利用15N同位素技术研究杉木不同发育阶段氮素获取策略

Nitrogen (N) is the essential nutrient for plants, which primarily limits the productivity of forest ecosystems globally. Chinese fir (Cunninghamia lanceolate (Lamb.) Hook) is one of the most important commercial timber species in south China, accounting for 21% of the total plantation areas of China. However, productivity decline of Chinese fir plantations has been observed as result of highly intensive management. Understanding N use efficiency is critical for improving productivity of Chinese fir plantation. Little is known about N uptake preference of soil ammonium, nitrate and organic N by Chinese fir, as well as the plasticity in the form of N utilized at different development stages. In this project, 15N stable isotope technique will be used to investigate N uptake strategies of Chinese fir at 2, 9 and 32 years of age in subtropical China. 15N labeled ammonium, nitrate and glycine will be applied in the field to examine whether Chinese fir show preferences in their use of chemical forms of soil N. Together with 15N natural abundance of plant and availability of soil N forms, we will further elucidate the contribution of different soil N forms to plant N acquisition. The findings of this project will enhance our understanding of plant N use strategies through forest stand development, which have important implications for the sustainable management of Chinese fir plantation.

氮（N）是植物生长发育所必需的营养元素，也是全球森林生态系统生产力的限制因素。杉木（Cunninghamia lanceolata（Lamb.）Hook）是我国南方重要的造林树种，长期集约化经营导致杉木人工林产量日趋下降。传统林木经营主要通过改土施肥等措施来提高产量，较少从提高杉木养分（N素）利用效率来考虑。有关杉木对土壤中不同形态N是否存在偏好吸收还不清楚，而且杉木在不同发育阶段的N素吸收偏好是否具有可塑性也尚待研究。本项目拟选择不同发育阶段（幼龄、中龄和成熟）杉木人工林为研究对象，在野外原位条件下采用15N标记和15N自然丰度相结合的方法，研究杉木对不同形态N（铵态氮、硝态氮和有机氮）的吸收偏好，并结合不同发育阶段杉木林地供N特征，量化土壤各形态N对杉木N吸收的贡献，旨在揭示不同发育阶段杉木的N素获取策略及其调控机理，从而为提高杉木养分利用效率、合理制定施肥措施提供理论依据。

本项目以中亚热带不同发育阶段（7年，15年, 24年和34年）杉木人工林为研究对象，分析了不同发育阶段杉木人工林土壤铵态氮、硝态氮和氨基酸组成和含量的季节性变化特征，运用15N同位素标记法量化了不同发育阶段杉木对不同形态氮的吸收速率以及不同形态氮对杉木氮吸收的贡献率。结果表明，杉木林土壤供氮能力呈现明显的季节性特征，夏季铵态氮、硝态氮和总氨基酸含量均显著高于冬季；土壤硝态氮含量随林龄增加呈现先升高后降低趋势，而土壤总氨基酸含量呈现逐渐下降趋势。不同林龄铵态氮含量差异因季节而异，夏季中龄林杉木林土壤铵态氮含量显著低于其他林龄，而在冬季不同林龄杉木林无显著差异。不同林龄杉木均偏好吸收铵态氮，而对硝态氮和甘氨酸的吸收偏好因林龄和季节而异。近熟林和成熟林杉木夏季偏好吸收甘氨酸，而在冬季对硝态氮和甘氨酸的吸收不存在偏好。因此，建议对不同发育阶段的杉木在生长季和非生长季施加氮肥是采取不同的配比，以提高杉木林氮肥利用效率，从而促进杉木人工林的可持续发展。