The effects of rhizobial inoculation, soybean-maize intercropping and plant growth stages on the diversity of soybean root endophytic bacteria were evaluated. PCR-based terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes and analyses of cloned partial 16S rRNA gene libraries were used to study the endophytic bacterial communities. The root endophytic bacterial populations during the whole growing season was significantly affected by the three factors analyzed, with plant growth and rhizobial inoculation showing the highest and lowest impact. The alphaproteobacteria and betaproteobacteria were the most predominant endophytes of soybean roots. Some undefined bacterial lineages were also found, indicating that the root endophytic populations might constitute an important source for the isolation of novel bacteria. Bradyrhizobium liaoningense (used as inoculant) occupied most of the soybean nodules formed and Sinorhizobium americanum-related bacteria were detected as the main root endophytes. Results also suggest that bacteria might be transferred from nodules to roots (as endophytic bacteria) when the seeds become mature, which might be a possible process in the life cycle of rhizobia. Rhizobial inoculation and intercropping practices could increase the diversity of the soybean root endophytes, which might have a positive influence on the growth of soybean plants.

Nutrient, water, and their interactions influence the allocation of investment by plants to resistance and tolerance traits. We used a completely crossed randomizedblock design experiment to examine the independent and interactive effects of nutrients and water availability on tannin production of C. equisetifolia seedlings. The results showed that nitrogen and phosphorus fertilizer have significant effects on total phenolics (TP) and extractable condensed tannins (ECT) concentrations of branchlets. TP and ECT concentrations decreased with fertilizer addition and increased in arid condition. This pattern lends to support source-sink hypothesis such as the carbon-nutrient balance (CNB) hypothesis and the growth-differentiation balance (GDB) hypothesis. Soluble sugars or starch concentrations were both inversely related to TP concentrations. However, there was no significant correlation between them and ECT concentrations. In addition, chlorophyll concentration had a positive linear correlation with TP and no significant correlation with ECT. On the contrary, chlorophyll a/b ratios were negatively correlated with TP and positively correlated with ECT. The discrepancy of relationship between carbohydrates and TP or ECT showed that the biosynthetic routes of different tannins were different. In this study, no significant correlation between TP and N, or ECT and N, did not support protein competition model (PCM). TP:N and ECT:N ratios were higher in nutrient deficiency and arid conditions, which were one of the important nutrient conservation strategies for C. equisetifolia.

No abstract