The retention dynamics of early-spring N input in a temperate forest ecosystem: Implications for winter N deposition

In N-limited temperate regions of China, rates of atmospheric N deposition remain high during winter due to industrial development and energy consumption. Winter-deposited N accumulates and is then released after snowmelt. However, little is known about the retention dynamics of early-spring N input in temperate forest ecosystems. We applied 15N isotopic tracer after snowmelt, and then quantified 15N dynamics in litter, soils, microbes and vascular plants over the following growing season in a warm temperate forest of northern China. In early spring (7 days after 15N addition), approximately 80% of applied 15N was retained in the ecosystem. The 15N recovery was the highest in litter, followed by soils and microbes, with only trivial acquisition in vascular plants. After early spring, there was little change in total 15N recovery over the following season, which indicated that the temperate forest ecosystem had high potential for the retention of early-spring N input. The 15N levels gradually declined in litter and microbes, while they were gradually increased in the vascular plants. In late fall, substantial 15N tracer retained in litter and was resorbed from senescing tissues to roots. Evergreen coniferous trees presented higher 15N acquisition than deciduous broad-leaved trees. Our results suggest that substantial early-spring N input can be retained in warm temperate forest ecosystems. The findings highlight the importance of litter and plants in sustaining early-spring exogenous N resources, inferring the need to considering winter N deposition for a better understanding of N cycling in temperate ecosystems.

Automated summary

This study reveals the high potential of warm temperate forest ecosystems in retaining early-spring nitrogen input, with litter and plants playing significant roles in sustaining the nitrogen resources. Considering winter nitrogen deposition is important for better understanding nitrogen cycling in temperate ecosystems.