Isotopic steady state or non-steady state transpiration? Insights from whole-tree chambers.

Unravelling the complexities of transpiration can be assisted by understanding the oxygen isotope composition of transpired water vapour (δE). It is often assumed that δE is at steady state, thereby mirroring the oxygen isotope composition of source water (δsource), but this assumption has never been tested at the whole-tree scale. This study utilized the unique infrastructure of 12 whole-tree chambers enclosing Eucalyptus parramattensis E.

H O vapour labelling reveals evidence of radial Péclet effects, but in not all leaves.

Contradictory evidence exists regarding the relevance of Péclet-like gradients in leaf water isotopes, making it difficult to accurately predict variation in isotope composition. Here, we use H O vapour labelling to directly test whether leaf water isotopes diffuse back into the xylem to be carried forward to more distal leaf portions. Backward diffusion has been assumed, due to observations of increasing enrichment towards the tip and outer edges of some leaves.

Adaptation of stomatal conductance, photosynthesis and water-use efficiency at shoot and canopy scales in adjacent stands of Dacrycarpus dacrydioides and Podocarpus totara.

We tested an approach to estimate daily canopy net photosynthesis, A, based on estimates of transpiration, E, using measurements of sap flow and water-use efficiency, ω, by measuring δ13C in CO2 respired from shoots in the canopies of two conifers (Podocarpaceae) native to New Zealand. The trees were planted in adjacent 20-year-old stands with the same soil and environmental conditions. Leaf area index was lower for Dacrycarpus dacrydioides D.

Expanding collaborative autoethnography into the world of natural science for transdisciplinary teams.

Wicked problems such as climate change and the COVID-19 pandemic require authentically transdisciplinary approaches to achieving effective collaboration. There exist several research approaches for identifying the components and interactions of complex problems; however, collaborative autoethnography provides an empirical way to collect and analyze self-reflection that leads to transformative change. Here, we present a case study of collaborative autoethnography, applied as a tool to transform research practice among a group of natural and social scientists, by constructively revealing and resolving deep, often unseen, disciplinary divides.

Mesophyll conductance exerts a significant limitation on photosynthesis during light induction.

Past studies have established mesophyll diffusion conductance to CO (g ) as a variable and significant limitation to plant photosynthesis under steady-state conditions. However, the role of g in influencing photosynthesis (A) during the transient period of light induction is largely unknown. We combined gas exchange measurements with laser-enabled carbon isotope discrimination measurements to assess g during photosynthetic induction, using Arabidopsis as the measurement species.

Open source 3D phenotyping of chickpea plant architecture across plant development.

Background: Being able to accurately assess the 3D architecture of plant canopies can allow us to better estimate plant productivity and improve our understanding of underlying plant processes. This is especially true if we can monitor these traits across plant development. Photogrammetry techniques, such as structure from motion, have been shown to provide accurate 3D reconstructions of monocot crop species such as wheat and rice, yet there has been little success reconstructing crop species with smaller leaves and more complex branching architectures, such as chickpea.

Understanding airspace in leaves: 3D anatomy and directional tortuosity.

The leaf intercellular airspace is a tortuous environment consisting of cells of different shapes, packing densities, and orientation, all of which have an effect on the travelling distance of molecules from the stomata to the mesophyll cell surfaces. Tortuosity, the increase in displacement over the actual distance between two points, is typically defined as encompassing the whole leaf airspace, but heterogeneity in pore dimensions and orientation between the spongy and palisade mesophyll likely result in heterogeneity in tortuosity along different axes and would predict longer traveling distance along the path of least tortuosity, such as vertically within the columnar cell matrix of the palisade layer. Here, we compare a previously established geometric method to a random walk approach, novel for this analysis in plant leaves, in four different Eucalyptus species.

The effects on isotopic composition of leaf water and transpiration of adding a gas-exchange cuvette.

An expression was earlier derived for the non-steady state isotopic composition of a leaf when the composition of the water entering the leaf was not necessarily the same as that of the water being transpired (Farquhar and Cernusak 2005). This was relevant to natural conditions because the associated time constant is typically sufficiently long to ensure that the leaf water composition and fluxes of the isotopologues are rarely steady. With the advent of laser-based measurements of isotopologues, leaves have been enclosed in cuvettes and time courses of fluxes recorded.

Identification of quantitative trait loci for dynamic and steady-state photosynthetic traits in a barley mapping population.

Enhancing the photosynthetic induction response to fluctuating light has been suggested as a key target for improvement in crop breeding programmes, with the potential to substantially increase whole-canopy carbon assimilation and contribute to crop yield potential. Rubisco activation may be the main physiological process that will allow us to achieve such a goal. In this study, we assessed the phenotype of Rubisco activation rate in a doubled haploid (DH) barley mapping population [131 lines from a Yerong/Franklin (Y/F) cross] after a switch from moderate to saturating light.

Can hydraulic design explain patterns of leaf water isotopic enrichment in C plants?

H O enrichment develops when leaves transpire, but an accurate generalized mechanistic model has proven elusive. We hypothesized that leaf hydraulic architecture may affect the degree to which gradients in H O develop within leaves, influencing bulk leaf stable oxygen isotope enrichment (Δ ) and the degree to which the Péclet effect is relevant in leaves. Leaf hydraulic design predicted the relevance of a Péclet effect to Δ in 19 of the 21 species tested.

No evidence of homeostatic regulation of leaf temperature in Eucalyptus parramattensis trees: integration of CO flux and oxygen isotope methodologies.

Thermoregulation of leaf temperature (T ) may foster metabolic homeostasis in plants, but the degree to which T is moderated, and under what environmental contexts, is a topic of debate. Isotopic studies inferred the temperature of photosynthetic carbon assimilation to be a constant value of c. 20°C; by contrast, leaf biophysical theory suggests a strong dependence of T on environmental drivers.

Cell and chloroplast anatomical features are poorly estimated from 2D cross-sections.

Leaf function is intimately related to the size, shape, abundance and position of cells and chloroplasts. Anatomy has long been assessed and quantified in two dimensions with 3D structure inferred from 2D micrographs. Serial block face scanning electron microscopy (SBF-SEM) was used to reconstruct 95 cells and 1173 chloroplasts from three wheat and nine chickpea leaves (three samples each from three chickpea genotypes).

The role of leaf water potential in the temperature response of mesophyll conductance.

Variation in temperature (T) is usually accompanied by changes in leaf water potential (Ψ ), which may influence mesophyll conductance (g ). However, the effects of Ψ on g have not yet been considered in models of the g response to temperature. Temperature responses of g and Ψ and the response of g to Ψ were studied in rice (Oryza sativa) and wheat (Triticum aestivum), and then an empirical model of Ψ was incorporated into an existing g -T model.

The temperature response of mesophyll conductance, and its component conductances, varies between species and genotypes.

The temperature response of mesophyll conductance to CO diffusion (g) has been shown to vary considerably between species but remains poorly understood. Here, we tested the hypothesis that increases in chloroplast surface area with increasing temperature, due to the formation of chloroplast protrusions, caused observed positive responses of g to temperature. We found no evidence of chloroplast protrusions.

The response of mesophyll conductance to short- and long-term environmental conditions in chickpea genotypes.

. Mesophyll conductance ( ) has been shown to vary between genotypes of a number of species and with growth environments, including nitrogen availability, but understanding of variability in legumes is limited. We might expect in legumes to respond differently to limited nitrogen availability, due to their ability to fix atmospheric N.

Embracing 3D Complexity in Leaf Carbon-Water Exchange.

Leaves are a nexus for the exchange of water, carbon, and energy between terrestrial plants and the atmosphere. Research in recent decades has highlighted the critical importance of the underlying biophysical and anatomical determinants of CO and HO transport, but a quantitative understanding of how detailed 3D leaf anatomy mediates within-leaf transport has been hindered by the lack of a consensus framework for analyzing or simulating transport and its spatial and temporal dynamics realistically, and by the difficulty of measuring within-leaf transport at the appropriate scales. We discuss how recent technological advancements now make a spatially explicit 3D leaf analysis possible, through new imaging and modeling tools that will allow us to address long-standing questions related to plant carbon-water exchange.

Leaf day respiration: low CO flux but high significance for metabolism and carbon balance.

Contents 986 I. 987 II. 987 III.

Understanding regulation of leaf internal carbon and water transport using online stable isotope techniques.

83 I. 83 II. 84 III.

The response of mesophyll conductance to nitrogen and water availability differs between wheat genotypes.

Increased mesophyll conductance (gm) has been suggested as a target for selection for high productivity and high water-use efficiency in crop plants, and genotypic variability in gm has been reported in several important crop species. However, effective selection requires an understanding of how gm varies with growth conditions, to ensure that the ranking of genotypes is consistent across environments. We assessed the genotypic variability in gm and other leaf gas exchange traits, as well as growth and biomass allocation for six wheat genotypes under different water and nitrogen availabilities.

Leaf vein fraction influences the Péclet effect and O enrichment in leaf water.

The process of evaporation results in the fractionation of water isotopes such that the lighter O isotope preferentially escapes the gas phase leaving the heavier O isotope to accumulate at the sites of evaporation. This applies to transpiration from a leaf with the degree of fractionation dependent on a number of environmental and physiological factors that are well understood. Nevertheless, the O enrichment of bulk leaf water is often less than that predicted for the sites of evaporation.

Leaf water oxygen isotope measurement by direct equilibration.

The oxygen isotope composition of leaf water imparts a signal to a range of molecules in the atmosphere and biosphere, but has been notoriously difficult to measure in studies requiring a large number of samples as a consequence of the labour-intensive extraction step. We tested a method of direct equilibration of water in fresh leaf samples with CO2 , and subsequent oxygen isotope analysis on an optical spectrometer. The oxygen isotope composition of leaf water measured by the direct equilibration technique was strongly linearly related to that of cryogenically extracted leaf water in paired samples for a wide range of species with differing anatomy, with an R(2) of 0.

Online CO2 and H2 O oxygen isotope fractionation allows estimation of mesophyll conductance in C4 plants, and reveals that mesophyll conductance decreases as leaves age in both C4 and C3 plants.

Mesophyll conductance significantly, and variably, limits photosynthesis but we currently have no reliable method of measurement for C4 plants. An online oxygen isotope technique was developed to allow quantification of mesophyll conductance in C4 plants and to provide an alternative estimate in C3 plants. The technique is compared to an established carbon isotope method in three C3 species.