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Leaf structural and nutrient traits are key attributes of plant ecological strategies, as these traits are related to resource-use strategies and plant growth. However, leaf structure and nutrient composition can vary among different habitats, leaf habits or phylogenetic groups. In this study, we measured 13 leaf traits (one structural—leaf mass per area, LMA—and 12 nutrient traits) in 98 Mediterranean woody species growing over a wide range of environmental conditions, with the final aim of discerning the main causes of leaf trait variability. The variance decomposition results show that phylogeny, leaf habit and habitat type affected in several ways the structural and nutrient traits studied. Leaf nutrient concentrations are strongly positively correlated amongst themselves, and negatively correlated with LMA, in accordance with the “leaf economics spectrum”. We found that leaf habit and phylogeny were important causes of variation in LMA and in a broad number of leaf nutrients (i.e., C, N, Mg, S, K), while other micronutrients seemed to be more dependent on the environment (i.e., Cu and Mn). In summary, our study reinforces the existence of the leaf economics spectrum in a broad pool of Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as the main drivers of variability in some leaf structural and nutrient traits.
Background and aimsRoot traits play a critical role inplant resource-use strategies and ecosystem functioning,but there is great controversy regarding their identityand functionality in different dimensions of below-ground functional variation. Here, we explored the levelof covariation among a suite of key root traits (i.e.specific root length, root dry matter content, diameterand density) as well as between them and two above-ground traits related with plant function (leaf nutrientconcentration and specific leaf area). We also evaluatedwhether these patterns of trait covariation were consis-tent at different spatial scales and organisational levels.MethodsWe collected fine root (< 2 mm) samples of 534individuals (of 80 woody species) along a wide regionalrange of environmental conditions in southern Spain.
El género Quercus constituye el grupo de especies leñosas más importante del hemisferio norte, con una amplia distribución tanto en España como en México. El estudio de sus rasgos funcionales nos permite conocer su grado de diversificación y su adaptación al medio, así como las limitaciones morfológicas y fisiológicas que restringen su evolución. El principal objetivo del presente estudio es comprender como se segregan los rasgos funcionales foliares dentro del género Quercus, y que factores determinan dicha segregación. Para ello hemos medido cinco rasgos foliares en un total de 28 especies del generó Quercus de España y México a lo largo de un gradiente de evapotranspiración potencial. Nuestros resultados muestran dos dimensiones independientes de variación funcional foliar: por un lado, las especies se distribuyen de acuerdo con el espectro de economía foliar a lo largo del gradiente de humedad edáfica, encontrándose las especies más conservativas en el uso de recursos en regiones con mayor evapotranspiración potencial y las especies más adquisitivas en zonas con menor evapotranspiración. Por otro lado, el tamaño foliar esta principalmente condicionado por el origen geográfico de las especies. Estos resultados sugieren que las variaciones evolutivas dentro de un mismo linaje están asociadas a la variación coordinada de sus rasgos, siendo la humedad un factor clave en la variación funcional del género Quercus. Además, destacar que no se aprecia relación entre la longevidad foliar y el espectro de economía foliar, lo cual podría deberse a que la historia evolutiva del hábito foliar en los robles de ambos países ha sido diferente.
Iberian oak forests and woodlands are vital providing a variety of ecosystem services. They provide raw materials like cork, wood and fuel, and fodder (acorns) for wild and domestic animals. Oak trees provide a climate regulating service by their capacity to sequester carbon and therefore to mitigate the effects of climatic change. There is an increasing demand for cultural services provided by oak woodlands, mainly for recreation and ecotourism. However, some global-change drivers are negatively affecting oak forests, therefore diminishing their ecosystem services and in consequence undermining human well-being. The main drivers affecting Iberian oaks are: land use changes, introduction of exotic pathogens, air and soil pollution deteriorating oak health, and climatic change, in particular the combined reduction of rainfall and the rise in temperature. In this chapter we focus on the ecology of Iberian oaks and how they are affected by global change. Firstly, we introduce a literature overview of the research conducted on Quercus, analysed by species, countries and topics. Secondly, we review the main biological processes related with the oak responses to global change: i) genetic diversity, climatic refuges and adaptation to climatic change; ii) ecophysiological responses to stress and disturbance, functional diversity, growth patterns, and scaling up from leaf to ecosystem; iii) demographic responses, causes of regeneration failures, spatial patterns of recruitment, drivers of decline and dieback. Thirdly, we review the management strategies in three case studies: the agro-silvo-pastoral systems (dehesas and montados), the cork oak woodlands, and the afforestation of a polluted-land for phytostabilization of contaminants.
1. Many studies have quantified the functional variation of fine root traits to un-derstand the overarching trade-off between maximizing resource acquisition or conservation (root economics spectrum [RES]). However, we know remarkably less on how plant strategies along the RES are actually constrained by the amount of photosynthates required to construct roots (i.e. construction costs, CC) or how below- ground interactions with symbiotic organisms modify root trait patterns and their relationships with CC.2. Our main aim was to quantify CC of fine roots (<2 mm) and their underlying compo-nents (carbon, minerals and organic nitrogen concentrations) in 60 Mediterranean woody species with contrasting symbiotic association types (ectomycorrhizas, ar-buscular and ericoid mycorrhizas and N-fixing bacteria). We examined (a) whether the covariation among fine root traits along the RES was related to the intrinsic cost of producing roots and whether this relationship was dependent on the type of root symbiosis; (b) whether the relationship of each CC component with the RES was dependent on the type of root symbiosis and (c) whether soil water and nutrient availability determined differences in CC across sites.3. According to the RES hypothesis, fine root traits showed a main covariation trend (acquisition vs. conservation), defined by the first PCA axis, which also segregated species by their two main contrasting symbiotic types (arbuscular and ectomycor-rhizal). We found a positive relationship between root CC and the RES (i.e. PCA axis 1) and, interestingly, slopes differed among symbiotic types, in response to the different role of each specific CC component. In addition, independently of symbiotic type, root CC decreased linearly with soil nutrient availability and quad-ratically with plant water availability.4. Synthesis. Our study demonstrates that woody plants display different functional strategies in their root CC, related with their position on the RES, and that CC differ among symbiotic groups. The influence of the root CC components across species varied among symbiotic associations, pointing to a trade-off between structural and metabolic compounds. Root CC were also strongly modulated by soil resource availability (nutrients and water). This study highlights that root CC are fundamental to better understand below- ground resource-use strategies.
Plant functional traits are highly plastic to changes in climatic factors and nutrient availability. However, the intraspecific plant response to abiotic factors and the overall effect on tree growth and productivity is still under debate. We studied forest productivity for 30 Quercus ilex subsp. ballota forests in Spain along a broad climatic gradient of aridity (mean annual precipitation from 321 to 858 mm). We used linear mixed models to quantify the effect of climatic and edaphic (soil nutrients, topography, and texture) factors on tree functional traits (leaf and branch traits), and subsequently, the effect of such functional traits and abiotic factors on the relative growth rate (RGR) of adult trees. We used piecewise structural equation models (SEMs) to determine the causal effect of intrinsic and extrinsic factors on forest productivity. Our results showed that tree functional traits were mainly explained by climatic and edaphic factors. Functional traits and tree biomass explained forest biomass and RGR, respectively, which ultimately explained forest productivity. In conclusion, intraspecific variability of functional traits has a significant effect on plant biomass and growth, which ultimately may explain forest productivity in Quercus ilex forests.
Extensive research efforts are devoted to understand fine root trait variation and to confirm the existence of a belowground root economics spectrum (RES) from acquisitive to conservative root strategies that is analogous to the leaf economics spectrum (LES). The economics spectrum implies a trade-off between maximizing resource acquisition and productivity or maximizing resource conservation and longevity; however, this theoretical framework still remains controversial for roots. We compiled a database of 320 Mediterranean woody and herbaceous species to critically assess if the classic economics spectrum theory can be broadly extended to roots. Fine roots displayed a wide diversity of forms and properties in Mediterranean vegetation, resulting in a multidimensional trait space. The main trend of variation in this multidimensional root space is analogous to the main axis of LES, while the second trend of variation is partially determined by an anatomical trade-off between tissue density and diameter. Specific root area (SRA) is the main trait explaining species distribution along the RES, regardless of the selected traits. We advocate for the need to unify and standardize the criteria and approaches used within the economics framework between leaves and roots, for the sake of theoretical consistency.
BACKGROUND AND AIMS: Leaf litter decomposition is an important process controlling nutrient cycling in most terrestrial ecosystems. We evaluated the relationships among traits of green leaves and decomposition rates of leaf litter (k) at different environmental scales and organisational levels (species and community). We also assessed the relationships at community level between k and the Leaf Economic Spectrum (LES) and between k and different soil variables. METHODS: We measured leaf traits in 38 woody species distributed in nine sampling sites along a topographic gradient in southern Spain. Leaf litter was collected for each species in each sampling site and incubated in a microcosm experiment with soil collected from the top 20 cm of each site. RESULTS: We found positive relationships between k and specific leaf area (SLA), leaf N, K and P and negative relationships with leaf dry matter content (LDMC) and leaf C isotopic composition (δ¹³C), both at species and community levels. Decomposability was positively related with the first PCA axis describing the LES and the relationships were consistent across all sites and within different zones or topographic positions. In addition, community weighted mean values of leaf traits (LESCWM) were stronger predictors of litter decomposition than soil variables. CONCLUSIONS: A major finding of the present study is the main role that leaf traits, and the covariation among them (LES), play on decomposition process in Mediterranean ecosystems both at the species and community levels. In summary, our results support the idea that the suites of leaf traits have a strong control on the pace of C cycling, being the best drivers of decomposition processes under similar climatic conditions.