Spatio-temporal functional variation of the sub-Mediterranean mountain grasslands

Abstract

Predicting plant responses to changing environments can be effectively achieved by investigating the species functional traits. However, we are still far away from having a precise scheme of plant functional strategy that allow the prediction of plant distribution along environmental gradient. First of all inferring processes from trait patterns has its unresolved issues since different processes may lead to the same functional pattern. Disentangling assembly rules may request to study the relationship between different functional metrics along a given environmental gradient (Chapter 1). Secondly, relevant functional topics are poorly assessed. Functional ecology studies have mainly focused on aboveground trait related to plant performances of competition, resource acquisition and dispersal, neglecting belowground functional dimension (Chapter 3b). Evidence on belowground traits variation are therefore urgently needed. We propose a new trait, belowground organ dry matter content, suggesting that it can capture an independent axis of plant performance related to resource conservation strategy (Chapter 3a). Moreover, considering intraspecific trait variability in the functional ecology is fundamental task since it may affect plant responses to abiotic and biotic factors, and additionally, it can influence ecosystem functions (Chapter 2-3a). Finally, predicting ecosystem responses to global change, needed the use of “direct” approach concerning monitoring of dynamic, long-term vegetation changes. Evidences about species loss affecting ecosystem functioning and services via species traits are increasing. Thus, assessing ecosystem functioning with a species composition and trait approach may lead avoid misleading interpretation. The hypothesis are: 1) does relationship between the dispersion and the mean of a trait in a given community represent a useful approach to disentangling community assembly rules? (Chapter 1); 2) How does environmental condition changing affect intraspecific trait variability of the grass species Brachypodium genuense ? (Chapter 2); 3) Do belowground functional traits showed opposite pattern to aboveground across habitat (Chapter 3a) and within habitat? (Chapter 3b); moreover, what is the relative contributions of intraspecific trait variability and species composition on belowground functional trait variation? (Chapter 3b) Finally, 4) How changed the community functional traits and species composition along temporal gradient? (Chapter 4). We tested these hypothesis on semi-natural grasslands because they represent priority habitat hosting high biodiversity. In the Chapter 1 we proposed a methodological approach to disentangle the different processes that lead to the same functional pattern. I found that the trait-environmental relationship is climatic context dependent, leading to unimodal variation in sub-Mediterranean grassland. Moreover, we highlighted also that combining the mean and the dispersion of a given trait within the community may represent a useful approach to disentangle the processes only for traits related to size-asymmetric competition. In the Chapter 2, contrary to suggestion asserting that plasticity is more affected by variation in the microenvironmental condition, we found an even contribute from microenvironmental as well as macroenvironmental condition. However, the leaf plasticity of Brachypodium genuense is quite high, ranging from competition performances in productive environment, to stress tolerant performance in unproductive environment. In the Chapter 3a we highlighted that the contribute of intraspecific trait variation is higher than species composition. Disentangling the contribute of these two effects, allow a better understanding of plant-environmental relationship, in particular along short gradient or whitin the same habitat, where considering only interspecific variation may lead to misleading results. Moreover, for the belowground traits we found at species level the lack of any correlation with other traits, suggesting a new axis of plant performances that this new trait is supposed to capture. Instead, at community level, we found a opposite pattern with respect to the aboveground counterpart, suggesting that these traits are shaped by different assembly processes. This latter findings is also highlighted by Chapter 3b, in which we add new evidence on how belowground traits are fundamental in predicting plant response to environmental variation more than aboveground traits, at least at higher scale. Finally, in the last Chapter of my thesis (4) we found that in more unproductive condition, increasing in species diversity and richness is not followed by a variation in the diversity in functional traits, while in the middle part at this increasing we found also an increasing of traits diversity. This highlighted that the pool of available niche for these traits is not yet saturated, leading to an increase in the ecosystem services.