Aims The arid region in central Asia, in the hinterland of Eurasia, is characterized by low precipitation and extremely fragile ecological environment. Study of energy and matter exchange between atmosphere and the land surface is essential to understanding the balance of water resources and ecosystem functioning in arid region. The objective of this study was to investigate the characteristics of water and carbon fluxes and responses to environmental factors in a typical ecosystem of central Asia.
Methods Eddy covariance measurements were made at three sites representing desert and grassland ecosystems in the central Asia. We analyzed the responses of evaporation and gross primary productivity to selective environmental factors using the enveloped curve fitting method, which determines the response of a dependent variable to a given independent factor while fixing other factors at their best values.
Important findings During growing season from April to October, the diurnal variations of energy, water vapor, net ecosystem CO₂ exchange and gross primary productivity showed patterns of “single peak curve” at the three sites; whereas ecosystem respiration in the desert ecosystem kept relatively stable. The ratio of latent heat flux to net solar radiation in the grassland ecosystem (76.3%) was greater than in the desert ecosystem (32.7%). The grassland ecosystem occurred as a strong carbon sink, whilst the desert ecosystem showed weak carbon fixation. Evapotranspiration and gross primary productivity in the two types of ecosystems were susceptible to changes in precipitation, net solar radiation or photosynthetically active radiation, vapor pressure deficit and air temperature.

Aims The objectives of this study were to investigate the effects of experimental warming on the fluxes of CO₂, CH₄ and N₂O of biological soil crusts (BSCs) and soil system, and to determine the relationships of the greenhouse gas fluxes with soil temperature and soil moisture.
Methods We used open top chamber to imitate climate warming. Intact soil columns covered with three types of biological soil crusts, including moss, algae and mixed crusts of moss and algae, were collected at the southeast fringe of the Tengger Desert. The fluxes of CO₂, CH₄ and N₂O under warming and non-warming treatments were measured using static chamber and gas chromatography method during the period from July 2012 to June 2013.
Important findings Warming and BSCs types had no significant effects on the fluxes of CO₂, CH₄ and N₂O. The CO₂ and CH₄ fluxes were significantly affected by sampling date as well as interactions between crust type and sampling date and among warming treatment, crust type and sampling date. An interaction between warming treatment and sampling date also significantly affected the CH₄ flux. However, no difference was found in the annual CO₂, CH₄ and N₂O fluxes and global warming potentials (GWP) in the three BSC types between the warming and non-warming treatments. CO₂ flux had a significant and positive exponential correlation with soil temperature at 5 cm depth and a significant and negative linear correlation with soil moisture at 10 cm depth. The CH₄ fluxes of moss and mixed crusts were significantly and negatively correlated with both soil temperature at 5 cm depth and soil moisture at 10 cm depth. No relationship was found between the N₂O flux and soil temperature, while the N₂O flux of moss crust was significantly and negatively correlated with soil moisture at 10 cm depth. Differences in CO₂ and CH₄ fluxes of moss crust between the warming and non-warming treatments were significantly and negatively correlated with the difference of soil temperature at 5 cm depth between the two treatments; whereas the difference in N₂O flux of algae crust was marginally and positively correlated (p = 0.051) with the difference in soil temperature. All results mentioned above suggest that the fluxes of greenhouse gases would not experience a significant change for the BSCs-soil system under global warming, meaning that the feedback of greenhouse gases in the desert ecosystem to climate warming would not be large in the future.

Aims Land-use change is one of the key factors affecting global carbon cycle, and plant functional traits have been widely used to study the linkage between environmental factors and ecosystem functioning. With the help of plant functional traits, we can better understand how plants respond to land-use changes. This study aims to 1) determine how plant traits related to carbon sequestration differ among different functional groups, organs and species of common plants in a Stipa grandis steppe in Nei Mongol; 2) explore the underlying impacts of four different land-use types on traits related to carbon sequestration of the studied plants.
Methods The study was conducted in Maodeng pastureland, Xilinhot, Nei Mongol. Samples of common plant species were collected in four plots, including a long-term reserved plot, a long-term free grazing plot, a 4-year enclosed plot and a 4-year enclosed plot with hay harvesting. We separated the plants into organs and determined the contents of carbon, total nitrogen, cellulose, lignin and acid detergent fiber, and then calculated the ratio of carbon to nitrogen. All data were analyzed in IBM SPSS Statistics for Windows 19.0.
Important findings There were marked differences in the traits related to carbon sequestration among different plant functional groups, species and organs. Land-uses significantly affected these traits at the three organizational levels. Four-year enclosure with hay harvesting resulted in a decrease in nitrogen content of the plants compared with other three land-use types. Both Cleistogenes squarrosa and Salsola collina were susceptible in the traits related to carbon sequestration to long-term free grazing, but their patterns of responses were reversed.

Aims The role that litter plays is essential for shaping C, N and P cycling in forest ecosystems. The objective of this study was to investigate how organic C, N and P in differently decomposed litter layers would vary with forest succession.
Methods The study site is located in Tiantong National Forest Park, Zhejiang Province, China. Stands of five successional stages were selected to measure forest floor litter mass and concentrations of C, N and P in litter samples for each of the un-decomposed layer (L), the semi-decomposed layer (F), and the decomposed layer (Y). The successional dynamics of forest floor litter mass and C, N and P were then analyzed.
Important findings Along the forest succession gradient, forest floor litter mass and C stock decreased significantly (p < 0.05). Across successional stages, litter C concentration was greatest in the L layer, intermediate in the F layer, and lowest in the Y layer. C stock was larger in the Y layer than in the F layer (p < 0.05). Both concentration and stock of N were significantly lower in the early successional stage than in the intermediate and late successional stages (p < 0.05). Amongst different layers, N concentration showed an increasing trend with succession, and a decreasing trend from the top to the bottom litter layers (Y > F > L). P concentration was lowest in the intermediate successional stage relative to other two stages, and ranked in the order of Y > F > L among the three litter layers of differential decompositions. There was no apparent successional trend in P stock for the whole litter horizon, but in the L layer, P stock decreased with forest succession. With the succession, litter C:N, C:P and N:P decreased (p < 0.05). Among the litter layers of different decompositions, C:N and C:P were in the order of Y < F < L, whereas N:P showed no apparent trend. Overall, during the secondary forest succession of evergreen broadleaved forests in Tiantong region, forest floor litter mass and stocks of C, N and P in litter horizon decreased, but concentrations of C, N and P increased. The patterns of C, N and P among differently decomposed layers demonstrate that C and nutrient cycling in forest ecosystems is optimized with succession.

Aims Leaf area index (LAI) is a commonly used parameter for quantifying canopy structure and can be quickly measured by indirect optical methods in a forest stand, but few studies have evaluated the accuracy of optical methods to estimate seasonal variations of LAI in a mixed conifer-broadleaved forest. The aims of this study are to (1) develop a practical field method for directly measuring seasonal variations in LAI for mixed conifer-broadleaved forest; (2) evaluate the accuracy of optical methods (digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer) for measuring the seasonality of LAI; and (3) determine how much the accuracy of estimating the seasonality of LAI can be improved by using optical methods after correcting for influencing factors (e.g., woody materials and clumping effects within a canopy).
Methods The seasonal variations of LAI in a mixed broadleaved-Korean pine (Pinus koraiensis) forest were estimated from litterfall and used to evaluate optical LAI (effective LAI, L_e) measurements using the DHP and the LAI-2000 plant canopy analyzer. We corrected a systematic error due to incorrect automatic photographic exposure for DHP measurements. In addition to optical L_e, we also measured the seasonality of other major factors influencing the determination of LAI, including woody-to-total area ratio (α), clumping index (Ω_E) and needle-to-shoot area ratio (γ_E).
Important findings The LAI from different methods all showed a unimodal form, and peaked in early August. Effective LAIs from the optical methods underestimated LAI throughout the growing seasons (from May to November). L_e from DHP underestimated LAI by an average of 55% (ranging from 50% to 59%) and from LAI-2000 plant canopy analyzer by an average of 27% (ranging from 19% to 35%). The accuracy of L_e from DHP after correcting for the automatic exposure, α, Ω_E and γ_E was greatly improved, but the LAI was underestimated by 6%-15% (with mean value of 9%) from May to November. In contrast, the accuracy of L_e from LAI-2000 plant canopy analyzer after correcting for the α, Ω_E and γ_E was also greatly improved, the difference between corrected L_e from LAI-2000 plant canopy analyzer and observed LAI was less than 9%. The results from our study demonstrate that seasonal variations in LAI in mixed conifer-broadleaved forests can be optically measured with high accuracy (85% for DHP and 91% for LAI-2000 plant canopy analyzer), as long as corrections are made for the influences of woody materials and foliage clumping on the measurement.

Aims Our objectives were to examine the community structure of phytoplankton and the associated environmental factors in Lake Changhu in the summer of 2012, and to investigate the degree of eutrophication in the lake.
Methods Biological characteristics of the alga and integrative nutritional state index were used for evaluation of eutrophication in Lake Changhu. Phytoplankton and water samples were collected at 20 sites. The water samples were fixed, precipitated and concentrated for qualitative and quantitative analysis. Variables related to water conditions such as chlorophyll a, total phosphorus, total nitrogen, total suspended solids, secchi disk depth and chemical oxygen demand were monitored.
Important findings Fifty-three species (genera) of phytoplankton were identified, belonging to Chlorophyta, Cyanophyta, Bacillariophyta, Xanthophyta, Euglenophyta, Pyrrophyta and Cryptophyta, respectively. Chlorophyta (24 species), which accounted for 38.9% of the total, was the most abundant, followed by Cyanophyta (15 species, accounting for 36.0% of the total) and Bacillariophyta (7 species, accounting for 14.1% of the total). There were 10 dominant species and Oscillatoria amphibia was a common species in four areas, with maximum dominancy of 0.72. The phytoplankton density varied from 12.03 × 10 ⁶ to 62.13 × 10 ⁶cell·L ^-1 with an average of 27.71 × 10 ⁶ cells·L ^-1. The highest cell density occurred in the Yuanxinhu area, followed by the Haizihu area and the Mahongtai area; the Miaohu area was observed to have the lowest cell density. Biodiversity index of phytoplankton varied from 0.89 to 3.24, and evenness index varied in a range of 0.23-0.83. Based on the two methods of eutrophication evaluation, the water was in moderately eutrophic and eutrophic state in Lake Changhu in the summer of 2012. Canonical correlation analysis suggested that the total nitrogen, total suspended solids, total phosphorus, dissolved oxygen and nitrite nitrogen were the main environmental factors affecting the spatial distribution of phytoplankton community in Lake Changhu in summer. Most of the Cyanophyta (Dactylococcopsis acicularis, Oscillatoria amphibia, Phormidium and Anabeana) had a great demand for total nitrogen. Affected by geographical feature, human activities and the hydrodynamic features, the sampling sites showed apparent regional differentiations as revealed by canonical correspondence analysis.

Aims Stomata are critical in controlling the exchange of water vapour and carbon dioxide and maintaining the balance between plant water and carbon relations. Here, we investigated the effects of habitat (open and understory) and plant type (ferns and angiosperms) on stomatal morphology and stomatal responses to changing light intensity.
Methods We measured stomatal morphology and stomatal conductance in response to transitions in light intensity in five ferns and four angiosperms from different habitats. To increase the sample size, we also collected data on stomatal characteristics for 45 ferns and 70 angiosperms from published studies.
Important findings For all the nine species, the plants in open-habitat had significantly greater stomatal density, shorter stomatal length and greater sensitivity to decreasing light intensity than those in the understory, but the effect of plant type was not significant. Combined analysis with published data indicated that the effects of both habitat and plant type on stomatal morphology were significant. As stomatal sensitivity was closely linked to stomatal morphology, more and smaller stomata might enable angiosperms to respond more quickly to environmental perturbations than ferns. We conclude that both habitat and plant type affect the stomatal response to light.

Aims Grazing is one of the major measures for grassland management in Nei Mongol steppe. The growth and reproductive strategies of grassland plants are developed under their long-term co-evolution with ungulates in grassland ecosystems. This study was conducted to understand how Thalictrum petaloideum would change its growth and reproductive strategies with increasing stocking rate.
Methods By using a grazing experiment in a typical steppe ecosystem initiated by the Nei Mongol Grassland Ecosystem Research Station in 2006, we examined the responses of T. petaloideum to stocking rates at population, individual and organ levels during the 2012 and 2013 growing seasons.
Important findings With increasing stocking rate, the number of reproductive individuals decreased and the reproductive process ceased in T. petaloideum at the population level. The threshold for ceasing the reproductive process was at a stocking rate of 7.5 sheep per hm ². The plant height, plant biomass and the numbers of reproductive branches, flowers and seeds all decreased with increasing stocking rate at an individual level. Two shifts were detected for the reproductive allometric relationships with increases in stocking rate. With the increase of stocking rates, T. petaloideum reduced the number of flowers per reproductive branch decreased but the individual seed weight increased with increasing stocking rate at the organ level. A trade-off between the number of seed and the weight of seed was found, which might be an important mechanism in T. petaloideum responding to grazing disturbance.

Aims Roots are an important part of plants; they not only facilitate the utilization of soil water and nutrients, but also successively anchor the plants against wind and water wave erosion. This study was conducted to determine the adaptive strategy of root architectural characteristics in different plant life forms, in order to assist the selection of most suitable plant species for the coastal dune restoration.
Methods After a detailed field investigation of sand dunes in South China, four species were sampled on a damaged coastal sand dune, including Casuarina equisetifolia, Ipomoea pes-caprae, Spinifex littoreus and Cynodon dactylon, and roots were excavated for analyzing their architectural characteristics such as root bifurcation ratio, root link length, root topological index and root-shoot ratio.
Important findings There were great differences as well as similarities in the root architectural characteristics among the four plant species. The total root bifurcation ratios in Spinifex littoreus and Cynodon dactylon were apparently higher than in other two species, and was lowest in Ipomoea pes-caprae, indicating that herbaceous plants are more competitive for soil resources by having a higher root bifurcation ratio. With except of Casuarina equisetifolia, all other three species were easily sand buried due to their flatten and extended shoots, which might further improve the transportation efficiency of soil resources. The average root link lengths of the four species were smaller in coastal sandy dunes than which in inland areas; Casuarina equisetifolia had the greatest average root link length of 19.25 cm among the four species studied, and greater proportion of transportation roots than other three species. This demonstrated that an increase in average root link length and proportion of transportation roots would favor the reduction of root competition for soil resources and high efficiency of resources transportation. Ipomoea pes-caprae had a smaller proportion of the assimilation roots, but the adventitious roots on the shoot compensated for the low assimilation efficiency of resources. All the four species showed a dichotomous structure, of which the herbaceous species had more similar root architectures, indicating that herbaceous species are less affected by limitation of environmental resources and better to colonize the coastal dunes if being used in restoration. Compared with species in inland areas, there are greater differences for the species in coastal sandy areas in the acquisition of soil resources and spatial expansion, indicating different adaptive strategies among the four species. Herbaceous species should be used as preferred plants for the restoration of coastal dunes, especially those with adventitious roots, but not the trees.

Aims In order to understand the effects of acid rain on Phyllostachys pubescens seedlings, we analyzed the composition and content of green leaf volatiles (GLVs) and the activity of antioxidant enzyme in 3-year-old seedlings of P. pubescens under simulated acid rain stress (i.e. at pH values of 5.6, 4.0 and 2.5). We aim to elucidate the adaptation mechanisms of P. pubescens leaves to acid rain stress from aspects of GLVs emission and their biochemical characteristics.
Methods The composition and content of GLVs were analyzed under near-natural conditions using the thermal desorption system/gas chromatography/mass spectrometer technique (TDS-GC-MS), and the content of soluble protein and malondialdehyde (MDA), activity of antioxidant enzymes in the leaves of P. pubescens seedlings were measured under different acid rain treatments.
Important findings Results showed that the MDA content did not respond to the pH 5.6 treatment in P. pubescens. The content of MDA was elevated in treatments of pH 4.0 and pH 2.5 after 75 days and 45 days, respectively (p < 0.01). The content of soluble protein in P. pubescens leaves was significantly influenced by acid rain; under the treatments of pH 4.0 and pH 2.5, the content of soluble protein was 32% and 65%, respectively, of the controls (p < 0.01). In the pH 5.6 treatment, the content of soluble protein was only slightly increased. There were differences in the timing of responses to acid rain stress among the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), reflecting possibly a coordinative reaction of those antioxidant enzymes to stress. Compared with the control, GLVs were increased by 26.4% and 132.9% (p < 0.01), respectively, under the treatments of pH 4.0 and pH 2.5. (E)-2-nonenal, 2-ethyl-hexanal, 2-hexenal and (E)-2-nonenal were newly found GLVs under the acid rain stress. The results indicated that P. pubescens could enhance its ability to resist acid rain stress by adjusting its activities of antioxidant enzymes, improving contents of soluble protein and releasing GLVs.