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Crassulacean acid metabolism (CAM) and the capacity to store large quantities of water are thought to confer high water use efficiency (WUE) and survival of succulent plants in warm desert environments. Yet the highly variable precipitation, temperature and humidity conditions in these environments likely have unique impacts on underlying processes regulating photosynthetic gas exchange and WUE, limiting our ability to predict growth and survival responses of desert CAM plants to climate change. We monitored net CO assimilation ( A), stomatal conductance ( g), and transpiration ( E) rates periodically over 2 years in a natural population of the giant columnar cactus Carnegiea gigantea (saguaro) near Tucson, Arizona USA to investigate environmental and physiological controls over carbon gain and water loss in this ecologically important plant. We hypothesized that seasonal changes in daily integrated water use efficiency (WUE) in this constitutive CAM species would be driven largely by stomatal regulation of nighttime transpiration and CO uptake responding to shifts in nighttime air temperature and humidity. The lowest WUE occurred during time periods with extreme high and low air vapor pressure deficit ( D). The diurnal with the highest D had low WUE due to minimal net carbon gain across the 24 h period. Low WUE was also observed under conditions of low D; however, it was due to significant transpiration losses. Gas exchange measurements on potted saguaro plants exposed to experimental changes in D confirmed the relationship between D and g. Our results suggest that climatic changes involving shifts in air temperature and humidity will have large impacts on the water and carbon economy of the giant saguaro and potentially other succulent CAM plants of warm desert environments. [ABSTRACT FROM AUTHOR]

Immediate leaf functional responses to drought, such as stomatal closure and photosynthetic rate reduction, are already known from short-term studies. We tested the hypothesis that long-term acclimation of leaves to drought includes hydraulic and stomatal anatomical changes and that gas exchange and nitrogen allocation patterns are inevitably adjusted to the new structural status. 26 structural and functional traits in one sensitive cultivar (Simeto) and two drought resistant landraces (Ntopia Heraklion 184, Kontopouli 17) of field- grown wheat ( Triticum turgidum L. var. durum) were examined under four water shortage levels. Drought acclimation responses were more intense in Simeto than in the two landraces. In accordance to the working hypothesis, drought-acclimated leaves showed lower hydraulic conductance due to narrower vessels and higher stomatal and vein densities than the control leaves, resulting in a safe mode of water transfer and consumption which is essential for the survival in water limiting conditions.Irrespectively of genotype and water regime, significant correlations among structural (hydraulic characteristics, stomatal and vein patterns) and functional (gas exchange, nitrogen content) parameters were found, indicating the functional adjustment to the new structural status. The Principal Component Analysis showed that these structure-function interactions reflected the trade-off between growth and protection against water losses (Axis 1), as well as the competition between different sinks (carbon gain vs structural reinforcement and reproductive effort) in N allocation (Axis 2). Drought acclimation in wheat leaf is integrally processed by the coordination of structural and functional parameters in order to compensate for the adverse effects of water shortage. This structure-function network that regulates the transition from normal growth-mode to protection- mode, includes at least two important 'nodal points': xylem conducting efficiency (water entry) and stomatal function (water exit). This transition also includes the redirection of nitrogen resources to different sinks. [ABSTRACT FROM AUTHOR]

Grafting is an easier and faster approach than plant breeding to take advantage of both existing resistant plants, especially wild cultivars, and high-bred cultivars. The aim of this study was to investigate the changes in leaf photosynthetic capacity of a hybrid eggplant Solanum melongena L., cv. Rima (R), widely used in Greece] when grafted on tomato rootstocks known for their resistance to nematodes and diseases. For this purpose, a hybrid egg-plant has been used as a control and has been self-grafted (grafting of a scion on its own roots used as rootstock) RR and also as a scion on two hybrid tomatoes rootstocks, as follows: Primavera (RP) and Heman (RH). Leaf photosynthetic capacity was estimated by measuring the leaf gas exchanges under several light levels at ambient CO2 concentration to approximate the leaf light response curve. The measurements performed control plant Rand self-grafted eggplants RR show that the leaf respiration per unit leaf area is not altered by the scion/rootstock combination. These elements point out a scion controlled respiration, independent of the rootstock. The leaf photosynthetic capacities of the R and RR treatments were not different, while one of the scion/rootstock combinations (RH) showed a significant change with respect to the control treatments. The rootstock therefore seems to be able to modify the scion leaf photosynthetic capacity, but this may not be true for some scion/rootstock combinations (RP in our case). Leaf stomatal conductance and transpiration were not modified by the grafting, so that the water use efficiency was only altered by the modifications of the net assimilation. [ABSTRACT FROM AUTHOR]

Leaf water 18O enrichment (Δo) influences the isotopic composition of both gas exchange and organic matter, with Δo values responding to changes in atmospheric parameters. In order to examine possible influences of plant parameters on Δo dynamics, we measured oxygen isotope ratios (δ18O) of leaf and stem water on plant species representing different life forms in Amazonia forest and pasture ecosystems. We conducted two field experiments: one in March (wet season) and another in September (dry season) 2004. In each experiment, leaf and stem samples were collected at 2-h intervals at night and hourly during the day for 50 h from eight species including upper-canopy forest trees, upper-canopy forest lianas, and lower-canopy forest trees, a C4 pasture grass and a C3 pasture shrub. Significant life form-related differences were detected in 18O leaf water values. Initial modeling efforts to explain these observations over-predicted nighttime Δo values by as much as 10‰. Across all species, errors associated with measured values of the δ18O of atmospheric water vapor (δv) appeared to be largely responsible for the over-predictions of nighttime Δo observations. We could not eliminate collection or storage of water vapor samples as a possible error and therefore developed an alternative, plant-based method for estimating the daily average δv value in the absence of direct (reliable) measurements. This approach differs from the common assumption that isotopic equilibrium exists between water vapor and precipitation water, by including transpiration-based contributions from local vegetation through 18O measurements of bulk leaf water. Inclusion of both modified δv and non-steady state features resulted in model predictions that more reliably predicted both the magnitude and temporal patterns observed in the data. The influence of life form-specific patterns of Δo was incorporated through changes in the effective path length, an important but little known parameter associated with the Péclet effect. [ABSTRACT FROM AUTHOR]

The banana ( Musa sp.) plant is one of the largest monocotyledoneous terrestrial herbaceous plants in the world. The measurement of transpiration (Tr) for a whole banana plant is always difficult to perform due to its size. However, the sap flow (SF) of the plant has been successfully measured by using the thermal dissipation probe (TDP) or ‘Granier’ method in the corm of the banana plant (Lu et al. J Exp Bot 53:1771–1779, ). The present study aimed to validate their method using a sizable number of banana plants in a greenhouse in Israel. The SF data was compared to the gravimetric measurement of transpiration. The lag time of SF behind Tr was also analyzed. Results showed that the daily SF agreed with the daily Tr when the effective radius for sap flow in the corm was taken as 0.63 R, where R is the radius of the corm. The SF lagged 45 min behind the Tr from 0630 to 1040 hours. Whereas the Tr was not statistically ( P>0.05) different from the SF between 1330 and 1700 hours. The reduction in water capacity of banana plant due to SF lag was about 10.5% of the daily Tr, and it recovered gradually in the afternoon. Using more plants can reduce the measurement error of the TDP method. The measured daily SF can be considered as an accurate estimation of the daily Tr for banana plant. [ABSTRACT FROM AUTHOR]