Effects of organic inputs derived from pea and wheat root functional traits on soil protease activities

Abstract

Legume-derived organic inputs such as crop residues or compounds derived from rhizodeposition can influence soil microbial activities implicated in the degradation of organic N. Crops succeeding legumes can also be important drivers of such microbial activities, and trait-based approaches can be employed to better understand the influence of plants on soil microbial activities. The objective of this study was to examine the effects of organic inputs (rhizodeposits and crop residues) of previously planted pea together with wheat root traits on soil protease activities. We measured soil protease activities, soil variables describing C and N availability and microbial biomass N and wheat root functional traits related to resource acquisition and rhizodeposition at 5 wheat developmental stages. Soil protease activities were significantly increased by the addition of pea crop residues, whereas previous pea cropping (i.e., soil containing organic inputs derived from pea rhizodeposition) did not influence these activities. The percentage of fine roots < 0.1 mm in diameter was the only root trait that contributed to variation in soil protease activities. Other belowground traits related to plant nutrient competitive abilities (specific root length, root N uptake, root biomass, and hot water-extractable root N) did not influence soil protease activities. We showed that pea crop residues, acting as substrates, are the main drivers of soil protease activities. However, our results highlight the importance of considering fine roots to understand the effects of plants on soil microbial activities implicated in N mineralization.