我国典型茶园土壤供氮途径及其控制因子

Tea plants require an acidic soil to grow and also can acidify soil during their cultivation. The soil microbial biomass, activity and community structure as well as nitrogen (N) transformations in tea soils could be clearly different from that in other ecosystems, due to its high tolerance to acid and aluminum, and distinct preference to ammonium rather than nitrate. However, nitrogen dynamics in tea soils and their controlling factors remains poorly understand. The influences of soil acidification arising from long-term tea cultivation and also from fertilization, and long-term fertilization on tea soil N supply are still not clear. In this study, 15N tracing technique and C2H2 inhibition method combined with numeric FLUAZ model are to be used to calculate gross N transformation rates, mainly including mineralization, autotrophic nitrification, heterotrophic nitrification, microbial immobilizations of NH4+ and NO3-, denitrification and re-mineralization in the typical tea soils and tea soils of varying stand age in the main tea production districts in China. The purposes are to 1) characterize gross N transformation rates in tea soils and their controlling factors, and elucidate the N supply pathway, capacity and the mechanism of N retention in the typical tea soils from the main tea production districts in China, 2) evaluate how cultivation and stand age affects the N supply pathway and net supply capacity. These results will provide deep insights into the reasonable application of N fertilizer, improving N use efficiency, reducing environmental pollution caused by N and the sustainable development in tea gardens.

茶树耐酸耐铝毒、喜铵厌硝的特性无疑决定其与其他生态系统存在不同的微生物以及氮循环特性。然而，对于酸性茶园土壤这个独特的生态系统，氮素的转化规律及其控制因子还未明确，长期种植茶园后酸化以及长期施用氮肥对土壤氮素供应的影响尚未引起足够的重视。本项目以我国典型茶园土壤和不同种植年限茶园土壤为研究对象，通过15N成对标记法和乙炔抑制法结合数值FLUAZ模型，测定茶园土壤有机氮矿化、有机氮异养硝化、铵态氮自养硝化、铵态氮和硝态氮的微生物同化、硝态氮反硝化、再矿化的初级转化速率，明确我国主要产茶区典型茶园土壤氮素初级转化速率及其控制因子，阐明茶园土壤供氮机理；揭示种植年限对茶园土壤供氮能力和供氮途径的影响。研究结果将为指导茶园土壤的合理施用氮肥、提高氮肥利用率、及茶园生态系统的可持续发展提供理论依据。

明确酸性茶园土壤中的氮素转化规律，在此基础上合理施用氮肥，恰当使用改良措施，对于提高氮肥利用率、最大限度的降低氮肥对环境的负面效应，并为茶园土壤的科学管理、提高茶叶产量品质及促进茶园生态系统可持续发展，显得尤为重要。本研究以我国典型茶园土壤为研究对象，采用室内常规培养方法、15N同位素成对标记法，主要研究：1）植茶年限对土壤净硝化速率和N2O排放的影响；2）长期化学氮肥施用对茶园土壤硝化途径和N2O排放途径的影响；3）筛选出针对茶园土壤有效的硝化抑制剂种类。结果表明，安徽地区林地改种茶园显著抑制了净硝化速率。与安徽地区的林地和茶园土壤相比，浙江和福建地区林地和茶园土壤净硝化速率很低(<0.2 mg N/(kg•d))，且林地改为茶园后对土壤净硝化速率没有显著影响。安徽地区植茶年限超过10年的茶园土壤N2O累积排放量均显著低于邻近的林地土壤，而植茶年限为10年的茶园土壤与邻近的林地土壤差异不显著。浙江和福建茶园土壤N2O累积排放量均高于各自对照的林地土壤。安徽地区土壤的N2O累积排放量与pH值呈显著的正相关关系，这表明林地改为茶园后，随着植茶年限的增加和氮肥的施用，pH降低抑制了硝化速率，进而降低N2O排放。长期施肥提高N2O排放的原因可能是刺激了自养和异养硝化速率，并提高了自养硝化、异养硝化和反硝化过程中N2O的排放比率。在好养条件下，土壤pH决定了N2O产生途径，pH阈值大概在4.4左右，低于4.4，反硝化起主导地位，反之，硝化是产生N2O的主导途径。土壤pH与反硝化对N2O排放的贡献呈很好的负指数相关关系。DCD并不能有效抑制茶园土壤硝化作用，而Nitrapyrin可以完全抑制茶园土壤硝化作用。