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How can we understand the limitations to plant growth at high altitudes? Our aim was to test the hypotheses that for alpine grasslands along a large altitudinal gradient in semi‐arid regions, plant growth is mainly limited by drought at low altitudes but by low temperature at high altitudes, resulting in a unimodal pattern of biomass and productivity associated with an optimal combination of temperature and precipitation. Such knowledge is important to understanding the response of alpine ecosystems to climate change.
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It is unclear whether annual ring widths (ARW) are good predictors of changes in net primary productivity (NPP) of trees or shrubs in cold environments. We test if the simulated NPP with inputs of observed leaf nitrogen concentration (N mass) and carbon isotope ratio (δ13C) explains altitudinal variations of ARW, relative growth rate (RGR), and maximum photosynthetic rate (P max) within a widespread woody species at moist timberline ecotones. We measured plant-level ARW and RGR, and related leaf traits (P max, N mass, δ13C etc.) for an alpine Rhododendron shrub (R. aganniphum var. schizopeplum) across ten altitudes (4,190–4,500 m) in the Sergyemla Mountains, southeast Tibet. Based on climate data available from Nyingchi station at 3,000 m, non-age-related ARW chronologies (1960–2008) for each of ten altitudes were positively correlated with June mean temperature, but related little with precipitation and other monthly mean temperatures. With increasing altitude, N mass and P max de
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Warming climate could affect leaf‐level carbon isotope composition (δ13C) through variations in hotosynthetic gas exchange. However, it is still unclear to what extent variations in foliar δ13C can be used to detect changes in net primary productivity (NPP) because leaf physiology is only one of many eterminants of stand productivity. We aim to examine how well site‐mean foliar δ13C and stand NPP co‐vary across large resource gradients using data obtained from the Tibetan Alpine Vegetation Transects (1900–4900 m, TAVT).
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It is unclear whether the shift in leaf traits between species of high‐ and low‐rainfall sites is caused by low rainfall or by species replacement, because leaf traits vary substantially among species and sites. Our objective was to test if the within‐species relationship between specific leaf area (SLA) and leaf N concentration (Nmass) shifts across a rainfall gradient in the semi‐arid sandy lands of northern China. Data for SLA and Nmass of dominant species and related canopy and soil variables were collected from 33 plots along a rainfall transect (270–390 mm) having similar temperatures in the Mu Us, Inner Mongolia. We further investigated the generality of Mu Us data using 12 additional plots in the southeastern Qaidam Basin, Qinghai. Artemisia ordosica is a widespread species in both regions. Across and within species, the positive SLA–Nmass relationship shifted between two plant groups in the lowest rainfall plots (270 mm) and other higher rainfall plots (320–
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Climatic variables explained the variations in MPH and R: S ratio of undegraded grasslands better than soil ariables (46–50% vs < 19%), while those of degraded grasslands generally showed insignificant correlations with climatic and soil variables. There was a general relationship between R: S ratio and MPH (negative, R2= 0.76, P< 0.001) across degraded and undegraded grasslands. The relationship was used to predict R: S ratio in 13 dditional plots in steppe grasslands of Inner Mongolia, and good agreement of expected and observed values has been found (R2= 0.87, P < 0.001).
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Knowledge of how leaf characteristics might be used to deduce information on ecosystem functioning and how this caling task could be done is limited. In this study, we present field data for leaf lifespan, specific leaf area SLA) and mass and area-based leaf nitrogen concentrations (Nmass, Narea) of dominant tree species and the ssociated stand foliage N-pool, leaf area index (LAI), root biomass, aboveground biomass, net primary roductivity (NPP) and soil available-N content in six undisturbed forest plots along subtropical to timberline gradients on he eastern slope of the Gongga Mountains. We developed a methodology to calculate the whole-canopy mean leaf raits to include all tree species (groups) in each of the six plots through a series of weighted averages scaled up from leaf-level measurements.
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Much uncertainty in estimating root biomass density (RBD, root mass per unit area) of all roots regionally exists because of methodological difficulties and little knowledge about the effects of biotic and abiotic factors on the magnitude and distribution pattern of RBD. In this study, we collected field data of RBD from 22 sites along the Tibetan Alpine Vegetation Transects executed with the same sampling method that covered a relatively undisturbed vegetation gradient from subtropical forests to alpine vegetation. Our field data indicated that RBD significantly decreased with increasing altitudes (r(2) = 0.60, P < 0.001) but had low or non-robust correlations with above.-round biomass density (r(2) = 0.10-0.34), suggesting that RBD can be predicted without reference to shoot biomass. The transect data further revealed that temperature and/or precipitation were likely the major limiting factors for geographical distribution patterns of RBD. The relationships could be expressed as logi
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Geographically, NPP and LAI both significantly decreased with increasing latitude (P < 0.02), but increased with increasing longitude (P < 0.01). Altitudinal trends in NPP and LAI showed different patterns. NPP generally decreased with increasing altitude in a linear relationship (r2 = 0.73, P < 0.001), whereas LAI showed a negative quadratic relationship with altitude (r2 = 0.58, P < 0.001). Temperature and precipitation, singly or in combination, explained 60–68% of the NPP variation with logistic relationships, while the soil organic C and total N variables explained only 21–46% of the variation with simple linear regressions of log‐transformed data. LAI showed significant logistic relationships with both climatic and soil variables, but the data from alpine spruce‐fir sites diverged greatly from the modelled patterns associated with temperature and precipitation. Soil organic C storage had the strongest correlation with LAI (r2 = 0.68, P < 0.001).
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实测了青藏高原植被样带22个地区不同植被类型的地上部分生物量并进行了格局分析，对于未受人为干扰的以常绿阔叶林为基带的亚高山天然植被，随着海拔升高，地上生物量呈递增趋势，在一定海拔高度达最大，海拔继续升高上生物量则迅速下降，这一垂直分异规律在一定程度上反映了全球地带性森林植被最大生物量分布的纬向分异性。基于Weber定律的回归分析表明，地上生物量与水势因子的相关关系可用Logistic函数拟合，1月平均气温，7月平均气温，年平均气温，年降水量及其组合因子可解释高原植被样带地上生物量变化的28％－53％，其中年降水量及其同年平均气温的组合与地下生物量的相关性最高（R^2为0．46－0．53，p＜0．001），但是，年降水量和平均气温的变化不足以解释西藏色齐拉山暗针叶林具有最高的地上生物量。我们认为，自然植被地上部分生物量的分布格局受到更为复杂的气候因子的制，例如太阳辐射，湿度，风、水分和能量平衡等。
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We developed a methodology for linking together data from forest and grassland inventories and ecological research sites, and provided a comprehensive report about live biomass and net primary productivity (NPP) on the Tibetan Plateau, the ‘‘Third Pole’’ of the earth where little information about plant biomass and production had been available outside China. Results were as follows. (1) The total live biomass of the natural vegetation in the Xizang (Tibet) Autonomous Region and Qinghai Province was estimated as 2.17 Gg dry mass, of which 72.9% was stored in forests where spruce–fir accounted for 65.1%.
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We have constructed a phenological model of leaf area index (LAI) of forests based on biological principles of leaf growth. Field data of maximum LAI from 794 plots with mature or nearly mature stand ages over China were used to parameterize and calibrate the model. New measurements of maximum LAI from 16 natural forest sites were used to validate the simulated maximum LAI. The predictions of seasonal LAI patterns were compared with seasonal changes derived from the 1‐km satellite AVHRR‐NDVI data for nine undisturbed forest sites in eastern China. Then, we used the model to map maximum LAI values for forests in China.
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高山林线作为极端环境条件下树木生存的界限,由于其对气候变化的敏感性,在全球变化研究中得到了广泛关注。研究高山林线形成机理以及林线地带植物相关生理生态学特性成为预测未来气候变化条件下植被动态变化的出发点。对于高山林线形成机理研究主要关注两方面问题:(1)林线地带外界环境如何限制乔木生长和分布,其内在机理如何;(2)灌木及草本相对于乔木在林线地区有哪些生存优势,从乔木到灌木及草本生活型演变的功能及意义如何。综述了当前高山林线形成机理及相关生理生态特性的国内外最新研究成果,指出尽管温度(尤其是生长季低温)在全球尺度上能解释大部分高山区域林线的分布,但树木生长和生存受限的内在机理并没有弄清楚,目前主要存在"碳受限"以及"生长受限"假说两大争论焦点。另外,理论上受温度控制的高山林线对气候变化的响应表现出不同的模式,表明全球变化对林线分布和植被生长影响的复杂性和不确定性。因此,未来的研究应该关注影响林线地区植被生长的多种生理生态学过程,比如水分及养分利用过程,以及从乔木到灌木及草本生活型演变的功能意义,从而为林线形成机理以及对气候变化的响应提供更好的解释。
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高山林线因其对气候因子的敏感性和自身结构的不稳定性而被视为气候变化的"监视器",通过自动微气象站对藏东南色季拉山急尖长苞冷杉(Abies georgeivar.smithii)林线气象因子的连续监测,探讨了色季拉山高山林线的生态气候特征。结果表明:在色季拉山急尖长苞冷杉林线处,年平均温度为1.3℃,年平均相对湿度为79.4%,全年降水量为892.6 mm,主要集中在6、7、8、9月4个月份。林线最热月平均温度为9.4℃,最冷月平均温度为-6.4℃,年生物温度为3.1℃,温暖指数是11.6℃月,寒冷指数是-55.9℃月,生长季内平均温度为7.7℃,生长季长度为133d,大陆度指数为34.0,湿润指数为217.5。其温暖指数与我国两种山地森林树种祁连圆柏和喜马拉雅冷杉的分布上限较为接近。林线的最热月温度、年生物学温度和生长季平均温度与全国高山林线的平均值十分接近。从全球范围来看,色季拉山林线最热月平均温度9.4℃与全球均值10℃很接近。生长季内10cm深度的土壤均温为6.22℃,接近Krner观测的(6.7±0.8)℃全球均值。
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