Effect Of Decomposing Walnut Leaf Litter On Growth Of Wheat And The Alleviation Effect Of Nitrogen Application

Nowdays global population boom and excessive consumption of natural resources is becoming great trouble in the world. Mankind is facing with ecological environment deterioration, less land resources, Agroforestry which has the characteristics of the sustainable development of land utilization, is increasing people’s attention. The negative ecological effects of walnut (Juglans regia L.) allelopathy has been a concern for many years. The dominant narrative has remained roughly the same:Juglone is believed to be major allelochemical released by living walnut roots. Decomposition of plant litter is one of the most significant ways in which allelochemicals release. However, little information is known about the allelochemicals of walnut leaf litter. Therefore, this study identified the responsible for the allelopathic phenomenon and preliminary experiments were conducted regarding the ways that allelochemicals could influence plant growth. The objectives of this study were to gain in-depth knowledge of the walnut allelopathy. Furthermore, this study provided the reference thoroughly for choosing matching crop correctly, for adopting reasonable configuration way and management measures in a walnut-based agroforestry intercropping system.Pot experiments were conducted using wheat (Triticum aestivum L.) as receptor, to simulate the effects of decomposing leaf litter of walnut and fertilizer treatments in natural environment on wheat. Experiments were divided into two groups. In experiment A, four different levels of leaf litter treatments were designed:CK (0 g·pot-1),X1 (30 g·pot-1), X2 (60 g·pot-1), and X3 (90 g·pot-1), a total of 40 pots, each containing 8 kg soil mixed with prepared leaf litter. In experiment B, Seedlings under 20 days, Selecting 5 pots of each parallel in experiment A for nitrogenous fertilizer treatment, the dosage of litter leaves respectively is 30 g (NX1),60 g (NX2) and 90 g (NX3), and no litter leaf (NCK), the nitrogenous fertilizer rate is 1 g·pot-1. Seedlings under 20 d,50 d,80 d measuring its growth, oxidation resistance index, photosynthetic index, soil enzyme activity and production indexes.The results of the study are as follows:1. In experiment A, during 0-80 d, theplant height, and fresh weight of aboveground wheat were significantly inhibited by the walnut leaf litter, and the inhibition effect increased with increasing leaf litter addition. This showed walnut litter leaf of allelochemicals influenced on wheat growth. In nitrogen treatment group. walnut leaves had no significant effect on wheat growth of plant height and fresh weight. The reason might be that nitrogen could alleviate wheat growth inhibition.2. Resistance physiology of wheat was significantly influenced by decomposing leaf litter of walnut. At the beginning of the decomposing of walnut litter leaves, the activity of superoxide dismutase (SOD) was characterized by significant inhibitory effect(p<0.05). With the increasing of the amount of litter, the SOD activity compared with CK reached significant level(p<0.05). The peroxidase(POD) activity was characterized by inhibition compared with CK (RI<0).20-80 d the catalase(CAT) activity was tend to rise with the increaseing amount of litter,80 d, the CAT activity of X2, X3 treatment significantly increased.20 to 50 d the Malondialdehyde(MDA) content had little changed,80 d, the MDA content increased significantly(p<0.05). Different amount of litter leaf showed a trend of declineof soluble sugar content, but soluble protein, on the other hand, presented the increasing trend; during 80 d, the soluble protein content of X2, X3 is significantly higher than that of CK treatment3. In experiment B, during 50 d, no significant of SOD activity changed in the rest in addition to the X3 processing (p< 0.05), during 80 d, each treatment the SOD activity was higher than CK(p<0.05). During 20 to 50 d, with the increasing amount of litter leaves a marked changing increased in the activity of POD, in 80 d there was no significant difference among treatments(p>0.05).The CAT activity of each treatment had less change, and its activity showed promoting effect compared CK treatment (RI> 0). Nitrogen processing could reduce SS content changing, at the same time enhance the content of SP.4. Photosynthetic characteristics of wheat was significantly influenced by decomposing leaf litter of walnut. Photosynthetic pigments of wheat were significantly inhibited with increasing leaf litter addition(p<0.05); Pn and gs also decreased with the increasing amount of leaf litter, but Ci of X1、X2 were higher compared with CK, and the difference between CK and X3 was not significant (p> 0.05); AQY, Pn msx, LSP, LCP and Rd of leaf litter treatments were significantly inhibited by the walnut leaf litter, and except of AQY and Rd of X3, the inhibition effect increased with increasing leaf litter addition5. In nitrogen treatment group, the content of chlorophyll a, chlorophyll b, and the Car showed different degrees of reduction, the chlorophyll a of NX3 significantly decreased by 27% than that of NCK, the chlorophyll b significantly decreased by 31%, the Car significantly decreased by 22% with the increasing of the litter leaf. AQY, Rd of each treatment showed the trend of decline gradually, the Pn max、LSP of NX2 and NX3 were significantly higher than that of NCK treatment.Pn, gs, Ci and Tr still showed a trend of decline (p> 0.05), but NX3 treatment Pn was significantly higher than NCK.6. Grain yield was significantly inhibited and yield components of wheat were significantly influenced by decomposing leaf litter of walnut. Kernels per spike were significantly inhibited with the increasing amount of leaf litter (p<0.05); but 1000-Kernel weight increased by decomposing leaf litter of walnut.7. During 20,50, and 80 d under the treatment of walnut litter leaves, the soil catalase activity had no significant effect (p< 0.05), however the urease activity was promoted, and the urease activity was significantly higher than that of CK treatment, but in 80 d, the promoting effected weakened, and only the X1, X3 treatment was significantly higher than that of CK.A small amount of walnut litter leaf in the decomposition time was short on saccharase activity, decomposition to the 80 d saccharase activity was significantly higher than that of CK treatment (p< 0.05).During 20 d the Phosphatase activity was significantly improved (p<0.05.But as the processing time was extended, litter decomposition had a tendency to reduce the activity of phosphatase,in 80 d, only the X1 treatment soil phosphatase activity was significantly higher than that of CK.8. In nitrogen treatment group, the catalase activity, saccharase activity and soil urease activity were no significant difference(p<0.05).In 50 d,the soil phosphatase activity was all significantly higher than NCK, but to 80 d, only NX3 treatment soil phosphatase activity was significantly higher than NCK.In conclusion, the decomposition of walnut litter leaves release of allelochemicals, which had an adverse effect on the growth of wheat by destroying the oxidation protective enzyme system, reducing the soil enzyme activity, and dropping the photosynthesis of wheat indirectly inhibit the growth of wheat, eventually reduced the yield of wheat. Nitrogen treatment can effectively alleviate the allelopathic inhibition of walnut litter leaves. In the process of actual operationcan, considering to remove too much walnut litter leaves, or joining into a moderate amount of n fertilizer, that could avoid the inhibition of wheat growth.