Fine root distribution and belowground interactions in an alley silvopasture system in northern China

Successful agroforestry management depends on the interactions between the mixed species. Belowground interactions between shrubs and native grasses are complicated and poorly understood in China's agroforestry practice, especially in the silvopasture systems of droughty northern China. The distribution of fine roots (<2 mm) in an alley sllvopasture system consisting of Caragana microphylla Lam. and local grasses was compared to those in a degraded pasture plot using soil cores. Fine root production was examined in these plots using ingrowth cores. We found that the introduction of C. microphylla did not change the vertical distribution pattern of fine roots of grassy plants but had a great impact on belowground production in the ecosystem. Grass fine roots decreased with depth in both the silvopasture system and the degraded pasture. Grass fine roots were mostly distributed in the top 40 cm of the soil, but they extended to deeper soil layers through root elongation. C. microphylla, in contrast, occupied the deeper soil layer, in which water was continuously available. We conclude that the belowground interactions between native grasses and C. microphylla in sandy soil can be explained by Walter's 2-layer hypothesis, which is used to explain the coexistence of trees and grasses. Our results draw attention to the interspecific configuration of the silvopasture system and belowground interactions of plants in semiarid and arid regions.