Effect Of Low Phosphorous Stress On Root Growth And Soil Microbial Diversity In Rhizoplane Of Tomatos

Tomato is one of the most popular vegetables in the world. With the increase of the planting area of tomato, the nutritional deficiency and monocultural problems are getting more severe in tomato production area. During the process of tomato growth, phosphorus deficiency will lead to slow growth, flowering delay, etc. Based on the traditional and modern analyzed techniques, such as WinRHIZO root analysis system, dilution-plate method, PCR-DGGE etc., the effect of low phosphorus stress on root growth, soil microbial properties and diversity under low phosphorus stress were analyzed. The main results are as follows:(1) The results showed that the root length, surface area, volume and tip numbers were all decreased under low phosphorus stress. But the effects of low phosphorus stress on root growth of different tomato cultivars were not consistent. Meawhile, the growth of the upper part of the tomato was also declined and the ratio of root-shoot significantly increased under low phosphorus stress.(2) Soil pH, total phosphorus, potassium and available phosphorus contents in rhizosphere of tomato under low phosphere stress were significantly lower than those in balanced fertilization.(3) In contrast, Soil microbial number, which including bacteria, fungi and actinomycetes, soil enzyme (β-glucosidase, aminopeptidase and phosphatase) activities, microbial biomass (C, N and P) in rhizosphere of tomato were all decreased under low phosphorus stress than those in balanced fertilization.(4) The morphological indexes of tomato root were correlated with the contents of soil total phosphorus, available phosphorus, and available potassium respectively. Meanwhile, they were aslo significantly correlated with some of the biological properties, such as the activity of the β-glucosidase and microbial biomass carbon, etc.(5) To compare with the balanced fertilization, soil bacterial community structure was significantly changed, for instance, Methylbacterium (sp.), which has the function of soluble phosphorus, disappeared in rhizosphere under low phosphorus stress. Meanwhile, sequencing results showed that most of the dominant bacteria in rhizosphere under low phosphorus stress were uncultivatable bacterium species, but some of the cultivable bacteria species, such as Penicillium (sp.), Fusarium (sp.), Aspergillus (sp.), which have the soluble function of phosphorus, were aslo found in rhizosphere under the low phosphorus stress too. However, the indexes of soil bacterial diversity (H), richness (S) and evenness (Eh) under low phosphorus stress were all decreased than those in balanced fertilization.(6) Soil fungal community structure in rhizosphere has the same trend with bacterial community structure under low phosphorus stress. It also showed that the indexes of fungal diversity (H), richness (S) and evenness (Eh) were all decreased under low phosphorus stress. Even though the dominant populations of fungi in rhizosphere under low phosphorus were uncultivatable, but some of the phosphate solubilizing fungi, such as Penicillium (sp.), Fusarium (sp.), Aspergillus (sp.) were aslo detected.In summary, the degradation of soil fertility and poor microorganisms, bad structure in rhizosphere were the important reason for the poor growth of tomatoes. Higher growth of tomatoes, soil fertility and health could be improved by balanced fertilization.