Plant Origin, but Not Phylogeny, Drive Species Ecophysiological Response to Projected Climate

Effect of DNA methylation, modified by 5-azaC, on ecophysiological responses of a clonal plant to changing climate

Epigenetic regulation of gene expression is expected to be an important mechanism behind phenotypic plasticity. Whether epigenetic regulation affects species ecophysiological adaptations to changing climate remains largely unexplored. We compared ecophysiological traits between individuals treated with 5-azaC, assumed to lead to DNA demethylation, with control individuals of a clonal grass originating from and grown under different climates, simulating different directions and magnitudes of climate change. We linked the ecophysiological data to proxies of fitness. Main effects of plant origin and cultivating conditions predicted variation in plant traits, but 5-azaC did not. Effects of 5-azaC interacted with conditions of cultivation and plant origin. The direction of the 5-azaC effects suggests that DNA methylation does not reflect species long-term adaptations to climate of origin and species likely epigenetically adjusted to the conditions experienced during experiment set-up. Ecophysiology translated to proxies of fitness, but the intensity and direction of the relationships were context dependent and affected by 5-azaC. The study suggests that effects of DNA methylation depend on conditions of plant origin and current climate. Direction of 5-azaC effects suggests limited role of epigenetic modifications in long-term adaptation of plants. It rather facilitates fast adaptations to temporal fluctuations of the environment.

The role of plant-soil feedback in long-term species coexistence cannot be predicted from its effects on plant performance

BACKGROUND

Despite many studies on the importance of competition and plants' associations with mutualists and pathogens on plant performance and community organization, the joint effects of these two factors remain largely unexplored. Even less is known about how these joint effects vary through a plant's life in different environmental conditions and how they contribute to the long-term coexistence of species.

METHODS

We investigated the role of plant-soil feedback (PSF) in intra- and interspecific competition, using two co-occurring dry grassland species as models. A two-phase PSF experiment was used. In the first phase, soil was conditioned by the two plant species. In the second, we assessed the effect of soil conditioning, competition and drought stress on seedling establishment, plant growth in the first and second vegetation season, and fruit production. We also estimated effects of different treatments on overall population growth rates and predicted the species' potential coexistence.

RESULTS

Soil conditioning played a more important role in the early stages of the plants' life (seedling establishment and early growth) than competition. Specifically, we found strong negative intraspecific PSF for biomass production in the first year in both species. Although the effects of soil conditioning persisted in later stages of plant's life, competition and drought stress became more important. Surprisingly, models predicting species coexistence contrasted with the effects on individual life stages, showing that our model species benefit from their self-conditioned soil in the long run.

CONCLUSIONS

We provide evidence that the effects of PSF vary through plants' life stages. Our study suggests that we cannot easily predict the effects of soil conditioning on long-term coexistence of species using data only on performance at a single time as commonly done in PSF studies. We also show the importance of using as realistic environmental conditions as possible (such as drought stress experienced in dry grasslands) to draw reasonable conclusions on species coexistence.

The importance of ecophysiological traits in response of Festuca rubra to changing climate

Knowledge of the ability of plants to respond to climate change via phenotypic plasticity or genetic adaptation in ecophysiological traits and of the link of these traits to fitness is still limited. We studied the clonal grass Festuca rubra from 11 localities representing factorially crossed gradients of temperature and precipitation and cultivated them in growth chambers simulating temperature and moisture regime in the four extreme localities. We measured net photosynthetic rate, F_v /F_m , specific leaf area, osmotic potential and stomatal density and length and tested their relationship to proxies of fitness. We found strong phenotypic plasticity in photosynthetic traits and genetic differentiation in stomatal traits. The effects of temperature and moisture interacted (either as conditions of origin or growth chambers), as were effects of growth and origin. The relationships between the ecophysiological and fitness-related traits were significant but weak. Phenotypic plasticity and genetic differentiation of the species indicate the potential ability of F. rubra to adapt to novel climatic conditions. The most important challenge for the plants seems to be increasing moisture exposing plants to hypoxia. However, the plants have the potential to respond to increased moisture by changes in stomatal size and density and adjustments of osmotic potential. Changes in ecophysiological traits translate into variation in plant fitness, but the selection on the traits is relatively weak and depends on actual conditions. Despite the selection, the plants do not show strong local adaptation and local adaptation is thus likely not restricting species ability to adjust to novel conditions.

Opportunities and Threats of Mediterranean Evergreen Sclerophyllous Woody Species Subjected to Extreme Drought Events

Climate change and extreme drought and heat events impact the Mediterranean evergreen sclerophyllous vegetation in South Europe, especially in Iberian and Italian peninsula, where widespread crown defoliation and dieback have been observed since the 90s of the XX century. Field observations and long-term experiments showed different sensitivity of the various woody species, Quercus ilex and Arbutus unedo being prone to drought, whereas Phillyrea latifolia and Pistacia lentiscus appeared to be resistant. The present review aims at exploring the phylogenetic and evolutionary basis of the resistance (or susceptibility) to drought of Mediterranean vegetation and its possible mechanisms of resilience. The main findings are summarized as follows: (1) Mediterranean regions in the world are refuge areas for several plant evolutive lineages and migratory routes. Evergreen sclerophyllous species, currently presented in Mediterranean basin, evolved under different climatic conditions; (2) the evergreen habitus represents an adaptation to mild drought conditions. Deciduous (specially summer deciduous) species are better performing under severe drought and low air relative humidity than evergreen species; (3) severe drought events acts selectively by favouring the species evolved in the Quaternary era and those originated in drier regions; (4) the evergreen trees and shrubs are resilient to the severe drought events and can restore the pre-event condition by resprouting from dormant buds in the cambium tissue. This ability is related to the non-structural carbohydrate content in the parenchyma-rays in woody stems. The amount and availability of these strategic reserve can be compromised by frequent drought events; (5) plant seed regeneration can be affected by drought and seedling establishment may be limited by soil dryness and microenvironment conditions; (6) the role of phenotypic plasticity of the species and epigenetic responses in Mediterranean-type ecosystems, although discussed in few papers, is still poorly known. We hypothesize that instead of latitudinal (South to North) or altitudinal (lowland to upland) plant migrations, Mediterranean forest ecosystems may respond to climate change by modulating their species composition and community structure with genetic resources (i.e., taxonomic diversity) already present in loco. Changes in vegetation assemblages and community structure may lead changes in ecological and landscape ecosystem values, with changes in related ecosystem services. A redefinition of management criteria of natural resources and a pro-active silviculture to make forest ecosystems more resilient are required.

Plant palatability and trait responses to experimental warming

Climate warming is expected to significantly affect plant-herbivore interactions. Even though direct effects of temperature on herbivores were extensively studied, indirect effects of temperature (acting via changes in host plant quality) on herbivore performance have rarely been addressed. We conducted multiple-choice feeding experiments with generalist herbivore Schistocerca gregaria feeding on six species of genus Impatiens cultivated at three different temperatures in growth chambers and a common garden. We also studied changes in leaf morphology and chemistry. We tested effects of temperature on plant palatability and assessed whether the effects could be explained by changes in the leaf traits. The leaves of most Impatiens species experienced the highest herbivory when cultivated at the warmest temperature. Traits related to leaf morphology (specific leaf area, leaf dry matter content and leaf area), but not to leaf chemistry, partly mediated the effects of temperature on plant palatability. Herbivores preferred smaller leaves with lower specific leaf area and higher leaf dry matter content. Our study suggests that elevated temperature will lead to changes in leaf traits and increase their palatability. This might further enhance the levels of herbivory under the increased herbivore pressure, which is forecasted as a consequence of climate warming.