Spatial and temporal variations in diurnal CO2fluxes of different Mediterranean ecosystems in Turkey

Abstract

Diurnal rates of net CO2 assimilation (PN) and soil respiration (Rh) in the summer were measured in six Mediterranean ecosystems through an automatic continuous monitoring system. The six sites include a typical evergreen Pinus pinea L. forest with two co-occurring sclerophyllous shrubs (Pistacia terebinthus L. and Phillyrea latifolia L.), citrus (Citrus limon L.), corn (Zea mays L.), cotton (Gossypium hirsutum L.), soybean (Glycine max L.) and vineyard (Vitis vinifera L.). All six sites exhibited similar behaviour in that low soil water availability and high evaporative demand not only depressed PN and Rh rates, but also changed the diurnal time course of their peak rates. Except for P. terebinthus and corn, PN rates of all the species peaked in the morning (7:30–9:30), and Rh rates in all the sites were higher during the night than during the day (p < 0.05). Mean rates of net ecosystem emission (NEE) of CO2 to the atmosphere were highest (−23.9 μmol CO2 m−2 s−1) in the corn site and lowest (−0.6 μmol CO2 m−2 s−1) in the vineyard site. On average, all six ecosystems were a net source of CO2 to the atmosphere, due to Rh effluxes exceeding PN rates. Net CO2 assimilation and Rh explained 25% (for corn) to 87% (for citrus) of the diurnal fluctuations of the atmospheric CO2 concentration. Multiple linear regression (MLR) models accounted for 42% (P. pinea) to 95% (cotton) of diurnal variations in PN rates and 30% (forest) to 92% (citrus) of diurnal variations in Rh rates (p ⩽ 0.001). The dependence of diurnal PN and Rh rates on water vapour pressure deficit and soil water deficit for dry and hot summer days appeared to be major and needs to be re-examined for biogeochemical models of climate change effects on CO2 dynamics of Mediterranean ecosystems.