Abstract
A field experiment was conducted to evaluate the effects of regulated deficit irrigation (RDI) on the fine root redistribution of mature pear trees in 2009 and 2010. The experiment consisted of four RDI treatments: MRDI-1 and SRDI-1, in which the trees received irrigation replacing 60% and 40% of pan evaporation (Ep) during Stage 1 (cell division stage), and MRDI-1+2 and SRDI-1+2, in which the trees received irrigation replacing 60% and 40% of Ep during Stage 1+2 (cell division and slow shoot growth stage). All the RDI-treated trees received irrigation replacing 80% of Ep (full irrigation) in other stages, and the control trees were fully irrigated during the whole growth season. The results showed that the fine root length density (RLD) of mature pear trees was reduced by water stress. The resumption of full irrigation boosted fine root growth. The RLD of the SRDI-1-treated trees in the irrigated zones recovered in early July, they maintained water and nutrient absorption during the fruit enlargement stage, and the final fruit yield was significantly improved. The RLD of trees in the irrigated zones with MRDI-1 and MRDI-1+2 recovered in July and September, respectively, but there were no significant differences in fruit yield between the MRDI-1, MRDI-1+2, and the control. This indicates that the fruit yield was not negatively or positively impacted by the redistribution of moderate water stress applied during either Stage 1 or Stage 1+2.
Highlights
Fine roots are mainly responsible for the uptake of water and nutrients [1], especially in arid regions with high competition for water between trees and crop plants
The water deficit applied before the fruit enlargement stage (0–86 days after full blooming (DAB)) inhibited fine root and shoot growth in the irrigated zones, but only the water stress applied during the cell division stage inhibited shoot development more effectively than root growth due to the near cessation of shoot growth in other stages (31–147 DAB)
The root length density (RLD) of SRDI-1-treated trees in the irrigated zones recovered before the fruit enlargement stage (87–90 DAB) and maintained water and nutrient absorption during the fruit enlargement stage (87–147 DAB), which resulted in significantly higher fruit yields as compared to the controls
Summary
Fine roots are mainly responsible for the uptake of water and nutrients [1], especially in arid regions with high competition for water between trees and crop plants. Knowledge of fine root distribution is essential for the effective design and management of agroforestry systems [2,3,4,5]. Fine root growth and distribution are affected by many factors, and soil water status is one of the key factors. Soil water status is impacted by irrigation scheduling and affects the growth and redistribution of fine roots. Soil water deficit irrigation usually induces restricted root growth and activity [6,7,8]. Full irrigation produces higher root length density in potatoes compared to deficit irrigation [9], and winter wheat enduring water stress has less root biomass and a lower ratio of root biomass to root length [10]. The size of a root system has long been recognized as crucial to cope with drought conditions [11], and water stress inhibits shoot growth more significantly than root growth, leading to a greater root/shoot ratio [6,11,12]
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