Interactions between litter quality, surface area, and the microbial community in two contrasting soils during the earliest stage of decay

Background/Question/Methods

Few empirical studies have simultaneously monitored microbial and litter characteristics in early stages of decay with enough temporal resolution to evaluate the relationship between microbial activity and substrate chemistry. The addition of fresh litter often stimulates a quick increase in microbial respiration, which usually precedes or is concomitant with an increase in biomass. Soil organic matter decomposition may also be stimulated by fresh litter addition, yet the impact of different soil types on this priming effect is unclear. We hypothesize that early microbial dynamics during litter decay varies with litter particle size, soil texture, and litter quality. These interactions influence the availability of soluble low molecular mass compounds to microorganisms, thus influencing the magnitude of the associated priming effect. In order to examine these relationships, a 2-week laboratory incubation was conducted using different sized particles of Acer saccharum and Quercus alba litter mixed with either a 0.4% carbon (C) sandy soil or a 4.1% C silty loam soil. Microbial respiration, biomass-C, extracellular enzyme activities, and extractable nitrogen (N) and phosphorus (P) availability were monitored.

Results/Conclusions

We observed rapid increases in microbial biomass and respiration throughout the first 3 days of the incubation in all treatments with added litter. A. saccharum litter had a higher respiration rate compared to Q. alba throughout the entire incubation for all litter particle sizes and soil types, probably reflecting a higher content of labile materials in Acer litter. More C was respired over the 2-week period in ground litter compared to larger particles in all treatments, demonstrating the importance of particle size. The priming effect accounted for a 27% increase in cumulative respiration in the loam litter treatments compared to the litter-only and soil controls, which was 2.5 times higher than the same comparison in the sandy soil. The priming effect was more pronounced in ground litter treatments, probably due to increased surface area for microbial colonization. β-glucosidase and N-acetyl glucosaminadase activities were low in all litter treatments until Day 14, following the peak values of respiration and biomass that occurred within the first 3 days. Overall, our results suggest that microbial dynamics and the magnitude of the priming effect are regulated by several controls that likely influence the availability of soluble monomeric compounds.