Climatic drivers of plant traits variation along a cline in Artemisia californica, a long-lived shrub

Understanding the pattern and process of plant adaptation to the abiotic environment may help ecologists predict future potential states of ecological communities with predicted and on-going climate change. We measured performance and defense traits both in the wild (in situ) and in a common garden for the long lived shrub, Artemisia californica. We studied 21 populations within the common garden and five in situ populations distributed along a 5.7o latitudinal gradient characterized by northward decreases in temperature and climatic variability and increases in precipitation. Photosynthesis-related traits showed genetically based clinal variation, with northward increases in specific leaf area (SLA), leaf water content (%H2O) and leaf nitrogen content (%N) that was associated with increasing source site mean temperature but not temperature variability, precipitation variability, or total precipitation. Traits of importance to interactions with herbivores showed inconsistent patterns of clinal variation, although a genetically based cline of northward decrease in sesquiterpene concentration was associated with increasing mean annual precipitation. Average flowering date showed genetically based clinal variation of advancing northward onset of flowering, but this could not be clearly linked to any single climatic factor. A genetically based cline of northward decrease in plant biomass in the common garden was associated with variation in photosynthesis-related and water relation traits. Accordingly, our results suggest that latitudinal clines in temperature select for local adaptation of photosynthesis-related (but not herbivore resistance) traits that in turn underlie corresponding clines in plant biomass