Yanming Gong

Responses of CH4, CO2 and N2O fluxes to increasing nitrogen deposition in alpine grassland of the Tianshan Mountains

To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH(4), CO(2) and N(2)O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH(4) uptake, CO(2) and N(2)O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO(2) and N(2)O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO(2) and N(2)O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO(2) and N(2)O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers.

A Multiyear Assessment of Air Quality Benefits from China’s Emerging Shale Gas Revolution: Urumqi as a Case Study

China is seeking to unlock its shale gas in order to curb its notorious urban air pollution, but robust assessment of the impact on PM2.5 pollution of replacing coal with natural gas for winter heating is lacking. Here, using a whole-city heating energy shift opportunity offered by substantial reductions in coal combustion during the heating periods in Urumqi, northwest China, we conducted a four-year study to reveal the impact of replacing coal with natural gas on the mass concentrations and chemical components of PM2.5. We found a significant decline in PM2.5, major soluble ions and metal elements in PM2.5 in January of 2013 and 2014 compared with the same periods in 2012 and 2011, reflecting the positive effects on air quality of using natural gas as a heating fuel throughout the city. This occurred following complete replacement with natural gas for heating energy in October 2012. The weather conditions during winter did not show any significant variation over the four years of the study. Our results indicate that China and other developing nations will benefit greatly from a change in energy source, that is, increasing the contribution of either natural gas or shale gas to total energy consumption with a concomitant reduction in coal consumption.

Response of alpine grassland to elevated nitrogen deposition and water supply in China.

Species composition and productivity are influenced by water and N availability in semi-arid grasslands. To assess the effects of increased N deposition and water supply on plant species composition and productivity, two field experiments with four N addition treatments, and three N and water combination treatments were conducted in alpine grassland in the mid Tianshan mountains, northwest China. When considering N addition alone, aboveground biomass (AGB) of forbs (FAGB) responded less to N addition than AGB of grasses (GAGB). GAGB increased as an effect of N combined with water addition but FAGB did not show such an effect, reflecting a stronger response of grasses to the interaction of water availability and N than forbs. Under all treatments, N allocation to the aboveground tissue did not change for either forbs or grasses. N deposition and water addition did not alter species richness in the present study. These results suggest that N addition generally promoted AGB but had little effect on species richness in wet years. Snowfall in winter combined with rainfall in the early growing season likely plays a critical role in regulating plant growth of the subsequent year in the alpine grassland.

Fluxes of methane, carbon dioxide and nitrous oxide in an alpine wetland and an alpine grassland of the Tianshan Mountains, China

Methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) are known to be major greenhouse gases that contribute to global warming. To identify the flux dynamics of these greenhouse gases is, therefore, of great significance. In this paper, we conducted a comparative study on an alpine grassland and alpine wetland at the Bayinbuluk Grassland Eco-system Research Station, Chinese Academy of Sciences. By using opaque, static, manual stainless steel chambers and gas chromatography, we measured the fluxes of CH4, N2O and CO2 from the grassland and wetland through an in situ monitoring study from May 2010 to October 2012. The mean flux rates of CH4, N2O and CO2 for the experimental alpine wetland in the growing season (from May to October) were estimated at 322.4 μg/(m2·h), 16.7 μg/(m2·h) and 76.7 mg/(m2·h), respectively; and the values for the alpine grassland were −88.2 μg/(m2·h), 12.7 μg/(m2·h), 57.3 mg/(m2·h), respectively. The gas fluxes showed large seasonal and annual variations, suggesting weak fluxes in the non-growing season. The relationships between these gas fluxes and environmental factors were analyzed for the two alpine ecosystems. The results showed that air temperature, precipitation, soil temperature and soil moisture can greatly influence the fluxes of CH4, N2O and CO2, but the alpine grassland and alpine wetland showed different feedback mechanisms under the same climate and environmental conditions.

Carbon storage and vertical distribution in three shrubland communities in Gurbantünggüt Desert, Uygur Autonomous Region of Xinjiang, Northwest China

This study was carried out in the Gurbantünggüt Desert, Uygur Autonomous Region of Xinjiang, Northwest China in August, 2009. To quantify the storage, contribution and vertical distribution patterns of plant biomass carbon (PBC) and soil organic carbon (SOC) in the study area, we investigated the carbon concentrations and its vertical distribution in three different desert shrubland communities dominated by Reaumuria soongorica, Haloxylon ammodendron + R. soongorica and Tamarix ramosissima + R. soongorica, respectively. We analyzed vertical distribution of root biomass carbon and soil carbon contents by excavating soil profiles for each dominated community. The results show that SOC is considerably the larger carbon pool in the soil layers of 1.0–3.0 m (the mean value of three shrubland communities is 38.46%) and 3.0–5.0 m (the mean value is 40.24%). In contrast, 70.74% of belowground biomass carbon storage in 0–1.0 m layer, and its content decrease with increasing soil depth. The Haloxylon ammodendron + R. soongorica shrubland community has the highest belowground biomass carbon among three selected communities. This study highlights the importance of SOC stored in deep soil layers (lower than 3.0 m from the surface) in arid shrubland communities in the global carbon balance. In addition, it provides the data support for revealing deep soil solid carbon potential, and offers scientific basis for the further research in the carbon cycle of terrestrial ecosystem.

Volume fractal dimension of soil particles and relationships with soil physical-chemical properties and plant species diversity in an alpine grassland under different disturbance degrees

Fractal geometry is an important method in soil science, and many studies have used fractal theory to examine soil properties and the relationships with other eco-environmental factors. However, there have been few studies examining soil particle volume fractal dimension in alpine grasslands. To study the volume fractal dimension of soil particles (D) and its relationships with soil salt, soil nutrient and plant species diversity, we conducted an experiment on an alpine grassland under different disturbance degrees: non-disturbance (N0), light disturbance (L), moderate disturbance (M) and heavy disturbance (H). The results showed that (1) Ds varied from 2.573 to 2.635 among the different disturbance degrees and increased with increasing degrees of disturbance. (2) Shannon-Wiener diversity index, Pielou’s evenness index and Margalef richness index reached their highest values at the M degree, indicating that moderate disturbance is beneficial to the increase of plant species diversity. (3) In the L and M degrees, there was a significant positive correlation between D and clay content and a significant negative correlation between D and soil organic matter (SOM). In the H degree, D was significantly and positively correlated with total salt (TS). The results suggested that to a certain extent, D can be used to characterize the uniformity of soil texture in addition to soil fertility characteristics. (4) For the L degree, there was a significant negative correlation between D and the Shannon-Wiener diversity index; while for the M degree, there was a significant negative correlation between D and Pielou’s evenness index.

A five-year study of the impact of nitrogen addition on methane uptake in alpine grassland.

It remains unclear how nitrogen (N) deposition affects soil methane (CH4) uptake in semiarid and arid zones. An in situ field experiment was conducted from 2010 to 2014 to systematically study the effect of various N application rates (0, 10, 30, and 90 kg N ha−1 yr−1) on CH4 flux in alpine grassland in the Tianshan Mountains. No significant influence of N addition on CH4 uptake was found. Initially the CH4 uptake rate increased with increasing N application rate by up to 11.5% in 2011 and then there was gradual inhibition by 2014. However, the between-year variability in CH4 uptake was very highly significant with average uptake ranging from 52.9 to 106.6 μg C m−2 h−1 and the rate depended largely on seasonal variability in precipitation and temperature. CH4 uptake was positively correlated with soil temperature, air temperature and to a lesser extent with precipitation, and was negatively correlated with soil moisture and NO3−-N content. The results indicate that between-year variability in CH4 uptake was impacted by precipitation and temperature and was not sensitive to elevated N deposition in alpine grassland.

Impacts of water and nitrogen addition on nitrogen recovery in Haloxylon ammodendron dominated desert ecosystems

Desert ecosystems are likely to change in response to global climate change and nitrogen (N) deposition. The effects of increased precipitation and N deposition on plant growth and the N cycle largely depend on N allocation and N recovery efficiency in the plant-soil ecosystem, but there is limited research on this in desert ecosystems. Here we report results using double-labeled 15NH415NO3 (30 and 60kgNha-1yr-1) as a tracer under ambient (no additional water addition) and enhanced precipitation (60mm water addition) in a Haloxylon ammodendron dominated ecosystem in the Gurbantunggut Desert of Northwest China. Herbaceous plants were a significantly larger sink for added 15N than the H. ammodendron trees, and N retention varied with water and N addition, relative to growing season precipitation. The retention of added 15N varied within the components of H. ammodendron, with the stems retaining most, followed by the assimilation branches. Soil was the dominant sink for added 15N, in which the topsoil and subsoil respond differently to water and N addition over the two-year period. Nitrogen relative recovery percentage in the whole ecosystem ranged from 43% to 61%, lower than average recovery rate in temperate forests; N tracer recovery percentage significantly increased with water addition but decreased with enhanced N deposition. Future N cycling in central Asian deserts will depend on changes in precipitation.

N-P Fertilization Inhibits Growth of Root Hemiparasite Pedicularis kansuensis in Natural Grassland

Fertilization has been shown to affect interactions between root hemiparasitic plants and their host plants, alleviating damage to the hosts by parasitism. However, as a majority of studies were conducted in pot cultivation, the influence of fertilizer application on root hemiparasites and the surrounding plant community in field conditions as well as relevant mechanisms remain unclear. We manipulated soil nutrient resources in a semi-arid subalpine grassland in the Tianshan Mountains, northwestern China, to explore the links between fertilization and plant community composition, productivity, survival, and growth of a weedy root hemiparasite (Pedicularis kansuensis). Nitrogen (at a low rate, LN, 30 kg N ha-1 year-1 as urea; or at a high rate, HN, 90 kg N ha-1 year-1 as urea) and phosphorus [100 kg ha-1 year-1 as Ca(H2PO4)2⋅H2O] were added during two growing seasons. Patterns of foliar nutrient balances were described with isometric log ratios for the different plant functional groups receiving these fertilization regimes. Fertilization with LN, HN, and P reduced above-ground biomass of P. kansuensis, with above-ground biomass in the fertilization treatments, respectively, 12, 1, and 39% of the value found in the unfertilized control. Up to three times more above-ground biomass was produced in graminoids receiving fertilizers, whereas forb above-ground biomass was virtually unchanged by the fertilization regimes and forb species richness was reduced by 52% in the HN treatment. Fertilization altered foliar nutrient balances, and distinct patterns emerged for each plant functional group. Foliar [C | P,N] balance in the plant community was negatively correlated with above-ground biomass (P = 0.03). The inhibited competitiveness of P. kansuensis, which showed a much higher [C | P,N] balance, could be attributed to reduced C assimilation rather than mineral nutrient acquisition, as shown by significant increase in foliar N and P concentrations but little increase in C concentration following fertilization.