The role of nutritional impairment in carbon‐water balance of silver fir drought‐induced dieback

21 páginas, figuras, 4 tablas

Rear-edge populations at the xeric distribution limit of tree species are particularly vulnerable to forest dieback triggered by drought. This is the case of silver fir (Abies alba) forests located in Southwestern Europe. While silver fir drought-induced dieback patterns have been previously explored, information on the role played by nutritional impairment is lacking despite its potential interactions with tree carbon-water balances. We performed a comparative analysis of radial growth, intrinsic water-use efficiency (iWUE), oxygen isotopes (δ18 O) and nutrient concentrations in leaves of declining (DD) and non-declining (ND) trees in silver fir in four forests in the Spanish Pyrenees. We also evaluated the relationships among dieback predisposition, intraspecific trait variation (wood density and leaf traits) and rhizosphere soil physical-chemical properties. The onset of growth decline in DD trees occurred more than two decades ago, and they subsequently showed low growth resilience against droughts. The DD trees presented consistently lower foliar concentrations of nutrients such as P, K, Cu and Ni than ND trees. The strong effects of foliar nutrient status on growth resilience indices support the key role played by mineral nutrition in tree functioning and growth before, during and after drought. In contrast, variability in wood density and leaf morphological traits, as well as soil properties, showed weak relationships with tree nutritional status and drought performance. At the low elevation, warmer sites, DD trees showed stronger climate-growth relationships and lower δ18 O than ND trees. The uncoupling between iWUE and δ18 O, together with the positive correlations between P and K leaf concentrations and δ18 O, point to deeper soil/bedrock water sources and vertical decoupling between nutrient and water uptake in DD trees. This study provides novel insights into the mechanisms driving silver fir dieback and highlights the need to incorporate tree nutrition into forest dieback studies.

This study was financially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) via competitive grant RTI2018-096884-B-C31 (FORMAL project), RTI2018-096884-B-C33 (LESENS project) and by the Government of Aragón via competitive grant LMP242_18. AG acknowledges financial support from the Spanish Ministry of Science and the AEI through the Ramón y Cajal grant (RyC2020- 030647-I). JIQ acknowledges the financial support from Spanish Ministry of Science through the project (PID2019-107382RB-I00). JMI acknowledges financial support from the Project “CLU-2019-05—IRNASA/CSIC Unit of Excellence”, funded by the Junta de Castilla y León and cofinanced by the European Union (ERDF “Europe drives our growth”). RSS and JCL acknowledge the financial support from the Andalusian government (P20_00813 VUERCLIM), (IE19_074 UPO DendroOlavide) and (UPO-1263216 VULBOS), and from the Spanish Ministry of Science trough the project (EQC2018-005303-P)