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Carbohydrates are the energy source for most root activities, including membrane maintenance and osmotic adjustment. Yet, the relationship between root carbohydrate status and selective sodium chloride uptake remains unknown. The following study examined the effects of root carbohydrate starvation due to girdling on sodium and chloride uptake in mature citrus trees. Trees were girdled during the spring or during the autumn, when girdling is known to have more dramatic affects. In spring-girdled trees, 4 days after girdling, root total carbohydrate and starch decreased by 25% and 30%, respectively. The decrease in root carbohydrates was followed by a 20% reduction in root respiration rate. Based on root mineral analysis, spring-girdled trees were characterized by having 42% more sodium and 30% more chloride. The effects of girdling on shoot xylem sap mineral concentration were similar to trends in root mineral status; xylem sap from spring-girdled trees had 43% more sodium and 22% more chloride. Leaf chloride concentration measured 6 months after girdling was 74% higher in girdled trees and reached toxicity levels (0.65% vs. 0.37% dry mass, for girdled and nongirdled trees, respectively). The differences in leaf sodium, however, were nonsignificant (0.14% vs. 0.13% dry mass, for girdled and nongirdled trees, respectively). In autumn-girdled trees, the effects on leaf sodium and chloride concentration were more dramatic. Leaves from autumn-girdled trees (sampled 10 months later) had about two times more sodium and about five times more chloride in comparison to nongirdled trees (0.39 % vs. 0.20% dry mass sodium and 1.02% vs. 0.22% dry mass chloride, respectively). The above results link root carbohydrate status and selective sodium or chloride uptake in citrus trees.

Chloride stress in commercial citrus is predominantly a result of increased osmotic pressure in the plant as a result of excess chloride. The source of the chloride is usually from the soil solution, where it is absorbed by the roots. After being absorbed, chloride flows through the xylem in the transpiration stream to the shoot, where it is accumulated by transpiring tissues such as leaves and fruit. Monitoring chloride concentration along any of these steps can be used to assess potential stress in the tree. Since some of these tissues tend to accumulate chloride (fruit and leaves) while others do not (root and xylem), analyses should be interpreted within the context of these differences. Having high chloride concentration in roots or xylem-water at a specific sampling time does not necessarily mean that leaves have already accumulated chloride to a toxic level, while having high chloride concentration in fruit or leaf analysis does not necessarily mean that the trees are still being exposed to high salinity in the soil solution. The advantages of the various analyses, as well as their difficulties, are discussed. It was concluded that a combination of xylem sap chloride analysis and leaf chloride analysis are the most useful tools for assessing potential chloride stress in citrus trees.

This study examined the response of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus to two CO₂ regimes [enrichment (1000 μmol·mol⁻¹) vs. ambient control (380 μmol·mol⁻¹)] and to two fertilization regimes [0.5- vs. 0.1-strength Hoagland's solution (designated high and low, respectively)]. CO₂ enrichment increased total daily net CO₂ uptake, nocturnal acid accumulation, shoot elongation, and total dry mass by 39%, 24%, 14%, and 6% (averaging the two fertilization regimes) versus ambient CO₂ treatment, respectively. Plants exposed to high fertilization demonstrated 36%, 21%, 198%, and 79% (averaging the two CO₂ regimes) increases versus those receiving the low fertilization regime in total daily net CO₂ uptake, nocturnal acid accumulation, stem elongation, and total dry mass, respectively. Plants exposed to high fertilization and elevated CO₂ demonstrated 108%, 77%, 264%, and 111% increases versus those receiving the low fertilization regime at the ambient CO₂ concentration in total daily net CO₂ uptake, nocturnal acid accumulation, stem elongation, and total dry mass, respectively. This response was 25% to 71% higher than the summed effects of the separate responses to each factor, indicating a synergistic effect of elevated CO₂ and high fertilization. Thus, it is apparent that H. undatus crops grown under a high-fertilization agromanagement regime may benefit from elevated CO₂ to a greater extent than those grown with low fertilization.