Abstract
This study investigated the influence of nitrogen (N) fertilizer and straw on intact amino acid N uptake by soil microorganisms and the relationship between amino acid turnover and soil properties during the wheat growing season. A wheat pot experiment was carried out with three treatments: control (CK), N fertilizer (NF) and N fertilizer plus rice straw (NS). We used stable isotope compound-specific analysis to determine the uptake of 13C,15N-glycine by soil microorganisms. In the NF treatment, microbial 13C,15N-glycine uptake was lower compared with CK, suggesting that inorganic N was the preferred N source for soil microorganisms. However, The application of straw with N fertilizer (in NS treatment) increased microbial 13C,15N-glycine uptake even with the same amount of N fertilizer application. In this treatment, enzyme activities, soil microbial biomass C and microbial biomass N increased simultaneously because more C was available. Soil mineral N and plant N contents all decreased substantially. The increased uptake of intact 13C,15N-glycine in the NS treatment can be attributed to direct assimilation by soil microorganisms to satisfy the demand for N when inorganic N was consumed.
Highlights
Amino acids represent an important component of soil organic nitrogen (N) pools, accounting for 20–50% of the identifiable soil N pool upon acid hydrolysis[1, 2]
The present study provides information about the influence of inorganic N alone and N plus plant residue on amino acid N utilization by soil microorganisms under controlled conditions with actively growing plants
The highest NO3--N concentrations occurred in the NF treatment and the addition of straw plus N fertilizer (NS) led to a significant decrease compared with the N addition treatment at all four sampling dates
Summary
Amino acids represent an important component of soil organic nitrogen (N) pools, accounting for 20–50% of the identifiable soil N pool upon acid hydrolysis[1, 2]. Studies with isotopic tracers have indicated that the half-life of the amino acid pool in soil solution ranges from 0.8 h to 5.9 h [3, 4]. Due to the rapid turnover of the free amino acid pool, they have been considered as a potentially important source of N for soil microorganisms and plants [5,6,7]. Soil microorganisms can assimilate amino acids directly or as NH4+ produced by ammonification [5, 8, 9]. If the N is not needed for metabolism, directly assimilated amino acids can be deaminated intracellularly and the surplus N may be excreted into soil solution.
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