ABSTRACT
We analyzed the particle size distribution of soil aggregates in 0-20 and 20-40 cm soil layers of rice-wheat rotation field based on a field plot test with two treatments, conventional straw returning (CK) and straw returning with the addition of straw decomposition promoting microbial inoculants (IT). We evaluated the water stability indices of soil aggregates (the number of soil water stable large aggregates R0.25, the average weight diameter MWD, and the geometric average diameter GMD), and measured the contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the soil aggregates of ï¼0.053, 0.053-0.25, 0.25-1, ï¼1 mm. The results showed that: 1) The number of aggregates ï¼0.053, 0.053-0.25, ï¼0.25 mm in the 0-20 and 20-40 cm soil layers under IT decreased by 10.0% and 6.8%, increased by 3.0% and 5.7%, and 17.9% and 26.1% compared with CK, respectively. IT effectively increased R0.25, MWD, and GMD by 26.4%, 20.0%, 18.2% and 18.2%, 10.5%, 10.0% in 0-20 and 20-40 cm soil, respectively. 2) Compared to CK, the TP content of 0.25-1 mm aggregates in 0-20 and 20-40 cm soil under IT was significantly increased by 40.3% and 37.5%, respectively, without difference in TN and SOC contents. There was no significant difference in nutrient contents of the other aggregates between the treatments. The contents of SOC and TN in large aggregates (>0.25 mm) were higher than those in silty aggregates (<0.053 mm). Compared to CK, the cumulative contribution rates of SOC, TN and TP of <0.053 mm aggregates under IT were decreased in two soil layers. There was no significant difference in the nutrient cumulative contribution rates of 0.053-0.25 mm aggregates between treatments. The cumulative contribution rates of SOC, TN, and TP of large aggregates (>0.25 mm) under IT were 32.1%, 19.6%, 52.8% and 22.8%, 11.8%, 42.9% higher than those under CK in 0-20 and 20-40 cm soils, respectively. 3) The number of <0.053 mm aggregates was significantly negatively correlated with SOC and TP contents, while that of 0.053-0.25 mm aggregates was negatively correlated with nutrient content. The number of large aggregates (>0.25 mm) were significantly positively correlated with SOC, TN, and TP contents. In conclusion, straw returning with microbial-inoculant addition could promote the formation of soil macroaggregates (>0.25 mm), and improve the water stability of soil aggregates, increasing nutrient contents in soil macroaggregates, with the nutrients transferring from silty aggregates to macroaggregates.
Subject(s)
Agricultural Inoculants , Soil , Carbon/analysis , Nitrogen/analysis , Nutrients , Phosphorus , Water , Agriculture/methods , ChinaABSTRACT
Cupriavidus basilensis is a species with diverse metabolic capabilities, including degradation of xenobiotics and heavy metal resistance. Although the genomes of several strains of this species have been sequenced, no plasmid has yet been constructed for genetic engineering in this species. In this study, we identified a novel plasmid, designated pWS, from C. basilensis WS with a copy number of 1-3 per cell and a length of 2150 bp. pWS contained three protein-coding genes, among which only rep was required for plasmid replication. Rep showed no homology with known plasmid replication initiators. Unlike most plasmids, pWS did not have a cis-acting replication origin outside the region of rep. The minimal replicon of pWS was stable in C. basilensis WS without selection. A conjugative C. basilensis/Escherichia coli shuttle vector, pCB5, was constructed using the minimal replicon of pWS. Interestingly, the copy number of pCB5 was flexible and could be manipulated. Enhancing the expression level of Rep in pCB5 by either doubling the promoter or coding region of rep resulted in doubling of the plasmid copy number. Moreover, replacing the native promoter of rep with the lac promoter increased the copy number by over fivefold. Finally, using two different ß-galactosidase reporting systems constructed with pCB5, we successfully demonstrated the different regulatory patterns of bph and dmp operons during diphenyl ether (DE) degradation in C. basilensis WS. Thus, this shuttle vector provided an efficient tool for DNA cloning and metabolic engineering in C. basilensis.
