• Energy Research

AbstractTrees' functional strategies to cope with extreme drought are essential under climate change. In a mixed Mediterranean forest, we analyzed the functional strategy in response to drought of four co‐occurring species (Pinus pinea, Pinus pinaster, Juniperus oxycedrus, and Quercus ilex) during two years. Specifically, we assessed functional traits related to tree water status, leaf water relations, and gas exchange. Different trait‐syndrome metrics and the functional strategies under water stress observed suggested a species drought‐tolerance differentiation, with the more anysohidric Q. ilex and J. oxycedrus showing a much higher drought tolerance than the more isohydric P. pinea and P. pinaster. All species recovered from negative leaf turgor reached during peak water stress in summer. Q. ilex and J. oxycedrus kept lower leaf osmotic potentials and lower sensitivity of leaf gas exchange and leaf photochemistry to water stress. In contrast, the pine species exhibited more drought‐avoidant and water‐conservative strategies, yet this behavior was less effective in mitigating water stress's impact on their physiology. The pine species were the most affected by drought, with prolonged near‐zero net photosynthesis during summer. P. pinaster was more isohydric than P. pinea and exhibited a lower capacity to maintain leaf turgor. Physiological processes regulating leaf turgor under drought constitute a key functional strategy involved in the carbon and water‐related mechanisms, ultimately inducing mortality under hot drought. The currently observed mortality dynamics for P. pinaster, and to a lower extent in P. pinea, may be exacerbated by loss of functional homeostasis.

Pines produce and accumulate oleoresin, which is part of the preformed defensive system or is synthesized de novo in response to biotic and abiotic challenges. Fusarium circinatum is a fungal pathogen that causes Pine Pitch Canker disease and is characterized by cankers with abundant resin at the infection site. F. circinatum colonizes the plant using both constitutive and traumatic resin ducts, indicating a resin tolerance that needs to be evaluated. Using a spectrophotometric technique, we assessed the effects of constitutive and induced resin on the growth of F. circinatum. The pathogen was grown in minimum medium supplemented with resin (at 0.8, 1.5 and 3 % concentrations) in the wells of a microplate for 6 days, and the absorbance at 570 nm was measured as an indicator of fungal biomass. The results showed that resin from Pinus pinaster and Pinus radiata enhanced fungal growth, as the absorbances measured with the addition of volatile or nonvolatile fractions extracted from constitutive and induced resins increased above 100 % relative to the solvent used in resin extraction. F. circinatum grew 40 % more in the hexane extract of the induced resin than in the constitutive resin of P. radiata. Terpene profiles determined by GC-MS analysis differed quantitatively and qualitatively by resin type (constitutive or induced) and pine species. The F. circinatum growth with various single terpene components of resin at different concentrations was also measured. The absorbance results showed that α-pinene and citronellol (monoterpenes) promoted growth at specific concentrations, while all others inhibited or did not affect it.

Impact of drought under enriched CO2 atmosphere on ecophysiological and leaf metabolic response of the sub-mediterranean Q. pyrenaica oak was studied. Seedlings growing in climate chamber were submitted to moderate drought (WS) and well-watered (WW) under ambient ([CO2]amb =400 ppm) or CO2 enriched atmosphere ([CO2]enr =800 ppm). The moderate drought endured by seedlings brought about a decrease in leaf gas exchange. However, net photosynthesis (Anet) was highly stimulated for plants at [CO2]enr. There was a decrease of the stomatal conductance to water vapour (gwv) in response to drought, and a subtle trend to be lower under [CO2]enr. The consequence of these changes was an important increase in the intrinsic leaf water use efficiency (WUEi). The electron transport rate (ETR) was almost a 20 percent higher in plants at [CO2]enr regardless drought endured by seedlings. The ETR/Anet was lower under [CO2]enr, pointing to a high capacity to maintain sinks for the uptake of extra carbon in the atmosphere. Impact of drought on the leaf metabolome, as a whole, was more evident than that from [CO2] enrichment of the atmosphere. Changes in pool of non-structural carbohydrates were observed mainly as a consequence of water deficit including increases of fructose, glucose, and proto-quercitol. Most of the metabolites affected by drought back up to levels of non-stressed seedlings after rewetting (recovery phase). It can be concluded that carbon uptake was stimulated by [CO2]enr, even under the stomatal closure that accompanied moderate drought. In the last, there was a positive effect in intrinsic water use efficiency (WUEi), which was much more improved under [CO2]enr. Leaf metabolome was little responsible and some few metabolites changed mainly in response to drought, with little differences between [CO2] growth conditions.

This study develops a new method to produce more complex wines by means of an indirect diffusion of wood aromas from yeast cell-walls. An exogenous lyophilized biomass was macerated with an ethanol wood extract solution and subsequently dried. Different times were used for the adsorption of polyphenols and volatile compounds to the yeast cell-walls. The analysis of polyphenols and volatile compounds (by HPLC/DAD and GC-MS, respectively) demonstrate that the adsorption/diffusion of these compounds from the wood to the yeast takes place. Red wines were also aged with Saccharomyces cerevisiae lees that had been impregnated with wood aromas and subsequently dried. Four different types of wood were used: chestnut, cherry, acacia and oak. Large differences were observed between the woods studied with regards to their volatile and polyphenolic profiles. Sensory evaluations confirmed large differences even with short-term contact between the wines and the lees, showing that the method could be of interest for red wine making. In addition, the results demonstrate the potential of using woods other than oak in cooperage.