The impact of elevated CO2, increased nitrogen availability and biodiversity on plant tissue quality and decomposition

Summary

This field experiment tested whether increases in net primary productivity driven by elevated CO2, nitrogen deposition, and plant biodiversity are matched by corresponding increases in decomposition rates. Whilst litter chemistry responded significantly to all three global change factors—elevated CO2 decreased nitrogen and lignin content, nitrogen addition increased nitrogen but decreased lignin, and higher diversity reduced nitrogen and lignin but increased cellulose—decomposition rates showed markedly weaker responses, with only a 2.5% decrease in carbon loss under elevated CO2 and negligible responses to nitrogen addition or species richness. This uncoupling between production and decomposition suggests that productivity gains may be offset by nutrient accumulation in the litter pool, potentially limiting future productivity increases.

Regional applicability

The study was conducted in experimental grassland plots in the United States and may not directly reflect United Kingdom field conditions, which differ in climate, soil types, and native plant communities. However, the findings are relevant to UK policy on carbon sequestration, nitrogen deposition impacts, and biodiversity conservation, as they suggest that productivity gains from these global change drivers may not be sustainably supported by ecosystem decomposition processes.

Key measures

Plant tissue %N, %lignin, %cellulose; litter carbon loss over 1-2 years; aboveground litter quality; belowground root quality; decomposition rates under three-way factorial manipulation (CO2 ambient vs. 560 ppm; N ambient vs. 4 g N m⁻² yr⁻¹; plant species richness 1, 4, 9, 16 species)

Outcomes reported

The study measured changes in plant tissue chemistry (nitrogen, lignin, cellulose content) and litter decomposition rates in response to elevated CO2, nitrogen deposition, and plant species richness manipulations. Decomposition was quantified over one and two-year periods using in situ litterbags in experimental grassland plots.

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