| Agroforestry cropping patterns is an important way to improve the efficiency of land use. However, in previous studies, nutrient use of complementary and the collocation of plant morphological structure are major considerations, while ignoring the role of allelopathy. Walnut trees have strong allelopathic effects, which is an important factor in the implementation of mixed cropping systems between walnut trees and crops. Therefore, this experiment use wheat(Triticum aestivum L.), oat (Avena sativa. L.), ryegrass (Lolium perenne L.) and orchardgrass (Dactylis glomerata L.), the four Poaceae plants as target plants. Four different levels of leaf litter treatments were designed:0 g·ml-1(CK:0 g·pot-1, poured 100 ml aqueous extracts into pots once every 5 d,18 times in three months, the same below),0.0167 g·ml-1 (A1:30 g·pot-1),0.0333 g·ml-1 (A2:60 g·pot-1),0.050 g·ml-1 (A3:90 g·pot-1). The aim is to study the allelopathic effects of aqueous extracts of walnut leaf litter which extracts of leaf litter decomposing microorganisms in soil nutrient cycling and on the growth, resistance physiology and photosynthetic characteristics of the four Poaceae plants, to investigate the mechanisms that the aqueous extracts affect the plants, and provide a reference for choosing matching crops and take reasonable steps to operations walnut agroforestry cropping patterns. Preliminary results are as follows:(1) The effects of aqueous extracts of walnut leaf litter on growth of four Poaceae plantsOn 60 d, the ground diameter, stem height, height, and dry weight of wheat, ryegrass and orchardgrass were significantly lower with increasing concentration of aqueous extracts of walnut leaf litter (p<0.05), effects on oats showed inconsistent trends.60 d; Compound effects of aqueous extracts of walnut leaf litter on four allelopathic grasses were in the order:wheat> ryegrass> orchardgrass> Oats, which showed aqueous extracts had strongest inhibitory effects on wheat and rye grass, followed by orchardgrass and oats.(2) The effects of aqueous extracts of walnut leaf litter on resistance physiology of four Poaceae plantsWith increasing concentration of aqueous extracts of walnut leaf litter, leaf SOD activity of wheat, oats and ryegrass increased fisrt but decreased later, however, SOD activity of orchardgrass showed a downward trend; aqueous extracts have significantly inhibitory effects on leaf POD activity of oat, ryegrass and orchardgrass; CAT activity of four Poaceae plants showed a downward trend with increasing concentration of aqueous extracts of walnut leaf litter.(3) The effects of aqueous extracts of walnut leaf litter on osmoregulation of four Poaceae plantsMDA content of wheat and ryegrass showed an upward trend with increasing concentration of aqueous extracts of walnut leaf litter, but MDA content of oat were significantly lower than CK, and no significant difference of MDA content of orchardgrass were observed among treatments. Soluble sugar content of wheat under A1 treatment was significantly higher than CK, however, aqueous extracts increased the soluble sugar content of ryegrass and oat; no significant difference of soluble sugar content of orchardgrass were observed among treatments; With increasing concentration of aqueous extracts, soluble protein content of oats and ryegrass decreased, while soluble protein content of orchardgrass showed a upward trend.(4) The effects of aqueous extracts of walnut leaf litter on photosynthetic characteristics of four Poaceae plantsWith increasing concentration of aqueous extracts of walnut leaf litter, total chlorophyll content of wheat, oats, ryegrass showed a downward trend; Compound effects of aqueous extracts of walnut leaf litter on chlorophyll content of four Poaceae plants were in the order:Wheat (RI=-0.537)> ryegrass (RI=-0.382)> orchardgrass (RI=-0.100)> oat (RI=-0.285); With increasing concentration of aqueous extracts, Pn of four Poaceae plants showed a downward trend, compound effects of aqueous extracts on Pn were in the order:ryegrass (-0.511)> wheat (-0.320)> orchardgrass (-0.260)> oat (-0.239); no significant change or increase in Ci were observed among all treatments, indicating that the decrease in Pn is caused by non-stomatal factors, considered as the decrease in mesophyll photosynthetic activity. This decrease in Pn are in magnitude to the decrease in the chlorophyll content caused by aqueous extracts. Aqueous extracts inhibited the Gs and Tr of wheat, but no significant difference of Gs and Tr in oat were observed, Gs and Tr of ryegrass showed a downward trend after increase; AQY, Pn max, LSP, LCP and Rd of wheat were significantly decreased by aqueous extracts, and these of A3 treatment decreased over 50% compared with CK(5) The effects of aqueous extracts of walnut leaf litter on grain yield and yield components of wheatWheat spike length, kernels per spike,1000-kernel weight and yield per spike were significantly decreased with increasing concentration of aqueous extracts of walnut leaf litter; The strongest effects were observed under A2 treatment, after this falling trend toward to flat. Furthermore, significantly decrease in 1000-kernel weight showed the decline of quality of wheat grain, and increased the proportion of wheat bran, but reduced the output of flour.In summary, aqueous extracts of walnut leaf litter have significant effects on the resistance physiology of four Poaceae plants. Wheat and ryegrass showed less tolerance, resulted in membrane lipid peroxidation and damage of cell, then inhibit the photosynthetic pigments, reduced absorption、conversion and utilization capacity of light energy, resulted in reduced photosynthetic rate, finally caused inhibitory effects on the growth of plants; Compound effects of aqueous extracts of walnut leaf litter on four Poaceae plants were in the order:wheat> ryegrass>orchardgrass>oats, which showed that from ecological context, walnut+oat and walnut+orchardgrass intercropping agroforestry model are more suitable than wheat and ryegrass. |
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