Carbon Sequestration Enhancement by Irrigation in a Mediterranean Pine Forest

Sequestration of atmospheric CO₂ in the Yatir Mediterranean semi-arid Aleppo Pine Forest (<i>Pinus halepensis</i>) close to the border of the semi-arid timberline was characterized and quantified under field conditions. Measurements of organic and inorganic CO₂ sequestration with gas exchange, stock counting approach, and remote sensing were made in both rainfed control (~12% average annual Soil Moisture) and long-term experiment of irrigation (~10 years with ~24% annual average SM) plots, providing the opportunity to separate the effects of atmospheric water demand from soil water stress on the atmospheric CO₂ sequestration responses. Measurements yield an organic carbon sequestration (OCS) rate of ~550 g CO₂ m^-2 yr^-1, 60% in soil and 40% in biomass (standing and removed). In addition, measurements yield an inorganic carbon sequestration (ICS) rate of ~65 g CO₂ m^-2 yr^-1 (for half meter soil depth) via calcite (CaCO₃) precipitation in the soil due to root exhalation of CO₂ (25%) and microbial activity (75%). The drip-irrigated plot showed approximately 3 times higher organic CO₂ sequestration than the control plot, divided equally between the soil and the biomass. For the irrigated plot, the inorganic CO₂ sequestration rate was ~1.8 times higher than that of the control plot. These measured values demonstrate the relatively high potential for carbon sequestration in Mediterranean drylands forests under irrigated and non-irrigated conditions.