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.
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.
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.