaves of Eremurus inderiensis and Erodium oxyrrhynchum and stems of Erodium oxyrrhynchum and Seriphidium santolinum with natural precipitation were 40.59%, 35.50%, 36.00% and 63.96%, respectively. The mass remaining was positively related to nitrogen remaining, which meant the litter nitrogen loss was faster than mass loss. Correlation analysis showed that decay rates were positively related to initial nitrogen content and inversely related to initial C/N. Initial C/N could explain 71% of the variation in decomposition rate. Results suggest that water addition in different seasons will not promote decomposition of surface litters, and initial litter chemical composition is critical to surface litter decomposition in the Gurbantunggut Desert.

AimsStomata play a key role in plant adaptation to changing environmental conditions and environmental stress because they control both water losses and CO₂ uptake.
Methods Based on observation of leaf gas exchange parameters of Tamarix ramosissma in an extreme arid region in northwest of China, the relative humidity (h_s) (or vapor pressure deficit (D_s)) of the BWB and BBL model were evaluated by introducing diagnosis function f(H). After that, the results were imported into the Ye and Yu mechanism model for simulation of stomatal conductance (g_s) of T. ramosissma.
Important findings A significant difference was found for h_s (or D_s) of the BWB and BBL model with R² of 0.5354 and 0.1103, respectively, and the g_s is significantly related to h_s and D_s with a Gauss model with R² of 0.593 and 0.258, respectively. It suggests that the relationship between g_s and h_s is closer than D_s. Both the simplified model (referred to Simple model) proposed by Ye and Yu and its correction (referred to Gauss-h model) behaved well with R² of 0.8707 and 0.8286 and η of 0.1245 and 0.0171 (range from 0 to 1), respectively. The model validation shows that the Gauss-h model clearly underestimated the observations more than the Simple model, and the performance of the Simple model was significantly improved (R² of 0.9606) when the observed condition was close to the hypothesis of model infinitely.

Aims Stability can comprehensively reflect the structural and functional characteristics of communities. Our objective was to evaluate the stability of 13 riparian forest communities in the upper reaches of Wenyuhe.
Methods The evaluation was based on fuzzy comprehensive appraisement theory. In considering integrity stability and structural stability, five indexes were selected which could reflect the current situations of the 13 communities: regeneration of dominant species of the tree layer, total species diversity, Godron index, site quality and protection intensity. The five indexes were measured by 12 factors. Community stability was determined by the means of five subordinate function values.
Important findings Most subordinate function values were 0.40-0.60. The stability of two communities, Populus cathayana + Quercus wutaishanica and Pinus tabulaeformis + Betula platyphylla, classified them in the middle of a low-mountain forest succession series. Among middle (high)-mountain forest succession series, stability increased with succession progressing from Populus cathayana forest as the lowest to Picea wilsonii as the highest. In addition, the stability of Picea meyeri + Populus cathayana + Betula platyphylla mixed forest, Larix principis-rupprechtii + Picea meyeri mixed forest and Larix principis-rupprechtii + Picea wilsonii mixed forest were also high, probably in response to disturbance caused by tree canopy or environmental heterogeneity.

Aims In recent years, Miscanthus sinensis and M. floridulus have attracted considerable attention as two of the most promising non-food energy crops in China. We attempt to determine the potential distributions of the two Miscanthus species to provide a reference for developing non-food energy crops using marginal lands in China.
Methods We predicted the potential distribution and fundamental niches of M. sinensis and M. floridulus in China based on the maximum entropy (MAXENT) model using distribution data of the two species combined with 19 climatic factors.
Important findings The potential distribution area for M. sinensis covers west Sichuan, north Shaanxi, Ningxia, central Inner Mongolia, Heilongjiang, west Jilin, west Liaoning, southeast Qinghai, etc. Its fundamental niche parameters are: precipitation of warmest quarter of 400-1 000 mm, average precipitation in August of 100-350 mm, average minimum air temperature in July of 15 °C, average precipitation in July of 100-350 mm, average maximum air temperature in November of -10 to 22 °C, mean temperature of driest quarter of -15 to 20 °C and average precipitation in December <100 mm. The potential distribution area for M. floridulus includes Yunnan, Shaanxi, Shanxi, Ningxia, Henan, Shandong, Jilin, Liaoning, west Sichuan, south Gansu and east Inner Mongolia, etc. Its fundamental niche parameters are: precipitation of warmest quarter > 400 mm, mean precipitation in June of 150-550 mm, average minimum air temperature of 15-30 °C in July and 10 °C in June and average precipitation in April of 50-100 mm. The results show that there are abundant land resources for growing M. sinensis and M. floridulus in China.

Aims As a typical region of soil erosion on the Loess Plateau, the Jinghe River watershed has had long-term land exploitation and soil erosion. Our objective was to study trends in the change of vegetation cover and to explore driving factors, including both climatic and anthropogenic aspects.
Methods We calculated normalized difference vegetation index (NDVI) trends using GIMMS NDVI data from 1982 to 2005 in the Jinghe River watershed. Its trends were compared with precipitation and air temperature trends calculated from climate data from the 19 meteorological stations in the watershed. A 3 × 3 pixel buffer area centered on each station was used to analyze relationships between climate and vegetation. Anthropogenic factors were represented by land use data obtained from the Resource-Environment Database of the Chinese Academy of Sciences. We analyzed the proportion of each land type in areas of different NDVI trends to illustrate the effects of human activities.
Important findings NDVI had no significant trends in 79.64% of the Jinghe River watershed in the 24-year period. NDVI had significant positive trends in 16.33% of the area, located in the middle and southern parts of the watershed. NDVI had significant negative trends in 4.03% of the area, located in the northern part of the watershed. Precipitation had no significant trends, and temperature had significant positive trends forall of the 19 weather stations. The spatial differences of NDVI trends could not explained by changes in precipitation and air temperature. The anthropogenic factors seemed more important. Land use analysis indicated that the percentages of land use types in areas of different NDVI trends changed little. Plantation was dominant in the area where NDVI had significant positive trends, and grassland was dominant in the area where NDVI had significant negative trends. Results suggest that the changes in plantations resulted in the significant positive trends of NDVI, and woodland loss and grassland degeneration resulted in the significant negative trends of NDVI.

Aims Paeonia delavayi (Paeoniaceae) is an endangered plant restricted to southwestern China. Our objective was to study the numerical population dynamics of the largest and most concentrated natural population in Shangri-La, Yunnan Province, China.
Methods The distribution area of P. delavayi was investigated from 2009 to 2011. We studied the numerical dynamics of the population using static life table, survivorship and mortality curves, fecundity schedule and Leslie matrix model.
Important findings P. delavayi underwent strong environmental screening at ages three to six years. The physiological life span was about 15 years, and generation span was eight years. The net reproductive rate (R₀ = 0.9857), intrinsic rate of increase (r_m = -0.0017) and finite rate of increase (λ = 0.9983) were relatively low, indicating that the population was decreasing. The Leslie matrix model showed that plant numbers from seedlings and sprouts declined about 50% during the past 30 years. The survival rate exhibited a steep curve (B1 type). The mortality rate of individuals was different at every stage, and the killing power (K_x) was high at the ages of six and 12 years. The present population is maintained mainly by sprouts and seedlings. Likely key threats to the species are the damaged ecological environment and human disturbances.

Aims Land use change may alter nitrogen (N) dynamics in terrestrial ecosystems, but its effects remain poorly quantified. Due to reorganization of the land use by government, a large cultivated area has converted to woodland and shrubland plantation since the 1980’s in Danjiangkou Reservoir area, China. Our objective was to investigate effects of agricultural land use change on soil N dynamics in this area.
Methods We conducted in situ close-top tube incubation experiment to determine soil inorganic N (NH₄⁺-N, NO₃^--N), soil net nitrogen mineralization and nitrification in three adjacent land use types (afforestation, shrubland and cropland) in the Qingtang river basin around Danjiangkou Reservoir in Spring of 2011.
Important findings Soil NO₃^--N concentration (mg·kg^-1) was 1.27 ± 0.18, 3.51 ± 0.11 and 9.00 ± 0.73 in afforestation, shrubland and cropland, respectively. Soil NO₃^--N concentration significantly increased from afforestation to shrubland to cropland, whereas NH₄⁺-N concentration (mg·kg^-1) was not significantly different among afforestation (1.33 ± 0.20), shrubland (1.67 ± 0.17) and cropland (1.62 ± 0.13). We found that NO₃^--N was the main form of inorganic N under shrubland and cropland, and the proportion of NO₃^--N to soil inorganic N content was 67.8% and 84.8% in shrubland and cropland, respectively; however, the concentration of NO₃^--N was approximately equal to NH₄⁺-N under afforestation. Soil net N mineralization rate (mg·kg^-1·30 d^-1) were 0.98 ± 0.12, 2.52 ± 1.25 and 6.58 ± 2.29, respectively in afforestation, shrubland to cropland. Soil net N mineralization rate was not significantly different among the land use types, whereas nitrification rate (mg·kg^-1·30 d^-1) was significantly different: cropland (7.13 ± 2.19), shrubland (2.56 ± 1.07) and afforestation (0.85 ± 0.10). Soil net N mineralization rate was positively correlated with nitrification rate. Nitrification rate accounts for approximately 87% of soil mineralization rate in afforestation, whereas nitrification was higher than mineralization rate in shrubland and cropland soil due to the ammonification rate being below zero. Both soil N mineralization and nitrification were regulated by soil water content and soil temperature with more sensitive to soil water content during the incubation period. Additionally, soil N mineralization and nitrification were negatively correlated with soil C:N ratio. Our results suggest that change in soil microclimate and soil C:N ratio under land use change would impact soil N dynamics.

Aims The δ¹⁸O of soil evaporation (δ_E) is an important factor controlling the variations of atmospheric δ¹⁸O (δ_v), and it is also one of the key challenges of partitioning evapotranspiration into evaporation and transpiration components. δ_E is mostly simulated by the Craig-Gordon model, which is constrained by the δ_v of water vapor, the relative humidity (h), the equilibrium and kinetic factors and the δ¹⁸O of soil water (δ_s) at the evaporating front. Our objective is to investigate the diurnal variations of δ_E and factors affecting it.
Methods We determined the δ¹⁸O of water vapor in a winter wheat-summer maize cropland based on the in-situ and continuous water vapor isotope ratio measurement system. We sampled soil water at different depths and analyzed it using the cryogenic vacuum distillation technique to acquire the δ¹⁸O of soil water at the evaporating front.
Important findings During the growing period of winter wheat-summer maize, the diurnal variation of δ_E exhibited a bimodal pattern with peaks at 6:00 and 15:00. The h has a significant effect on the diurnal variation of δ_E in cropland ecosystems, and causes the Craig-Gordon model to be invalid under high humidity condition of h > 95%. The in-situ and high resolution measurement of δ_v overcomes the uncertainty of using the local precipitation equilibrium method to evaluate δ_v, which improves the accuracy of δ_E. Different equilibrium factors have no significant influence on the accuracy of δ_E. Different kinetic factors, especially the canopy scale kinetic factor, influence the accuracy of δ_E significantly. The location of the evaporating front determines the h normalized to soil temperature and the δ¹⁸O of soil water directly and also influences the accuracy of δ_E significantly. Further research is needed to attain direct measurement of δ_E by combining isotope ratio infrared spectroscopy (IRIS) with the static chamber or dynamic chamber.

Aims Bryophytes are an important component of forest vegetation. Their species diversity is vital to protecting plant resources and ecosystem diversity. Our objective was to explore the diversity and distribution of bryophytes and the relationship between bryophyte diversity and environment factors in seven dominant forest vegetation types (deciduous broad-leaved shrubs, DBS; deciduous broad-leaved forest, DBF; evergreen and deciduous broad-leaved mixed forest, EDF; evergreen broad-leaved forest, EBF; coniferous broad-leaved mixed forest, CBF; coniferous forest, CF; bamboo forest, BF) of West Tianmu Mountain, Zhejiang Province, China.
Methods Thirty-two sites (10 m × 10 m) were established in the seven forest vegetation types. Sixteen plots were selected by systematic sampling in each sampling site. Coverage of floor bryophytes and abundance of epiphytic bryophytes of each site were recorded. Species richness, importance value, diversity index and Sørensen’s similarity index were examined at the different vegetation types.
Important findings Based on collection and identification of a total of 969 specimens, we recorded 142 bryophytes belonging to 82 genera and 41 families, among which were 33 liverworts belonging to 18 genera of 33 families and 109 mosses belonging to 66 genera of 28 families. Hypanceae, Brachytheciaceae and Thuidiaceae were three dominant families. The species richness and diversity of bryophytes in two kinds of mixed forest types (EDF and CBF) were higher than the five pure forest types (DBS, DBF, EBF, CF and BF). EDF had the highest species diversity and CBF had the highest species richness. BF was lowest in both diversity and richness. There was high similarity between environment factors such as neighboring altitudinal forest types, with the highest value between EBF and CF, and the lowest value between DBS and BF. The number of microhabitats showed significant positive correlation with floor bryophyte diversity.

Aims Our objectives were to investigate phenotypic variation of Azadirachta indica in cultivated populations and to describe the relationship between phenotypic variation of the cultivated populations and different distribution areas.
Methods We investigated 14 phenotypic traits for 90 individuals in nine cultivated populations of A. indica from Yunnan Province of China and used variance analysis, nested analysis, correlation analysis, principal component analysis, UPGMA cluster analysis and multi-comparison to analyze results.
Important findings Rich phenotypic variation existed both among and within populations, and variation was greater within populations than among populations. Duncan’s test of CV and the principal component analysis of phenotypic traits both indicated that the traits of fructification and seed chemical composition were the main factors accounting for the phenotypic variations. According to UPGMA cluster analysis, the populations of A. indica could be divided into four groups. These cluster results were not due to geographic distances. Findings will lay a foundation for genetic improvement in A. indica, and provide a scientific basis for working out breeding strategy in this species and for countermeasures of natural forest sustained utilization.

Aims Our objectives were to examine the response of biofuel plant hybrid Pennisetum (P. americanum × P. purpureum) to NaCl stress and determine its salt tolerance mechanism and salinity threshold.
Methods We cultured plants of this hybrid in plastic pots filled with sand containing 0, 0.3%, 0.5%, 0.9%, and 1.2% NaCl. After four weeks, we measured the fresh weight, dry weight, water content, plant height, tillering number and ion contents of different parts of the plants.
Important findings NaCl treatment significantly reduced shoot fresh weight and dry weight by 50% at 0.568% and 0.570% NaCl, respectively. With increasing NaCl concentration, Na⁺ content of functional leaves did not change significantly, whereas Na⁺ content of old leaves and roots increased significantly. Especially when the concentration of NaCl was 0.9%, Na⁺ content of old leaves and roots increased two and three fold more than that of the control, meaning that Na⁺ content in functional leaves, old leaves and roots increased gradually. With increasing NaCl concentration, K⁺ content in the shoots and roots was not affected, whereas Na⁺/K⁺ in the roots increased significantly, and Na⁺/K⁺ in the shoot increased significantly only at 0.9% NaCl. These results indicated that the salt-tolerant mechanism of hybrid Pennisetum is salt exclusion, and its salinity threshold is 0.57% (about 100 mmol·L ^-1).

Aims Little information has been available on the effects of soil Pb pollution on plant nutrition. Our objective was to characterize the responses of poplar (Populus deltoids × P. nigra) in C, N and P accumulation and N and P use efficiency under different Pb stresses in acidic purple soil and alkaline purple soil.
Methods A controlled pot experiment using one-year old poplar was arranged with different treatments of four Pb concentrations (CK: 0, T1: 200, T2: 450 and T3: 2000 mg·kg^-1) in the field. Concentrations of C, N and P in plant components were measured over one growing season. We calculated C, N and P accumulation and N and P use efficiency.
Important findings Accumulations of C, N and P in poplar declined with increased Pb supplies in both acidic purple soil and alkaline purple soil. Accumulations of C, N and P in alkaline purple soil were larger than in acidic purple soil. Distribution patterns of C, N and P in poplar were altered in both soils when supplied with different Pb concentrations. C, N and P accumulation in fine roots significantly increased with increased Pb supplies in acidic purple soil, but decreased in fallen leaves. In contrast, C, N and P accumulation in fine roots decreased with increased Pb supplies in alkaline purple soil, but increased in fallen leaves. In addition, P use efficiency of the poplar in both soils increased with increased Pb supplies, but the N use efficiency significantly decreased under treatments T2 and T3. Results indicated that the accumulation of C, N and P in poplar had been inhibited and nutrient use efficiency of the plant had been altered by Pb stress. Moreover, the effects of Pb stress on nutrient accumulation, distribution and utilization by poplar were much less in alkaline soil compared to acidic soil.

Clonal plants have many advantages over non-clonal plants, such as longevity, spatial mobility and two modes of reproduction. Therefore, clonal plants are dominant or constructive species in many natural ecosystems. We review the adaptive strategies of clonal plants to interspecific competition and elaborate the differences of competitive ability. It accounts for the responses to interspecific competition from those aspects, including modular morphology, clonal architecture, reproductive strategy and the relationship between physiological integration and interspecific competition. Those factors lead to different results, such as diversities of experimental materials, conditions of habitat, design of experiments and dynamic spatial changes of morphology and physiology of clonal plants. Key issues that need research are proposed, including clonal plants and interspecific competition under global change and its molecular ecological mechanism.