Partitioning of ecosystem respiration of CO2 released during land-use transition from temperate agricultural grassland to Miscanthus x giganteus: Ecosystem respiration under Miscanthus

Conversion of large areas of agricultural grassland is inevitable if European and UK domestic production of biomass is to play a significant role in meeting demand. Understanding the impact of these land-use changes on soil carbon cycling and stocks depends on accurate predictions from well parameterised models. Key considerations are cultivation disturbance and the effect of autotrophic root input stimulation on soil carbon decomposition under novel biomass crops. This paper presents partitioned parameters from the conversion of semi-improved grassland to Miscanthus bioenergy production and compares the contribution of autotrophic and heterotrophic respiration to overall ecosystem respiration of CO2 in the first and second years of establishment. Repeated measures of respiration from within and without root exclusion collars were used to produce time series model integrations separating live root inputs from decomposition of grass residues ploughed in with cultivation of the new crop. These parameters were then compared to total ecosystem respiration derived from eddy covariance sensors. Average soil surface respiration was 13.4% higher in the second growing season, increasing from 2.9 to 3.29 g CO2-C m-2 day-1. Total ecosystem respiration followed a similar trend, increasing from 4.07 to 5.4 g CO2-C m-2 day-1. Heterotrophic respiration from the root exclusion collars was 32.2% lower in the second growing season at 1.20 g CO2-C m-2 day-1 compared to the previous year at 1.77 g CO2-C m-2 day-1. Of the total respiration flux over the two year time period, above ground autotrophic respiration plus litter decomposition contributed 38.46% to total ecosystem respiration while below ground autotrophic respiration and stimulation by live root inputs contributed 46.44% to soil surface respiration. This figure is notably higher than mean figures for non-forest soils derived from the literature and demonstrates the importance of crop specific parameterisation of respiration models.