Sap flow, leaf gas exchange and chlorophyll fluorescence of container-grown cashew (Anacardium occidentale L.) trees subjected to repeated cycles of soil drying

Abstract

Summary. Cashew (Anacardium occidentale L.) is an emerging horticultural crop in tropical northern Australia. Supplementary watering is required during the dry season to achieve high yields but irrigation guidelines are not well defined. As an introduction to large-scale field experiments which will aim to define the irrigation requirements for cashew, this experiment was conducted on small, container-grown cashew trees to examine their response to drying soil and to evaluate a range of techniques for measuring tree water use and photosynthesis with possible application in the proposed field experiments. Measurements of sap flow, leaf chlorophyll fluorescence and leaf gas exchange were made on all trees throughout the experimental period. The water use of trees in drying soil was measured using Granier’s sap flow system. Sap flux density (L/dm2 sapwood area . h) of drying trees declined progressively over a 4-day period to a minimum level that was only 10% of the sap flow in the well watered trees. Measurements of leaf gas exchange showed similarly large reductions in photosynthesis and transpiration which were associated with a low (0.05 mol/m2 . s) stomatal conductance in the drying trees. After rewatering, sap flow and leaf gas exchange recovered to the high levels of the well watered trees over 3–4 days. Similar behaviour was observed during the second drying period. Measurements of the ratio of variable to maximum fluorescence, Fv : Fm, an indicator of photoinhibition, were made on dark-adapted leaves before dawn and during the day. Fv : Fm was in the range 0.65–0.80 with no large or sustained differences between drying and well watered trees. When stomatal conductance and net photosynthetic rate progressively declined during the period following irrigation, the quantum yield of photochemical energy conversion in photosystem II, ΦPSII, remained almost constant. It is possible that by providing a pathway for electron flow as an alternative to CO2 assimilation during this period, photorespiration played an important role in avoiding photoinhibition.

Physiology of cashew plants grown under adverse conditions

“…The same behavior was observed for stomatal conductance to water vapor such that a close relationship between these two variables was found (Blaikie and Chacko, 1998).…”

Photosynthetic responses of young cashew plants to varying environmental conditions

“…As a consequence, the values of effective quantum yield of PSII, that were high in early morning, decreased to 0.2 and remained at low values until 16h. Here again, these values of effective quantum yield were similar to those reported in other studies (Blaikie & Chacko, 1998;Blaikie et al, 2001). Since no damages to the photosynthetic system were evident, the photoinhibition in young cashew plants was effective in protecting the photochemical apparatus, at the high irradiance levels, to which plants were exposed in their natural environments.…”

“…A small recovery began to occur during the afternoon (Figure 6). Small decreases of F v /F m ratio during the day were also observed by Blaikie & Chacko (1998), Figure 4. CO 2 assimilation rates (A), stomatal conductances (g s ), transpiration rates (E), and intercellular CO 2 concentration (C i ) responses to increasing VPD leaf-to-air , in young cashew plants at 1,200 µmol m -2 s -1 PPFD, 30°C leaf temperature and at atmospheric CO 2 concentration.…”

“…The decrease of PPFD around midday, because of the presence of clouds, was accompanied by decreases in CO 2 assimilation rates and stomatal conductance ( Figure 5). Blaikie & Chacko (1998) showed that gas exchange was closely related to fluctuation in stomatal conductances, with these values generally being lower in the afternoon than in the morning. These observations are also valid for this study, since curves of CO 2 assimilation rates and stomatal conductances varied similarly during the day.…”

“…The lack of information about the species is due to limited research considering physiological aspects (Marler et al, 1994). Some studies were developed in Australia, such as: Schaper & Chacko (1993), on the influence of leaf age and branch girdling on gas exchange; Schaper et al (1996), on the effects of irrigation on gas exchange and leaf water status; and Blaikie & Chacko (1998) and Blaikie et al (2001), on sap flow and leaf photosynthesis as affected, respectively, by soil drying and irrigation strategies. Balasimha (1991), and Palanisamy & Yadukumar (1993) have also studied the photosynthetic characteristics of adult cashew trees in India.…”