Effects of Nitrogen Addition and Fire on Plant Nitrogen Use in a Temperate Steppe

Hai-Wei Wei,Xing-Guo Han,Xiao-Tao Lü,Fu-Mei Lü,Fei-Hai Yu

doi:10.1371/journal.pone.0090057

Abstract

Plant nitrogen (N) use strategies have great implications for primary production and ecosystem nutrient cycling. Given the increasing atmospheric N deposition received by most of the terrestrial ecosystems, understanding the responses of plant N use would facilitate the projection of plant-mediated N cycling under global change scenarios. The effects of N deposition on plant N use would be affected by both natural and anthropogenic disturbances, such as prescribed fire in the grassland. We examined the effects of N addition (5.25 g N m−2 yr−1) and prescribed fire (annual burning) on plant N concentrations and N use characters at both species and community levels in a temperate steppe of northern China. We found that N addition and fire independently affected soil N availability and plant N use traits. Nitrogen addition increased aboveground net primary productivity (ANPP), inorganic N, and N uptake, decreased N response efficiency (NRE), but did not affect biomass-weighed N concentrations at community level. Prescribed fire did not change the community level N concentrations, but largely decreased N uptake efficiency and NRE. At the species level, the effects of N addition and fire on plant N use were species-specific. The divergent responses of plant N use at community and species levels to N addition and fire highlight the importance of the hierarchical responses of plant N use at diverse biological organization levels to the alteration of soil N availability. This study will improve our understanding of the responses of plant-mediated N cycling to global change factors and ecosystem management strategies in the semiarid grasslands.

Highlights

Nitrogen (N) availability is the dominant limiting factor for primary productivity in most terrestrial ecosystems [1,2,3,4]
We found no interactive effect of N addition and fire on primary production at community level, implying that the positive effects of N deposition on primary production would not be affect by natural fire or prescribed burning in the temperate steppe of northern China
The positive effects of N addition on plant N uptake were resulted from the enhancement of aboveground net primary productivity (ANPP), as we found no impacts of N addition on plant N concentrations at both species and community levels

Summary

Introduction

Nitrogen (N) availability is the dominant limiting factor for primary productivity in most terrestrial ecosystems [1,2,3,4]. The responses of plants to the variation in soil N availability would have great implications for plant growth and species competition. It is well established that plant N economy plays an important role in affecting plant productivity and ecosystem N cycling [5,6]. Both plant N concentration and N response efficiency (NRE) are widely used to evaluate the responses of plant N economy to changes of soil N availability. Changes of plant N concentration have great implications for their N use efficiency (NUE), which is generally defined as the dry mass productivity per unit N taken up from the soil [7]. There is increasing empirical evidence that both plant N use indices should be simultaneously examined as they involve different processes linking the plant-soil system [11]

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Conclusion