Abstract
The actual climate crisis scenario is aggravating the abiotic stress episodes that crop plants have to face. Salinity is one of the most important abiotic stresses directly impairing plant growth and productivity. Several strategies have been developed to minimize the negative effects of salinity in agricultural industry, mainly at the plant level, while management strategies, such us the control of microclimate conditions and light quality over plant canopy, have also been used. Indeed, shading plants with photoselective nets has been considered an efficient management strategy to modulate solar radiation to improve crop productivity. The aim of this work was to gain insights about the physiological factors underlying the salinity-alleviating effect of using red shading nets. For that, pepper plants (Capsicum annuum L.) were grown under control (0 mM NaCl) and moderate salinity (35 mM NaCl) conditions, with half of the plants covered with a red net (30% shading). The shoot growth impairment provoked by salinity was in part minimized by shading plants with red nets, which can be explained by their higher capacity to exclude Na+, control of K+ homeostasis and regulation of hormonal balance. Indeed, the concentrations of the most active cytokinin in pepper, trans-zeatin, as well as its metabolic precursor, zeatin riboside, increased in shaded plants, associated to shoot growth recovery and photosynthetic rate maintenance under salinity. Furthermore, the stress-related hormone abscisic acid (ABA) increased with salinity but in a lower extend in the plants shaded with red nets, suggesting a fine tune of stomata opening by ABA which, in crosstalk with salicylic acid increment, improved plant water relations. Likewise, the concentrations of gibberellins and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid, also changed during salinity stress in shaded plants but those changes were uncoupled of growth responses as indicated by the principal component analysis and thus they seem to play a minor role. Our data demonstrate that shading pepper plants with red nets is an efficient management strategy to modulate microclimate conditions at crop level thus controlling the ion homeostasis and hormonal balance of the plant to cope with salinity stress. This is especially important due to the actual and expected changes of the global climatic conditions.
Highlights
The need of feeding an increasing world’s population together with the environmental threatens provoked by the climate change, have changed the actual cultivation paradigm, entailing crop production in marginal soils with high salinity levels
1. (a) Average temperature and (b) incident photosynthetically active radiation (PAR) during the growingFigure period over the canopy of pepper plants cultivated under control (0 mM NaCl) and salinity the growing period over the canopy of pepper plants cultivated under control (0 mM NaCl) and
Salinity stress decreased shoot growth of pepper plants associated with leaf fresh weight (FW) and plant height reduction, whereas shading plants with red nets improved growth, especially under salinity conditions
Summary
The need of feeding an increasing world’s population together with the environmental threatens provoked by the climate change, have changed the actual cultivation paradigm, entailing crop production in marginal soils with high salinity levels. This is contributing to maintain food supply but has a very high environmental cost, aggravating water and soil salinity problems [1], especially in the Mediterranean basin. Shading has been used as an efficient technology to mitigate the extreme climatic fluctuations and pest incidence in arid and semiarid areas and to improve water use efficiency (WUE) while maintaining photosynthesis [10,11,12,13]. Radiation characteristics are perceived by biological photoreceptors, mainly phytochromes, phototropins and cryptochromes, and their effects on different physiological and stress responses are largely driven by red/far-red (600–800 nm), green/yellow (500–600 nm) and UV-A/UV-B/blue (280–500 nm) wavelengths of the electromagnetic spectrum [16]
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