Drought-Induced Changes in C and N Stoichiometry in a Quercus ilex Mediterranean Forest

A 6-year field experiment of drought manipulation was performed in a Mediterranean forest with the aim of determining the effects of the drought predicted by most climate and ecophysiological models on the C and N concentration, accumulation, and stoichiometry in plants and soil. Drought had different effects among dominant species. In Quercus ilex, it increased the C/P ratio in wood and roots, N concentrations in roots and litter, and N/P ratio in wood and roots and decreased the C concentration in roots, C/N ratio in roots and litter, and C/P ratio in litter. In Arbutus unedo, drought increased the N concentration in litter and decreased the N concentration in leaves, thus decreasing N leaf reabsorption. No significant changes in C and N concentrations were found in Phillyrea latifolia. Drought affected the P plant absorption capacity more than that of N (more mobile). There was a general decreasing trend of C and N accumulation in aboveground biomass, with this effect being significant in A. unedo, which accumulated 80% less C and lost 2 kg ha 1 of N in aboveground biomass in drought plots in the period 1999 -2005, whereas in this same period it accumulated 9 kg ha 1 of N in total aboveground biomass in control plots. Total soil N and soil organic C increased in droughted soils. The effects of drought on C/N/P stoichiometry and N uptake capacity were different among the three dominant plant species. Q. ilex and A. unedo were more sensitive to drought than P. latifolia. The increase in C/P and N/P ratios in Q. ilex and the decrease in N uptake in A. unedo might decrease their competitive capacity under drought by decreasing water use efficiency. These results altogether indicated slower C and N mineralization and lower N plant capture, N leaf reabsorption, and N accumulation in some dominant plant species in response to drought, thus reducing C and N soil turnover, increasing C and N accumulation in soil, and reducing C and N at the stand level. FOR .S CI. 54(5):513-522.

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