分次施氮对我国典型农田土壤碳转化的激发效应及其机制

Soil organic carbon (SOC) mineralization can be promoted by external organic input, so called priming effect. Priming effect has attracted lots of attention due to its close correlation with soil C transformation and C stability. Our previous study found that nitrogen (N) fertilization influenced priming effect in a certain extent, while the mechanisms of microbiology of the priming effect influenced by N addition are still unclear. In this program, we hypothesize that the relative N limitation is one of the key reasons for soil C priming effect, and split application of N would change soil C priming effect by continuously altering soil enzyme activities and the community and biomass of soil microbes. An 1-2 yr incubation study (with 13C-labeled residue, black soil and fluvo-aquic soil, N application) will be conducted to investigate the response of priming effect on SOC fractions to N application in typical farmland soils in China, and to explore the relationships between soil C cycling and the changes of soil enzyme activities, the community and biomass of soil microbes after N application. We aim to clarify the response and its mechanisms of priming effect on soil C loss/stabilization due to N application. The results will enrich the knowledge of relationships between soil C priming effect, microbiological characteristics and N fertilization, at the same time, supply with theoretical evidence for maintaining SOC storage and soil fertility sustainability.

添加外源有机物料促进土壤有机碳矿化的过程即激发效应，因与土壤碳转化和碳稳定性密切相关而受到人们长期广泛的关注。申请者在博士论文研究期间发现，施氮肥在一定程度上影响土壤碳素激发效应，但其微生物学机制尚不十分明确。针对这一科学问题，本项目假设氮素相对缺乏是土壤碳激发效应的主要原因之一，适量、多次施用氮肥可通过持续地改变微生物数量与酶活性，从而影响土壤碳激发效应。因此，本项目拟通过1-2年的室内土壤培养试验，借助13C标记小麦秸秆、施氮肥来阐明我国典型农田中氮肥不同施用方式下土壤各有机碳组分中的激发效应对施氮肥的响应特征，以及土壤中微生物群落结构、数量和酶活性变化与土壤有机碳周转的关系，进而解析不同农田土壤有机碳激发效应和碳素固定对施氮肥的响应及其机理。研究结果将丰富农田土壤中激发效应及微生物特征与氮肥施用的关系认识，为土壤有机碳库及土壤肥力可持续性管理提供理论依据。

土壤碳素固持受到了人们的长期广泛关注，添加外源有机物可以相对增加土壤碳含量，但施氮肥对该过程的影响及其微生物学机制尚不明确。本项目通过540天的室内培养试验，借助13C标记的小麦秸秆来探索我国典型农田中氮肥不同施用方式下土壤各组分中的碳素转化过程及对施氮肥的响应特征，以及土壤中微生物群落结构和酶活性变化与土壤碳周转的关系。研究发现：在培养初始，秸秆源性碳（Cres）主要存在于轻质组分（LF）中，随着培养的进行LF可以降解并使其碳素转化进入闭蓄态颗粒有机质组分（OPOM）和重组（HF）。至培养结束，在有机质含量较高的黑土中添加秸秆后，施氮比不施氮更能增加HF中Cres残留率（23.25% vs 20.34%，P<0.05），减少HF中土壤原有碳（Csoil）的矿化损失。在潮土中，分次施氮比一次性施氮更有利于LF-Cres的降解，促进Cres进入到OPOM和HF中，进而增加土壤中Cres总残留率。土壤Csoil损失率表现为HF>OPOM>LF，添加秸秆提高了两种土壤的Csoil损失率，存在正激发效应，而施氮肥减轻了黑土中的该激发效应，且分次施氮比一次性施氮的减轻作用更明显。通过对两种土壤微生物群落组成的研究发现，黑土的微生物群落数目比潮土丰富。添加秸秆提高了黑土中变形杆菌门和拟杆菌门的相对丰度，潮土中添加外源碳氮则提高了绿菌门的丰度。施氮会增加两种土壤中绿弯菌门的相对丰度，说明该菌群对碳的固定可能需要氮的参与。与分次施氮相比，一次性施氮降低了两种土壤中硝化螺旋菌门的相对丰度。从土壤酶活性的角度来看，土壤过氧化氢酶活性在培养过程中呈下降趋势，添加秸秆可以在短期内提高土壤过氧化氢酶活性，且分次施氮比一次性施氮能相对改善土壤微生态环境，从而提高土壤微生物活动和过氧化氢酶活性。研究结果增强了人们对农田土壤中激发效应及微生物特征与施用氮肥关系的认识，为土壤有机碳库及土壤肥力可持续性管理提供了一定的理论依据。