Allelopathic effects of tree-leaf litter on the germination and seedling phase of wheat in inter-planted systems of trees (fruits trees) and grain crops

Allelopathic effects of tree-leaf litter on crops is one of the most important considerations in constructing inter-planting systems of trees or fruits trees and grain crops. In this study, a bench-scale experiment was conducted on wheat seed germination and growth under different concentrations of water extracts from decomposed leaf litter (the culture substrate) of 12 different trees in Guanzhong (Shaanxi Province). Nine index indicators (including germination ratio, germination rate, shoot height, root length, shoot dry weight, root dry weight, CAT activity, root activity and chlorophyll content) of wheat were measured and the allelopathic effects of the tree-leaf litter on wheat discussed. The results were as follows: (1) While Eucommia ulmoides and Acer truncatum stimulated shoot height growth and CAT activity of wheat, they inhibit root activity. Also Paulownia fortunei and Populus canadensis stimulated wheat seed germination and seedling growth. Then Zanthoxylum bungeanum inhibited seedling root length, biomass, CAT activity and root activity of wheat. Furthermore, Juglans regia significantly inhibited seed germination rate, root length, CAT activity and chlorophyll content at high concentrations. Pyrus bretschneideri was inhibitory to seed germination rate, root length and chlorophyll content at high concentrations but stimulatory at lower concentrations. Malus pumila stimulated seed germination rate, shoot height, growth biomass and chlorophyll content. Diospyros kaki and Ziziphus jujuba inhibited seedling root length and biomass. Also Prunus persica and P. armeniaca inhibited seed germination at high concentrations but stimulated it at low concentrations. (2) Based on comprehensive analysis of allelopathic effects, P. fortunei, M. pumila and P. canadensis significantly stimulated wheat seed germination and growth, followed by P. armeniaca and A. truncatum. Then D. kaki, J. regia and Z. jujuba significantly inhibited wheat seed germination and growth, followed by Z. bungeanum and P. persica. On the contrary, P. bretschneideri inhibited wheat seed germination and growth at high concentrations but stimulated them at low concentrations. The effect was the direct reverse for E. ulmoides.