Stomatal responses of Eucalyptus species to elevated CO2 concentration and drought stress

Five species of Eucalyptus (E. grandis, E. urophylla, E. camaldulensis, E. torelliana, and E. phaeotrica), among the ten species most commonly used in large scale plantations, were selected for studies on the effects of elevated CO2 concentration [CO2] and drought stress on stomatal responses of 2.5-month old seedlings. The first three species belong to the subgenus Smphyomyrtus, whereas the fourth species belongs to the subgenus Corymbia and E. phaeotrica is from the subgenus Monocalyptus. Seedlings were grown in four pairs of open-top chambers, arranged to have 2 plants of each species in each chamber, with four replications in each of two CO2 concentrations: 350 ± 30 mumol mol-1 and 700 ± 30 mumol mol-1. After 100 days in the chambers, a series of gas exchange measurements were made. Half the plants in each chamber, one plant per species per chamber, were drought-stressed by withholding irrigation, while the remaining plants continued to be watered daily. Drought stress decreased stomatal conductance, photosynthesis and transpiration rates in all the species. The effect of drought stress on stomatal closure was similar in both [CO2]. The positive effects of elevated [CO2] on photosynthesis and water use efficiency were maintained longer during the stress period than under well-watered conditions. The photosynthetic rate of E. phaeotrica was higher even in the fourth day of the drought stress. Drought stress increased photoinhibition of photosynthesis, as measured by chlorophyll fluorescence, which varied among the species, as well as in relation to [CO2]. The results are in agreement with observed differences in stomatal responses between some eucalyptus species of the subgenera Symphyomyrtus and Monocalyptus

Estimated Reductions in Added Sugar Intake among US Children and Youth in Response to Sugar Reduction Targets

Background: In 2021, the National Salt and Sugar Reduction Initiative (NSSRI) released voluntary sugar reduction targets for packaged foods and drinks in the United States. Objective: The objectives of this study were to describe trends in added sugar intake from NSSRI foods and beverages among children and youth and estimate possible reductions if industry were to meet the targets. Design: This study consisted of cross-sectional and trend analyses of demographic and 24-hour dietary recall data from eight survey cycles (2003-2004 to 2017-2018) of the National Health and Nutrition Examination Survey. Participants/setting: The study sample included 23,248 children and youth (aged 2 to 19 years). Main outcome measures: The main outcome measure was the percent of daily calories from added sugar for foods and beverages in NSSRI categories. Statistical analyses performed: Foods and beverages reported by participants were mapped to one of the NSSRI's categories or coded as a non-NSSRI item. Trends over time in added sugar intake were assessed using regression models. To assess possible reductions in added sugar intake if industry were to meet the targets, sales-weighted mean percent reductions for 2023 and 2026 targets were applied to NSSRI items in the 2017-2018 National Health and Nutrition Examination Suvey data. Results were examined overall and by demographic characteristics. Results: From 2003-2004 to 2017-2018, added sugar intake from NSSRI foods and beverages declined, but consumption remained high. During 2017-2018, NSSRI categories accounted for 70% of US child and youth added sugar intake. If industry met the NSSRI targets, US children and youth would consume 7% (2023 targets) to 21% (2026 targets) less added sugar. Conclusions: Although added sugar intake from NSSRI foods and drinks has declined over the past decade, added sugar intake from all sources remains high and consumption of added sugar from certain NSSRI categories has remained steady over time. If met, the NSSRI targets are expected to result in meaningful reductions in added sugar intake for US children and youth. © 2022 Academy of Nutrition and Dietetic

Changes in Photon Flux Can Induce Stomatal Patchiness

Images of chlorophyll fluorescence were used to detect the occurrence of stomatal patchiness in leaves from eight species under variable photon flux conditions. Pronounced stomatal patchiness was induced within 5–10 min after PFD was changed from intermediate (∼450 μmol quanta m−2 s−1) to low (∼150 μmol quanta m−2 s−1) levels. This effect was completely reversible by returning PFD to intermediate levels. The pattern of heterogeneous fluorescence for each leaf was usually similar during repeated applications of medium and low PFD. In three species, stomatal patchiness could only be induced in slightly water-stressed plants. Leaves of more severely water-stressed Xanthium strumarium plants in low air humidity exhibited oscillations in fluorescence that corresponded with oscillatory changes in leaf diffusion conductance for water vapour. Stomatal patchiness was also induced by illuminating dark-adapted leaves with low PFD (below 200–300 μmol quanta m−2 s−1). Infiltration of leaves with distilled water showed that heterogeneous chlorophyll fluorescence was caused by changes in stomatal apertures