Abstract
Human activities enhance the atmospheric CO2 concentration and modify climatic patterns, which could change the growth and quality of plant materials, as well as their subsequent decomposition, thus altering stream ecosystem functioning. These effects could be modulated by interactions between plant species differing in biological traits and competitive capacity. We cultivated the forb Trifolium pratense and the grass Agrostis capillaris under different CO2 concentration (ambient or elevated), water availability (control or drought), and competition (monoculture or mixture). The material thus grown was conditioned in a stream for microbial colonization, and its subsequent decomposition was measured in laboratory microcosms. Elevated CO2 reduced the quality of T. pratense but not that of A. capillaris. Water shortage limited plant quality but did not interact with CO2 concentration. Interspecific competition only affected nitrogen concentration in A. capillaris. Elevated CO2 did not affect decomposition rate, and A. capillaris, the species richer in nutrients, decomposed more slowly. Our results showed that the decomposition rates of plant materials grown under elevated CO2 are difficult to predict due to species-specific responses and interactions with other factors.
Highlights
Future scenarios of global environmental change forecast a doubling of the atmospheric CO2 concentration by the end of the 21st century (Intergovernmental Panel on Climate Change (IPCC) 2013)
N concentration of A. capillaris was not affected by elevated CO2 but decreased under water stress and under interspecific competition (Fig. 1B; Table 1)
For T. pratense, P concentration tended to decrease under elevated CO2 (p = 0.092; Fig. 1C; Table 2), and for A. capillaris, it tended to be higher at elevated CO2 under competition
Summary
Future scenarios of global environmental change forecast a doubling of the atmospheric CO2 concentration by the end of the 21st century (Intergovernmental Panel on Climate Change (IPCC) 2013). The interaction between elevated CO2 and water stress may alter plant quality, which is important for consumers, and modify key ecological processes such as decomposition and carbon (C) cycling (Aerts 1997; Hladyz et al 2009). The combination of elevated CO2 and water stress could produce a large decrease in the quality of plant tissues. It has been suggested that the detrimental effects of water stress could be partially mitigated by the elevated CO2 (Pérez-López et al 2014), as it would increase the efficiency of water use, enhancing soil moisture, nutrient availability, plant growth, and N uptake (Morgan et al 2004; Dijkstra and Cheng 2008). It has been shown that high CO2 and drought increase C:N in isolation but not when acting together (Larsen et al 2011)
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