Spatial D/H Heterogeneity of Leaf Water

Abstract

The mean deltaD value of petiole water of Pterocarpus indicus Willd (deltaD = -9.0 +/- 2.5 per thousand, n = 3) was not significantly different from the mean value of stem water (-8.3 +/- 2.8 per thousand, n = 3). deltaD values of main vein water ranged from -11.1 to + 12.0 per thousand (n = 14) and increased along the main vein from petiole to the tip of leaves. Mesophyll water was highly enriched in deuterium (mean deltaD = +32.0 +/- 2.0 per thousand, n = 19) when compared with stem, petiole, and vein water. deltaD values of mesophyll water for different areas of the lamina, however, were not homogenous and could differ by as much as 20 per thousand.

Are leaf physiological traits related to leaf water isotopic enrichment in restinga woody species?

“…The reasons for these discrepancies are especially affected by life form and plant hydraulic properties (Lai et al 2008) which are related to (i) nonuniform stomatal closure that promote different enrichments between cells adjacent to open and closed stomata (Flanagan et al 1991, Luo andSternberg 1992) and (ii) different pools of water within leaves (apoplastic and symplastic water as well as water in veins) some of which may not be exposed directly to evaporative conditions (Yakir et al 1989, 1990, 1993, Yakir and Sternberg 2000. The cell wall surfaces, which are exposed to evaporation, correspond to part of the apoplastic water fraction that have its isotopic composition influenced by environmental conditions, showing diurnal isotope ratio fluctuations (Yakir et al 1989(Yakir et al , 1990.…”

“…The symplastic water is not completely exposed to evaporation but may be affected by the isotopically enriched apoplastic water (Yakir and Sternberg 2000). The third pool consists of the water in the veins showing a high proportion of unfractionated water that reflects the water absorbed from roots (Flanagan andEhleringer 1991, Luo andSternberg 1992). Farquhar and Lloyd (1993) modeled leaf water isotopic composition by invoking the Péclet effect, which explained the above discrepancies and other observed characteristics of leaf water isotopic enrichment.…”

18O Spatial Patterns of Vein Xylem Water, Leaf Water, and Dry Matter in Cotton Leaves

“…Previous sampling of vein water by pressurizing a detached leaf in a pressure chamber indicated good agreement between the isotopic composition of irrigation water and that assigned to vein water (Yakir et al, 1989). In contrast, based on vacuum distillation of excised vein segments, ␦ 2 H of vein water had been shown to increase along the main vein from the leaf base to the tip (Luo and Sternberg, 1992). The data of Figure 2 give direct evidence of xylem water enrichment in the leaf veins of an intact transpiring leaf.…”

“…In relatively close agreement with these observations, our independent assessment of this water fraction by gravimetric analysis gave a value of 14.2% Ϯ 1.9% total leaf water. Such a high proportion of non-fractionating water has previously been noted (Leaney et al, 1985;Walker et al, 1989) but criticized as unlikely (Luo and Sternberg, 1992) given independent estimates of vein water fraction to be Յ5%. Anatomical analysis of mesophyll and vessel areas in young barley (Hordeum vulgare) leaves suggested 0.8% total tissue water was found in the lumen of vessels (Rayan and Matsuda, 1988).…”

“…Although the Craig-Gordon model basically describes water enrichment at the sites of evaporation compared with locally transpired water, it cannot adequately account for other aspects of leaf water enrichment, particularly the spatial variation of leaf water 18 O and/or D contents (Luo and Sternberg, 1992;Bariac et al, 1994;Wang and Yakir, 1995;Helliker and Ehleringer, 2000). Also, the Craig-Gordon model has often been found to overestimate the isotopic enrichment of bulk leaf water (Allison et al, 1985;Bariac et al, 1989;Walker et al, 1989;Walker and Brunel, 1990;Yakir et al, 1990;Flanagan et al, 1991aFlanagan et al, , 1991bFlanagan et al, , 1994Wang et al, 1998).…”