Response Of Soil Microbial Communities To Drought And Elevated CO₂under The Background Of Climate Change

Microorganisms play a key role in the response of soil ecosystems to the rising atmospheric carbon dioxide and drought as they mineralize organic matter and drive nutrient cycling. Using phytotron growth chambers, a short-term pot experiment under bare soil and soil with soybean was conducted to investigate the individual and interactive effects of elevated carbon dioxide (700±50μmol mol-1vs. ambient) and different levels of soil moisture (80%,60%, and40%WHC) on soil microbial in a stagnic anthrosol. The objective of this study was to understand how microbial community structure and soil enzymatic activity profiles were affected elevated CO2under different soil moisture regimes. The results were mainly concluded as below.(1) LI-6400analyzer was used to determine the physiological properties of soybean and the biomass was measured under drought and elevated CO2. Results show that the photosynthetic rate of soybean was significantly promoted by elevated CO2, which had relieved the inhibition of drought on photosynthesis. By regulating of the stomata, elevated CO2had inhibited the transpiration of soybean, thus the water use efficiency was improved and mitigated the negative effects of drought on microbial community. Root biomass of plant was tend to be increased by elevated CO2which had no significant impact on the shoot biomass due to the restriction of soil nutrigen. Drought and elevated CO2tended to allocat the carbon to root.(2) The response of soil nutrient properties under drought and elevated CO2were analyzed and the results show that an increasing concentration of dissolved organic carbon (DOC) were found under drought. There was no significant effect of elevated CO2on DOC. Elevated CO2lead to an increase of carbon input from plant and the soil nitrogen was unavailable, thus there would be a high C:N ratio. There was no impact of soil moisture on soil C:N ratio.(3) The response of soil microbial biomass and the soil enzyme activities were meatured under drought and elevated CO2. The results show that there were no significant effects of drought on soil microbial biomass carbon (MBC) which were mainly due to the restriction of soil nutrient. Drought had an negative effect on soil MBC. The input of plant would aggravate the drought stress under severe drought, which were probably due to some unknow root exudate would stop the fungi growth. Elevated CO2could stimulate the activity of soil invertase and catalase and increased the microbial activity significantly. The soil enzymes could accelerate the degradation of soil organic matter (SOM) and the turn-over rate of soil carbon pools. Drought had a significant negative effect on soil enzymes which would slow down the soil carbon pool turn over.(4) PCR-DGGE was used to reseach the response of soil microbial community structure under drought and elevated CO2. The results show that elevate CO2had a small impact on the soil and rhizosphere microbial community structure. There were some new species and some old ones were disappeared. But most of the exsisted species were unaffected. Shannon-Wiener diversity index (H’), Pielou index (E), Simpson index (D) and Mclntonsh index (DMc) were calculated and demonstrated a small impact of elevated CO2on soil microbial community structure. The soil microbial community abundance and evenness were affected mostly by drought. The bacteria abundance decreased and the fungi abundanc increased as fungi were more adaptable under drought.(5) Metabolic characteristics of the soil microbial community were determined using31C substrates on Biolog-EcoPlateTM. Community level physiological profile (CLPP) was assessed by calculating average well color development (AWCD) and4diversity index. The results show that drought apparently restrain the metabolic activity of soil microbial. The soil function diversity were decreased. However, there were no effect of drought on carbon utilization profile of soil microbial. There were a small impact of elevated CO2on soil microbial function diversity. By analyzing the carbon utilization profile we can conclude that the soil microbial tend to use carbohydrate instead of carbohydrate under elevated CO2. Most of the microbial tend to use carbohydrate, carbohydrate, amine and esters.