Drip Irrigation Depth Alters Root Morphology and Architecture and Cold Resistance of Alfalfa

Abstract

Combined stress from water and temperature is considered an effective approach for improving the cold resistance of alfalfa (Medicago sativa L.). However, the relationships among irrigation depth, root morphology and architecture, and cold resistance of alfalfa remain unclear. In this study, we investigated the effects of drip irrigation at the soil surface (Deep-0), at 20 cm depth (Deep-20), and at 40 cm depth (Deep-40) on root morphology and architecture and cold resistance of alfalfa. The Deep-0 treatment had the highest aboveground biomass and belowground biomass, and the root system in the Deep-40 treatment tended to a ‘herringbone’ branching type, which increases the cost of water uptake. After cold acclimation for 3 days, the cold resistance of Deep-0 was strongest, and was associated with higher soluble sugar content and fewer reactive oxygen species in the roots. Deep-40 enhanced the severity of drought stress on the crown and increased the risk of crown exposure to low-temperature stress. The results showed that Deep-0 promoted alfalfa growth and development by regulating root morphology and architecture and improving water absorption efficiency, thereby enhancing the ability of the root system to withstand low-temperature stress.