Decoupling the direct and indirect effects of nitrogen deposition on ecosystem function

Abstract

Elevated nitrogen (N) inputs into terrestrial ecosystems are causing major changes to the composition and functioning of ecosystems. Understanding these changes is challenging because there are complex interactions between 'direct' effects of N on plant physiology and soil biogeochemistry, and 'indirect' effects caused by changes in plant species composition. By planting high N and low N plant community compositions into high and low N deposition model terrestrial ecosystems we experimentally decoupled direct and indirect effects and quantified their contribution to changes in carbon, N and water cycling. Our results show that direct effects on plant growth dominate ecosystem response to N deposition, although long-term carbon storage is reduced under high N plant-species composition. These findings suggest that direct effects of N deposition on ecosystem function could be relatively strong in comparison with the indirect effects of plant community change.

A comparison of the strength of biodiversity effects across multiple functions

“…Nutrient cycling will probably be less severely affected by plant species loss. In this case, direct effects of nitrogen deposition on nutrient cycling may be more severe than indirect effects mediated through changing species composition (Manning et al 2006), although a loss of species from the particular functional group of legumes could have strong indirect effects. However, in more nitrogen-limited systems, where the plant species richness-biomass relationship is more likely to be driven by resource complementarity for nitrogen, loss of plant species richness might have larger effects on nitrogen cycling.…”

Effect of nitrogen fertilizer on nitrogen pools and soil communities under grazed pastures

“…This is higher than with other studies showing that fungi and fungal-feeding organisms are often reduced when soil N fertility and recycling increases (Coleman et al 1983;Bardgett et al 1999;De Vries et al 2006, 2007Lauber et al 2008;Krumins et al 2009). The mechanism is unknown but both are direct effects of fertilizer itself, and changes in the plant community and litter associated with fertilizers could be involved (Donnison et al 2000;Manning et al 2006). Fungal DNA profiles can also undergo a reduction in diversity in response to fertilizer (Allison et al 2007), but others found that the bacterial communities (but not fungi) can be altered by high rates of fertilizer (Gray et al 2003;Kennedy et al 2004Kennedy et al , 2005.…”

The Role of Plants in the Effects of Global Change on Nutrient Availability and Stoichiometry in the Plant-Soil System

“…As a consequence of the increases in P uptake, the concentration of P in soils tends to decrease (Kowalenko, 2006), and increases in P limitation in plants are observed after long-term N deposition (Bragazza et al, 2004;Güsewell, 2004;Menge and Field, 2007;Lund et al, 2009; and in experiments simulating N deposition (Braun et al, 2010, which can lead to high N-P ratios in soils (Fenn et al, 1998;Manning et al, 2006;Braun et al, 2010). This P limitation can scale up through trophic webs and affect herbivores (Tao and Hunter, 2012).…”