Moisture dependence of above- and belowground responses to warming in an old-field ecosystem
To examine the degree to which species and ecosystem responses to warming are nonlinear and moisture-dependent, we exposed plots of an old field with tree seedlings to factorial combinations of warming (four levels, from ambient to +4°C) and precipitation (-50%, ambient, and +50%). We measured responses of plant growth and soil processes to the treatments over six years.
In general, responses of plant and soil processes to warming depended strongly on precipitation treatments. Warming typically decreased plant growth under dry conditions, but had no effect or increased growth under ambient or wet conditions. Warming affected growth of seedlings of some tree species (Acer rubrum, Betula lenta) more strongly than others (Pinus strobus, Quercus rubra). Heterotrophic respiration and nitrogen transformations accelerated under warming, but only in treatments and/or seasons with sufficient soil moisture. These processes also became less sensitive to temperature in warmed plots. Understanding the character of land and soil process responses to warming, and their dependence on soil moisture, improves our ability to represent these processes in models and correspondingly improves our ability to realistically model carbon feedbacks to climate from the land surface.