Response of photosynthetic nitrogen use efficiency in Betula utilis to altitudinal variation along Balang Mountain, Sichuan, China.

To better understand the response and adaptation of plants to altitudinal changes, four sites at the altitude of 2200 m, 2500 m, 3100 m and 3400 m on Balang Mountain were selected to test and calculate the eco-physiological parameters in leaves of Betula utilis, including photosynthetic nitrogen use efficiency (PNUE), CO2 diffusion conductance (stomatal conductance gs and mesophyll conductance gm) and nitrogen allocation in each component (fractions of leaf nitrogen allocated to Rubisco PR, to bioenergetics PB, to light-harvesting components PL, and to cell wall PCW). Their changes with altitudinal variations and the relationships between leaf PNUE and the other parameters were analyzed. The results showed that PNUE, PR, and PB of the leaves were relatively higher at 2500 m and 3100 m. With the increases of altitude, gs and gm increased and PL decreased. The correlations between PR, PB and PNUE were significant, indicating that PR and PB were the main factors driving the changes in leaf PNUE in response to altitudinal variations. Besides, the fraction of leaf nitrogen allocated to photosynthetic apparatus (PP) was relatively higher at 2500 m and 3100 m. With increasing altitude, PCW decreased and the fraction of leaf nitrogen allocated to the other components (Pother) increased, which suggested that B. utilis leaves tended to allocate more nitrogen to the other components instead of the photosynthetic apparatus and cell wall with the increasing altitude to well adapt environmental changes.

[Phenotypic variations in cones and seeds of natural Cupressus chengiana populations in China]. / 岷江柏天然种群种实表型变异特征.

A total of 13 phenotypic traits from 11 natural populations of Cupressus chengiana were investigated by using nested analysis, variation coefficient, phenotypic traits differentiation coefficient, and un-weighted pair-group method by arithmetic averages (UPGMA) cluster analysis. Phenotypic variations among and within populations of C. chengiana were discussed, the relationship among phenotypic traits and that between phenotypic traits and environmental factors were analyzed, and the 11 populations were divided. The results showed that there was significant difference in phenotypic variation both between and within populations. Variation within populations (49.7%) was greater than that between populations (28.6%). The mean coefficient of phenotypic differentiation between populations was 43.4% suggesting the differentiation between populations was relatively larger. The average variation coefficient of cone mass was the highest (37.2%), followed by seed mass in single cone, and that of cone length was the smallest (8.0%) indicating the cone length was the most stable phenotypic trait. The phenotypic diversity was greatest in Kangding County and smallest in Wudu County. The mean annual temperature of the hottest month and mean annual precipitation of growing season were the main environmental factors on phenotypic diversity in cones and seeds of C. chengiana in the study region. According to the 13 phenotypic traits, the 11 populations could be divided into two groups and three subgroups, which showed how C. chengiana distributed in three watersheds. Phenotypic traits in cones and seeds of C. chengiana populations were the best in Daduhe River watershed, and those were the worst in Minjiang River watershed.

[Functional diversity characteristics of canopy tree species of Jianfengling tropical montane rainforest on Hainan Island, China.] / æµ·å—å°–å³°å²­çƒ­å¸¦å±±åœ°é›¨æž—æž—å† å±‚æ ‘ç§åŠŸèƒ½å¤šæ ·æ€§ç‰¹å¾.

Based on three 1-hm2 plots of Jianfengling tropical montane rainforest on Hainan Island, 11 commom used functional traits of canopy trees were measured. After combining with topographical factors and trees census data of these three plots, we compared the impacts of weighted species abundance on two functional dispersion indices, mean pairwise distance (MPD) and mean nearest taxon distance (MNTD), by using single- and multi-dimensional traits, respectively. The relationship between functional richness of the forest canopies and species abundance was analyzed. We used a null model approach to explore the variations in standardized size effects of MPD and MNTD, which were weighted by species abundance and eliminated the influences of species richness diffe-rences among communities, and assessed functional diversity patterns of the forest canopies and their responses to local habitat heterogeneity at community's level. The results showed that variation in MPD was greatly dependent on the dimensionalities of functional traits as well as species abundance. The correlations between weighted and non-weighted MPD based on different dimensional traits were relatively weak (R=0.359-0.628). On the contrary, functional traits and species abundance had relatively weak effects on MNTD, which brought stronger correlations between weighted and non-weighted MNTD based on different dimensional traits (R=0.746-0.820). Functional dispersion of the forest canopies were generally overestimated when using non-weighted MPD and MNTD. Functional richness of the forest canopies showed an exponential relationship with species abundance (F=128.20; R2=0.632; AIC=97.72; P＜0.001), which might exist a species abundance threshold value. Patterns of functional diversity of the forest canopies based on different dimensional functional traits and their habitat responses showed variations in some degree. Forest canopies in the valley usually had relatively stronger biological competition, and functional diversity was higher than expected functional diversity randomized by null model, which indicated dispersed distribution of functional traits among canopy tree species in this habitat. However, the functional diversity of the forest canopies tended to be close or lower than randomization in the other habitat types, which demonstrated random or clustered distribution of the functional traits among canopy tree species.

[Soil microbial community structure of monoculture and mixed plantation stands of native tree species in south subtropical China].

The effects of three plantation stands, Erythrophleumf ordii (EF), Pinus massoniana (PM), and their mixed plantation (MP), on soil microbial biomass and microbial community structure in south subtropical China were studied by the method of phospholipid fatty acids (PLFAs) analysis. The results showed that the amounts of microbial total PLFAs and PLFAs of each microbial group in these three plantation stand soils were significantly higher in dry season than in rainy season. In dry season, the amounts of microbial total PLFAs, bacteria PLFAs, fungi PLFAs, and actinomycetes PLFAs were the highest in the PM soil, moderate in the MP soil, and the lowest in the EF soil. But in rainy season, the amounts of microbial total PLFAs, bacteria PLFAs, fungi PLFAs, and arbuscular mycorrhizal fungi (AMF) PLFAs in the EF soil were higher than in the MP soil, and were significantly higher than in the PM soil. Principal component analysis (PCA) indicated that the variations in soil microbial community structure composition were affected by both plantation types and seasons. Redundancy analysis (RDA) of soil microbial community structure and environmental factors showed that soil temperature and moisture, pH, total nitrogen content, and ammonium nitrogen content had significant correlations with PLFA signatures. In addition, the ratio of fungi PLFAs to bacteria PLFAs in the MP soil was the highest among the three stand soils within the whole year, indicating that mixed plantation stands could facilitate the stability of the soil ecosystem.