Plasticity of root traits in a seedling apple intercropping system driven by drought stress on the Loess Plateau of China

Background Agroforestry has been advocated as a climate-smart agricultural approach to counter extreme climate and as an important sustainable intensification practice to meet Sustainable Development Goals (SDGs). However, its efficacy remains under dispute in drylands where resources, especially water, are limited. Aim and methods This study aimed to study how annual bioenergy crops, soybean (Glycine max) and canola (Brassica rapa), influence soil water availability and fine root distribution in a young apple orchard exposed to varying to drought intensity on the semiarid Loess Plateau of China. Drought was simulated by reducing natural precipitation by 15% (moderate drought) and 25% (severe drought). Result and conclusions Intercropping soybean and canola increased the fine root biomass (FRB) of apple trees in the 80-180 cm soil layer, improved moisture status below the 80 cm soil layer in the wet season, and promoted apple tree growth. Under moderate drought, FRB in the 0-80 cm soil layer increased, making use of the shallow soil water replenished by precipitation. However, the trees switched to absorbing soil water in the 80-180 cm in the dry season. Under severe drought, the apple trees increased FRB in the 0-80 cm and 180-280 cm soil layers and increased the proportion of the total roots in the 180-280 cm layer, aggravating the deep soil desiccation and inhibiting apple tree growth. These findings offer insights into drought effects on root plasticity and soil management practices in rainfed orchards.