Photosynthetic variability along an elevational gradient in the chaparral

Abstract

A field study was conducted on the incorporation of the Carbon-14 by several chaparral species along an elevational transect from the coast to inland California in San Diego county. Measurements were carried out under natural conditions and included photosynthesis, xylen water potentials, light intensity, air temperature, and leaf density. The results show that the evergreen sclerophyllous shrubs have higher rates of daily carbon uptake at high elevations than at low elevation. This is correlated with higher precipitation at high elevations of the chaparral. Among the evergreen shrubs, the shallow rooted(e.g. C.greggii shrubs)indicated more water stress and an earlier decline in their carbon uptake with advancing drought than did the deep rooted shrubs (e.g. A. fasciculatum and Q. dumosa). The dependence of the daily carbon uptake on dawn water potentials is well illustrated in A. fasciculatum, an evergreen shrub that was sampled at all elevations, and in the drought-deciduous shrubs S. apiana and S. mellifera that occurred at low elevations of the transect.