Table_2_Differential effects of cow dung and its biochar on Populus euphratica soil phosphorus effectiveness, bacterial community diversity and functional genes for phosphorus conversion.docx

IntroductionContinuous monoculture leading to soil nutrient depletion may cause a decline in plantation productivity. Cow dung is typically used as a cheap renewable resource to improve soil nutrient status. In this study, our purpose was to compare the effects of different cow dung return methods (direct return and carbonization return) on soil microbial communities and phosphorus availability in the root zone (rhizosphere soil and non-rhizosphere soil) of P.euphratica seedlings in forest gardens and to explore possible chemical and microbial mechanisms.
MethodsField experiments were conducted. Two-year-old P.euphratica seedlings were planted in the soil together with 7.5 t hm-2 of cow dung and biochar made from the same amount of cow dung.
ResultsOur findings indicated that the available phosphorus content in soil subjected to biochar treatment was considerably greater than that directly treated with cow dung, leading to an increase in the phosphorus level of both aboveground and underground components of P.euphratica seedlings. The content of Olsen-P in rhizosphere and non-rhizosphere soil increased by 134% and 110%, respectively.This was primarily a result of the direct and indirect impact of biochar on soil characteristics. Biochar increased the biodiversity of rhizosphere and non-rhizosphere soil bacteria compared with the direct return of cow dung. The Shannon diversity index of carbonized cow manure returning to field is 1.11 times and 1.10 times of that of direct cow manure returning to field and control, and the Chao1 diversity index is 1.20 times and 1.15 times of that of direct cow manure returning to field and control.Compared to the direct addition of cow dung, the addition of biochar increased the copy number of the phosphorus functional genes phoC and pqqc in the rhizosphere soil. In the biochar treatment, the abundance of the phosphate-solubilizing bacteria Sphingomonas and Lactobacillus was significantly higher than that in the other treatments, it is relative abundance was 4.83% and 2.62%, respectively, which indirectly improved soil phosphorus availability.
DiscussionThe results indicated that different cow dung return methods may exert different effects on phosphorus availability in rhizosphere and non-rhizosphere soils via chemical and microbial pathways. These findings indicated that, compared to the direct return of cow dung, biochar return may exert a more significant impact on the availability of phosphorus in both rhizosphere and non-rhizosphere soils, as well as on the growth of P.euphratica seedlings and the microbial community.

引言 连作引发土壤养分耗竭，可能导致人工林生产力下降。牛粪作为廉价可再生资源，常被用于改善土壤养分状态。本研究旨在对比不同牛粪还田方式（直接还田与炭化还田）对林园胡杨（P.euphratica）幼苗根区（根际土壤与非根际土壤）的土壤微生物群落及磷素有效性的影响，并探讨其潜在的化学与微生物学机制。

方法 本研究开展田间试验。将2年生胡杨幼苗种植于土壤中，分别施加7.5 t·hm⁻²的牛粪，以及等量牛粪制备的生物炭。

结果 本研究结果显示，施加生物炭处理的土壤有效磷含量显著高于直接施加牛粪的处理，进而提升了胡杨幼苗地上与地下部分的磷素水平。根际与非根际土壤的Olsen-P（奥尔森有效磷）含量分别提升了134%与110%。该现象主要源于生物炭对土壤特性的直接与间接调控作用。与直接还田牛粪相比，生物炭提升了根际与非根际土壤细菌的生物多样性。炭化牛粪还田的香农多样性指数（Shannon diversity index）分别为直接牛粪还田与对照组的1.11倍与1.10倍，Chao1多样性指数（Chao1 diversity index）则分别为直接牛粪还田与对照组的1.20倍与1.15倍。相较于直接添加牛粪，添加生物炭提升了根际土壤中磷功能基因phoC与pqqc的拷贝数。在生物炭处理组中，溶磷细菌鞘氨醇单胞菌属（Sphingomonas）与乳杆菌属（Lactobacillus）的丰度显著高于其他处理组，其相对丰度分别为4.83%与2.62%，间接提升了土壤磷素有效性。

讨论 研究结果表明，不同牛粪还田方式可通过化学与微生物途径对根际与非根际土壤的磷素有效性产生差异化影响。本研究结果同时显示，相较于直接还田牛粪，生物炭还田对根际与非根际土壤的磷素有效性、胡杨幼苗生长以及微生物群落均具有更为显著的调控作用。