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Dissolved organic carbon leaching from montane grasslands under contrasting climate, soil and management conditions

Jin Fu, Rainer Gasche, Na Wang, Haiyan Lu, Klaus Butterbach-Bahl, Ralf Kiese
Biogeochemistry 2019 v.145 no.1-2 pp. 47-61
aboveground biomass, adsorption, altitude, biomass production, climate, cutting, dissolved organic carbon, ecosystems, global warming, grasslands, leachates, leaching, lysimeters, net ecosystem exchange, rooting, soil depth, soil organic carbon, soil water, subsoil, topsoil
Grasslands are thought to be more vulnerable than many other ecosystems to climate change since their soils are characterized by high organic carbon contents and warming in montane regions is twice the global average rate. Despite these expected vulnerabilities, little is known about how climate change and management influence dissolved organic carbon (DOC) losses from montane grasslands and how relevant these losses are compared to other ecosystem carbon fluxes. In this study, 36 large (1 m², 140 cm height) grassland lysimeters were filled with undisturbed soil monoliths and operated at three different sites located along an elevational gradient from 860 to 600 m a.s.l. From 2012 to 2014, changes in soil DOC concentrations and DOC leaching losses were quantified under different climate, soil and management (intensive vs. extensive; i.e., differing in the frequency of cutting and manuring events) conditions. The annual DOC leaching losses ranged between 6.6 and 27.5 kg C ha⁻¹ year⁻¹, which was only a minor (< 3%) component of the net ecosystem carbon exchange. DOC leaching losses were not affected by management intensity but were positively correlated with soil organic carbon in the top soil. Climate warming (~ + 2 °C) significantly increased DOC leaching rates for intensive (+ 43%) and extensive management (+ 58%), but only if simultaneous reductions in leachate were moderate. The DOC concentrations in soil water significantly decreased with soil depth. In 10, 30 and 50 cm DOC concentration were positively correlated with aboveground biomass production, indicating that plants play a crucial role in topsoil DOC dynamics. However, this relationship did not occur for DOC in soil water collected at 140 cm, suggesting that adsorption and degradation processes in the subsoil ultimately determine the dynamics of DOC losses below the rooting zone.