The development of smartphones, specifically their cameras, and imaging technologies has enabled their use as sensors/measurement tools. Here we aimed to evaluate the applicability of a fast and noninvasive method for the estimation of total chlorophyll (Chl), Chl a, Chl b, and carotenoids (Car) content of soybean plants using a smartphone camera. Single leaf disc images were obtained using a smartphone camera. Subsequently, for the same leaf discs, a Chl meter was used to obtain the relative index of Chl and the photosynthetic pigments were then determined using a classic method. The RGB, HSB and CIELab color models were extracted from the smartphone images and correlated to Chl values obtained using a Chl meter and by a standard laboratory protocol. The smartphone camera was sensitive enough to capture successfully a broad range of Chl and Car contents seen in soybean leaves. Although there was a variation between color models, some of the proposed regressions (e.g., the S and b index from HSB and Lab color models and NRI [RGB model]) were very close to the Chl meter values. Based on our findings, smartphones can be used for rapid and accurate estimation of soybean and Car contents in soybean leaves., J. P. G. Rigon, S. Capuani, D. M. Fernandes, T. M. Guimarães., and Obsahuje bibliografii
C3 photosynthesis at high light is often modeled by assuming limitation by the maximum capacity of Rubisco carboxylation (VCmax) at low CO2 concentrations, by electron transport capacity (Jmax) at higher CO2 concentrations, and sometimes by
triose-phosphate utilization rate at the highest CO2 concentrations. Net photosynthetic rate (PN) at lower light is often modeled simply by assuming that it becomes limited by electron transport (J). However, it is known that Rubisco can become deactivated at less than saturating light, and it is possible that PN at low light could be limited by the rate of Rubisco carboxylation (VC) rather than J. This could have important consequences for responses of PN to CO2 and temperature at low light. In this work, PN responses to CO2 concentration of common bean, quinoa, and soybean leaves measured over a wide range of temperatures and PPFDs were compared with rates modeled assuming either VC or J limitation at limiting light. In all cases, observed rates of PN were better predicted by assuming limitation by VC rather than J at limiting light both below and above the current ambient CO2. One manifestation of this plant response was that the relative stimulation of PN with increasing the ambient CO2 concentration from 380 to 570 µmol mol-1 did not decrease at less than saturating PPFDs. The ratio of VC to VCmax at each lower PPFD varied linearly with the ratio of PN at low PPFD to PN at high PPFD measured at 380 µmol(CO2) mol-1 in all cases. This modification of the standard C3 biochemical model was much better at reproducing observed responses of light-limited PN to CO2 concentrations from
pre-industrial to projected future atmospheric concentrations., J. A. Bunce., and Obsahuje bibliografii
Net photosynthetic rate, radiation use efficiency, chlorophyll (Chl) fluorescence, photochemical reflectance index (PRI), and leaf water potential were measured during a 25-d period of progressive water deficit in quinoa plants grown in a glasshouse in order to examine effects of water stress and ontogeny. All physiological parameters except Fv/Fm were sensitive to water stress. Ontogenic variations did not exist in Fv/Fm and leaf water potential, and were moderate to high in the other parameters. The complete recovery of photosynthetic parameters after re-irrigation was related with the stability in Fv/Fm. PRI showed significant correlation with predawn leaf water potential, Fm', and midday Fv/Fm. Thus PRI and Chl fluorescence may help in assessing physiological changes in quinoa plants across different developmental stages and water status. and T. Winkel, M. Méthy, F. Thénot.