长期施氮引起的旱地土壤有机碳氮累积机制研究

Nitrogen (N) is one of the three major nutrients for crops, and N fertilizers have not only played an important role in the increase of crop yield and development of agriculture, but also affected the ammount of orgainc matter return to soil, soil biochemical environment and cycles of soil organic nitrogen (SON) and carbon (SOC). The concentrations of SOC and SON in soil directly determine the soil fertility and sustainable use of soil. So, does long-term N fertilizer application to soil increase SOC and SON concentrations and improve the soil fertility. The researches have shown that there had the different effects and mechanisms in different regins. Aiming at revealing the mechanism of SOC and SON increment on a low organic matter dryland in southern Loess Plateau, long-term field experiment and incubation experiment are interacted in this study. The physical-chemical joint grouping method and high-throughout pyrosequencing technology are used to separate the factions of SOC and SON (unprotected, physically stabilized, chemically stabilized and biochemically stabilized fraction) and analyze the microbes community (bacteria and fungus), respectively. The labile factions of SOC and SON (light fraction organic C and N, microbial biomass C and N, dissolved organic C and N), mineralization of SOC and SON, and soil enzymes are also determined. The results will reveal the relationships between SON/SOC fractions and microbial diversity, soil enzymes, the mechanism of SOC and SON increment in dryland in Loess Plateau and give some suggestion for nitrogen fertilization and soil fertility improvement.

氮肥施用不仅能提高作物产量，还能通过影响有机物归还和土壤生化环境等间接作用于有机碳氮累积与矿化，进而影响到土壤培肥过程。长期施氮是否可以提高有机碳氮含量和培肥土壤？不同区域结论不一，其累积机制也不同。本项目针对长期施氮后黄土高原南部旱地土壤有机碳氮含量增加机制尚不明确的科学问题，将野外长期试验、室内培养试验相结合，采用物理-化学联合分组方法、高通量测序等技术，分析长期施氮后旱地麦田土壤（包括历史样品和现有样品）未受保护游离态、物理保护、化学保护和生物化学保护不同机制有机碳氮组分的时空演变特征、活性有机碳组分（轻组、微生物量、可溶性有机碳氮）特征和有机碳氮矿化特征，并解析它们与有机碳氮循环密切相关的土壤酶活性、功能微生物群落结构和多样性的关系，揭示施氮引起旱地有机碳氮累积的机制。研究结果将为有机质含量较低的黄土高原旱地冬小麦氮肥施用和培肥土壤提供科学依据。

氮肥施用不仅能提高作物产量，还能通过影响有机物归还和土壤生化环境等间接作用于有机碳氮累积与矿化、微生物多样性，进而影响到土壤培肥过程。本项目通过黄土高原南部旱地野外长期试验、室内培养试验，采用物理-化学联合分组方法、高通量测序等技术，分析了长期施氮后旱地麦田土壤不同保护机制有机碳氮组分变化规律、活性有机碳氮组分变化规律、有机碳氮矿化特征、土壤酶活性和土壤真菌、细菌多样性、群落组成及其功能变化特征，并解析了有机碳氮累积与有机碳氮循环密切相关的土壤酶活性、微生物群落结构和多样性的关系。结果表明，长期施氮肥显著增加了土壤氮素氮素残留量，显著提高了该区域土壤有机碳（9.5%）、有机氮（7.4%）、微生物生物量氮（12.2%）、氮素净矿化量（31.3%）和碳素净矿化量（12.0%）含量，但对微生物生物量碳含量无影响。氮肥的施入提高了0-20 cm土层氮素矿化潜力，降低了氮素矿化速率，有利于土壤氮素的持久供应，且有机氮、有机碳作为氮素矿化的底物分别在0-20 cm土层土壤氮素矿化中起决定作用。氮肥施用提高了未保护游离细颗粒fPOM中有机碳（73.0%）、游离粗颗粒cPOM中TN（14.9%）和生物化学保护组分NH-fCS的TN（38.0%）含量。氮肥施用均未显著降低或提高土壤酸性磷酸酶活性、木糖酶、纤维素酶、对乙酰氨基葡萄糖苷酶活性，但这些酶活性均随着施氮量的增加有升高的趋势。氮肥施用对土壤真菌多样性影响较小，但改变了真菌群落组成结构；氮肥施用显著提高了细菌多样性及改变了群落结构组成，且细菌多样性及群落结构与土壤有机碳、全氮、速效磷和pH密切相关。此外，土壤中的真菌主要是腐生营养型为主，细菌以化能异养型为主，且氮肥施用显著提高了土壤中参与氮素转化的功能细菌的相对丰度。由此可见，适宜的氮肥用量有利于旱地土壤有机碳氮的累积和土壤肥力的提高。研究结果为该区域旱地小麦氮肥施用提供了技术支撑，为氮肥减施提供了理论依据。