Objective To provide a theoretical basis for optimizing the intensive management technology in Populus tomentosa-wheat agroforestry system under wide- and narrow-row spacing planting schemes, the distribution and morphological characteristics of fine root length density (FRLD) in this system were studied.
Method In a four-year-old triploid P. tomentosa-wheat agroforestry system under wide- and narrow-row spacing planting schemes, a soil coring method was adopted for root sampling around three average standard trees after wheat harvest. The sampling locations were 75 cm away from tree lines for narrow row and 75 cm away from trees for tree row, while 100, 200, 300, and 400 cm away from tree lines for the wide row, sampling depth was 80 cm. A total of 288 root samples were obtained. All fine root samples were scanned, dried and weighed to obtain the distribution and morphological data in different depths and horizontal distances.
Result Vertically, the fine roots of P. tomentosa and wheat were mainly concentrated in the shallow soil layer. The FRLD in 0–20 cm soil layer accounted for 68% and 45% of the total FRLD, respectively. The FRLD decreased exponentially with depth for both P. tomentosa (R2 = 0.679 3, P < 0.05) and wheat (R2 = 0.922 9, P < 0.05). There was no significant difference in FRLD between the two species in the shallow soil layer (P > 0.05). However, in the deep soil layer, the FRLD of wheat was significantly higher than that of P. tomentosa (P < 0.05). Horizontally, fine roots of P. tomentosa were mainly concentrated in narrow row and tree row, while fine roots of wheat were widely distributed in wide row. On a two-dimensional scale, two species had their own dense distribution zones of fine roots and did not interfere with each other. The fine root diameter of P. tomentosa was significantly higher than that of wheat, while its specific root length was significantly lower than that of wheat (P < 0.05).
Conclusion In P. tomentosa-wheat agroforestry system under wide- and narrow-row spacing planting schemes, the spatial distribution of the fine roots of P. tomentosa and wheat was separated, and the dense distribution area overlapped less. Also, in order to absorb soil resources more effectively and occupy a competitive advantage, wheat would produce more fine roots with higher absorption efficiency. The results can provide a theoretical basis for optimizing the intensive management technology in agroforestry system under this planting schemes.