S12 - Session P3 - Protection net and the canopy layer decouple gas exchanges, affecting carbon and water net fluxes: the case of a kiwi orchard in a Mediterranean environment

Authors: Francesco Reyes *, Bartolomeo Dichio, Cristos Xiloyannis, Andrea Pitacco

The use of protection nets is rapidly increasingly in orchards to mitigate adverse conditions, such as pests or extreme climatic events, and enhance microclimate, especially in dry climates, where radiation is typically not limiting. The physical separation introduced by the net affects the mass and heat exchanges between inner and outer atmosphere (through increasing aerodynamic resistance and reducing turbulent fluxes), and the availability of photosynthetic active and longwave radiation. This determines a reduction in orchard coupling to the (outer) atmosphere and a shift in plant canopy microclimate. Such effects are known by growers, who empirically make technical choices (net type and mesh, heigths, openings, etc.), but miss the advantages of detailed experiments. In summer 2021, we carried out an intensive experiment in a kiwifruit (cv Hayward ) orchard located in Bernalda (Southern Italy). The orchard, a pergola-like system, is a peculiar model, as the environment is split into three separate sub-systems: from the soil to the canopy surface; the above-canopy zone up to the net and the outer environment. During ten days we partitioned the fluxes of radiation (short- and long-wave), momentum, heat, water vapour and carbon dioxide, having deployed 3 full eddy-covariance systems (each provided of sonic anemometer, IR Gas Analyzer and net radiometer) along a vertical tower, synchronously recorded at high frequency. Additional measurements of air and soil temperature and humidity, and leaves and fruits temperature, provided a comprehensive picture of orchard environment. Netting and canopy layering greatly affected radiation fluxes, both in the short- and long-wave, and the turbulent mass and energy fluxes between compartments. The substantial build-up of air moisture and carbon dioxide, observed within the canopy space, is likely beneficial to leaf physiology and could reduce irrigation water requirements, thereby improving the environmental sustainability of this crop system in the arid Mediterranean conditions.