| Nitrogen deposition is global,including northwest loess hilly-gully region that is the sensitive ecological environment in our country suffered the serious effects of nitrogen deposition,so the research about the response of this ecological environment for nitrogen deposition is particularly urgent.This test selected the artificial Pinus tabulaeformis forest,which is a typical forest ecosystem in the loess hilly-gully region ecosystems,as the research object for the experiment of simulated nitrogen deposition in the wild.There are 4 levels of nitrogen addition treatments: 0(CK),3(N3),6(N6),9(N9)g N·m-2·a-1.Soil organic carbon,soil water soluble organic matter,soil microbial community characteristics and soil ecological stoichiometry were studied.The main conclusions are as follows:(1)Components of C1 and C2 can be more sensitively reflect the effects of nitrogen addition to soil carbon pool;Short-term nitrogen addition can change soil carbon pool,but does not increase soil carbon activity;Nitrogen addition will affect components in the upper soil by influencing the soil total nitrogen and organic matter content,also as leaching action change the properties in the lower soil to affect the different carbon components.(2)Nitrogen addition increases the water soluble total nitrogen and the water soluble nitrate nitrogen content,reduces the water soluble organic nitrogen content,but has little effect on water soluble ammonium nitrogen;Nitrogen addition increases the content of water soluble organic carbon in the upper soil,when it reached a certain threshold can be producing inhibition;However,nitrogen addition has no significant effect on water soluble organic carbon in the lower soil.After three dimensional fluorescence analysis,we can know that the water soluble organic matter in the region is mainly composed of high molecular weight aromatic humus and related humus,and they are significantly reduced under the addition of nitrogen.(3)Short-term nitrogen addition increases the content of total PLFA in soil,bacterial PLFA and G-PLFA,only the content of PLFA in the lower soil is inhibited by high nitrogen addition treatment.(4)The middle nitrogen addition treatment increases the utilization ratio of the microbial community to the carbon source,and the high nitrogen addition treatment can inhibit it.Nitrogen addition can improve the utilization efficiency of bacterial community to carbohydrate,phenolic compounds and amine compounds.(5)The addition of nitrogen changes the structure of bacterial community,and the increase of bacterial diversity by nitrogen deposition has a threshold limit,that is,the effect of low concentration nitrogen addition on bacterial community structure is relatively small,the variation of bacterial community is greatest with the addition of medium concentration nitrogen,however,the nitrogen addition of high concentration inhibits the soil bacterial community.In the Pinus tabulaeformis forest land soil,the Proteobacteria and Acidobacteria are the main groups,Acidobacteria is negatively related with soil nitrogen content,and the Acidobacteria reduces with the increase of nitrogen deposition after rise.(6)Our data indicated that the soil microbial communities of this ecosystem are limited by N and co-limited by P at N3 and N6(when SOC content was significantly higher).Enzymatic activities and most ecoenzymatic stoichiometries do not differ significantly along the N-addition gradient,the activities of the ecoenzymes for acquiring organic N and organic P scale with the activity of the ecoenzyme for acquiring C,with patterns of allocation to nutrient acquisition similar to the global pattern.N addition do not generally interfere with soil microbial homeostasis.Our findings also suggest that the contents of resources(SOC,TN and TP)and relative concentrations(stoichiometries)have an impact on the soil microbial communities. |
PDF Full Text Request