L. varieties (cv. Cabernet Sauvignon and Chardonnay) vary in leaf water flux in response to elevated CO growing conditions and a gradual water deficit.

Grapevine ( L.) stomata are highly sensitive to atmospheric changes and influence the tradeoff between water and carbon, as estimated by intrinsic water use efficiency (WUE). The aim of this study was to examine how elevated CO concentrations and water deficit affect the WUE and whole plant evapotranspiration of two grapevine varieties (cv.

Diversity in stomatal and hydraulic responses to post-flowering drought in common (Phaseolus vulgaris) and tepary (P. acutifolius) beans.

Plants differ widely in how soil drying affects stomatal conductance (g) and leaf water potential (ψ), and in the underlying physiological controls. Efforts to breed crops for drought resilience would benefit from a better understanding of these mechanisms and their diversity. We grew 12 diverse genotypes of common bean (Phaseolus vulgaris L.

Hyperspectral Remote Sensing for Phenotyping the Physiological Drought Response of Common and Tepary Bean.

Proximal remote sensing offers a powerful tool for high-throughput phenotyping of plants for assessing stress response. Bean plants, an important legume for human consumption, are often grown in regions with limited rainfall and irrigation and are therefore bred to further enhance drought tolerance. We assessed physiological (stomatal conductance and predawn and midday leaf water potential) and ground- and tower-based hyperspectral remote sensing (400 to 2,400 nm and 400 to 900 nm, respectively) measurements to evaluate drought response in 12 common bean and 4 tepary bean genotypes across 3 field campaigns (1 predrought and 2 post-drought).

TSWIFT: Tower Spectrometer on Wheels for Investigating Frequent Timeseries for high-throughput phenotyping of vegetation physiology.

Background: Remote sensing instruments enable high-throughput phenotyping of plant traits and stress resilience across scale. Spatial (handheld devices, towers, drones, airborne, and satellites) and temporal (continuous or intermittent) tradeoffs can enable or constrain plant science applications. Here, we describe the technical details of TSWIFT (Tower Spectrometer on Wheels for Investigating Frequent Timeseries), a mobile tower-based hyperspectral remote sensing system for continuous monitoring of spectral reflectance across visible-near infrared regions with the capacity to resolve solar-induced fluorescence (SIF).

Structural and functional leaf diversity lead to variability in photosynthetic capacity across a range of Juglans regia genotypes.

Similar to other cropping systems, few walnut cultivars are used as scion in commercial production. Germplasm collections can be used to diversify cultivar options and hold potential for improving crop productivity, disease resistance and stress tolerance. In this study, we explored the anatomical and biochemical bases of photosynthetic capacity and response to water stress in 11 Juglans regia accessions in the U.

Desiccation of the leaf mesophyll and its implications for CO diffusion and light processing.

Leaves balance CO and radiative absorption while maintaining water transport to maximise photosynthesis. Related species with contrasting leaf anatomy can provide insights into inherent and stress-induced links between structure and function for commonly measured leaf traits for important crops. We used two walnut species with contrasting mesophyll anatomy to evaluate these integrated exchange processes under non-stressed and drought conditions using a combination of light microscopy, X-ray microCT, gas exchange, hydraulic conductance, and chlorophyll distribution profiles through leaves.

A double-ratio method to measure fast, slow and reverse sap flows.

Sap velocity measurements are useful in fields ranging from plant water relations to hydrology at a variety of scales. Techniques based on pulses of heat are among the most common methods to measure sap velocity, but most lack ability to measure velocities across a wide range, including very high, very low and negative velocities (reverse flow). We propose a new method, the double-ratio method (DRM), which is robust across an unprecedented range of sap velocities and provides real-time estimates of the thermal diffusivity of wood.

Maximum CO diffusion inside leaves is limited by the scaling of cell size and genome size.

Maintaining high rates of photosynthesis in leaves requires efficient movement of CO from the atmosphere to the mesophyll cells inside the leaf where CO is converted into sugar. CO diffusion inside the leaf depends directly on the structure of the mesophyll cells and their surrounding airspace, which have been difficult to characterize because of their inherently three-dimensional organization. Yet faster CO diffusion inside the leaf was probably critical in elevating rates of photosynthesis that occurred among angiosperm lineages.

Silencing of OsCV (chloroplast vesiculation) maintained photorespiration and N assimilation in rice plants grown under elevated CO.

High CO concentrations stimulate net photosynthesis by increasing CO substrate availability for Rubisco, simultaneously suppressing photorespiration. Previously, we reported that silencing the chloroplast vesiculation (cv) gene in rice increased source fitness, through the maintenance of chloroplast stability and the expression of photorespiration-associated genes. Because high atmospheric CO conditions diminished photorespiration, we tested whether CV silencing might be a viable strategy to improve the effects of high CO on grain yield and N assimilation in rice.

PARbars: Cheap, Easy to Build Ceptometers for Continuous Measurement of Light Interception in Plant Canopies.

Ceptometry is a technique used to measure the transmittance of photosynthetically active radiation through a plant canopy using multiple light sensors connected in parallel on a long bar. Ceptometry is often used to infer properties of canopy structure and light interception, notably leaf area index (LAI) and effective plant area index (PAIeff). Due to the high cost of commercially available ceptometers, the number of measurements that can be taken is often limited in space and time.

Root and shoot variation in relation to potential intermittent drought adaptation of Mesoamerican wild common bean (Phaseolus vulgaris L.).

Background: Wild crop relatives have been potentially subjected to stresses on an evolutionary time scale prior to domestication. Among these stresses, drought is one of the main factors limiting crop productivity and its impact is likely to increase under current scenarios of global climate change. We sought to determine to what extent wild common bean (Phaseolus vulgaris) exhibited adaptation to drought stress, whether this potential adaptation is dependent on the climatic conditions of the location of origin of individual populations, and to what extent domesticated common bean reflects potential drought adaptation.

A multiplexed gas exchange system for increased throughput of photosynthetic capacity measurements.

Background: Existing methods for directly measuring photosynthetic capacity () have low throughput, which creates a key bottleneck for pre-breeding and ecological research. Currently available commercial leaf gas exchange systems are not designed to maximize throughput, on either a cost or time basis.

Results: We present a novel multiplexed semi-portable gas exchange system, OCTOflux, that can measure with approximately 4-7 times the throughput of commercial devices, despite a lower capital cost.

Beyond Porosity: 3D Leaf Intercellular Airspace Traits That Impact Mesophyll Conductance.

The leaf intercellular airspace (IAS) is generally considered to have high conductance to CO diffusion relative to the liquid phase. While previous studies accounted for leaf-level variation in porosity and mesophyll thickness, they omitted 3D IAS traits that potentially influence IAS conductance (g). Here, we reevaluated the standard equation for g by incorporating tortuosity, lateral path lengthening, and IAS connectivity.

The bias of a two-dimensional view: comparing two-dimensional and three-dimensional mesophyll surface area estimates using noninvasive imaging.

The mesophyll surface area exposed to intercellular air space per leaf area (S ) is closely associated with CO diffusion and photosynthetic rates. S is typically estimated from two-dimensional (2D) leaf sections and corrected for the three-dimensional (3D) geometry of mesophyll cells, leading to potential differences between the estimated and actual cell surface area. Here, we examined how 2D methods used for estimating S compare with 3D values obtained from high-resolution X-ray microcomputed tomography (microCT) for 23 plant species, with broad phylogenetic and anatomical coverage.

Excess Diffuse Light Absorption in Upper Mesophyll Limits CO Drawdown and Depresses Photosynthesis.

In agricultural and natural systems, diffuse light can enhance plant primary productivity due to deeper penetration into and greater irradiance of the entire canopy. However, for individual sun-grown leaves from three species, photosynthesis is actually less efficient under diffuse compared with direct light. Despite its potential impact on canopy-level productivity, the mechanism for this leaf-level diffuse light photosynthetic depression effect is unknown.

The light response of mesophyll conductance is controlled by structure across leaf profiles.

Mesophyll conductance to CO (g ) may respond to light either through regulated dynamic mechanisms or due to anatomical and structural factors. At low light, some layers of cells in the leaf cross-section approach photocompensation and contribute minimally to bulk leaf photosynthesis and little to whole leaf g (g ). Thus, the bulk g will appear to respond to light despite being based upon cells having an anatomically fixed mesophyll conductance.

Drought Adaptation Mechanisms Should Guide Experimental Design.

The mechanism, or hypothesis, of how a plant might be adapted to drought should strongly influence experimental design. For instance, an experiment testing for water conservation should be distinct from a damage-tolerance evaluation. We define here four new, general mechanisms for plant adaptation to drought such that experiments can be more easily designed based upon the definitions.

Physiological trade-offs of stomatal closure under high evaporative gradients in field grown soybean.

Limited rainfall is the main constraint to agriculture, making agricultural research to understand plant behaviour that leads to avoidance of soil water deficit a matter of priority. One focus has screened for crop varieties that decrease stomatal conductance under high vapour pressure deficit (VPD), a proxy for the leaf evaporative gradient. However, the link between stomatal closure and physiological consequences in field environments is not yet clear.

Transcriptome response to embolism formation in stems of Populus trichocarpa provides insight into signaling and the biology of refilling.

The mechanism of embolism repair in transpiring plants is still not understood, despite significant scientific effort. The refilling process is crucial to maintaining stem transport capacity and ensuring survival for plants experiencing dynamic changes in water stress. Refilling air-filled xylem vessels requires an energy and water source that can only be provided by adjacent living parenchyma cells.

On measuring the response of mesophyll conductance to carbon dioxide with the variable J method.

The response of mesophyll conductance to CO(2) (g(m)) to environmental variation is a challenging parameter to measure with current methods. The 'variable J' technique, used in the majority of studies of g(m), assumes a one-to-one relationship between photosystem II (PSII) fluorescence and photosynthesis under non-photorespiratory conditions. When calibrating this relationship for Populus trichocarpa, it was found that calibration relationships produced using variation in light and CO(2) were not equivalent, and in all cases the relationships were non-linear-something not accounted for in previous studies.

The role of bundle sheath extensions and life form in stomatal responses to leaf water status.

Bundle sheath extensions (BSEs) are key features of leaf structure with currently little-understood functions. To test the hypothesis that BSEs reduce the hydraulic resistance from the bundle sheath to the epidermis (r(be)) and thereby accelerate hydropassive stomatal movements, we compared stomatal responses with reduced humidity and leaf excision among 20 species with heterobaric or homobaric leaves and herbaceous or woody life forms. We hypothesized that low r(be) due to the presence of BSEs would increase the rate of stomatal opening (V) during transient wrong-way responses, but more so during wrong-way responses to excision (V(e)) than humidity (V(h)), thus increasing the ratio of V(e) to V(h).

Independent variation in photosynthetic capacity and stomatal conductance leads to differences in intrinsic water use efficiency in 11 soybean genotypes before and during mild drought.

Intrinsic water use efficiency (WUE(intr)), the ratio of photosynthesis to stomatal conductance to water, is often used as an index for crop water use in breeding projects. However, WUE(intr) conflates variation in these two processes, and thus may be less useful as a selection trait than knowledge of both components. The goal of the present study was to determine whether the contribution of photosynthetic capacity and stomatal conductance to WUE(intr) varied independently between soybean genotypes and whether this pattern was interactive with mild drought.

Biomass reallocation and the mobilization of leaf resources support dune plant growth after sand burial.

The stimulation of dune plant growth in response to burial is a vital attribute allowing survival in areas of mobile sand. Numerous resource-related and physiological mechanisms of growth stimulation have been suggested in the past, but few have been tested comparatively. Manipulation experiments using Scaevola plumieri, an important subtropical coastal dune forming species, demonstrated that physiological shifts were of great importance in determining the nature of the stimulation response to burial.

Seasonal differences in photosynthesis between the C3 and C4 subspecies of Alloteropsis semialata are offset by frost and drought.

The regional abundance of C(4) grasses is strongly controlled by temperature, however, the role of precipitation is less clear. Progress in elucidating the direct effects of photosynthetic pathway on these climate relationships is hindered by the significant genetic divergence between major C(3) and C(4) grass lineages. We addressed this problem by examining seasonal climate responses of photosynthesis in Alloteropsis semialata, a unique grass species with both C(3) and C(4) subspecies.

Low temperature effects on leaf physiology and survivorship in the C3 and C4 subspecies of Alloteropsis semialata.

The species richness of C(4) grasses is strongly correlated with temperature, with C(4) species dominating subtropical ecosystems and C(3) types predominating in cooler climates. Here, the effects of low temperatures on C(4) and C(3) grasses are compared, controlling for phylogenetic effects by using Alloteropsis semialata, a unique species with C(4) and C(3) subspecies. Controlled environment and common garden experiments tested the hypotheses that: (i) photosynthesis and growth are greater in the C(4) than the C(3) subspecies at high temperatures, but this advantage is reversed below 20 degrees C; and (ii) chilling-induced photoinhibition and light-mediated freezing injury of leaves occur at higher temperature thresholds in the C(4) than the C(3) plants.