Seasonal Carbon Flow and Decomposer Parameter Relationships in a Semiarid Grassland Soil

The microbial activities of soil cores removed from a semiarid grassland at 3—wk intervals from February to November 1972 were evaluated both with and without nutrient enrichments. Control, wetted, and substrate—treated core O2 utilization rates were measured over the first 3 h of incubation to provide information on seasonal changes in microbial substrate use patterns. Relationships between changes in decomposer parameters also were evaluated on a seasonal basis. Unamended soils showed highest microbial activity in the spring, followed by minimum O2 use and CO2 evolution in the dry summer period, the time when H2O additions caused maximum stimulation of O2 utilization with lower (° 0.7) respiratory quotients. Protein use was strongly correlated with field soil H2O content, followed by increased utilization of amino acids suggesting a sequential breakdown process. Glucose, starch, and cellulose use was independent of short—term changes in soil H2O content and appeared related to seasonal changes in plant root carbohydrage reserves, being minimum in summer and maximum in fall, the only time when marked cellulose use occurred. An all—year correlation showed strong relationships between changes in substrate availability, soil H2O content, respiration, and microbial populations, while on a seasonal basis shifts in the parameters controlling decomposer processes were observed. Respiratory quotients became more positive only during the spring period, a trend which was reflected in seasonal matrix correlations.