外源易利用碳氮在潮土秸秆还田过程中的激发分解效应研究

To return plant residues back to the fields has been proved to be helpful for soil fertility improvement. However, short-term decrease in crop yield following the application of plant residues is often found, probably because of shortage of soil nutrition resulting from slow decomposition of the residues to meet plant requirement, which has inhibited the extensive application of the residues. We hypothesize that certain substrate additions to soils may accelerate decomposition of the residues. Research on these so called "priming effects" has caused much concern, in which most of them was conducted in laboratory scale with plant residues and easily available C and N sources as additives, with C and N being added simultaneously or separately. But up to now, mechanisms on accelerated decomposition of the plant residues induced by easily available C and N sources and their significance on practical use remain uncertain. In this study, using 13C and 15N labeled plant residues, the effects of original soil fertility, soil water status, and root exudates and/or root hairs on the accelerated decomposition of plant residues induced by addition of glucose with and without N, and by the addition of chicken composts rich in microbial biomass and diverse in microbial community composition, will be investigated in laboratory incubation, greenhouse, and field scale experiments in the soils in the North China Plain. Fate of C and N derived from the plant residues will also be traced, and contribution of microbial biomass contained in the chicken compost be evaluated by monitoring the change in microbial community structure. In addition, the significance on practical use of accelerated decomposition induced by easily available C and N sources will be assessed in terms of soil nutrition change, fate of soil organic matter, and crop yield. The novelty of the study include: (1) scaling up the research experiments from laboratory to field, and (2) comprehensively considering the effect of environmental factors that the plant residues retain in the soil on the accelerated decomposition of the residues, especially considering the presence of microbial biomass in the source of easily available C and N. The results obtained from the study will provide theoretical basis for further extensive use of plant residues in the North China Plain.

秸秆不能及时分解而导致作物产量短期内降低的现象是阻碍秸秆还田广泛推广的主要原因之一。利用外源易利用碳氮，比如葡萄糖、无机氮、鸡粪中的易利用碳氮，激发分解土壤有机质的研究正在国际上引起关注，但研究往往局限于实验室培育，因而激发机理和激发分解秸秆的实际应用前景尚不确定。本项目拟通过室内培育、温室盆栽、田间试验尺度不断扩展的方式，以潮土为研究对象，利用13C和15N同位素标记秸秆，系统考虑土壤本身肥力水平、土壤含水量、作物种植（主要考虑其根际分泌物等）对葡萄糖、无机氮和本身携带微生物比较丰富的鸡粪激发秸秆分解的影响；同时追踪分解秸秆去向、评估鸡粪中微生物对激发秸秆分解的贡献；从土壤养分含量变化、有机质去向、作物产量三个方面分析外源易利用碳氮激发秸秆分解的实际应用前景。其创新点在于：（1）扩展了研究尺度，（2）综合考虑秸秆存在环境条件对激发秸秆分解的影响，尤其是易利用碳氮中本身携带微生物的影响。

以黄淮海平原的典型潮土为研究对象，采用13C标记和核磁共振（NMR）等技术，通过县域尺度的布点采样、室内培育实验、温室盆栽试验、大田试验等研究方法，主要获取了以下几方面结果（1）基于县域尺度，明确了潮土有机碳含量是决定当地土壤质量和作物产量的主要因子，（2）明确长期施用秸秆来源有机肥显著提升土壤有机碳含量、改善土壤生物性质；但当等碳量添加时，秸秆地上部对有机碳累积的贡献少于根部，（3）基于NMR技术，发现土壤腐殖物质的形成路径是原始有机物料先转化为胡敏素（HM），HM进一步被降解、氧化，最后转化为胡敏酸（HA），富里酸（FA），（4）模拟实验结果表示在秸秆还田的基础上同时添加无机氮和一些易利用碳源可以全面提升土壤的微生物活性，从而可能激发秸秆分解；但潮土的质地也影响着秸秆分解，（5）盆栽试验发现作物种植改变了土壤微生物群落组成，单独作物种植以及秸秆还田配合作物种植均显著增加丛枝真菌含量，从而显著增加> 0.25 mm粒径土壤团聚体数量，提高团聚体稳定性；采用标记磷脂脂肪酸（13C-PLFA）技术发现根际微生物数量和群落结构受作物品种的显著影响，暗示种植不同品种作物有可能导致秸秆激发分解的方向不同，（6）有机无机肥联用与单独使用化肥相比显著增加秸秆还田潮土的闭蓄态C、闭蓄态N、热水提取可溶性有机N、微生物生物量C含量，并且这些变化不受制于施肥量高低。除了随有机肥添加而增加的碳源能激发微生物生长和刺激微生物活性外，有机肥通过刺激本土微生物生长导致的微生物组成变化同样是造成易利用土壤有机质库变化的主要原因。表明有机无机肥联用能加速秸秆转化，从而增加潜在作用可利用N。基于本项目部分研究技术 “激发式秸秆还田技术”集成的技术体系已得到地方的认可，获得了2014年河南省科技进步二等奖1项（基金主持人排名第八）。共发表相关学术论文11篇，其中SCI收录论文6篇。培养研究生3名。