Effects Of Precipitation Exclusion On Soil Respiration And Microbial Community In A Natural Castanopsis Carlesii Forest

Effects of precipitation exclusion on soil respiration and microbial community composition were studied in a natural Castanopsis carlesii forest, located at nature reserve of Castanopsis in Sanming, Fujian. There were three treatments in situ:1) 30% precipitation reduction (T1); 2) 60% precipitation reduction (T2);3) normal rainfall (control, CK). The effect of soil water content on soil organic carbon mineralization and microbial community in a natural C. carlesii forest were also estimated through laboratory incubation. This study will help illustrating the effect of precipitation exclusion on soil respiration and its mechanism. There were two incubation experiments. Firstly, soil incubation was in four soil moisture contents:1) 10% of water holding capacity (10%WHC); 2) 30% of water holding capacity (30%WHC); 3) 60% of water holding capacity (60%WHC); 4) 80% of water holding capacity (80%WHC). Secondly, alternate drying and wetting incubation:1) alternate drying and wetting (30%WHC-80%WHC); 2) constant drought (30%WHC) 3); constant humidity (80%WHC). The results showed that: (1) the patterns of monthly soil respiration rates in three treatments were similar. Mean annual soil respiration rate was characterized by T2> T1> CK. There were no significant differences in soil respiration rate and annual CO2 flux between the three treatments. (2) The precipitation exclusion treatment effects on soil microbial community were mainly on the 0-10 cm soil layer. The principal component analysis showed that soil microbial community in 0-10 cm soil layer in 30% precipitation reduction treatment was different significantly from those in 60% precipitation reduction and control in November 2013. But in April 2014 and September 2014, there was no significant difference in soil microbial community of 0-10 cm soil layer between the three treatments. The factor analysis for 17 kinds of phospholipid fatty acids in 0-10 cm soil layer showed that the effects of precipitation exclusion treatments on soil microbial community were characterized by gram-positive bacteria>actinomycetes>arbuscular mycorrhizal fungi>gram-negative bacteria>fungi. (3) Laboratory incubation showed that, the cumulative mineralized carbon increased with the content of soil moisture. The four different water content treatments had great influence on gram-positive bacteria.The cumulative CO2 during the rewetting period was significantly greater than that of drought period. The difference in cumulative CO2 was more significant between treatment times. Factor analysis showed that alternate wetting and drying did not affect soil arbuscular mycorrhizal fungi, gram-negative bacteria and fungi community structure, but had a great influence on actinomycetes and gram-positive bacteria.