Pearl netting improves photosynthetic light use associated with modification of structural and physiochemical traits of sweet pepper leaves

Abstract

The light-scattering Pearl shade net (ChromatiNet®) is compared here with a conventional black shade net of equivalent shading capacity for their effects on photosynthetic light use by sweet pepper (Capsicum annuum L.) leaves. The following leaf parameters were studied in 'Vergasa', 'Tirza' and 'Milna' cultivars: net CO2 assimilation rate (An), leaf photosynthetic light loss, the efficiency parameters photosynthetic light use efficiency (LUE), photochemical reflectance index (PRI), and effective quantum yield (△F/F'm); and several structural and physiochemical traits. The results showed higher values of An, LUE, PRI, and △F/F'm under the Pearl net compared with the black net, for all three cultivars. The increased levels of An and LUE did not depend on the time of day, or time of year (measured only in 'Vergasa'). Chlorophyll a/b ratio was increased by the Pearl shading, despite of the lower chlorophyll and carotenoid content, relative to the black shading. Leaf reflectance and the partition of photosynthetic light into thermal dissipation were reduced under the Pearl, compared with the black shading. The Pearl net additionally reduced the ratio of palisade/sponge mesophyll thickness, the leaf surface wax content, and the relative epidermis thickness. These results are indicating the improving of photosynthetic light use efficiency via both biochemical/biophysical, as well as structural/morphological leaf responses to the Pearl netting. The advantage of the Pearl over conventional black shading can be related to its high light-scattering capacity in the PAR spectral region, and/or its filtering-out the UVB+A region. Taken together with our previously reported specific effects on pepper pest- and disease-control, as well as pre- and post-harvest fruit quality, the Pearl ChromatiNet® provides a multi-benefit covering for pepper cultivation.