Summer drought influence on CO₂ and water fluxes of extensively managed grassland in Germany

• Published in: Agriculture, ecosystems & environment Vol. 141; no. 1-2; pp. 67 - 76
• Main Authors: Hussain, M.Z, Grünwald, T, Tenhunen, J.D, Li, Y.L, Mirzae, H, Bernhofer, C, Otieno, D, Dinh, N.Q, Schmidt, M, Wartinger, M, Owen, K
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01.04.2011; Elsevier
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agricultural and forest meteorology; Agronomy. Soil science and plant productions; Annual precipitation; atmospheric precipitation; Biological and medical sciences; Biomass; Canopies; canopy; Carbon; carbon sinks; carboxylation; drought; Droughts; ecosystem respiration; Ecosystems; eddy covariance; environmental factors; evapotranspiration; Fundamental and applied biological sciences. Psychology; General agroecology; General agroecology. Agricultural and farming systems. Agricultural development. Rural area planning. Landscaping; General agronomy. Plant production; Generalities. Agricultural and farming systems. Agricultural development; Grasslands; net ecosystem exchange; primary productivity; Reduction; senescence; summer; temperature; water balance; Water balance and requirements. Evapotranspiration; water use efficiency; Central Europe; Europe; Germany; Primary productivity; Water deficit; Carbon dioxide; Evapo-transpiration; Gross primary production; Light response; Summer; Ecology; Water flow; VPD; Water vapor; Net CO; Grassland management; Ecosystem; Evapotranspiration; Ecosystem respiration; exchange; Gas exchange; Respiration; Drought
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/j.agee.2011.02.013

Net ecosystem CO₂ exchange (NEE) and water fluxes of extensively managed grassland in Germany were measured in a dry year, 2003 and a normal year, 2004 using eddy covariance. Empirical descriptions of canopy capacities (light utilization efficiency and canopy capacity for maximum carboxylation) and inherent water use efficiency (IWUE*) were computed to indicate the grassland's response to environmental and management conditions. Compared with 2004, 2003 was characterized by a 2.5°C rise in summer mean temperature and an annual precipitation deficit of 286mm, which was almost one-third below the average precipitation of the normal year 2004 and the long-term annual average (1959–2005). Annual net water balance (precipitation minus evapo-transpiration) in 2003 and 2004 were 85mm and 361mm, respectively. Slightly higher IWUE* in 2003 indicates the grassland's sensitivity to drought. The grassland provided an annual gross primary production (GPP) and ecosystem respiration (Rₑcₒ) of 1022 and 728gCm⁻² respectively in 2003, as compared to their corresponding values of 1233 and 973gCm⁻² in 2004. Drought-induced biomass senescence caused GPP reduction in 2003, which in turn affected the ecosystem respiration. Light explained more than 80% of NEE variability during canopy development and as a result, annual NEE in 2003 and 2004 were −295 and −260gCm⁻², respectively. Taking into account the exported carbon by biomass harvest, we calculated net biome productivity (NBP) of −113gCm⁻²yr⁻¹. We conclude that this managed grassland acted as a moderate carbon sink, despite the difference in environmental and management conditions.