Ecosystem carbon (C) balance is hypothesised to be sensitive to the mycorrhizal strategies that plants use to acquire nutrients. To test this idea, we coupled an optimality-based plant nitrogen (N) acquisition model with a microbe-focused soil organic matter (SOM) model. The model accurately predicted rhizosphere processes and C-N dynamics across a gradient of stands varying in their relative abundance of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees. When mycorrhizal dominance was switched - ECM trees dominating plots previously occupied by AM trees, and vice versa - legacy effects were apparent, with consequences for both C and N stocks in soil. Under elevated productivity, ECM trees enhanced decomposition more than AM trees via microbial priming of unprotected SOM. Collectively, our results show that ecosystem responses to global change may hinge on the balance between rhizosphere priming and SOM protection, and highlight the importance of dynamically linking plants and microbes in terrestrial biosphere models.

Abstract:A progressive perceptual understanding approach was used to identify a model structure able to represent the non-linear behaviour of the hydrological cycle in a small intermittent Mediterranean stream. The initial lumped model structure consisting of a series of four connected water tanks (LU3) progressed to a model with five tanks (LU4), and finally to a semidistributed model structure (SD4) in which spatial variability of the evapotranspiration according to the vegetation cover and to the local aspect was considered. In the final model structure, which gave the best fit (Nash-Sutcliffe efficiency index D 0Ð78), an additional tank representing the riparian zone was included (SD4-R). Results showed that the abrupt changes of the riparian water table during summer and the formation of a perched water table during the transition from dry to wet conditions were the main mechanisms leading to the non-linear hydrological behaviour. The transpiration process from the saturated zone and the spatial variability of evapotranspiration resulted in key factors successfully representing the annual water balance. The spatial and temporal validations carried out for each of the four model structures considered in this study supported the hypothesis adopted during the calibration process.

Large portions of Earth's terrestrial surface are arid or semiarid. As in these regions the hydrological cycle and the vegetation dynamics are tightly interconnected, a coupled modelling of these two systems is needed to fully reproduce the ecosystem behaviour and to predict possible responses to climate change. In this paper, the performance of two parsimonious dynamic EVI is reported in literature to be highly correlated with leaf area index so it is compared with modelled LAI mod (r WUE-model =0.45; r LUE-model =0.57). In contrast, NDVI appears highly linked to soil moisture, through the control exerted by this variable on chlorophyll production, and is therefore used to analyze LAI* mod , models' output corrected by plant water-stress (r WUE-model =0.62; r LUE-model =0.59).MODIS LAI and ET are found to be unrealistic in the studied area. The performance of both models in this semiarid region is found to be reasonable.However, the LUE-model presents the advantages of a better performance, the possibility to be used in a wider range of climates and to have been extensively tested in literature.

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