The ecological effect of different substrates on soil microbial biomass, activity and carbon sequestration

The scarcity of organic matter in agricultural soils of arid regions, especially orchards, is considered as one of the most important difficulties for yield production. Plant residue (substrate) quality added to soil would play a very important role in soil organic matter decomposition and nutrient cycling. However, very little is known about the effect of orchard little on microbial activities and biomass C. This experiment was conducted to determine effects of litter quality of different orchard plants on soil respiration and microbial activity and to estimate the decomposition rate of different organic residues during a 100 days incubation period. We arranged the experiment using a completely randomized design with three replicates. Four substrates including almond, walnut, grape and L-glutamine amino acid were mixed with a clay loam soil and the evolved CO2 was monitored for 100 days under controlled conditions. The results of this study showed that the addition of plant residues and amino acid resulted in a substantial increase (184-219%) in soil microbial activity measured as respiration. Decomposition rate and microbial respiration in plant-amended soils were significant too. Initially, there was an increase in soil respiration rate (219%) in soils treated with L-glutamine. However, soil respiration was not affected by L-glutamine at the end of incubation, indicating C could be a limiting factor for the activity of soil microorganisms. Microbial respiration in soils amended with almond litter was the highest (2310 mg kg-1) and in soils amended with grape litter was the lowest (2045 mg kg-1) at the end of incubation period. Significant differences in microbial respiration and biomass among various plant residues indicate that litter quality, especially N contents, play an important role in litter decomposition rates. In summary, significant differences occurred in residue decomposition affecting C and nutrient dynamics, and therefore crop productivity and atmospheric CO2 level.