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

Abstract

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 (δ18O) 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 δ18O than ND trees. The uncoupling between iWUE and δ18O, together with the positive correlations between P and K leaf concentrations and δ18O, 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.

Nutritional changes in trees during drought‐induced mortality: A comprehensive meta‐analysis and a field study

“…They could play critical roles in plant protection against the oxidative damage resulting from drought and might also contribute to plant drought stress responses via their involvement in phytohormone signaling (Hendrix et al., 2022). Our results also agree with previous findings that Mn concentration in tree tissues tends to accumulate with drought‐induced mortality (González de Andrés et al., 2022; Hevia et al., 2019; Houle et al., 2007). One explanation is that the metabolism of Mn and other nutrients interfere with each other, and its accumulation in turn inhibits tree photosynthesis and survival (St Clair et al., 2005).…”

“…Indeed, the accumulation and allocation of other resources, particularly nutrients, also profoundly influence tree performance and survival during drought (Gessler et al., 2017; Millard et al., 2007). However, the role of tree nutritional status during drought‐induced forest dieback has received limited research attention (but see González de Andrés et al., 2022; Grossiord et al., 2018), hindering our ability to predict forest responses to prolonged drought stress.…”

“…Consequently, it is widely observed that trees in the process of death by drought commonly experience nutritional imbalances and deficiencies due to the multiple negative effects of drought stress. However, studies have also shown that nutrient concentrations in trees subjected to drought may remain stable (Ivanov et al., 2022) or even accumulate due to nutrient imbalance (González de Andrés et al., 2022; Hevia et al., 2019), depending on the species and ontogenetic stage. Moreover, these discrepancies can be attributed to the complex and context‐specific responses of plant mineral nutrition to drought, involving factors such as nutrient type, organ specificity, and plant species (He & Dijkstra, 2014).…”

Mineral Nutrition of Naturally Growing Scots Pine and Norway Spruce under Limited Water Supply

“…The wood manganese concentrations were lower by the end of the rainless period in pine and in the arid plot in spruce, thus demonstrating an accumulation pattern opposite to that of the majority of other elements in each species. It is well known that changes in Mn accumulation are characteristic of different disturbances in trees [see, e.g., [ 10 , 13 ]]. Drought-stressed beech seedlings had decreased Mn concentrations in roots and stems but not in leaves [ 5 ], and a large analysis of leaf element concentrations in almost 2000 plant species in China demonstrated that leaf Mn concentrations increased with increasing site mean annual precipitation, in contrast to other essential elements, which increased from more humid to more arid sites [ 19 ].…”

“…Drought-stressed seedlings of several drought-sensitive pine species were proposed to face an “isohydric trap”—a feedback cycle of nutrient deficit in leaves that exacerbates the negative drought effect on the plant’s performance [ 8 ]. The use of deeper water sources during drought is often correlated with lower element contents in the wood [ 9 ] and leaves [ 10 ]. However, manipulative experiments demonstrated that increased temperature and not water deficit per se can be responsible for a deterioration of leaf mineral nutrition and for corresponding photosynthetic disturbances in drought-stressed plants [ 7 , 11 ].…”