Aims Grassland desertification is being accelerated because of adverse climate change effects and unsustainable land uses, resulting in several major environmental problems. However, there are few studies on the economics spectrum of different plant functional types in desert steppe. The objectives of the current study are to examine the relationships among leaf functional traits of native plant species, to compare the functional traits among different plant functional types, and to determine whether an economic spectrum exists for the majority of species in the desert steppe of Damao Banner, Nei Mongol, China.
Methods Photosynthetic and chlorophyll fluorescence parameters, specific leaf area (SLA), and leaf nitrogen contents across 24 species of different functional types were measured in situin the desert steppe ecosystem. Non-parametric tests were used to analyze leaf trait differences in plant species of different functional types. Linear regression analysis was used to determine the relationships among leaf traits in different plant species. Finally, a comprehensive analysis on these leaf traits in different plant species was conducted using the principal component analysis. All data analyses were performed using SPSS 16.0 (SPSS, Chicago, USA).
Important findings Significant differences among plant functional types were found in most of the leaf traits. SLA and mass-based nitrogen concentration (N_mass) in grasses were 2.39 and 1.20 folds, respectively, of that in shrubs; area-based photosynthetic capacity (A_area), SLA, and photosynthetic nitrogen use efficiency (PNUE) in annual species were 1.93, 2.13, and 4.24 folds, respectively, of that in perennial species; and A_area,SLA, and PNUE in C₄ species were 2.25, 1.73, and 3.61 folds, respectively, of that in C₃ species. Almost all relationships significantly differed (p< 0.01) among the leaf traits, with exception of the relationships betweenA_area and area-based nitrogen concentration (N_area) and between quantum yield of PSII electron transport (Φ_PSII) and SLA, implying that an economic spectrum may exist in the desert steppe ecosystem. The relationships of N_area, mass-based photosynthetic capacity (A_mass), andPNUE with SLA were most significantly strong (R²= 0.54, 0.62, 0.60, respectively; p < 0.01). Results in this study suggest that the annuals, grasses, and C₄ species might be located at the end of the leaf economic spectrum with high area-based photosynthetic rate, high nitrogen concentration on mass basis, short leaf lifespan, and high SLA;whereas the perennials, shrubs, and C₃ species could be located at the another end of the economic spectrum with contrasting traits.

Aims Little is known on the stoichiometric characteristics of nitrogen (N) and phosphorus (P) in wetland vegetation across China. This work is aimed to study the stoichiometric characteristics of wetland vegetation in China, which are of great significance for revealing the coupling relationship between vegetation and habitats.
Methods Based on previous studies, a data set comprising N and P contents and N:P of wetland vegetation attained from 649 observations in 52 study sites, was classified and analyzed, which concerned vegetation organs, growth periods, plant life forms, climate zones and wetland types.
Important findings The geometric mean of N, P and the N:P of different organs occurred in descending order as follows: leaf (N, 16.07 mg·g^-1; P, 1.85 mg·g^-1; N:P, 8.67) > aboveground organ (N, 13.54 mg·g^-1; P, 1.72 mg·g^-1; N:P, 7.96) > stem (N, 7.86 mg·g^-1; P, 1.71 mg·g^-1; N:P, 4.58). Leaf N showed a three-peak seasonal distribution, with the peaks occurring in May, July and September, whilst stem N exhibited a bimodal distribution with peaks in May and September. Leaf N:P fluctuated in conformity to N before maturity, but changed corresponding to P in senescence phase. The type of wetlands was found to be the key factor significantly impacted the stoichiometric characteristics of wetland vegetation in China. Specifically, the highest and lowest leaf N and P contents were found in the bottom lands and marshes, respectively, while the N:P displayed a reversed trend. The geometric mean of leaf N, P contents and the N:P followed the order of: tropics > temperate zone > subtropics, albeit no significant differences ( p > 0.05) among them. In addition, most of the leaf N:P were less than 14, indicating that the wetland vegetation in China was under the conditions of N limitation.

Aims The influence of elevated atmospheric CO₂ concentration and nitrogen (N) addition on soil carbon pool is one of the foci among international ecological research communities. The changes of soil carbon pool induced by atmospheric CO₂ concentration and/or N deposition will lead to changes in atmospheric carbon pool and thus the global climate change. However, few studies have been carried out in the subtropical China. Our objective was to understand the effect of elevated CO₂ concentration and N addition on soil carbon stability in south subtropical experimental forests.
Methods Experimental forest ecosystems were constructed in open top chambers. Six native tree species in southern China were planted in these experimental forest ecosystems. The species were exposed to elevated CO₂ and N addition in the open top chambers beginning in May 2005. The four treatments were: elevated CO₂ and high N addition (CN), elevated CO₂ and ambient N deposition (CC), high N addition and ambient CO₂ (NN), and ambient CO₂ and ambient N deposition (CK). The elevated CO₂ was (700 ± 20) µmol·mol^-1. The total amount of added NH₄NO₃-N was 100 kg N·hm^-2·a^-1. In January 2010, soil samples were collected from the open top chambers and then relevant variables were measured.
Important findings Elevated CO₂ concentration and N addition (CN) effectively increased the soil total organic carbon in different soil layers, among which the increases in the lower soil layers (5-60 cm) were statistically significant. Different components of the active organic carbon pool differed in the responses to treatments. The differences in microbial biomass carbon were significant in the 0-5 cm, 5-10 cm and 10-20 cm soil layers among the treatments, and the readily oxidized carbon showed significant responses to the elevated CO₂ concentration and N addition treatments in the 10-20 cm and 20-40 cm soil layers, while there was no significant difference in the dissolved organic carbon among different treatments in all the soil layers. The responses of carbon in different aggregate fractions differed among the treatments. The carbon in the 250-2000 μm aggregates was significantly different among treatments in the 20-40 cm and 40-60 cm soil layers. The carbon in the 53-250 μm aggregates was susceptible to treatments in the 40-60 cm soil layer as both the CC and NN treatments facilitated the chronic carbon accumulation in deeper soil layers, especially under the CN treatment. Carbon in the <53 μm fraction showed significant differences among treatments in deeper soil layers (10-20 cm, 20-40 cm and 40-60 cm). In conclusion, elevated CO₂ concentration and N addition increased soil organic carbon in the experimental forest ecosystems, and facilitated the accumulation of carbon in micro-aggregates and silt-clay fraction in deep soil layers, thus strengthened the stability of soil organic carbon pool.

Aims The yield and growth of maize (Zea mays) have changed due to the influence of climate change. Increasing CO₂ concentration ([CO₂]) and changes in precipitation are two important aspects of climate change affecting maize. Our objective was to explore the interactive effects of elevated [CO₂] and an increase in precipitation on yield and growth in maize, in order to evaluate the effects of future changes in climate change on plant in Northeast China.
Methods This experiment was conducted in Jinzhou, with the maize cultivar ‘Danyu 39’ as plant materials. Open top chambers (OTCs) were used to simulate the elevated [CO₂] (control at 390 μmol·mol^-1, and elevated at 450 and 550 μmol·mol^-1, respectively) and increased precipitation (0 and +15% increase based on the average monthly precipitation from June through August during 1981-2010). Totally six treatments, i.e. C₅₅₀W_+15%, C₅₅₀W₀, C₄₅₀W_+15%, C₄₅₀W₀, C₃₉₀W_+15% and C₃₉₀W₀ were included in this study.
Important findings Significant interactive effects between elevated [CO₂] and increased precipitation on corn grain yield and biological yield (p< 0.05) were found. The grain yield and biological yield were increased by the positive effects of the two factors. An increase in precipitation increased the grain yield by 15.94%, 9.95% and 9.45%, and the biological yield by 13.06%, 8.13% and 6.49%, respectively, at [CO₂] of 390, 450 and 550 μmol·mol^-1. The increase in grain yield was slightly greater than that of the biological yield, resulting in an increase in the economical coefficient. The ear characteristics of maize were significantly affected by the two factors. For example, kernels number, kernels weight, ear length and ear diameter were all increased by elevated [CO₂], as well as by an increase in precipitation. However, the shriveled kernels showed a reversed trend of changes. It is noteworthy that the axle diameter was increased by the interactive effects between elevated [CO₂] and an increase in precipitation, which constrained the increase in the grain yield. Moreover, there were highly significant interactive effects between elevated [CO₂] and an increase in precipitation on net photosynthetic rate (P_n) and leaf area (p< 0.01), and significant interactive effects on plant height and dry matter accumulation (p< 0.05). An increased precipitation increasedP_n of the leaves at each [CO₂] level. The results also showed that plant height, ear position height, stem diameter, leaf area were all increased by the interactive effects between the two factors, leading to enhanced dry matter accumulation and the yield. It can be concluded that future elevated [CO₂] may favor the growth of maize if coupled with increasing precipitation.

Aims Plant species diversity often declines when nutrients are added in grassland. However, the mechanisms for explaining biodiversity loss due to nutrient enrichment have remained controversial. Our objective was to explore the potential mechanisms of diversity decline.
Methods In this paper, based on a four-year experiment of nutrient addition and grazing in an alpine plant community, we investigate the potential mechanisms of diversity loss by comparing the above- and below-ground competitions using coefficient of variation and nitrogen use efficiency under fertilization scenario both in grazed and non-grazed plots.
Important findings Fertilization increased the size inequality of individuals by 15%, increased species height by different degrees, and reduced the number of species pairs that differed significantly in nitrogen content by 65% in the non-grazed plots. The results indicate that the large-sized individuals out-competed the small-sized individuals due to competition for light, which led to a decline in species richness by 29.6% in the non-grazed plots following fertilization. In contrast, fertilization did not change the size inequality of individuals and species height in the grazed plots, and increased the number of species pairs that differed significantly in nitrogen content by 11.4%, implying that an increased competition for soil nitrogen among species reduced the species richness by 17.3%. Our study also suggests that grazing delayed the effect of fertilization on species richness as inferred by the lower rate of species loss in the grazed plots.

Aims Defoliation by insects leads to significant changes in tree growth and physiological metabolism. However, how fine root dynamics would respond to defoliation is still poorly understood. The objectives of this study were to: 1) compare the responses of height and stem collar diameter to defoliation in manchurian ash (Fraxinus mandschurica) and Dahurian larch (Larix gmelinii) seedlings; 2) quantify the effects of defoliation on the seasonal dynamics of fine root production and mortality in the two species.
Methods Manchurian ash and Dahurian larch seedlings, with different biomass allocation and height growth strategy, were used to investigate the effects of different levels of artificial defoliation (0% (control), 40% and 80% leaf area removal) on the growth of aboveground (height and stem collar diameter) and belowground (production and mortality of fine roots (diameter ≤ 2 mm)). Minirhizotron approach was employed to determine the seasonal dynamics of fine roots, and seedling height and stem collar diameter were measured concurrently.
Important findings The results showed that: 1) defoliation reduced the growth of seedling height (but statistically not significant) and stem collar diameter in both species, with a stronger effect on the stem collar diameter. Effects on aboveground growth by defoliation were enhanced by increasing defoliation intensity in both species. Compared with the control seedlings, the height and collar diameter of ash were reduced by 3.3% to 12.1% and 5.7% to 23.1%, respectively, while the height and collar diameter of larch were only slightly reduced (< 12%). 2) Defoliation significantly reduced live fine roots in both species (p< 0.001), with the reduction in relative growth rate of fine roots being enhanced with defoliation intensity. 3) Defoliation significantly reduced fine root production in both species (p< 0.05), had not apparent effect on fine root mortality. We conclude that defoliation imposes significant effects on aboveground growth (especially stem collar diameter) in ash and belowground growth (particularly root production) in larch. Our findings provide some insights into the inter-specific difference in the response of fine root dynamics to canopy carbon supply.

Aims In order to explore the main reasons and the invasive processes of water hyacinth (Eichhornia crassipes) in the dike-pond district in southern China, we reviewed and comprehensively analysed the historical documents and files on the water hyacinth concerning the latest research progress on its invasion ecology.
Methods We obtained the data through searches and reviews of relevant historical documents and files.
Important findings We found that water hyacinth invaded water networks and channels of the Hangzhou- Jiaxing-Huzhou plain from 1911, and was a common aquatic plant in the Pearl River Delta region since 1911. The dike-pond system was a typical organic cycling farming system in the two regions between 1911 and 1980, when farmers generally used water hyacinth as organic fertilizer. Although local government extended cultivation techniques for water hyacinth from the late 1950s to the 1980s and farmers increased water hyacinth production in large scales, the species was still contained. However, the dike-pond ecological farming systems between the Changjiang River Delta and the Zhujiang River Delta were widely abandoned because of the rapid urbanization and industrialization, and the water environments of the wetlands deteriorated since 1980. These are the main reasons for the situation of aggressive water hyacinth invasion in southern China.

Aims Populus euphratica is an important tree species and its leaf shape changes along the growth stages. Adult trees commonly comprise polymorphic leaves, including lanceolate, oval and serrated broad-oval leaves. Our objective were to elucidate the ecophysiological mechanisms of P.euphratica adapting to high temperature and strong light environment and its survival strategy by comparing photosynthetic efficiency and chlorophyll fluorescence parameters in heteromorphic leaves in an extremely arid desert area, and to explore the causes of changes in leaf shape in P.euphratica, in order to provide a scientific basis for the protection of desert P.euphratica forests.
Methods Individuals with 10 cm diameter at breast height from a planted P.euphratica forest were selected. Measurements were made on the parameters of gas changes and chlorophyll fluorescence of three different leaf shapes on branches at the similar height using a LI-6400 Portable Photosynthesis System and a PAM-2100 chlorophyll fluorometer. The light/CO₂ response curves of net photosynthetic rate (P_n) and rapid light curves of chlorophyll fluorescence in heteromorphic leaves were fitted and analyzed.
Important findings The light and CO₂response curves, rapid light curves of the three different leaf shapes in P.euphraticawere better fitted by the modified rectangular hyperbola models, and the model values of key photosynthetic parameters were very close to the measured data. There were significant differences in the light responses, biochemical parameters and the parameters of rapid light curves among the oval, serrated broad-oval leaves and lanceolate leaves, but the heteromorphic leaves did not significantly differ in carbon assimilation efficiency. The maximum net photosynthetic rate (P_nmax) of the heteromorphic leaves under saturated intercellular CO₂concentration was higher than under saturated irradiance, indicating that photosynthetic efficiency was limited to the great extent by CO₂supply and regeneration rate of ribulose biphosphate (RuBP). Initial quantum yield (α), initial carboxylation efficiency (CE),P_nmax, photosynthetic capacity (A_max), maximum carboxylation rate (V_cmax) were greater in the oval and serrated broad-oval leaves than in the lanceolate leaves; the serrated broad-oval leaves had the highest light saturation point (LSP), photosynthetic electron transportation rate (ETR_max) and rate of photorespiration (R_p), whereas the lanceolate leaves had the lowest light compensation point (LCP), LSP, α and CE. All the results above indicate that the serrated broad-oval leaves having greater resistance to strong light and higher R_p may be an important mechanism for dissipating excessive light energy and protecting the photosynthetic apparatus from light damage. In contrast, the oval leaves had higher values in α, CE, triose-phosphate utilization efficiency (TPU), PSII actual photochemical efficiency (Φ_PSII), leaf nitrogen allocation strategy and low LCP and therefore could maintain high photosynthetic rate in extremely arid areas. The lanceolate leaves had the lowest values in P_n, Φ_PSII, and ETR, which would be difficult to meet the individual growth demand because of the low production of photosynthate, and their number declined with growth and distributed mainly toward the lower tree crowns.

Aims Despite the increasing attention given to the rate of mitochondrial respiration under light (R_d), considerable confusion persists over whether mitochondrial respiration in the dark (R_n) is inhibited by light and whether R_d is affected by light intensity. The objective of this study is to test the hypotheses: 1)R_n is not inhibited by light; 2) the rate of R_d changes with light intensity; and 3) the photosynthetic refixation of CO₂ produced by R_n accounts for the apparent disparity between R_d and R_n.
Methods In the present study, 0.02 mol·mol^-1 O₂ (i.e. 2% O₂) was used to saturate R_n and to inhibit photorespiration (R_p). By using combined gas exchange measurements and a low O₂ (2% O₂) method, the post-illumination CO₂ release rate of R_n, photosynthetic rate (P_n) in response to photosynthetically active radiation (PAR) in 2% O₂ at either 380 or 0 μmol·mol^-1 CO₂, of C₃ (Triticum aestivum and Glycine max) and C₄(Zea mays and Amaranthus hypochondriacus) plants, were measured.
Important finding R_n was not inhibited by light. At 2% O₂ and 0 μmol·mol^-1 CO₂, the measured parameters could be used to accurately estimate R_d when CO₂ concentration was set for 0 μmol·mol^-1. R_d decreased with increasing light intensity. Although R_d was lower in the dark, this could be accounted for by photosynthetic re-fixing of respiratory CO₂. For all plants tested, CO₂recovery rates increased with increasing light intensity (from 50 and 2 000 μmol·m^-2·s^-1).

Aims Although adenosine 5′-triphosphate (ATP) is usually considered to be localized in intracellular spaces, plant and animal cells can secrete ATP from the cytosol into the extracellular matrix. This extracellular ATP (eATP) is an important signal molecule for many physiological responses in plants. However, whether eATP could also have effects on photosynthesis in plants has not been extensively studied.
Methods With bean (Phaseolus vulgaris) leaves as experiment material, the effects of eATP on the chlorophyll fluorescence characteristics and photosynthetic O₂evolution rate were studied under different light intensities.
Important findings The maximal photosystem II (PSII) quantum yield in light adaptation (F_v′/F_m′), effective photochemical quantum yield of PSII (Y(II)), and photochemical quenching coefficient (q_P) gradually decreased, and the electron transport rate (ETR), non-photochemical quenching coefficient (q_N), and the quantum yield of regulated energy dissipation (Y(NPQ)) increased, with increases in light intensity. Treatment of leaves with eATP significantly increased the values of the potential maximal photochemical efficiency of PSII (F_v/F_m), F_v′/F_m′,Y(II), q_P, ETR, and photosynthetic O₂evolution rate, but did not affect the values of q_N and Y(NPQ). In contrast, treatment of leaves with β,γ-methyleneadenosine triphosphate (AMP-PCP, an inhibitor of eATP receptors) significantly reduced the values of F_v/F_m, F_v′/F_m′,Y(II), ETR, and photosynthetic O₂evolution rate, but increased the values of q_N and Y(NPQ). These results show that the levels of eATP exert important influences on the photochemical reaction in photosynthesis.

Aims The objective of this study was to investigate the responses of photosynthetic traits to varying degrees of low temperature stress and recovery treatment, in order to provide a theoretical basis for enhancing the cold tolerance of cotton seedlings and avoiding chilling damage under natural conditions.
Methods The cotton cultivars ‘Xinluzao 33’ (cold sensitive) and ‘Zhongmiansuo 50’ (cold tolerant) were used in this study. Gas exchange parameters, energy conversion and electron transmission of seedling leaves were determined under different levels and durations of low temperature stresses and subsequent recovery treatment. The adaptive capacity to light was also analyzed by developing photosynthetic light response curves of leaves under recovery treatment after 48 h of low temperature stresses.
Important findings The results showed that the values of net photosynthesis (P_n), stomatal conductance (G_s), stomatal limitation (L_s), intercellular CO₂ concentration (C_i), maximum photochemical efficiency (F_v/F_m), maximal photochemical efficiency in light adaptation (F_v′/F_m′), actual quantum yield (Φ_PSII) and relative electron transport rate (rETR) varied very little such that they reached the normal levels after being released from less-intense chilling stresses (15 °C or 24 h). In this situation, the damage of photosystem II (PSII) reaction center was reversible and the P_n was subjected to stomatal limitation. With decreasing temperature and treatment time, the parameters changed significantly and performed less well under recovery treatment in the two cotton cultivars. The limiting factor for P_n had changed from stomatal to non-stomatal, and the absorption, conversion of light energy, and electron transmission were severely inhibited. In addition, with a decrease in temperature, the maximum photosynthetic rate (P_nmax), the initial slope of photosynthetic light response curve (AQY) and the light saturation point (LSP) of cotton seedlings declined rapidly, and the light compensation point (LCP) and dark respiration (i.e. mitochondrial respiration; R_d), displayed an upward trend, indicating that the ability of radiation utilization decreased. Those results indicated that, low temperature stress decreased the adaptability to light environment, the activity of PSII reaction centers and photochemical electron transfer rate, inhibited pathways of photosynthetic electron transport, and reduced the CO₂ fixation capacity, which led to the structural damage of photosynthetic apparatus and functional reduction in photosynthetic capacity. The cold tolerant cultivar could maintain higher photosynthetic rate by keeping higher photochemical electron transfer, transport, and low-light utilization ability, and lower respiration, and by adjusting the reduction of G_s to be more rapid and sensitive, which could enhance the recovery capability and chilling adaptability.

The concept of leaf economics spectrum (LES) has attracted much attention and debate since its emergence. It for the first time provides quantitative analysis of plant functional traits and their relationships on the global scale, hence quantifying and generalizing the context and variations of the trade-off strategies. This is of great theoretical value, and provides a useful research method and scientific ideas for subsequent study on plant traits and their functions. In this paper, we try to comprehensively review the meaning, contents, relevant verifications and objections about LES, and to explore its underlying mechanisms. In addition, we emphasize the multi-scale and multidimensional extensions, integration and potential applications of LES. Currently there are still several shortcomings about LES research in China, and we outlook the development of LES theory domestically and abroad. It may be of significance for ecological researchers to establish and exploit jointly a global database on plant traits.