The Effect of Nitrogen Deposition on Plant Performance and Community Structure: Is It Life Stage Specific?

Elise M Tulloss,Mary L Cadenasso,Lucas C.R Silva

doi:10.1371/journal.pone.0156685

Elise M Tulloss, Mary L Cadenasso + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0156685

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Abstract

Nitrogen (N) deposition is a key global change factor that is increasing and affecting the structure and function of many ecosystems. To determine the influence of N deposition on specific systems, however, it is crucial to understand the temporal and spatial patterns of deposition as well as the response to that deposition. Response of the receiving plant communities may depend on the life stage-specific performance of individual species. We focus on the California oak savanna because N deposition to this system is complex—characterized by hotspots on the landscape and seasonal pulses. In a greenhouse experiment, we investigated the relative influence of N deposition on plant performance during early growth, peak biomass, and senescent life stages across different soil types, light, and community compositions. To represent the community we used three grass species—a native, naturalized exotic, and invasive exotic. At early growth and peak biomass stages performance was measured as height, and shoot and root biomass, and at the senescent stage as seed production. Simulated N deposition 1) increased shoot biomass and height of the native and, even more so, the naturalized exotic during early growth, 2) positively affected root biomass in all species during peak biomass, and 3) had no influence on seed production at the senescent stage. Alone, N deposition was not a strong driver of plant performance; however, small differences in performance among species in response to N deposition could affect community composition in future years. In particular, if there is a pulse of N deposition during the early growth stage, the naturalized exotic may have a competitive advantage that could result in its spread. Including spatial and temporal heterogeneity in a complex, manipulative experiment provides a clearer picture of not only where N management efforts should be targeted on the landscape, but also when.

Highlights

Nitrogen (N) deposition is an element of global change that affects plant community structure, typically driving increases in exotic species abundance and decreases in species richness [1,2]
The effect of N fertilization on plant performance varied across life stages, shifting from a mostly aboveground response in early growth to a belowground response at peak biomass (Table 1)
In contrast to early growth, at peak biomass the invasive exotic and native responded to high N through greater root biomass, and the naturalized exotic through increased shoot and root biomass (N, Wilks’ Lambda F4,423 = 2.928, P = 0.0335)

Summary

Introduction

Nitrogen (N) deposition is an element of global change that affects plant community structure, typically driving increases in exotic species abundance and decreases in species richness [1,2]. We focus on the effects of N deposition in semi-arid savannas, using the California oak savanna as a model ecosystem. Deposition to this system and across the western US is expected to increase due mostly to agricultural and urban development [6]. Effects of N deposition on this system have included increases in exotic grass abundance, decreases in native species, decreases in sensitive lichen species, and changes in mycorrhizal communities [7]. To understand how N deposition may structure plant communities in this system, incorporating the characteristic spatial and temporal variability of this deposition into experimental tests is required

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