Abstract
Abstract. Declines in plant diversity will likely reduce soil microbial biomass, alter microbial functions, and threaten the provisioning of soil ecosystem services. We examined whether increasing temporal plant biodiversity in agroecosystems (by rotating crops) can partially reverse these trends and enhance soil microbial biomass and function. We quantified seasonal patterns in soil microbial biomass, respiration rates, extracellular enzyme activity, and catabolic potential three times over one growing season in a 12-year crop rotation study at the W. K. Kellogg Biological Station LTER. Rotation treatments varied from one to five crops in a 3-year rotation cycle, but all soils were sampled under a corn year. We hypothesized that crop diversity would increase microbial biomass, activity, and catabolic evenness (a measure of functional diversity). Inorganic N, the stoichiometry of microbial biomass and dissolved organic C and N varied seasonally, likely reflecting fluctuations in soil resources during the growing season. Soils from biodiverse cropping systems increased microbial biomass C by 28–112 % and N by 18–58 % compared to low-diversity systems. Rotations increased potential C mineralization by as much as 53 %, and potential N mineralization by 72 %, and both were related to substantially higher hydrolase and lower oxidase enzyme activities. The catabolic potential of the soil microbial community showed no, or slightly lower, catabolic evenness in more diverse rotations. However, the catabolic potential indicated that soil microbial communities were functionally distinct, and microbes from monoculture corn preferentially used simple substrates like carboxylic acids, relative to more diverse cropping systems. By isolating plant biodiversity from differences in fertilization and tillage, our study illustrates that crop biodiversity has overarching effects on soil microbial biomass and function that last throughout the growing season. In simplified agricultural systems, relatively small increases in crop diversity can have large impacts on microbial community size and function, with cover crops appearing to facilitate the largest increases.
Highlights
Research manipulating aboveground biodiversity in grasslands has shown a strong link between plant species richness and soil functions (Tilman et al, 1997; Zak et al, 2003; Eisenhauer et al, 2010; Mueller et al, 2013)
Microbial biomass C, N, potential mineralization, and catabolic potential were all altered by crop rotations, the rotation effect for some of these indicators of microbial functioning depends upon the season
Our results clearly indicate that diversifying agroecosystems enhances this aspect of soil health, and is likely linked to changes in soil organic matter (SOM) dynamics (Tiemann et al, 2015) as well as the observed differences in yield among crop rotations (Smith et al, 2008; Fig. S8)
Summary
Research manipulating aboveground biodiversity in grasslands has shown a strong link between plant species richness and soil functions (Tilman et al, 1997; Zak et al, 2003; Eisenhauer et al, 2010; Mueller et al, 2013). Crop rotations have been shown to have large positive effects on soil C, N, and microbial biomass (McDaniel et al, 2014a), plant pathogen suppression (Krupinsky et al, 2002), and yields (Smith et al, 2008; Riedell et al, 2009). These positive effects on crop production have been colloquially referred to as the “rotation effect”.
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