Onset Of Drying Research Articles

Phenotyping drought tolerance and yield performance of barley using a combination of imaging methods

Drought resistance represents a complex of traits that are differently employed depending on drought type, severity and timing. Hence, a relatively comprehensive assessment of morphological and physiological phenotypic response to drought is required. We evaluated the dynamic responses of six barley genotypes, representing a wide range of drought tolerance, to continuous drying and re-watering using non-invasively measured parameters based on red-green-blue (RGB), thermal infrared and chlorophyll fluorescence imaging within an automated phenotyping platform. We identified three critical points in drought progress: i) 50% level of available soil water, ii) wilting point, iii) full plant recovery after re-watering. However, the individual monitored parameters showed the potential to evaluate drought sensitivity at different points since the onset of drying. The correlation with relative yield response gradually increased for the side projected leaf area (SPA) and reached the maximum at the point of full recovery. The actual quantum yield of photosystem II (ΦPSII) showed the highest correlation with a relative grain yield around wilting point. In contrast, the relative leaf temperature difference demonstrated a high correlation with yield response earlier, at 50% of available water. The highest correlations with the relative yield response were obtained for the colour RGB analysis at the wilting point and after recovery, particularly for khaki, beige, dark-green and olive-green colours. Multiple regression with parameters providing Pearson’s correlation coefficient R > 0.5 slightly improved the estimation of relative yield response to drought but ensured significant improvement of absolute grain yield estimation under drought stress. This study shows that combining the phenotyping methods representing different morphological and physiological traits allows not only the assessment of drought tolerance (based on relative yield response to drought) which is crucial for selecting the genetic resources for the subsequent breeding process but also allows to test the yield performance of new genotypes under drought stress.

Removal of high heat flux from solid surface by contact with water-containing porous plate

When a plate made of a porous material containing liquid is brought into contact with a solid body subjected to a high heat load, the body surface will be cooled by evaporation. The resulting vapor escapes from the side of the solid body through the clearance between the contacting surfaces due to surface unevenness. If the opposite surface of the porous plate is immersed in bulk liquid during contact with the solid body, the wetting of and evaporation on the solid surface will be maintained by liquid flow toward the heated surface. This occurs via the drawing-in of liquid from the opposite surface induced by a capillary force, enhanced by the decrease in the liquid content of the porous plate. However, increasing the heat flux generates a dry region in the porous material close to the heated surface, which significantly deteriorates its performance as a heat sink due to the increase in thermal resistance. The present study assessed two-phase flow in a porous plate containing water in contact with a solid surface under a high heat load, based on a one-dimensional model, and derived an expression for the heat flux at the onset of drying. In addition, the drying-onset heat flux was determined experimentally and was found to be an order of magnitude higher than the critical heat flux for saturated pool boiling of water. The onset heat flux markedly increased with decreasing thickness of the porous plate and with increasing permeability of the plate, in keeping with predictions based on a theoretical model.

Intermittent inland waters as important carbon sources

A large part of the world’s inland waters, including streams, rivers, ponds, lakes, and reservoirs is subject to occasional, seasonal, or even permanent drying. Moreover, the intermittent inland waters are increasing in many areas of the world because of climate change, anthropogenic influence, and land-use change. However, information on the carbon dioxide (CO2) fluxes from intermittent inland waters is scarce. Thus, a comprehensive assessment of CO2 emissions in intermittent inland waters is necessary and is a research gap in China. Here, we review the current knowledge on CO2 fluxes from lotic (streams and rivers) and lentic (ponds, lakes, and reservoirs) inland waters during dry and rewetting phases, considering controls and sources as well as implications of the two phases for local and global scale estimates. In exposed sediments of dry riverbeds, it can be a long time between wet and dry conditions. At the onset of drying, the increased oxygen availability can stimulate enzymatic activities and overall microbial growth, leading to an increased breakdown of organic matter and the subsequent release of CO2. As in any ecosystem, carbon emissions derive from a set of abiotic and biotic sources, the relative importance of which is tied to intrinsic features, such as geology, microbial communities and available organic substrates, and environmental controls, such as moisture and nutrient availability. Besides microbial respiration, geologic carbon can be a relevant source of CO2 emissions. Particularly in carbonate-rich regions, photodegradation of organic matter on dry light-exposed sediments can also lead to increased CO2 losses. In addition, covered vegetation metabolism, including photosynthesis and respiration, can be a relevant part of dry riverbed sediment CO2 emissions. Short rewetting episodes can trigger microbial respiration and CO2 release from the exposed sediments, and marked increases in the CO2 flux from dry sediments are to be expected during rewetting after a dry period, similar to soils, and it is known as the Birch effect. Immediately after rewetting, gases in pore spaces are displaced by water, potentially causing a significant efflux of CO2, impacting the overall annual CO2 flux. Rewetting events can also cause the remobilization of organic matter and nutrients. At the micro-scale, pore-filling will increase the dissemination of water-soluble substrates and mobilize labile substances from dead biomass. Aggregate disruption and the destabilization of organic-mineral complexes will also liberate carbon otherwise protected from microbial action. Other major drivers of CO2 fluxes from dry riverbeds include the presence or absence of vegetation or micro-phyto benthos in the exposed sediments, sediment texture, sediment temperature, and sediment organic matter. The organic matter quantity may be more important than the quality in controlling the magnitude of CO2 fluxes from the exposed sediments. Our conservative estimates indicate that adding emissions from intermittent inland waters to current global estimates of CO2 emissions from inland waters could result in an increase of 0.51 Pg C a−1 or ~1/4 of total fluxes. Therefore, intermittent internal waters should be considered when estimating the CO2 emissions of global inland water. Future investigations should focus on the in-depth study of the main sources of uncertainty involved in carbon emissions from intermittent internal waters to understand the physical and biological mechanisms behind this flux, and the impact on the global carbon cycle. Important study topics include: (1) Accurate estimation of the area of intermittent inland waters, in particular, the area of small-flow rivers, scattered ponds, and the area of headwaters; (2) CO2 efflux measurement of dry riverbeds, including the determination of CO2 efflux directly and indirectly, and combining the two methods; (3) the mechanism of CO2 release from dry riverbeds and factors driving CO2 fluxes from intermittent inland waters, such as the ratio of autochthonous and allochthonous carbon in sediments during dry and rewetting episodes; and (4) deep understanding of the changes in extension and seasonality of intermittent internal waters, particularly those in response to climate oscillations, land-use changes, and potential feedback related to climate at decadal time-scales. The results from these additional studies will help explain completely the inland water carbon emissions and identify potential implications for regional and global carbon cycles.

Quinolizidine alkaloids are transported to seeds of bitter narrow-leafed lupin.

Narrow-leafed lupin (NLL, Lupinus angustifolius) is a promising legume crop that produces seeds with very high protein content. However, NLL accumulates toxic quinolizidine alkaloids (QAs) in most of its tissues, including the seeds. To determine the level of in situ biosynthesis in the seeds, we compared the accumulation of QAs with the expression of the biosynthetic gene lysine decarboxylase (LDC) in developing seeds and pods of a bitter (high-QA) variety of NLL. While QAs accumulated steadily in seeds until the drying phase, LDC expression was comparatively very low throughout seed development. In contrast, both QA accumulation and LDC expression peaked early in pods and decreased subsequently, reaching background levels at the onset of drying. We complemented these studies with MS imaging, which revealed the distribution patterns of individual QAs in cross-sections of pods and seeds. Finally, we show that a paternal bitter genotype does not influence the QA levels of F1 seeds grown on a maternal, low-QA genotype. We conclude that the accumulation of QAs in seeds of bitter NLL is mostly, if not exclusively, transported from other tissues. These results open the possibility of using transport engineering to generate herbivore-resistant bitter NLL varieties that produce QA-free seeds.

Onset of drying and dormancy in relation to water dynamics of semi-arid grasslands from MODIS NDWI

Our knowledge of autumn phenology and its response to climate variability is currently limited. One way to improve our understanding of autumn phenology at the landscape scale is to investigate autumn vegetation dynamics based on multiple vegetation indices from remote sensing data. In this study, we derived two autumn phenological metrics (phenometrics), onset of drying and dormancy, for semi-arid grasslands from MODIS normalized difference water index (NDWI) time series. The onset of drying represents the start of decline in the vegetation’s metabolism during autumn, and the onset of NDWI-based dormancy signifies the end of metabolic activity. These NDWI-based phenometrics were then compared with enhanced vegetation index (EVI)-based phenometrics in northeastern China from 2001 to 2013. Influences of climatic variability on autumn phenology were analyzed using partial correlation analysis. We found that, in general, the onset of drying was slightly later than the onset of EVI-based senescence. Both did not strongly correlate with precipitation and mean minimum temperature in August. The onset of NDWI-based dormancy had, on average, a time lag of seven days, relative to the onset of EVI-based dormancy during 2001–2013. Moreover, it showed a much stronger response to mean minimum temperature in September than EVI-based dormancy. A colder autumn generally advanced the onset of NDWI-based dormancy, while it had little effect on the onset of EVI-based dormancy in the study area. These results suggest that phenological studies using NDWI could expand our understanding of land surface phenology. Furthermore, considering the different responses of the onset of NDWI- and EVI-based dormancy to climate variability, a combination of these phenometrics could contribute to the study of the ecosystem processes (e.g., carbon cycle) in semi-arid grasslands.

Temporal and spatial development of drying shrinkage cracking in cement-based materials

In optical microscopy and acoustic emission (AE) experiments, the development in time and space of drying shrinkage cracks in hardened cement paste and a cement composite containing mono-sized glass particles has been studied. The results indicate two types of restraint, i.e. self-restraint of the specimen/structure, and aggregate restraint. In plain cement paste cracks initially develop perpendicular to the drying surface, but may subsequently grow parallel to the drying surfaces. In composites containing glass particles, aggregate restraint causes continuous growth of microcracks. AE monitoring has revealed that drying shrinkage cracks develop almost instantaneously at the onset of drying. Several AE parameters elucidate the details of the process. The two techniques are complementary: AE monitoring is suitable for temporal development assessment, whereas optical microscopy is very well suited for measuring crack geometry.

Axes and cotyledons of recalcitrant seeds of Castanea sativa Mill. exhibit contrasting responses of respiration to drying in relation to desiccation sensitivity

Oxidative damage originating from uncontrolled metabolism is thought to be responsible for the sensitivity to drying in recalcitrant seeds. This study compares the responses of respiration to drying and the loss of membrane integrity in isolated axes and cotyledons of the recalcitrant seeds of Castanea sativa Mill. Electron spin resonance spectroscopy of two nitroxide spin probes introduced into the seed tissues was used to assess the cytoplasmic viscosity and the membrane permeability during fast and slow drying. Drying rates had no effect on the rise in viscosity in axes and cotyledons. In both tissues, the cytoplasmic viscosity during drying remained constant at 0.2 Poise until 1.6 g water/g DW (g/g), thereafter it increased exponentially. Axes were found to be more tolerant to drying than cotyledons: membranes showed minor changes in their permeability during drying and 50% viability was retained in dried axes containing 0.12 g/g. In contrast, plasma membranes in cotyledons lost their integrity below 0.6 g/g, regardless of the drying rate. Drying axes and cotyledons exhibited contrasting responses of their metabolism to drying. At the onset of drying, the rates of O2 uptake declined rapidly in drying axes. However, respiration in drying cotyledons sequentially increased to c. 1.4-fold at 1.2 g/g then decreased concomitantly with the loss of membrane integrity. The respiratory quotients (CO2 output/O2 input) remained constant around 0.9 until the loss of membrane integrity, then rose to 2.8. As a symptom of mitochondrial injury, the levels of reduction of cytochromes were assessed in situ in fresh and dried cotyledons using light spectroscopy. The levels of reduced cytochrome c and aa3 were lower in dried C. sativa cotyledons than in dried orthodox cotyledons of cowpea, indicating that a disruption in the electron transport chains may have occurred during drying. Desiccation sensitivity in recalcitrant seeds may be due to the inability to actively depress their metabolism during drying, thereby increasing the chances of initiating peroxidative damage during drying.

Aroma retention during the drying of liquid foods

Summary. Factors determining aroma retention during the drying of food liquids have been investigated with the aid of a model system. Slabs of an aqueous solution of partially hydrolysed starch, containing a small amount of acetone, were dried in air and the percentage of acetone retained was measured.Acetone was lost almost exclusively during the ‘constant‐rate’ period of drying and its rate of loss could be described in terms of a binary diffusion process. At high moisture contents, the rate of loss of a component from a drying solution is mainly dependent on its volatility, while at low moisture contents the diffusion coefficient of the component becomes the determining factor.Loss of volatile components will be only very slight if, at the onset of drying, the value of the dimensionless group BiwoKwo is sufficiently large. Here BiBiwo is the Biot number for water transport and Kwo is the ratio of the equilibrium water concentration in the gas phase and the water concentration in the solution to be dried. the minimum value of the group necessary to ensure high aroma retention increases with increasing relative humidity of the drying air. This value is larger for a drop than for a slab and is equal to 22 for a droplet under normal spray‐drying conditions.