Trends in Stomatal Density and ¹³ C/ ¹² C Ratios of Pinus flexilis Needles During Last Glacial-Interglacial Cycle

Abstract

Measurements of stomatal density and delta(13)C of limber pine (Pinus flexilis) needles (leaves) preserved in pack rat middens from the Great Basin reveal shifts in plant physiology and leaf morphology during the last 30,000 years. Sites were selected so as to offset glacial to Holocene climatic differences and thus to isolate the effects of changing atmospheric CO(2) levels. Stomatal density decreased approximately 17 percent and delta(13)C decreased approximately 1.5 per mil during deglaciation from 15,000 to 12,000 years ago, concomitant with a 30 percent increase in atmospheric CO(2). Water-use efficiency increased approximately 15 percent during deglaciation, if temperature and humidity were held constant and the proxy values for CO(2) and delta(13)C of past atmospheres are accurate. The delta(13)C variations may help constrain hypotheses about the redistribution of carbon between the atmosphere and biosphere during the last glacial-interglacial cycle.

The influence of CO2concentration on stomatal density

“…Analyses outside these restrictions might well explain observations of extreme values of responses (Korner, 1988). Even time sequences of fossil leaves can be selected from very similar temperatures during periods of changing temperature, by adjusting the altitude and latitude of collection (Van der Water et al, 1994), and there is little problem in identifying the same area of leaf for observations. The fact that some publications do not indicate the precise method of sampling suggests the possibility that differences in stomatal density might he recorded as responses to CO^ concentration, when the actual responses might be due to systematic sampling errors on the leaf surface or to microclimatic differences, such as collections of sun and shade leaves.…”

A natural experiment on plant acclimation: lifetime stomatal frequency response of an individual tree to annual atmospheric CO2 increase.

“…Stomatal density changes in fossil leaves of Pinus flexilis and Salix herbacea correlate with glacialinterglacial CO2 dynamics (9,10). Stomatal indices for fossil Quercus petraea reflect fluctuating atmospheric CO2 concentrations in late Miocene, Pliocene, and early Pleistocene time intervals between 10 million and -2 million years ago (5)(6)(7).…”

Leaf morphological and physiological responses of Quercus aquifolioides along an altitudinal gradient

“…Stomata parameters reflect two important physiological processes, absorption of CO 2 in photosynthesis and transpiration of water. Environmental changes, such as atmospheric CO 2 concentration, temperature, light and humidity can influence stomatal parameters ( Van de Water et al 1994, Hultine and Marshall 2000, Li et al 2002, Qiang et al 2003. Moreover, levels of N in plant tissues have been positively correlated with altitude, and increased CO 2 demand at the site of carboxylation (Körner 1989, Sparks andEhleringer 1997).…”