Below-ground functional resilience along drought-induced forest die-off and species replacement

Abstract

Understanding how ecosystems functioning may respond to increments of temperature and climatic variability is crucial in the global change context. We studied the plant-and-soil interaction in a mixed Mediterranean forest where several drought events since 1990’s have resulted in Scots pine defoliation and mortality, with a subsequent replacement by Holm oak (HO). The study focused on how this die-off and species replacement affected soil respiration (SR) and its heterotrophic and autotrophic components. It dealt with SR dependency on abiotic and biotic controls (i.e. soil temperature and moisture, photosynthetic activity, forest structure, litter inputs on soil, fine roots biomass) at different temporal and spatial scales. The study also determined rates of litter decomposition (both leaves and fine roots) along the die-off process. Soil temperature and moisture strongly regulated temporal variability of SR (from daily to seasonal), including both autotrophic and heterotrophic components. Plant activity exerted strong control over temporal variability of SR, with higher influence on living pines at daily time scales but stronger effect on HO at seasonal scale. SR and its components remained apparently unaffected by drought-induced Scots pine die-off denoting a high functional resilience of the studied plant-and-soil system. This functional resilience of SR was the result of colonization by HO of the gaps created by the dead of pines. Additionally, litter decomposition rates, specific root respiration, plant activity and soil bacterial communities compared between living pines, dead pines and HO also supported the role of HO rhizosphere colonization on below-ground functioning resilience.