Drought’s impact on Ca, Fe, Mg, Mo and S concentration and accumulation patterns in the plants and soil of a Mediterranean evergreen Quercus ilex forest

Abstract

We conducted a 6-year field manipulation drought experiment in an evergreen Quercus ilex forest where we simulated the drought predicted by GCM and ecophysiological models for the coming decades (an average of 15% soil moisture reduction). We thereby tested the hypothesis that enhanced drought will change Ca, Fe, Mg, Mo and S availability, concentrations and accumulation patterns in Mediterranean ecosystems. The strongest effects of drought occurred in the soil. Drought increased the total soil concentrations of S, the soil extract concentrations of Fe, Mg and S, the Mg saturation in the soil exchangeable complex and tended to increase the percentage base saturation of the soil exchangeable complex. These increased soil concentrations were related to a decrease of plant uptake capacity and not to an increase of soil enzyme activity, which in fact decreased under drier conditions. Drought increased leaf Mg concentrations in the three dominant species although only significantly in Quercus ilex and Arbutus unedo (20 and 14%, respectively). In contrast, drought tended to decrease Ca in Phillyrea latifolia (18%) and Ca and Fe concentrations in the wood of all three species. Drought increased Ca and Fe concentrations in the roots of Quercus ilex (26 and 127%). There was a slight general trend to decrease total biomass accumulation of nutrients that depend on water flux such as Mg, Fe and S. This effect was related to a decrease of soil moisture that reduced soil flow, and to a decrease in photosynthetic capacity, sap flow, transpiration and growth, and therefore plant uptake capacity under drought observed in Quercus ilex and Arbutus unedo. On the contrary, drought increased Mo accumulation in aboveground biomass in Phillyrea latifolia and reduced Mo accumulation in Arbutus unedo by reducing growth and wood Mo concentrations (51%). Phillyrea latifolia showed a great capacity to adapt to drier conditions, with no decrease in growth, an increase of Mo uptake capacity and a decrease in leaf Ca concentration, which was related to a decrease in transpiration under drought. The results indicate asymmetrical changes in species capacity to accumulate these elements, which are likely to produce changes in inter-specific competitive relations among dominant plant species and in their nutritional quality as food sources. The results also indicate that drought tended to decrease nutrient content in aboveground biomass, mainly through the decrease in growth and transpiration of the most sensitive species and caused an increase in the availability of these nutrients in soil. Thus, drought decreased the ecosystem's capacity to retain Mg, Fe and S, facilitating their loss in torrential rainfalls.

Impacts of Global Change on Mediterranean Forests and Their Services

“…Studies of climatic gradients have found that the foliar C/N/P/K stoichiometric ratios of the main forest species were mostly dependent on the meteorological conditions, especially rainfall in Catalan forests [40,41]. We have also observed changes in C/N/P/K stoichiometry and the concentrations of macro-and micronutrients in plants and soil in our field climatic-manipulation experiments [42,43]. Water availability was not only associated with shifts in nutrient concentrations but also with their allocation to different organs [41,44], the stoichiometric relationships among the main nutrients [41,44,45] and the distribution of nutrients between plant and soil [43,[45][46][47].…”

“…Field studies simulating climate change have found decreases in the contents and concentrations of macro-and micronutrients in a Mediterranean forest [42,43,46], except for K, which can increase in the aerial organs of some species [42]. Our field experiments have also shown that drought can increase foliar C:N and C:P concentration ratios, which is associated with morphological strategies for adapting to drought such as sclerophylly [132].…”

“…We have also observed changes in C/N/P/K stoichiometry and the concentrations of macro-and micronutrients in plants and soil in our field climatic-manipulation experiments [42,43]. Water availability was not only associated with shifts in nutrient concentrations but also with their allocation to different organs [41,44], the stoichiometric relationships among the main nutrients [41,44,45] and the distribution of nutrients between plant and soil [43,[45][46][47]. Drought tends to decrease total nutrient contents in plant-soil systems, mainly in plants, that transfer nutrients from above-to belowground biomass and from plant to soil [44,48].…”

Interactions between Glomus species and Rhizobium strains affect the nutritional physiology of drought-stressed legume hosts

“…This could be alleviated by AM and/or Rhizobium symbioses (Zahran, 1999;Aroca et al, 2007). Water limitation in the growing medium reduces diffusion, uptake by roots and transport of nutrients from roots to shoots due to restricted transpiration rate, impaired active transport, and altered membrane permeability (Sardans et al, 2008). It has been found that dual symbiosis of Rhizobium-AM fungi enhances drought tolerance of the legume host plant in terms of the total plant growth (Zahran, 1999;Valdenegro et al, 2001).…”

Seed priming and sulfur effects on soybean cell membrane stability and yield in saline soil

“…Sulfur availability is partially related to soil moisture (Itanna, 2005). Sardans et al (2006Sardans et al ( , 2008 reported a negative correlation between leaf sclerophylly and leaf S concentration in a Mediterranean forest. The amino acid profile of soybean meals could be improved with greater amounts of S-containing amino acids, methionine and cysteine.…”