delta(13)C and stomatal density variability in modern and fossil leaves of key plants in the western United States

Titledelta(13)C and stomatal density variability in modern and fossil leaves of key plants in the western United States
Publication TypeThesis
Year of Publication1999
Authorsvan der Water, P
Academic DepartmentGeosciences
UniversityUniversity of Arizona
KeywordsAtriplex, Carbon-13, Fossil leaves, Stomatal density

During the last deglaciation, 15,000 to 12,000 calendar years ago, global warming and wholesale shifts in regional precipitation patterns produced dramatic changes in vegetation worldwide. Paleobotanical records, namely pollen and macrofossils, have been used not only to reconstruct shifts in plant distributions and abundances, but also to quantify changes in temperature and precipitation amounts or seasonality. In addition to climatic change, during the full glacial period atmospheric CO 2 values had dropped 30% to 200 ppmv compared to the Holocene, preindustrial value of 280 ppmv. Hypothetically, variations in atmospheric CO 2 affect plant water-use efficiency (carbon gained to plant-water transpired) and thus may have modulated vegetation response as climates change. The studies incorporated in this dissertation focused upon carbon isotope and morphological changes in leaves of key functional groups. The studies concentrated on plant species that are abundant in the fossil record and comprise major floral components of past and present vegetation. Key findings include: (1) that shifts in δ 13 C in modern populations along steep environmental gradients seldom exceeds inter-plant variability at a given site, (2) inter-plant and intra-site variability in modern and historic herbarium collections of the C 4 halophytes Altriplex canescens and A. confertilfolia and packrat midden macrofossils of A. canescens excludes their use as a reliable proxy for atmospheric δ 13 C, (3) calcium-oxalate crystals are common component in plant tissue and can have a significantly different δ 13 C value that increases inter-plant variability, especially in C 4 plants such as Atriplex canescens and A. confertifolia , (4) carbon isotope and stomatal density/index measurements of macrofossils from packrat middens show species specific adaptation in ecophysiological processes as atmospheric CO 2 rose from the full glacial, and (5) the greatest adaptation to low atmospheric CO 2 during the last ice age was in the C 3 species and that C 4 and CAM plants showed few changes in their discrimination against 13 C or in the number of stomata on their leaf surfaces.