Use of Heating Configuration to Control Marangoni Circulation during Droplet Evaporation

The present work presents a numerical study of the evaporation of a sessile liquid droplet deposited on a substrate and subjected to different heating configurations. The physical formulation accounts for evaporation, the Marangoni effect, conductive transfer in the support, radiative heating, and diffusion-convection in the droplet itself. The moving interface is solved using the Arbitrary Lagrangian-Eulerian (ALE) method. Simulations were performed using COMSOL Multiphysics. Different configurations were performed to investigate the effect of the heating conditions on the shape and intensity of the Marangoni circulations. A droplet can be heated by the substrate (different natures and thicknesses were tested) and/or by a heat flux supplied at the top of the droplet. The results show that the Marangoni flow can be controlled by the heating configuration. An upward Marangoni flow was obtained for a heated substrate and a downward Marangoni flow for a flux imposed at the top of the droplet. Using both heat sources generated two vortices with an upward flow from the bottom and a downward flow from the top. The position of the stagnation zone depended on the respective intensities of the heating fluxes. Controlling the circulation in the droplet might have interesting applications, such as the control of the deposition of microparticles in suspension in the liquid, the deposition of the solved constituent, and the enhancement of the evaporation rate

The Dexi-SH* model for a multivariate assessment of agro-ecological sustainability of dairy grazing systems

Dexi-SH* is an ex ante multivariate model for assessing the sustainability of dairy cows grazing systems. This model is composed of three sub-models that evaluate the impact of the systems on: (i) biotic resources; (ii) abiotic resources, and (iii) pollution risks. The structuring of the hierarchical tree was inspired by that of the Masc model. The choice of criteria and their aggregation modalities were discussed within a multi-disciplinary group of scientists. For each cluster, a utility function was established in order to determine weighting and priority functions between criteria. The model can take local and regional conditions and standards into account by adjusting criterion categories to the agroecological context, and the specific views of the decision makers by changing the weighting of criteria

Crops yield increase under water limited conditions: review of recent physiological advances in soybean genetic improvement.

Due to future requirements for more crop production there will be greater needs to increase yields for crops subjected to water deficits. In recent years, substantial progress has been made with soybean (Glycine max (L.) Merr.) in understanding the water deficit limitation on yield using model assessments, physiological investigations, and plant breeding. This knowledge has been applied in developing higher yielding genotypes. This review examines physiological options and genetic advances made with soybean as possible guides for studies with other crops. Three approaches exist for minimizing the negative impact of water deficit on crop production: (1) conserve soil water, (2) access more water, and (3) overcome special water deficit sensitivities. Water conservation in soybean has been achieved by exploiting a genotype that has limited hydraulic conductance in its leaves. A consequence of this trait is that transpiration rate is limited at times of high vapor pressure deficit resulting in soil water conservation for use later in the season. Acquisition of more water is most likely to be achieved by greater depth of rooting or greater root length density deep in the soil. Although promising genetic variability has been identified, breeding efforts for these rooting traits are still required. A special sensitivity in soybean that results in a major limitation in yield is a decrease in symbiotic nitrogen fixation rate with only modest soil drying. Germplasm has now been released that results in increased yields due to a capacity for sustained nitrogen fixation with drying soil. This review highlights that soybean investigations combining physiological investigations, simulations studies, and field-based phenotyping of traits have resulted in the identification of genotypes with increased yield potential in water deficit environment

Potential involvement of root auxins in drought tolerance by modulating nocturnal and daytime water use in wheat

Background and Aims The ability of wheat genotypes to save water by reducing their transpiration rate (TR) at times of the day with high vapour pressure deficit (VPD) has been linked to increasing yields in terminal drought environments. Further, recent evidence shows that reducing nocturnal transpiration (TRN) could amplify water saving. Previous research indicates that such traits involve a root-based hydraulic limitation, but the contribution of hormones, particularly auxin and abscisic acid (ABA), has not been explored to explain the shoot–root link. In this investigation, based on physiological, genetic and molecular evidence gathered on a mapping population, we hypothesized that root auxin accumulation regulates whole-plant water use during both times of the day. • Methods Eight double-haploid lines were selected from a mapping population descending from two parents with contrasting water-saving strategies and root hydraulic properties. These spanned the entire range of slopes of TR responses to VPD and TRN encountered in the population. We examined daytime/night-time auxin and ABA contents in the roots and the leaves in relation to hydraulic traits that included whole-plant TR, plant hydraulic conductance (KPlant), slopes of TR responses to VPD and leaf-level anatomical traits. • Key Results Root auxin levels were consistently genotype-dependent in this group irrespective of experiments and times of the day. Daytime root auxin concentrations were found to be strongly and negatively correlated with daytime TR, KPlant and the slope of TR response to VPD. Night-time root auxin levels significantly and negatively correlated with TRN. In addition, daytime and night-time leaf auxin and ABA concentrations did not correlate with any of the examined traits. • Conclusions The above results indicate that accumulation of auxin in the root system reduces daytime and night-time water use and modulates plant hydraulic properties to enable the expression of water-saving traits that have been associated with enhanced yields under drought

Differential sensitivities of transpiration to evaporative demand and soil water deficit among wheat elite cultivars indicate different strategies for drought tolerance

In order to satisfy increasing wheat demands, scaling up wheat production will require boosting yield in suboptimal, drought-prone areas. Under rain-fed environments, one promising option is the identification of traits allowing for soil water conservation until the next rain episode. This can be achieved either by limiting transpiration rate (TR) of the crop to a maximum level when atmospheric drought (or VPD for vapor pressure deficit) is too high or by decreasing stomata conductance earlier in the soil drying cycle. Although promising, those strategies were never explored in wheat. A first objective of this study was to investigate the extent of the genetic variability of TR sensitivity to both VPD and soil water deficit among a group of eight elite wheat lines, which are cultivated under south Australian conditions. Those consisted of seven differentially drought-adapted lines and one check cultivar. TR responses to VPD were highly variable among genotypes, with six lines displaying a breakpoint in their TR response to VPD that ranged from 2.4 to 3.9. kPa, while two others had their TR increasing linearly as VPD increased. Transpiration response to a progressively decreasing fraction of transpirable soil water (FTSW) was investigated in those lines. A significant genetic variability in the responses among genotypes was observed. They revealed different FTSW thresholds at which transpiration started to decrease at levels ranging from 0.43 to 0.52, and different slopes for the decrease. A second objective was to investigate the existence of phenotypic correlations between the parameters characterizing transpiration sensitivities to both sources of water deficit (i.e., VPD and FTSW). Significant correlations were observed revealing that genotypes with conservative water use in their response to high VPD were also conservative in response to decreasing FTSW and that the drought tolerance of other lines might stem from an apposite strategy, invoking decreased sensitivity of TR to both sources of drought. Those findings provide new options for breeding drought tolerant lines based on this germplasm. © 2012 Elsevier B.V.

Transpiration response of "slow-wilting" and commercial soybean (glycine max (L) Merr.)genotypes to three aquaporin inhibitors under high evaporative demand

The slow-wilting soybean [Glycine max (L.) Merr.] genotype, PI 416937, exhibits a limiting leaf hydraulic conductance for transpiration rate (TR) under high vapour pressure deficit (VPD). This genotype has a constant TR at VPD greater than 2 kPa, which may be responsible for its drought tolerance as a result of soil water conservation. However, the exact source of the hydraulic limitation between symplastic and apoplastic water flow in the leaf under high VPD conditions are not known for PI 416937. A comparison was made in the TR response to aquaporin (AQP) inhibitors between PI 416937 and N01-11136, a commercial genotype that has a linear TR response to VPD in the 1–3.5 kPa range. Three AQP inhibitors were tested: cycloheximide (CHX, a de novo synthesis inhibitor), HgCl2, and AgNO3. Dose–response curves for the decrease in TR following exposure to each inhibitor were developed. Decreases in TR of N01-11136 following treatment with inhibitors were up to 60% for CHX, 82% for HgCl2, and 42% for AgNO3. These results indicate that the symplastic pathway terminating in the guard cells of these soybean leaves may be at least as important as the apoplastic pathway for water flow in the leaf under high VPD. While the decrease in TR for PI 416937 was similar to that of N01-11136 following exposure to CHX and HgCl2, TR of PI 416937 was insensitive to AgNO3 exposure. These results indicate the possibility of a lack of a Ag-sensitive leaf AQP population in the slowwilting line, PI 416937, and the presence of such a population in the commercial line, N01-11136

Genetic variability of transpiration response of soybean (Glycine max [L.] Merr.) plants to leaf hydraulic conductance inhibitor AgNO3

Transpiration rate (TR) of a slow-wilting soybean [Glycine max (L.) Merr.] line, PI 416937, is constant with increasing vapor pressure deficit (VPD) at high VPD (> ?2 kPa). The basis of such a limitation on TR was recently linked to limited leaf hydraulic conductance. It was hypothesized that this genotype may lack an AgNO3-sensitive protein-mediated water pathway in the leaf, possibly involving aquaporins (AQPs), causing it to have a low hydraulic conductance. The possibility of genetic variability for sensitivity of derooted plants exposed to 200 ìM AgNO3 was investigated among 12 soybean genotypes including progeny of PI 416937. Segregation among genotypes in their response to AgNO3 was observed. Genotype PI 416937 and two of its progeny lines were insensitive to the AgNO3 treatment indicating that they lacked a protein-mediated water pathway that is sensitive to this inhibitor. The remaining nine genotypes were sensitive to the AgNO3 treatment, and the decrease in TR indicated that the AgNO3 sensitivity accounted for 25 to 50% of the usual hydraulic pathway in the leaves. Among the AgNO3-sensitive lines, the genotypes could be further segregated based on previous observations in the response of intact plants to increasing VPD. It is hypothesized that this additional segregation might be a result of a difference in hydraulic limitation in their roots

Endogenous Root Auxin Accumulation Drives the Expression of Daytime and Nighttime Water-Saving Traits in a Wheat Mapping Population

In wheat, restricted transpiration rate (TR) under high vapor pressure deficit (VPD) has been shown to increase yields under terminal drought conditions. Furthermore, new evidence indicates that such behaviour is amplified by reducing nocturnal transpiration (TR ). We have shown that such limitation involves a decrease in root hydraulic conductivity, xylem vasculature size and a lack of mercury-sensitive aquaporin (AQP) population. In this work, we examined the hypothesis of involvement of root auxins to explain the link between root hydraulics and canopy TR. This was motivated by the discovery of root-specific genes involved in auxin synthesis and xylem differentiation underneath a major QTL controlling TR responses to VPD in a wheat mapping population descending from parents that exhibited contrasted levels of drought tolerance, root hydraulic conductivities and TR restriction under high VPD. We selected eight lines which spanned the entire range of nighttime and daytime TR responses to VPD in this population. On those lines, we examined auxin and ABA contents in the roots and the leaves during both times of the day, in relation to hydraulic traits including whole-plant TR, plant hydraulic conductance (K ), slopes of TR responses to VPD and several leaf anatomical traits. Leaf auxin and ABA concentrations during daytime and nighttime were not correlated with any of the examined traits. In sharp contrast, daytime root auxin concentrations were found to be strongly and negatively correlated with daytime TR, K and the slopes of TR response to VPD. Similarly, nighttime root auxin levels significantly and negatively correlated with TR . The findings provide a ‘hormonal link’ between root hydraulic restrictions and canopy TR and reveal for the first time a potential role for root auxins accumulation in regulating daytime and nighttime water use, thereby modulating the expression of a water-saving trait that has been associated with enhanced yields under drought

ZINC TREATMENT RESULTS IN TRANSPIRATION RATE DECREASES THAT VARY AMONG SOYBEAN GENOTYPES

Zinc (Zn) pollution of croplands can have negative impacts on yields through its effects on key physiological functions such as transpiration rate (TR). Previous long-term experiments indicated that differential tolerance among soybean genotypes following exposure to high Zn levels existed in the shoots. There are, however, no studies of the possibility that short-term responses to Zn directly limit shoot TR. Measurements of TR of eight soybean genotypes were measured over 220 minutes after placing de-rooted shoots in 500 μM Zn solution. Six genotypes exhibited TR that decreased slowly in a linear fashion over time while two genotypes ('PI 416937' and 'N01-11136') exhibited very rapid decrease in TR following a Boltzmann sigmoid response. One possibility to explain these results is that there exists a Zn-sensitive AQP population in the leaves of 'PI 416937' and 'N01-11136' with abundance or activity that is much higher than in the leaves of the remaining six lines. © 2012 Copyright Taylor and Francis Group, LLC