Variation of maximum tree height and annual shoot growth of Smith fir at various elevations in the Sygera Mountains, southeastern Tibetan Plateau

Little is known about tree height and height growth (as annual shoot elongation of the apical part of vertical stems) of coniferous trees growing at various altitudes on the Tibetan Plateau, which provides a high-elevation natural platform for assessing tree growth performance in relation to future climate change. We here investigated the variation of maximum tree height and annual height increment of Smith fir (Abies georgei var. smithii) in seven forest plots (30 m×40 m) along two altitudinal transects between 3,800 m and 4,200/4,390 m above sea level (a.s.l.) in the Sygera Mountains, southeastern Tibetan Plateau. Four plots were located on north-facing slopes and three plots on southeast-facing slopes. At each site, annual shoot growth was obtained by measuring the distance between successive terminal bud scars along the main stem of 25 trees that were between 2 and 4 m high. Maximum/mean tree height and mean annual height increment of Smith fir decreased with increasing altitude up to the tree line, indicative of a stress gradient (the dominant temperature gradient) along the altitudinal transect. Above-average mean minimum summer (particularly July) temperatures affected height increment positively, whereas precipitation had no significant effect on shoot growth. The time series of annual height increments of Smith fir can be used for the reconstruction of past climate on the southeastern Tibetan Plateau. In addition, it can be expected that the rising summer temperatures observed in the recent past and anticipated for the future will enhance Smith fir's growth throughout its altitudinal distribution range.     

Phenological responses of upland rice grown along an altitudinal gradient

High altitude upland rice (Oryza sativa L.) production systems are expected to benefit from climate change induced increase in temperatures. The potential yield of rice genotypes is governed by the thermal environment experienced during crop development phases when yield components are determined. Thus, knowledge on genotypic variability in phenotypic responses to variable temperature is required for assessing the adaptability of rice production to changing climate. Although, several crop models are available for this task, genotypic thermal constants used to simulate crop phenology vary strongly among the models and are under debate. Therefore, we conducted field trials with ten contrasting upland rice (O. sativa L.) genotypes on three locations along an altitudinal gradient with five monthly staggered sowing dates for two years in Madagascar with the aim to study phenological responses at different temperature regimes. We found that, crop duration is equally influenced by genotype selection, sowing date and year in the high altitude. In contrast, in mid altitudes genotype has no effect on crop duration. At low altitudes crop duration is more affected by sowing date. Grain yield is strongly affected by low temperatures at high altitudes and severly influenced by frequent tropical cyclones at low altitudes. In high altitude, genotype explained 68% of variation in spikelet sterility, whereas in mid and low altitudes environment explained more than 70% of the variation. The phenological responses determining crop duration and yield, the basic genotypic thermal constants, and the analyses of genotypic thermal responses with regard to spikelet sterility reported here, provide valuable information for the improvement of rice phenological models urgently needed to develop new genotypes and better adapted cropping calendars.     

Growth variation in Abies georgei var. smithii along altitudinal gradients in the Sygera Mountains, southeastern Tibetan Plateau

A network of nine Smith fir (Abies georgei var. smithii) ring-width chronologies was constructed from sites ranging in elevation from 3,550 to 4,390 m above sea level (a.s.l.) in the Sygera Mountains, southeastern Tibetan Plateau. High-elevation trees had lower growth rates than did low-elevation trees. The mean tree-ring series intercorrelation (RBAR) increased with elevation. Principal component analysis identified three elevation zones (around 3,600, 3,800, and >4,200 m a.s.l.) with distinctive tree-ring growth patterns. Five chronologies with elevation >4,200 m a.s.l. were highly correlated. Overall, the initiation of tree-ring growth in Smith fir is controlled by common climatic signals, such as July minimum temperature, across a broad altitudinal range. Precipitation was not a growth-limiting factor across stands. Regardless of differences in stand elevation, topographical aspect, and tree age, the radial growth of Smith fir trees was markedly similar in response to common climatic signals, perhaps as a result of the relatively high-elevation of these forests (above 3,550 m a.s.l.) and the abundant summer monsoon rainfall. In addition, radial tree growth along the altitudinal gradients was indicative of a recent warming trend on the southeastern Tibetan Plateau.     

Contribution of arbuscular mycorrhizal fungi of sedges to soil aggregation along an altitudinal alpine grassland gradient on the Tibetan Plateau

The diversity of arbuscular mycorrhizal fungi (AMF) in sedges on the Tibetan Plateau remains largely unexplored, and their contribution to soil aggregation can be important in understanding the ecological function of AMF in alpine ecosystems. Roots of Kobresia pygmaea C.B. Clarke and Carex pseudofoetida Kük. in alpine Kobresia pastures along an elevational transect (4149–5033 m) on Mount Mila were analysed for AMF diversity. A structural equation model was built to explore the contribution of biotic factors to soil aggregation. Sedges harboured abundant AMF communities covering seven families and some operational taxonomic units are habitat specific. The two plant species hosted similar AMF communities at most altitudes. The relative abundance of the two sedges contributed largely to soil macroaggregates, followed by extraradical mycorrhizal hyphae (EMH) and total glomalin‐related soil protein (T‐GRSP). The influence of plant richness was mainly due to its indirect influence on T‐GRSP and EMH. There was a strong positive correlation between GRSP and soil total carbon and nitrogen. Our results indicate that mycorrhization might not be a major trait leading to niche differentiation of the two co‐occurring sedge species. However, AMF contribute to soil aggregation and thus may have the potential to greatly influence C and N cycling in alpine grasslands.     

Morphological variation in the Common Fiscal Lanius collaris along an altitudinal gradient in southern Africa

Geographic variation among four Common Fiscal subpopulations along an altitudinal gradient in South Africa demonstrated significant variation of 13 morphological features and 38 skeletal characters. Common Fiscals were largest in cooler, less humid, more arid areas and smallest in warmer, wetter, more humid localities, supporting Bergmann's Rule. Patterns of variation in morphology, anatomy and skeletal trends were significantly correlated with 11 climatic trends. Cardiopulmonary organ mass and blood haematocrit increased with altitude and reflected adaptations to low ambient temperatures and decreased oxygen pressures associated with high altitudes. These trends are concordant with those reported in various other avian species.     

Intraspecific variation in morphology of spiny pollen grains along an altitudinal gradient in an insect-pollinated shrub

• Intraspecific variations in pollen morphological traits are poorly studied. Interspecific variations are often associated with pollination systems and pollinator types. Altitudinal environmental changes, which can influence local pollinator assemblages, provide opportunities to explore differentiation in pollen traits of a single species over short distances. The aim of this study is to examine intraspecific variations in pollen traits of an insect-pollinated shrub, Weigela hortensis (Caprifoliaceae), along an altitudinal gradient.
• Pollen spine phenotypes (length, number and density), pollen diameter, lipid mass (pollenkitt) around pollen grains, pollen production per flower and pollinator assemblages were compared at four sites at different altitudes.
• Spine length and the spine length/diameter ratio of pollen grains were greater at higher altitudes but not correlated with flower or plant size. Spine number and density increased as flower size increased, and pollen lipid mass decreased as plant size increased. Bees were the predominant pollinators at low-altitude sites whereas flies, specifically Oligoneura spp. (Acroceridae), increased in relative abundance with increasing altitude.
• The results of this study suggest that the increase in spine length with altitude was the result of selection favouring longer spines at higher-altitude sites and/or shorter spines at lower-altitude sites. The altitudinal variation in selection pressure on spine length could reflect changes in local pollinator assemblages with altitude.

     

Mitochondrial DNA variation along an altitudinal gradient in the greater white-toothed shrew, Crocidura russula

The distribution of mitochondrial control region-sequence polymorphism was investigated in 15 populations of Crocidura russula along an altitudinal gradient in western Switzerland. High-altitude populations are smaller, sparser and appear to undergo frequent bottlenecks. Accordingly, they showed a loss of rare haplotypes, but unexpectedly, were less differentiated than lowland populations. Furthermore, the major haplotypes segregated significantly with altitude. The results were inconsistent with a simple model of drift and dispersal. They suggested instead a role for historical patterns of colonization, or, alternatively, present-day selective forces acting on one of the mitochondrial genes involved in metabolic pathways.     

Phenological and growth responses of Papaver radicatum along altitudinal gradients in the Canadian High Arctic

Phenology and growth of Papaver radicatum Rottb. was monitored over four summers (1990–1993) at 12 sites, along a dolomitic and a granitic altitudinal gradient (330 m a.s.l.–770 m a.s.l.) at Sverdrup Pass, central Ellesmere Island, Canada. The gradients provided substantial differences in environmental characteristics. Three of the four seasons (1990, 1991 and 1993) had more than 400 thawing degree-days (TDD) in the valley, while the 1992 season had less than 300. The granitic sites had consistently higher temperatures than the dolomitic sites, despite their northerly aspect. Increasing elevation reduced total degree-day accumulation ( c . 40 degree-days/100 m) and length of potential growing season. The proportion of the population producing flower buds was similar at all sites in any given year, but there were differences among years. Production of flowers and fruits per site, decreased with altitude along the dolomitic gradient in 1991 and 1992. There was no difference in the number of buds or flowers produced per plant with increasing altitude, although larger plants with multiple flowers were found only on low elevation granitic sites. Plants from the dolomitic sites were smaller and flowered, on average, after the site accumulated 150 degree-days, while plants on the granitic sites were larger and bloomed after 200 degree-days. Papaver is able to grow and reproduce over a wide range of environmental conditions and moderate climate warming would likely promote its growth and establishment, unless other factors, especially snow-free periods and water availability, become limiting.     

岷江源区两种优势针叶树当年生小枝性状与生物量分配随海拔的分异规律

当年生小枝具有较少的次生组织,同时是植物分支系统中最具活力的部分,木本植物当年生小枝性状与生物量分配的海拔变化是理解物种对不同生境适应策略的重要内容。通过分析青藏高原东缘岷江源区两种优势亚高山针叶乔木(紫果云杉和岷江冷杉)当年生小枝性状(茎长、茎粗、比茎长)与不同部位器官(茎、叶)的生物量随天然生境的海拔(3500-3550 m、3650-3700 m和3800-3850 m)变化,尝试揭示两物种当年生小枝在不同海拔下的生物量权衡及其生长策略。结果表明:(1)不同海拔下茎生物量种间差异大于种内差异,3650-3700 m处的茎生物量变异最大(128.4%)。(2)云杉的茎生物量、总叶生物量与海拔间存在显著的负相关关系(P<0.05),比茎长与海拔呈显著正相关(P<0.05);冷杉的总叶生物量与海拔间为显著负相关关系(P<0.05)。(3)随着海拔的升高,云杉茎生物量分配比逐渐从33.0%降低到27.0%;而冷杉的茎生物量分配比则从23.0%渐增至28.0%。(4)3500-3550 m和3650-3700 m两处的云杉茎生物量与总叶生物量、茎长与茎粗呈异速生长关系;3500-3550 m、3650-3700 m和3800-3850 m三处的冷杉茎生物量与总叶生物量、茎长与茎粗一直呈现异速生长关系。两种针叶树的茎生物量分配比及相关性状随海拔的变化差异表明冷杉更适应高海拔的胁迫环境。     

Rotifer species richness along an altitudinal gradient in the Alps

Aim Biodiversity patterns along altitudinal gradients are less studied in aquatic than terrestrial systems, even though aquatic sites provide a more homogeneous environment independent of moisture constraints. We studied the altitudinal species richness pattern for planktonic rotifers in freshwater lakes and identified the environmental predictors for which altitude is a proxy. Location Two hundred and eighteen lakes of Trentino–South Tyrol (Italy) in the eastern Alps; lakes covered 98% (range 65–2960 m above sea level) of the altitudinal gradient in the Alps. Methods We performed: (1) linear regression between species richness and altitude to evaluate the general pattern, (2) multiple linear regression between species richness and environmental predictors excluding altitude to identify the most important predictors, and (3) linear regression between the residuals of the best model of step (2) and altitude to investigate any additional explanatory power of altitude. Selection of environmental predictors was based on limnological importance and non‐parametric Spearman correlations. We applied ordinary least squares regression, generalized linear, and generalized least squares modelling to select the most statistically appropriate model. Results Rotifer species richness showed a monotonic decrease with altitude independent of scale effects. Species richness could be explained (R²= 51%) by lake area as a proxy for habitat diversity, reactive silica and total phosphorus as proxies for productivity, water temperature as a proxy for energy, nitrate as a proxy for human influence and north–south and east–west directions as covariates. These predictors completely accounted for the species richness–altitude pattern, and altitude had no additional effect on species richness. Main conclusions The linear decrease of species richness along the altitudinal gradient was related to the interplay of habitat diversity, productivity, heat content and human influence. These factors are the same in terrestrial and aquatic habitats, but the greater environmental stability of aquatic systems seems to favour a linear pattern.     

Little change in the fir tree-line position on the southeastern Tibetan Plateau after 200 years of warming

? As one of the world's highest natural tree lines, the Smith fir (Abies georgei var. smithii) tree line on the southeastern Tibetan Plateau is expected to vary as a function of climate warming. However, the spatial patterns and dynamics of the Smith fir tree line are not yet well understood. ? Three rectangular plots (30 m × 150 m) were established in the natural alpine tree-line ecotone on two north-facing (Plot N1, 4390 m asl; Plot N2, 4380 m asl) and one east-facing (Plot E1, 4360 m asl) slope. Dendroecological methods were used to monitor the tree-line patterns and dynamics over a 50-yr interval. ? The three study plots showed a similar pattern of regeneration dynamics, characterized by increased recruitment after the 1950s and an abrupt increase in the 1970s. Smith fir recruitment was significantly positively correlated with both summer and winter temperatures. However, Smith fir tree lines do not show a significant upward movement, despite warming on the Tibetan Plateau. ? The warming in the past 200 yr is already having a significant impact on the population density of the trees, but not on the position of the Smith fir tree line.     

Vegetation variation within and among palustrine wetlands along an altitudinal gradient in KwaZulu-Natal,South Africa

The variation in graminoid species composition and diversity and the distribution of photosynthetic pathways among 66 wetlands in KwaZulu-Natal, South Africa, and within six of these wetlands was described and related to measured physical parameters, using multivariate and univariate techniques. Altitude, which ranged from 550 m to 2120 m, accounted for most variation among wetlands, with an almost complete turnover of species along this gradient. Landform setting was less important in explaining overall species composition, but relationships of individual species were revealed (e.g. Eleocharis dregeana showed an affinity for depressions). Within a wetland there was an almost complete turnover of species along a gradient of wetness, as described using soil morphological criteria. Most species were consistently associated with the same wetness zones across different wetland sites, e.g., Phragmites australis with the wettest zone, Pycreus macranthus with the intermediate zone, and Eragrostis plana with the least wet zone. The occurrence and abundance of different photosynthetic pathway types depended on altitude and degree of wetness. At high altitudes, C₃ sedges, notably Carex acutiformis, dominated the wettest zone and C₃ and C₄ grasses and sedges dominated the intermediate and least wet zones. At mid altitudes, C₃ and C₄ sedges and C₃ grasses dominated the wettest zone, C₃ and C₄ grasses and sedges dominated the intermediate zone and C₄ grasses dominated the least wet zone. Low altitude sites showed a similar distribution of photosynthetic pathways as mid-altitude sites, but C₃ species were less abundant. Species richness was positively associated with the log of wetland size and, at the level of an individual wetland, species richness and evenness were found to be consistently greater in the intermediate and least wet zone compared with the wettest zone. The management implications of the results are discussed in the light of continuing anthropogenic loss of wetlands in the study area and global climate change.     

Climate sensitivity of purple cone spruce (Picea purpurea) across an altitudinal gradient on the eastern Tibetan Plateau

Picea purpurea (Purple cone spruce) is a dominant and widely distributed tree species in the subalpine area of the Wanglang Nature Reserve. We investigated variations in radial growth and its response to climate in P. purpurea along an altitudinal gradient. In this study, P. purpurea chronologies were developed from three altitudinal sites ranging from 2850 to 3250 m above sea level. Correlation analysis and principal component analysis were used for all the chronologies to detect the growth patterns at different altitudes. Correlation analysis was used to assess the relationships between chronologies and climatic factors. Tree-ring widths among the three elevations were all positively correlated with June maximum temperature in the current year. Radial growth at the higher altitude was more sensitive to temperature than those of the two lower altitudes. Ring-widths at the low and middle sites were mainly negatively affected by temperatures in the previous growing season (June and August). Spruce growth at the upper site was strongly positively affected by temperatures in the previous winter, the current spring and current growing season. Climatological analysis revealed that elevation-dependent and elevation-independent signals were present in this semi-humid subalpine area. Precipitation was not the main factor affecting the tree growth in the growing season throughout the study area. The noteworthy findings were that the lag effects of temperatures to spruce growth was more significant at the low and middle altitude sites, and spruce growth at the high altitude site clearly benefited from the warmer climate before and during the growing season. This study will provide a basis for better predicting forest dynamics and carrying out vegetation restoration in the future.     

Pattern of flower size variation along an altitudinal gradient differs between Impatiens textori and Impatiens noli-tangere

Studies of factors influencing spatial variation in flower size offer insights into floral evolution. We investigated altitudinal variations in five flower dimensions of two native Japanese Impatiens species (I. textori and I. noli-tangere) and their interactions with their faunal visitors. These two species have similar floral traits, including flower shape, flowering time, and pollinator species; both species are pollinated mainly by Bombus diversus. In I. textori, all measured flower dimensions were negatively correlated with altitude. In contrast, in I. noli-tangere, no measured flower dimensions correlated with altitude. Thus, the altitudinal pattern of flower size variation differed between these congeneric co-habiting herbaceous plant species. The different patterns suggest that the factors (e.g. altitudinal variations of abiotic factors) that cause variation of flower size differ between these two Impatiens species even though focal species have similar floral traits (e.g. flower shape, flowering time, and pollinator species).     

长白山不同海拔树木生长对气候变化的响应差异

以长白落叶松和红松为例,探讨了长白山地区不同海拔树木生长对气候变化的响应。利用长白山北坡不同海拔4个长白落叶松样点和6个红松样点的树轮宽度资料建立差值年表,通过聚类分析、相关分析和响应分析等方法,研究树木生长特征及其气候响应。结果表明:两个树种年表的平均敏感度、树轮宽度指数的年际变率、信噪比等特征值较高,反映年表含有较强的环境信息。随海拔升高,长白落叶松年表特征值呈先下降后增加的趋势,红松年表特征值则呈先增加后下降的趋势。聚类分析将长白落叶松年表分成高、低海拔两类,红松年表分成高、中、低海拔三类。树木生长对气候响应存在海拔差异。高海拔长白落叶松生长受当年气温影响;低海拔长白落叶松生长对气候存在"滞后响应"。高海拔红松不仅受降水限制,且对气温有"滞后响应";中海拔红松不仅受气温限制,且对降水有"滞后响应";低海拔红松生长主要受气温限制。     

武夷山不同海拔梯度土壤微生物生物量微生物呼吸及其商值(qMB,qCO2)

土壤微生物生物量、土壤微生物呼吸及微生物商值(微生物商(qMB)、微生物呼吸商(qCO2))是土壤质量的敏感性指标.本文对武夷山不同海拔梯度具有代表性的中亚热带常绿阔叶林、针叶林、亚高山矮林以及高山草甸土壤微生物生物量、土壤微生物呼吸及其qMB、qCO2进行了研究.结果表明:土壤微生物生物量、土壤微生物呼吸均随海拔梯度的升高而加大,随土层深度的加深而降低,qMB、qCO2没有表现出随海拔变化的规律,qMB的最大值(2.23%±0.28%)出现在高山草甸0～10 cm土层的土壤,最小值(0.51%±0.09%)为常绿阔叶林25～40 cm土层土壤,针叶林的值大于亚高山矮林;qCO2的最大值(5.88%±0.94%)为针叶林25～40 cm土层土壤,最小值(1.38%±0.09%)为高山草甸0-10 cm土层的土壤.在同一林分,qMB值随土层加深而减小,qCO2值在亚高山矮林和高山草甸无此规律.土壤微生物生物量、微生物呼吸及其qMB、qCO2与土壤总有机碳、全氮、全磷具有显著的线性相关关系(P<0.05),可用来评价土壤质量.