Effects of atmospheric CO2 concentration on soil-water retention and induced suction in vegetated soil

Current atmospheric CO2 (400 ppm) is increasing 2 ppm annually and might reach up-to 1000 ppm by year 2100 due to global climate change. Different plant growth was observed under elevated CO2 in the previous studies. However, plant induced soil suction besides plants growth due to increasing atmospheric CO2 concentration in heavily compacted soil remain elusive. The objective of this study is to quantify transpiration and evapo-transpiration induced soil suction by Schefflera heptaphylla in heavily compacted soil under different atmospheric CO2 concentration. Three replicates of the plant were grown, and their characteristics were measured under 400 ppm and 1000 ppm CO2 concentration for three months. Leaf area index of plants decreased by 35% under 1000 ppm CO2 concentration due to soil nitrogen scarcity which impedes the plants ability to metabolize increased atmospheric CO2 concentration. Despite having LAI of 0.5-0.7, plant induced suction decreased by 10-25 kPa during transpiration and evapo-transpiration test under 1000 ppm CO2 concentration. Although a strong positive linear correlation (R2 = 0.8-0.9; P-value < 0.1) of LAI and root-shoot biomass ratio with induced peak soil suction under 400 ppm CO2 concentration, a weak linear correlation (R2 = 0.6-0.8; P-value > 0.1) of the same plant traits under 1000 ppm CO2 concentration was observed. This is because leaves cannot open stomata wide enough to transpire more water when they absorb more CO2 from the atmosphere resulting in soil suction reduction. This implies that the effects of atmospheric CO2 concentration on plant induced soil suction must be considered in vegetated soils.