Warming and drought alter C and N concentration, allocation and accumulation in a Mediterranean shrubland

Abstract

We investigated the effects of warming and drought on C and N concentrations, nitrogen use efficiency (NUE), and C and N accumulation in different ecosystem compartments. We conducted a 6-year (1999)(2000)(2001)(2002)(2003)(2004)(2005) field experiment to simulate the climate conditions projected by IPCC models for the coming decades in a Mediterranean shrubland. We studied the two dominant species, Globularia alypum and Erica multiflora, and an N-fixing species, Dorycnium pentaphyllum, also abundant in this shrubland. Warming (1 1C) decreased N leaf concentrations by 25% and increased N stem concentrations by 40% in G. alypum. Although warming changed the available ammonium in soil in some seasons, it did not increase total soil N contents. Drought (19% average reduction in soil moisture) decreased leaf N concentrations in the two dominant shrub species, E. multiflora and G. alypum by 16% and 19%, respectively, and increased stem N concentrations by 56% and 40%, respectively. Neither warming nor drought changed the leaf N concentrations in the N-fixing species D. pentaphyllum, although warming increased stem N concentration by 9%. In G. alypum, the increase of stem N concentrations contributed to the observed increase of N accumulation in stem biomass in drought treatments with respect to control plots (8 kg N ha À1 ). Neither warming nor drought changed NUE in the period 1999-2005.Warming increased soil organic C relative to drought. The effects of warming and drought on C and N concentrations, on N accumulation and on leaf/stem N distribution were not the result of dilution or concentration effects produced by changes in biomass accumulation. Other factors such as the changes in soil N availability, photosynthetic capacity, and plant internal C and N remobilization must be involved. These changes which differed depending on the species and the plant tissue show that the climate change projected for the coming decades will have significant effects on the C and N cycle and stoichiometry, with probable implications for ecosystem structure and function, such as changes in plant-herbivore relationships, decomposition rates or community species composition.

Density-dependent responses of Picea purpurea seedlings for plant growth and resource allocation under elevated temperature

“…In addition, the increase in the needle C:N ratio observed in P. purpurea in response to warming is a widely observed phenomenon in other tree species (Hobbie et al 2001;Olszyk et al 2003;Sardans et al 2008). The increases in the needle C:N ratio may influence plant-herbivore relationships because grazing pressure is correlated with foliar N concentrations (Sardans et al 2008). On the other hand, the increase in C:N ratio caused by LDET indicates relatively larger N-limitation.…”

“…Moreover, this increase of N allocation to woody tissue instead of leaves can affect the production capacity and seedling survival under long-term warming and competition conditions. In addition, the increase in the needle C:N ratio observed in P. purpurea in response to warming is a widely observed phenomenon in other tree species (Hobbie et al 2001;Olszyk et al 2003;Sardans et al 2008). The increases in the needle C:N ratio may influence plant-herbivore relationships because grazing pressure is correlated with foliar N concentrations (Sardans et al 2008).…”

Plant-soil interactions in Mediterranean forest and shrublands: impacts of climatic change

“…The nutrient content of aboveground biomass, mainly in leaves, tends to decrease with drought (Sardans et al 2008a;b), with the exception of K that increases in some aboveground tissues of some plant species (Sardans and Peñuelas 2007a;Sardans et al 2008g). Drought increases the C:N and C:P ratios of Mediterranean shrubs and trees, associated with a protective and conservative mechanism (Inclan et al 2005;Sardans et al 2008b, c, d;Matías et al 2011) and with sclerophylly and increases in lignin content (Bussotti et al 2000;Sardans et al 2006a).…”

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

“…Most studies show that decreases in soil moisture also reduce N and/or P uptake by plants (Jupp and Newman, 1987;Sardans and Peñuelas, 2007;Cramer et al, 2009;Waraich et al, 2011), suggesting a negative feedback of less water and fewer nutrients on the production capacity and fitness of plants when drought persists or becomes more severe. As a result, plants under drought tend to produce leaves and litter with high C-nutrient ratios (Yarie and Vancleve, 1996;Sardans et al, 2008b;Limousin et al, 2010). The few studies of the specific effects of drought on the N-P ratio in plants, however, have not provided a clear conclusion (Sardans and Peñuelas, 2008;Sardans et al, 2008c, in spite of studies in gradients of water availability in Mediterranean regions that have observed a negative correlation between water supply and leaf N-P ratio (Sardans et al, 2011), an effect linked to higher growth capacity in plants with lower N-P ratios .…”

“…Plants respond by activating mechanisms for water conservation, which can frequently increase C-nutrient ratios in photosynthetic tissues (Sardans et al, 2008b(Sardans et al, , 2008c.…”