ObjectiveAgro-forestry is an effective way to solve the dispute between forest land and agricultural land. In order to explore the distribution of the new roots of Populus tomentosa in the forest-agricultural compound model after one year of afforestation, the spatial distribution of fine root length density (FRLD) and fine root biomass density (FRBD) under different afforestation densities and intercropping patterns under intercropping conditions of P. tomentosa were studied. The purpose of this study was to screen a better intercropping pattern and provide a theoretical basis for the rational allocation of species under young P. tomentosa forests.

Method1-year-old 'Beilin Xiongzhu No 1', a new variety of P. tomentosa was used as the experimental material. The split-plot experimental design was used, the main area was set with two common plantation space of 2 m×3 m and 3 m×4 m, two common intercropping modes were set in the sub-zone, P. tomentosa + peanut + spinach (peanut, spinach rotation), P. tomentosa + peanut, with one conventional tending of plantation as control, a total of 6 treatments, repeated 3 times. After 1 year of outplanting, three standard saplings were selected for each treatment, root samples were taken at intervals of 30 cm along the horizontal direction between rows of trees, both planting densities were taken at 150 cm, root samples were taken at intervals of 20 cm from the surface to 80 cm in the vertical direction, a total of 1 080 root samples were taken. By analyzing the FRLD and FRBD of P. tomentosa saplings, the effects of different agro-forestry patterns on the root system of P. tomentosa saplings were studied.

ResultThe planting space had no significant effects on the total average fine root length density (FRLD) and fine root biomass density (FRBD) after one year of afforestation, need to continue observation later. However, different intercropping patterns had significant effects on the FRLD and FRBD of 2-year-old P. tomentosa saplings(P < 0.05), the interaction between them had no significant effects on FRLD and FRBD. Different agro-forestry patterns were similar in the fine root distribution areas in horizontal and vertical directions. In the horizontal direction, more than 56.36% of the FRLD and FRBD of P. tomentosa + peanut + spinach, P. tomentosa + peanut and conventional tending accounted for 0-30 cm. FRLD and FRBD in vertical direction accounted for more than 78.95% of 0-80 cm in 0-20 cm and 20-40 cm soil layer. After comparing the three models in horizontal and vertical directions, The FRLD and FRBD in both the horizontal and vertical directions of P. tomentosa + peanut + spinach and P. tomentosa + peanut were higher than the conventional tending of P. tomentosa saplings.

ConclusionIt is concluded that under the different intercropping patterns, the horizontal distribution of FRLD and FRBD was mainly in 0-30 cm, and the vertical distribution is mainly in 0-20 cm and 20-40 cm, the intercropping of agricultural crops after planting could promote the root growth of P. tomentosa trees after one year of afforestation.