Management effects on European cropland respiration

Abstract

Increases in respiration rates following management activities in croplands are considered a relevant anthropogenic source of CO 2. In this paper, we quantify the impact of management events on cropland respiration fluxes of CO 2 as they occur under current climate and management conditions. Our findings are based on all available CarboEurope IP eddy covariance flux measurements during a 4-year period (2004–2007). Detailed management information was available for 15 out of the 22 sites that contributed flux data, from which we compiled 30 types of management for European-scale comparison. This allowed us to address the question of how management activities influence ecosystem respiration. This was done by comparing respiration fluxes during 7, 14, and 28 days after the management with those observed during the matching time period before management. Median increases in respiration ranged from +83% (early season tillage) to −50% (rice paddy flooding and burning of rice residues) on the 28 days time scale, when only management types with a minimum of 7 replications are considered. Most management types showed a large variation among events and between sites, indicating that additional factors other than management alone are also important at a given site. Temperature is the climatic factor that showed best correlation with site-specific respiration fluxes. Therefore, the effect of temperature changes between the time periods before and after management were taken into account for a subset of 13 management types with adequate statistical coverage of at least 5 events during the years 2004–2007. In this comparison, late-season moldboard ploughing (30–45 cm) led to highest median increase in respiration on the 7 days timescale (+43%), which was still +15% in the 28 days comparison. On average, however, management-induced increases in respiration losses from croplands were quite moderate (typically <20% increase over 28 days). An assessment of extreme values in daily respiration fluxes using the Gumbel distribution approach revealed that sites with larger average respiration fluxes also experience the larger extremes in respiration fluxes. This suggests that it is very unlikely that sites that generally have low respiration rates will have exceedingly high respiration rates as a result of certain specific management events.