Responses Of Soil Microbial Biomass To Simulated Nitrogen Deposition In Pinus Tabulaeformis Forests In The Taiyuemountain, China

Atmospheric nitrogen deposition directly or indirectly affects the reproduction and activity of soil microbes, alters soil microbial structure and function, and also influences soil material transition and nutrient availability. This experiment was conducted in Pinus tabulaeformis forests in the Taiyue Mountain, Shanxi Province to study the responses of soil microbial biomass to simulated nitrogen addition. Nitrogen addition was carried out monthly within the forests since September,2009. Nitrogen treatments included control (CK,0kg N hm-2a-1), low nitrogen (LN,50kg N hm-2a-1), medium nitrogen (MN,100kg N hm-2a-1) and high nitrogen (HN,150kg N hm-2a-1). Soil samples were collected at0-10cm and10-20cm depths in June, August and October respectively in2011. Soil microbial biomass carbon (MBC) and nitrogen (MBN) were measured by chloroform fumigation. The soil MBC and MBN were different between two forest types (P<0.01), soil microbial biomass in natural forest was significantly higher than that in plantation forest. The MBC of0-10cm depth in plantation forest and natural forest varied in the ranges of189.55～358.51mg kg-1,200.64～666.34mg kg-1, MBN varied in the ranges of43.41～～77.21mg kg-1,68.82～151.70mg kg-1. Under the same nitrogen treatment, microbial biomass at0-10cm depth were higher than that at10-20cm depth (P<0.01). Nitrogen deposition did not showany effect on soil MBC (P>0.05) whereas affected soil MBN significantly (P<0.01). Soil MBC changed significantly with the season (P<0.01), with the highest MBC in June followed by August and October, but MBN changed little (P>0.05).