Impact of Liming on Soil CO2 Emissions and Oil Palm Physiology in Tropical Peatlands

Southeast Asia hosts the largest areas of tropical peatland in the world, with Malaysia’s contribution being significant, covering approximately 2.7 million hectares. Many of these areas have been converted to oil palm plantations and face distinctive challenges due to the high acidity of peat soil, about pH 3.3 – 3.5. Liming is implemented to decrease soil acidity and enhance soil fertility. However, the impact of liming on soil CO₂ emissions and oil palm physiology in tropical peatlands remains underexplored. This study investigates the effects of liming on soil CO₂ emissions and oil palm physiological variables such as assimilation rate (A), stomatal conductance (G_sw), intercellular CO₂ concentration (Ci), transpiration (E), and intrinsic water use efficiency (iWUE) on tropical peat soils. The experiment was arranged in a randomized complete block design with four liming treatments: 0 (T1), 2 (T2), 4 (T3), and 8 (T4) t ha⁻¹. Soil pH increased significantly with an increase in lime application. The soil CO₂ emission was significantly higher in T4 (203 g C m^-2 yr^-1), followed by T3 (184 g C m^-2 yr^-1), T2 (140 g C m^-2 yr^-1) and T1 (111 g C m^-2 yr^-1). Similarly, assimilation rate (A)exhibited significant differences across treatments, with T4 recorded the highest rate (15.1 µmol m^-² s^-¹), and the lowest is T1 (10.8 µmol m^-² s^-¹). Conversely, G_sw was higher in the T1 (0.32 mol m^-² s^-¹) than T4 (0.24 mol m^-² s^-¹). Soil CO₂emissions positively correlated (p < 0.01) with soil pH, A, Ci, and chlorophyll content. In contrast, a significant negative correlation (p < 0.01) was observed with Gsw, and E. These findings highlight that liming improves soil acidity, and oil palm physiological variables but also accelerates soil carbon loss as CO₂ emissions.