Aims Many past practices in afforestation and forest management were instrumented for addressing the issues of tree species selection, planting regimes and development of overstory structure, but neglected understory vegetation. Our objective was to determine the controlling factors of herb-layer plant distribution and the importance of topography in determining local-scale spatial patterns of herbaceous plants.
Methods The occurrence and distribution of herb-layer plants were investigated on 26 plots in the Xiaoshegou catchment of Lingkong Mountain, Shanxi Province, China. Community types were classified using two-way indicator species analysis (TWINSPAN) and the relationship between the distribution and abundance of herb-layer species and environmental gradients was analyzed using the canonical correspondence analysis (CCA) ordination method. Forward selection and Monte Carlo permutation test were used to select the factors important in determining the herb-layer plant distribution. Partial CCA (PCCA) was also performed to partition the variance that was explainable by categorical habitat and biotic factors studied.
Important findings The 26 survey plots were classified into six groups characterized by the dominant overstory tree species. The results of CCA ordination reflected the relationship between herb-layer community structure and selective environmental variables. The classification of 26 plots in CCA ordination was consistent with the result of TWINSPAN. Forward selection and Monte Carlo test suggested that stand type, soil nutrients and slope position were the most important factors determining understory plant distribution. PCCA revealed that habitat and biotic factors together explained 42.9% of variance in the distribution of understory herbaceous plants. Habitat factors alone explained 31.8% of the variance, biotic factors alone explained 7.8% of the variance and interaction between habitat and biotic factors explained 3.2% of the variance. The partitioning of variance using the PCCA helped with identifying the important habitat factors regulating understory herbaceous plant distribution at the study site. However, the fact that more than half of the variance was unaccounted for by the factors studied suggests that other factors we did not measure could also play a role in determining the occurrence and distribution of herbaceous plants on the forest floor, e.g., human activities and random events. Our study demonstrates the importance of both topography and overstory tree species in determining the occurrence and distribution of herb-layer plant species in temperate forest of mountainous areas.

Aims Our objective was to study vegetation dynamics and changes in ecosystem functions based on plant traits and characteristics of plant functional types (PFTs).
Methods A field manipulation experiment with a split-plot design was conducted in alpine meadow at the Haibei Research Station of the Chinese Academy of Sciences from 2007 to 2011. Three clipping levels (stubbled 1 cm, 3 cm and unclipped) were used on the whole plot and subplots were treated with or without fertilizer and watering. The recursive algorithm and multivariate analysis were implemented to search for optimal trait subsets and plant response types (PRTs), which could response to experimental treatments, and to identify plant effect types (PETs) impacting the aboveground net primary productivity of community.
Important findings Under each of four resource conditions, i.e., unfertilized and unwatered (NFNW), fertilized only (F), watered only (W) and fertilized and watered (FW), the optimal response trait subsets were different, i.e., leaf margin-plant height-leaf weight-specific leaf area, life cycle-plant height-leaf weight-specific leaf area, life cycle-chlorophyll content-leaf surface-plant height-leaf weight-specific leaf area, and propagative organ-leaf margin-plant height, respectively. Of these responses, plant height, leaf weight and specific leaf area were more sensitive to treatments than others. Under the resource conditions, we found 14 optimal PRTs and four PETs in all of the PFTs. These PETs can explain 50.3%-86.4% of variation in productivity. The optimal PRTs and the optimal PETs account for 70% and 20% of all PFTs. PETs account for 28.5% of PRTs, therefore, there was partial overlap between PETs and PRTs. These results indicate that both vegetation response to grazing disturbance and ecosystem functioning changes could be accurately reflected by easily measurable plant functional traits. However, the optimal trait subsets and PFTs could be different depending on when the heterogeneity of resources is taken into account. PETs are the optimal PFTs reflecting vegetation response to grazing disturbance, but also changes in ecosystem functioning.

Aims Soil microbes play a key role in material recycling and energy conversion in forest ecosystems. We studied the functional diversity of microbial communities and soil physical-chemical properties in order to illustrate variations of soil microbial community diversity along an elevational gradient in the Wuyi Mountains of China and influencing factors.
Methods Evergreen broad-leaved forest (EBF), coniferous forest (CF), dwarf forest (DF) and alpine meadow (AM) were chosen as experimental sites along an elevation gradient in the National Natural Reserve of the Wuyi Mountains. We used Biolog EcoPlate analysis to study the functional diversity of microbial communities.
Important findings There were significant differences in functional diversity of microbial communities in different soil elevations. The average well color development (AWCD), which directly reflected microbial activity and functional diversity, increased over time, while AWCD at the same soil depth gradually decreased along with increasing altitude and in the order of EBF > CF > DF > AM. The AWCD of different soil depths for the same vegetation type was in the order of 0-10 cm > 10-25 cm > 25-40 cm. The Simpson index, Shannon-Wiener index, richness index and McIntosh index of EBF were all higher than AM. There was variation among substrates used by soil microbial communities in different soil elevations. The substrate used in EBF was significantly higher than the substrate used in AM. The carbon sources mostly used by soil microbes were carbohydrates and carboxylic acids, followed by amino acids, phenolic acids and polymers; the lowest was amines. Principal component analysis (PCA) identified two factors in relation to carbon sources; they explained 75.27% and 16.14% of the variation. The carbon sources used by soil microbial communities were different among different vegetation types. Amino acids and amides were the two main carbon sources separating the two principal component factors. Soil microbial community diversity decreased along the elevation gradient and with soil thickness, and vegetative biomass, forest litter, soil nutrient, microzoon and plant roots might be the major factors controlling this diversity.

Aims Zelkova, belongs to the Ulmaceae, consists of only six species and has a disjunct distribution in East Asia, West Asia and South Europe. Molecular phylogenetic analysis and dispersal and vicariance analysis (DIVA) were employed to analyze phylogenetic relationships and biogeographic pattern of Zelkova.
Methods The phylogenetic tree was reconstructed based on DNA sequences of trnL-trnF and ITS regions. The analysis of DIVA was used to deduce the biogeographic pattern.
Important findings Results showed that three phylogenetic clades exist in Zelkova, and they correspond to groups from East Asia, West Asia and South Europe. The present phylogenetic tree is different from that in previous study based on nrITS region. DIVA analyses of this genus indicated that the ancestral area of Zelkova was a larger area including East Asia, West Asia and South Europe. The speciation process was dominant by vicariance. Each of the three areas was gradually separated from vicariant events. Based on the high level of species diversity of Zelkova in East Asia, the center of origin is probably the northern Pacific, i.e., north of China and Japan. The current distribution pattern of this genus was likely shaped by historical geological and environmental events, such as the retreat of Tethys, the Qinghai-Xizang Plateau uplift and the Quaternary glaciations that shrank distribution areas.

Aims A major challenge in studies of tropical forest successional dynamics is to reveal the relative importance of deterministic versus stochastic processes affecting species composition, spatial distributions and their rates of change. Here, we tested succession trajectory of tropical secondary forests follow equilibrium or non-equilibrium dynamics by evaluating community reassembly for tropical lowland rainforest recovery on the abandoned shifting cultivation lands on Hainan Island of south China.
Methods We explored species composition and dominance of different size classes (seedlings, saplings and adult trees) of communities along a chronosequence of secondary forest plots ranging from 15 to 60 years since abandonment after shifting cultivation. We included two old-growth forest plots for comparison.
Important findings Both species diversity for the three size classes and the species similarity index among size classes in old-growth forests were significantly higher than in secondary forests. However, the proportion of dominant species in old-growth community was lower than that of secondary forests. Species similarity between secondary forests and old-growth forests increased with forest recovery, supporting the view of equilibrium succession dynamics. In each recovery stage, the number of individuals, species richness and abundance-based coverage estimator of seedlings were lower than those of both saplings and adult trees. Moreover, the species composition of seedlings in secondary forests differed significantly from that of both saplings and adult trees, suggesting that seedling recruitment might be an unpredictable process. Our results highlighted that the community assembly processes during secondary forest recovery are driven simultaneously by stochastic and deterministic processes.

Aims Essential resources for plant growth are heterogeneously distributed in natural systems, and clonal plants can efficiently use heterogeneously distributed resources. Many studies have addressed effects of heterogeneous water supply on the growth, morphology and physiology of clonal plants, but few have tested effects of water heterogeneity on the ability of clonal plants to store water.
Methods We grew ramets of two rhizomatous clonal plants Leymus secalinus and Calamagrostis pseudophragmites under both homogeneous and heterogeneous water supply. The experiment was conducted from 15 August to 14 October 2010 under a rain shelter at Ordos Sandland Ecological Station (39°29′ N, 110°11′ E). Water content and biomass of roots, shoots, spacers (rhizomes) and buds were measured.
Important findings Spacer water content, shoot water content and root water content were significantly higher under the heterogeneous water condition than under the homogeneous water condition in both species, suggesting that clonal plants could increase the ability to store water when growing in heterogeneous water conditions. Leymus secalinus decreased single ramet biomass and increased bud number to adapt to water heterogeneity, while C. pseudophragmites increased belowground biomass, including rhizome biomass, root biomass and bud biomass, to deal with water heterogeneity. Increasing water storage may increase the ability of clonal plants to adapt to unpredictable water conditions.

Aims Our objective was to demonstrate the influence of leaf size on leaf transpiration and temperature in arid regions.
Methods Based on energy and material exchange theory and the results of previous studies, we set up a single leaf energy and material exchange model combined with arid environmental conditions.
Important findings Leaf transpiration decreased with increasing stomatal resistance, but leaf temperature increased. Leaf transpiration and temperature decreased with decreasing leaf radiation absorption rate in the same environmental conditions. Moreover, leaf width and wind speed were important parameters in understanding leaf energy and material exchange. Leaf transpiration and temperature generally decreased with decreasing leaf width with wind speed <0.1 m·s ^-1 and stomatal resistance about 1000 s·m ^-1. Low leaf transpiration and temperature could encourage plant growth with the low water availability, high radiation and high temperature conditions in arid regions.

Aims Sonneratia apetala, a native mangrove species in India, Bengal and Sri-Lanka, was introduced in 1985 to Dongzhaigang Mangrove Nature Reserve in Hainan Island, China from Sundarban, southwest of Bangladesh. Laguncularia racemosa, another mangrove species from Mexico was introduced to the same reserve in 1999. Our objective was to investigate the salinity tolerance mechanism of S. apetala and L. racemosa in order to elucidate adaptive strategies of the halophytes in stressful saline habitat.
Methods We investigated the effects of increasing soil NaCl (100-400 mmol·L^-1) on gas exchange, O₂^-_· production rate, activity of antioxidant enzymes, and the relevance to salt tolerance over four weeks in 1-year-old seedlings of S. apetala and L. racemosa.
Important findings Seedlings of the two mangrove species acclimated to different salinity levels through changing physiological and morphological traits. However, there were significant differences between S. apetala and L. racemosa in photosynthesis and anti-oxidant defense under salt stress. Increasing NaCl stress significantly elevated net photosynthetic rate (P_n), and stomatal conductance (G_s), intercellular CO₂ concentration (C_i) and transpiration rate (T_r) decreased. As a result, water use efficiency (WUE) increased in leaves of S. apetala seedlings. But L. racemosa showed a rapid increase of P_n in the initiation of salt stress, and P_n remained lower than control levels at the end of the experiment. As a result, C_i and G_s increase with the decrease of P_n, T_r and WUE. The reduction occurred after exposure of L. racemosa seedlings to severe salinity, 400 mmol·L^-1 NaCl (28 d). These results indicated that the inhibitory effects of severe salinity were more pronounced in L. racemosa under the same salinity. Moreover, the magnitude of variation of S. apetala maximum photochemical efficiency of PSII (F_v/F_m) was significantly less than that of L. racemosa leaves. We speculated that photosynthetic capacity of S. apetala was higher than L. racemosa. O₂^-_· production rate markedly increased after the two seedlings were subjected to 100 mmol·L^-1 NaCl and 200 mmol·L^-1 NaCl for 7 days and 14 days, respectively. However, O₂^-_· production rate in S. apetala leaves markedly increased upon increasing salinity and reached the highest level after seedlings were subjected to 400 mmol·L^-1 NaCl for 28 days, which was 5.3 fold of that in controls. In contrast to S. apetala, O₂ ^-_· production rate in L. racemosa leaves remained lower than control levels at the end of the experiment. Activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD) and glutathione reductase (GR) was elevated corresponding to the increased O₂^-_· production in the salt-stressed two mangrove plants; however, the magnitude of increase of L. racemosa antioxidant enzyme activities was significantly greater than that of S. apetala, during the period of salt stress. We suggest that L. racemosa plants were able to sense salt stress and up-regulated the antioxidant enzymes to reduce salt-induced lipid peroxidation and membrane permeability, which contributed to maintenance of membrane integrity and salt tolerance in L. racemosa. Sonneratia apetala seedlings might adapt resistance to severe salinity through improving photosynthesis by higher WUE and maximum photochemical efficiency of PSII (Fv/Fm).

Aims Drought is one of the numerous environmental factors which affect the growth and development of plants, and it becomes more severe in many regions of the world due to climate change. To examine the mechanisms of responses of the plant Rosemarinus offcinalis to drought stress, we measured the physiological and biochemical changes and volatile organic compounds (VOCs) emission of 2-year-old seedlings of this species under conditions of light drought (LD), intermediate drought (MD) and severe drought (SD).
Methods The VOCs emission was measured using the dynamic headspace air-circulation method, and the composition and content of VOCs were analyzed using the thermal desorption system/gas chromatography/mass spectrometer technique (TDS-GC-MS). We measured ion leakage of cell membranes and the content of soluble sugar, soluble protein and malondialdehyde (MDA), activities of lipoxygenase and protective enzymes of R. offcinalis under the different drought treatments.
Important findings The content of osmotic adjustment materials in R. offcinalis leaves was significantly influenced by drought stress. The content of soluble sugar was increased by 51.5% and 87.4% (p < 0.01) under MD and SD stresses after 12 days, respectively. The content of soluble protein was increased by 82% and 140% (p < 0.01), respectively. There were differences among the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in response to drought stress, which was a coordination reaction of those three enzymes to the stress. With prolonged drought stress, the MDA content (p < 0.01) and cell injury rate (p < 0.05) were increased significantly. Terpenoids were the main components of R. offcinalis VOCs and their relative content was more than 46% of the total VOCs. Compared with the control, it was increased by 14.4%, 17.0% and 23.7%, respectively, under LD, MD and SD stresses, respectively. Meanwhile, green leaf volatiles (GLVs) and aldehydes were markedly induced by drought stress, and (E)-2-hexenal, leaf alcohol, sorbaldehyde and n-decanal were newly found under the drought stress. The results indicated that R. offcinalis could enhance its drought-resistant ability by adjusting activities of protective enzymes, improving contents of osmotic adjustment materials and releasing VOCs.

Aims We studied single desert shrubs and their role in sand accumulation to provide references for monitoring and evaluating soil wind erosion and for scientifically establishing controlling measures. This research is important for strengthening sand fixation effects of vegetation.
Methods We obtained percentage composition of soil particles in wind erosion surfaces around single shrubs of Nitraria tangutorum and Ammopiptanthus mongolicus in the Gobi Desert north of Jilantai salt lake with digital image processing technology. We analyzed their horizontal spatial heterogeneities by classic descriptive statistics and geostatistical methods.
Important findings Enrichment of soil fine particles appeared on the base of nebkhas and in the downwind direction. The percentage of soil particles (<0.42 mm) decreased from the center of shrubs to the sample plot. The maximum value of soil particles enrichment was on the windward side around N. tangutorum and on the leeward side of A. mongolicus. In the Gobi Desert where sand material is limited, the effect of wind prevention and sand fixation was concentrated around N. tangutorum, although the spatial scale affected was smaller than with A. mongolicus. This explained that the degree of coarse grains in the N. tangutorum sample plot was higher than that of A. mongolicus. The spatial heterogeneity scales of soil particles (>0.84 mm, 0.42-0.84 mm and <0.42 mm) in wind erosion surface around N. tangutorum and A. mongolicus were 17.80, 66.63 and 8.41 m and 9.82, 15.33 and 14.91 m, respectively, all of which were beyond the shrub canopy cover. The proportion (C/(C₀ + C)) of structured elements was 63.40% to 99.96%, which indicated that wind-drift sand characteristic around nebkhas was the most important factor in the spatial heterogeneity of soil particles of corresponding scale. The spatial heterogeneity scale of highly erodible soil particles was greater than the average space of nebkhas (8.77 m, which included the semidiameter of nebkhas). The prevention of soil wind erosion by the relation between nebkhas and species is beneficial for stabilization and development of vegetation in this area.

Understory vegetation in boreal forests is the most diverse and least understood component of boreal plant com- munities. In addition, the aboveground net primary productivity of understory vegetation is almost comparable to that of the trees, and the biomass turns over more rapidly than does that of the trees. Fire disturbance is an important landscape process, driving understory structure and function in boreal forests. We review recent research about how fire, interacting with topography and overstory canopy, affects environmental resources (e.g., light and soil nutrients) and understory vegetation. Recent studies have demonstrated that understory vegetation in boreal forests can also influence post-fire tree seedling regeneration, rate of recovery and successional pathways. It can also affect the quantity and heterogeneity of environmental resources by influencing biogeochemical processes such as decomposition and nutrient flow. Understanding understory vegetation dynamics after fire, especially during early succession, is very important for biodiversity conservation and management of boreal forest.