青藏高原气候变化与高寒草地

综述了近五十年来青藏高原气候和高寒草地的变化趋势,阐述了气候变化对高寒草地的可能影响。气候变化主要通过水、热过程及其诱导的环境变化对青藏高原高寒草地产生显著的影响。主要过程包括：气候变化对气候带、植被带、植物、植物群落、农业生产以及生态系统固碳潜力等的影响。从目前的观测和研究结果来看,有关青藏高原气候变化及其对高寒草地的可能影响都还很难得出一致的结论。因此,如何科学评价气候变化及其预测和评价对高寒草地结构和功能的潜在影响,以及如何将已经发生的变化纳入到全球变化模型或评价体系中,以便更加精确地评估气候变化的长期影响,将成为必须要回答的关键科学问题。     

Soil seed bank dynamics in alpine wetland succession on the Tibetan Plateau

The primary goal was to address several questions with regard to how soil seed banks change in a successional series. How does the composition of the viable seed bank change, and how does the relationship of the soil seed bank and vegetation change with succession? Can the seed bank be regarded as a potential as a source of seeds for wetland restoration? We collected soil seed bank samples and sampled the vegetation in four different successional stages and used the NMDS (nonmetric multidimensional scaling) to evaluate the relationship of species composition between the seed banks and vegetation. The difference of seed density and species richness in different habitats and soil depths also was compared. Viable seeds of half (37) the species in the early-successional stage were found in all the successional stages. Similarity between seed bank and vegetation increased with succession. Both seed density and species richness in the seed bank increased with successional age and decreased with soil depth. The majority of species from the early-successional stage produced long-lived seeds. Seed density and species richness increased with succession, mainly as a result of increasing seed production, and hypotheses predicting decreasing density of buried seeds and species richness were not confirmed. Seed banks play a minor role in contributing to the regeneration of vegetation, and managers cannot rely on soil-stored seed banks for restoration of wetlands.     

光辐射对青藏高原高寒草甸凋落物分解的影响

光照对干旱半干旱生态系统凋落物分解有显著作用。然而,在太阳辐射强度大、高寒湿润的青藏高原东部高寒草甸,光辐射在凋落物分解中的作用尚不明确。本试验采用凋落物袋法,研究自然光照和遮光2种处理下10种高寒草甸常见物种(披针叶黄华Thermopsis lanceolata、珠芽蓼Polygonum viviparum、线叶嵩草Kobresia capillifolia、小花草玉梅Anemone rivularis、黄帚橐吾Ligularia virgaurea、麻花艽Gentiana straminea、大籽蒿Artemisia sieversiana、瑞苓草Saussurea nigrescens、垂穗披碱草Elymus nutans和矮藨草Scirpus pumilus)叶片凋落物分解特点。结果表明:(1)不同物种凋落物的木质素含量存在显著差异,其中珠芽蓼木质素含量最高(达29.44%),黄帚橐吾木质素含量最低(为4.91%);(2)整体上,遮光显著降低了凋落物质量损失率,而光照的影响程度也因物种而异;(3)无论在自然光照还是在遮光处理下,凋落物质量损失率与初始木质素含量均呈显著负相关关系;遮光明显降低木质素质量损失率,其降低程度也因物种而异。     

Dendrochronological potential of the alpine shrub Rhododendron nivale on the south-eastern Tibetan Plateau

Background and Aims

Shrubs and dwarf shrubs are wider spread on the Tibetan Plateau than trees and hence offer a unique opportunity to expand the present dendrochronological network into extreme environments beyond the survival limit of trees. Alpine shrublands on the Tibetan Plateau are characterized by rhododendron species. The dendrochronological potential of one alpine rhododendron species and its growth response to the extreme environment on the south-east Tibetan Plateau were investigated.

Methods

Twenty stem discs of the alpine snowy rhododendron (Rhododendron nivale) were collected close to the tongue of the Zuoqiupu Glacier in south-east Tibet, China. The skeleton plot technique was used for inter-comparison between samples to detect the growth pattern of each stem section. The ring-width chronology was developed by fitting a negative exponential function or a straight line of any slope. Bootstrapping correlations were calculated between the standard chronology and monthly climate data.

Key Results

The wood of snowy rhododendron is diffuse-porous with evenly distributed small-diameter vessels. It has well-defined growth rings. Most stem sections can be visually and statistically cross-dated. The resulting 75-year-long standard ring-width chronology is highly correlated with a timberline fir chronology about 200 km apart, providing a high degree of confidence in the cross-dating. The climate/growth association of alpine snowy rhododendron and of this timberline fir is similar, reflecting an impact of monthly mean minimum temperatures in November of the previous year and in July during the year of ring formation.

Conclusions

The alpine snowy rhododendron offers new research directions to investigate the environmental history of the Tibetan Plateau in those regions where up to now there was no chance of applying dendrochronology.Key words: South-east Tibetan Plateau, Rhododendron nivale, alpine shrub, growth ring, cross-dating, dendroclimatological potential, climate/growth association     

青藏高原高寒草原碳排放及其迁移过程研究

采用箱式法通过对青海省五道梁地区高寒草原生态系统表层土壤含碳温室气体的研究发现 ,该地区高寒草原系统表层土壤 CO2 和 CH4 在 7～ 8月份的平均排放通量分别为 0 .46μmol· m- 2 · s- 1和 - 0 .43× 1 0 - 3μmol·m- 2 ·s- 1,此两种气体的排放通量随时间都有明显的变化特征 ,它们的日变化均为明显的单峰型 ,而且其中 CO2 排放通量的变化明显受大气温度变化的影响。地下土壤中 CO2 和 CH4 气体浓度随深度的增加呈递减趋势 ,进一步的分析表明这两种气体浓度在土壤中与相邻层次的气体浓度有很明显的相关关系 ,尤以永久冻土上层边界附近最为显著。     

Temperature controls ecosystem CO2 exchange of an alpine meadow on the northeastern Tibetan Plateau

Alpine ecosystems are extremely vulnerable to climate change. To address the potential variability of the responses of alpine ecosystems to climate change, we examined daily CO₂ exchange in relation to major environmental variables. A dataset was obtained from an alpine meadow on the Qinghai‐Tibetan Plateau from eddy covariance measurements taken over 3 years (2002–2004). Path analysis showed that soil temperature at 5 cm depth (T_s5) had the greatest effect on daily variation in ecosystem CO₂ exchange all year around, whereas photosynthetic photon flux density (PPFD) had a high direct effect on daily variation in CO₂ flux during the growing season. The combined effects of temperature and light regimes on net ecosystem CO₂ exchange (NEE) could be clearly categorized into three areas depending on the change in T_s5: (1) almost no NEE change irrespective of variations in light and temperature when T_s5 was below 0 °C; (2) an NEE increase (i.e. CO₂ released from the ecosystem) with increasing T_s5, but little response to variation in light regime when 0 °C≤T_s5≤8 °C; and (3) an NEE decrease with increase in T_s5 and PPFD when T_s5 was approximately >8 °C. The highest daily net ecosystem CO₂ uptake was observed under the conditions of daily mean T_s5 of about 15 °C and daily mean PPFD of about 50 mol m⁻² day⁻¹. The results suggested that temperature is the most critical determinant of CO₂ exchange in this alpine meadow ecosystem and may play an important role in the ecosystem carbon budget under future global warming conditions.     

Relative pollen productivity estimates for alpine meadow vegetation,northeastern Tibetan Plateau

Vegetation History and Archaeobotany - A promising method of reconstructing past vegetation from pollen records uses mathematical models of the relationship between pollen and vegetation. These can...     

Downward-Shifting Temperature Range for the Growth of Snow-Bacteria on Glaciers of the Tibetan Plateau

Fifty-seven snow-bacteria strains were isolated from the snow of the Zadang and Mengdagangri Glaciers located in the central and southern part of the Tibetan Plateau, respectively. 16S rRNA gene sequence analysis showed that strains isolated from the Zadang Glacier belonged to the Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, Firmicutes and Bacteroidetes, and were dominated by the Firmicutes. Strains from the Mengdagangri Glacier belonged to the Actinobacteria, Alphaproteobacteria and Gammaproteobacteria, and were dominated by the Actinobacteria. Sixty-one percent of the isolates were colored with pigment. Sixty-nine percent of isolates from the Zadang Glacier were psychrotolerants, and there were no psychrophiles. We compared the growth-temperature range of 26 snow-bacteria strains to their closest mesophilic type strains and found that 46% of them had an optimum growth-temperature at or lower than 20°C, and 65% were all able to grow at 0°C. However, only 5.3% of mesophilic strains had optimum growth-temperatures at or lower than 20°C, and 9% could grow at 0°C. Snow-bacteria shift their growth-temperature downward; and doing this, in terms of the minimum and optimum temperatures for growth, might be an important strategy for them to adapt to low temperature after they have been deposited on the glacier. Our results suggested that, in order to adapt from mesophilic environments to a cold habitat, snow-bacteria widen their temperature range for growth, convert from mesophiles to psychrotolerants, but not to psychrophiles. In addition, eight isolates formed pigmented colonies, while their mesophilic counterparts were achromogenic. This helped us to confirm through comparative analysis that pigmented microorganisms were more abundant in high-altitude glaciers than in mesophilic environments.     

Plant and soil responses of an alpine steppe on the Tibetan Plateau to multi-level nitrogen addition

Background

Although plant growth in alpine steppes on the Tibetan Plateau has been suggested to be sensitive to nitrogen (N) addition, the N limitation conditions of alpine steppes remain uncertain.

Methods

After 2 years of fertilization with NH₄NO₃ at six rates (0, 10, 20, 40, 80 and 160 kg N ha^?1 yr^?1), the responses of plant and soil parameters as well as N₂O fluxes were measured.

Results

At the vegetation level, N addition resulted in an increase in the aboveground N pool from 0.5?±?0.1 g m^?2 in the control plots to 1.9?±?0.2 g m^?2 in the plots at the highest N input rate. The aboveground C pool, biomass N concentration, foliar δ¹⁵N, soil NO₃ ^?-N and N₂O flux were also increased by N addition. However, as the N fertilization rate increased from 10 kg N ha^?1 yr^?1 to 160 kg N ha^?1 yr^?1, the N-use efficiency decreased from 12.3?±?4.6 kg C kg N^?1 to 1.6?±?0.2 kg C kg N^?1, and the N-uptake efficiency decreased from 43.2?±?9.7 % to 9.1?±?1.1 %. Biomass N:P ratios increased from 14.4?±?2.6 in the control plots to 20.5?±?0.8 in the plots with the highest N input rate. Biomass N:P ratios, N-uptake efficiency and N-use efficiency flattened out at 40 kg N ha^?1 yr^?1. Above this level, soil NO₃ ^?-N began to accumulate. The seasonal average N₂O flux of growing season nonlinearly increased with increased N fertilization rate and linearly increased with the weighted average foliar δ¹⁵N. At the species level, N uptake responses to relative N availability were species-specific. Biomass N concentration of seven out of the eight non-legume species increased significantly with N fertilization rates, while Kobresia macrantha and the one legume species (Oxytropics glacialis) remained stable. Both the non-legume and the legume species showed significant ¹⁵N enrichment with increasing N fertilization rate. All non-legume species showed significant increased N:P ratios with increased N fertilization rate, but not the legume species.

Conclusions

Our findings suggest that the Tibetan alpine steppes might be N-saturated above a critical N load of 40 kg N ha^?1 yr^?1. For the entire Tibetan Plateau (ca. 2.57 million km²), a low N deposition rate (10 kg N ha^?1 yr^?1) could enhance plant growth, and stimulate aboveground N and C storage by at least 1.1?±?0.3 Tg N yr^?1 and 31.5?±?11.8 Tg C yr^?1, respectively. The non-legume species was N-limited, but the legume species was not limited by N.     

祁连山典型高山灌丛树干茎流特征

2010年6—10月,对祁连山中段托勒南山金露梅、高山柳、沙棘和鬼箭锦鸡儿灌丛树干茎流进行试验观测,研究了高山灌丛树干茎流特征,以及降雨和冠层结构对灌丛树干茎流的影响.结果表明:灌丛产生树干茎流需要2.1mm的前期降雨量;金露梅、高山柳、沙棘和鬼箭锦鸡儿灌丛树干茎流率分别为3.4%、3.2%、8.0%和4.2%,树干茎流量与降雨量之间成显著正线性相关;随着雨量级的增加,树干茎流率呈增加-减少-增加的趋势;4种灌丛茎干集流率分别为59、30、110和49,树干茎流对根际区水分补给作用明显;灌丛树干茎流率与最大10min雨强(I10)呈指数关系,当I10>6.0mm·h-1时,高山柳和沙棘树干茎流率继续增大,而金露梅和高山柳树干茎流率趋于稳定;冠层结构对树干茎流的影响较复杂,相同降雨条件下,株高和投影面积是祁连山高山灌丛树干茎流的主要影响因子.     

Stochastic and deterministic processes together determine alpine meadow plant community composition on the Tibetan Plateau

To predict the consequences of environmental change on the structure and composition of communities, it is necessary to also understand the regional drivers underlying the structuring of these communities. Here, we have taken a hypothesis-based approach to test the relative importance of niche versus neutral processes using niche overlap, species traits and population asynchrony in two crossed treatments of fertilization and grazing in an alpine meadow community. Our results suggested that the observed species biomass overlap was not significantly different between treatments of grazing, grazing × fertilization and grazer exclusion. In contrast, the species biomass overlap was higher than expected in fertilization treatments when grazers were excluded. On the one hand, we found no relationship between species traits and relative abundance in grazing, grazing × fertilization and grazer-exclusion treatments; on the other hand, mechanistic trait-based theory could be used to predict species relative abundance patterns in fertilization treatments when grazers were excluded. From grazing to fertilization, when grazers were excluded, there was a slight increase in species synchrony, which indicated that the complementary dynamic of species gradually changed from complete independence into synchronously fluctuating with increasing fertilization. Based on the above results, we concluded that stochastic and deterministic processes formed ends of a continuum from grazing to fertilization when grazers were excluded in an alpine meadow plant community, and the importance of niche differences between species in structuring grassland communities increased with increasing fertilization and decreased with grazing.     

青藏高原高寒草地植物物种丰富度及其与环境因子和生物量的关系

在青藏高原进行了大范围的群落调查 ,研究高原的两种主要草地群落类型———高寒草甸和高寒草原的植物物种丰富度及其变化。结果表明 :(1)在 5 0个样地 2 5 0个 1m× 1m的样方中 ,共出现 2 6 7种植物 ,其中高寒草甸179种 ,高寒草原 135种。在高寒草甸 ,1m2 样方内物种数最多为 32种 ,最少的仅为 3种 ;在高寒草原 ,物种数最多为 18种 /m2 ,最少的仅为 2种 /m2 。 (2 )物种丰富度随经度和纬度的增加呈增加趋势 ;随海拔的上升呈减少趋势。对物种丰富度与环境因子之间进行逐步回归 ,发现物种丰富度与生长季降水和温暖指数呈显著正相关。 (3)物种丰富度与地上生物量呈显著正相关。     

Effects of disturbance intensity on seasonal dynamics of alpine meadow soil seed banks on the Tibetan Plateau

Background and Aims

Information on soil seed bank processes is crucial for understanding vegetation dynamics. Despite the documented importance of soil seed banks in many ecosystems, their role is not fully understood in some sensitive habitats, such as the alpine meadows of the Tibetan Plateau.

Methods

We studied the seasonal dynamics of the germinable soil seed bank under four disturbance intensities in an alpine meadow on the Tibetan Plateau as well as seed size distribution relative to disturbance intensity. Composition of the seed bank was compared with that of the standing vegetation.

Results

Density of buried seeds increased with disturbance intensity, but species richness and species diversity decreased. Seed density and species richness of the seed bank varied seasonally in all layers (0–2, 2–7, 7–12 cm) and the whole (0–12 cm). The species composition of seed bank was not significantly influenced by season. There was no trend in seed size distribution as disturbance increased. Seasonal seed bank turnover rates increased with increase in disturbance. The result of the NMDS showed that species composition of seed bank and vegetation exhibited a fairly uniform pattern in each season.

Conclusions

Although as a whole the species composition of the vegetation and seed bank showed a relatively low degree of similarity in each season, similarity was highest in the most disturbed habitat. There was no alteration in species composition of seed bank regardless of disturbance intensity, but seed density decreased as disturbance increased. Disturbances in alpine plant communities might increase persistence of regeneration niches. Regeneration from the seed bank together with vegetative reproduction contributed to aboveground vegetation in highly disturbed habitats. Clonal species played an important role in regeneration of vegetation in slightly disturbed areas, where there was little contribution of ruderals from soil seed banks.     

Methanotrophic community structure and activity under warming and grazing of alpine meadow on the Tibetan Plateau

Knowledge about methanotrophs and their activities is important to understand the microbial mediation of the greenhouse gas CH₄ under climate change and human activities in terrestrial ecosystems. The effects of simulated warming and sheep grazing on methanotrophic abundance, community composition, and activity were studied in an alpine meadow soil on the Tibetan Plateau. There was high abundance of methanotrophs (1.2–3.4 × 10⁸ pmoA gene copies per gram of dry weight soil) assessed by real-time PCR, and warming significantly increased the abundance regardless of grazing. A total of 64 methanotrophic operational taxonomic units (OTUs) were obtained from 1,439 clone sequences, of these OTUs; 63 OTUs (98.4%) belonged to type I methanotrophs, and only one OTU was Methylocystis of type II methanotrophs. The methanotroph community composition and diversity were not apparently affected by the treatments. Warming and grazing significantly enhanced the potential CH₄ oxidation activity. There were significantly negative correlations between methanotrophic abundance and soil moisture and between methanotrophic abundance and NH₄–N content. The study suggests that type I methanotrophs, as the dominance, may play a key role in CH₄ oxidation, and the alpine meadow has great potential to consume more CH₄ under future warmer and grazing conditions on the Tibetan Plateau.     

施肥和刈割对青藏高原东部高寒草甸群落生物量补偿效应的影响

通过对青藏高原东部高寒草甸植物群落在4个施肥处理及7个刈割水平下的群落生物量、物种丰富度和补偿指数的比较,分析了该类草甸群落主要特征对施肥及刈割强度差异的响应.结果表明:施肥显著增加了群落生物量,并降低物种丰富度,而刈割处理虽然增加了物种丰富度,但对群落生物量无显著影响;随着施肥量的增加,高寒草甸由莎草科和杂草类物种占优势的群落构成逐渐向禾本科物种占优势的群落构成转变;施肥可提高群落的补偿能力,在不同施肥梯度中,刈割后植物群落补偿能力也不相同;随着施肥量的增加,增加刈割强度,减少刈割次数,发生超补偿的机率增大;可见,施肥是主效应,刈割对群落主要特征的影响随营养水平的不同而发生变化.     

Indicator of flower status derived from in situ hyperspectral measurement in an alpine meadow on the Tibetan Plateau

Flowering status including flowering date and flower amount could reflect ecological process in assessing plant phenological response to global warming. However, little information is available so far for monitoring flowering status through remote sensing. To provide an ecological indicator for monitoring plant phenology from remotely sensed data, we conducted a field survey in an alpine meadow on the Tibetan Plateau where flower color in July is dominantly yellow due to flowering of Halerpestes tricuspis (Ranunculaceae). We used flower coverage to indicate the flowering status of this species and proposed a flower index derived from in situ hyperspectral data (HFI) to estimate the flower coverage. Results demonstrate that the flower coverage of H. tricuspis can be estimated with high accuracy from the hyperspectral measurements. The indicating ability was further improved when the flower coverage was higher than 0.10 or the fractional coverage of soil was low or known in advance. A simulation also shows that a quadrat or pixel with flower coverage higher than 0.066 can be detected with existence of flower by HFI if soil fraction is less than 50%. These results indicate that HFI is applicable for estimating flower coverage of this species from hyperspectral measurement. The study suggests that the hyperspectral remote sensing technique can be applied for monitoring flowering status, and therefore the technique can provide an important ecological indicator for monitoring plant phenology.