Xavier Aranda

Leaf morphology, photochemistry and water status changes in resprouting Quercus ilex during drought

Functional and morphological (structural) characteristics of Quercus ilex L. leaves under drought stress were studied in the forest and in a nursery. We compared undisturbed individuals (controls) with resprouts emerging after clear-cut or excision. When soil water availability was high, gas-exchange was similar in resprouts and controls, despite higher midday leaf water potential, midday leaf hydration and relative water content (RWC). In moderate drought, stomatal closure was found to limit photosynthesis in controls, and in severe drought non-stomatal limitations of photosynthesis were also greater than in resprouts. Leaf structure and chemical composition changed under drought stress. Leaves tended to be smaller in controls with increasing drought, and resprouts had larger leaves and lower leaf mass area (LMA). The relationship between nitrogen (N) content and LMA implied lower N investment in photosynthetic components in controls, which could be responsible for their increased non-stomatal limitation of photosynthesis. Changes were more apparent in leaf density (D) and thickness (T), components of LMA. Decreases in D were related to reductions in cell wall components: hemicellulose, cellulose and lignin. In resprouts, reduced D and leaf T accounted for the higher mesophyll conductance (gmes) to CO2 measured.

Resource remobilization in Quercus ilex L. resprouts

We studied the source of the nitrogen used for the growth and resprouting of holm-oak (Quercus ilexL.), and the contribution of nitrogen and carbohydrate root reserves to these processes. Three-year-old plants were grown in a greenhouse with either a sufficient or restricted nitrogen supply for one year. Half the individuals were subjected to shoot excision to provoke resprouting, and a 15N solution was given to these plants and to controls for two months. Nitrogen, Total Non-structural Carbohydrate (TNC), Total Soluble Protein content, and 15N and 13C composition were determined, and histological analyses of woody tissue were performed. Our results show that N-deprived plants used nitrogen from root reserves to support a growth rate similar to that of non-deprived plants. However, deprived plants lost their resprouting capacity in spite of the high TNC accumulation and nitrogen resupply to the soil. After the supply of nitrogen was restored to N-deprived plants, this nutrient mainly accumulated in under-ground organs, which limited the above-ground growth. Resprouting plants first remobilized the nitrogen stored in roots, and thereafter took it up from the solution. The root-crown region did not behave as a specialised reserve organ in three-year-old Quercus ilex L. plants.

Tumour necrosis factor-alpha uncouples respiration in isolated rat mitochondria

Recent studies have demonstrated the existence of an intracellular (associated with mitochondria) tumour necrosis factor-alpha (TNF) binding protein. In an attempt to elucidate if this receptor could be involved in TNF action, we have incubated liver isolated mitochondria in the presence of recombinant murine TNF. The results show that the addition of TNF at concentrations as low as 10(-6) U/microl resulted in a clear uncoupling respiration of liver isolated mitochondria, therefore suggesting that TNF can indeed exert intracellular effects, which are possibly linked with its cytotoxic mechanism.

Variations in Quercus ilex chloroplast pigment content during summer stress: involvement in photoprotection according to Principal Component Analysis

We examined chloroplast pigment variation in holm oak (Quercus ilex L.) leaves for two periods under two climatic conditions, at midday during summer. We compared variation between control (unburned) plants and plants burned the preceding summer, since post-fire resprouts show higher photosynthetic rates and lower thermal energy dissipation. Principal component (PC) analysis was performed on nine pigment-content variables for the two periods separately. Two PC factors (PC1 and PC2) explained 83 and 84% of the variance of the data for each period. In both periods, PC1 was marked by positive loading of pigments associated with light absorption or structural function namely neoxanthin, lutein, β-carotene, chlorophyll a, and chlorophyll b. These pigments were only affected by leaf age. In contrast, PC2 was marked by high loadings of xanthophyll-cycle pigments (associated with photoprotection), and lutein-5,6-epoxide. Leaf content of these pigments was affected by climatic conditions. In the situations considered in PC analysis (leaf types, periods), the lutein-5,6-epoxide content presented a variation pattern similar to that of violaxanthin, and was significantly correlated with thermal dissipation of excess energy (represented by non-photochemical quenching or NPQ). These results suggest a relationship of lutein and lutein-5,6-epoxide with photoprotection.

Total antioxidant activity in Quercus ilex resprouts after fire

Abstract After fire, holm oak ( Quercus ilex L.) resprouts have a higher light availability and photosynthetic activity than control plants in intact vegetation. To assess the differences in protection between these plants, we determined, in two forests, changes in gas-exchange rates, chlorophyll fluorescence parameters, chloroplast pigment content and total antioxidant activity (TAA) in different seasons, at different times of the day and in relation to leaf age. The end-point method used for TAA determination allowed the evaluation of the relative contribution of hydrophilic and lipophilic antioxidants in leaf extracts. High correlations were obtained between lipophilic TAA and certain chloroplast pigment content, the highest contribution being provided by β-carotene and the components of the xanthophyll cycle (zeaxanthin + antheraxanthin, violaxanthin). All leaves showed a much higher contribution (94–99%) of hydrophilic than lipophilic antioxidants to TAA. In summer, at midday, photosynthetic rates and TAA were higher in resprouts. In these plants, reduced xanthophyll-cycle participation (as shown by non-photochemical quenching (NPQ) and xanthophyll pool content) was compensated by an increased participation of hydrophilic antioxidants. No effect of time of day or plant age was observed. The results suggest that energy dissipation as heat, and detoxification mechanisms contribute to the protective strategies of control plants and resprouts, albeit to a different extent.

Mesophyll conductance to CO2 and leaf morphological characteristics under drought stress during Quercus ilex L. resprouting

Abstract• Quercus ilex L., the dominant species in Mediterranean forests and one with a great capacity for resprouting after disturbances, is threatened by the expected increase in fire frequency and drought associated with climate change.• The aim of this study was to determine the contribution of photosynthesis limitants, especially mesophyll conductance (gmes) during this species’ resprouting and under summer drought.• Resprouts showed 5.3-fold increased gmes and 3.8-fold increased stomatal conductance (gs) at mid-day with respect to leaves of undisturbed individuals. With increased drought, structural changes (decreased density and increased thickness) in resprouts contributed to the observed higher photosynthesis and increased gmes. However, gmes only partially depended on leaf structure, and was also under physiological control. Resprouts also showed lower non-stomatal limitations (around 50% higher carboxylation velocity (Vc,max) and capacity for ribulose-1,5-bisphosphate regeneration (Jmax)). A significant contribution of gmes to leaf carbon isotope discrimination values was observed.• gmes exhibits a dominant role in photosynthesis limitation in Q. ilex and is regulated by factors other than morphology. During resprouting after disturbances, greater capacity to withstand drought, as evidenced by higher gmes, gs and lower non-stomatal limitants, enables increased photosynthesis and rapid growth.Résumé• Quercus ilex L., l’espèce dominante dans les forêts méditerranéennes qui a une grande capacité de rejets après des perturbations, est menacée par l’augmentation prévue de la fréquence des incendies et de la sécheresse associées au changement climatique.• Le but de cette étude était de déterminer, chez cette espèce, la contribution des limitations de la photosynthèse, en particulier de la conductance du mésophylle (gmes) au cours de la repousse et sous sécheresse estivale.• Les feuilles des rejets ont présenté une conductance mésophylienne (gmes) 5,3 fois plus élevée et une conductance stomatique (gs) à midi 3,8 fois plus élevée par rapport aux feuilles d’arbres non perturbés. Avec l’accroissement de la sécheresse, les changements de structures (diminution de la densité et épaisseur accrue) dans les rejets ont contribué à augmenter la photosynthèse et à accroître gmes. Toutefois, gmes dépendait partiellement de la structure des feuilles, et était également sous contrôle physiologique. Les rejets ont aussi montré une abscence de limitation stomatique (vitesse de carboxylation (Vc,max) environ 50% plus élevée et une capacité de régénération pour le ribulose-1,5-bisphosphate (Jmax). Une contribution significative de gmes à la discrimination isotopique du carbone dans les feuille a été observée.• La conductance mésophylienne (gmes) a présenté un rôle dominant dans la limitation de la photosynthèse chez Q. ilex et est régulée par des facteurs autres que la morphologie. Au cours de la repousse après des perturbations, une plus grande capacité à résister à la sécheresse, mise en évidence par une gmes et une gs plus élevées, et une diminution des limitations non stomatiques, permettent une augmentation de la photosynthèse et une croissance rapide.

Light energy dissipation in Quercus ilex resprouts after fire

Holm oak (Quercus ilex) plants that have resprouted after fire have higher photosynthetic capacity than control plants in intact vegetation. In this study, branches detached from forest plants were fed with dithiothreitol (DTT) in the laboratory to inhibit zeaxanthin production and thus reduce the dissipation of light energy as heat. This allowed us to test the hypothesis that plants with greater photosynthetic capacity, and therefore greater photo-chemical sink strength, would suffer a lower reduction in photochemical efficiency under stressful conditions. Greater rates of photochemistry in resprouts, which exhibited increased photosynthesis (A), leaf conductance (g), quantum yield of PSII (ΔF/Fm′) and photochemical quenching (qP), were related to lower non-radiative dissipation of excess energy as indicated by 1 – (Fv′/Fm′). However, the fraction of energy remaining of that used in photo-chemistry or dissipated thermally in the PSII antennae was similar in resprouts and controls and was not affected by DTT, especially under high irradiance conditions. Zeaxanthin involvement in PSII protection operated in resprouts and controls since DTT induced the same kind of response (NPQ decrease) but was lower in resprouts. These chloro-phyll fluorescence results suggest the participation of some additional mechanism for energy dissipation. Light capture characteristics of the photosynthetic apparatus did not differ between resprouts and controls, and leaf age did not play a determining role in the differences observed.

California perennial grasses are physiologically distinct from both Mediterranean annual and perennial grasses

In the Central Valley of California, native perennial grass species have been largely replaced by Eurasian annual species, while in many parts of the Mediterranean Basin native perennial grasses continue to dominate, even on disturbed or degraded sites. We assessed whether differences in summer rainfall patterns have lead to the development of different plant-water strategies between grasses from these two regions. We compared six measures of plant-water physiology for three guilds of grasses: California perennial grasses, Mediterranean perennial grasses, and Mediterranean annual grasses. Discriminant analysis distinguished between the three guilds; Mediterranean perennial grasses were characterized by a more conservative water-relations physiology than Mediterranean annual grasses, whereas California perennial grasses were in some ways intermediate between the two Mediterranean grass guilds. For individual traits, California perennial grasses were either intermediate or more like Mediterranean annuals than Mediterranean perennials. Our results suggest California perennials are more drought tolerant than Mediterranean annuals but less drought tolerant than Mediterranean perennials, despite the fact that California’s Central Valley has a more intense summer drought than the Mediterranean Basin. These patterns may help explain why Mediterranean annuals, but not Mediterranean perennials, have been more successful invaders of interior California grasslands.

Grapevine Roots and Soil Environment: Growth, Distribution and Function

As for many plants, belowground processes occurring in grapevine are much lesser well known than above ground processes. Root biomass, root distribution, root physiology need further study as well as their responses to the soil environment in relation to the performance of the grapevine (yield and quality). This chapter gives an overview of the methodologies used to study grapevine roots and their environment. First of all, root characteristics and soil environment must be described. Monitoring of soil water status is approached with different methods. Root sampling methods such as direct excavation, soil coring, root profiles, rhizotrons, minirhizotrons, and ingrowth cores are described and some results presented. Finally, ecophysiological measurements such as root biomass and distribution, root composition, hormones, and water uptake in roots are commented.

Allometric relationships for estimating vegetative and reproductive biomass in grapevine (Vitis vinifera L.)

Background and Aims Vineyards, one of the most widespread agricultural systems, have significant but scarcely evaluated carbon sequestration potential. Allometry is a cost-effective approach to estimate plant biomass, but few studies – focused mainly on permanent structure carbon fixation – have dealt with it in grapevine. This study develops allometric models that accurately estimate grapevine standing biomass (total vine biomass at harvest), using extensive field-collected data sets. Methods and Results Data were obtained in vineyards located in Spanish regions representative of the variability found in warm semi-arid Mediterranean regions. We developed and validated functions to estimate vine biomass for all vine organs. The models obtained estimated accurately the biomass fixed by each organ separately and even more accurately at the whole plant scale. To illustrate the potential of the models, they satisfactorily assessed the influence of seasonal vine water status on vine biomass production and partitioning using an independent data set. Conclusions and Significance of the Study The models constitute a powerful tool to determine in a non-destructive and cost-effective manner standing biomass from simple vine measurements, which makes them suitable for quantifying carbon stocks and allocation patterns, and for evaluating the influence of climate or cultural practices at large scale to estimate better – at a regional or international level – the contribution of grapevine culture to CO2 balances.