PARENT SESSION
Oral Session 104: Photosynthesis and Respiration IV: CO₂; Light; Hydraulic Architecture .
Presiding: R Brooks
Thursday, August 5, 8:00 AM to 11:30 AM, Meeting Room D 136.

Variation in ecophysiological characteristics of Nassella pulchra across a coast-inland gradient in California.

Corbin, Jeffrey^*,1, Conly, Dana ¹, ¹ University of California, Berkeley, Berkeley, CA, USA

ABSTRACT- The ability of a species to adapt to climate change is enhanced if variation in ecologically important traits already exists within the population as ecotypic variation or phenotypic plasticity. However, the extent to which populations of a given species vary in their patterns of water use or physiological activity along environmental gradients has been little studied in grasslands. Nassella pulchra, one of the most abundant and widespread of California's native perennial bunchgrasses, experiences widely ranging summertime climatic conditions across its range – from the cool, fog-laden coast to the hot, dry interior. We hypothesized that physiological characteristics of populations of N. pulchra would vary along this coastal–inland gradient. We compared the photosynthetic rates, stomatal conductance, predawn water potential, and depth of water use of individuals in six populations ranging from 0.4 to 95 km from the coast. Photosynthesis and stomatal conductance were measured using a LiCor 6400 twice during summer 2003 – in June and September. Predawn water potential (using a pressure bomb) and depth of water use (by comparing stable oxygen isotopes in plant and soil water) were measured in September 2003. Our results indicate that there are significant differences in physiological characteristics between N. pulchra populations in coastal habitats versus those further inland. Specifically, coastal N. pulchra populations were significantly less water stressed and had higher rates of photosynthetic activity (in September) than inland populations. Coastal populations also relied on water from shallow soil horizons, particularly from the prevalent fog, while inland populations used water from deeper soil horizons. This study does not indicate whether the population differences are the result of ecotypic variation or phenotypic plasticity, but it does indicate that variation in these ecologically important traits exists within this important species.

Key words: Photosynthetic rates, Stable isotopes, Water relations, California grasslands