Temperton, V. | Search bioRxiv

bioRxiv2019

Plant traits are poor predictors of long-term ecosystem functioning

Earth is home to over 350,000 vascular plant species1 that differ in their traits in innumerable ways. Yet, a handful of functional traits can help explaining major differences among species in photosynthetic rate, growth rate, reproductive output and other aspects of plant performance2-6. A key challenge, coined "the Holy Grail" in ecology, is to upscale this understanding in order to predict how natural or anthropogenically driven changes in the identity and diversity of co-occurring plant species drive the functioning of ecosystems7, 8. Here, we analyze the extent to which 42 different ecosystem functions can be predicted by 41 plant traits in 78 experimentally manipulated grassland plots over 10 years. Despite the unprecedented number of traits analyzed, the average percentage of variation in ecosystem functioning that they jointly explained was only moderate (32.6%) within individual years, and even much lower (12.7%) across years. Most other studies linking ecosystem functioning to plant traits analyzed no more than six traits, and when including either only six random or the six most frequently studied traits in our analysis, the average percentage of explained variation in across-year ecosystem functioning dropped to 4.8%. Furthermore, different ecosystem functions were driven by different traits, with on average only 12.2% overlap in significant predictors. Thus, we did not find evidence for the existence of a small set of key traits able to explain variation in multiple ecosystem functions across years. Our results therefore suggest that there are strong limits in the extent to which we can predict the long-term functional consequences of the ongoing, rapid changes in the composition and diversity of plant communities that humanity is currently facing.

ecology↗

bioRxiv2019

The exotic species Senecio inaequidens pays the price for arriving late in temperate European grasslands

The South African ragwort (Senecio inaequidens DC.) is one of the fastest exotic plant invaders in Central Europe but, despite its large distribution area, it is still not commonly found in European grasslands. In order to better understand the mechanisms behind invasion resistance of grassland communities to S. inaequidens, we determined (1) to what extent the timing of arrival of S. inaequidens in the community affected its invasiveness as well as the performance of the native species, and (2) how the direction and strength of priority effects were affected by the composition of the native community being invaded, particularly with regard to the presence of N2-fixing species (legumes). In a greenhouse experiment, we manipulated the timing of arrival of the exotic species in the community and the composition of the native background community to test the influence of these factors on the productivity and N content of exotic and native species. Using a set of interaction indices, we also investigated if the plant species origin (native or exotic) and the native community composition affected the benefit of arriving early and the cost of arriving late (i.e., priority effects) in the community. We showed that both exotic and native species created inhibitory priority effects for late-arriving species. The establishment success of S. inaequidens strongly depended on its timing of arrival in a grassland community. On average, S. inaequidens benefited more from arriving early than the natives. We did not find any evidence to support that the presence of legumes in the background community would favour invasion by S. inaequidens. When natives arrived later than S. inaequidens, however, priority effects were weaker when legumes were present in the native community. Synthesis: we showed that priority effects created by natives can lower the risk of invasion by S. inaequidens and are an important mechanism to explain why this exotic species is not commonly found in European grasslands yet. Our results suggest that an early arrival of this species at a site with low native species abundance (e.g., following a disturbance) is a scenario that could favour invasion by S. inaequidens.

ecology↗