Low Nitrogen Retention in Soil and Litter under Conditions without Plants in a Subtropical Pine Plantation

Yanmei Xiong,Huimin Wang,Xingliang Xu,Fusheng Chen,Hui Zeng,Dali Guo

doi:10.3390/f6072387

Abstract

Soil acts as a major sink for added nitrogen (N) in forests, but it remains unclear about the capacity of soil to immobilize N under conditions without plant roots and whether added N interacts with ecosystem N to affect N retention. We added 15NH415NO3 to in situ soil columns (with leaching) and leaf litter (without leaching) of two tree species in a subtropical Pinus elliottii plantation. Soil and litter were collected three or eight months after N addition to measure concentrations of indigenous and exogenous N. About 70% of exogenous N was retained in soil three months after N addition, of which 65.9% were in inorganic forms. Eight months after N addition, 16.0% of exogenous N was retained in soil and 9.8%–13.6% was immobilized in litter. N addition increased the mineral release and nitrification of soil indigenous N. Loss of litter indigenous N was also increased by N addition. Our results suggest that N deposition on lands with low root activities or low soil carbon (C) contents may lead to increased N output due to low N immobilization. Moreover, the effects of added N on ecosystem indigenous N may decrease the capacity of soil and litter in N retention.

Highlights

Human activities have greatly increased the inputs of atmospheric nitrogen (N) to the Earth’s land surface globally through agricultural fertilization and combustion of fossil fuel [1,2,3]
Tracer studies across global forests showed that the mean 15N tracer recovery from soil was around 80% for short-term (
By applying 15N labeled inorganic N at a rate similar to ambient N deposition to intact soil columns and litter, we evaluated the capacity of soil and litter in N retention without plants

Summary

Introduction

Human activities have greatly increased the inputs of atmospheric nitrogen (N) to the Earth’s land surface globally through agricultural fertilization and combustion of fossil fuel [1,2,3]. Increased N deposition can result in N saturation when it exceeds the biotic demand, leading to increased rates of N cycling and losses of nitrate, soil and water acidification, plant nutrient imbalances and even forest decline [11,12,13]. A meta-analysis of 15N tracer studies across global forests showed that the mean 15N tracer recovery from soil (organic and mineral layer) was around 80% for short-term (

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Discussion

Conclusion