Climatic history, constraints, and the plasticity of phytochemical traits under water stress

Elevation drives intraspecific metabolomic differentiation in natural and experimental populations

A recent paradigm shift in ecology supports that the classic functional trait space should be extended to include the metabolome. Accordingly, metabolomic signatures differ between plant species or genotypes depending on where they grow along ecological gradients. Yet, it remains unclear whether environmental gradients alone induce intraspecific phytochemical shifts in natural populations, and if these differences can be replicated experimentally. To address this gap, we combined an observational and experimental study to explore how elevation drives differences in the diversity, endemism and composition of specialized metabolites within the widely distributed perennial grass Festuca rubra. We show that both natural and experimental populations (consisting of identical sets of unique genotypes) exhibit distinct metabolic profiles, unique to each elevation. While natural populations growing in alpine environments displayed lower phytochemical diversity and endemism than those inhabiting lower elevations, phytochemical diversity and endemism peaked at intermediate elevation for the experimental populations. In addition, elevation caused shifts in overall composition of metabolomic groups for experimental populations, reflected in alterations in the over- and under-representation of metabolites within specific superclasses. Our study demonstrates that elevation plays an important role in shaping the metabolome. Rapid shifts in abiotic and biotic environments following climate change may act to alter the plant metabolome, which can impact future ecosystem-level dynamics.

Clinal variations in seedling traits and responses to water availability correspond to seed-source environmental gradients in a foundational dryland tree species

BACKGROUND AND AIMS

In dryland ecosystems, conifer species are threatened by more frequent and severe droughts, which can push species beyond their physiological limits. Adequate seedling establishment will be critical for future resilience to global change. We used a common garden glasshouse experiment to determine how seedling functional trait expression and plasticity varied among seed sources in response to a gradient of water availability, focusing on a foundational dryland tree species of the western USA, Pinus monophylla. We hypothesized that the expression of growth-related seedling traits would show patterns consistent with local adaptation, given clinal variation among seed source environments.

METHODS

We collected P. monophylla seeds from 23 sites distributed across rangewide gradients of aridity and seasonal moisture availability. A total of 3320 seedlings were propagated with four watering treatments representing progressively decreasing water availability. Above- and below-ground growth-related traits of first-year seedlings were measured. Trait values and trait plasticity, here representing the degree of variation among watering treatments, were modelled as a function of watering treatment and environmental conditions at the seed source locations (i.e. water availability, precipitation seasonality).

KEY RESULTS

We found that, under all treatments, seedlings from more arid climates had larger above- and below-ground biomass compared to seedlings from sites experiencing lower growing-season water limitation, even after accounting for differences in seed size. Additionally, trait plasticity in response to watering treatments was greatest for seedlings from summer-wet sites that experience periodic monsoonal rain events.

CONCLUSIONS

Our results show that P. monophylla seedlings respond to drought through plasticity in multiple traits, but variation in trait responses suggests that different populations are likely to respond uniquely to changes in local climate. Such trait diversity will probably influence the potential for future seedling recruitment in woodlands that are projected to experience extensive drought-related tree mortality.

Plant water limitation and its impact on the oviposition preferences of the monarch butterfly (Lepidoptera: Nymphalidae)

Intensifying drought conditions across the western United States due to global climate change are altering plant-insect interactions. Specialist herbivores must find their host plants within a matrix of nonhosts, and thus often rely upon specific plant secondary chemistry for host location and oviposition cues. Climate-induced alterations to plant chemistry could thus affect female selection of larval food plants. Here, we investigated whether host-plant water limitation influenced oviposition preference in a threatened invertebrate: the monarch butterfly (Danaus plexippus). We found that females deposited more eggs on reduced-water than on well-watered narrowleaf milkweed plants (Asclepias fascicularis), but we could not attribute this change to any specific change in plant chemistry. Specialist herbivores, such as the monarch butterfly, which are tightly linked to specific plant cues, may experience shift in preferences under global-change conditions. Understanding oviposition preferences will be important to directing ongoing habitat restoration activities for this declining insect.