Aims As one of the biological legacies in degraded forest ecosystems after severe disturbance, remnant trees have many ecological effects in biodiversity maintenance and recovery of ecosystem structure and functioning. This study aims to understand the effects of remnant old-growth trees on other tree stems in a secondary Betula albosinensis-Abies faxoniana forest on the eastern edge of Qinghai-Xizang Plateau, China.

Methods We established a 4 hm ² forest plot in a sub-alpine Betula albosinensis-Abies faxoniana stand in Miyaluo in western Sichuan, China. The species names, tree heights, diameters at breast height (DBH) (>1.3 m in height), and basal diameters (≥4 years, and ≤1.3 m in height) of all woody stems were recorded and the specific locations of all trees were mapped. Hegyi’s competition index model was used to calculate the competition intensity between remnant old-growth trees and other dominant trees of different size-classes as well as the intra- and inter-specific competition intensity of the two dominant tree species, Abies faxoniana and Betula albosinensis. We used mark correlation functions k_d(r) to explore the associations of the remnant old-growth trees with seedlings and saplings of A. faxoniana.

Important findings The value of the inter-specific competition index (Hegyi’s competition index (CI) = 2.484) between B. albosinensis and A. faxoniana was significantly greater (p < 0.05) than the values of the intra-specific competition indices of B. albosinensis (CI = 1.711) and A. faxoniana (CI = 1.548). The value of the competition index between remnant old-growth trees and the small trees of B. albosinensis was largest among the competition indices between the remnant old-growth trees and tree stems of different size-classes. The competition indices between remnant old-growth trees of B. albosinensis and small trees of A. faxoniana, between remnant old-growth trees and small trees of A. faxoniana and between remnant old-growth trees of A. faxoniana and small trees of B. albosinensis did not differ significantly, and were smallest among the competition indices between trees of different size-classes. Saplings of A. faxoniana showed a significantly positive association with remnant old-growth trees of B. albosinensis at scale 14.5-15.5 m, and a significantly negative association with remnant old-growth trees of A. faxoniana at scale 6.5-7.5 m. The seedlings of A. faxoniana showed a spatial independence to remnant old-growth trees of both B. albosinensis and A. faxoniana at all spatial scales (0-100 m).

Aims Dominant species play a major role in the formation of community. Our objectives were to detect and assess the spatial pattern of Gironniera subaequalis, which is a dominant species with the second largest importance value in the tropical montane rainforest of Jianfengling, and to explore the effects of environmental heterogeneity, density-dependent mortality and dispersal limitation on the formation of its current spatial pattern.

Methods 10022 individuals were categorized into six size classes and three life-history stages, i.e. young trees, middle-aged trees and adult trees, respectively. The spatial pattern of each age class was analyzed by pair-correlation function. The spatial associations between paris of life-history stages were analyzed by bivariate pair-correlation function and mark-connection function. The impacts of topographic factors on the distributions of young trees, middle-aged trees and adult trees were analyzed by Berman test.

Important findings Results showed that the size classes I, II, III, and IV of G. subaequalis occurred in aggregated distributions. The aggregation intensities declined with increasing size classes. Size classes V and VI exhibited a uniform distribution at the smaller scales and a random distribution mainly at the larger scales. Young trees and middle-aged trees had a positive association; whereas young trees and adult trees had a negative association. Middle-aged trees and adult trees had a negative association at smaller scales and a weakly positive association at larger scales. The individuals of different life-history stages were separated from each other. There were no direct facilitative interactions between pairs of individuals. The tree topographic factors, slope degree, altitude and concave-convex, had significant impacts on the distribution of small trees; slope degree and concave-convex had significant impacts on the distribution of the middle-aged trees; whilst only slope degree had significant impacts on the adults trees. We inferred that the environmental heterogeneity and density-dependent mortality contributed to current spatial pattern of G. subaequalis, while the effects of dispersal limitation were not obvious.

Aims The Exochorda giraldii community is a secondary shrubland developed following destruction of warm temperate and deciduous broad-leaved forests. The objective of this study was to explore the distribution and inter-relationships of dominant species in E. giraldii communities in Taiyue Mountains, Shanxi, China.

Methods Based on the vegetation survey data on a 50 m × 50 m plot, point pattern analysis (O-ring) and fractal analyses (including box-counting dimension analysis, information dimension analysis and correlation dimension analysis) were performed to determine the spatial patterns of dominant species in a E. giraldiicommunity.

Important findings In the E. giraldii community, most of the dominant species showed the characteristics of aggregated distribution at smaller scales. However, Periploca sepium and Spiraea salicifolia showed an aggregation distribution at all scales. With increases in scale, the distributions of E. giraldii and Forsythia suspensa changed from aggregation to random and to uniform. Based on the point pattern analysis, the dominant species in the E. giraldii community showed aggregation distribution characteristics at different scales. The box-counting dimension analysis indicated that the ability of dominant species to occupy the space in the E. giraldii community was in the order of E. giraldii > F. suspensa > S. salicifolia > P. sepium. The information dimension analysis indicated that the degree of changes in pattern intensity of dominant species with scale in the E. giraldii community was in the order of P. sepium > S. salicifolia > E. giraldii > F. suspensa. The correlation dimension analysis showed that the spatial correlations of dominant species in the E. giraldii community was in the order of P. sepium > E. giraldii > F. suspensa > S. salicifolia. On a smaller scale, the E. giraldii population showed aggregated distribution; the F. suspensa population and the E. giraldii population had a positive correlation; the S. salicifolia population and the E. giraldii population had a positive correlation; the P. sepium population and the E. giraldii population had a negative correlation. Point pattern analysis and fractal analyses produced consistent results, revealing the spatial distribution patterns of secondary shrubs following destruction of the warm temperate and deciduous broad-leaved forests.

Aims Our objectives were to investigate the inter- and intra-specific interactions of trees in a natural Pinus kesiya forest after three different selective logging disturbances, and to examine the impact of selective logging on disturbance intensity for sustainable forest management.

Methods Niche breadth, niche overlap, interspecific associations, Hegyi’s single-tree competition index model and M. Godron methods were used to analyze the inter- and intra-specific interactions of trees based on the field data collected from 81 small quadrats in nine plots in a natural P. kesiya forest in Jinggu County, Yunnan Province.

Important findings (1) Selective logging disturbance changed the relative dominance of most tree species except P. kesiya. The niche breadth of P. kesiya population increased with increases in disturbance intensity. The niche breadth was greatest in P. kesiya and Schima wallichii among all tree species under a severe disturbance. (2) The interspecific relationship of tree populations changed was affected by disturbance intensity. The niche overlap in the intermediate disturbance communities was apparently higher than those without disturbance or under a severe disturbance. In all the three communities, the niche overlap between P. kesiya and other tree species was very small. The proportion of species pairs with positive and negative associations became gradually increased with increases in disturbance intensity. 3) Hegyi’s competition index showed that the main competitive stress of P. kesiya population mainly came from inter-specific competition. Disturbance intensity increased the inter-specific competition between P. kesiya and other trees, and the mean competition index decreased with increasing diameter at the breast height in P. kesiya. 4) The formation of forest gap was the main reason for changes in inter- and intra-specific relationships of P. kesiya forest. Although all communities were unstable under different disturbance intensities, species richness and community stability were both higher when under intermediate disturbance compared with no or severe disturbances. The principle of selective logging should be determined by the aim of forest management, which should be considered as the basis for timber production and forest ecosystem service.

Aims The relationship between stem and leaf growth is a strategy that plant canopy enhances photosynthetic efficiency and competitiveness through configuration adjustments; this relationship indicates the ratio between xylem and photosynthetic area in a heterogeneous environment. Our objective was to examine how Melica przewalskyi modulated leaf and stem traits in adaptation to changes in slope.

Methods In the alpine grassland of Qilian Mountains, Gansu Province, China, 80 plots were set up along four transects corresponding to contrasting aspects with 20 m distance between adjacent plots. A GPS was used to record latitude, longitude and altitude of each plot and ArcGIS software was used for constructing a digital elevation model (DEM) and extracting information on elevation, aspect, and slope. Community characteristics were investigated and 10 random individuals of M. przewalskyi were cut at the soil surface in each plot, and leaf mass, leaf area and stem mass were measured in laboratory. The 80 plots were grouped into 0°-10°, 10°-20°, 20°-30° slope gradients. Stem and leaf traits were log-transformed and then standardized major axis (SMA) estimation method was used to examine the allometric relationships of stem mass with leaf area or leaf mass.

Important findings The stem mass, leaf mass and leaf area of M. przewalskyi gradually decreased, but the leaf number increased, with slope gradient. An isometric relationship was found between stem mass and leaf area in plots within each slope gradient, whereas an allometric relationship was found between stem mass and leaf mass. Melica przewalskyi grown on steeper slopes tended to have smaller leaf area and greater leaf number at a given stem mass, and leaves with greater stem mass had greater leaf mass. A significant difference in the SMA slope among the three slope gradients of the plots suggested that the slope of the growth site constrained leaf area and leaf mass by stem mass, reflecting plant adaptation to heterogeneous environment.

Aims Phoebe chekiangensis is a rare and protected species in China. Our objectives were to determine the phenotypic variations of leaves and seeds in P. chekiangensis populations and the relationship between phenotypic variation and distribution of populations.

Methods Field investigations and examinations of the natural distribution of P. chekiangensis led to our selection of five leaf characteristics and five seed characteristics as phenotypic traits from nine populations. We studied morphological variations among and within populations based on analysis of the 10 phenotypic traits. Nested analysis of variance, coefficient of variation, multi-comparison and correlation analysis were used to analyze the resulting data.

Important finding Analysis of nested variance on leaf and seed traits revealed significant differences among and within populations. The variation was greater within populations (21.74%) than among populations (18.45%). Mean phenotypic differentiation coefficient was 41.43% among populations, indicating that the variance within population is the main source of the phenotypic variation of the species. The variation in coefficient of variance (CV) among 10 traits ranged 6.50%-19.38%, with an average of 12.78%. The CV of leaf traits (16.99%) among populations was higher than that of seed traits (8.58%), implying higher stability of seed traits than the leaf traits. There were significant or highly significant correlations of leaf width and leaf area with other leaf traits. The thousand seeds weight was significantly correlated with seed width and seed volume, but no significant correlations were found between seed and leaf traits. Seed width, seed volume and thousand seeds weight decreased with increasing altitude. The seed volume also appeared to be under control of latitude, showing a tendency of increase with latitude.

Aims Our objectives were to disclose why evergreen shrubs, but not deciduous shrubs, dominate above timberline in humid southeastern Qinghai-Xizang Plateau, and to test if different functional types converge in response to the warming climate from aspect of nitrogen limitation.

Methods Based on investigations of nitrogen concentration in senesced leaves of seven shrubs across timberline ecotones in the Sergymla Mountains, Southeast Xizang, we analyzed differences in leaf mass- and area-based nitrogen resorption proficiency among different functional types (evergreen vs. deciduous), altitudes and aspects at 4200-4400 m a.s.l.

Important findings Leaf mass-based nitrogen resorption proficiency was higher in the evergreen shrub Rhododendron aganniphum var. schizopeplum than in deciduous shrubs. However, the leaf area-based N resorption proficiency was relatively higher in deciduous shrubs due to their lower leaf mass per unit area. Although no significant difference in the resorption proficiency was found between altitudes or aspects for the deciduous shrubs of Salix oritrepha and Berberis hemsleyana, leaf mass-based N resorption proficiency was higher at higher altitude for the evergreen shrub Rhododendron aganniphum var. schizopeplum. Decreasing N concentration in senesced leaves, i.e., increasing resorption proficiency, which can improve N use efficiency, is an important strategy for the evergreen shrub to cope with the stressful alpine environment across timberline ecotones. Compared with the deciduous shrubs, N resorption proficiency in the evergreen shrub Rhododendron aganniphum var. schizopeplum is assumed to be more sensitive to future climate warming.

Aims Our objective was to determine the effects of irrigation schedule on grain yield, water use efficiency (WUE), and accumulation and distribution of dry matter in winter wheat (Triticum aestivum) ‘Lingkang-2’ in the arid Hexi corridor of Northwest China.

Methods Based on pre-winter irrigation quota of 180 mm, we set up five irrigation treatments, i.e., irrigation quota of 165 mm at the jointing stage (W1), irrigation quota of 120 mm at the jointing stage and 105 mm at the heading stage (W2), irrigation quota of 105 mm at the jointing, heading and grain filling stages, respectively (W3), irrigation quota of 75 mm at the jointing, heading and grain filling stages, respectively (W4), and irrigation quota of 105 mm at the jointing stage, 75 mm at the heading stage, and 45 mm at the grain filling stage (W5).

Important findings Available soil water content (AWC) in the 0-150 cm layer across different irrigation treatments changed with wheat growth stages. The grain yield in both W3 and W4 treatments was obviously improved by higher leaf area index (LAI) and dry matter accumulation. Higher AWC was found in the W3 and W4 treatments, but there was no significant difference in the grain yield between the two treatments. Nevertheless, the highest water use efficiency (WUE) in the W4 treatment was associated with its higher value of growth index than those in the W1, W2 and W5 treatments. In contrast, LAI in the W1, W2 and W5 treatments quickly decreased after anthesis, corresponding to lower dry matter accumulation, shorter grain filling duration and fewer numbers of spike and lower 1000-grain weight. We also observed that drought stress after anthesis promoted dry matter translocation from vegetative organs to grains, with a complementary effect on grain yield occurring as drought stress increased. In the grain filling stage, drought stress stimulated average filling rate, but shortened the duration of grain filling. The duration of grain filling, effective period of grain filling, the value of increases in grain weight during effective period of grain filling, and the timing of the maximum filling rate were positively correlated with 1000-grain weight and grain yield of winter wheat (p < 0.05). In consideration of all results, winter wheat should be irrigated at 75 mm at the jointing, heading and filling stages to achieve reasonable water use efficiency and grain yield. Our findings may help with the decision makers by providing hydrological and ecological evidence in development of sustainable agriculture in arid regions.

AimsOur main purposes were to explore effects of phosphorus deficiency and soil acidification on growth, water balance and phosphorus nutrition in Juglans regia seedlings and to investigate the hydraulic mechanism involved in reduced photosynthesis and growth.

Methods We measured growth, hydraulic characteristics, and gas exchanges in J. regia seedlings. The effects of phosphorus deficiency and soil acidification on xylem anatomic structure, water balance and photosynthetic characteristics were also analyzed.

Important findings Soil acidification inhibited the phosphorous uptake and utilization efficiency in J. regia seedlings. A combination of soil acidification and phosphorous deficiency interrupted water balance, and reduced photosynthesis and growth of J. regia seedlings. Under soil acidification and phosphorus deficiency, non-stomatal factors also played a role in inhibiting photosynthesis.

Aims The objective of this study was to compare the values of respiration under light derived by fitting a photosynthetic CO₂ response model and measurements, in order to provide information for model optimization.

Methods Using combined gas exchange measurements and a low O₂ (2% O₂) method, the responses of photosynthetic rate (P_n) to CO₂ at different light intensities (2000, 1500, 1000 and 500 μmol·m^-2·s^-1) in the flag leaves of wheat were measured. The measured data were fitted by a biochemical model, a rectangular hyperbola model and a modified rectangular hyperbola model of the photosynthetic response to intercellular CO₂ concentration (A/C_i) and air CO₂ concentration (A/C_a), aiming to approach the reasonability of the fitted results obtained from the models.

Important findings The sequence of fitting effect of the three CO₂ response models in descending order was as follows: modified rectangular hyperbola model > rectangular hyperbola model > biochemical model. Fitted values of A/C_a curve was more reasonable than A/C_i curve, because the photorespiration and mitochondrial respiration under light (R_d) estimated by the former better matched the measured values. However, there were significant differences in the whole between the fitted and measured values. The reason could be that the effect of CO₂ concentrations on R_d and apparent photorespiration (R_pa) is neglected in all the current CO₂ response models. Our results showed that CO₂ concentration had a marked effect on R_pa and R_d. With increasing CO₂ concentration, R_pa and R_d increased first, and then decreased sharply. Take 2000 μmol·m^-2·s^-1 for example, R_pa varied between 5.035 and 11.670 μmol CO₂·m^-2·s^-1, and R_d varied between 0.491 and 2.987 μmol CO₂·m^-2·s^-1. Regression analyses indicated that R_pa and R_d were well related to CO₂ concentrations at different light intensities.