Nowadays, almost all forests in the world are fragmented, and thus, it is necessary to understand how forest fragmentation influence assembly of forest communities. This review summarized the main community assembly processes in the field of community ecology, namely ecological drift, dispersal, selection and speciation, and summarized the relative roles of these community assembly processes in fragmented forests. Due to differences in formation trajectory of different forests in fragmented region, the relative effects of the above four ecological processes are different for different types of forest communities: reassembled community (i.e., forest communities re-assembled through secondary succession in fragmented habitats) and disassembled community (i.e., continuous forest disassembled into fragmented forests). The effects of ecological processes can be effectively tested by analyzing short-term observed species distribution pattern within and among communities (e.g., species abundance distribution analyses, null model combined with beta diversity analyses, and convergence and divergence of functional trait distribution, etc.), controlled experiments, and long-term community monitoring (e.g., community dynamics analysis). Yet, it is insufficient to assess ecological processes undergoing habitat fragmentation by controlled experiments. In the future, studies should focus on developing and testing theoretical models, designing controlled experiments to investigate varied ecological processes undergoing habitat fragmentation, and combining ecological theory with practical biodiversity conservation.

Aims Forests in Nanpan River Basin are under severe effects by drought because of the warming and drying climate. As the typical dominant coniferous forests in this region, Pinus yunnanensis forests occur over a broad range and present a good potential for dendroclimatological studies. However, little is known about the relationship between radial growth and climate in this tree species. Our objectives were to determine the constraining factors of radial growth and examine the stability of growth-climate relationships in P. yunnanensis in response to climate warming and drying.Methods We used standardized dendrochronological method, combined with trend analysis of meteorological data from 1952 to 2016, to study the effects of climate variabilities on the radial growth in P. yunnanensis. We extracted increment cores from 87 trees and measured annual ring-width. Response analysis and multiple regression analysis were used to determine the constraining factors of radial growth. Moving correlation was used to detect the stability of growth-climate response.Important findings The annual mean temperature (T_mp), mean maximum temperature (T_mx), and mean minimum temperature (T_mn) in the research region have increased at a rate of 0.044, 0.041 and 0.050 °C·a ^-1, respectively. The annual total precipitation showed a significant decreasing trend at a rate of 6.02 mm·a ^-1 during 1985-2016. The growth of P. yunnanensis trees was less sensitive to temperature but more sensitive to moisture; prior to and after warming and drying period, the explainable variance of radial growth by temperature decreased from 44.95% to 21.97%, and that by moisture-related factors increased from 55.05% to 78.03%. Warming and drying climate enhanced the influence of climatic factors on radial growth of the current year and weakened the influence of climatic factors of the previous year, while increasing the climatic factors of the current year significantly affecting radial growth by three and explanation rate by 16.05%. The “hysteresie effect” weakened and the effects of climate change on growth became more promptly. The growth-climate relationship in P. yunnanensis could become more moisture sensitive under a warming and drying climate. Tree growth and forest productivity of P. yunnanensis in the Nanpan River Basin is likely to decline if the warming and drying climate trend continues.

Aims To explore the feasibility of thermal infrared technology for monitoring the shoot beetle damage to Yunnan pine (Pinus yunnanensis), the relationship between temperature and biochemical and/or physiological factors of healthy and damaged shoots of Yunnan pine was analyzed.Methods The temperatures were extracted with the software FLIR-TOOLS from the thermal images of damaged shoots. The temperature differences between damaged shoots and healthy shoots (ΔT) in the same thermal image were analyzed. The relationships between ΔT and physiological and biochemical parameters were used to clarify the mechanism that caused needle temperature increase with infested duration.Important findings Results indicated: (1) The chlorophyll and water content of damaged shoots decreased with the infested duration, and the chlorophyll content decreased faster than water content; (2) The net photosynthetic rate (P_n), stomata conductance (G_s) and transpiration rate (T_r) also decreased with infested duration, and the temperature difference between needle and atmosphere (ΔT_l-a) increased with infested duration; (3) ΔT reached the maximum at 14:00 to 15:00; the temperature differences of lightly-infested, mid-infested and heavily-infested needles reached 0.6, 0.7 and 2.5 °C, respectively; (4) A strong negative correlation was found between ΔT and G_s, water content. Our study concluded that the water imbalance of damaged needles caused needle temperature changes. Therefore, thermal infrared technology could be applied to monitor shoot beetle damage of Yunnan pine at different stages.

Aims The diameter variation of fine roots plays an important role for the study of fine root variation. Phylogeny is a significant factor. In order to examine the diameter variation of the first-order roots in subtropical evergreen broadleaved forests, we investigated 89 woody plant species from a natural evergreen broadleaved forest in Wanmulin Nature Reserve, Jianou, Fujian Province.Methods We selected three trees of each species with similar diameters at breast height or ground diameters, and sampled the root system with intact soil block method. We classed fine root with root order method. One-way ANOVA was used to test the first-order root diameter difference among the life forms (evergreen and deciduous trees), growth forms (tree, semi-tree or shrub and shrub) and the taxonomic classes. Then the Blomberg’s K value was calculated to determine phylogenetic signal. We analyzed the correlation between divergence time and first-order root diameter by using linear regression from family perspective.Important findings 1) The coefficient of variation for the first-order root diameter was 23% in this subtropical evergreen broad-leaved forest. 2) There were no differences in first-order root diameter between evergreen and deciduous trees, but that of the shrubs was significantly different from that of the semi-tree, shrub and tree species. 3) Phylogenetic signal in first-order root diameter was not significant. In addition, the divergence time was positively correlated with the first-order root diameter in the family-level. These results showed that, the variations for first-order root diameter in the tested subtropical woody species was little affected by phylogenetic structure.

Aims There would be a trade-off between enhancing water use efficiency and decreasing leaf construction cost in arid plants. We hypothesized that plants in lower precipitation areas could have higher water use efficiency at a given leaf construction cost compared to plants in higher precipitation areas by altering relationships between leaf functional traits (i.e. increasing area-based leaf nitrogen concentration, N_area).Methods Artemisia ordosica is a widespread species in the Mau Us sandy land. Variations of leaf construction cost of A. ordosica along a precipitation gradient and its relationships to other leaf traits such as specific leaf area (SLA), mass-based leaf nitrogen concentration (N_mass), N_area and leaf stable carbon isotopes ratio (δ ¹³C) value were analyzed.Important findings There were no significant differences in mass-based leaf construction cost (CC_m) among different precipitation areas. Although area-based leaf construction cost (CC_a) showed significant differences among different precipitation areas, they did not increase significantly with decreasing precipitation. The relationship between CC_m and SLA was not significant while CC_m positively correlated with leaf δ ¹³C value. There was a strategy shift in the positive relationship of leaf construction cost to N_area between plant-groups in the lowest precipitation (264 mm) areas and other higher precipitation (310-370 mm) areas, i.e. plants from low precipitation areas have higher N_area at a given leaf construction cost. Our results indicated that although high water use efficiency was accompanied by high leaf construction cost, the high N_area for plants from lower precipitation areas did not increase their leaf construction cost.

Aims Over the past decades, the precipitation patterns in subtropical regions markedly changed in response to global climate change. The impacts of changing precipitation patterns on plant growths and forest water balance remain unclear. In this study, the effects of varying precipitation patterns on whole tree water were tested in a natural forest in South China.Methods The study was conducted in the Heshan National Field Research Station of Forest Ecosystem in Guangdong Province, from September 2012 to December 2014. Throughfalls were intercepted by installing rain-shelters underneath the tree canopy and transferred to a nearby water reservior in dry season (from October to March of the next year), which were then reapplied to the field plots in equal quantity of the interception in wet season (from April to September), to simulate changed rainfall pattern to drier dry season and wetter wet season (DD). Sap flux density was continually measured on two tree species, Schima superba and Michelia macclurei. Student t-test was used to determine the significance of differences in mean maximum sap flux density (¯J_S) between the two species in the control plots (AC), and between AC and DD treatments during the experiment.Important findings The average ¯J_S was (49.5 ± 1.7) mL∙m ^-2∙s ^-1in M. macclurei and (43.6 ± 2.0) mL∙m ^-2∙s ^-1 in S. superba in the AC treatment when the active photosynthetic radiation (PAR) was greater than 1 100 μmol·m ^-2·s ^-1. M. macclurei showed higher sensitivity to increasing PAR. The ¯J_S ratio (DD/AC) in both species initially increased significantly, followed by a short-term decrease. In S. superba, the ratio decreased from 0.74 to 0.68 in DD from October 2012 to March 2013, and then increased to 0.93 in March 2014 and 1.04 in November 2014. In M. macclurei, the ratio decreased from 1.00 to 0.94 in DD from October 2012 to March 2013, and then increased to 1.06 in March 2014. We found that S. superba could maintain higher ¯J_S in response to the increasing PAR and vapor pressure deficit (VPD) in the DD treatment. Our results showed that the short-term drought would lead to a decline in tree transpiration; but in the long run, plants tended to compensate for the drought induced growth loss by elevating the ¯J_S. Compared to M. macclurei, S. superba could maintain higher water transport capacity due to its more extensive ¯J_S plasticity in response to the extended drought.

Aims Altitude-induced changes in temperature, moisture, vegetation types and other conditions would significantly affect soil carbon (C_soil), nitrogen (N_soil), phosphorus (P_soil) concentrations and their stoichiometry. How soil microorganisms adapt to the variability of soil resource stoichiometry by regulating their biomass and extracellular enzymatic stoichiometry remains uncertain. The objective of this study was to quantify the altitudinal trends of soil-microbe-exoenzyme C:N:P stoichiometry and to explore the correlations among soil-microbe- exoenzyme stoichiometry.Methods In the present study, we investigated the C_soil, N_soil, P_soil concentrations, microbial biomass C (C_mic), N (N_mic), P (P_mic) concentrations, and the activities of C (β-1,4-glucosidase, BG), N (N-acetyl-β-glucosaminidase, NAG), and P (acid phosphatase) acquiring extracellular enzymes for microorganisms in four ecosystems along an altitudinal gradient on Mt. Datudingzi, Northeast China. These four ecosystems are a mixed broadleaf-coniferous forest at 800 m, a coniferous forest at 1 100 m, a Betula ermanii forest at 1 600 m and a grassland at 1 700 m.Important findings The results showed that: (1) altitude had no significant effect on C_soil and C_mic concentrations but had significant effects on soil and microbial biomass N and P concentrations. (2) The activities of BG and NAG decreased significantly with increasing altitude, likely due to the high elevation induced low temperature that inhibits microbial activities. (3) Altitude had significant effects on soil C:N, microbe C:N:P, and exoenzyme C:N:P; exoenzyme C:N:P decreased with the increasing stoichiometric imbalances between microorganisms and soils (ratios of soil C:N:P to microbe C:N:P, respectively). Overall, these results suggested that microorganisms can adapt to the variability of soil C:N:P by regulating their biomass C:N:P and exoenzyme C:N:P, and supported the microbial resource allocation theory.

Aims Due to human activities, nitrogen (N) deposition is increasingly serious, and phosphorous (P) fertility is widely applied in the soils of subtropical forests suffering from P deficiency, but there are relatively few researches of N and P additions on soil characteristics of subtropical forests. Difference in stand density may affect light, temperature, water and litter water holding capacity, which may influence soil characteristics. The effects of external nitrogen and phosphorus and stand density on soil chemical property were investigated in 10 years-old Acacia auriculiformis stands in order to provide a scientific basis for stand density and forest soil management.Methods In this study, five subsample plots were established in the stands with four densities (1 667, 2 500, 4 444 and 10 000 trees·hm ^-2) and treated with N addition, P addition, N+P addition and control from 2013 to 2015. At the end of experiment, soils at 0-10 cm depth with different treatments were collected and pH value, organic matter content, N, P and K contents were analyzed in the A. auriculiformis stands.Important findings The results indicated that soil pH value and available potassium (K) content significantly decreased, whereas soil alkalized N content significantly increased after N and N+P additions in the four density stands, and soil total N content significantly increased after N addition. Soil pH value significantly increased and soil total N content significantly decreased after P addition. Contents of soil organic matter, total P and available P significantly increased after P and N+P additions. With the increase of stand density, the contents of soil organic matter, total N, alkaline N, total P, available P and available K significantly increased. The interactive effects of density and N and P additions on soil pH value, organic matter, N, P and K contents were significant in the stands. Generally, the effects of N and P additions, stand density and the both interaction on soil chemistry property were significant.