Effects of phosphorus supply on microbial carbon source utilization and functional diversity of maize rhizosphere

Phosphorus (P) is a key nutrient which influences the growth, development and yield of crops. P availability can regulate soil microbial community structure and diversity by altering the quantity and components of root exudates. Whether P addition increases carbon resources utilization and functional diversity of soil microorganisms remains highly debatable. Also how P addition affects carbon resources utilization and functional diversity of soil microorganisms is not fully understood. In this study, a pot soil culture experiment with 2 P application treatments low P of 5.7 mg(P)kg^-1(soil) and high P of 200 mg(P)kg^-1(soil) was carried out to investigate the effect of P on carbon resources utilization and functional diversity of microorganisms in maize rhizosphere soil. After 35 d of growth, maize rhizosphere soil was collected using the nylon mesh method under 2 P treatments. The Biolog microplate technique was used to examine the color change of micro-well solutions containing 31 carbon sources every 24 h for consecutively 240 h. The results showed that with prolonged culture time, the utilization of 31 types of carbon sources by soil microorganisms obviously increased until the carbon sources in the micro-well solution were exhausted. High P treatment significantly increased average well color development (AWCD) and improved the utilization of carbohydrate carbon and its derivatives, amino acids and metabolites, but not affected the utilization of fatty acids and lipids. Functional diversity of soil microorganisms in maize rhizosphere soil was regulated by P availability, which depended largely on culturing time. During 72 h cultivation, high P treatment significantly increased the diversity index, dominance index and evenness index of soil microorganisms. However, after 72 h of cultivation, high P treatment had no significant effect on soil microorganism diversity. Based on principal component analysis (PCA), extracted first 3 components explained 75.15% of carbon sources utilization and separated 2 categories based on P treatments. A total of 23 carbon sources was correlated with PC1, 8 correlated with PC2 and 3 correlated with PC3. Multivariate analysis showed that the pattern of carbon sources utilization of soil microorganisms under high P supply was significantly different from that under low P supply (Hotelling trace = 2.485, F = 62.95, P < 0.001). In conclusion, carbohydrate and the derivatives, amino acids and metabolites were the major carbon sources utilized by soil microorganisms in maize rhizosphere soil. P addition significantly increased carbon sources utilization by soil microorganisms. To some extent, it also improved soil microbial functional diversity in maize rhizosphere soil.