Aims Assessment of the ecological benefits of forest in soil water retention based on conventionally monitored factors and exploration of the relation between forest carbon-sink function and hydrological benefits has special meaning in Millennium Ecosystem Assessment. Our objectives were to 1) characterize the spatial and temporal variations of soil moisture in three subtropical forests and 2) determine the controlling action of soil organic matter on soil moisture retention during vegetation succession.
Methods Standard plots were established in Pinus massonnianaconiferous forest (PF), mixedPinus massonniana-broad-leaved forest (PBF) and monsoon evergreen broad-leaved forest (MBF). We measured soil water content every 10 days from 2002 to 2008 using neutron probes and analyzed soil organic matter content in the laboratory by the potassium dichromate oxidation method.
Important findings With natural succession from planted PF to climax MBF, soil water content (0-30 cm soil layer) increased significantly; soil water content was highest in MBF and lowest in PBF. The distribution patterns of soil moisture in the three forests were different: the soil moisture of MBF decreased with soil depth, was more homogeneous in the soil profile in PBF and was lower at the surface than in deeper layers in PF. The soil water characteristic curves showed that under the same matrix suction the magnitude of soil water content (0-40 cm soil layer) was: MBF > PBF > PF; the soil of MBF was the most retentive. Further analysis indicated that soil porosity had the greatest impact on soil moisture, followed by saturated soil water content and soil organic matter content, while soil bulk density had a minimal impact. In the process of natural succession, soil moisture was significantly correlated with the soil organic matter content ( p = 0.014), as the soil organic matter could affect soil moisture holding (p = 0.030). Accordingly, we recommend soil organic matter as an effective and integrated index for appraising forest ecosystem services.

Aims Organ stoichiometric characteristics are the bridge that connects environment and plant organ traits. The relationships among environment, organ stoichiometric characteristics and organ traits reveal mechanisms of environmental effects on plant organ traits and make it possible to regulate plant traits. Our objective was try to find the relationships among soil and leaf nitrogen (N), phosphonium (P) stoichiometric characteristics and leaf chlorophyll content for Oligostachyum lubricum.
Methods Total N, P concentrations of the original soil in pots were 421.76 and 37.35 mg·kg^-1, respectively, and the original soil was treated as the control (1N1P). Total experimental N, P concentration were two, three and four times as high as the control. Different N, P levels were combined into 10 combinations (2N2P, 2N3P, 2N4P, 3N2P, 3N3P, 3N4P, 4N2P, 4N3P, 4N4P and 1N1P) and every combination except the control was achieved by adding different amounts of NH₄NO₃ and NH₄H₂PO₄. Leaf samples were collected from ramets of O. lubricum after grown in the pot soil with different N, P level combinations for 45 days. Leaf total N concentration was determined by employing the Kjeldahl method and leaf total P concentration by the acid melt-molybdenum stibium anti-color method. Leaf chlorophyll concentrations were measured based on acetone-ethanol mixture (1 : 1) extraction method. Soil and leaf total N, P concentrations were expressed as mg·kg^-1DW.
Important findings Soil total N concentration was significantly positively correlated with leaf total N concentration and leaf N : P ratio, whereas soil total P concentration had no significant correlation with leaf total P concentration and leaf N : P ratio. Leaf N : P ratio increased with the increasing of soil N : P ratio, and the rate of increase of soil N : P ratio was faster than that of leaf N : P ratio. At the same soil condition, leaf N : P ratio of ramets growing in soil with 2N2P and 3N3P had no significant difference, but the both were higher than the control (1N1P) and lower than that growing in soil with 4N4P. Leaf N : P was the main factor that affected leaf chlorophyll content. Results suggested that soil total N concentration had more effect on leaf N, P stoichiometric characteristics than soil total P. Sufficient supply of soil total N lead to the luxury uptake of N by leaves of O. lubricum. The growth of O. lubricum was limited by low soil total N concentration before N and P addition.

Aims Our aim was to investigate the genotypic variations among semi-sib families of Pinus massoniana for adaptive changes in root morphology and architecture in response to different types of low soil phosphorus (P) availability and their relationships to plant growth and P efficiency.
Methods Pot experiments were conducted during the 2010 growing season in a nursery located in Chun’an County of Zhejiang Province, China. Seven semi-sib families ofP. massoniana contrasting in root architecture and P efficiency were compared for their root morphological and architectural traits and their relationships to plant growth and P efficiency under both heterogeneous and homogeneous low P conditions.
Important findings Large genotypic variations were observed under different types of low-P conditions. The adaptive mechanism for P deficiency was different under heterogeneous and homogeneous low-P conditions. Under homogeneous low-P conditions, adaptive responses of root growth parameters were present in genotypes with high-P efficiency such as ‘3201’ and ‘1217’, while it was not observed in genotypes with low-P efficiency. Root architecture was not closely related to plant P efficiency under homogeneous low-P conditions. Under heterogeneous low-P conditions, root architecture was found to closely related to P efficiency. Genotypes with shallow root architecture had optimal root parameters including root length, surface area and biomass in the top layer of soil, thus having the greater ability for P absorption and having higher P efficiency and biomass. The heritability for the root biomass and the proportion of root in the top soil layer was 0.88 and 0.72, respectively. A significant interactive effect between patterns of low-P conditions and P efficiency was observed. Given that P. massonianahas great genetic potential for adaptation to low-P soils, the selection of high-P efficiency genotypes with optimal root architecture may significantly increase wood production of P. massoniana under low-P conditions.

Aims My aims were to (a) study the effects of mulching materials on microbial quantities, enzyme activities and soil nutrient contents and their relationships and (b) explore feasibility of using soil microbial quantities and soil enzyme activities as indicators of soil health.
Methods Straw of wheat (Triticum aestivum), stalks of corn (Zea mays) and weeds with 3.25, 1.97 and 3.67 kg·m^-2of covering weight, respectively, and living grass (Trifolium repens, Medicago sativaandFestuca arundinacea) with 50 kg·hm^-2 of sowings were used as mulching materials, with no covering as the control.
Important findings The contents of alkali-hydrolyzable nitrogen (N), available potassium (K), total N, total K and organic matter of the rhizospheric and non-rhizospheric soils were significantly increased by straw and living grass mulching, except for total phosphorus (P) and available P in the living grass treatment. Quantities of ammonification bacteria, fungi and actinomycetes, as well as soil moisture, pH value and activities of urease and phosphatase significantly increased in all treatments. Greatest mean increases of alkali-hydrolyzable N (99%), available K (270%), total N (267%), total K (117%), organic matter (272%), quantities of ammonification bacteria (158%) and fungi (141%) and activities of urease (156%) and phosphatase (64%) occurred in the Trifolium repenstreatment. Soil alkali-hydrolyzable N, available K, total N, total K and organic matter showed significantly positive correlation with the amount of ammonification bacteria, fungi and actinomycetes and activities of urease and alkaline phosphatase, except for soil available K with actinomycetes and phosphatase. Path analysis indicated that soil urease activity was the most important factor affecting the accumulation of alkali-hydrolyzable N, available K, total N, total K and organic matter in the three types of soil microbes and two kinds of enzymes.

Aims The content and allocation of nonstructural carbohydrates (NSC) in trees reflect whole-tree carbon balance regimes, and are crucial to determine growth / survivorship trade-off of trees and model tree carbon balance between uptake and investments in structure or loss. Our objective was to examine the concentration and allocation patterns of NSC for three temperate tree species, i.e., Korean pine (Pinus koraiensis), Dahurian larch (Larix gmelinii) and Mongolian oak (Quercus mongolica).
Methods During the mid-growing season (July of 2010), all biomass tissues, including foliage, branch, stem and root, were randomly sampled from three dominant trees for each species. The stem samples were taken from mid-canopy and breast height, and divided into sapwood and heartwood, while the root samples were divided into fine (diameter < 2 mm), medium (2-5 mm) and coarse roots (>5 mm). All samples were dried, ground, and analyzed for NSC concentrations (including soluble sugar and starch) with a modified phenol-sulfuric acid method.
Important findings The concentrations of NSC and its component differed significantly among species and tissues. Concentration ranges were 0.65-8.45, 1.96-5.95 and 3.00-13.90 g·100 g^-1 DM for soluble sugar, starch, and NSC, respectively. On average, the contents of NSC and its components followed the order of: larch > oak > pine. Concentrations in the foliage and roots were higher than those in other tissues. Within the stems, the longitudinal variations in the concentrations of NSC and its components were insignificant, whereas the differences between sapwood and heartwood varied with species and NSC components. There was no significant difference in soluble sugar concentration between sapwood and heartwood, but significant differences in starch and total NSC concentration. The concentrations of NSC and its components varied insignificantly with root diameters for larch and pine, but significantly for oak. Oak invested more soluble sugar to aboveground growth, whereas the two conifers did more to roots. Nevertheless, starch was mainly reserved in stems, and the intra-tree allocation pattern of starch exhibited an opposite trend to soluble sugar, leading the total NSC to be relatively balanced between roots and branches. In the stems, heartwood was the major reserve of NSC and starch, while sapwood was the major reserve of soluble sugar for the two conifers. In the roots, coarse root was the dominant reserves of NSC and its components. We concluded that the inter- and intra-specific variations in the NSC and its components in this study reflect differences in growth strategies and within-tree carbon source / sink strength for the three temperate tree species.

Aims Determination of species abundance distribution is important in research on species diversity. Our major objective was to determine species abundance distribution models to advance understanding of distribution mechanisms and to assist preservation of biological diversity.
Methods Based on data collected from field surveys, we examined the species abundance patterns of tree, shrub and herb layers in Pinus tabulaeformis forest in Huoshan Mountain, Shanxi Province. We used niche preemption (NPM), broken stick (BSM) and overlapping niche (ONM) models and two species abundance statistical models (log-series distribution model (LSD) and log-normal distribution model (LN)) and neutral theory model (NT). The simulation effects were verified by Chi-square tests, Likelihood-ratios (L-R) tests, Kolmogorov-Smirnov (K-S) tests and Akaike Information Criterion (AIC).
Important findings The best niche model for the tree layer is NPM, because it had the smallest AIC value and no significant difference (p > 0.05) between the theory predictions and observed species abundance distributions. The next best is ONM; BSM does not fit the tree layer. All three niche models are suitable for the shrub layer. ONM is the best for the herb layer, followed by BSM and NPM. LSD is good for understanding distribution mechanisms in Pinus tabulaeformisforest. LN can fit both the herb and shrub layers, but not the tree layer. NT cannot explain any layer. These findings indicate that the community has relatively few dense species and more sparse species, the species richness and diversity indices of the tree and shrub layers are much smaller than those of the herb layer, and the community evenness is relatively smaller. We conclude that one model cannot fit different data but that more than one model can fit the same data even for the same layer. Therefore, we should choose different models to study the species abundances of forest communities. We suggest that these methods might be useful for the protection of the biodiversity of forest dominated by Pinus tabulaeformis.

Aims Pinus sylvestris var. mongolica (Mongolian pine) is one of the main tree species used for forestation in the northern China and grows well in the early growth stage on sandy lands in the semi-arid area. In recent years, some of trees of Mongolian pine plantations in the sandy lands have been found to be degraded. Study of foliar traits is key to understanding the adaptability and survival strategy of this tree species on sandy land. Our major objective is to examine the impact of needle age on the main eco-physiological foliar traits of Mongolian pine in Horqin sandy land and thus to highlight the importance of needle age for coping with water and nutrients in the semi-arid area.
Methods We chose trees of Mongolian pine planted in early 1980s on a sand dune in the southern margin of Horqin sandy land, located in the permanent experimental plot of the Naiman Desertification Research Station, Cold and Arid Regions Environment and Engineering Research Institute, Chinese Academy of Sciences (42°55′ N,120°43′ E). We measured foliar photosynthetic rate, transpiration rate, carbon content, nitrogen content and morphological parameters (leaf length, width and thickness) for different-age needles. Based on these measurements we calculated transpiration coefficient (K_c) and photosynthetic nitrogen use efficiency (PNUE).
Important findings Net photosynthetic rate (P_n), K_c and PNUE varied among different needle ages and were significantly lower for 4-year old needles than 1-, 2- and 3-year old needles. This can be accounted for by foliar nitrogen content, with decrease in nitrogen leading to the decline in photosynthesis. Strong correlations were found between foliar form (e.g., leaf length, width, thickness and specific leaf area) and precipitation of the year prior to leaf formation and between foliar carbon content and precipitation of the year prior to leaf formation. In terms of transpiration coefficient and PNUE, juvenile needles (mainly 1- and 2-year old needles) were more efficient in using water and nutrients than old needles (4-year old needles), and hence a tradeoff between juvenile and old needles in water and nutrient use is a mechanism for growth and survival of Mongolian pine on sandy land. In addition, shedding old leaves under environmental stresses, as we observed in the field, has significant implication for this species to adapt to harsh habitat in the semi-arid area.

Aims Steppe dominated byStipa grandis and Leymus chinensis is the zonal vegetation in the temperate steppe region of China and eastern Eurasia. It has been heavily disturbed by overgrazing in China. Our objective was to investigate the spatial patterns of dominant populations in a degraded community of steppe.
Methods We used photography orientation to measure the patterns of dominant populations in a degraded community of typical steppe. We used complete spatial randomness, Poisson cluster process and double-cluster process to analyze the patterns of dominant populations based on point pattern.
Important findings The patterns of dominant populations ofL. chinensis, Agropyron michnoi, S. grandis and Cleistogenes squarrosa fit the nested double-cluster process at all scales in the community block of 5 m × 5 m. This ecological phenomenon may be induced by facilitation.

Aims Variation in intra-inflorescence sex expression and allocation is a common phenomenon in Angiosperms. The typical pattern is that the size and number of reproductive structures decrease from early to late blooming flowers within the same inflorescence, and the late ones tend to male. Resource competition and architectural effects are regarded as the main causes of these variations. Within the cyme of Camptotheca acuminata, the early capitula demonstrate more significant differences in the diameters of capitulum and corolla, length of short stamen, fruit set rate, and infructescence mass than the late capitula. Our main objective is to determine the causes behind the intra-inflorescence sex expression and allocation variations in C. acuminata.
Methods The distribution of resources within inflorescences of C. acuminata was manipulated by removing the primary or primary and secondary capitula to determine the factors influencing flower sex allocation and reproductive capacity in an inflorescence.
Important findings After removing part of the capitula, the diameters of capitulum and corolla in the remaining capitula increased significantly, the length of short stamen decreased significantly, and the differences between positions disappeared. The differences, however, in fruit set and infructescence mass remained unchanged. This suggests that resource constraints rather than architectural effects have stronger influence on the diameters of capitulum and corolla as well as the length of short stamen, while architectural effects play a dominant role on fruit set and infructescence mass. The andromonoecy in C. acuminatamay be the result of adaptation to specific reproduction and resources competition.

Aims The traits of seedlings are often directly related to the performance and function of adult plants in an ecosystem. Measurements of seedling traits are easy and accurate compared to adult traits. Many studies have been conducted on the trait-based assembly of trees in tropical forests in recent years; however, studies on functional traits of seedlings with diameter at breast height (DBH) < 1 cm are scarce. Our objective was to explore the variation of functional traits of woody seedlings in the old-growth tropical lowland rain forest on Hainan Island, China.
Methods We selected the 16 most abundant species of woody plant seedling with a DBH < 1 cm. They represented three growth forms: trees (nine species), shrubs (three species) and lianas (four species). They were also grouped into four growth stages according to the seedling height ( H) classes: I (5 ≤ H < 20 cm), II (20 ≤ H < 40 cm), III (40 ≤ H < 80 cm) and IV (80 ≤ H < 120 cm). The major functional traits of these seedlings, specific leaf area ( SLA), leaf mass fraction (LMF), specific stem density (SSD) and stem mass fraction (SMF) were measured. We assessed the variation in seedling functional traits among different growth forms and height classes and examined the correlations among functional traits.
Important findings There were significant differences among varied growth stages in seedling functional traits.SLA and LMF decreased gradually, butSMF increased with the growth stages of seedlings. SSD was lowest in the first growth stage, but showed no significant difference among the subsequent three growth stages. There were no significant differences between trees and shrubs for any functional traits. Seedlings adapt to the stressful rainforest understory environment (such as low light) by decreasing SLA andLMF and increasing SMF. However, lianas adapt to the environment through the opposite strategy. There were significant correlations between the different functional traits of seedlings. Our study suggests that the seedlings of different growth forms in the tropical lowland rainforest adapt to their environment by changing the value of different functional traits.

Aims Stem water storage plays a significant role in maintaining a favorable leaf water and carbon balance and minimizing temporal imbalances between water supply and demand. Few measurements, however, have been made on the daily dynamics of discharge and recharge of stem water storage, especially for Chinese temperate trees. Our objectives were to (1) examine diurnal courses of stem water storage of three temperate trees with different characteristics in Northeast China, i.e., coniferous needle-leaved Korean pine (Pinus koraiensis), broadleaved diffuse-porous aspen (Populus davidiana) and ring-porous Mongolian oak (Quercus mongolica), (2) quantify the contribution of stem water storage to the daily transpiration loss for these trees and (3) explore biotic factors influencing stem water storage.
Methods Sapflow was measured simultaneously at the crown base and trunk base with calibrated thermal dissipation probes from mid-August to late-September 2010. The daily stem water storage was calculated by comparing the diurnal patterns of trunk basal and crown basal sapflow for each of three replicated trees per species.
Important findings Crown basal sapflow started earlier than trunk basal sapflow in the morning for all trees, and a distinct time lag existed during the daytime. This suggested stem water storage was significant in regulating tree transpiration losses. The diurnal course of stem water storage was divided into four stages, i.e., full discharge, mainly discharge supplemented with recharge, mainly recharge supplemented with discharge, and saturated steady stages. However, the duration and pattern of each stage varied with species. The pine experienced two periods of discharge and recharge of stem water storage, while the two broad-leaved species experienced only one. The daily amount of water withdrawn from storage and subsequently replaced that was normalized to the mean sapwood volume (0.29 m³) was (3.4 ± 1.5), (2.4 ± 0.6) and (1.5 ± 0.4) kg·d ^-1 (mean ± SD) for the pine, aspen, and oak, respectively, accounting for 18.9%, 17.1% and 8.8% of the total daily water loss, respectively. Use of stem-stored water exponentially increased with daily water loss, and was positively correlated with the basal sapwood area and tree height. These results emphasize the effects of tree size (i.e., tree height and sapwood area) and timber properties on stem water storage and its contribution to daily water losses.