我国温带地区土壤微生物冬季氮固持对植物养分吸收的贡献

氮是绝大多数陆地生态系统生产力的主要限制因素。从晚秋到初春氮在生态系统中被保持的程度对生长季植物的养分利用十分重要。在高山苔原中发现，土壤微生物冬季氮固持是植物春季养分供给的关键。然而，该假说是否适用于温带地区尚未得到验证；植物春季是否吸收了微生物释放的氮仍不确定；植物通过向土壤释放新固定的光合产物对微生物冬季氮固持的影响尚不清楚。本项目沿干暖到湿冷的气候梯度，选择3个观测站（河北塞罕坝、内蒙古塞罕乌拉和黑龙江大兴安岭）的主要植被类型（常绿和落叶针叶林、阔叶落叶林、常绿和落叶灌丛、草甸草原和典型草原），开展土壤微生物冬季氮固持对植物养分吸收的贡献以及植物通过同化产物分配对微生物冬季氮循环影响方面的研究。本项目旨在提高人们对温带冬季土壤微生物代谢过程和生物地化功能的认识、验证在高山苔原所观测到的微生物冬季氮固持假说在更多的陆地生态系统类型中的适用性，以及全面理解植物对生态系统氮循环的影响。

Nitrogen is a major limiting factor of net primary production for most of the terrestrail ecosystems. The ecosystem retention capacity of nitrogen from late autuman to early spring is vital for plant nutrient uptake during growing season. In tundra soils, microbial biomass nitrogen was found to peak under late-winter snowpack followed by a significant decline when soils thawed, thereby leading to increased nitrogen availability for plants at the start of the growing season. This pattern characterizes tundra soils at the winter-spring transition, but whether the similar pattern occurs in temperate soils is unclear. On the other hand, by releasing recently fixed photosynthates to the soil, plants may thus actively control microbial nitrogen cycling in winter. However, this control of the plants has, to our knowledge, not yet been explored in grassland ecosystems. To address these problems, we will examine the temporal variability in nitrogen pools of plant, soil and microorganisms, in the dominant vegetation types, including evergreen and deciduous conifereous forests, deciduous broadleaved forests, evergreen and deciduous shrublands, meadow and typical steppe, from three long-term observation sites of Saihanba, Saihanwula and Daxinganling. In addition, we will explore the control of photosynthates allocation on seasonal changes of microbial nitrogen cycling...Our major objectives are (1) to explicitly test whether the general pattern derived from observed dynamics in the alpine area being linked to microbial nitrogen retention in winter is applicable to a wide range of terrestrial ecosystems; (2) to enlarge our understanding of microbial nitrogen cycling in winter and its biogeochemical functions in temperate areas and (3) to fully understand the control of plant on ecosystem nitrogen cycling.