Plant responses to decadal scale increments in atmospheric CO2 concentration: comparing two stomatal conductance sampling methods

There are several lines of evidence suggesting that the vast majority of C3 plants respond to elevated atmospheric CO2 by decreasing their stomatal conductance (gs). However, in the majority of CO2 enrichment studies, the response to elevated CO2 are tested between plants grown under ambient (380–420 ppm) and high (538–680 ppm) CO2 concentrations and measured usually at single time points in a diurnal cycle. We investigated gs responses to simulated decadal increments in CO2 predicted over the next 4 decades and tested how measurements of gs may differ when two alternative sampling methods are employed (infrared gas analyzer [IRGA] vs. leaf porometer). We exposed Populus tremula, Popolus tremuloides and Sambucus racemosa to four different CO2 concentrations over 126 days in experimental growth chambers at 350, 420, 490 and 560 ppm CO2; representing the years 1987, 2025, 2051, and 2070, respectively (RCP4.5 scenario). Our study demonstrated that the species respond non-linearly to increases in CO2 concentration when exposed to decadal changes in CO2. Under natural conditions, maximum operational gs is often reached in the late morning to early afternoon, with a mid-day depression around noon. However, we showed that the daily maximum gs can, in some species, shift later into the day when plants are exposed to only small increases (70 ppm) in CO2. A non-linear decreases in gs and a shifting diurnal stomatal behavior under elevated CO2, could affect the long-term daily water and carbon budget of many plants in the future, and therefore alter soil–plant–atmospheric processes.Irish Research CouncilScience Foundation Irelan

Wicking and evaporation of liquids in porous wicks: a simple analytical approach to optimization of wick design

Wicking and evaporation of volatile liquids in porous, cylindrical wicks is investigated where the goal is to model, using simple analytical expressions, the effects of variation in geometrical parameters of a wick, such as porosity, height and bead-size, on the wicking and evaporation processes, and find optimum design conditions. An analytical sharp-front flow model involving the single-phase Darcy’s law is combined with analytical expressions for the capillary suction pressure and wick permeability to yield a novel analytical approach for optimizing wick parameters. First, the optimum beadradius and porosity maximizing the wicking flow-rate are estimated. Later, after combining the wicking model with evaporation from the wick-top, the allowable ranges of bead-radius, height and porosity for ensuring full saturation of the wick are calculated. The analytical results are demonstrated using some highly volatile alkanes in a polycarbonate sintered wick

Application of the Lattice-Boltzmann method to the modeling of population blob dynamics in 2D porous domains

AbstractIn the present paper, the Lattice-Boltzmann method is employed for the simulation of immiscible two-phase flow through a 2D porous domain when the volume fraction of the non-wetting phase is relatively low and thus it flows in the form of disconnected blobs. The flow problem is solved using an immiscible two-phase LB model where interfacial forces are expressed in terms of the chemical potential through the Gibbs–Duhem equation. We study the population dynamics of the non-wetting fluid blobs, namely the temporal evolution of the average blob size, with respect to the applied body force and the wetting phase volume fraction. Our results show that the system reaches a “steady state” where the average values of the studied parameters, such as the superficial velocities of both phases, and the number and size distribution of the blobs remain practically constant in time, although the temporal fluctuations around average values may be significant. We show that the average volume of the blobs decreases (and the population of the blobs increases) as the body force increases, namely as the viscous forces become dominant over capillary forces. The effect of the wetting volume fraction on the number of the blobs is more complex; as the wetting volume fraction decreases at constant body force, the blobs cover larger areas within the pore space producing larger pressure gradients and the dynamic breakup of blobs intensifies resulting in increasing blob numbers. However, below a critical value of the wetting volume fraction, the number of blobs begins to decrease and the non-wetting phase begins to span the entire pore network

Was atmospheric CO2 capped at 1000ppm over the past 300 million years?

AbstractAtmospheric carbon dioxide concentration has shifted dynamically over the Phanerozoic according to mass balance models and the majority of proxy estimates. A new paleo-CO2 proxy method underpinned by mechanistic understanding of plant stomatal, isotopic and photosynthetic responses to CO2 has provocatively claimed that maximum paleoatmospheric CO2 was capped at 1000ppm for the majority of the past 300 million years. Here we evaluate the robustness of the new paleo-proxy CO2 model by testing its sensitivity to initial parameterization and to scaling factors employed to estimate paleophysiological function from anatomical and morphological traits. A series of sensitivity analyses find that the model is robust to modification in some of the constants employed, such as CO2 compensation point and mesophyll conductance, resulting in variability in paleo-CO2 estimates which are already accounted for in the error propagation of the model. We demonstrate high sensitivity in the model to key input parameters such as initial fossil plant assimilation rate, termed A0 and scaling factors used to estimate stomatal conductance from measurements of fossil stomata. Incorrect parameterization of A0 has resulted in under estimation of pCO2 by as much as 600ppm. Despite these uncertainties, our analysis highlights that the new mechanistic paleo-CO2 proxy of Franks et al. (2014) has significant potential to derive robust and more accurate CO2 estimates from fossil plant stomata, as long as parameterization of A0 is strongly justified with species appropriate morphological and anatomical data. We highlight methods that can be used to improve current estimates of fossil plant assimilation rates, reduce uncertainty associated with implementation of the Franks et al. (2014) model and importantly add to understanding of patterns of plant productivity over the Phanerozoic, for which there currently is no consensus

A Meshless Solution to the Vibration Problem of Cylindrical Shell Panels

The Meshless Analog Equation Method (MAEM) is a purely mesh-free method for solving partial differential equations (PDEs). In the present study, the method is applied to the dynamic analysis of cylindrical shell structures. Based on the principle of the analog equation, MAEM converts the three governing partial differential equations in terms of displacements into three uncoupled substitute equations, two of 2nd order (Poisson's) and one of 4th order (biharmonic), with fictitious sources. The fictitious sources are represented by series of Radial Basis Functions (RBFs) of multiquadric (MQ) type, and the substitute equations are integrated. The integration allows the representation of the displacements by new RBFs, which approximate the displacements accurately and also their derivatives involved in the governing equations. By inserting the approximate solution in the governing differential equations and taking into account the boundary and initial conditions and collocating at a predefined set of mesh-free nodal points, we obtain a system of ordinary differential equations of motion. The solution of the system gives the unknown time-dependent series coefficients and the solution to the original problem. Several shell panels are analyzed using the method, and the numerical results demonstrate its efficiency and accuracy

Impact of spatially correlated pore-scale heterogeneity on drying porous media

We study the effect of spatially-correlated heterogeneity on isothermal drying of porous media. We combine a minimal pore-scale model with microfluidic experiments with the same pore geometry. Our simulated drying behavior compares favorably with experiments, considering the large sensitivity of the emergent behavior to the uncertainty associated with even small manufacturing errors. We show that increasing the correlation length in particle sizes promotes preferential drying of clusters of large pores, prolonging liquid connectivity and surface wetness and thus higher drying rates for longer periods. Our findings improve our quantitative understanding of how pore-scale heterogeneity impacts drying, which plays a role in a wide range of processes ranging from fuel cells to curing of paints and cements to global budgets of energy, water and solutes in soils

Consistent Relationship between Field-Measured Stomatal Conductance and Theoretical Maximum Stomatal Conductance in C₃ Woody Angiosperms in Four Major Biomes

Premise of research. Understanding the relationship between field-measured operating stomatal conductance (gop) and theoretical maximum stomatal conductance (gmax), calculated from stomatal density and geometry, provides an important framework that can be used to infer leaf-level gas exchange of historical, herbarium, and fossil plants. To date, however, investigation of the nature of the relationship between gop and theoretical gmax remains limited to a small number of experiments on relatively few taxa and is virtually undefined for plants in natural ecosystems. Methodology. We used the gop measurements of 74 species and 35 families across four biomes from a published contemporary data set of field-measured leaf-level stomatal conductance in woody angiosperms and calculated the theoretical gmax from the same leaves to investigate the relationship between gop and gmax across multiple species and biomes and determine whether such relationships are widely conserved. Pivotal results. We observed significant relationships between gop and gmax, with consistency in the gop ∶ gmax ratio across biomes, growth habits (shrubs and trees), and habitats (open canopy and understory subcanopy). An overall mean gop ∶ gmax ratio of 0.26 ± 0.11 (mean ± SD) was observed. The consistently observed gop ∶ gmax ratio in this study strongly agrees with previous hypotheses that an ideal gop ∶ gmax ratio exists. Conclusions. These results build substantially on previous studies by presenting a new reference for a consistent gop ∶ gmax ratio across many levels and offer great potential to enhance paleoclimate proxies and vegetation-climate models alike

APPLICATION OF ADJOINT CMAQ CHEMICAL TRANSPORT MODEL IN THE ATHENS GREATER AREA: SENSITIVITIES STUDY ON OZONE CONCENTRATIONS

An operational meteorology and air quality forecasting system is currently under development by the Environmental Research Laboratory of NCSR “Demokritos”. The system is based on the meteorological model MM5, the in-house EMISLAB emissions processing system and the chemical transport model CMAQ. It is configured to apply on the Greater Athens Area with a 4-domains nested configuration focusing on a high spatial resolution (1x1 km2) inner domain. The system produces meteorological and air quality predictions for a 72-hours time horizon with 1 hour time step. This paper uses the output of the operational system to apply the CMAQ adjoint for ozone sensitivity calculations, focusing for the two days of 18 and 19 July 2005. In the current study, the calculated ground level ozone concentrations at certain defined locations and times are considered as the “response functional”. Sensitivities of the response functional with respect to the state variables (species concentrations on the grid points and species emissions, e.g., NOX, CO, VOCs) are calculated by running the adjoint model backwards in time (reverse mode). The distribution of the sensitivities in the computational domain, obtained for different times, provides essential information for the analysis: isosurfaces of sensitivities delineate influence regions, i.e., areas where perturbations in some concentrations will result in significant changes in the ozone concentrations in the area of interest at the final time

Evaporation in capillary porous media at the perfect piston-like invasion limit: Evidence of non-local equilibrium effects

The classical continuum modeling of evaporation in capillary porous media is revisited from pore network simulations of the evaporation process. The computed moisture diffusivity is characterized by a minimum corresponding to the transition between liquid and vapor transport mechanisms confirming previous interpretations. Also the study suggests an explanation for the scattering generally observed in the moisture diffusivity obtained from experimental data. The pore network simulations indicate a noticeable nonlocal equilibrium effect leading to a new interpretation of the vapor pressure‐saturation relationship classically introduced to obtain the one‐equation continuum model of evaporation. The latter should not be understood as a desorption isotherm as classically considered but rather as a signature of a nonlocal equilibrium effect. The main outcome of this study is therefore that nonlocal equilibrium two‐equation model must be considered for improving the continuum modeling of evaporation

Rising CO₂ drives divergence in water use efficiency of evergreen and deciduous plants

Intrinsic water use efficiency (iWUE), defined as the ratio of photosynthesis to stomatal conductance, is a key variable in plant physiology and ecology. Yet, how rising atmospheric CO2 concentration affects iWUE at broad species and ecosystem scales is poorly understood. In a field-based study of 244 woody angiosperm species across eight biomes over the past 25 years of increasing atmospheric CO2 (~45 ppm), we show that iWUE in evergreen species has increased more rapidly than in deciduous species. Specifically, the difference in iWUE gain between evergreen and deciduous taxa diverges along a mean annual temperature gradient from tropical to boreal forests and follows similar observed trends in leaf functional traits such as leaf mass per area. Synthesis of multiple lines of evidence supports our findings. This study provides timely insights into the impact of Anthropocene climate change on forest ecosystems and will aid the development of next-generation trait-based vegetation models