Stable Oxygen and Carbon Isotopic Composition of Rice (Oryza sativa L.) Grains as Recorder of Relative Humidity

Abstract

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 (δ18OOM, δ13COM) 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 δ18OOM and δ13COM. Based on regression analyses, the δ18OOM variation across sites showed significant dependence on the δ18O of source water (δ18OSW) used by the crops, with the humid region registering the strongest correlation (r2 = 0.95, p < 0.0001). After normalizing δ18OOM values with respect to δ18OSW and expressing the deviation as Δ18OOM, we obtained a significant relationship between the growing‐season average RH and Δ18OOM (r2 = 0.90, p < 0.0001). This is represented by a linear response function: Δ18OOM = (− 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 (Δ13COM) with RH gradient demonstrates the role of the evaporative demand in governing the dual‐isotope variability.

Comprehensive review of the annual haze episode in Northern Thailand

“…32 Figure 4.9. Discriminative plot of the haze carbon and nitrogen isotopic signature (red dots) and trend through time (purple arrow) compared to unspecific sources (motor vehicles, C3-& C4-plants) and potential specific sources (local deciduous forests, corn, soy, rice, sugarcane) (modified from Kawichai et al, 2020bKawichai et al, , 2022 with additional data from Spain & Le Feuvre, 1996;Turekian et al, 1998;Yoneyama et al, 2001;Marinaeli et al, 2002;Krull et al, 2003;Kell et al, 2005;Widory, 2007;Jahren & Kraft, 2008;Das et al, 2010;Pavuluri et al, 2010;Kaushal & Ghosh, 2018;Ma et al, 2021;Kato et al, 2023. This paper is a non-peer reviewed draft -currently not submitted to any journal Sulfate anthropogenic source component makes it less variable than other components and is preponderant outside the haze episode (Sopajaree et al, 2011;Tsai et al, 2013;Khamkaew et al, 2017;Janta et al, 2020;Chansuesubsri et al, 2021a,). However, sulfate production is also found in biomass burning (Sillapapiromsuk et al, 2013) but the negative correlation with increasing particulate matter concentration indicates that biomass is possibly not the dominant source (Chansuebsri et al, 2022).…”

High-Frequency Water Isotopic Analysis Using an Automatic Water Sampling System in Rice-Based Cropping Systems

“…They can be used as a tool for studying hydrological process [10], including climate-driven changes [11], soil hydrological processes [12], and catchment-scale hydrological fluxes [13,14]. Stable isotopes of water in rice grains have been used to identify the geographical origin [15], reconstruction of relative humidity (RH) level [16] and air temperature (T) [17], while stable isotopes of liquid water have been used to estimate the root water uptake [18], evaporation [5,19], and transpiration [20] from rice fields. Stable isotopes of water have also been applied in maize studies, such as water uptake estimations [21][22][23], beverage production [24], and evaporation measurements [25].…”

“…Previous studies mainly used methods such as balancing water inputs and outputs [28][29][30], the pan evaporation method [31], or the lysimeter method [32], where we applied an isotope-based method. Because the isotopic composition fluctuations between rice fields are mostly caused by evaporation [16], stable isotopes of water provide great insight into the effect of seasonal, temporal, and crop changes on the water sources.…”