Simulating and modeling CO2 flux emitted from decomposed oil palm root cultivated at tropical peatland as affected by water content and residence time

Abstract

Determining the oil palm dead roots contribution to total (R<sub>t</sub>) and heterotrophic (R<sub>h</sub>) respiration as a source of greenhouse gas/GHG emission in tropical peatland is urgently required, as well as predicting their magnitude to cope with difficulties of direct in-situ measurement. This study is designed to simulate the CO<sub>2</sub> flux emitted from oil palm dead roots/R<sub>dr</sub> in tropical peatland as affected by water content/WC and residence time/RT. The dead oil palm roots were cleaned, treated with control/15, 100, 150, 300, and 450%WC, and then incubated for three months. CO<sub>2</sub> flux measurement, C, N, and CN ratio determination were conducted every month. This study demonstrated the importance R<sub>dr</sub> among other CO<sub>2</sub> emission sources, ranging from 0.05-2.3 Mg CO<sub>2</sub> ha<sup>-1</sup> year<sup>-1</sup> with an average of 0.7 Mg CO<sub>2</sub> ha<sup>-1</sup> year<sup>-1</sup>. R<sub>dr</sub> contribution for literature R<sub>t</sub> and R<sub>h</sub> were around 0.3 to 1.3 and 0.9 to 3.5%, respectively. As a product of microbial respiration, R<sub>dr</sub> was affected by WC and RT, supported by analysis of variance, linear mixed effect model/REML, and multivariate analysis. 100-150%WC resulting in significant and highest R<sub>dr</sub>, whereas the increase (300-450%WC) or decrease (15%WC) would generate lower emission. R<sub>dr</sub> culminated in the first month after incubation; meanwhile, it declined in the following months. This study also emphasized non-linear relationships between CO<sub>2</sub> flux and other root properties, which can be modeled conveniently using non-linear approach, particularly using polynomial and artificial intelligence-based models. The simulation presented in this study served as an initial attempt to separate R<sub>dr</sub> from R<sub>h</sub>, as well as to predict CO<sub>2</sub> flux with reasonable accuracy and interpretable methods.