To elucidate the role of electrical signaling in the phloem of maize the tips of attached leaves were stimulated by chilling and wounding. Two different signals were detected in the phloem at the middle of the leaf using the aphid stylet technique: (1) action potentials (AP) arose in the phloem after chilling; and (2) variation potentials (VPs) were evoked after wounding the leaf tip. Combined electric potential and gas exchange measurements showed that while the wound-induced VP moved rapidly towards the middle of the leaf to induce a reduction in both the net-CO₂ uptake rate and the stomatal conductance, there was no response in the gas exchange to the cold-induced AP. To determine if electrical signaling had any impact on assimilate transport the middle of the leaf was exposed to ¹⁴CO₂. Autoradiography of labeled assimilates provided evidence that phloem and intercellular transport of assimilates from mesophyll to bundle sheath cells was strongly reduced while the cold-induced AP moved through. In contrast, wound-induced VP did not inhibit assimilate translocation but did reduce the amount of the labeled assimilate in phloem and bundle sheath cells. Biochemical analysis revealed that callose content increased significantly in chilled leaves while starch increased in chilled but decreased in wounded leaves. The results led to the conclusion that different stimulation types incite characteristic phloem-transmitted electrical signals, each with a specific influence on gas exchange and assimilate transport.

The effects of elevated CO₂ and interaction effects between elevated CO₂ and nutrient supplies on growth and the C/N ratio of European beech (Fagus sylvatica L.) saplings were studied. One-year-old beech saplings were grown in a greenhouse at ambient (385 ppm) and elevated CO₂ (770 ppm/950 ppm), with or without fertilization for two growing seasons. In this study, emphasis is placed on the combined fertilization including phosphorus, potassium and nitrogen with two level of elevated CO₂. The fertilized plants grown under elevated CO₂ had the highest net leaf photosynthesis rate (Ac). The saplings grown under elevated CO₂ had a significantly lower stomatal conductance (gs) than saplings grown under ambient air. No interaction effect was found between elevated CO₂ and fertilization on Ac. A interaction effect between CO₂ and fertilization, as well as between date and fertilization and between date and CO₂ was detected on gs. Leaf chlorophyll content index (CCI) and leaf nitrogen content were strongly positively correlated to each other and both of them decreased under elevated CO₂. At the end of both growing seasons, stem dry weight was greater under elevated CO₂ and root dry weight was not affected by different treatments. No interaction effect was detected between elevated CO₂ and nutrient supplies on the dry weight of different plant tissues (stems and roots). However, elevated CO₂ caused a significant decrease in the nitrogen content of plant tissues. Nitrogen reduction in the leaves under elevated CO₂ was about 10% and distinctly higher than in the stem and root. The interaction effect of elevated CO₂ and fertilization on C/N ratio in plants tissues was significant. The results led to the conclusion that photosynthesis and the C/N ratio increased while stomatal conductance and leaf nitrogen content decreased under elevated CO₂ and nutrient-limited conditions. In general, under nutrient-limited conditions, the plant responses to elevated CO₂ were decreased.

Juvenile Eucalyptus grandis were exposed to drought and elevated CO₂ to evaluate the independent and interactive effects on growth, gas exchange and wood structure. Trees were grown in a greenhouse at ambient and elevated CO₂ (aCO₂, 410 ppm; eCO₂, 950 ppm), in combination with daily irrigation and cyclic drought during one growing season. The results demonstrated that drought stress limited intercellular CO₂ concentration, photosynthesis, stomatal conductance, and transpiration, which correlated with a lower increment in height, stem diameter and biomass. Drought also induced formation of frequent and narrow vessels accompanied by a reduction in vessel lumen area. Conversely, elevated CO₂ increased intercellular CO₂ concentration as well as photosynthesis, and partially closed stomata, leading to a more efficient water use, especially under drought. There was a clear trend towards greater biomass accumulation at eCO₂, although the results did not show statistical significance for this parameter. We observed an increase in vessel diameter and vessel lumen area at eCO₂, and, contrarily, the vessel frequency decreased. Thus, we conclude that eCO₂ delayed the effects of drought and potentialized growth. However, results on vessel anatomy suggest that increasing vulnerability to cavitation due to formation of larger vessels may counteract the beneficial effects of eCO₂ under severe drought.