Hydrogen isotope discrimination in higher plants: Correlations with photosynthetic pathway and environment

Abstract

The ratio of deuterium to hydrogen (expressed as δD) in hydrogen released as water during the combustion of dried plant material was examined. The δD value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C3 plants show mean δD values of-132‰ for shoots and -117‰ for roots; C4 plants show mean δD values of -91‰ for shoots and-77‰ for roots and CAM plants a δD value of-75‰ for roots and shoots. The difference between the δD value of shoot material from C3 and C4 plants was confirmed in species growing under a range of glasshouse conditions. This difference in δD value between C3 and C4 species does not appear to be due to differences in the δD value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C3 and C4 plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in δD values are discussed. In CAM plants grown in the laboratory or collected from the field δD values range from-75‰ to +50‰ and are correlated with δ(13)C values. When deprived of water, the δD value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different δD value of available water in areas of increasing aridity. Whatever the origin of the variable δD value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.

Carbon, Hydrogen, and Oxygen Isotope Ratios of Cellulose from Plants Having Intermediary Photosynthetic Modes

“…1). In contrast, Ziegler et al (25) observed a correlation between AD and 6 3C values of total organic matter of CAM plants. The basis for the difference between these observations can be understood by considering the factors which …”

“…2). Within the group of plants with 6'3C values ranging from -30%o to -25%o, there is a broad overlap in the oxygen isotope ratio among C3 plants having 680 Ziegler et al (25) proposed that CAM plants are enriched in deuterium relative to C3 and C4 plants because of their ability to maintain metabolic activity under water stress. They argued that, under water stress, plant water becomes enriched in deuterium during evaotranspiration (23), and this enrichment is passed on to the organically bound hydrogen.…”

Stable Hydrogen Isotope Fractionations during Autotrophic and Mixotrophic Growth of Microalgae

“…Cyt involved in electron transport in either photosynthesis or respiration, or both (4,11 above that seen in the dark. The primary isotope fractionation may occur during the reduction of NADP during photosynthesis because, in the dark, reducing power is generated from different pathways, glucose 6-P dehydrogenase and the tricarboxylic acid cycle, without fractionating hydrogen isotopes.…”

“…Plants grown under controlled conditions show a reproducible and measurable discrimination (fractionation) of as much as 20o between the isotopes of hydrogen, deuterium (D), and protium (H) (1,11). Cultures of microalgae, natural populations of phytoplankton, macroalgae, mosses, and higher terrestrial plants all have lower concentrations of the heavy isotope of hydrogen (deuterium) than the environmental water.…”

Oxygen and Hydrogen Isotope Ratios of Water from Photosynthetic Tissues of CAM and C3 Plants

“…The patterns of diurnal variation (or lack thereof) in isotope ratios of plant water are consistent with the gross anatomical and physiological characteristics of the plants studied here. Our observations support the previously advanced hypothesis that high D/H ratios in cellulose nitrate prepared from CAM plants relative to those for C3 plants are not caused by greater deuterium enrichment in the water in CAM plants, but rather by isotopic fractionations associated with different biochemical reactions in the two types of plants.It is now well established that the stable isotopic composition of the nonexchangeable hydrogen in cellulose (measured as cellulose nitrate) is related to a plant's photosynthetic mode (7,8,11,13). Cellulose nitrate prepared from CAM plants has more deuterium than that from C4 and C3 plants that grew under the same climatic regime and used the same water source.…”