Abstract
Atmospheric nitrogen (N) deposition profoundly alters the soil microbial communities and will thus affect nutrient cycles. The effects of N availability on microbial community, however, are not clear. We used PLFA analysis to evaluate the effects of a gradient of N addition (0, 2.8, 5.6, 11.2, and 22.4 g N m-2 y-1) for three years on the rhizospheric microbial community of Pinus tabuliformis seedlings. The main factors influencing the community were quantified using structural equation modelling and redundancy analysis. At the microbial-community level, N addition increased the total phospholipid fatty acids content by increasing the dissolved organic carbon (DOC) and root biomass. Increases in soil microbial biomass carbon and N, however, was attributed to the increased DOC, N content and decreased pH. At the microbial-groups level, Fungal, arbuscular mycorrhizal fungal (AMF), gram-positive bacterial (GP) abundances and the GP:GN ratio first increased and then decreased with N addition. Nitrogen addition increased the abundances of bacteria, fungi, and actinomycetes mainly by increasing the DOC content and decreasing root biomass. Additionally, the decrease of pH and ammonium N caused by N addition increased the fungal abundances and reduced actinomycete abundances, respectively. Nitrogen addition shifted the rhizospheric microbial community mainly by altering the DOC content and root biomass. The current rate of N deposition (2.5 g N m-2 y-1) benefits plant growth and increases the abundances of fungi, arbuscular mycorrhizal fungi, GP, actinomycetes and the GP:GN ratio.
Highlights
Recent anthropogenic activities have dramatically increased the levels of available nitrogen (N) in soil ecosystems [1] and have substantially changed soil microbial communities in forest ecosystems
Aboveground and root biomasses had similar hump-shaped responses to increasing N addition, peaked at 5.6 g N m-2 y-1 (Table 1). pH was decreased at the level of 22.4 g N m-2 y-1, significantly
Lower levels of N addition had no significant influence on the microbial biomass C (MBC) ( 11.2 g N m-2 y-1) or microbial biomass N (MBN) ( 5.6 g N m-2 y-1) content, but higher levels increased both MBC (22.4 g N m-2 y-1) and MBN (!11.2 g N m-2 y-1) content (Table 1)
Summary
Recent anthropogenic activities (e.g. fossil-fuel combustion and application of artificial fertilisers) have dramatically increased the levels of available nitrogen (N) in soil ecosystems [1] and have substantially changed soil microbial communities in forest ecosystems. Changes in the composition of soil microbial communities, especially those of rhizospheric microbes, can PLOS ONE | DOI:10.1371/journal.pone.0172382. Nitrogen addition and the microbial community structure Changes in the composition of soil microbial communities, especially those of rhizospheric microbes, can PLOS ONE | DOI:10.1371/journal.pone.0172382 February 24, 2017
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