细根性状对土壤养分有效性的直接影响与机制——以亚热带杉阔混交林为例

细根性状对土壤养分有效性的影响由微生物介导或由细根与土壤的直接互作而发生，然而前者受到了大量关注，后者却鲜有报道。本研究以亚热带杉阔混交林中6个混交树种（资源获取和资源保守型各3种）为研究对象，采用原位网袋试验，研究了细根对土壤氮、磷有效性的直接、间接和总体效应，及其与细根性状与的关系。结果显示，在两种资源利用策略下，细根与土壤直接接触均能提高土壤氮和磷的有效性；获取型树种对土壤磷的影响更为显著，表现为更强的直接、间接和总体效应，而保守型树种对土壤氮的间接效应更强。细根碳氮比是调控其对土壤氮、磷有效性影响的首要因素。资源利用策略对氮有效性的直接影响差异主要取决于对养分摄取的强弱，间接影响则由有机氮矿化主导。低碳氮比的细根提高了磷有效性，该影响通过产生更多的磷酸酶直接产生，或通过降低土壤pH而间接实现。本研究丰富了细根性状对土壤养分有效性的调控机制，并为杉阔混交林伴生树种选择提供了理论支撑。

The direct effect and mechanism of fine root traits on soil nutrient availability: A case study of subtropical Chinese fir and broad-leaved mixed forest

The effect of fine root traits on soil nutrient availability is mediated by microorganisms or by direct interaction between fine roots and soil. However, the former has received a lot of attention, while the latter has rarely been reported. In this study, six mixed tree species (3 resource-acquisitive and 3 resource-conservative) in a subtropical Chinese fir-broadleaf mixed forest were used as the research object. The direct, indirect, and overall effects of fine roots on soil nitrogen and phosphorus availability and the relationship between fine root traits and them were studied by an in-situ net bag test. The results showed that fine root direct contact with soil could improve the availability of soil N and P under both resource utilization strategies. The effect of acquisitive tree species on soil phosphorus was more significant, showing stronger direct, indirect, and overall effects, while the indirect effect of conservative tree species on soil nitrogen was stronger. Moreover, the C/N ratio of fine roots is the primary factor regulating its effect on soil N and P availability. The direct effect of resource utilization strategies on nitrogen availability mainly depends on the strength of nutrient uptake, and the indirect effect is dominated by organic nitrogen mineralization. Fine roots with a low C/N ratio directly promote P availability by producing more phosphatases or indirectly promote P availability by reducing soil pH. This study enriched the regulatory mechanism of fine root traits on soil nutrient availability and provided theoretical support for the selection of associated tree species in mixed forests.