Heat and moisture budgets from airborne measurements and high-resolution model simulations

High-resolution simulations with a mesoscale model are performed to estimate heat and moisture budgets of a well-mixed boundary layer. The model budgets are validated against energy budgets obtained from airborne measurements over heterogeneous terrain in Western Germany. Time rate of change, vertical divergence, and horizontal advection for an atmospheric column of air are estimated. Results show that the time trend of specific humidity exhibits some deficiencies, while the potential temperature trend is matched accurately. Furthermore, the simulated turbulent surface fluxes of sensible and latent heat are comparable to the measured fluxes, leading to similar values of the vertical divergence. The analysis of different horizontal model resolutions exhibits improved surface fluxes with increased resolution, a fact attributed to a reduced aggregation effect. Scale-interaction effects could be identified: while time trends and advection are strongly influenced by mesoscale forcing, the turbulent surface fluxes are mainly controlled by microscale processes

The limited importance of size-asymmetric light competition and growth of pioneer species in early secondary forest succession in Vietnam

It is generally believed that asymmetric competition for light plays a predominant role in determining the course of succession by increasing size inequalities between plants. Size-related growth is the product of size-related light capture and light-use efficiency (LUE). We have used a canopy model to calculate light capture and photosynthetic rates of pioneer species in sequential vegetation stages of a young secondary forest stand. Growth of the same saplings was followed in time as succession proceeded. Photosynthetic rate per unit plant mass (Pmass: mol C g−1 day−1), a proxy for plant growth, was calculated as the product of light capture efficiency [Φmass: mol photosynthetic photon flux density (PPFD) g−1 day−1] and LUE (mol C mol PPFD−1). Species showed different morphologies and photosynthetic characteristics, but their light-capturing and light-use efficiencies, and thus Pmass, did not differ much. This was also observed in the field: plant growth was not size-asymmetric. The size hierarchy that was present from the very early beginning of succession remained for at least the first 5 years. We conclude, therefore, that in slow-growing regenerating vegetation stands, the importance of asymmetric competition for light and growth can be much less than is often assumed

Effects of abiotic stress on sink and source affecting grain yield and quality of durum wheat : a model evaluation

Heat and drought affect grain yield and quality of wheat through sink development and source capacity. Improving grain yield and quality requires an optimization of dynamic interactions of both storage and photosynthetic processes. Seed nitrogen accumulation and the resulting quality traits can be simulated using ecophysiological models. Differences in stress tolerance between genotypes are reflected in individual grain weights and grain yields per culm rather than in rate of leaf photosynthesis. Narrowing the gap between genetic potential and phenotypic expression requires knowledge about the physiological mechanism of increasing sink strength and source capacity A new model to study genotype-by-environment interaction (GECROS) is used to integrate effects of stresses on sink-source processes and on grain yield and quality. GECROS models each process with a consistent level of detail and deals with interactive aspects and feedback mechanisms of crop growth. This applies to photosynthesis-transpiration-coupling via stomatal conductance, carbon-nitrogen interaction on leaf area index, functional balance between shoot and root activities, and the interplay between supply and demand affecting reserve formation and remobilization An evaluation of abiotic stress effects on durum wheat in a Mediterranean climate, aiming at a time-resolved simulation of sink-source interactions during stress periods at different stages of development, will b