| Agroforestry is a comprehensive land use, which has the characteristic of utilization of resources and increase yield. Under the condition of pot cultivation, this research explored the interaction of aboveground and underground part in mulberry/alfalfa intercropping system. Plant growth characteristic, soil nutrient content, soil enzyme activity, soil microbial number, soil microbial carbon metabolize and bacterial community structural diversity were studied in this research. The results showed that the plant height, stem diameter, leaf area index (LAI), branch number and yield were increased with the increase of growth period. Plant high, stem diameter, leaf area index and the number of branches of yield were higher in intercropping mulberry compared with monoculture mulberry, which leading to the increase of mulberry yield; on the contrary, plant height, branch number and yield were less in intercropping alfalfa than monoculture alfalfa.The root length, root dry weight and root length density were significantly increased in the intercropping system of mulberry and alfalfa. The root length and root length density were significantly positively correlated with plant height, stem diameter, leaf area index and yield. The root dry weight was significantly positively correlated with number of branches. The accumulation of nitrogen, phosphorus and potassium increased significantly with the increase of the growth period in mulberry and alfalfa intercropping system, and reached the maximum in the mature period. The absorption and accumulation of nitrogen, phosphorus and potassium was significantly higher in intercropping mulberry than that of the monoculture mulberry, and the absorption and accumulation of nitrogen, phosphorus and potassium was lower in intercropping alfalfa than that of monoculture alfalfa. Plant height, stem diameter, leaf area index, yield, root length and root density and the accumulation of nitrogen, phosphorus and potassium were significant correlation. The correlation coefficient between plant heights, accumulation of nitrogen, phosphorus and potassium were the highest, which could be used as an important indicator of plant growth.Soil nutrients, enzymes and microbes in mulberry and alfalfa intercropping system were studied. The content of organic matter, available nitrogen and available phosphorus could be improved in intercropping system. Soil urease, catalase and phosphatase in intercropping system were higher than that of monoculture treatment, but this was no significance on the invertase activity between intercropping and monoculture systems. Soil bacteria, actinomycetes and total microbes significantly increased, but the number of soil fungi reduced in mulberry and alfalfa intercropping system. The correlation analysis showed that the soil urease and soil bacteria, actinomycetes number and the total number of microorganisms showed significant positive correlation; A significant positive correlation between catalase, phosphatase and the number of bacteria, actinomycetes and the total number of microorganisms, and catalase, phosphatase and fungi showed a significant negative correlation, respectively.Phosphorus plays an important role in plant growth. Impacts of different phosphorus forms in mulberry and alfalfa intercropping system were studied. The results showed that the biomass of mulberry and alfalfa supplied with phosphorus treatment were higher than that of no phosphorus treatment. The effects of different forms of phosphorus sources on the biomass of mulberry and alfalfa were as follows:mulberry biomass was the highest supplied with inorganic phosphorus, and the second was organic phosphorus treatment, mulberry biomass was the lowest supplied without phosphorus. The acid phosphatase activities were higher supplied with phosphorus than that of no phosphorus treatment, and the mulberry and alfalfa intercropping system significantly enhanced the activity of acid phosphatase. The acid phosphatase activity of legume crops (alfalfa) was 21.67% higher than that of mulberry when the phosphorus supply was insufficient (no phosphorus and inorganic phosphorus treatments).Based on the Biolog-Eco plate method, the study of microbial carbon metabolize showed that AWCD increased significantly in intercropping mulberry treatment compared with monoculture mulberry in the course of cultivation. Whereas, the AWCD decreased in intercropping alfalfa treatment compared with monoculture alfalfa. Soil microbial utilization of sole carbon source of the principal component analysis showed that the carbon source utilization is related to principal component 1 and 2 respectively explain the variance 50.8%and 12.9%. The principal component analysis is the main contribution of the carbon source is carboxylic acid, polymer and carbohydrate. Among them, other compounds and carboxylic acids were utilized by monoculture mulberry; ammonia/amines, amino acids and polymers were utilized by intercropping mulberry; ammonia/amines, other compounds and polymers; amino acids and other compounds for intercropping alfalfa. In addition, soil microbial communities formed their unique characteristics of metabolic function in intercropping and monoculture systems.Using high-throughput sequencing the composition of the bacterial communities in the four soil samples was analyzed. The results showed that 23,047 sequences that belong to 28 phyla respectively were identified. Proteobacteria, Firmicutes, Acidobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, Nitrospirae and Planctomycetes were the dominant groups, which accounting for about 80% of whole bacterial communities relative abundance. Proteobacteria have the highest relative abundance, followed by Firmicutes. Compared bacterial community diversity (ACE, Chao 1, Shannon and Simpson), the results showed that Shannon index was higher in intercropping mulberry compared with monoculture mulberry. Whereas, the impact of planting patterns on the Shannon index of alfalfa was not significant. In addition, Ace and Chao 1 richness index were lower in intercropping mulberry than that of monoculture of mulberry. Cluster analysis and principal component analysis showed monoculture alfalfa and intercropping alfalfa showed similar microbial community diversity; while, soil microbial community structure between monoculture mulberry and intercropping mulberry is different. Canonical correspondence analysis (CCA) was used to analyze the relationship between soil bacterial and environmental factors. The results showed that the organic matter, the available nitrogen and available phosphorus were the main factors influencing the soil bacterial. Soil physical and chemical factors influence bacterial phyla classification. The content of available nitrogen and Protebacteria, Bacteroidetes, Nitrospirae showed a significant positive correlation; while available phosphorus and Acidobacteria, Actinobacteria and Gemmatimonadetes showed a significant positive correlation. In addition, the analysis of soil nutrients, enzymes and the relative abundance and diversity index on the class and genus levels is correlated. Soil available nitrogen, available phosphorus, urease and invertase are main factors in influencing soil bacterial community structure and bacterial diversity index.In conclusion, the growth of aboveground and the root of the underground were promoted in mulberry and alfalfa intercropping system. The increase of mulberry yield in intercropping system may be due to the increase of soil nutrient, the activity of soil enzyme and microbial diversity. |
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