Responses of leaf traits to altitude in Quercus aquifolioides and Sorbus rehderiana on the eastern edge of the Qinghai-Tibet Plateau, China.

As the most senstitive plant organs to environmental changes, leaves serve as crucial indicators of plant survival strategies. We measured the morphology, anatomical traits, gas exchange parameters, and chlorophyll fluorescence parameters of Quercus aquifolioides (evergreen broad-leaved) and Sorbus rehderiana (deciduous broad-leaved) at altitudes of 2600, 2800, 3000, 3200 and 3400 m on the eastern edge of the Qinghai-Tibet Plateau, China. We explored the similarity and difference in their responses to altitude change and the ecological adaptation strategy. The results showed that as the altitude increased, leaf dry matter content of Q. aquifolioides decreased, that of S. rehderiana increased, leaf size for both species gradually decreased, and the palisade coefficient of Q. aquifolioides showed a decreasing trend, contrasting with the increasing trend in S. rehderiana. As the altitude increased, the thickness of leaves, palisade tissue, spongy tissue, upper epidermis, and lower epidermis of both species increased significantly, with the increment of 22.4%, 4.9%, 45.1%, 23.3%, 19.6%, and 28.2%, 46.9%, 8.9%, 25.9%, 20.8% at altitude of 3400 m, respectively, compared with the altitude of 2600 m. The gas exchange and chlorophyll fluorescence parameters of S. rehderiana significantly increased with increasing altitude, while Q. aquifolioides showed the opposite trend. Leaf anatomical traits, gas exchange, and chlorophyll fluorescence parameters of both species displayed considerable plasticity. There were significant correlations among most leaf traits and between leaf traits and altitude. The survival strategy of Q. aquifolioides was more conservative in response to altitude changes, while that of S. rehderiana was more active. Both species adapted to different altitudes by adjusting their own traits.

Effects of slope aspect on soil enzyme activity and microbial nutrient limitation in subalpine region of wes-tern Sichuan, China.

Exploring the resource limitation of soil microbial metabolism is essential to understand ecosystem functions and processes. However, the spatially divergent patterns and drivers of soil microbial nutrient limitation cha-racteristics in montane ecosystems at small scales, especially at the slope aspect scale, are still unclear. In this study, we measured soil enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycle and quantified the microbial nutrient limitations by enzyme stoichiometry in two representative mountain sites in subalpine region of western Sichuan, including the sunny and shady slopes with different vegetation types (shrubland and forest, respectively) in Miyaluo of Lixian County, and with the same vegetation type (shrubland) in Yakexia of Heishui County. The results showed that soil enzyme activities and their stoichiometric ratios were significantly different between slope aspects in Miyaluo, while the differences were not significant in Yakexia. The stoichiometry ratio of C-, N- and P-acquiring enzymes on the sunny slope of Miyaluo was 1:0.96:0.92, approaching the 1:1:1 ratio at the global scale, but deviated from 1:1:1 on the shady slope of Miyaluo (1:1.39:0.75) and the different slopes of Yakexia (1:1.09:1.35). There was no significant difference in vector length between slope aspects at both sites, indicating no significant effect of slope aspect on the microbial C limitation. The vector angle was significantly higher on the sunny slope (43.6°) than that on the shady slope (28.7°) in Miyaluo, suggesting that the microorganisms were mainly N-limited. Partial least squares path model showed that the vector angle was mainly directly influenced by the soil nutrient ratios. The vector angle ranged from 50.3° to 51.4°, and did not differ between slope aspects in Yakexia. Therefore, differences in vegetation types between slope aspects drove variations in soil enzyme activity and microbial nutrient limitation through soil properties. It would provide a scientific basis for predicting the spatial pattern of soil enzyme activity and microbial nutrient limitation.

[Vertical distribution of natural abundance of stable carbon and nitrogen isotopes along the soil profile and the underlying mechanisms]. / åœŸå£¤å‰–é¢ç¢³æ°®ç¨³å®šåŒä½ç´ è‡ªç„¶ä¸°åº¦çš„åž‚ç›´åˆ†å¸ƒæ¨¡å¼åŠå ¶å½±å“æœºåˆ¶.

Understanding the changes of natural abundance of stable carbon and nitrogen isotopes (δ13C and δ15N) along soil profile is of great importance in revealing the mechanisms of soil carbon and nitrogen cycling in terrestrial ecosystems. Based on a comprehensive review on the distribution of δ13C and δ15N along soil profile, the mechanisms underlying their vertical distribution were mainly introduced here. There were three mechanisms driving the δ13C vertical distribution in soil profile: 1) historical changes of vegetation δ13C value, 2) changes of C3-C4 species dominance in plant communities, 3) accumulation of 13C-enriched microbial-derived carbon during decomposition. The effects of 13C Suess effect on the vertical distribution of δ13C in soil profile were also discussed. There were four mechanisms underlying the vertical distribution of δ15N in soil profile: 1) 15N-depletion gas loss during denitrification, 2) accumulation of 15N-enriched microbial-derived nitrogen during decomposition, 3) accumulation of 15N-encriched mycorrhizal fungi residues in deep soil as a result of transferring 15N-depleted nitrogen compounds to plants by mycorrhizae, 4) intera-ction between soil organic matter and mineral substance. We proposed important concerning points for the future study on vertical distribution of natural abundance of stable carbon and nitrogen isotopes in soil profile.

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.

[Short-term effects of litter treatment on soil C and N transformation and microbial community structure in Erythrophleum fordii plantation.] / æž¯è½ç‰©å¤„ç†å¯¹æ ¼æœ¨æž—åœŸå£¤ç¢³æ°®è½¬åŒ–å’Œå¾®ç”Ÿç‰©ç¾¤è½ç»“æž„çš„çŸ­æœŸå½±å“.

In southern subtropical China, the seasonal variations of soil carbon (C) and nitrogen (N) transformation rates and microbial community structure under different litter treatments (control, litter removal, litter double) in Erythrophleum fordii plantation were studied by the methods of barometric process separation (BaPS) and phospholipid fatty acids (PLFAs) profiles. The results showed that there were significant seasonal variations in soil respiration and gross nitrification rates under different litter treatments, with significantly higher rates in the rainy season than in the dry season. In the initial stage of litter treatment, soil respiration and gross nitrification rates decreased with increasing litter inputs. With prolonged litter treatment, both of them increased with increasing litter inputs. The total microbial PLFAs and each microbial group PLFAs under different litter treatments were significantly higher in the dry season than those in the rainy season. The fungal PLFAs/bacterial PLFAs in the rainy season were significantly higher than that in the dry season. In the dry season, litter removal significantly increased the total microbial PLFAs, bacterial PLFAs, fungal PLFAs and arbuscular mycorrhizal fungal (AMF) PLFAs by 30.9%, 28.8%, 44.4% and 31.6%, respectively. In the rainy season, litter removal significantly decreased the bacterial PLFAs and AMF PLFAs by 10.6% and 33.3%, respectively. Soil microbial community structure was affected by both litter input treatments and seasons. Soil temperature and NH4+-N were the key determinants influencing the microbial community structure. The litter input treatments in E. fordii plantation had significant impacts on soil C and N transformation rate and microbial community structure in short-term, which were dependent on seasons.

[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.

[Soil microbial community structure in Picea asperata plantations with different ages in subalpine of western Sichuan, Southwest China.] / 川西亚高山不同林龄云杉人工林土壤微生物群落结构.

The effects of four Picea asperata plantations with different ages (50-, 38-, 27- and 20-year-old), in subalpine of western Sichuan, on the characteristics of soil microbial diversity and microbial community structure were studied by the method of phospholipid fatty acid (PLFA) profiles. The results showed that, with the increase of age, the contents of soil organic carbon and total nitrogen gradually improved, while Shannon's diversity index and Pielou's evenness index of soil microorganisms increased at first and then decreased. The amounts of microbial total PLFAs, bacterial PLFAs, fungal PLFAs, actinobacterial PLFAs, and arbuscular mycorrhizal fungal (AMF) PLFAs in soils consistently increased with increasing age. The principal component analysis (PCA) indicated that the soil microbial communities in different plantations were structurally distinct from each other. The first principal component (PC1) and the second principal component (PC2) together accounted for 66.8% of total variation of the soil microbial community structure. The redundancy analysis (RDA) of soil microbial community structure and environmental factors showed that soil organic carbon, total nitrogen, total potassium, and fine root mass were the key determinants influencing the microbial community structure. Our study suggested that, with the extension of artificialafforestation time, the soil fertility and microbial biomass were enhanced, and the restoration processes of forest ecosystem were stable.

Differential effects of conifer and broadleaf litter inputs on soil organic carbon chemical composition through altered soil microbial community composition.

A strategic selection of tree species will shift the type and quality of litter input, and subsequently magnitude and composition of the soil organic carbon (SOC) through soil microbial community. We conducted a manipulative experiment in randomized block design with leaf litter inputs of four native subtropical tree species in a Pinus massoniana plantation in southern China and found that the chemical composition of SOC did not differ significantly among treatments until after 28 months of the experiment. Contrasting leaf litter inputs had significant impacts on the amounts of total microbial, Gram-positive bacterial, and actinomycic PLFAs, but not on the amounts of total bacterial, Gram-negative bacterial, and fungal PLFAs. There were significant differences in alkyl/O-alkyl C in soils among the leaf litter input treatments, but no apparent differences in the proportions of chemical compositions (alkyl, O-alkyl, aromatic, and carbonyl C) in SOC. Soil alkyl/O-alkyl C was significantly related to the amounts of total microbial, and Gram-positive bacterial PLFAs, but not to the chemical compositions of leaf litter. Our findings suggest that changes in forest leaf litter inputs could result in changes in chemical stability of SOC through the altered microbial community composition.

[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.

[Dynamics of carbon and nitrogen storage of Cupressus chengiana plantations in the arid valley of Minjiang River, Southwest China].

The carbon and nitrogen storage and distribution patterns of Cupressus chengiana plantation ecosystems with different stand ages in the arid valley of Minjiang River were studied. The results showed that carbon contents in different organs of C. chengiana were relatively stable, while nitrogen contents were closely related to different organs, and soil organic carbon and nitrogen contents increased with the stand age. Carbon and nitrogen storage in vegetation layer, soil layer, and the whole ecosystem of the plantation increased with the stand age. The values of total carbon storage in the 13-, 11-, 8-, 6- and 4-year-old C. chengiana plantation ecosystems were 190.90, 165.91, 144.57, 119.44, and 113.49 t x hm(-2), and the values of total nitrogen storage were 19.09, 17.97, 13.82, 13.42, and 12.26 t x hm(-2), respectively. Most of carbon and nitrogen were stored in the 0-60 cm soil layer in the plantation ecosystems and occupied 92.8% and 98.8%, respectively, and the amounts of carbon and nitrogen stored in the top 0-20 cm soil layer, accounted for 54.4% and 48.9% of those in the 0-60 cm soil layer, respectively. Difference in distribution of carbon and nitrogen storage was observed in the vegetation layer. The percentage of carbon storage in tree layer (3.7%) were higher than that in understory vegetation (3.5%), while the percentage of nitrogen storage in tree layer (0.5%) was lower than that in understory (0.7%). The carbon and nitrogen storage and distribution patterns in the plantations varied obviously with the stand age, and the plantation ecosystems at these age stages could accumulate organic carbon and nitrogen continuously.

[Characteristics of carbon storage and its allocation in Erythrophleum fordii plantations with different ages].

Carbon storage and its allocation of 7-, 29- and 32-year-old Erythrophleum fordii plantation ecosystems in Guangxi were studied on the basis of biomass survey. The results showed that the carbon contents in different organs of E. fordii, ranging from 509.0 to 572.4 g x kg(-1), were in the order of stem > branch > root > bark > leaf. No significant differences in carbon content were observed among the shrub, herb and litter layers of the E. fordii plantations with different ages. Carbon content in the soil layer (0-100 cm) decreased with increasing the soil depth, but increased with increasing the stand age. The carbon storage of the arbor layer was 21.8, 100.0 and 121.6 t x hm(-2) for 7-, 29- and 32-year-old stands, respectively, and the order of carbon storage allocation in different organs was same as the order of carbon content. The 7-, 29- and 32-year-old E. fordii plantation ecosystems stored carbon at 132.6, 220.2 and 242.6 t x hm(-2), respectively. The arbor layer and soil layer were the main carbon pools, accounting for more than 97% of carbon storage in the ecosystem. Carbon storage allocation increased in arbor layer but decreased in soil layer with increasing the stand age. The influence of stand age on carbon storage allocation in shrub, herb and litter layers did not show a obvious regular pattern.

[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.

[Characteristics of soil microbial biomass and community composition in three types of plantations in southern subtropical area of China].

By using fumigation-extraction method and phospholipid fatty acids (PLFAs) analysis, this paper studied the characteristics of soil microbial biomass and community composition in the Erythrophleum fordii, Castanopsis hystrix, and Pinus massoniana plantations in south subtropical China. The soil microbial biomass, total PLFAs, bacterial PLFAs, and fungal PLFAs in the plantations were significantly affected by the plantation type and season, and the soil microbial biomass, total PLFAs, and individual PLFA signatures were higher in dry season than in rainy season. The C. hystrix plantation had the highest soil microbial biomass carbon and total PLFAs, while the E. fordii plantation had the highest soil microbial biomass nitrogen. There was a significant positive correlation between the soil pH and arbuscular mycorrhizal fungal (AMF) PLFA (16:1omega5c). The soil total PLFAs, gram-positive bacterial PLFAs, saprophytic fungal PLFA (18:2omega6,9c), and the ratio of gram-positive to gram-negative bacterial PLFAs were significantly positively correlated with soil organic carbon, total nitrogen, and total phosphorus, suggesting that the soil organic carbon, total nitrogen, and total phosphorus contents were the most important nutrient factors affecting the numbers and types of the soil microorganisms. In addition, the ectomycorrhizae fungal PLFA (18:1omega9c) and AMF PLFA were significantly correlated with the soil C/N ratio.

[Effects of altitudinal gradient on Salix atopantha foliar delta13C].

In 2010, measurements were conducted on the foliar delta13C, photosynthesis, CO2 diffusive conductivity, nitrogen content, photosynthetic nitrogen use efficiency (PNUE), and special leaf area (SLA) of Salix atopantha at different altitudes (2350 m, 2700 m, 3150 m, and 3530 m) in Wolong Natural Reserve. With the increase of altitude, the foliar nitrogen content (especially the nitrogen content per unit leaf area, N(area)) and the PNUE increased, and the foliar delta13C had a significant increase, with an increment of 1.4 per thousand per 1000 m altitude. The stomatal and mesophyll CO2 diffusion conductance also increased with increasing altitude, which had definite negative effect on the increase of foliar delta13C, but the effect was not strong enough. Comparing with CO2 diffusion conductance, carboxylation capacity was a more important factor limiting the P(c)/P(a), and even, the foliar delta13C. At altitude 2350-2700 m, air temperature was the main factor affecting the allocation of nitrogen in S. atopantha photosynthetic system, whereas at altitude 2700-3530 m, light could be the main affecting factor. No significant difference was observed in the SLA at different altitudes.

[Spatial patterns of dominant tree species in sub-alpine Betula-Abies forest in West Sichuan of China].

Based on the investigation in a 4 hm2 Betula-Abies forest plot in sub-alpine area in West Sichuan of China, and by using point pattern analysis method in terms of O-ring statistics, the spatial patterns of dominant species Betula albo-sinensis and Abies faxoniana in different age classes in study area were analyzed, and the intra- and inter-species associations between these age classes were studied. B. albo-sinensis had a unimodal distribution of its DBH frequency, indicating a declining population, while A. faxoniana had a reverse J-shaped pattern, showing an increasing population. All the big trees of B. albo-sinensis and A. faxoniana were spatially in random at all scales, while the medium age and small trees were spatially clumped at small scales and tended to be randomly or evenly distributed with increasing spatial scale. The maximum aggregation degree decreased with increasing age class. Spatial association mainly occurred at small scales. A. faxoniana generally showed positive intra-specific association, while B. albo-sinensis generally showed negative intra-specific association. For the two populations, big and small trees had no significant spatial association, but middle age trees had negative spatial association. Negative inter-specific associations of the two populations were commonly found in different age classes. The larger the difference of age class, the stronger the negative inter-specific association.

Seasonal variation and correlation with environmental factors of photosynthesis and water use efficiency of Juglans regia and Ziziphus jujuba.

Both the photosynthetic light curves and CO(2) curves of Juglans regia L. and Ziziphus jujuba Mill. var. spinosa in three seasons were measured using a LI-6400 portable photosynthesis system. The maximal net photosynthetic rate (A(max)), apparent quantum efficiency(phi), maximal carboxylation rate (V(cmax)) and water use efficiency (WUE) of the two species were calculated based on the curves. The results showed that A(max) of J. regia reached its maximum at the late-season, while the highest values of A(max) of Z. jujuba occurred at the mid-season. The A(max) of J. regia was more affected by relative humidity (RH) of the atmosphere, while that of Z. jujuba was more affected by the air temperature. Light saturation point (LSP) and Light compensation point (LCP) of J. regia had a higher correlation with RH of the atmosphere, those of Z. jujuba, however, had a higher correlation with air temperature. V(cmax) of both J. regia and Z. jujuba had negative correlation with RH of the atmosphere. WUE of J. regia would decrease with the rise of the air temperature while that of Z. jujuba increased. Thus it could be seen that RH, temperature and soil moisture had main effect on photosynthesis and WUE of J. regia and Z. jujuba. Incorporating data on the physiological differences among tree species into forest carbon models will greatly improve our ability to predict alterations to the forest carbon budgets under various environmental scenarios such as global climate change, or with differing species composition.

Nitrogen and carbon source-sink relationships in trees at the Himalayan treelines compared with lower elevations.

No single hypothesis or theory has been widely accepted for explaining the functional mechanism of global alpine/arctic treeline formation. The present study tested whether the alpine treeline is determined by (1) the needle nitrogen content associated with photosynthesis (carbon gain); (2) a sufficient source-sink ratio of carbon; or (3) a sufficient C-N ratio. Nitrogen does not limit the growth and development of trees studied at the Himalayan treelines. Levels of non-structural carbohydrates (NSC) in trees were species-specific and site-dependent; therefore, the treeline cases studied did not show consistent evidence of source/carbon limitation or sink/growth limitation in treeline trees. However, results of the combined three treelines showed that the treeline trees may suffer from a winter carbon shortage. The source capacity and the sink capacity of a tree influence its tissue NSC concentrations and the carbon balance; therefore, we suggest that the persistence and development of treeline trees in a harsh alpine environment may require a minimum level of the total NSC concentration, a sufficiently high sugar:starch ratio, and a balanced carbon source-sink relationship.

[Quantitative analysis of different restoration stages during natural succession processes of subalpine dark brown coniferous forests in western Sichuan, China].

By adopting space as a substitute for time, and based on the approaches of inter-specific association, PCA and optimal division, the restoration stages of various secondary forest communities originated from the natural succession processes of bamboo-dark brown coniferous and moss-dark brown coniferous old-growth forests after clear-cut were quantified at different temporal series (20, 30, 30, 40, 50 and 160-200 years). The results showed that Betula albo-sinensis, Salix rehderiana, Acer mono, A. laxiflorum, Prunus tatsienensis, Hydrangea xanthoneura, Tilia chinensis and Salix dolia were the declining species groups with progressive restoration processes from secondary forest to mature moss and bamboo-dark brown coniferous forests, Sorbus hupehensis, S. koehneana and P. pilosiuscula were the transient species groups, and Abies faxoniana, Picea purpurea, Tsuga chinensis and P. wilsonii were the progressive species groups. During the period of 20-40 years restoration, the secondary forests were dominated by broad-leaved tree species, such as B. albo-sinensis, and the main forest types were moss--B. albo-sinensis forest and bamboo--B. albo-sinensis forest. Through 50 years natural succession, the secondary forests turned into conifer/broad-leaved mixed forest dominated by B. albo-sinensis and A. faxoniana, and the main forest types were moss--B. albo-sinensis--A. faxoniana forest and bamboo--B. albo-sinensis--A. faxoniana forest. The remained 160-200 years old coniferous forests without cutting were dominated by old-growth stage A. faxoniana, and the main forest types were moss--A. faxoniana forest and bamboo--A. faxoniana forest.