Abstract
Soil extracellular enzymes are the proximal drivers of decomposition. However, the relative influence of climate, soil nutrients and edaphic factors compared to microbial community composition on extracellular enzyme activities (EEA) is poorly resolved. Determining the relative effects of these factors on soil EEA is critical since changes in climate and microbial species composition may have large impacts on decomposition. We measured EEA from five sites during the growing season in March and 17 sites during the dry season in July throughout southern California and simultaneously collected data on climate, soil nutrients, soil edaphic factors and fungal community composition. The concentration of carbon and nitrogen in the soil and soil pH were most related to hydrolytic EEA. Conversely, oxidative EEA was mostly related to mean annual precipitation. Fungal community composition was not correlated with EEA at the species, genus, family or order levels. The hyphal length of fungi was correlated with EEA during the growing season while relative abundance of taxa within fungal phyla, in particular Chytridiomycota, was correlated with the EEA of beta-glucosidase, cellobiohydrolase, acid phosphatase and beta-xylosidase in the dry season. Overall, in the dry season, 35.3 % of the variation in all enzyme activities was accounted for by abiotic variables, while fungal composition accounted for 27.4 %. Because global change is expected to alter precipitation regimes and increase nitrogen deposition in soils, EEA may be affected, with consequences for decomposition.
Highlights
Extracellular enzymes are the proximal drivers of decomposition in soils (Sinsabaugh et al 2008)
Soil extracellular enzyme activity (EEA) has been explained by correlations with abiotic factors (Sinsabaugh et al 2008); because soil fungi are responsible for a large portion of enzyme production (Schneider et al 2012), they may play a role in determining soil EEA
The relative influence of abiotic factors such as climate, soil pH, and soil nutrient concentrations compared to fungal community composition on EEA is unknown
Summary
Extracellular enzymes are the proximal drivers of decomposition in soils (Sinsabaugh et al 2008). The relative influence of abiotic factors such as climate, soil pH, and soil nutrient concentrations compared to fungal community composition on EEA is unknown. Recent meta-genomic and proteomic studies have shown that fungi produce the majority of extracellular enzymes in litter and soil that degrade labile and recalcitrant C, organic N, and organic P polymers (Schneider et al 2012, 2010) This supports previous research showing that soil fungi comprise a significant portion of microbial biomass belowground (Joergensen and Wichern 2008; Strickland and Rousk 2010) and regulate C and nutrient cycling in terrestrial ecosystems (Hattenschwiler et al 2005). We expected oxidative EEA to be positively correlated with soil pH, since these enzymes have active sites with optimal configurations at pH *8 (Frankenberger and Johanson 1982). We anticipated abiotic factors to be more related to EEA than fungal composition since we expected fungal community composition itself to be affected by abiotic factors
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