Partitioning of Respiration in an Intensively Managed Grassland

Total (RTOT) and heterotrophic (RH) respiration were measured in an intensively managed perennial ryegrass (Lolium perenne L.) grassland. The overall aim of the study was to partition RTOT into RH and autotrophic respiration (RA). This was achieved as follows: (1) analyse the effect of air temperature, soil moisture content and leaf area index on RTOT and the influence of soil temperature and soil moisture content on RH; (2) combine these effects into separate empirical models for RTOT and RH and; (3) use these models to determine temporal trends in RTOT and RH and to assess the relative contribution of RH and RA to RTOT. CO2 fluxes were measured using a vented and thermostatically controlled perspex chamber in conjunction with a portable infrared gas analyser. RTOT was measured in plots with grass and RH in plots with bare soil. RTOT was related to air temperature and RH to soil temperature using exponential relationships. Both RTOT and RH were related to soil moisture content using lognormal relationships. RTOT was related to leaf area index using a linear relationship. These relationships were combined to produce statistical response functions that explained 87% and 84% of the variation in RTOT and RH, respectively. These relationships were combined with meteorological and leaf area index data to reconstruct daily and seasonal fluxes. RTOT values in wintertime were ~4 g C m−2 day−1 increasing to ~10 g C m−2 day−1 in summertime when temperatures and leaf area index were higher and soils were drier. RH has a similar seasonal trend to RTOT but was consistently lower. Wintertime values were ~2 g C m−2 day−1 and increased to ~5 g C m−2 day−1 in summertime. Before day of year 143, and after day of year 259 RH and RA represented 62% and 38% of RTOT, respectively. In the period between these days RH and RA both accounted for 50% of RTOT. In total during 2004 RTOT, RH and RA were 2.34, 1.31 and 1.03 kg C m−2, respectively.