Soil Respiration in European Grasslands in Relation to Climate and Assimilate Supply

Abstract

Soil respiration constitutes the second largest flux of carbon (C) between terrestrial ecosystems and the atmosphere. This study provides a synthesis of soil respiration (R(s)) in 20 European grasslands across a climatic transect, including ten meadows, eight pastures and two unmanaged grasslands. Maximum rates of R(s) (R(s(max) )), R(s) at a reference soil temperature (10°C; R(s(10) )) and annual R(s) (estimated for 13 sites) ranged from 1.9 to 15.9 μmol CO(2) m(-2) s(-1), 0.3 to 5.5 μmol CO(2) m(-2) s(-1) and 58 to 1988 g C m(-2) y(-1), respectively. Values obtained for Central European mountain meadows are amongst the highest so far reported for any type of ecosystem. Across all sites R(s(max) ) was closely related to R(s(10) ).Assimilate supply affected R(s) at timescales from daily (but not necessarily diurnal) to annual. Reductions of assimilate supply by removal of aboveground biomass through grazing and cutting resulted in a rapid and a significant decrease of R(s). Temperature-independent seasonal fluctuations of R(s) of an intensively managed pasture were closely related to changes in leaf area index (LAI). Across sites R(s(10) ) increased with mean annual soil temperature (MAT), LAI and gross primary productivity (GPP), indicating that assimilate supply overrides potential acclimation to prevailing temperatures. Also annual R(s) was closely related to LAI and GPP. Because the latter two parameters were coupled to MAT, temperature was a suitable surrogate for deriving estimates of annual R(s) across the grasslands studied. These findings contribute to our understanding of regional patterns of soil C fluxes and highlight the importance of assimilate supply for soil CO(2) emissions at various timescales.

Figure 1

Soil respiration at a reference temperature (10°C) in relation to A mean annual soil temperature (r² = 0.69, P < 0.001), B soil C content in the uppermost 20–25 cm of the soil (r² = 0.50, P < 0.05), C peak leaf area index (r² = 0.55, P < 0.01) and D annual gross primary productivity (r² = 0.88, P = 0.001). Meadows (▲), pastures (●), unmanaged Northern grasslands (◇).

Figure 2

Maximum rates of soil respiration in relation to A the associated soil temperature and B soil respiration at a reference temperature (10°C) (r² = 0.87, P < 0.001). Meadows (▲), pastures (●), unmanaged Northern grasslands (◇). Error bars denote standard deviations obtained for the highest spatially replicated soil respiration rates (n = 3–9) recorded at a single point of time.

Figure 3

Soil respiration (◆), soil temperature (dashed line) and soil moisture (solid line) before and after rainfall during summer periods in A 2003 and B 2004 at Alinya. Bars indicate the timing and the amount rainfall. Soil respiration was measured using a continuous system on five collars, which were changed on DOY 206 in 2003, as indicated by different symbols. Note the different scales in A and B.

Figure 4

Diurnal changes of soil respiration (R_s) in response to temperature at 1, 3 and 10 cm soil depth on a clear (18 June 2004; A–C) and a subsequent cloudy day (19 June 2004; D–F) at Alinya. Consecutive hourly means have been connected by lines, inserts indicate time of the day. For further details on the time course of soil respiration, soil temperature and soil water content refer to Figure 3B.

Figure 5

Effects of clipping and grazing on A soil CO₂ efflux and B soil temperature at Amplero during the summer of 2004 (for each treatment n = 9).

Figure 6

Residuals of observed minus predicted values of soil respiration at Carlow in relation to seasonal values of leaf area index (LAI) in 2003 (r² = 0.70, P < 0.001, when excluding the data point indicated with an open symbol from the regression).

Figure 7

Annual soil respiration in relation to A mean annual soil temperature (r² = 0.81, P < 0.001), B peak leaf area index (r² = 0.74, P < 0.001) and C annual gross primary productivity (r² = 0.94, P < 0.001). Meadows (▲), pastures (●), unmanaged Northern grasslands (◇).