Cumulative nitrogen input drives species loss in terrestrial ecosystems

Abstract

Aim Elevated inputs of biologically reactive nitrogen (N) are considered to be one of the most substantial threats to biodiversity in terrestrial ecosystems. Several attempts have been made to scrutinize the factors driving species loss following excess N input, but generalizations across sites or vegetation types cannot yet be made. Here we focus on the relative importance of the vegetation type, the local environment (climate, soil pH, wet deposition load) and the experimentally applied (cumulative) N dose on the response of the vegetation to N addition. Location Mainly North America and Europe.Methods We conducted a large-scale meta-analysis of in situ N addition experiments in different vegetation types, focusing on the response of biomass and species richness.Results Whereas the biomass of grasslands and salt marshes significantly increased with N fertilization, forest understorey vegetation, heathlands, freshwater wetlands and bogs did not show any significant response. Graminoids significantly increased in biomass following N addition, whereas bryophytes significantly lost biomass; shrubs, forbs and lichens did not significantly respond. The yearly N fertilization dose significantly influenced the biomass response of grassland and salt marshes, while for the other vegetation types none of the collected predictor variables were of significant influence. Species richness significantly decreased with N addition in grasslands and heathlands [Correction added on 23 March 2011, after first online publication: 'across all vegetation types' changed to 'in grasslands and heathlands']. The relative change in species richness following N addition was significantly driven by the cumulative N dose. Main conclusionsThe decline in species richness with cumulative N input follows a negative exponential pathway. Species loss occurs faster at low levels of cumulative N input or at the beginning of the addition, followed by an increasingly slower species loss at higher cumulative N inputs. These findings lead us to stress the importance of including the cumulative effect of N additions in calculations of critical load values.

Herbivores and nutrients control grassland plant diversity via light limitation

“…2d and Extended Data Table 5, P , 0.001). This result is consistent with eutrophication-induced loss of niches for coexistence 8,9,19,28 and demonstrates the generality of eutrophication as a primary force controlling the diversity of grassland communities by reducing ground-level light 20 .…”

Microbially mediated nitrogen retention and loss in a salt marsh soil

“…Sea level rise may increase the dominance of forbs in some coastal ecosystems (Warren and Niering 1993) whereas N inputs may allow graminoids to outcompete forbs (Bowman et al 1993, De Schrijver et al 2011. It is unclear if N retention by plants is greater under forbs or graminoids because graminoids tend to have both higher net primary production and N use efficiency than forbs Roths 1999, Scharfy et al 2011).…”

Testing mechanisms of N-enrichment-induced species loss in a semiarid Inner Mongolia grassland: critical thresholds and implications for long-term ecosystem responses

“…To address the first and second questions, we used several statistical approaches for assessing long-term changes in species diversity and ecosystem functioning at the levels of plant species, functional group and the whole community resulting from N enrichment. To address the third question, using functional trait-based approach, we tested six interrelated hypotheses which have been proposed to be the major mechanisms driving the N 2 enrichment-induced changes in plant species diversity and ecosystem functioning [7,19,22,23,29,35]. These hypotheses include the random loss, shift from below-ground competition to above-ground or light competition, recruitment limitation, N addition duration, water and N co-limitation, and soil acidification.…”