LINGRA-CC: a sink-source model to simulate the impact of climate change and management on grassland productivity

A simulation model for the prediction of grassland (Lolium perenne) product ivity under conditions of climate change is described and validated for gra ss growing in the Wageningen Rhizolab, Wageningen, The Netherlands. In this work the model was used to study the impact of different management strate gies on the productivity of grassland under present and increased atmospher ic CO2 concentrations. In LINGRA-CC simulated key processes are light utili zation, leaf formation, leaf elongation, tillering and carbon partitioning. The daily growth rate is determined by the minimum of a sink and a source term. As in a previous model (LINGRA), the potential growth of the sink dep ends on the mean daily temperature, and can be modified by the effects of t he availability of assimilates on tillering. The growth of roots is calcula ted from the amount of carbohydrates the shoot is unable to utilize when th e number or activity of the sinks is small (overflow hypothesis). The main difference between LINGRA and LINGRA-CC is the way the source of assimilate s for growth is calculated. Assimilate production depends on intercepted ra diation, and a photosynthetic light-use efficiency (LUE) calculated as a fu nction of CO2, temperature, light intensity and the Rubisco concentration o f upper leaves. Other differences are that in LINGRA-CC, the specific shoot area for new growth depends on the level of reserves. Data from two indepe ndent experiments with L, perenne swards, grown in enclosures at two levels of CO2 during 1994 and 1995, were used to calibrate and validate the model , respectively. The model predicted well the observed amounts of harvested biomass, and the dynamics of the leaf area index, tiller number and specifi c shoot area. LINGRA-CC was used to stud? the effects of different combinat ions of cutting interval and cutting height on biomass production, at ambie nt (350 mu mol mol(-1) CO2) and double (700 mu mol mol(-1) CO2) CO2 conditi ons. Under both ambient and doubled CO2, maximum biomass was produced with cuttings of leaf area index >1, and at cutting intervals of 20 and 17 d for ambient and increased CO2 environments, respectively. Under high CO2 condi tions the curling interval for maximum yield was 15% shorter than at ambien t CO2. However, the gain in harvested biomass obtained by reducing the cutt ing interval by 3 d under high CO2 conditions was negligible.