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Mesophyll conductance (gm) is known to affect plant photosynthesis. However, gm is rarely explicitly considered in land surface models (LSMs), with the consequence that its role in ecosystem and large‐scale carbon and water fluxes is poorly understood. In particular, the different magnitudes of gm across plant functional types (PFTs) are expected to cause spatially divergent vegetation responses to elevated CO2 concentrations. Here, an extensive literature compilation of gm across major vegetation types is used to parameterize an empirical model of gm in the LSM JSBACH and to adjust photosynthetic parameters based on simulated An − Ci curves. We demonstrate that an explicit representation of gm changes the response of photosynthesis to environmental factors, which cannot be entirely compensated by adjusting photosynthetic parameters. These altered responses lead to changes in the photosynthetic sensitivity to atmospheric CO2 concentrations which depend both on the magnitude of gm and the climatic conditions, particularly temperature. We then conducted simulations under ambient and elevated (ambient + 200 μmol/mol) CO2 concentrations for contrasting ecosystems and for historical and anticipated future climate conditions (representative concentration pathways; RCPs) globally. The gm‐explicit simulations using the RCP8.5 scenario resulted in significantly higher increases in gross primary productivity (GPP) in high latitudes (+10% to + 25%), intermediate increases in temperate regions (+5% to + 15%), and slightly lower to moderately higher responses in tropical regions (−2% to +5%), which summed up to moderate GPP increases globally. Similar patterns were found for transpiration, but with a lower magnitude. Our results suggest that the effect of an explicit representation of gm is most important for simulated carbon and water fluxes in the boreal zone, where a cold climate coincides with evergreen vegetation. [ABSTRACT FROM AUTHOR]

We investigated the fate of carbon dioxide (CO2) absorbed by roots or internally produced by respiration using gas exchange and stable isotopic labeling. CO2 efflux from detached leaves supplied with bicarbonate/CO2 solutions was followed over six cycles. CO2 effluxes were detected when bicarbonate solution at high pH was used, corresponding to 71–85% of the expected efflux. No CO2 efflux was detected when CO2 solutions at low pH were used but CO2 efflux was subsequently detected as soon as bicarbonate solutions at high pH were supplied. By sealing the leaf and petiole in a plastic bag to reduce diffusion to the atmosphere, a small CO2 efflux signal (14–30% of the expected efflux) was detected suggesting that CO2 in the xylem stream can readily escape to the atmosphere before reaching the leaf. When the root‐zones of intact plants were exposed to CO2 solutions, a significant efflux from leaf surface was observed (13% of the expected efflux). However, no signal was detected when roots were exposed to a high pH bicarbonate solution. Isotopic tracer experiments confirmed that CO2 supplied to the root‐zone was transported through the plant and was readily lost to the atmosphere. However, little 13C moved to the shoot when roots were exposed to bicarbonate solutions at pH 8, suggesting that bicarbonate does not pass into the xylem. [ABSTRACT FROM AUTHOR]

This article addresses the lack of attention paid to research on the development of Indigenous sporting expertise from a socio-cultural perspective. It inquires into the role that informal games played in the development of Australian Indigenous AFL and NRL players up to the age of thirteen. The study adopted a combined narrative inquiry and constructivist grounded theory methodology. The study highlighted to central role that informal games played in the development of expertise and a distinctive Aboriginal style of play shaped by Indigenous culture. This article suggests the central role that informal games shaped by Aboriginal culture played in the development of expertise and an Aboriginal style of play. It also suggests the need for coaching beyond Indigenous players to consider the use of games in training regimes. [ABSTRACT FROM AUTHOR]

This article reports on an ongoing study that investigates the development of expertise in rugby league and Australian football by Indigenous Australians as a socially and culturally situated process of learning. Focused on the sampling phase of the Development Model of Participation in Sport (6–12 years of age), it combines narrative inquiry and grounded theory methodologies to identify the important role that participation in a range of different sports and in informal games plays in the participants’ development of expertise, as a process of socialisation. [ABSTRACT FROM PUBLISHER]

Chl fluorescence has been used widely to calculate photosynthetic electron transport rates. Portable photosynthesis instruments allow for combined measurements of gas exchange and Chl fluorescence. We analyzed the influence of spectral quality of actinic light on Chl fluorescence and the calculated electron transport rate, and compared this with photosynthetic rates measured by gas exchange in the absence of photorespiration. In blue actinic light, the electron transport rate calculated from Chl fluorescence overestimated the true rate by nearly a factor of two, whereas there was closer agreement under red light. This was consistent with the prediction made with a multilayer leaf model using profiles of light absorption and photosynthetic capacity. Caution is needed when interpreting combined measurements of Chl fluorescence and gas exchange, such as the calculation of CO2 partial pressure in leaf chloroplasts. [ABSTRACT FROM AUTHOR]

We examined the effects of leaf temperature on the estimation of maximal Rubisco capacity ( V cmax) from gas exchange measurements of wheat leaves using a C3 photosynthesis model. Cultivars of spring wheat ( Triticum aestivum (L)) and triticale ( X Triticosecale Wittmack) were grown in a greenhouse or in the field and measured at a range of temperatures under controlled conditions in a growth cabinet (2 and 21% O2) or in the field using natural diurnal variation in temperature, respectively. Published Rubisco kinetic constants for tobacco did not describe the observed CO2 response curves well as temperature varied. By assuming values for the Rubisco Michaelis-Menten constants for CO2 ( K c) and O2 ( K o) at 25 °C derived from tobacco and the activation energies of V cmax from wheat and respiration in the light, R d , from tobacco, we derived activation energies for K c and K o (93.7 and 33.6 kJ mol−1, respectively) that considerably improved the fit of the model to observed data. We confirmed that temperature dependence of dark respiration for wheat was well described by the activation energy for R d from tobacco. The new parameters improved the estimation of V cmax under field conditions, where temperatures increased through the day. [ABSTRACT FROM AUTHOR]

The role of some aquaporins as CO2 permeable channels has been controversial. Low CO2 permeability of plant membranes has been criticized because of unstirred layers and other limitations. Here we measured both water and CO2 permeability ( Pos, PCO2) using stopped flow on plasma membrane vesicles (pmv) isolated from Pisum sativum (pea) and Arabidopsis thaliana leaves. We excluded the chemical limitation of carbonic anhydrase (CA) in the vesicle acidification technique for PCO2 using different temperatures and CA concentrations. Unstirred layers were excluded based on small vesicle size and the positive correlation between vesicle diameter and PCO2. We observed high aquaporin activity ( Pos 0.06 to 0.22 cm s−1) for pea pmv based on all the criteria for their function using inhibitors and temperature dependence. Inhibitors of Pos did not alter PCO2. PCO2 ranged from 0.001 to 0.012 cm s−1 (mean 0.0079 + 0.0007 cm s−1) with activation energy of 30.2 kJ mol−1. Intrinsic variation between pmv batches from normally grown or stressed plants revealed a weak ( R2 = 0.27) positive linear correlation between Pos and PCO2. Despite the low PCO2, aquaporins may facilitate CO2 transport across plasma membranes, but probably via a different pathway than for water. [ABSTRACT FROM AUTHOR]

Aquaporins are channel proteins that function to increase the permeability of biological membranes. In plants, aquaporins are encoded by multigene families that have undergone substantial diversification in land plants. The plasma membrane intrinsic proteins (PIPs) subfamily of aquaporins is of particular interest given their potential to improve plant water relations and photosynthesis. Flowering plants have between 7 and 28 PIP genes. Their expression varies with tissue and cell type, through development and in response to a variety of factors, contributing to the dynamic and tissue specific control of permeability. There are a growing number of PIPs shown to act as water channels, but those altering membrane permeability to CO2 are more limited. The structural basis for selective substrate specificities has not yet been resolved, although a few key amino acid positions have been identified. Several regions important for dimerization, gating and trafficking are also known. PIP aquaporins assemble as tetramers and their properties depend on the monomeric composition. PIPs control water flux into and out of veins and stomatal guard cells and also increase membrane permeability to CO2 in mesophyll and stomatal guard cells. The latter increases the effectiveness of Rubisco and can potentially influence transpiration efficiency. [ABSTRACT FROM AUTHOR]

Concentrations of [sup.18.O] and deuterium in ground waters beneath the Hanford Reservation, Washington State, suggest that the meteoric waters recharging the basalt aquifers have been progressively depleted in these isotopes since at least Pleistocene time. This conclusion is supported by oxygen-isotope analyses of low-temperature secondary minerals filling vugs and fractures in the basalts, which are used to approximate the [sup.18.O] content of ground water at the time the mineral assemblage formed. A fossil profile of [[delta]sup.18.O] values projected for ground water in a 1500 m vertical section beneath the reservation suggests that the vertical mixing of shallow and deep ground water indicated by present-day hydrochemical data was also occurring during Neogene time. These data also suggest that a unidirectional depletion of [sup.18.O] and deuterium recorded in Pleistocene ground waters may have extended considerably further back in time. This shift is tentatively attributed to the orographic depletion of [sup.18.O] associated with the progressive uplift of the Cascade Range since the middle Miocene.