Posted by: oikosasa | April 15, 2014

Climate effects on plant chemistry

Lots of traits are climate dependent! In the Early View paper in Oikos Genetically based latitudinal variation in Artemisia californica secondary chemistry” by Jessica Pratt and co-workers, terpenes are studied under different climatic situations.Below is a summary of the paper: 

Gradients in environmental conditions can serve as a ‘space for time’ substitution when trying to understand how species might respond to current and future environmental change and have thus become the focus of much recent work. Environmental gradients and gradients in biotic interactions often result in corresponding gradients in plant traits within a species. In our study, we examined variation in leaf terpene chemistry for the foundation species California Sagebrush (Artemisia californica) in Coastal Sage Scrub habitat across a 700 km latitudinal gradient in California. This gradient is characterized from south to north by a four-fold increase in precipitation.

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

We collected California Sagebrush from five source populations distributed across this gradient and grew them in one common environment where we manipulated precipitation. Such common environment studies, when done in conjunction with environmental manipulations, provide a powerful approach to pinpoint the underlying causes of variation in plant traits and determine how such variation relates to large-scale ecological variation.

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

Pratt_sagebrush

Terpenes – one of the most diverse groups of plant secondary compounds – are important in providing defense against herbivores and also play several additional roles in the community. They are involved in plant-plant communication, drought and thermal tolerance, and adaptation to fire, and can influence plant relationships with other plants, animals, and microorganisms. We tested for genetically based variation in leaf terpene richness, diversity, concentration, and composition and examined whether precipitation was a key selective force on terpene chemistry.

California Sagebrush experimental garden plot

California Sagebrush experimental garden plot

Our results showed that California Sagebrush source populations differed in terpene richness, diversity, concentration, and composition, with terpene composition and concentration varying clinally along the gradient. Plants from source populations that were closer together geographically had a more similar composition of terpenes than those farther apart, and terpene concentration decreased clinally from south to north. Our manipulation of precipitation suggests that selection for lower terpenes under increased precipitation may underlie this clinal pattern that we observed. Interestingly, we did not see a direct influence of the precipitation manipulation on terpene chemistry indicating these traits may not be phenotypically plastic in response to altered precipitation.

Pratt_sagebrush

We conclude that changes in terpene chemistry under projected future climates will likely occur only through the relatively slow process of adaptation, and this will have important consequences for California Sagebrush’s interactions with the environment and a diverse community of associated species.

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