RESUMEN
Accurate estimation of photosynthetic parameters is essential for understanding plant physiological limitations and responses to environmental factors from the leaf to the global scale. Gas exchange is a useful tool to measure responses of net CO2 assimilation (A) to internal CO2 concentration (Ci), a necessary step in estimating photosynthetic parameters including the maximum rate of carboxylation (Vcmax) and the electron transport rate (Jmax). However, species and environmental conditions of low stomatal conductance (gsw) reduce the signal-to-noise ratio of gas exchange, challenging estimations of Ci. Previous works showed that not considering cuticular conductance to water (gcw) can lead to significant errors in estimating Ci, because it has a different effect on total conductance to CO2 (gtc) than does gsw. Here we present a systematic assessment of the need for incorporating gcw into Ci estimates. In this study we modeled the effect of gcw and of instrumental noise and quantified these effects on photosynthetic parameters in the cases of four species with varying gsw and gcw, measured using steady-state and constant ramping techniques, like the rapid A/Ci response method. We show that not accounting for gcw quantitatively influences Ci and the resulting Vcmax and Jmax, particularly when gcw exceeds 7% of the total conductance to water. The influence of gcw was not limited to low gsw species, highlighting the importance of species-specific knowledge before assessing A/Ci curves. Furthermore, at low gsw instrumental noise can affect Ci estimation, but the effect of instrumental noise can be minimized using constant-ramping rather than steady-state techniques. By incorporating these considerations, more precise measurements and interpretations of photosynthetic parameters can be obtained in a broader range of species and environmental conditions.
Asunto(s)
Fotosíntesis , Estomas de Plantas , Fotosíntesis/fisiología , Estomas de Plantas/fisiología , Dióxido de Carbono/metabolismo , Agua/metabolismo , Hojas de la Planta/fisiología , Hojas de la Planta/metabolismoRESUMEN
Recently in Florida, foliar treatments using products with the antibiotics oxytetracyclineand streptomycin have been approved for the treatment of citrus Huanglongbing (HLB), which iscaused by the putative bacterial pathogen 'Candidatus Liberibacter asiaticus'. Herein, we assessedthe levels of oxytetracycline and 'Ca. L. asiaticus' titers in citrus trees upon foliar applications withand without a variety of commercial penetrant adjuvants and upon trunk injection. The level ofoxytetracycline in citrus leaves was measured using an oxytetracycline ELISA kit and 'Ca. L.asiaticus' titer was measured using quantitative PCR. Low levels of oxytetracycline were taken upby citrus leaves after foliar sprays of oxytetracycline in water. Addition of various adjuvants to theoxytetracycline solution showed minimal effects on its uptake by citrus leaves. The level ofoxytetracycline in leaves from trunk-injected trees was higher than those treated with all foliarapplications. The titer of 'Ca. L. asiaticus' in the midrib of leaves from trees receiving oxytetracyclineby foliar application was not affected after four days and thirty days of application, whereas thetiter was significantly reduced in oxytetracycline-injected trees thirty days after treatment.Investigation of citrus leaves using microscopy showed that they are covered by a thick lipidizedcuticle. Perforation of citrus leaf cuticle with a laser significantly increased the uptake ofoxytetracycline, decreasing the titer of 'Ca. L. asiaticus' in citrus leaves upon foliar application.Taken together, our findings indicate that trunk injection is more efficient than foliar spray evenafter the use of adjuvants. Our conclusion could help in setting useful recommendations for theapplication of oxytetracycline in citrus to improve tree health, minimize the amount of appliedantibiotic, reduce environmental exposure, and limit off-target effects.