Utilization of Glycine by Microorganisms along the Altitude Changbai Mountain, China: An Uptake Test Using 13C,15N Labeling and 13C-PLFA Analysis

Abstract

External organic nitrogen (N) inputs can contrastingly affect the transformation and availability of N in forest soils, which is an important potential N resource and is possibly vulnerable to soil properties. Little is known about the transformation and availability of external small molecule organic N in forest soils and the underlying microbial mechanisms. Soil samples from Changbai Mountain at different altitudes (from 750 m to 2200 m) that ranged widely in soil properties were incubated with 13C, 15N-labeled glycine. The fate of 15N-glycine and the incorporation of 13C into different phospholipid fatty acids (PLFAs) were measured at the same time. The addition of glycine promoted gross N mineralization and microbial N immobilization significantly. Mineralization of glycine N accounted for 6.2–22.5% of the added glycine and can be explicable in the light of a readily mineralizable substrate by soil microorganisms. Assimilation of glycine N into microbial biomass by the mineralization-immobilization-turnover (MIT) route accounted for 24.7–52.1% of the added label and was most mightily affected by the soil C/N ratio. We also found that the direct utilization of glycine is important to fulfill microorganism growth under the lack of available carbon (C) at upper elevations. The labeled glycine was rapidly incorporated into the PLFAs and was primarily assimilated by bacteria, indicating that different groups of the microbial community were answerable to external organic N. G+ bacteria were the main competitors for the exogenous glycine. Increased intact incorporation of glycine into microbial biomass and the concentration of PLFAs in general, particularly in G+ bacteria, suggest a diversified arrangement to response changes in substrate availability.