Peng Luo

Determinants influencing seasonal variations of methane emissions from alpine wetlands in Zoige Plateau and their implications

To understand the seasonality of methane flux from alpine wetlands in Zoige Plateau, 30 plots were set to measure the methane emissions in the growing and nongrowing seasons in three environmental types: dry hummock (DH), Carex muliensis (CM), and Eleocharis valleculosa (EV) sites. There were clearly seasonal patterns of methane flux in different environmental types in the growing and nongrowing seasons. Mean methane emission rate was 14.45 mg CH4 m(-2) h(-1) (0.17 to 86.78 mg CH4 m(-2) h(-1)) in the growing season, and 0.556 mg CH4 m(-2) h(-1) (0.002 to 6.722 mg CH4 m(-2) h(-1)) in the nongrowing season. In the growing season, the main maximum values of methane flux were found in July and August, except for a peak value in September in CM sites. In the nongrowing season, the similar seasonal variation pattern was shared among all the three sites, in which the methane emissions increased from February to April. In the growing season, the determining factors were surface temperatures (r(2) = 0.55, P < 0.05), standing water depths (r(2) = 0.32, P < 0.01) and plant community heights (r(2) = 0.61, P < 0.01), while in the nongrowing season, ice thickness (r(2) = 0.27, P < 0.05; in CM and EV sites) was found most related to flux. In our understanding, the seasonality of methane emissions in our study areas was temperature- and-plant-growth-dependent, and the water table position was also very important to shape the temperature- and-plant-growth-dependent seasonal variation of flux with its vigorous variations in alpine wetland ecosystems. Different environmental types within the wetland also influenced the seasonal pattern of methane flux. For an accurate estimate of the global methane source strength of alpine wetlands, the pronounced seasonal or even temporal variability in methane emission from alpine wetlands should be taken into consideration.

Spatial variations on methane emissions from Zoige alpine wetlands of Southwest China.

This study was aimed to understand the spatial variation of CH(4) emissions from alpine wetlands in Southwest China on a field-scale in two phenological seasons, namely the peak growing season and the spring thaw. Methane emission rates were measured at 30 plots, which included three kinds of environmental types: dry hummock, Carex muliensis and Eleocharis valleculosa sites. There were highly spatial variations of methane emissions among and within different environmental types in both phenological seasons. Mean methane emission rates ranged from 1.1 to 37.0 mg CH(4) m(-2) h(-1) in the peak growing season and from 0.004 to 0.691 mg CH(4) m(-)(2) h(-1) in the spring thaw. In the peak growing season, coefficients of variation (CV) averaged 38% among environmental types and 64% within environmental types; while in the spring thaw, CV were on the average 61% among environmental types and 96% within environmental types. The key influencing factors were the standing water table and the plant community height in the peak growing season, while in the spring thaw, no significant correlations between factors and methane emissions were found.

Predominance of Precipitation and Temperature Controls on Ecosystem CO2 Exchange in Zoige Alpine Wetlands of Southwest China

Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured at Zoige wetland using the eddy covariance technique. Analysis of CO2 fluxes in twoxa0years showed Zoige wetland was a net CO2 sink of −47.1 and −79.7xa0gu2009C m−2 a−1 in 2008 and 2009, respectively. The peak NEE value was −0.54xa0mg CO2 m−2 s−1 (the negative value signifies net ecosystem carbon gain from air). The maximal daily integrated NEE was −4.1xa0gu2009C m−2 d−1 during the peak growth season (from July to August). Gross ecosystem photosynthesis was likely more variable than ecosystem respiration at both seasonal and interannual timescales in this wetland. Our data strongly suggested that the combination of precipitation and temperature, as well as phenological stage of vegetation, controlled the dynamics of ecosystem carbon gain, even in drought years. Therefore, an accurate representation of these parameters in climate models is critical to the success of forecasting carbon budgets of alpine wetlands.

Agricultural heritage in disintegration: Trends of agropastoral transhumance on the southeast Tibetan Plateau

This paper examines agropastoral transhumance in 12 sampled villages on the southeast Tibetan Plateau. By analysing trends in this indigenous livelihood system and examining causes and potential consequences, we conclude that Tibetan agropastoral transhumance is a fragile system extremely vulnerable to external impacts. Within the context of Chinas rapid development and globalisation, this agricultural heritage is changing rapidly, as is most saliently reflected in herd size and structure, movement patterns, relative economic importance of pastoral activities and the relations between pastoralism and crop cultivation. Immediate causes of changes are local changes in livestock management objectives, land uses and labour availability, which are driven by more fundamental changes of environmental, political, socioeconomic, technological and cultural profiles, from local to global scales. Changes in local livelihood systems can have multifaceted and profound political, socioeconomic, cultural and ecological consequences, in both constructive and destructive terms. Policy-makers and/or project designers must have a holistic perspective so as to integrate multiple objectives of promoting sustainable socioeconomic development, preserving biological and cultural diversities and maintaining the environmentally stable balance of human society, animal population and ecosystem that has existed in the area for centuries.

Different growth and physiological responses to experimental warming of two dominant plant species Elymus nutans and Potentilla anserina in an alpine meadow of the eastern Tibetan Plateau

The effects of experimental warming on the growth and physiology of grass Elymus nutans and forb Potentilla anserina were studied by using open-top chambers (OTCs) in an alpine meadow of the eastern Tibetan Plateau. The warming treatment increased mean air and soil surface temperatures by 1.53°C and 0.50°C, respectively, but it reduced soil relative water content in the surface layer. Experimental warming enhanced the growth and gas exchange of E. nutans, while it reduced those of P. anserina. Experimental warming resulted in an increased efficiency of photosystem II (PSII) in E. nutans, while decreasing it in P. anserina; significantly stimulated non-photochemical quenching, antioxidative enzymes and non-enzymes in both species; and significantly reduced malondialdehyde content in E. nutans, while promoting it in P. anserina. The results of this study indicated that the two species showed different growth responses to experimental warming and their different physiological performances further indicated that experimental warming alleviated the negative effect of low temperature on the growth and development of E. nutans, but limited the competitive ability of P. anserina in the study region.

Quantifying the impact of drought on soil-plant interactions: a seasonal analysis of biotic and abiotic controls of carbon and nutrient dynamics in high-altitudinal grasslands

Background and aimsUnderstanding the impacts of ever more severe and widespread drought events has become a central focus of recent ecological research. Accordingly, the objective of this study is to investigate fundamental mechanisms that control drought effects on climate sensitive ecosystems by regulating soil-plant interactions.MethodsField experiments were conducted in high altitudinal grasslands of the Tibetan Plateau. Based on historical records, we simulated extreme drought events, intercepting water inputs in early (spring), mid (summer), and late (autumn) periods of the plant-growing season (PGS). We measured vegetation responses to changes in soil physical, chemical, and biological properties, examining how the interplay of abiotic and biotic processes regulate the impacts of drought above and below ground.ResultsDecreasing water input resulted in proportional increases in summer and autumn soil temperature, but reduced soil temperature during the spring drought. As a result, soil microbial biomass and available N and P concentrations remained stable during the early-PGS drought, while enzymatic activity, decomposition of organic materials, and nutrient release increased during the mid- and late-PGS. Concerted changes in microbial and plant activity determined seasonal fluctuations in carbon assimilation, microbial activity and nutrient dynamics, with varying degrees of resistance and resilience to drought stress observed at different PGS periods.ConclusionsSignificant interactions were observed between plant productivity and microbial activity in response to moisture variability and associated changes in soil temperature, with the largest deleterious drought effects registered during the summer, when competition for limiting resources between plants and microorganisms was strongest.

Ecosystem Evapotranspiration as a Response to Climate and Vegetation Coverage Changes in Northwest Yunnan, China.

Climate and human-driven changes play an important role in regional droughts. Northwest Yunnan Province is a key region for biodiversity conservation in China, and it has experienced severe droughts since the beginning of this century; however, the extent of the contributions from climate and human-driven changes remains unclear. We calculated the ecosystem evapotranspiration (ET) and water yield (WY) of northwest Yunnan Province, China from 2001 to 2013 using meteorological and remote sensing observation data and a Surface Energy Balance System (SEBS) model. Multivariate regression analyses were used to differentiate the contribution of climate and vegetation coverage to ET. The results showed that the annual average vegetation coverage significantly increased over time with a mean of 0.69 in spite of the precipitation fluctuation. Afforestation/reforestation and other management efforts attributed to vegetation coverage increase in NW Yunnan. Both ET and WY considerably fluctuated with the climate factors, which ranged from 623.29 mm to 893.8 mm and –51.88 mm to 384.40 mm over the time period. Spatially, ET in the southeast of NW Yunnan (mainly in Lijiang) increased significantly, which was in line with the spatial trend of vegetation coverage. Multivariate linear regression analysis indicated that climatic factors accounted for 85.18% of the ET variation, while vegetation coverage explained 14.82%. On the other hand, precipitation accounted for 67.5% of the WY. We conclude that the continuous droughts in northwest Yunnan were primarily climatically driven; however, man-made land cover and vegetation changes also increased the vulnerability of local populations to drought. Because of the high proportion of the water yield consumed for subsistence and poor infrastructure for water management, local populations have been highly vulnerable to climate drought conditions. We suggest that conservation of native vegetation and development of water-conserving agricultural practices should be implemented as adaptive strategies to mitigate climate change.

A study of soil-dynamics based on a simulated drought in an alpine meadow on the Tibetan Plateau

Extreme weather events have played an important role in driving the ecosystem dynamics in high altitude areas, but the underlying mechanism remains unclear. To understand if and how the soil processes of an ecosystem react to extreme drought, we manipulated a once-in-a-century meteorological extreme drought in an alpine meadow on the Tibetan Plateau, which is also known as the “forerunner of global weather changes”. The extremity was determined by statistical extreme weather events with respect to a historical reference period from April to September during 1962–2004, where the local historical precipitation data was calculated and intensified to 100-year recurrent drought event with Gumbel I distribution. The indicators we measured included soil microbial biomass C/N/P and soil enzymatic activities of phosphatase (AP) disbounding organic phosphate, cellobiohydrolase (CBH), β-glucocidase (BG), N-releasing enzyme N-acetylglucosaminidase (NAG) as well as soil respirations, during and after the treatments. It was found that the manipulated event induced a rapid shift in microbial biomass and activities, indicating a lower resistance of the underground process. However, the microbial and biochemical parameters saw rapid recovery after the event, which meant the soil processes enjoyed high resilience. The high responsiveness and lag-time effects of the soil indicators rendered new horizons for us to evaluate the interaction between the extremes and the ecosystem stability. Our study indicated that the once-in-a-century extreme drought induced very short term response in the soil biotic process, and the soil processes worked to buffer against such events under the observation period.

Nitrification and denitrification in an alpine meadow soil of the eastern Tibetan Plateau

Nitrification and denitrification represent two of the main biological processes involved in the N cycle, which contribute to the regulation of NO3 availability to plants reduction to N2 (Vitousek et al., 1982; Conen et al., 2000). Moreover, they represent the main source of the greenhouse gas N2O in terrestrial ecosystems (Williams et al., 1992). Both processes are directly limited by substrate availability (NH4 , NO3 , organic C) and low temperatures, and indirectly by water content and soil capacity to retain water (Granli & Bøkman, 1994). In an alpine meadow ecosystem on the Tibetan Plateau, being characterized by an extreme climate with low temperatures and a short vegetation season, inorganic (available) N is usually present in low concentrations, although alpine meadow soils are noted for their large quantities of total N; most of this resides in organic (unavailable) form (Cao & Zhang, 2001). Therefore, knowledge of N transformation in highly N limited and fragile alpine ecosystems is necessary for managing both the N supply to the pasture grass crop and the potential N losses to the environment. However, there are no available data on soil nitrification and denitrification activities in the region. In this study we measured the seasonal dynamics of nitrification and denitrification in an alpine meadow soil on the eastern Tibetan Plateau.

Different responses of alpine plants to nitrogen addition: effects on plant-plant interactions

The different responses of plant species to resource stress are keys to understand the dynamics of plant community in a changing environment. To test the hypothesis that nitrogen (N) increase would benefit N competitive species, rather than N stress-tolerant species, to compete with neighbours, we conducted an experiment with neighbour removal, N addition and soil moisture as treatments in an alpine grassland on the southeastern Tibetan Plateau. Both growths and competitive-response abilities (CRA, the ability to tolerate the inhibitory effects of neighbors) of Kobresia macrantha, Polygonum viviparum and Potentilla anserine in wet site were facilitated by N addition, conversely, both growths and CRA of Taraxacum mongolicum and Ligularia virgaurea were suppressed by N addition, indicating that the responses of CRA of target species under N addition were consistent with the N utilization strategies of them. Moreover, the facilitative effects of N addition on competitive-response abilities of Kobresia macrantha and Polygonum viviparum were not found at the dry site, illustrating that soil moisture can alter the changes of neighbour effects caused by N addition. Life strategy of dominant species in plant community on the undisturbed southeastern Tibetan Plateau may shift from N stress-tolerant to N competitive, if the N increases continuously.