Foliage application of nitrogen has less influence on soil microbial biomass and community composition than soil application of nitrogen

Abstract

Many studies have shown the simulated effects of nitrogen (N) deposition on soil microbial community composition by adding N directly to the forest floor but have ignored the N retention process by the canopy. This study was conducted to compare the responses of soil microbial biomass and community composition between soil application of N (SAN) and foliage application of N (FAN). A pot experiment was designed with (1) two N application methods (SAN and FAN), (2) three N application levels (5.6, 15.6 and 20.6 g N m−2 year−1), and (3) two tree species (Schima superba Gardn. et Champ. and Pinus massoniana Lamb.) following a nested factorial design. Soil microbial biomass and community composition were determined using phospholipid fatty acids (PLFAs) techniques after 1 and 1.5 years of treatments. Nitrogen addition increased (P < 0.05) soil NH4+-N content and soil NO3−-N content and decreased (P < 0.05) soil pH and soil microbial (bacterial, fungal, and actinomycete) biomass for both N application methods. Compared with the SAN treatment, the FAN treatment had higher (P < 0.05) pH and lower (P < 0.05) contents of soil NH4+-N and soil NO3−-N. Soil microbial biomass and community composition were significantly different between the different N addition levels under the SAN treatment, but they showed no significant difference (P < 0.05) between the different N addition levels under the FAN treatment. The soil microbial biomass in the S. superba soil was higher (P < 0.05) than that in the P. massoniana soil for the FAN treatment, with the opposite trend observed under the SAN treatment. Moreover, redundancy analysis showed that soil microorganisms were significantly correlated with soil pH, soil water content, NH4+-N, and NO3−-N. The results showed that N addition affected soil properties, microbial biomass, and the composition of microbial communities; however, the FAN treatment had less influence on soil properties and soil microorganisms than did the SAN treatment over short time scales, and the extent of this effect was different between coniferous and broadleaf trees.