Aims We aim to construct a national database for decomposition rate of forest foliar litter and to investigate the effects of controlling factors concerning geography (i.e. latitude, longitude, and altitude), climate (i.e. mean annual temperature and mean annual precipitation), and litter quality (i.e. the concentrations of N, P, K, and lignin, C:N ratio, and lignin:N ratio) on litter decomposition.
Methods We compiled a large dataset on decomposition constant (i.e. k value, which indicates the rate of litter decomposition) for foliar litter in Chinese forest ecosystems covering 74 study sites, and conducted simple and multiple regression analyses to explore the relationships of the k value with the controlling factors at the national scale.
Important findings The k value showed a tendency to decrease with latitude, longitude, altitude, lignin content, C:N, and lignin:N of litter, and to increase with mean annual temperature, mean annual precipitation, and litter nutrient concentrations (N, P and K) at the national scale. Single factors such as climate, litter quality, and geographic variable only explained 0.1%-30.3% of the variation in the rate of litter decomposition. However, a combination of climatic factors (mean annual temperature and mean annual precipitation) and latitude accounted for 34.1% of the variation in the rate of litter decomposition. Similarly, a combination of N, K, lignin, and lignin:N accounted for 21.7% of the variation in the rate of litter decomposition. Altitude, mean annual temperature, mean annual precipitation, N, K, and lignin:N collectively accounted for 74.4% of the variation in the rate of litter decomposition. Our results suggest that climate is the most important regulator of litter decomposition at the national scale and that the effects of litter quality is relatively small compared to climate.

Aims Foliar litter humification is an important ecological process relating to soil carbon and nutrient budget in subalpine forest ecosystems, and the process of foliar litter humification can be affected by various snowpacks with different thicknesses in winter. However, little is known on the effects of snowpack on foliar litter humification. The objective of this study is to explore the effects of snowpack on early foliar litter humification during the first winter in subalpine forest.
Methods A field litterbag experiment was conducted in a subalpine forest in southwestern China from November 2012 to April 2013. Air-dried foliar litter of fir (Abies faxoniana), cypress (Sabina saltuaria), larch (Larix mastersiana), birch (Betula albo-sinensis), willow (Salix paraplesia), and azalea (Rhododendron lapponicum) were incubated under snowpacks with varying thicknesses (deep snowpack, medium snowpack, thin snowpack, and no snowpack) due to variations in the canopy openness. Net accumulation of humus carbon, humification degrees, and humification rates were measured at snow formation, snow cover, and snow melt stage as foliar litter humification proceeded.
Important findings Significant humification was observed in the six foliar litter types during the first winter regardless of the condition of snowpacks. The highest humification degree was observed in birch foliar litter (4.45%-5.67%), and the humification degrees were 1.91%-2.15%, 1.14%-2.03%, 1.06%-1.97%, 0.01%-1.25%, and 0.39%-1.21%, respectively, for fir, azalea, willow, larch, and cypress foliar litter under varying snowpacks. The net accumulation of humus carbon of all foliar litters increased at the snow formation, snow melt stage, and the whole winter, which exhibited an increasing tendency with the decrease of snow cover thickness. In contrast, net accumulation of humus carbon showed a declining trend at the snow cover stage, and significantly increased with the decrease of snow cover thickness. In addition, correlation analysis results indicated that the humification degree was positively correlated with total nitrogen and acid-insoluble residues and negatively related to the organic carbon, total phosphorus, and water- and organic-soluble components. These results clearly suggest that foliar litter humification in subalpine forest can be enhanced by reduced snow cover in a scenario of climate warming, although the humification degree is controlled by snowpack and litter qualities at different stages of snow cover in winter.

Aims Snow patches of varying thickness could play an important role in potassium (K) and sodium (Na) dynamics during litter decomposition in subalpine forests due to significant freeze-thaw events, but the detailed processes are unclear. Our objective was to understand how snow patches would affect the dynamics of K and Na during litter decomposition of six representative woody species in different snow cover periods.
Methods A field experiment was conducted to investigate litter decomposition in a subalpine forest of western Sichuan by using litterbag method. Air-dried litter of Salix paraplesia, Larix mastersiana, Abies faxoniana, Rhododendron lapponicum, Betula albosinensis, and Sabina saltuaria were placed in nylon litterbags, and placed on the forest floor along a snow thickness gradient from forest gap to under the canopy cover. The samples were retrieved at snow formation, during snow cover period, and at snow melt.
Important findings Net Na immobilization during litter decomposition was observed over the entire snow cover season regardless of species, with the highest net immobilization rate occurring during the snow cover stage. In contrast, K was mainly released from litter during the snow cover period, showing rapid K release at the snow melt stage. Compared with the treatments with thin and absence of snow patches, the treatments with thick and moderate snow patches had higher rates of K release during litter decomposition. Although showing less effect on the release of Na compared with K, the snow cover significantly enhanced Na release from decomposing litter of Salix paraplesia, L. mastersiana, A. faxoniana, and R. lapponicum. Statistical analysis indicates that the dynamics of K and Na during litter decomposition are significantly influenced by species and snow cover at different snow cover stages. The rate of K release was positively related to daily mean temperature regardless of species, while the rate of Na release was positively related to daily mean temperature in litter of all species but B. albosinensis and Sabina saltuaria. Results in this study suggest that a decrease in snow cover under the scenario of winter warming would inhibit K and Na release during litter decomposition in winter in the subalpine forests, with the degree of release being related to litter quality.

Aims Providing indispensably theoretical evidence for establishing indices of evaluation on drought tolerance in shrubs, and screening for tree species that are drought tolerant for afforestation in arid regions or for matching their characteristics with suitable habitat conditions are the key to vegetation restoration in the Qinghai-Xizang Plateau. However, these issues are not adequately addressed in recent research due to lack of systematic methods. Therefore, our objective was to make a comprehensive evaluation on drought tolerance in 20 shrub species collected from different areas in Qinghai-Xizang Plateau, and to study their underlying mechanisms in drought tolerance.
Methods We made measurements on variables depicting root characteristics, including the root length (TRL), surface area (TRSA), volume (TRV), and tips number (TRTN) of all roots, the root length (FRL), surface area (FRSA), volume (FRV), and tips number (FRTN) of fine roots (d≤2 mm), and derived plant characteristic indices including thickness of cuticle (CT), thickness of palisade tissue (TPT), thickness of spongy tissue (TST), TPT/TST, thickness of leaf (LT), palisable tissue cell density, and tissue structural tense ratio (CTR = TPT/LT × 100%) and spongy tissue loosened ratio (SR = TST/LT × 100%) of leaf anatomical structure, root to shoot ratio (RSR), leaf transpiration rate (T_r), instantaneous water use efficiency (WUE_i), and carbon isotopic composition (δ¹³C) of the 20 shrub species through field experiments. Correlation analysis and principal component analysis were performed on the 19 variables and indices.
Important findings Different shrubs had different mechanisms of drought tolerance. In this study, the character- istics of drought tolerance were mainly categorized into 6 types, involving modifications of (1) root systems, (2) leaf anatomical structure, (3) leaf pattern, and (4) biomass allocation, or via (5) low water-consumption and (6) high WUE_i. Different genera or different tree species within the same genus clearly differed in drought tolerance. The species of the genus Hippophae were relatively poorly tolerant to drought, whereas several shrubs including Potentilla fruticosa, Berberis julianae, Caragana arborescens, Spiraea salicifolia and Hippophae rhamnoides ssp. mongolica occurred to be more drought tolerant than other shrub species investigated in this study. On the other hand, there were highly significant correlations among the characteristics of root systems and among characteristics of leaf anatomical structure. The results of principal component analysis on 19 variables and indices showed that TRL, TRSA, TRV, TRTN, FRL, FRSA, FRV, FRTN, CT, TPT, TST and WUE_i could be effective indicators of drought tolerance of shrubs in the Qinghai-Xizang Plateau. In addition, the drought tolerance of shrubs had a close connection with their origin of collections; the shrubs collected from Xining prefecture in Qinghai Province were more drought tolerant than those from Tianshui Prefecture in Gansu and Lasa Prefecture in Xizang.

Aims An understanding on the living communities of the state’s key protected wild plants and the ability in utilizing resources and occupying ecological spaces by different populations is essential to the protection and propagation of rare and endangered plant species. We use our findings to highlight the knowledge gaps in the conservation strategies for the endangered species.
Methods Field investigations were conducted during 2009-2011. Based on the survey data on 70 forest plots in the Bawangling protected area, the niche breadths and overlaps of 12 species listed as the state’s key protected plants were calculated and analyzed.
Important findings The 12 species, by their niche breadth values in descending order, include Aquilaria sinensis, Nephelium topengii, Camellia sinensis var. assamica, Alseodaphne hainanensis, Keteleeria hainanensis, Podocarpus imbricatus, Firmiana hainanensis, Parakmeria lotungensis, Cephalotaxus mannii, Michelia hedyosperma, Ixonanthes reticulata, Dacrydium pierrei. The niche breadth value of a species is closely related to its range of geographical distribution; both Dacrydium pierrei and Parakmeria lotungensis had a narrow niche breadth corresponding to their narrow ranges of altitudinal distribution. In general, the niche overlap value is higher between species with greater niche breadth; the highest niche overlap value of 0.872 was found between Camellia sinensis var. assamica and Keteleeria hainanensis. However, the niche overlap value between species with smaller niche breadth could also be high; e.g. the niche overlap value was relatively high (0.693) between two species with smaller niche breadth, Michelia hedyosperma and Firmiana hainanensis, indicating that niche overlap value is dependent upon the biological characteristics and requirements for environmental resources of the species of comparison. Some species with low niche breadth values (e.g. Michelia hedyosperma and Ixonanthes reticulata) were found to have smaller populations. Due to lack of suitable community and habitats, these plant species are in dire need of more attention and prioritization for conservation. In conclusion, for the better protection and propagation of these endangered plants in the future, we should combine knowledge of their biological characteristics with that of their living communities such as the montane rainforests, etc.

Aims Our objective was to determine the impacts of climate change (mainly temperature and precipitation) on the phenology of tropical evergreen forests at the community and species level.
Methods Two phenophases—the onset of leaf unfolding and the onset of first flowering—had been monitored in 12 evergreen broadleaf tree species in the tropical arboretum in Jianfengling, Hainan Island, since 2003. Observations were made on three mature and healthy individuals for each species once every two days in the same sunny direction in the afternoon by the same person. After the phenological data were collected, they transformed into the number of days from the first day of a calendar year (DOY, i.e. from 1th January). The outliers were excluded used the Grubbs principle. Meteorological data for the corresponding time period were derived from the National Climate Centre. Ultimately, the phenological and meteorological data were combined with the integrate regression method and used to identify the impacts of changing climate on the onset of leaf unfolding and the onset of first flowering in the 12 tree species and to determine their responses in the two phenophases to climate change.
Important findings Both the onset of leaf unfolding and the onset of first flowering in the tree species were affected by climate change; the starting dates of the two phenophases in nearly all the tree species were closely related to changes in monthly temperature and precipitation. The onset of leaf unfolding was affected by the monthly mean temperature of the preceding winter and spring, and the impacts became more apparent with the time approaching the occurrence of specific phenophases. Monthly precipitation in the preceding autumn had more effects on the onset of the first flowering than any other time period, in support of the hypothesis that the effect of precipitation on phenology had a hysteretic nature. Furthermore, the onset of leaf unfolding was more susceptible to climate change than the onset of first flowering in the native tree species, whereas the introduced tree species showed reversed responses. Generally, if the monthly mean temperature increases by 0.1 ℃ and the monthly precipitation increases by 10 mm in the month with the strongest effects, and given that the conditions of other 11 months preceding the occurrence of the specific phenophases remains unchanged, then most of the species would advance or delay the phenophases by about one to three days. Ultimately, the Integrate Regression method provides an effective and operational approach to understanding the dynamic and complex relationships between climate change and the phenology in tropical plants, as demonstrated by the high values of the coefficient of determination (R²≥ 0.943) for the integrate temperature and precipitation regression models for phenological predictions based on climatic factors. These models can well be used for predicting the trend of phenological changes in tropical evergreen broadleaf tree species in response to changing climate.

Aims The fractal-like network model of plants (the WBE model) considers that the branching exponents 1/a and 1/b determine the metabolic exponent θ in plants. However, the constant 3/4 metabolic exponent does not completely reflect the plant metabolic scaling. Price, Enquist and Savage extended the WBE model by assuming that branching exponents are not constant but covary with each other, and developed the branching traits covariation model of plants (the PES model). In this paper, we study and compare branching exponents and metabolic exponents in seven woody plants based on leaf area and leaf biomass by using the PES model.
Methods To test the PES model, data on leaf area and leaf biomass of seven woody species were used to determine the values of branching and metabolic exponents. Standardized major axis (SMA) regression protocols were used to determine the numerical values of scaling exponents and normalization constants for each species and across the seven species using the software SMATR. Furthermore, test of a common slope across all species and comparisons between the estimated values and theoretical values proposed by the WBE model were also performed by using the SMATR. Specifically, if the value of p exceeds a critical level, then it is considered that there would be no significant differences among the groups compared and that a common slope can be determined; if the value of p is below the critical level, then it would indicate that the estimated value would be significantly different from the theoretical value.
Important findings Significant allometric relationships between leaf area and leaf biomass were verified within and across species. Specifically, leaf area scaled as 0.86-power of leaf biomass across the entire data sets. Therefore, values of branching and metabolic exponents were determined by using leaf biomass and leaf area separately. Values of the branching exponent 1/a and the metabolic exponent θ based on leaf area were statistically indistinguishable among the seven woody species. On the contrary, values of the branching exponents 1/a and 1/b and the metabolic exponent θ based on leaf biomass differed significantly among the seven woody species. Values of the branching exponents and the metabolic exponent estimated from both leaf area and leaf biomass across the entire data set were all statistically indistinguishable from the theoretical values. Furthermore, compared with the value of metabolic exponent based on leaf biomass, the value of metabolic exponent based on leaf area was statistically more comparable to the theoretical value. The effect of allometric relationship between leaf area and leaf biomass on metabolic rate and relative functional traits of plants should be paid more attention in future research.

Aims Soil microbes play a key role in matter recycling and accumulation of allelochemicals. We studied the functional diversity of microbial communities in order to illustrate variations in soil microbial community diversity among different Casuarina equisetifolia woodlands.
Methods Young, middle-aged, and mature forest of C. equisetifolia woodlands in the Haikou Guilinyang littoral zone were chosen as subjects of the study. Soil microbial functional diversity in those stands was determined by using Biolog micro-plate technique.
Important findings The soil microbial carbon utilization was higher in bare land and the mature forest than the middle-aged and young forest. With increasing stand age, the values of Shannon-Wiener index (H') and McIntosh and Simpson diversity indices all increased. The H' significantly differed among different woodlands. However, there were no significant differences in the McIntosh and Simpson diversity indices between the young and middle-aged forest. Principal component analysis demonstrated that there was a significant difference in the soil microbial metabolic activities among different woodlands, in particular concerning monosaccharides and amino acids. The soil microbial community diversity increased with increasing stand age, which might be due to a joint action among many factors such as litter, the secondary metabolites of plant root secretion, soil nutrients, and specific soil microorganisms.

Aims Over the past 20 years, alpine wetlands have been subjected to a rapid change in climate, resulting in water table drawdown and increased nitrogen deposition. In wetland ecosystems, the water table drawdown can improve soil aeration, hence leading to a higher soil respiration rate; whereas an increased nitrogen deposition could reduce the microbial biomass and pH value, suppressing soil respiration. Understanding the responses of soil respiration to reduced water table and increased nitrogen deposition in alpine wetlands is thus critical to predicting the carbon cycle of wetland ecosystems and its feedbacks to ongoing climate changes. This study tests the effects of water table reduction and nitrogen addition on soil respiration in the Luanhaizi wetland on the Qinghai-Xizang Plateau.
Methods We imposed four treatments, including control (WT⁰N⁰), reduced water table (WT^-N⁰), nitrogen addition (WT⁰N⁺), and a combination of reduced water table and nitrogen addition (WT^-N⁺), on 20 peat monoliths collected from the Luanhaizi wetland at the Haibei station. Soil respiration was measured from late July through mid-September under all treatments.
Important findings A reduction in water table significantly increased the rate of soil respiration. In contrast, nitrogen addition suppressed soil respiration only when water table was not reduced. A positive correlation was found between the aboveground biomass and soil respiration, while no correlation was detected between root biomass and soil respiration. The temperature sensitivity of soil respiration was increased by reduced water table, but was not affected by nitrogen addition. Our results suggest that nitrogen deposition is likely to reduce soil CO₂ emission in alpine wetlands where water level remains high. However, future warmer and drier conditions could result in reduced water table, and consequently alpine wetlands would be predicted to release substantially more CO₂ than previously estimated.

Aims Large tracts of land have been abandoned since last century and the trend continues. Our objectives were to seek an effective solution for facilitating plant diversity on abandoned red paddy soils at an early stage, and to investigate the dynamics of soil organic carbon in relation to changes in vegetation.
Methods The experiment consisted of four treatments, including control (no disturbance from human activities), waterlogging, winter wildfire, and a combination of waterlogging and winter wildfire. Measurements were made in each treatment within quadrate sampling method. In each quadrate, the maximum plant height, density, coverage, and composition were surveyed and recorded by species. The above and belowground biomass and soil organic carbon content were determined with the methods of harvesting, soil coring, and K₂Cr₂O₇ calefaction, respectively.
Important findings The results showed that waterlogging and winter wildfire significantly altered the vegetation richness, evenness, diversity, and species composition on the abandoned red paddy soils at the early stage. Paspalum paspaloides and Murdannia triquetra were the dominant plant species when the abandoned paddies had suffered waterlogging for the first few years, and Microstegium vimineum was the dominant species on sites experienced winter wildfire. Bidens frondosa was a co-dominant species in all the treatments. Compared with the control, the belowground biomass at the depth of 0-20 cm was increased by 49.84%, 73.34%, and 28.94%, respectively, in the waterlogging treatment in the year 2011, 2012 and 2013, and the aboveground biomass was increased by 25.74%, 64.30%, and 50.24%, respectively, in the winter wildfire treatment. The roots collected from the upper 5 cm soil layer accounted for 66.50%-80.34% of the total from the 0-20 cm layer. Winter wildfire resulted in greater values in the Shannon-Wiener diversity index of the vegetation. Different from the uptrend before abandonment, the soil organic carbon in the treatments of control, waterlogging, winter wildfire, and a combination of waterlogging and winter wildfire was reduced by 11.16%, 18.99%, 9.17%, and 19.12%, respectively, after six years of abandonment, and it was significantly lower in the waterlogging treatment (p < 0.05). Plant species richness, evenness, diversity, composition, biomass, and soil organic carbon all had strong relationships with waterlogging and winter wildfire on abandoned red paddy soils (p < 0.05).

Aims Maximum leaf carboxylation rate is one of the key parameters determining the photosynthetic capacity of plants. It is affected by irradiance, temperature, moisture, atmospheric CO₂ concentration, leaf nitrogen content, and some other factors. Accurate simulation of the responses of the maximum leaf carboxylation rate to varying environmental conditions is the premise for predicting the changes in vegetation productivity and carbon cycle in future environments. Most of the process-based terrestrial carbon cycle models use the Farqhuar photosynthesis model to simulate plant photosynthesis. However, the methods in simulating the relationship between maximum leaf carboxylation rate and leaf nitrogen content differ from each other.
Methods We collected data on maximum leaf carboxylation rate and leaf nitrogen content from literature published during 1990-2013, and analyzed the variations in the relationship between maximum leaf carboxylation rate at 25 ℃ (V_cmax,25) and area-based leaf nitrogen concentration (N_a) across different plant functional types and seasons, and in responses to rising atmospheric CO₂ and nitrogen supply. Moreover, we reviewed possible causes of those variations and the influencing factors.
Important findings The results showed that: 1) the relationship between V_cmax,25 and N_a varied with plant functional types, and the average values of the slope ranged from 16.29 to 50.25 μmol CO₂·g N^-1·s^-1. Deciduous trees generally showed a steeper slope and greater photosynthetic nitrogen use efficiency than evergreen trees due to the differences in leaf mass per area (LMA) and nitrogen allocation to Rubisco. 2) The relationship between V_cmax,25 and N_a had seasonal and annual variations. In years without water stress, the highest value of the slope mostly occurred in spring or summer. A change of the slope was related to seasonal variations in LMA and nitrogen allocation to Rubisco. The slope increased in drought seasons or years. 3) The slope of the linear relationship between V_cmax,25 and N_a for perennial needle leaf was reduced due to a decrease in Rubisco content in response to elevated CO₂. The maximum leaf carboxylation rate, nitrogen content, and the slope of their linear relationship increased with increment of nitrogen application rate. On the basis of these analyses, we suggest that simulating the relationship between maximum leaf carboxylation and leaf nitrogen should consider seasonal variations in LMA and nitrogen allocation to Rubisco, the influences of water stress, atmospheric CO₂ concentration, and nitrogen supply level. More multi-factor experimental studies are needed to further investigate the underlying mechanisms of the variations in the relationship between maximum leaf carboxylation rate and leaf nitrogen content, to obtain more observational data with systematic approaches, and thus to further improve ecosystem process-based models.