[Impacts of biochar and phosphorus application on soil phosphorus availability and soybean phosphorus uptake]. / ä¸åŒç£·æ°´å¹³é æ–½ç”Ÿç‰©ç‚­å¯¹åœŸå£¤ç£·æœ‰æ•ˆæ€§.

Biochar is beneficial to soil phosphorus (P) availability and crop growth, but the effects vary greatly across different soil types. We investigated the effects of rice straw biochar (4% of total mass) and P application (0, 30, and 90 kg P·hm-2) on soil P availability, phosphomonoesterase activity, and soybean P uptake by using lateritic red soil (pH 4.91) and cinnamon soil (pH 7.24) as test materials. The results showed that biochar application at different P levels significantly increased available P and total P in both soils. Biochar application with 30 kg P·hm-2 increased soil available P with maxima at 192.6% and 237.1% in lateritic red soil and cinnamon soil, respectively. Biochar application with 30 kg P·hm-2 in lateritic red soil significantly increased the activity of alkaline phosphomonoesterase by 78.9%, decreased the content of active organic P by 39.3%, and subsequently stimulated soybean P absorption and growth. Biochar amendment significantly reduced active organic P content in cinnamon soil, but did not affect soil phosphomonoesterase activity and plant growth. The content of active organic P was significantly negatively correlated with soil available P content. In summary, the effect of biochar on soil P availability varied across different soil types (lateritic red soil > cinnamon soil) and P levels (better at 30 kg P·hm-2). Our results could provide scientific basis for a promising application of biochar in reducing the amount of P fertilizer and increasing soybean P uptake, especially in lateritic red soil.

The Cd sequestration effects of rice roots affected by different Si management in Cd-contaminated paddy soil.

The application of exogenous silicon (Si) reportedly is one of the eco-friendly practices to mitigate cadmium (Cd) phytotoxicity and regulate the chemical behaviors of Cd in the soil-rice system. But the efficiency of Si on the Cd retention by rice root varies with the Si fertilizer management. The objective of this paper was to interpret the differences in Cd immobilization by rice roots and relevant mechanisms under different ways of Si application (T-Si, supplied at transplanting stage; TJ-Si, split at transplanting and jointing stage with the ratio of 50 % to 50 %; J-Si, supplied at jointing stage and CK, none of Si application) in Cd-contaminated paddy soils. The results showed that the Cd-retention capacity of rice root was increased by 0.60 % ~ 3.06 % under different Si management when compared to CK. The concentrations of monosilicic acid in soils and in apoplast and symplast of roots were increased significantly by Si application, while Cd concentrations in apoplast and symplast of root were decreased by 28.50 % (T-Si), 40.64 % (TJ-Si) and 30.26 % (J-Si), respectively. The distribution of Cd in rice cell wall was increased significantly by TJ-Si. The Cd concentrations of inert fractions (F3, F4 and F6) in root of TJ-Si were raised obviously. Si application downregulated the expression of OsIRT2 and OsNramp5 while upregulated OsHMA3, and the expression of OsHMA3 treated by TJ-Si was obviously higher than CK and J-Si. The distributions of the passive Cd in roots bound with thiol compounds (NPT, GSH and PCs) and polysaccharide components (pectin, hemicelluloses 1 and hemicellulose 2) were raised much more by TJ-Si than by T-Si and J-Si. On the whole, compared with T-Si and J-Si, TJ-Si could more easily replenish soil available Si and enhance Cd sequestration in roots as the result of the decrease of Cd transport factor in roots. This study unravels some mechanisms about different Si management on increasing Cd retention and decreasing Cd migration in rice roots, and TJ-Si is worthy of being recommended.

Biochar application under low phosphorus input promotes soil organic phosphorus mineralization by shifting bacterial phoD gene community composition.

Biochar has the potential to enhance microbial-mediated phosphorus (P) cycling in soils, but the underlying mechanisms remain largely unknown. We hypothesized that biochar amendment could enhance the production of acid and alkaline phosphomonoesterase, phosphodiesterase and P mineralization, which may vary depending on the P input. To test this hypothesis, we assessed the impacts of rice straw biochar application (0 and 4%) under different P-input rates (0, 30 and 90 kg P ha-1) on the relationships among P fractions, phosphatase activities and alkaline phosphomonoesterase-encoding bacterial (phoD gene) communities in an acidic soil. Biochar application under low P input (< 30 kg P ha-1) significantly increased the activities of phosphodiesterase and alkaline phosphomonoesterase but not that of acid phosphomonoesterase and depleted organic P. The results from the structural equation model revealed a dominant role of alkaline phosphomonoesterase in P mineralization. The increase in alkaline phosphomonoesterase activity was not related to an increase in phoD gene abundance but was due to a shift in community composition, which was primarily driven by the soil C:P ratio. Microbial network analysis demonstrated a more complex phoD gene community with more functionally interrelated groups as a result of biochar application under low P input than under high P input. Moreover, the specific enrichment of Micromonosporaceae under C-rich and P-poor conditions may play a critical role in alkaline phosphomonoesterase production and potential P mineralization. In conclusion, we demonstrated that biochar application under low P input supports a more organized phoD gene community and preferentially enriches taxa in terms of their capacity for P mineralization, which in turn may enhance P bioavailability and plant P acquisition.