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In addition to buffering plants from water stress during severe droughts, plant water storage (PWS) alters many features of the spatio-temporal dynamics of water movement in the soil-plant system. How PWS impacts water dynamics and drought resilience is explored using a multi-layer porous media model. The model numerically resolves soil-plant hydrodynamics by coupling them to leaf-level gas exchange and soil-root interfacial layers. Novel features of the model are the considerations of a coordinated relationship between stomatal aperture variation and whole-system hydraulics and of the effects of PWS and nocturnal transpiration (Fe,night) on hydraulic redistribution (HR) in the soil. The model results suggest that daytime PWS usage and Fe,night generate a residual water potential gradient (Δψp,night) along the plant vascular system overnight. This Δψp,night represents a non-negligible competing sink strength that diminishes the significance of HR. Considering the co-occurrence of PWS usage and HR during a single extended dry-down, a wide range of plant attributes and environmental/soil conditions selected to enhance or suppress plant drought resilience is discussed. When compared with HR, model calculations suggest that increased root water influx into plant conducting-tissues overnight maintains a more favorable water status at the leaf, thereby delaying the onset of drought stress.

The ability of plants to acquire and use water is critical in determining life‐history traits such as growth, flowering, and allocation of biomass into reproduction. In this context, a combination of functionally linked traits is essential for plants to respond to environmental changes in a coordinated fashion to maximize resource use efficiency. We analyzed different water‐use traits in Arabidopsis ecotypes to identify functionally linked traits that determine water use and plant growth performance. Water‐use traits measured were (i) leaf‐level water‐use efficiency (WUEi) to evaluate the amount of CO2 fixed relative to water loss per leaf area and (ii) short‐term plant water use at the vegetative stage (VWU) as a measure of whole‐plant transpiration. Previously observed phenotypic variance in VWU, WUEi and life‐history parameters, highlighted C24 as a valuable ecotype that combined drought tolerance, preferential reproductive biomass allocation, high WUEi, and reduced water use. We therefore screened 35 Arabidopsis ecotypes for these parameters, in order to assess whether the phenotypic combinations observed in C24 existed more widely within Arabidopsis ecotypes. All parameters were measured on a short dehydration cycle. A segmented regression analysis was carried out to evaluate the plasticity of the drought response and identified the breakpoint as a reliable measure of drought sensitivity. VWU was largely dependent on rosette area, but importantly the drought sensitivity and plasticity measures were independent of the transpiring leaf surface. A breakpoint at high rSWC indicated a more drought‐sensitive plant that closed stomata early during the dehydration cycle and consequently showed stronger plasticity in leaf‐level WUEi parameters. None of the sensitivity, plasticity, or water‐use measurements were able to predict the overall growth performance; however, there was a general trade‐off between vegetative and reproductive biomass. PCA and hierarchical clustering revealed that C24 was unique among the 35 ecotypes in uniting all the beneficial water use and stress tolerance traits, while also maintaining above average plant growth. We propose that a short dehydration cycle, measuring drought sensitivity and VWU is a fast and reliable screen for plant water use and drought response strategies.

We have explored leaf-level plastic response to light and nutrients of Quercus ilex and Q. coccifera, two closely related Mediterranean evergreen sclerophylls, in a factorial experiment with seedlings. Leaf phenotypic plasticity, assessed by a relative index (PI = (maximum value - minimum)/maximum) in combination with the significance of the difference among means, was studied in 37 morphological and physiological variables. Light had significant effects on most variables relating to photosynthetic pigments, chlorophyll fluorescence and gas exchange, whereas nutrient treatment had a significant effect in only 10% of the variables. Chlorophyll content was higher in the shade whereas carotenoid content and nonphotochemical quenching increased with light. Nutrient limitations increased the xanthophyll-cycle pool but only at high light intensities, and the same interaction between light and nutrients was observed for lutein. Predawn photochemical efficiency of PSII was not affected by either light or nutrients, although midday photochemical efficiency of PSII was lower at high light intensities. Photosynthetic light compensation point and dark respiration on an area basis decreased with light, but photosynthetic capacity on a dry mass basis and photochemical quenching were higher in low light, which translated into a higher nitrogen use efficiency in the shade. We expected Q. ilex, the species of the widest ecological distribution, to be more plastic than Q. coccifera, but differences were minor: Q. ilex exhibited a significant response to light in 13% more of the variables than Q. coccifera, but mean PI was very similar in the two species. Both species tolerated full sunlight and moderate shade, but exhibited a reduced capacity to enhance photosynthetic utilization of high irradiance. When compared with evergreen shrubs from the tropical rainforest, leaf responsiveness of the two evergreen oaks was low. We suggest that the low leaf-level responsiveness found here is part of a conservative resource use strategy, which seems to be adaptive for evergreen woody plants in Mediterranean-type ecosystems.

We revisit the theory connecting chlorophyll a fluorescence to photosynthesis in the spatiotemporal context of remote sensing. Physical, physiological, and methodological factors are discussed, and a roadmap to future research presented.

Recent advances in the retrieval of Chl fluorescence from space using passive methods (solar-induced Chl fluorescence, SIF) promise improved mapping of plant photosynthesis globally. However, unresolved issues related to the spatial, spectral, and temporal dynamics of vegetation fluorescence complicate our ability to interpret SIF measurements. We developed an instrument to measure leaf-level gas exchange simultaneously with pulse-amplitude modulation (PAM) and spectrally resolved fluorescence over the same field of view – allowing us to investigate the relationships between active and passive fluorescence with photosynthesis. Strongly correlated, slope-dependent relationships were observed between measured spectra across all wavelengths (Fλ , 670–850 nm) and PAM fluorescence parameters under a range of actinic light intensities (steady-state fluorescence yields, F t) and saturation pulses (maximal fluorescence yields, F m). Our results suggest that this method can accurately reproduce the full Chl emission spectra – capturing the spectral dynamics associated with changes in the yields of fluorescence, photochemical (ΦPSII), and nonphotochemical quenching (NPQ). We discuss how this method may establish a link between photosynthetic capacity and the mechanistic drivers of wavelength-specific fluorescence emission during changes in environmental conditions (light, temperature, humidity). Our emphasis is on future research directions linking spectral fluorescence to photosynthesis, ΦPSII, and NPQ.

The fraction of open Photosystem II (PSII) reaction centers (qL) is critical for connecting broadband PSII fluorescence (ChlFPSII) with the actual electron transport from PSII to Photosystem I. Accurately estimating qL is fundamental for determining ChlFPSII, which, in turn, is vital for mechanistically estimating the actual electron transport rate and photosynthetic CO2 assimilation. Chlorophyll fluorescence provides direct physiological insights, offering a robust foundation for qL estimation. However, uncertainties in the ChlFPSII–qL relationship across different plant functional types (PFTs) limit its broader application at large spatial scales. To address this issue, we developed a leaf-level instrument capable of simultaneously measuring actively and passively induced chlorophyll fluorescence. Using this system, we measured light response, CO2 response, and temperature response curves across 52 species representing seven PFTs. Our findings reveal the following: (1) a strong linear correlation between ChlFPSII derived from passively induced fluorescence and that from actively induced fluorescence (R2 = 0.85), and (2) while the parameters of the ChlFPSII–qL relationship varied among PFTs, ChlFPSII reliably modeled qL within each PFT, with the R2 ranging from 0.85 to 0.96. This study establishes quantitative ChlFPSII–qL relationships for various PFTs by utilizing passively induced fluorescence to calculate ChlFPSII. The results demonstrate the potential for remotely sensed chlorophyll fluorescence data to estimate qL and strengthen the use of fluorescence-based approaches for mechanistic GPP estimation at large spatial scales.

Soybean is one of the world’s most consumed crops. As the human population continuously increases, new phenotyping technology is needed to develop new soybean varieties with high-yield, stress-tolerant, and disease-tolerant traits. Hyperspectral imaging (HSI) is one of the most used technologies for phenotyping. The current HSI techniques with indoor imaging towers and unmanned aerial vehicles (UAVs) suffer from multiple major noise sources, such as changes in ambient lighting conditions, leaf slopes, and environmental conditions. To reduce the noise, a portable single-leaf high-resolution HSI imager named LeafSpec was developed. However, the original design does not work efficiently for the size and shape of dicot leaves, such as soybean leaves. In addition, there is a potential to make the dicot leaf scanning much faster and easier by automating the manual scan effort in the original design. Therefore, a renovated design of a LeafSpec with increased efficiency and imaging quality for dicot leaves is presented in this paper. The new design collects an image of a dicot leaf within 20 s. The data quality of this new device is validated by detecting the effect of nitrogen treatment on soybean plants. The improved spatial resolution allows users to utilize the Normalized Difference Vegetative Index (NDVI) spatial distribution heatmap of the entire leaf to predict the nitrogen content of a soybean plant. This preliminary NDVI distribution analysis result shows a strong correlation (R2 = 0.871) between the image collected by the device and the nitrogen content measured by a commercial laboratory. Therefore, it is concluded that the new LeafSpec-Dicot device can provide high-quality hyperspectral leaf images with high spatial resolution, high spectral resolution, and increased throughput for more accurate phenotyping. This enables phenotyping researchers to develop novel HSI image processing algorithms to utilize both spatial and spectral information to reveal more signals in soybean leaf images.

Background Leaves are structurally and functionally heterogeneous organs, and their photosynthetic performance often varies across the lamina. Environmental stress, particularly drought, is often assumed to increase this heterogeneity by disrupting stomatal behaviour, mesophyll function, and pigment content. However, the extent to which moderate water deficit alters the spatial organisation of gas exchange, photochemistry, and spectral traits within a single leaf remains unclear. This study investigated within-leaf variability in Phaseolus vulgaris under well-watered and moderate drought conditions by combining gas exchange with chlorophyll fluorescence and multispectral imaging. The aim was to determine whether drought amplifies or reduces intrinsic spatial patterns and to assess whether imaging-derived parameters reflect micro-scale variation in stomatal conductance. Results Control leaves showed subtle but consistent spatial gradients, including slightly lower photosynthetic activity, photochemical efficiency, and pigment-related indices at the apical region compared with basal and middle segments. Stomatal traits also varied modestly along the lamina, reflecting developmental polarity. Drought substantially reduced net photosynthesis, stomatal conductance, relative electron transport rate, and vegetation indices, yet generally reduced positional differences across measured traits. Leaf relative water content declined without significant positional differences, indicating coherent hydration under stress. Chlorophyll fluorescence and multispectral imaging demonstrated strong reductions in trait magnitude under drought but only weak spatial divergence, with widespread increases in non-photochemical quenching and pigment-related indices. Canonical discriminant analysis clearly separated leaf regions in control plants but showed reduced discrimination under drought, confirming a loss of spatial differentiation. Partial least squares regression revealed strong predictive links between imaging traits and stomatal conductance under control conditions but poor prediction under drought, indicating reduced predictive performance once stomatal conductance becomes strongly constrained. Conclusions Moderate drought did not intensify within-leaf heterogeneity. Instead, it promoted a higher degree of spatially coherent down-regulation of photosynthesis, photochemistry, and optical properties. These findings suggest that common bean maintains coordinated stomatal, hydraulic, and photoprotective responses across the lamina under moderate water deficit, preserving functional integrity despite reduced assimilation. The results underscore the importance of accounting for spatial stability when interpreting drought responses and highlight the utility of imaging-based phenotyping for assessing coordinated leaf-level acclimation.

Due to the mechanistic coupling between solar-induced chlorophyll fluorescence (SIF) and photosynthesis, SIF has an advantage over greenness-based vegetation indices in detecting drought. Since photosystem I (PSI) contributes very little to red SIF, red SIF is assumed to be more responsive to environmental stress than far-red SIF. However, in addition to affecting photosynthesis, drought also has an impact on vegetation chlorophyll concentration and thus affects the reabsorption process of red SIF. When these responses are entangled, the sensitivity of SIF in the red and far-red regions in response to drought is not yet clear. In this study, we conducted a water stress experiment on maize in the field and measured the upward and downward leaf SIF spectra by a spectrometer assembled with a leaf clip. Simultaneously, leaf-level active fluorescence was measured with a pulse-amplified modulation (PAM) fluorometer. We found that SIF, after normalization by photosynthetically active radiation (PAR) and dark-adapted minimal fluorescence (Fo), is a better estimation of SIF yield. By comparing the wavelength-dependent link between SIF yield and nonphotochemical quenching (NPQ) across the range of 660 to 800 nm, the results show that red SIF and far-red SIF have different sensitivities in response to drought. SIF yield in the far-red region has a strong and stable correlation with NPQ. Drought not only reduces red SIF due to photosynthetic regulation, but it also increases red SIF by reducing chlorophyll content (weakening the reabsorption effect). The co-existence of these two contradictory effects makes the red SIF of leaf level unable to reliably indicate NPQ. In addition, the red:far-red ratio of downward SIF and the ratio between the downward SIF and upward SIF at the red peak can be good indicators of chlorophyll content. These findings can help to interpret SIF variations in remote sensing techniques and fully exploit SIF information in red and far-red regions when monitoring plant water stress.

Mixed-stand plantations are not always as beneficial for timber production and carbon sequestration as monoculture plantations. Systematic analyses of mixed-stand forests as potential ideal plantations must consider the physiological-ecological performance of these plantations. This study aimed to determine whether mixed moso bamboo ( Phyllostachys pubescens (Pradelle) Mazel ex J. Houz.) and Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook.) stands exhibited better physiological-ecological performance than monoculture plantations of these species. We analyzed leaf photosynthesis, chlorophyll fluorescence, antioxidant enzyme activities, chlorophyll content and leaf chemistry in a moso bamboo stand, a Chinese fir stand and a mixed stand with both species. The results showed that both species in the mixed stand exhibited significantly higher leaf net photosynthesis rate (Amax), instantaneous carboxylation efficiency (CUE), chlorophyll content, maximum quantum yield of photosynthesis (Fv/Fm), photochemical quenching coefficient (qP), PSII quantum yield [Y(II)], leaf nitrogen content, and antioxidant enzyme activities than those in the monoculture plantations. However, the non-photochemical quenching (NPQ) in Chinese fir and 2-year-old moso bamboo was significantly lower in the mixed stand than in the monocultures. In addition, the water use efficiency (WUE) of Chinese fir was significantly higher in the mixed stand. The results suggest that the increase in leaf net photosynthetic capacity and the improved growth in the mixed stand could be attributed primarily to the (i) more competitive strategies for soil water use, (ii) stronger antioxidant systems, and (iii) higher leaf total nitrogen and chlorophyll contents in the plants. These findings suggest that mixed growth has beneficial effects on the leaf photosynthesis capacity and physiological resistance of moso bamboo and Chinese fir.