Foliar application of processed calcite particles improves leaf photosynthesis of potted <em>Vitis vinifera</em> L. (var. ‘Cot’) grown under water deficit

Abstract

<p style="text-align: justify;"><strong>Aim</strong>: To determine the effect of foliar sprays of processed mineral particles (micronized calcite, Megagreen<sup>®</sup>) on leaf water relations and photosynthesis in grapevines (<em>Vitis vinifera </em>L. var. Cot) grown under water deficit.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Potted plants were grown in a glasshouse in summer under natural light (Toulouse, lat. 43°32’14.50’’N; long. 1°29’44.25’’W; altitude 148 m a.s.l.). Well-watered and drought stressed vines were foliar sprayed with various doses of micronized calcite. Leaf water potential, gas exchange (light-saturated CO<sub>2</sub> assimilation rate, A<sub>CO2</sub>; stomatal conductance, g<sub>s</sub>) and chlorophyll fluorescence (quantum efficiency of PSII photochemistry, ФPSII) were measured. Water stress affected predawn and midday leaf water potentials, A<sub>CO2</sub>, g<sub>s</sub> and ФPSII of the 40-day-old (younger fully expanded) leaves. Megagreen<sup>®</sup> application did not lead to appreciable changes in leaf water potentials but was able to mostly restore A<sub>CO2</sub> and ФPSII in water stressed plants to levels of well-watered control plants. This effect was associated with a positive, although less pronounced, effect on g<sub>s</sub>. The beneficial effects of processed calcite particles were also observed on younger and older leaves, at low and high atmospheric vapor pressure deficit, and in the morning as well as in the afternoon. In well-watered plants, processed calcite particles had no effect on photosynthesis except under very high evaporative demand. In water stressed plants, A<sub>CO2</sub> was increased by increasing ambient CO<sub>2</sub> concentration. At elevated CO<sub>2</sub>, calcite particles did not increase CO<sub>2</sub> assimilation.</p><p style="text-align: justify;"><strong>Conclusion</strong>: Foliar application of processed calcite particles alleviated most of the adverse effects of water stress on grapevine photosynthesis. This was associated with enhanced g<sub>s</sub> in the whole plant canopy.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: In the context of climate change, grapevine will most likely experience long periods of drought during its seasonal cycle. Foliar application of processed mineral particles is widely used to reduce heat stress in perennial fruit crops. Here, the micronized calcite Megagreen<sup>®</sup> does improve photosynthesis of water stressed grapevines.</p>