Abstract: Atmospheric nitrogen (N) deposition is a serious threat to global ecosystems. Soil microbes are sensitive to environmental changes. Investigating the effects of N deposition on soil microbial community structure may provide theoretical basis for scientific management of forest ecosystems. A manipulative field experiment was conducted to investigate the effects of different forms (NH₄NO₃, (NH₄)₂SO₄, NaNO₃) and different levels (0, 50, 150 kg N·hm^-2·a^-1) of N addition on the microbial community structure in a temperate forest soil. Soil microbial community structure was measured using the method of phospholipid fatty acid analysis (PLFA) after three consecutive years of N addition treatments. Our results showed that the amounts of total PLFA, bacterial PLFA, G⁺ bacterial PLFA, G^- bacterial PLFA and fungal PLFA in N addition plots were significantly higher than that in control plots, and N addition increased the amount of microbial PLFA significantly in the order of high N addition > low N addition > control. The amounts of total PLFA, bacterial PLFA, fungal PLFA and actinomyces PLFA in NH₄NO₃N addition plots were generally higher than that in NaNO₃N addition and (NH₄)₂SO₄N addition plots at the same N addition level. Principal component analysis (PCA) showed that microbial community structures were changed in all Nadded plots except the low (NH₄)₂SO₄N addition plots. Overall, these results suggested that N addition would increase soil microbial biomass and change soil microbial community structure in forest soils when N addition level reaches a threshold, at least over the short term.

Key words: geographically weighted regression (GWR), Beijing-Tianjin-Tangshan urban agglomeration, land cover, land surface temperature (LST), spatial non-stationarity.