氮素有效性调控红壤微生物碳源利用效率的机制

The red soils, distributed in southern China is characteristic with “acid” and “skinny”, and is not high in fertility. Combination application with organic and inorganic fertilization that dominated by organic substitution is the principal measures to enhance soil quality and carbon sequestration in this area. The previous long-term experiments have showed that there are significant differences in soil carbon sequestration and efficiency under different substitution ratios of nitrogen. We speculate that it may be related to the interaction of soil microbial community and microbial carbon use efficiency (CUE) caused by nutrient availability. Against the issue, this project, based on the long-term field experiments of red soils in Qiyang, aiming to analyzing the characteristics soil nitrogen form and composition, microbial community diversity and also the correlation stoichiometry between microbial biomass and extracellular enzyme activity under different organic substitution. Meanwhile, clarify the relationship between microbial CUE and nitrogen form and availability. By experiments which combined with 13C isotope tracing and 13C-PLFA-SIP probe, we hope to reveal the response mechanism and priming effect of CUE and carbon related key functional microorganisms to nitrogen addition under the condition of equal carbon addition. The study will be contributed to understanding the soil carbon conversion to nitrogen management and providing scientific basis for soil organic matter upgrading and nitrogen management.

南方旱作红壤普遍具有“酸”、“瘦”、有机碳含量低等特点，以减少化肥用量、配施有机肥为主导的有机替代是提升红壤肥力、增加碳固定的有效措施之一。前期长期定位试验表明，不同氮有机替代下红壤固碳特征与效率存在显著差异，推测可能与养分有效性引起的微生物群落结构及其碳源利用效率（CUE）的改变有关。针对上述问题，本项目依托祁阳红壤长期试验平台，研究有机替代下土壤氮素形态及组分、微生物群落以及微生物量和胞外酶活性的计量关系特征，阐明红壤微生物CUE与不同氮素形态及有效性间的关联性；采用13C同位素示踪手段，并结合13C-PLFA-SIP探针技术，明确在等碳添加条件下，不同氮形态含量梯度土壤微生物CUE及参与碳转化的关键功能微生物对氮素添加的响应过程及其激发效应，揭示有机替代措施影响土壤碳转化的微生物学机制。研究结果将有助于深刻理解农田土壤碳转化对氮素管理的响应，为农田土壤肥力提升和氮素管理提供科学依据。

农田有机质是土壤肥力的核心，碳氮元素存在强烈的耦合关系。本项目以有机替代下土壤固碳特征与效率存在显著差异，推测可能与土壤氮素有效性及微生物碳源利用效率（CUE）有关为切入点。依托湖南祁阳旱地红壤长期定位试验平台，研究有机替代模式下土壤氮素形态及组分、微生物群落以及微生物量和胞外酶活性计量关系特征，结合土壤微生物碳源利用的变化，揭示氮素有效性影响土壤碳转化的相关微生物机制。结果表明，长期不同施肥模式影响土壤氮素有效性，施用有机肥能够有效缓解农田土壤氮素损失，可使土壤总氮含量提高66.71%-78.24%（相比CK处理）。同时，受耕作和施肥影响造成的土壤总氮变化与有机氮组分中酸解铵态氮、酸解氨基酸态氮和酸解未知态氮密切相关。通过13C同位素示踪技术的研究表明，矿质态氮的输入降低微生物CUE，而有机态氮的输入能够显著提高土壤微生物CUE（0.76-0.79）。微生物CUE与碳及氮磷养分计量（DOC: mineral N, DOC: available P and mineral N: available P）、碳氮磷水解酶（BG、NAG和AP）活性密切相关。因此，有机替代通过改变碳氮磷计量关系影响CUE和激发效应，促进土壤肥力提升。相关研究结果在《Biology and Fertility of Soils》等国际期刊发表论文2篇，另有2篇文章在投稿中。研究结果将有助于深刻理解土壤碳氮相互作用理论，为农田土壤有机质提升和氮素管理提供科学依据。