Abstract
To provide a scientific basis and technical support for agroforestry management practices, such as interrow configuration and soil water and fertilizer management, a stratified excavation method was performed both to explore the fine-root spatial distribution and niche differentiation and to quantify the below-ground interspecific competition status of 3-, 5-, and 7-year-old apple (Malus pumila M.)–soybean (Glycine max L. Merr.) intercropping systems and monocropping systems. The fine roots of older trees occupied a larger soil space and had both a greater fine-root biomass density (FRMD) and a greater ability to reduce the FRMD of soybean, but this ability decreased with the distance from the apple tree row. Similarly, the FRMD of apple trees was also adversely affected by soybean plants, but this effect gradually increased with a decrease in tree age or with the distance from the tree row. Compared with that of the 3- and 5-year-old monocropped apple trees, the FRMD of the 3- and 5-year-old intercropped apple trees increased in the 40–100 cm and 60–100 cm soil layers, respectively. However, compared with that of the 7-year-old apple and soybean monocropping systems, the FRMD of the 7-year-old intercropped apple trees and soybean plants decreased in each soil layer. Compared with that of the corresponding monocropped systems, the fine-root vertical barycenter (FRVB) of the intercropped apple trees displaced deeper soil and that of the intercropped soybean plants displaced shallower soil. Furthermore, the FRVB of both intercropped apple trees and intercropped soybean plants displaced shallower soil with increasing tree age. Intense below-ground interspecific competition in the 3-, 5-, and 7-year-old apple–soybean intercropping systems occurred in the 0–40 cm soil layer at distances of 0.5–0.9, 0.5–1.3, and 0.5–1.7 m from the apple tree row, respectively.
Highlights
Agroforestry management plays an important role in both alleviating conflicts between forestry and agriculture and improving land productivity
The fine roots of both intercropped apple trees and intercropped soybean plants were gradually displaced to the shallow soil with an increase in tree age, which was an adaptive tactic of the fine roots of each component in the apple–soybean intercropping systems in response to intense below-ground interspecific competition
The niche differentiation of the fine roots caused the niche overlap between the intercropped apple trees and the intercropped soybean plants to decrease as the distance from the apple tree row increased, while the overlap increased with increasing tree age
Summary
Agroforestry management plays an important role in both alleviating conflicts between forestry and agriculture and improving land productivity. The spatial distribution and morphology of the roots of trees and crops in an agroforestry system determine individual competitive ability to reach below-ground resources [8,9,10], and constitute the main factor that determines the degree of below-ground competition among species [1] Because of their morphological and physiological plasticity, the fine roots of trees and crops have the inherent capability to adapt to the spatial heterogeneity of soil water and nutrients in agroforestry systems [3]. It is necessary to understand the niche differentiation of the fine roots of both trees and crop species and to analyze the adaptive tactics of the fine-root niche responses to below-ground interspecific competition in agroforestry intercropping systems. After analyzing the spatial distribution of fine roots both in apple–soybean intercropping systems and their corresponding monocropping systems, it was possible to characterize the niche differentiation of intercropped apple trees and intercropped soybean plants and further quantitatively determine the below-ground competition status among species. The results from this study provide a scientific basis and technical support for management practices, such as interrow configuration and water and fertilizer management practices
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