Cary, Katharine , Pittermann, Jarmila .
Leaf and xylem function under extreme nutrient deficiency: an example from the pygmy forest.
Plant adaptations to edaphic stress are important to ecological processes and ecosystem functioning; however, they are extremely complex and varied, and yet not completely understood. The pygmy forest in Mendocino County, California, offers an ideal natural experiment for studying plant growth and function under extreme edaphic stress. In this system, soil acidity and nutrient limitation constrain tree height to 1-2 meters and create unique plant communities with several endemic species. A number of studies have examined these soils and plant communities, but little is known about the structure and function of these plants, or what the implications of these effects are on plant survival and community structure. We addressed this gap by examining numerous key physiological attributes of pygmy and nearby control plants of eight species. Our hypothesis was that nutrient limitation would constrain photosynthesis and related leaf functional traits, such as dark respiration, stomatal conductance, water-use efficiency, stomatal density, and specific leaf area. However, most of the thirteen leaf traits we measured did not vary substantially between pygmy and control individuals, except in Sequoia sempervirens, which is rare in the pygmy forest. Pygmy S. sempervirens had lower chlorophyll content, maximum photosynthetic rates, and water-use efficiency than control individuals. Furthermore, we constructed vulnerability curves and measured leaf- and xylem-specific xylem conductivity in four species. We predicted that nutrient limitation would increase vulnerability to hydraulic dysfunction (embolism). Compared to conspecific control plants, pygmy angiosperms were more vulnerable to embolism, but pygmy conifers were equally or more resistant to embolism than controls. Interestingly, these plants seem to be hydraulically overbuilt for their environment: even at the water potentials we measured at the end of the dry season, our vulnerability curves predict both pygmy and control plants experience little embolism. Given that the pygmy forest experiences little water stress, it appears that it is nutrient limitation, not water limitation, that determines xylem growth and function in this system. Leaf function, however, is surprisingly unaffected by this nutrient limitation, and it seems that taxa that are adapted to live on these soils do so by limiting their growth but not necessarily their metabolism.
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1 - University of California, Santa Cruz, Ecology and Evolutionary Biology, Pittermann Lab, 1156 High Street, Santa Cruz, CA, 95064, USA
2 - University Of California, Integrative Biology, 1156 High Street, Santa Cruz, CA, 95064, USA
Presentation Type: Oral Paper
Session: 3, Ecophysiology
Location: 104/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 11:15 AM
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize