Santiago, Louis , Dawson, Todd .
Photosynthetic light use efficiency of California redwood forest understory plants along a moisture gradient.
THE size, stature and distribution of trees in California’s coastal redwood forests have a marked influence on all aspects of forest microclimate. Therefore, redwood forests are among the darkest forests in the world and experience marked gradients in other resources like water from the northern to the southern range limits. We studied how understory plants common to redwood forests and growing along a moisture gradient that stretches 750 km from north to south along the California coast, respond to increased moisture in northern sites in terms of density, diversity, and physiological ability to photosynthesize in extremely low light conditions. Understory plant density increased with increasing precipitation suggesting that more water supports greater biomass. However, understory plants from the driest site had the highest photosynthetic rates for a given specific leaf area or leaf nitrogen consistent with higher light availability at the driest site. Plants from wetter sites maintained stomata in higher induction states and took advantage of sun flecks more quickly than plants from drier sites. Post illumination CO2 fixation was greatest in understory plants from wetter sites suggesting that higher water availability allows plant stomata to remain more open in deep shade, thus allowing plants in wet sites to take advantage of short duration sun flecks more effectively. The amount of CO2 fixed per unit light received in experimentally induced sun flecks was also greatest in plants from wetter sites. Overall, increased biomass and light use efficiency in wetter sites suggest that increased water availability allows California redwood understory plants to obtain more carbon for a given light availability. Further work should consider the proportion of plant water from rain versus fog because fog acts as a subsidy for both water and nutrients during the otherwise dry summer months when rain is rare and nutrients may limit growth.
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1 - University of California, Berkeley, Department of Integrative Biology, 3060 Valley Life Sciences Bldg #3140, Berkeley, California, 94720, USA
Light use efficiency.
Presentation Type: Oral Paper:Papers for Topics
Date: Tuesday, August 1st, 2006
Time: 10:45 AM