Aims Litter is the major input source of soil organic carbon and nutrients in natural ecosystems and considered as a key link between above- and belowground carbon cycles. Changes in litter input amount have been proven to exert significant impacts on plant productivity, community structure, and therefore ecosystem function. In Nei Mongol semiarid grasslands, different grassland management practices such as grazing, clipping, and fencing have caused dramatic changes in litter production and input. In addition, as a nitrogen-limited ecosystem, Nei Mongol semiarid grasslands also experienced increasing nitrogen deposition. However, how do changes in litter input and nitrogen addition impact the community productivity and composition of plant functional groups are still unclear in the semiarid grasslands. In this study, our objectives are: 1) to investigate the effects of altered litter input and nitrogen addition on community productivity; 2) to study the changes in aboveground biomass of different plant functional groups and their contribution to community productivity under different litter input and N addition treatments.
Methods We established a manipulative experiment with altered litter input and nitrogen addition treatments in a semiarid typical grassland in West Ujimqin Banner, Nei Mongol. A randomized block split-plot design was applied with five blocks. Three litter input treatments, including litter removal (C0), control (C1) and litter addition (C2), were assigned randomly in each block. Each plot (6 m × 7 m) of litter input treatment was separated into two subplots. One of the subplots was assigned as the N addition treatment (N1) and another subplot was considered as the control treatment without N addition (N0). In N addition treatment, 15 g N·m^-2·a^-1 N fertilizer (as NH₄NO₃) was applied every year since 2013. Aboveground net primary productivity (ANPP) in community and plant functional group levels of each treatment were determined during the peak season from 2013 to 2018.
Important findings Based on 6-year measurements, we found the following results. 1) Litter input increase and nitrogen addition increased community ANPP. Compared with the control, litter removal treatment significantly decreased ANPP by 8.4% and 7.6% in plots without and with N addition, respectively. Litter addition increased ANPP by 10.7% and 6.3% in plots without and with N addition, respectively. 2) Different responses of plant functional groups to altered litter input and N addition led to a change in plant functional group composition. The biomass of perennial bunch grass (PB) and perennial rhizome grass (PR) increased significantly with the increment of litter and nitrogen, which enhanced their dominant status in the community. 3) Improved soil water condition by litter input and nutrient supply by N addition are the major pathways that enhanced ANPP and changed the functional group composition. These results show that proper management, such as grazing exclusion and reducing grazing intensity, can promote productivity by increasing inputs of litter in semiarid grasslands, which leads to the maintenance of ecosystem stability. Suitable nutrients management, like nitrogen addition, is also helpful for productivity improvement and the recovery of degraded grasslands.

Aims Caragana liouana has been widely planted in northwest China for ecological restoration which has induced the planted shrub landscape in the desert steppe zone and changed the structure and function of the original ecosystem. These plantations would affect the water vapor interactions between land surface and atmosphere eventually. Therefore, studying the evapotranspiration characteristics of the planted shrub communities in the desert steppe zone is significant for us to understand its ecohydrological mechanism and guide local ecological restoration.
Methods The transpiration of shrubs and the evapotranspiration under shrub canopy in the desert steppe zone in Yanchi County, Ningxia, were measured by a coupled method of sap flow sensors and lysimeter from May to August in 2018. The effects of environmental factors on the evapotranspiration of the planted shrub communities were analyzed by path analysis.
Important findings (1) The evapotranspiration obtained by the coupled method of sap flow sensors and lysimeter was consistent with the estimations based on the water balance method and the eddy covariance method. Thus, the coupled method of sap flow and lysimeter can be used to measure the evapotranspiration and its components of the planted shrub communities in the desert steppe zone. (2) The diurnal variations of transpiration rate of shrubs and the evapotranspiration rate under shrub canopy were consistent with each other, and both presented an obvious single peak at noon. The evapotranspiration of the planted shrub communities mainly occurred in day time. However, the time of the maximum transpiration rate of shrubs was 1 h later than that of the maximum evapotranspiration rate under shrub canopy. (3) The cumulative transpiration of shrubs was 83.6 mm, the daily average transpiration was 0.7 mm·d^-1, and the series curve of daily transpiration had a parabolic shape from May to August. The cumulative evapotranspiration under shrub canopy was 182.5 mm, and the daily average evapotranspiration was 1.5 mm·d^-1 during the same period. The evapotranspiration under shrub canopy was higher than the transpiration of shrubs. It can be concluded that the water consumption in the planted shrub communities is mainly caused by evapotranspiration under shrub canopy. (4) The total evapotranspiration of the planted shrub communities from May to August was 266.1 mm, and the total precipitation in the same period was 222.6 mm. Therefore, the water balance in the planted shrub communities was in deficit. (5) Net radiation is the most important and direct driving factor that affected evapotranspiration of the planted shrub communities, and it coupled other environmental factors to drive the process of evapotranspiration. Therefore, the water deficit in the planted shrub communities encroaching desert steppe zone should be paid attention in ecological restoration and reconstruction.

Aims Accurate estimation of the variation of nutrient cycling along environmental gradients within an ecosystem is important for assessing their ecological functions. The aim of this study is to explore the effects of different habitats on the metal element content and nutrient return dynamics of Casuarina equisetifolia.
Methods Taking the litter of C. equisetifolia in Chihu State-owned Protective Forest Farm of Huian, Fujian Province as the research object. Five distances named T₁, T₂, T₃, T₄ and T₅ respectively, were selected in order of near to far from the coastline, and the litter was collected to determine the metal element content.
Important findings We found that: 1) Different coastal distances had significant effects on the content and return of each element of C. equisetifolia litter. The element content and return from the forest edge zone to interior forest were linear. In order of near to far from the coastline, sodium (Na) content gradually decreases. Iron (Fe), copper (Cu), zinc (Zn) and manganese (Mn) increased since T₄, and their changing trend and amount of the return and content along the gradient were similar. 2) There were significant differences on the content of litter elements among different months. Litter Na, Fe, Cu, and Zn had similarities, and had lowest value in June and November. Litter Mn fluctuated after falling from February to April. The return amount was generally similar between litter Na and Cu, with peaks in May, August, and next January; Litter Mn, Fe, and Zn showed similar return amount, with peaks in May, August, and next January. 3) Na content in soils at different distances from the coastline decreased gradually, while other elements fluctuated and did not show significant difference along the gradient. 4) Litter Na and Fe were significantly positively correlated, and litter Na and Zn, Fe and Cu, and Fe and Zn were extremely significantly positively correlated, respectively. There was a positive correlation for the same element between soil and litter and the correlation was significant for Na and Cu. The difference in litter element was greatly affected by the difference in resorption rate during litter falling at different timing along the distance gradient. The temporal difference among different months was due to the requirements from plant life activity. The difference in the return of the element was related to the amount of litterfall and the content of elements in the litter.

Aims Exploring the variation and the relationship between different functional traits of different growth forms and life forms woody species is helpful to understand the adaptation strategies of plants to the external environment, and is of great significance for understanding community assembly and biodiversity maintenance mechanisms.
Methods We measured leaf chlorophyll content (CHL), leaf thickness (LTH), leaf area (LA), leaf dry mass (LDM), specific leaf area (SLA), leaf dry matter content (LDMC), leaf tissue density (LTD), twig dry matter content (TDMC) and twig tissue density (TTD) of 18 main woody species from the Cyclobalanopsis glauca community in karst hills of Guilin, southwest China. Traits variations among different plant functional types (growth form and life form) of woody species were analyzed by a series of methods, including the one-way analysis of variance (one-way ANOVA), and the linear mixed-effects model. In addition, the relationships between nine functional traits on individual and species levels were assessed by the Pearson’s correlation test and principal component analysis (PCA).
Important findings The results showed that: (1) The nine functional traits had different degrees of variation. Specifically, LA and LDM had the maximum coefficient of intraspecific and interspecific variation, while the intraspecific and interspecific variation coefficients of TDMC and TTD were the lowest. (2) For different growth forms, there were significant differences in most functional traits between trees, shrubs and woody lianas. (3) For different life forms, except that the deciduous species showed significantly higher LA and SLA values than evergreen species, and for the other seven functional traits, evergreen species showed significantly higher values than those of deciduous species. (4) There were differences in the intraspecific and interspecific variation of functional traits between different growth forms and life forms plants. Except for some plant functional traits showing the intraspecific variation higher than interspecific variation, most of the other functional traits showed the interspecific variation was higher than intraspecific variation. (5) The relationships between nine functional traits are roughly the same at the individual level and the species level, while the significant correlation ratio at the individual level is higher than the species level. In conclusion, the interspecific variation of plant functional traits is basically higher than the intraspecific variation, but the intraspecific variation cannot be ignored. In addition, species with different growth forms and life forms adopt different ecological strategies to adapt to the karst habitat. Future research should be based on sampling at the individual level, and in combination with environmental factors to explore the variation and correlation in functional traits of different plant functional types at different scales.

Aims Fallen logs play important roles in maintaining the health and the renewal of forest ecosystems, but the difference of bryophyte societies on fallen logs with different decay classes is unclear.
Methods To understand the regularity and influencing factors of changes in bryophyte societies, we investigated the bryophytes with quadrats along the trunks on four fallen logs of Pinus armandii with different decay classes at the same site in Sygera Mountains, Xizang. Then, the measured data were collected and analyzed.
Important findings There were 22 families and 52 species of bryophytes inhabiting the four fallen logs, including 13 families and 38 species of Musci, 9 families and 14 species of Hepaticae. According to the characteristics of the shared dominant species, 14 societies were obtained. With the increase of decay classes of fallen logs and changes in surrounding environment, the bryophyte diversity increased gradually, while the number of societies and the total bryophyte coverage fluctuated. Bryophyte species varied from drought-tolerant tall turfs, such as Orthotrichaceae and Leucobryaceae, to fast-growing cushions or mats in humid and shady environments, such as Mniaceae, Thuidiaceae and Brachytheciaceae. The complexity of spatial structure of bryophytic society increased gradually. Fallen logs are important growth substrates for a variety of bryophytes. Bryophyte societies on fallen logs vary with decay classes, moisture and light conditions.

Aims The rapid economic growth has led to serious atmospheric compound pollution in China. Ozone and aerosol are the two main air pollutants that could greatly alter the photosynthesis of plants. Ozone often inhibits leaf photosynthesis through phototoxic effect, while aerosol could increase leaf photosynthesis through diffuse fertilization effect. This paper aims to investigate the relative impact of ozone and aerosol on leaf photosynthesis under atmospheric compound pollution.
Methods We planted Populus × canadensis at three sites along the air pollution gradient around Beijing metropolitan area. During the growing season of 2012-2013, ozone concentration (AOT40), aerosol optical depth (AOD), air temperature, photosynthetically active radiation (PAR) and photosynthetic rates of leaves were measured at these sites.
Important findings The results showed that: (1) AOT40 increased with increasing air temperature and AOD. Aerosol loadings reduced the external canopy PAR but increased internal canopy PAR. (2) The photosynthesis of sun leaves positively correlated with AOD and air temperature, and negatively correlated with AOT40, while the photosynthetic of shade leaves was positively correlated with AOD. (3) For sun leaves, ozone was the most important factor affecting their photosynthetic rates. Aerosol’s positive effect on photosynthesis of sun leaves was compensated by the negative effect of ozone. Meanwhile, by scattering solar radiation, aerosol contributed the most to the increased photosynthesis of the shade leaves. Overall, our results indicated that ozone and aerosol induced different impacts on the photosynthesis of sun and shade leaves, suggesting that plants with different canopy structures and ozone sensitivity may respond differently to compound pollution. Our results also indicated that aerosol and ozone pollution need to be controlled simultaneously to protect the productivity and function of ecosystem.

Aims To clarify the azimuthal regularity of nocturnal sap-flow activities of Populus tomentosa, which includes nocturnal transpiration (Nt) and stem water refilling (Sr), and explore the main impact factors of Nt and Sr in different orientations.
Methods The thermal dissipation method was used to monitor the nocturnal sap flow of P. tomentosa planted in wide and narrow rows patterns. The image method was used to distinguish Nt and Sr. An automatic weather station measured global solar radiation (R_s, kW·m^-2), air temperature (T_a, ℃), relative humidity (RH, %), wind speed (v, m·s^-1) and other environmental factors. Mechanical tensiometers measured soil water potential (ψ, kPa). The differences of nocturnal sap-flow among orientations and their main impact factors were determined by comparing the magnitudes of Nt and Sr and their correlations with the impact factors.
Important findings The results showed that, for trees on the east-wide-row, the west orientation has the largest Nt and Sr. The Sr in the west orientation was significantly larger than that in the other three orientations. In contrast, north oriented Nt was significantly smaller than that in the other three orientations. There was no significant difference in Nt and Sr among other orientations and the proportion of Sr accounted for the nighttime sap flow (Sr/Q) in all orientations. For trees on the west-wide-row, Nt and Sr in the west orientation were also the largest, and the Sr in the west orientation was significantly larger than that in the east and south. The Nt in the south orientation was the smallest and significantly smaller than that in the west and north. There was no significant difference in Nt and Sr among other orientations. The Sr/Q in the south orientation was significantly larger than that in the other three orientations. The Nt and Sr had significantly positive correlations with vapor pressure deficiency (VPD), and Nt and Sr in some orientations had significant correlations with T_a and RH, but Nt and Sr in all orientations had no significant correlation with v and ψ. The variation coefficient of Nt and Sr among the four orientations (Nt_CV and Sr_CV) had no significant correlation with VPD, T_a, RH, v and ψ. In addition, the Sr was significantly affected by the daytime sap flow. In conclusion, there were significant differences in nocturnal sap flow of P. tomentosa such as Nt and Sr, with west being the most dominant. VPD was the mainly meteorological impact factor of Nt and Sr in all orientations at night.

Aims Soil microbial community composition and structure were regulated by temperature and plant species. Picea asperata and Abies faxoniana were planted in the monoculture and mixture plantations of the subalpine region in southwestern China. However, the effects of these two species and their interactions on soil microbial community under future climate warming remain unclear.
Methods An experiment was conducted to examine the effects of warming and plant species on soil microbial community composition with two levels of temperature (unwarming and warming with infrared heater) and four planting patterns (single A. faxoniana, single P. asperata, mixture of A. faxoniana and P. asperata, and unplanted bare land). Root zone soil of different planting treatments were sampled to estimating the microbial biomass and microbial community composition by the phospholipid fatty acids (PLFAs) content analysis.
Important findings The results indicated that: (1) Both P. asperata and A. faxoniana mono-planting significantly increased the biomass (PLFAs content) of main soil microbial groups and the whole community, regardless of warming, but the PLFAs content was only increased by mixed planting in unwarming plots. On the other hand, warming enhanced fungi (F) in unplanted plots and gram-negative bacteria (GN) in the P. asperata plots, respectively. However, warming significantly decreased soil microbial biomass in A. faxoniana and the mixed planting plots. (2) Principal component analysis (PCA) showed that effects of planting P. asperata and A. faxoniana on soil microbial community composition were greater under unwarming than under warming conditions. All the planting treatments significantly decreased the ratio of gram-positive/gram-negative bacteria (GP/GN) and increased the ratio of fungi/bacteria (F/B) in unwarming plots. However, significant effects on GP/GN and F/B ratios were only observed in A. faxoniana plots under warming condition. (3) PLFAs content was positively correlated with soil organic carbon, and F/B ratio was significantly correlated with soil pH and inorganic N. These results showed that the effects of warming on soil microbial biomass and composition varied among the tree species, and the effects of P. asperata and A. faxoniana were weakened under warming condition than under unwarming condition. Our results provide a vital theoretical basis for further study on the responses of soil microbial communities to vegetation and global climate change in southwestern China.

Aims The dynamics and driving factors of soil enzyme activities and stoichiometry in the micro-scale elevation gradient is of great significance in the study of nutrient cycling processes.
Methods In the present study, the Quercus aliena var. acuteserrata forest belts at the elevation of 1 308, 1 403, 1 503, 1 603, 1 694 and 1 803 m in Taibai Mountain were sampled to determine the contents of carbon (C), nitrogen (N), and phosphorus (P) in leaves, litters, roots and soils, and the activities of alkaline phosphatase (AKP), β-1,4-glucosidase (βG), cellobiohydrolase (CBH), β-1,4-xylosidase (βX) and β-1,4-N-acetylglucosaminidase (NAG).
Important findings Our results showed that altitude had a great impact on the activities of five soil enzymes. CBH and βG increased first and then decreased with the altitude, while βX showed the opposite trend. The NAG and AKP activity showed a downward trend from 1 408 to 1 694 m and increased with elevation since 1 803 m. The total enzyme activity index exhibited a decreasing trend with altitudes increases. The correlation analysis results indicated that soil enzyme activities and their stoichiometry were controlled by plant, soil C, N, P resources, and soil water and heat conditions. Among these factors, the content of soil organic carbon had high correlation with these parameters and was the main factor affecting the change of soil enzyme activities in the Quercus aliena var. acuteserrata forest. In short, the soil enzyme activities and stoichiometry were different along the micro-scale elevation gradient, affected by the C, N, and P resources of plant and soil.