Great Basin Naturalist Memoirs


Photosynthetic production of two Mojave Desert shrubs was measured under natural growing conditions at UCLA. Measurements of photosynthesis, transpiration, resistances to water vapor flux, soil moisture potential, and tissue water potential were made. Atriplex canescens (Pursh) Nutt., a member of the C4 biochemical carbon dioxide fixation group was highly competitive in growth rate and production during conditions of adequate soil moisture. As soil moisture conditions declined to minus 40 bars, the net photosynthetic rate of Atriplex decreased to zero. However, the C3 shrub species Larrea tridentata (Sesse & Moc. ex DC.) Gov. was able to maintain positive net photosynthetic production during conditions of high temperature and extreme low soil moisture through the major part of the season. The comparative advantages of the C4 versus the C3 pathway of carbon fixation was lost between these two species as the soil moisture potential declined to minus 40 bars. Desert plants have different strategies for survival, one of the strategies being the C4 biochemical carbon fixation pathway. However, many of the plants are members of the G3 group. In this instance, the C4 fixation pathway does not confer an added advantage to the productivity of the species in the Mojave Desert. Species distribution based on comparative photosynthetic production is discussed.