Intercropping has little effect on root functional traits in a novel perennial grain-legume cropping system

Abstract

Perennial grain crops are a promising new tool for reducing agricultural impacts on global change because their extensive root systems build soil organic matter and retain nutrients, thereby increasing soil C storage and reducing nutrient export. The potential for advancing sustainability goals is even more pronounced if perennial crops are managed with agroecological principles, such as manipulating species diversity for reduced external inputs. Intercropping with legumes is an ecological nutrient management practice that has the potential to supply organic nitrogen, but this depends on the establishment of the intercrop and associated expression of functional traits. However, the impacts of intercropping on trait expression and ecosystem function in perennial grain systems is poorly understood. To address this gap, we examined variation in root functional traits and soil microbial functions in a field experiment established in 2019 with intermediate wheatgrass (Thinopyrum intermedium; IWG) and alfalfa (Medicago sativa), a common forage legume. We measured five root functional traits and microbial enzymatic activity in five cropping treatments: (i) an IWG monocrop with fertilizer addition; (ii) an IWG-alfalfa intercrop; (iii) an unfertilized IWG monocrop (iv) an IWG-alfalfa intercrop from which alfalfa shoots were removed throughout the growing season to simulate a dual-use grain and forage system; and (v) an alfalfa monocrop. We found that cropping treatment had little effect on root functional traits and soil microbial enzymatic activity, suggesting that crop life history and genetic controls over belowground form and function were more influential than agricultural management, and that different cropping treatments with IWG and alfalfa provided similar substrates for microbial growth. Root N content and specific root length of IWG in the intercrops were significantly higher than in the unfertilized monocrop, whereas root N was not different between fertilized and intercropped IWG. This suggests intercropping IWG with alfalfa supports a more acquisitive

resource allocation strategy in IWG. Moreover, it suggests that a dual-use intercrop is a viable management strategy for sustaining ecosystem function. This research expands our understanding of root trait expression in novel perennial cropping systems, which will help us refine ecological management strategies that increase agricultural sustainability