Geng Sun

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.

Effects of Warming on Chlorophyll Degradation and Carbohydrate Accumulation of Alpine Herbaceous Species during Plant Senescence on the Tibetan Plateau

Plant senescence is a critical life history process accompanied by chlorophyll degradation and has large implications for nutrient resorption and carbohydrate storage. Although photoperiod governs much of seasonal leaf senescence in many plant species, temperature has also been shown to modulate this process. Therefore, we hypothesized that climate warming would significantly impact the length of the plant growing season and ultimate productivity. To test this assumption, we measured the effects of simulated autumn climate warming paradigms on four native herbaceous species that represent distinct life forms of alpine meadow plants on the Tibetan Plateau. Conditions were simulated in open-top chambers (OTCs) and the effects on the degradation of chlorophyll, nitrogen (N) concentration in leaves and culms, total non-structural carbohydrate (TNC) in roots, growth and phenology were assessed during one year following treatment. The results showed that climate warming in autumn changed the senescence process only for perennials by slowing chlorophyll degradation at the beginning of senescence and accelerating it in the following phases. Warming also increased root TNC storage as a result of higher N concentrations retained in leaves; however, this effect was species dependent and did not alter the growing and flowering phenology in the following seasons. Our results indicated that autumn warming increases carbohydrate accumulation, not only by enhancing activities of photosynthetic enzymes (a mechanism proposed in previous studies), but also by affecting chlorophyll degradation and preferential allocation of resources to different plant compartments. The different responses to warming can be explained by inherently different growth and phenology patterns observed among the studied species. The results implied that warming leads to changes in the competitive balance among life forms, an effect that can subsequently shift vegetation distribution and species composition in communities.

Tree growth acceleration and expansion of alpine forests: The synergistic effect of atmospheric and edaphic change

Soil-plant-atmosphere interactions regulate the impact of climate on forest ecosystems. Many forest ecosystems have experienced recent declines in productivity; however, in some alpine regions, tree growth and forest expansion are increasing at marked rates. Dendrochronological analyses at the upper limit of alpine forests in the Tibetan Plateau show a steady increase in tree growth since the early 1900s, which intensified during the 1930s and 1960s, and have reached unprecedented levels since 1760. This recent growth acceleration was observed in small/young and large/old trees and coincided with the establishment of trees outside the forest range, reflecting a connection between the physiological performance of dominant species and shifts in forest distribution. Measurements of stable isotopes (carbon, oxygen, and nitrogen) in tree rings indicate that tree growth has been stimulated by the synergistic effect of rising atmospheric CO2 and a warming-induced increase in water and nutrient availability from thawing permafrost. These findings illustrate the importance of considering soil-plant-atmosphere interactions to understand current and anticipate future changes in productivity and distribution of forest ecosystems.

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.

Unpalatable weed Stellera chamaejasme L. provides biotic refuge for neighboring species and conserves plant diversity in overgrazing alpine meadows on the Tibetan Plateau in China

Steller chamaejasme L. (S. chamaejasme for short) is one of the most noxious unpalatable weeds in China, which has been frequently reported its negative interaction (i.e. competition and allelopathy) with other herbaceous species in grasslands. This study compared species diversity, biomass and sexual reproduction of herbaceous plants in meadows with S. chamaejasme and in open meadows without S. chamaejasme in overgrazing meadows on the Tibetan Plateau in China to determine whether positive facilitation exist between S. chamaejasme and other herbaceous species under livestock’s overgrazing. The results showed that there are more herbaceous species in meadows with S. chamaejasme than those in open meadows (35s and 30s, respectively). Diversity index and above-ground biomass were also significantly higher in meadows with S. chamaejasme. There were 39% (11/28) of all species with sexual reproduction found in meadows with S. chamaejasme, which was 7 times more than those in open meadows. Our study showed that S. chamaejasme could provide biotic refuge for neighboring plants and preserve plant diversity from livestock’s overgrazing in alpine meadows on the Tibetan Plateau. It also suggested that inter-specific facilitation between S. chamaejasme and other herbaceous species may play a key role in overgrazing alpine meadows.

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.

Growth and Reproduction Characteristics of Plant's Kin Recognition in Two Different Lifestyle Species

Some plant species grow with closely genetically related individuals, and may benefit from an ability to recognize kin and show cooperative behavior towards neighbors. Kin recognition has been demonstrated in few plant species till now and thus constrained the understanding of significance of kin recognition. We investigated different growth and reproduction characteristics of kin recognition in two lifestyle species, the annual plant Lolium multiflorum Lam. and the perennial plant Elymus sibiricus Linn., which the main differences between are in their root system types and nutrition demand. We observed less root biomass distribution in kin groups than stranger groups for L. multiflorum Lam., but no indication in shoot characteristics at either the individual level or group level. For E. sibiricus, there were no significant differences in any measured characteristic index between kin and stranger groups at any level. Our results suggest that kin selection or plant responses to kin may depend on plant features and life-form; the most sensitive traits to competition are more likely to respond to kin selection. In addition, we considered that kin selection was tensely associated with degree of competition. It could be that the moderate competition level in our experiment could not stimulate kin cooperation activity of E. sibiricus c 2018 Friends Science Publishers