Comparative gas exchange of four California beach taxa.

Laboratory gas exchange measurements were conducted on four pioneering beach species from southern California. Atriplex leucophylla (Moq.) D. Dietr., a C species, had a photosynthetic temperature optimum substantially higher than leaf temperatures normally experienced on the beach during the primary growing season. The C species, Cakile maritima Scop., Ambrosia chamissonis Less. and Abronia maritima Nutt. ex Wats., had photosynthetic temperature optima close to their growth temperature and higher photosynthetic rates than the C species at normal field growth temperatures. Atriplex leucophylla had higher mesophyll conductances which resulted in higher water use efficiencies at all measurement temperatures. Leaf chlorophyll and protein contents were not correlated with photosynthetic rates. The possible significance of water use efficiency is discussed in relation to the characteristics of the beach habitat.