Effects of Seasonal Asymmetric Warming on Soil CO2 Release in Karst Region

Abstract

Seasonal asymmetric warming is one of the distinguishing features of global warming. However, if this feature is not considered in studying the effects of global changes on terrestrial ecosystems, it might probably cause misunderstanding of these studies. The releasing features of soil CO2 in Karst regions under various warming scenarios were simulated following a four-year continuous warming period using infrared radiators. A total of six treatments was arranged:no warming (ambient temp, CK); symmetric warming (ambient plus 2.0℃ full year, SW); and, lowly, moderately, highly, and extremely asymmetric warming (ambient plus 2.5℃/1.5℃, 3.0℃/1.0℃, 3.5℃/0.5℃, and 4.0℃/0℃ in the winter-spring/summer-autumn seasons, respectively, LAW, MAW, HAW, and EAW). The results showed that compared to CK, soil CO2 efflux in all the warming plots significantly increased by 0.26 μmol·(m2·s)-1, or 17.41%. In the winter-spring seasons, soil CO2 efflux in the warming treatments increased by 0.23 μmol·(m2·s)-1. The Q10 values ranged from 1.53 to 3.24 with an average of 2.23 under the scenario of warming up by 2.0℃. The warming-induced contribution of CO2 efflux in the summer-autumn seasons (80%) was obviously higher than that in the winter-spring seasons (20%) in the SW treatment, whereas the mean contribution in the summer-autumn seasons (46%) was closer to that in the winter-spring seasons (54%) in the asymmetric warming treatments. Both soil CO2 efflux and Q10 showed a tendency towards decrease with the increase in the asymmetry of warming under the five warming scenarios. The soil CO2 efflux in the SW treatment was significantly (P<0.05) higher than those in the MAW, HAW, and EAW treatments. The Q10 values in the summer-autumn seasons was larger than those in the winter-spring seasons under each warming treatment or across all warming treatments, which was probably related to soil water content, soil microbe, dissolved inorganic carbon, and vegetation growth. The results revealed that it may potentially overestimate the effects of global warming on soil CO2 releasing subject to symmetric warming.