Ray Leuning

Bio: Ray Leuning is an academic researcher from CSIRO Marine and Atmospheric Research. The author has contributed to research in topics: Eddy covariance & Sensible heat. The author has an hindex of 64, co-authored 131 publications receiving 19297 citations. Previous affiliations of Ray Leuning include Commonwealth Scientific and Industrial Research Organisation & Cooperative Research Centre.

Correction of flux measurements for density effects due to heat and water vapour transfer

Abstract: When the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived. If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre-dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required. If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are required. These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.

A critical appraisal of a combined stomatal-photosynthesis model for C3 plants

Abstract: Gas-exchange measurements on Eucalyptus grandis leaves and data extracted from the literature were used to test a semi-empirical model of stomatal conductance for CO 2 , g sc = g 0 + a 1 /[(c s −Γ)(1 + D s /D 0 )], where A is the assimilation rate; D s and c s are the humidity deficit and the CO 2 concentration at the leaf surface, respectively; g 0 is the conductance as A → 0 when leaf irradiance → 0; and D 0 and a 1 are empirical coefficients. This model is a modified version of g sc = a 1 A h s /c s first proposed by Ball, Woodrow & Berry (1987, in Progress in Photosynthesis Research, Martinus Mijhoff, Publ., pp. 221-224), in which h s is relative humidity. Inclusion of the CO 2 compensation point, Γ, improved the behaviour of the model at low values of c s , while a hyperbolic function of D s for humidity response correctly accounted for the observed hyperbolic and linear variation of g sc and c i /c s as a function of D s , where c i is the intercellular CO 2 concentration. In contrast, use of relative humidity as the humidity variable led to predictions of a linear decrease in g sc and a hyperbolic variation in c i /c s as a function of D s , contrary to data from E. grandis leaves. The revised model also successfully described the response of stomata to variations in A, D s and c s for published responses of the leaves of several other species. Coupling of the revised stomatal model with a biochemical model for photosynthesis of C 3 plants synthesizes many of the observed responses of leaves to light, humidity deficit, leaf temperature and CO 2 concentration. Best results are obtained for well-watered plants

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

Abstract: The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

Relationships among Maximum Stomatal Conductance, Ecosystem Surface Conductance, Carbon Assimilation Rate, and Plant Nitrogen Nutrition: A Global Ecology Scaling Exercise

Abstract: This review provides a theoretical framework and global maps for relations between nitrogen-(N)-nutrition and stomatal conductance, gs' at the leaf scale and flUXe!1 of water vapor and carbon dioxide at the canopy scale. This theory defines the boundaries for observed rates of maximum surface conductance, Gsmax, and its relation to leaf area index, A, within a range of observed max­ imum stomatal conductances. gsmax. Soil evaporation compensates for the reduced contribution of plants to total ecosystem water loss at A < 4. Thus, Gsmax is fairly independent of changes in A for a broad range of vegetation types. The variation of Gsmax within these boundaries can be explained by effects of plant nutrition on stomatal conductance via effects on assimilation. Relations are established for the main global vegetation types among (i) maximum stomatal conductance and leaf nitrogen concentrations with a slope of 0.3 mm s-I per mg N g-I, (ii) maximum surface conductance and stomatal conductance with a slope of 3 mm s-I in G per mm S-I in g, and (iii) maximum surface CO2 uptake and surface conductance with a slope of 1 /lmol m-2 s-1 in A per mm S-1 in G. Based on the distribution of leaf nitrogen in different vegetation types, predictions are made for maximum surface conductance and assimilation of carbon dioxide at a global scale. The review provides a basis for modeling and predicting feedforward and feedback effects between terres­ trial vegetation and global climate.

The worldwide leaf economics spectrum

Abstract: Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.

Mechanisms of plant survival and mortality during drought: why do some plants survive while others succumb to drought?

Abstract: Summary Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, pre- diction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric

A handbook of protocols for standardised and easy measurement of plant functional traits worldwide

Abstract: There is growing recognition that classifying terrestrial plant species on the basis of their function (into 'functional types') rather than their higher taxonomic identity, is a promising way forward for tackling important ecological questions at the scale of ecosystems, landscapes or biomes. These questions include those on vegetation responses to and vegetation effects on, environmental changes (e.g. changes in climate, atmospheric chemistry, land use or other disturbances). There is also growing consensus about a shortlist of plant traits that should underlie such functional plant classifications, because they have strong predictive power of important ecosystem responses to environmental change and/or they themselves have strong impacts on ecosystem processes. The most favoured traits are those that are also relatively easy and inexpensive to measure for large numbers of plant species. Large international research efforts, promoted by the IGBP–GCTE Programme, are underway to screen predominant plant species in various ecosystems and biomes worldwide for such traits. This paper provides an international methodological protocol aimed at standardising this research effort, based on consensus among a broad group of scientists in this field. It features a practical handbook with step-by-step recipes, with relatively brief information about the ecological context, for 28 functional traits recognised as critical for tackling large-scale ecological questions.