干旱区生态环境知识资源中心

Carbon isotope discrimination (DELTA) is associated with long-term water-use efficiency (ratio of photosynthesis to transpiration), and varies within and among desert plant species. The variation of DELTA within aridland perennial plants may be related to life-history class attributes, while differences in DELTA between long- and shorter-lived species may be based on life-form dependent tradeoffs of growth and survival. We examined these patterns in two desert environments and asked if life-history class and life-form related differences in DELTA occurred in Coleogyne ramosissima, Larrea tridentata, Encelia farinosa, Ambrosia dumosa and Gutierrezia microcephala. The mean DELTA values of seedlings were greater than those of adults for all species except G. microcephala. The difference between life-history classes may represent a shift from low water-use efficiency (high DELTA) during establishment to high water-use efficiency (low DELTA) as an adult. Our results suggest that this shift is based on genetically-and/or environmentally-induced ontogenetic changes in plant metabolism. Such changes may be beneficial if a high DELTA and low DELTA are favored at different developmental stages. Interspecific comparisons showed that adult long-lived plants had lower DELTA values than adults of shorter-lived species in the same community, but for seedlings the same pattern was found for only one pair of species. Thus the previously shown trend for long-lived species to have lower DELTA values than shorter-lived species may depend on the stage of development.