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

摘要

Aim: To determine the effect of foliar sprays of processed mineral particles (micronized calcite, Megagreen?) on leaf water relations and photosynthesis in grapevines (Vitis vinifera L. var. Cot) grown under water deficit.Methods and results: 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 CO2 assimilation rate, ACO2; stomatal conductance, gs) and chlorophyll fluorescence (quantum efficiency of PSII photochemistry, ФPSII) were measured. Water stress affected predawn and midday leaf water potentials, ACO2, gs and ФPSII of the 40-day-old (younger fully expanded) leaves. Megagreen? application did not lead to appreciable changes in leaf water potentials but was able to mostly restore ACO2 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 gs. 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, ACO2 was increased by increasing ambient CO2 concentration. At elevated CO2, calcite particles did not increase CO2 assimilation.Conclusion: Foliar application of processed calcite particles alleviated most of the adverse effects of water stress on grapevine photosynthesis. This was associated with enhanced gs in the whole plant canopy.Significance and impact of the study: 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? does improve photosynthesis of water stressed grapevines. IntroductionDrought stress is one of the most important environmental factors inhibiting plant growth and production (Chaves et al., 2002). Severe water stress results in reduced metabolism and low gas exchange rate (Hsiao, 1973). Both stomatal and non-stomatal factors contribute to the effects of drought on photosynthesis and transpiration (Kaiser et al., 1981). Under mild drought stress, stomata closure can be the main factor since the photosynthetic apparatus is largely unaffected by water limitation in the whole plant (Cornic et al., 1992). However, reduction in net CO2 assimilation has also been attributed to non-stomatal factors such as carbohydrate accumulation, reduction in ribulose-1,5-biphosphate regeneration caused by inhibition of ATP synthesis, or photoinhibition (Lawlor, 2002; Medrano et al., 2003).Grapevine is generally grown in regions with dry summers and, therefore, must sometimes endure several months of drought during its seasonal cycle (Lovisolo et al., 2010). The visible symptoms of excessive water deficit during the vegetative phase are leaf wilting and decreases in plant height, leaf number and canopy leaf area (Cramer et al., 2007). Drought effects can also include injury to plasma membranes, disturbances in the water status of different organs, and a decrease in chlorophyll content (Medrano et al., 2003). Plants can resist drought stress by reducing their leaf canopy and by closing their stomata (Flexas et al., 2002). At the cellular level, drought stress in grapevines affects the transcript level of genes involved in metabolism, transport, and biogenesis (Cramer et al., 2007).In recent years, foliar sprays containing processed mineral particles have been developed in order to repel insects (Glenn et al., 1999; Showler, 2002), suppress disease incidence (Glenn and Puterka, 2005), and reduce heat stress and solar injury (Glenn et al., 2003; Jifon and Syvertsen, 2003), the latter leading to enhanced net carbon assimilation (Glenn et al., 2003). The presence of mineral particles on the leaf surface can reduce the amount of photosynthetically active radiation (PAR) reaching the leaf surface by reflecting PAR. However, under drought stress conditions, Glenn et al. (2001) reported that the application of a reflective coating on plants may provide a net benefit by sufficiently reducing the heat load in order to offset the potential loss in assimilation rate. Megagreen? is a micronized calcite elaborated from finely ground sedimentary limestone rock and activated by tribomechanical process (European Patent No. WO/2000/064586, 2000). Particles are grey in color and non reflective. The application of Megagreen? has been shown to have a beneficial effect on several horticultural crops such as olive tree, maize, strawberry and lettuce under drought conditions