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Stable Oxygen and Carbon Isotopic Composition of Rice ( Oryza sativa L.) Grains as Recorder of Relative Humidity
Author(s) -
Kaushal Ritika,
Ghosh Prosenjit
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2017jg004245
Subject(s) - oryza sativa , relative humidity , isotopes of carbon , growing season , δ13c , humidity , total organic carbon , seasonality , linear regression , chemistry , carbon fibers , stable isotope ratio , zoology , botany , biology , environmental chemistry , mathematics , ecology , geography , physics , meteorology , biochemistry , algorithm , quantum mechanics , composite number , gene , statistics
Southwest monsoon season over India exhibits spatial variation in the relative humidity (RH) levels. We took advantage of rice ( Oryza sativa L.), cultivated in varied RH condition during the southwest monsoon season, to study the relationship of oxygen and carbon isotopic composition in the bulk grain organic matter (δ 18 O OM , δ 13 C OM ) with the hydroclimatic parameter of RH. Seasonal harvests of the years 2010 through 2014, sampled from 23 sites located in different climatic zones over India, were used for this experiment. Several fields and different genotypes ( n = 105) were sampled at each site to arrive at representative values of δ 18 O OM and δ 13 C OM . Based on regression analyses, the δ 18 O OM variation across sites showed significant dependence on the δ 18 O of source water (δ 18 O SW ) used by the crops, with the humid region registering the strongest correlation ( r 2 = 0.95, p < 0.0001). After normalizing δ 18 O OM values with respect to δ 18 O SW and expressing the deviation as Δ 18 O OM , we obtained a significant relationship between the growing‐season average RH and Δ 18 O OM ( r 2 = 0.90, p < 0.0001) . This is represented by a linear response function: Δ 18 O OM = (− 0.45 ± 0.03) × RH + (66.4 ± 2.7) . The relationship established in this study enables the reconstruction of RH level from the isotopic measurement of rice grain OM in modern‐day and palaeo samples. Further, the relationship of the carbon isotope discrimination in rice grain OM (Δ 13 C OM ) with RH gradient demonstrates the role of the evaporative demand in governing the dual‐isotope variability.