Ecosystem sensitivity to land-surface models and leaf area index

The potential sensitivity of ecological models to differences in soil temperature and soil water from land-surface models was evaluated by using model output from the PILPS land-surface model comparison. Simulated soil water and temperatures from the land-surface models were used to calculate the abiotic decomposition factor (ADF). ADF is used by ecosystem models to directly control microbial activity, decomposition of organic matter and nutrient mineralization and indirectly control plant production. The results show that among model differences in soil water and temperature results in large differences in seasonal patterns of ADF, while the annual average ADF varied from 0.24 to 0.32. Differences in soil water had the largest impact on ADF during the summer. The results suggest that using a 0-50 cm soil depth causes ADF to be overestimated and that land-surface models need to include a 0-10 cm soil layer to interface with ecosystem models. ADF is more sensitive to model differences in soil water and temperature than it is in leaf area index (LAI), however, reducing LAI causes ADF to increase. Most of the models showed that reducing LAI caused transpiration water losses to decrease and evaporation water losses to increase.