David Sánchez-Gómez

Is Shade Beneficial for Mediterranean Shrubs Experiencing Periods of Extreme Drought and Late-winter Frosts?

BACKGROUND AND AIMS Plants are naturally exposed to multiple, frequently interactive stress factors, most of which are becoming more severe due to global change. Established plants have been reported to facilitate the establishment of juvenile plants, but net effects of plant-plant interactions are difficult to assess due to complex interactions among environmental factors. An investigation was carried out in order to determine how two dominant evergreen shrubs (Quercus ilex and Arctostaphylos uva-ursi) co-occurring in continental, Mediterranean habitats respond to multiple abiotic stresses and whether the shaded understorey conditions ameliorate the negative effects of drought and winter frosts on the physiology of leaves. METHODS Microclimate and ecophysiology of sun and shade plants were studied at a continental plateau in central Spain during 2004-2005, with 2005 being one of the driest and hottest years on record; several late-winter frosts also occurred in 2005. KEY RESULTS Daytime air temperature and vapour pressure deficit were lower in the shade than in the sun, but soil moisture was also lower in the shade during the spring and summer of 2005, and night-time temperatures were higher in the shade. Water potential, photochemical efficiency, light-saturated photosynthesis, stomatal conductance and leaf 13C composition differed between sun and shade individuals throughout the seasons, but differences were species specific. Shade was beneficial for leaf-level physiology in Q. ilex during winter, detrimental during spring for both species, and of little consequence in summer. CONCLUSIONS The results suggest that beneficial effects of shade can be eclipsed by reduced soil moisture during dry years, which are expected to be more frequent in the most likely climate change scenarios for the Mediterranean region.

Variation in functional leaf traits among beech provenances during a Spanish summer reflects the differences in their origin

We assessed the response of 11-year-old saplings from six beech provenances growing in a common-garden trial at the southwestern range limit. Provenances from distinct climatic regions across the European beech distribution were selected. The local Spanish provenance appeared well suited to the site conditions, maintaining high rates of assimilation even in midsummer, but so did the provenance of southern continental origin, from Gotze-Delchev, Bulgaria. Those provenances from cooler sites in central Europe, a continental mountain climate in the Czech Republic and a continental range-edge site in eastern Poland, along with a German provenance of mild maritime origin, had good physiological functionality in early summer but reduced carbon assimilation (Aarea) and apparent soil–leaf hydraulic conductivity (KL) in midsummer. The northern maritime provenance from Sweden demonstrated severely-reduced photosynthetic capacity. These groupings of provenances according to their photosynthetic performance, stable carbon isotope composition (δ13C; a proxy for water-use efficiency) and leaf water potential under marginal conditions, during late summer in the trial, suggest that they have divergent strategies for water use. The research highlights large intraspecific differences among beech provenances of distinct origin and strategies which are expected to modify their response to drought, requiring future genetic studies to explicitly determine the basis of this ecophysiological differentiation.

Effects of drought on mesophyll conductance and photosynthetic limitations at different tree canopy layers

In recent years, many studies have focused on the limiting role of mesophyll conductance (gm ) to photosynthesis (An ) under water stress, but no studies have examined the effect of drought on gm through the forest canopy. We investigated limitations to An on leaves at different heights in a mixed adult stand of sessile oak (Quercus petraea) and beech (Fagus sylvatica) trees during a moderately dry summer. Moderate drought decreased An of top and lowest beech canopy leaves much more than in leaves located in the mid canopy; whereas in oak, An of the lower canopy was decreased more than in sunlit leaves. The decrease of An was probably not due to leaf-level biochemistry given that VCmax was generally unaffected by drought. The reduction in An was instead associated with reduction in stomatal and mesophyll conductances. Drought-induced increases in stomatal limitations were largest in leaves from the top canopy, whereas drought-induced increases in mesophyll limitations were largest in leaves from the lowest canopy. Sensitivity analysis highlighted the need to decompose the canopy into different leaf layers and to incorporate the limitation imposed by gm when assessing the impact of drought on the gas exchange of tree canopies.

Functional traits and plasticity linked to seedlings' performance under shade and drought in Mediterranean woody species

Interspecific differences in morphology, biomass allocation and phenotypic plasticity along an experimental irradiance gradient and two contrasting water regimes were studied for eight Mediterranean woody species at the seedling stage; a critical demographic stage in Mediterranean plant communities. We tested whether species variation in these traits can explain previously reported interspecific differences in performance under shade and drought. Four irradiance levels (1%, 6%, 20% and 100% of full sunlight) and two water regimes (well watered and water-stressed conditions) in 6% and 100% irradiance levels were established. Quercus species exhibited the largest seeds, the highest total dry mass and also the highest root-shoot ratio, but their leaf mass fraction (LMF) and leaf area ratio (LAR) were low. Pistacia terebinthus, and Arbutus unedo exhibited the opposite traits. From those traits that correlated with seed size only LAR resulted significantly linked to survival in deep shade. None of the traits studied correlated with survival under water-stressed conditions. Overall phenotypic plasticity was negatively correlated with survival in deep shade but no correlation was found with survival under water-stressed conditions. Our results highlight the importance of low LAR and low phenotypic plasticity as potential determinants of enhanced performance under shade during the very early seedling stages of Mediterranean woody species. Low LAR was also positively correlated with seed size and consequently, its relationship with enhanced performance under shade might change at later life stages of the plant when seed reserves are no longer available.RésuméLes différences interspécifiques de morphologie, d’allocation de biomasse et de plasticité phénotypique ont été étudiées pour des semis de huit espèces ligneuses méditerranéennes sous un gradient d’ombrage et soumis à deux régimes d’alimentation hydrique. Le stade semis est un stade critique pour la démographie des communautés végétales méditerranéennes. Nous avons testé l’hypothèse que des différences dans ces traits pouvaient expliquer les différences inter-spécifiques de performances souvent décrites sous ombrage et sous sécheresse. Nous avons imposé quatre niveaux d’ombrage (1 %, 6 %, 20 % and 100 % du rayonnement incident) et deux régimes hydriques (irrigation abondante et déficit hydrique pour les traitements 6 % et 100 %). Les chênes présentaient les graines les plus grosses, la plus forte biomasse et également le rapport racine/parties aériennes le plus élevé, mais leurs rapports (biomasse foliaire/biomasse totale) et (surface foliaire/biomasse totale) (LAR) étaient faibles. Pistacia terebinthus, et Arbutus unedo présentaient des caractéristiques opposées. Parmi ces traits liés à la taille des graines, seul LAR était fortement corrélé à la survie sous ombre forte. Aucun des traits mesurés n’était corrélé à la survie sous sécheresse. Le degré de plasticité phénotypique était corrélé négativement avec la survie sous ombre forte, mais aucune corrélation n’a pu être détectée avec la survie sous sécheresse. Ces résultats soulignent l’importance d’un LAR faible et d’une faible plasticité phénotypique comme déterminants d’une survie sous fort ombrage pendant les tous premiers stades de développement des semis de ligneux méditerranéens. De faibles valeurs de LAR étaient également associées à de fortes biomasses initiales des graines; son effet sur la performance des semis à l’ombre risque de ce fait de disparaître lors des stades de développement ultérieurs quand les réserves des graines sont épuisées.

Variation in photosynthetic performance and hydraulic architecture across European beech (Fagus sylvatica L.) populations supports the case for local adaptation to water stress

The aim of this study was to provide new insights into how intraspecific variability in the response of key functional traits to drought dictates the interplay between gas-exchange parameters and the hydraulic architecture of European beech (Fagus sylvatica L.). Considering the relationships between hydraulic and leaf functional traits, we tested whether local adaptation to water stress occurs in this species. To address these objectives, we conducted a glasshouse experiment in which 2-year-old saplings from six beech populations were subjected to different watering treatments. These populations encompassed central and marginal areas of the range, with variation in macro- and microclimatic water availability. The results highlight subtle but significant differences among populations in their functional response to drought. Interpopulation differences in hydraulic traits suggest that vulnerability to cavitation is higher in populations with higher sensitivity to drought. However, there was no clear relationship between variables related to hydraulic efficiency, such as xylem-specific hydraulic conductivity or stomatal conductance, and those that reflect resistance to xylem cavitation (i.e., Ψ(12), the water potential corresponding to a 12% loss of stem hydraulic conductivity). The results suggest that while a trade-off between photosynthetic capacity at the leaf level and hydraulic function of xylem could be established across populations, it functions independently of the compromise between safety and efficiency of the hydraulic system with regard to water use at the interpopulation level.

Rank reversals in tree growth along tree size, competition and climatic gradients for four forest canopy dominant species in Central Spain

Abstract• Interspecific differences in tree growth patterns with respect to biotic and abiotic factors are key for understanding forest structure and dynamics, and predicting potential changes under climate change.• Repeated observations from the Spanish Forest Inventory (SFI) were used to parameterize maximum likelihood estimators of tree growth as a function of tree size, competition indices and climate for Pinus pinaster, P. sylvestris, Quercus ilex and Q. pyrenaica.• Significant responses to both biotic and abiotic factors were found, with interspecific differences in species performance along competition, temperature and precipitation gradients. Q. ilex was the species most tolerant to competition while P. pinaster was the species most sensitive to climatic variation. Species relative positions shifted along gradients of these factors with rank reversals in species performance along size, competition and climatic gradients.• The results based on average growth matched previous forestry classifications and experimental studies on relative growth rate (RGR).• When examining growth along studied abiotic and biotic gradients, a mismatch was found between species performance ranks as predicted by our models and information derived from previous knowledge. Those discrepancies highlight the relevance of ontogeny and environmental heterogeneity in defining species performance along competition gradients.Résumé• Les différences interspécifiques dans les modèles de croissance des arbres, pour ce qui concerne les facteurs biotiques et abiotiques, sont des clés pour la compréhension des structures et des dynamiques forestières, et pour prédire les changement potentiels avec le changement climatique.• Des observations répétées de l’Inventaire Forestier Espagnol (SFI) ont été utilisées pour paramétrer les estimateurs de probabilité maximum de croissance des arbres comme une fonction de la taille de l’arbre, des indices de compétition et du climat pour Pinus pinaster, Pinus sylvestris, Quercus ilex et Quercus pyrenaica.• Des réponses significatives aux facteurs biotiques et abiotiques ont été trouvées, avec des différences interspécifiques pour les performances des espèces en relation avec la compétition, les gradients de température et de précipitations. Quercus ilex a été l’espèce la plus tolérante à la compétition tandis que Pinus pinaster a été l’espèce la plus sensible aux variations climatiques. Les positions relatives des espèces ont changé en relation avec les gradients de ces facteurs avec des interversions de rang pour les performances des espèces en relation avec la taille, la compétition et les gradients climatiques.• Les résultats basés sur la moyenne de croissance sont en adéquation avec la classification forestière antérieure et les études expérimentales sur le taux relatif de croissance (RGR).• En examinant la croissance en relations avec les gradients biotiques et abiotiques étudiés, il a été trouvé une disparité entre les rangs de performance des espèces prédits par nos modèles et les informations provenant des connaissances antérieures. Ces divergences soulignent l’importance de l’ontogénie et de l’hétérogénéité environnementale pour la détermination des performances des espèces en relation avec les gradients de compétition.

Epigenetic Variability in the Genetically Uniform Forest Tree Species Pinus pinea L

There is an increasing interest in understanding the role of epigenetic variability in forest species and how it may contribute to their rapid adaptation to changing environments. In this study we have conducted a genome-wide analysis of cytosine methylation pattern in Pinus pinea, a species characterized by very low levels of genetic variation and a remarkable degree of phenotypic plasticity. DNA methylation profiles of different vegetatively propagated trees from representative natural Spanish populations of P. pinea were analyzed with the Methylation Sensitive Amplified Polymorphism (MSAP) technique. A high degree of cytosine methylation was detected (64.36% of all scored DNA fragments). Furthermore, high levels of epigenetic variation were observed among the studied individuals. This high epigenetic variation found in P. pinea contrasted with the lack of genetic variation based on Amplified Fragment Length Polymorphism (AFLP) data. In this manner, variable epigenetic markers clearly discriminate individuals and differentiates two well represented populations while the lack of genetic variation revealed with the AFLP markers fail to differentiate at both, individual or population levels. In addition, the use of different replicated trees allowed identifying common polymorphic methylation sensitive MSAP markers among replicates of a given propagated tree. This set of MSAPs allowed discrimination of the 70% of the analyzed trees.

Genetic control of functional traits related to photosynthesis and water use efficiency in Pinus pinaster Ait. drought response: integration of genome annotation, allele association and QTL detection for candidate gene identification

BackgroundUnderstanding molecular mechanisms that control photosynthesis and water use efficiency in response to drought is crucial for plant species from dry areas. This study aimed to identify QTL for these traits in a Mediterranean conifer and tested their stability under drought.ResultsHigh density linkage maps for Pinus pinaster were used in the detection of QTL for photosynthesis and water use efficiency at three water irrigation regimes. A total of 28 significant and 27 suggestive QTL were found. QTL detected for photochemical traits accounted for the higher percentage of phenotypic variance. Functional annotation of genes within the QTL suggested 58 candidate genes for the analyzed traits. Allele association analysis in selected candidate genes showed three SNPs located in a MYB transcription factor that were significantly associated with efficiency of energy capture by open PSII reaction centers and specific leaf area.ConclusionsThe integration of QTL mapping of functional traits, genome annotation and allele association yielded several candidate genes involved with molecular control of photosynthesis and water use efficiency in response to drought in a conifer species. The results obtained highlight the importance of maintaining the integrity of the photochemical machinery in P. pinaster drought response.

Functional and genetic characterization of gas exchange and intrinsic water use efficiency in a full-sib family of Pinus pinaster Ait. in response to drought

Drought is an important environmental factor in Mediterranean ecosystems affecting seedling recruitment, productivity or susceptibility to fires and pathogens. Studying water use efficiency in these environments is crucial due to its adaptive value allowing trees to cope with low water availability. We studied the phenotypic variability and genetic control of intrinsic water use efficiency (WUE(i)) and related traits in a full-sib family of Pinus pinaster under drought imposition. We detected significant differences in WUE(i) between clones of the same family and moderate heritability estimates that indicate some degree of genetic control over this trait. Stomatal conductance to water vapor was the trait most affected by drought imposition and it showed the strongest influence in WUE(i). Stomatal conductance to water vapor and specific leaf area (SLA) were the traits with highest heritabilities and they showed a significant genetic correlation with WUE(i), suggesting that selection of needles with low SLA values will improve WUE(i) in this species by reducing water losses through stomatal control.

Non-targeted metabolomic profile of Fagus sylvatica L. leaves using liquid chromatography with mass spectrometry and gas chromatography with mass spectrometry.

INTRODUCTION Fagus sylvatica L. is one of the most widely distributed broad-leaved tree species in central and western Europe, important to the forest sector and an accurate biomarker of climate change. OBJECTIVE To profile the beech leaf metabolome for future studies in order to investigate deeper into the characterisation of its metabolic response. METHODS Leaf extracts were analysed using LC-MS by electrospray ionisation in negative mode from m/z 100-1700 and GC-MS by electron ionisation in scan mode from m/z 35-800. RESULTS The LC-MS profile resulted in 56 compounds, of which 43 were identified and/or structurally characterised, including hydroxycinnamic acid derivatives, flavan-3-ols and proanthocyanidins, and flavonols. From a second analysis based on GC-MS, a total of 111 compounds were identified, including carbohydrates, polyalcohols, amino acids, organic acids, fatty acids, phenolic compounds, terpenoids, sterols and other related compounds. Many of the compounds identified were primary metabolites involved in major plant metabolic pathways, however, some secondary metabolites were also detected. Some of them play roles as tolerance-response osmoregulators and osmoprotectors in abiotic stress, or as anti-oxidants that reduce the effect of reactive oxygen species and promote many protective functions in plants. CONCLUSIONS This study provides a broad and relevant insight into the metabolic status of F. sylvatica leaves, and serves as a base for future studies on physiological and molecular mechanisms involved in biotic or abiotic stress.