Publication: Functional diversity of plant water and nutrient use strategies in Mediterranean ecosystems
Authors
Muñoz Gálvez, Francisco Javier
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Escuela Internacional de Doctorado
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Querejeta Mercader, José Ignacio ; Prieto Aguilar, Iván
Publisher
Universidad de Murcia
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DOI
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info:eu-repo/semantics/doctoralThesis
Description
Abstract
El incremento de la aridez asociado al cambio climático provoca cambios funcionales y estructurales en las comunidades vegetales, desde adaptaciones fisiológicas y morfológicas hasta reemplazos en los tipos funcionales dominantes. Dado que las zonas áridas y semiáridas cubren el 41% de la superficie terrestre, comprender las estrategias de uso de recursos de las plantas adaptadas a la sequía es clave para la conservación y gestión de estos ecosistemas. En ecosistemas mediterráneos, caracterizados por una fuerte estacionalidad hídrica, integrar rasgos del LES con indicadores hídricos permite una visión holística del funcionamiento vegetal desde la escala de especie hasta la de comunidad.
El objetivo general de la tesis es analizar la diversidad y coordinación de las estrategias de uso del agua, carbono y nutrientes en comunidades de plantas leñosas mediterráneas a lo largo de un gradiente de aridez. Los objetivos específicos son: I) evaluar la coordinación entre la profundidad de extracción de agua y las estrategias hídricas a nivel foliar dentro de cada sitio y a lo largo del gradiente de aridez; II) analizar la coordinación entre el eje adquisitivo-conservador del LES y las estrategias de uso del agua a escala foliar y de planta;III) examinar los cambios de estas estrategias a nivel de comunidad frente al aumento de la aridez. Para ello se estudiaron seis comunidades principales de plantas leñosas distribuidas a lo largo de un transecto de 600 km en la Península Ibérica, desde zonas costeras cálidas y secas hasta regiones montañosas frías y húmedas, abarcando un amplio gradiente climático, altitudinal y de estructura de la vegetación. Para algunos análisis se incorporaron cuatro comunidades adicionales. Los muestreos se realizaron en dos años contrastados climáticamente (2019 y 2022). Se analizaron 62 especies (121 combinaciones especie-sitio), midiendo rasgos foliares (SLA, LDMC), concentraciones de nutrientes (N, P, K), isótopos estables en hoja, agua del xilema y del suelo y, en 2022, variables de intercambio gaseoso.
Los resultados revelan una elevada diversidad de estrategias de uso del agua dentro de todas las comunidades, independientemente del nivel de aridez. Existe una fuerte coordinación entre la profundidad de extracción de agua y las estrategia de uso de agua a nivel de hoja. Las especies pequeñas, dependientes del agua superficial, presentan mayor conductancia estomática y menor eficiencia en el uso del agua, mientras que árboles y arbustos grandes, con acceso a agua profunda, muestran estrategias más conservadoras y eficientes. Los isótopos estables demostraron ser indicadores robustos e integradores de estas estrategias. Se confirmó la existencia de un eje adquisitivo-conservador del LES y su estrecha coordinación con el uso del agua, especialmente en ecosistemas estrictamente mediterráneos. Las especies adquisitivas combinan hojas poco esclerófilas, alta concentración de nutrientes, altas tasas fotosintéticas y baja eficiencia en el uso del agua. Las especies conservadoras presentan el patrón opuesto. A escala de comunidad, el aumento de la aridez se asocia a vegetación más abierta y a un mayor predominio de arbustos pequeños. Aunque las comunidades más áridas incrementan la conductancia estomática para evitar el sobrecalentamiento, mantienen o incluso aumentan su eficiencia en el uso del agua gracias a hojas más esclerófilas y ricas en nutrientes por área.
En conjunto, la tesis demuestra que el acceso al agua -superficial o profunda- determina de forma decisiva la coordinación entre el uso de agua, carbono y nutrientes. El aumento de la aridez restringe las estrategias viables y favorece una fuerte coordinación funcional, evidenciando la coexistencia de estrategias adquisitivas y conservadoras de agua, carbono y nutrientes en la vegetación leñosa mediterránea.
The increase in aridity associated with climate change induces functional and structural changes in plant communities, ranging from physiological and morphological adaptations to shifts in dominant plant functional types. Given that arid and semi-arid regions cover approximately 41% of the Earth's terrestrial surface, understanding the resource-use strategies of drought-adapted plants is crucial for the conservation and management of these ecosystems. In Mediterranean ecosystems, which are characterized by strong seasonal variability in water availability, integrating traits from the Leaf Economic Spectrum (LES) with plant water-use indicators provides a holistic understanding of plant functioning from the species to the community scale. The overall objective of this thesis is to analyse the diversity and coordination of water, carbon, and nutrient use strategies in Mediterranean woody plant communities along an aridity gradient. The specific objectives are: (I) to evaluate the coordination between rooting water uptake depth and leaf-level water-use strategies within sites and along the aridity gradient; (II) to analyse the coordination between the acquisitive-conservative axis of the LES and water-use strategies at both leaf and whole-plant scales; and (III) to examine changes in these strategies at the community level in response to increasing aridity. To address these objectives, six main woody plant communities distributed along a 600-km transect across the Iberian Peninsula were studied, ranging from warm and dry coastal areas to cold and humid mountainous regions, thereby encompassing a broad climatic, altitudinal, and vegetation-structure gradient. Four additional communities were included for specific analyses. Sampling was conducted in two climatically contrasting years (2019 and 2022). A total of 62 species (121 species-site combinations) were analysed, measuring leaf morphological traits (SLA, LDMC), nutrient concentrations (N, P, K), stable isotopes in leaves, xylem water, and soil water , as well as gas-exchange variables in 2022. The results reveal a high diversity of water-use strategies within all communities, regardless of aridity level. A strong coordination was found between the depth of water uptake and leaf-level water-use strategies. Small species dependent on shallow soil water exhibited higher stomatal conductance and lower water-use efficiency, whereas trees and large shrubs with access to deeper water sources showed more conservative and efficient strategies. Stable isotopes proved to be robust and integrative indicators of these strategies. The existence of an acquisitive-conservative axis of the LES was confirmed, together with its close coordination with water use, particularly in strictly Mediterranean ecosystems. Acquisitive species combine weakly sclerophyllous leaves, high nutrient concentrations, high photosynthetic rates, and low water-use efficiency, whereas conservative species exhibit the opposite pattern. At the community scale, increasing aridity was associated with more open vegetation and a greater dominance of small shrubs. Although the most arid communities increased stomatal conductance to prevent leaf overheating, they maintained or even enhanced water-use efficiency through more sclerophyllous leaves with higher nutrient content per unit leaf area. Overall, this thesis demonstrates that access to water-whether shallow or deep-plays a decisive role in shaping the coordination between water, carbon, and nutrient use. Increasing aridity constrains the range of viable strategies and promotes strong functional coordination, highlighting the coexistence of acquisitive and conservative strategies of water, carbon, and nutrient use in Mediterranean woody vegetation.
The increase in aridity associated with climate change induces functional and structural changes in plant communities, ranging from physiological and morphological adaptations to shifts in dominant plant functional types. Given that arid and semi-arid regions cover approximately 41% of the Earth's terrestrial surface, understanding the resource-use strategies of drought-adapted plants is crucial for the conservation and management of these ecosystems. In Mediterranean ecosystems, which are characterized by strong seasonal variability in water availability, integrating traits from the Leaf Economic Spectrum (LES) with plant water-use indicators provides a holistic understanding of plant functioning from the species to the community scale. The overall objective of this thesis is to analyse the diversity and coordination of water, carbon, and nutrient use strategies in Mediterranean woody plant communities along an aridity gradient. The specific objectives are: (I) to evaluate the coordination between rooting water uptake depth and leaf-level water-use strategies within sites and along the aridity gradient; (II) to analyse the coordination between the acquisitive-conservative axis of the LES and water-use strategies at both leaf and whole-plant scales; and (III) to examine changes in these strategies at the community level in response to increasing aridity. To address these objectives, six main woody plant communities distributed along a 600-km transect across the Iberian Peninsula were studied, ranging from warm and dry coastal areas to cold and humid mountainous regions, thereby encompassing a broad climatic, altitudinal, and vegetation-structure gradient. Four additional communities were included for specific analyses. Sampling was conducted in two climatically contrasting years (2019 and 2022). A total of 62 species (121 species-site combinations) were analysed, measuring leaf morphological traits (SLA, LDMC), nutrient concentrations (N, P, K), stable isotopes in leaves, xylem water, and soil water , as well as gas-exchange variables in 2022. The results reveal a high diversity of water-use strategies within all communities, regardless of aridity level. A strong coordination was found between the depth of water uptake and leaf-level water-use strategies. Small species dependent on shallow soil water exhibited higher stomatal conductance and lower water-use efficiency, whereas trees and large shrubs with access to deeper water sources showed more conservative and efficient strategies. Stable isotopes proved to be robust and integrative indicators of these strategies. The existence of an acquisitive-conservative axis of the LES was confirmed, together with its close coordination with water use, particularly in strictly Mediterranean ecosystems. Acquisitive species combine weakly sclerophyllous leaves, high nutrient concentrations, high photosynthetic rates, and low water-use efficiency, whereas conservative species exhibit the opposite pattern. At the community scale, increasing aridity was associated with more open vegetation and a greater dominance of small shrubs. Although the most arid communities increased stomatal conductance to prevent leaf overheating, they maintained or even enhanced water-use efficiency through more sclerophyllous leaves with higher nutrient content per unit leaf area. Overall, this thesis demonstrates that access to water-whether shallow or deep-plays a decisive role in shaping the coordination between water, carbon, and nutrient use. Increasing aridity constrains the range of viable strategies and promotes strong functional coordination, highlighting the coexistence of acquisitive and conservative strategies of water, carbon, and nutrient use in Mediterranean woody vegetation.
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