Changes In Transpiration Rate Research Articles

Vegetation water sources in California's Sierra Nevada (USA) are young and change over time, a multi‐isotope (δ18O, δ2H, 3H) tracer approach.

AbstractSierra Nevada forests transpire a significant amount of California's water resources, sparking interest in applying forest management to improve California's water supply. Determining the source water of evapotranspiration enables forest managers to make informed decisions. To this end, a significant interest in critical zone science is to develop new methods to work across time scales to predict subsurface water storage and use. In this study, forest vegetation accessed young water and switched sources depending on availability, suggesting that forest drought vulnerability may depend on the range of water sources available (rain, snowmelt and deeply stored water). This finding also suggests that changes in transpiration rates may have immediate effects on water sources in close proximity to vegetation, and delayed effects on storage and runoff. New δ18O, δ2H and 3H data were used to track precipitation, runoff, evapotranspiration and storage through the critical zone seasonally, including seasons where evapotranspiration and snowmelt were in phase (winter snowmelt) and out of phase (seasonally dry summer). The main source of this headwater catchment's runoff is derived from its meadow saturated zone water, which was dominated by snowmelt. Water that originated as snowmelt contributed to transpiration, unless other sources, such as recent rain, became available. In cases where xylem δ18O and δ2H signatures matched those of deeper saturated zone water, 3H data showed that xylem water was distinctly younger than the deep saturated zone water. During 2016, which experienced relatively normal snowpack in winter and seasonally dry summer conditions, mean summer saturated zone water and vegetation water were similar in δ18O, −12.4 ± 0.04 ‰ and − 12.5 ± 0.3 ‰, respectively, but were distinctly different in 3H, 5.5 ± 0.2 pCi/L and 13.7 ± 1.1 pCi/L, respectively. While δ18O shows that vegetation and meadow saturated zone water have similar origins, 3H shows they have dissimilar ages.

Proximal Hyperspectral Imaging Detects Diurnal and Drought-Induced Changes in Maize Physiology.

Hyperspectral imaging is a promising tool for non-destructive phenotyping of plant physiological traits, which has been transferred from remote to proximal sensing applications, and from manual laboratory setups to automated plant phenotyping platforms. Due to the higher resolution in proximal sensing, illumination variation and plant geometry result in increased non-biological variation in plant spectra that may mask subtle biological differences. Here, a better understanding of spectral measurements for proximal sensing and their application to study drought, developmental and diurnal responses was acquired in a drought case study of maize grown in a greenhouse phenotyping platform with a hyperspectral imaging setup. The use of brightness classification to reduce the illumination-induced non-biological variation is demonstrated, and allowed the detection of diurnal, developmental and early drought-induced changes in maize reflectance and physiology. Diurnal changes in transpiration rate and vapor pressure deficit were significantly correlated with red and red-edge reflectance. Drought-induced changes in effective quantum yield and water potential were accurately predicted using partial least squares regression and the newly developed Water Potential Index 2, respectively. The prediction accuracy of hyperspectral indices and partial least squares regression were similar, as long as a strong relationship between the physiological trait and reflectance was present. This demonstrates that current hyperspectral processing approaches can be used in automated plant phenotyping platforms to monitor physiological traits with a high temporal resolution.

Changes in Transpiration Rates and Growth of Cucumber and Tomato Scions and Rootstocks Grown Under Different Light Intensity Conditions in a Closed Transplant Production System

Changes in Transpiration Rates and Growth of Cucumber and Tomato Scions and Rootstocks Grown Under Different Light Intensity Conditions in a Closed Transplant Production System

Local and Systemic Changes in Photosynthetic Parameters and Antioxidant Activity in Cucumber Challenged with Pseudomonas syringae pv lachrymans.

We studied changes in gas exchange, photochemical activity and the antioxidant system in cucumber leaves locally infected with Pseudomonas syringae pv lachrymans and in uninfected systemic ones. Infection-induced declined net photosynthesis rate and the related changes in transpiration rate, the intracellular CO2 concentration, and prolonged reduction in maximal PSII quantum yield (Fv/Fm), accompanied by an increase in non-photochemical quenching (NPQ), were observed only in the infected leaves, along with full disease symptom development. Infection severely affected the ROS/redox homeostasis at the cellular level and in chloroplasts. Superoxide dismutase, ascorbate, and tocopherol were preferentially induced at the early stage of pathogenesis, whereas catalase, glutathione, and the ascorbate–glutathione cycle enzymes were activated later. Systemic leaves retained their net photosynthesis rate and the changes in the antioxidant system were partly like those in the infected leaves, although they occurred later and were less intense. Re-balancing of ascorbate and glutathione in systemic leaves generated a specific redox signature in chloroplasts. We suggest that it could be a regulatory element playing a role in integrating photosynthesis and redox regulation of stress, aimed at increasing the defense capacity and maintaining the growth of the infected plant.

Changes in 15NO3 - Availability and Transpiration Rate Are Associated With a Rapid Diurnal Adjustment of Anion Contents as Well as 15N and Water Fluxes Between the Roots and Shoots.

Background and Aims: Understanding interactions between water and nitrate fluxes in response to nitrate availability and transpiration rate is crucial to select more efficient plants for the use of water and nitrate.Methods: Some of these interactions were investigated in intact Brassica napus plants by combining a non-destructive gravimetric device with 15NO3- labeling. The set-up allowed high-resolution measurement of the effects of a cross-combination of two concentrations of KNO3 or KCl (0.5 and 5 mM) with two different rates of transpiration controlled by the relative humidity during a day–night cycle.Key Results: Results show that (1) high external nitrate concentrations increased root water uptake significantly whatever the transpiration rate, (2) nitrate translocation depended both on the rate of nitrate uptake and loading into xylem (3) dilution-concentration effect of nitrate in the xylem was mainly modulated by both external nitrate availability and transpiration rate, (4) dynamic changes in 15N translocation in the xylem modified shoot growth and capacitance, and (5) variations in tissue concentrations of NO3- induced by the experimental conditions were balanced by changes in concentrations of chloride and sulfate ions. These effects were even more amplified under low transpiration condition and 0.5 mM external nitrate concentration.Conclusion: Taken together, these results highlight the fine and rapid adjustment of anion contents, nitrate and water flows to changes in transpiration rate and nitrate availability during a day–night cycle. The use of this non-invasive gravimetric device is therefore a powerful tool to assess candidates genes involved in nitrogen and water use efficiency.

Application of anti-transpirants temporarily alleviates the inhibition of symbiotic nitrogen fixation in drought-stressed pea plants

Stomatal closure is one of the first plant responses under a water deficit situation. This leads to a decline in transpiration but also in the plant photosynthetic activity. Legume plants grown under symbiosis with rhizobium bacteria present an inhibition of nitrogen fixation that has been shown to occur even before this of photosynthesis. One of the hypotheses to explain this rapid inhibition is the accumulation of nitrogen (N) compounds in nodules due to reduced transpiration, which would provoke the N-feedback inhibition of nitrogenase activity. The current work analyzes the effects of changes in transpiration rates in the regulation of nitrogen fixation through the application of the anti-transpirant Vapor Gard (VG) to pea (Pisum sativum L.) plants subjected to a progressive water deficit. VG produced a rapid inhibition of nitrogen fixation upon application. This inhibition, however, did not coincide with the accumulation of either amino acids or soluble carbohydrates observed at later drought stages in nodules. Results show that the application of VG has a beneficial, albeit temporary, effect in both maintaining the plant water status and apparent nitrogenase activity of nodulated pea plants under water-deficit conditions.

Cadmium accumulation and its effects on physiological characteristics of Arundo donax L. in a simulated wetland

<p>A simulated wetland experiment was used to investigate the effect of cadmium (Cd) on the growth of Arundo donax, as well as its photosynthetic characteristics and antioxidant enzyme activities. Cd accumulation in the order of stem < roots < leaves increased gradually with increasing Cd concentrations. Due to the higher transport of Cd, its accumulation in the aboveground parts of A. donax was nearly 2 times that in belowground parts. There were no differences in physiological parameters, such as the relative chlorophyll content (SPAD), the potential (Fv/Fm) or effective (Y) photochemical efficiency of PSII, and photosynthetic rate (Pn). There were slight changes in transpiration rate (Tr), intercellular CO2 concentration (Ci) and stomatal conductivity (Gs). The activity of superoxide dismutase (SOD) was stimulated by Cd treatments, and the decrease in catalase (CAT) was compensated by the induction of peroxidase (POD) suggesting these two enzymes function concurrently to remove H2O2. These results indicate that despite the oxidative stress involved in the mechanism of Cd toxicity associated with the high transport of Cd in A. donax, its photosynthetic system was not harmed. This suggests a strong tolerance of this species to increased Cd pollution and its potential use for phytoremediation purposes in wetland environment.</p>

Leaf water maintains daytime transpiration in young Cryptomeria japonica trees.

Compared with stem water storage, leaf water storage is understudied although it may be important for alleviating water stress by contributing quickly and directly to transpiration demand. To quantify the relative contribution of stem versus leaf water storage to daily water deficit, we measured diurnal changes in transpiration rate, sap-flow velocity and stem radius of 10-year-old Cryptomeria japonica D. Don trees. We assumed that the duration of time lags between transpiration rate and sap-flow velocity reflected stored water in the stem and leaf, and that stem volume change represented water content of elastic tissue. The relationship between fresh mass and water potential of the whole tree indicated that the study trees had capacity to store, on average, 91.4 ml of water per kg fresh mass at turgor loss. Leaves, sapwood and elastic tissue contributed around 51%, 29% and 20% of stored water, respectively. During morning, transpiration rates were higher than sap-flow velocity suggesting depletion of stored water. During the first 2 h after onset of transpiration, stored water contributed more than 100% of whole-tree transpiration. Depletion of leaf water (PLeaf) and sapwood water (PSap) coincided with the onset of transpiration and became maximum around 15:00 h. Depletion of elastic tissue water (PElastic) lagged behind that of PLeaf and PSap by 1-2 h, indicating that replenishment of stored water occurs late in the day when low leaf water potentials resulting from daytime transpiration drive water uptake. Maximum depletion of PLeaf was about 1-3 times and 5-10 times that of PSap and PElastic, respectively. The contribution of PLeaf to total daily transpiration was 5-8%, while those of PSap and PElastic were 3-4% and 0.7-1%, respectively. Our results suggest the importance of leaf water storage in maintaining daily transpiration in young C. japonica trees.

Soil-water content characterisation in a modified Jarvis-Stewart model: A case study of a conifer forest on a shallow unconfined aquifer

Groundwater-vegetation-atmosphere fluxes were monitored for a subtropical coastal conifer forest in South-East Queensland, Australia. Observations were used to quantify seasonal changes in transpiration rates with respect to temporal fluctuations of the local water table depth. The applicability of a Modified Jarvis-Stewart transpiration model (MJS), which requires soil-water content data, was assessed for this system. The influence of single depth values compared to use of vertically averaged soil-water content data on MJS-modelled transpiration was assessed over both a wet and a dry season, where the water table depth varied from the surface to a depth of 1.4m below the surface.Data for tree transpiration rates relative to water table depth showed that trees transpire when the water table was above a threshold depth of 0.8m below the ground surface (water availability is non-limiting). When the water table reached the ground surface (i.e., surface flooding) transpiration was found to be limited. When the water table is below this threshold depth, a linear relationship between water table depth and the transpiration rate was observed. MJS modelling results show that the influence of different choices for soil-water content on transpiration predictions was insignificant in the wet season. However, during the dry season, inclusion of deeper soil-water content data improved the model performance (except for days after isolated rainfall events, here a shallower soil-water representation was better). This study demonstrated that, to improve MJS simulation results, appropriate selection of soil water measurement depths based on the dynamic behaviour of soil water profiles through the root zone was required in a shallow unconfined aquifer system.

Transpiration cooling effect of climber greenwall with an air gap on indoor thermal environment

Abstract We quantified the transpiration cooling effect by comparing a living climber greenwall (CGW) against a real but non-transpiring one after confirming the cessation of transpiration and similar vegetation coverages of both of them. We severed stems of plants in one of the CGWs to stop transpiration. By monitoring the changes in transpiration rate, leaf temperature, and percentage coverages of plants with and without severance of stems, we tried to confirm the cessation of transpiration and similar vegetation coverages. In parallel with it, we measured the indoor thermal environments in the well-covered houses of the two treatments, as well as a non-covered house, and calculated the transpiration cooling effect. The transpiration rates of plants with stem severance dropped to less than 1.0 mmol m −2 s −1 within 35 min after severance. Almost all leaf temperatures in the severed treatment were similar to the dry reference leaf temperatures. In contrast, those in the non-severed treatment remained the same as before severance. In addition, the percentage points of percentage coverages between the living CGW and the real but non-transpiring one was reduced to just 1.5% two days after severance. Thus, we quantified the transpiration cooling effect of CGWs using the indoor thermal environmental data two days after severance. The average transpiration cooling effect calculated from the indoor wall surface temperatures (=severed plant-covered house − intact plant-covered house) was 0.23 °C, although the average shading cooling effect (=non-covered house − severed plant-covered house) was 8.55 °C under global solar radiation on a vertical south surface between 400 and 600 W m −2 . In addition, those calculated from room temperatures under the same environmental conditions were 0.15 and 4.00 °C, respectively. Therefore, we concluded that the transpiration cooling effect of CGWs, which were separately set from the walls, on the indoor thermal environment of houses was much smaller than the shading cooling effect. Using these methodologies, we recommend further investigation of the appropriate distance between CGWs and walls to increase the transpiration cooling effect.

Aquaporin-mediated increase in root hydraulic conductance is involved in silicon-induced improved root water uptake under osmotic stress in Sorghum bicolor L.

The fact that silicon application alleviates water deficit stress has been widely reported, but the underlying mechanism remains unclear. Here the effects of silicon on water uptake and transport of sorghum seedlings (Sorghum bicolor L.) growing under polyethylene glycol-simulated osmotic stress in hydroponic culture and water deficit stress in sand culture were investigated. Osmotic stress dramatically decreased dry weight, photosynthetic rate, transpiration rate, stomatal conductance, and leaf water content, but silicon application reduced these stress-induced decreases. Although silicon application had no effect on stem water transport capacity, whole-plant hydraulic conductance (Kplant) and root hydraulic conductance (Lp) were higher in silicon-treated seedlings than in those without silicon treatment under osmotic stress. Furthermore, the extent of changes in transpiration rate was similar to the changes in Kplant and Lp. The contribution of aquaporin to Lp was characterized using the aquaporin inhibitor mercury. Under osmotic stress, the exogenous application of HgCl2 decreased the transpiration rates of seedlings with and without silicon to the same level; after recovery induced by dithiothreitol (DTT), however, the transpiration rate was higher in silicon-treated seedlings than in untreated seedlings. In addition, transcription levels of several root aquaporin genes were increased by silicon application under osmotic stress. These results indicate that the silicon-induced up-regulation of aquaporin, which was thought to increase Lp, was involved in improving root water uptake under osmotic stress. This study also suggests that silicon plays a modulating role in improving plant resistance to osmotic stress in addition to its role as a mere physical barrier.

Chemical Screen for Limited-Transpiration-Rate Trait Among Sorghum Genotypes

A limited-transpiration trait has been proposed for sorghum (Sorghum bicolor L.) as a desirable trait for water-deficit environments so that water conservation early in the growing season allows greater water availability during the latter stages of crop growth. This study was undertaken to explore if chemical inhibitors—mercury, silver, gold, zinc, cylcoheximide—could be used to screen for the limited-transpiration trait. Inhibitors were fed either to detached leaves or to the root systems of intact plants, and changes in transpiration rates were recorded. Only treatment with silver resulted in discrimination among genotypes. Those genotypes that most strongly expressed the limited-transpiration trait were less sensitive to being fed silver than those that either had weaker expressions of the limited-transpiration trait or did not express the trait. The results with leaves indicated the silver test could be effective as a negative screen for sorghum genotypes that potentially express the limited-transpiration trait.

Effects of elevated atmospheric [CO2] on instantaneous transpiration efficiency at leaf and canopy scales in Eucalyptus saligna

AbstractRising atmospheric concentrations of CO2 (Ca) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to Ca. We hypothesized that plants regulate stomatal conductance optimally in response to rising Ca. We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate‐controlled whole‐tree chambers for 2 years at ambient and elevated Ca. Elevated Ca was ambient + 240 ppm, 60% higher than ambient Ca. Leaf‐scale gas exchange was measured throughout the second year of the study and leaf‐scale ITE increased by 60% under elevated Ca, as predicted. Values of leaf‐scale ITE depended strongly on vapour pressure deficit (D) in both CO2 treatments. Whole‐canopy CO2 and H2O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between Ca treatments, which had important effects on values of canopy‐scale ITE. However, when Ca treatments were compared at the same D, canopy‐scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy‐scale ITE were not significantly different, indicating that ITE was not scale‐dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to Ca. The effect of elevated Ca on photosynthesis increased with rising D. At high D, Ca had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of Ca on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with Ca will allow us to predict the effects of Ca on transpiration rate.

Leaf-lamina conductance contributes to an equal distribution of water delivery in current-year shoots of kudzu-vine shoot, Pueraria lobata

Leaf-lamina resistance, R(L), accounts for a large fraction of branch resistance across a wide range of plant species. This work hypothesized that large R(L) is essential for distributing water equally to leaves on the shoot, and tested this hypothesis through theoretical analyses and measurements using over 10-m-long current-year shoots of kudzu vine, Pueraria lobata [Willd.] Ohwi. First, the hydraulic architecture and the distribution of the motive force achieving equal distribution of water delivery were theoretically obtained by simulating water flow through a hypothetical shoot comprising an axial pathway and several lateral pathways as a stem and leaves, respectively, in a kudzu-vine shoot. The model predicts that large resistance of the lateral pathway relative to that of the axial pathway is associated strongly with small variation in the hydraulic conductance of a pathway from the base of the axial pathways to the lateral pathway among the nodes, rendering water delivery to each lateral pathway equal under small variation in motive force for water flow. For the kudzu-vine shoot, the measured ratio of the lateral (a petiole) to the axial (a stem) resistance was 115. When R(L) was added to the lateral pathway, the ratio increased to 1136. According to the model prediction, these values imply that the hydraulic conductance of a pathway comprising a stem and a petiole, K(BP), is favored strongly at the basal nodes, while the hydraulic conductance of a pathway including a stem, a petiole and a lamina, K(SL), is slightly different across the nodes. For the shoots with leaf lamina, the diurnal change in transpiration rate was not different between the leaves on the three nodes dividing the shoot into four parts. K(SL) was not related significantly to node number. Conversely, K(BP) at the distal node was ~0.06-fold that at the basal node. Furthermore, the motive force for water flow should vary by 6.64-fold among nodes to compensate for the favored distribution of K(BP), which is an unrealistic value. These results indicate that R(L) contributes largely to an equal distribution of water delivery in a shoot, supporting our hypothesis.

Effect of wind speed on transpiration and biomass accumulation of potted amaranth

By using pot experiment under greenhouse condition, the effect of wind speed on amaranth transpiration and biomass accumulation was analyzed at wind speed of 2.0 m·s-1, 1.0 m·s-1, 0.4 m·s-1 and 0.0 m·s-1. The study shows similar changes in transpiration rate and daily transpiration of potted amaranth at different wind speed. There exist no remarkable differences among the treatments. In general, transpiration rate and daily transpiration are maximum at 1.0 m·s-1, followed by 0.4 m·s-1 and the 0.0 m·s-1, the lowest at 2.0 m·s-1. Meanwhile, stepwise regression analyses show strongest positive correlation between transpiration rate and illumination intensity under different wind speed, followed by that between transpiration rate and temperature at 2.0 m·s-1. However, transpiration rate of other treatments has significant negative correlation with relative humidity. Daily mean temperature is a major factor affecting daily transpiration rate. The biomass accumulation curve of the potted amaranth shows that biomass accumulation is highest at 1.0 m·s-1 and lowest at 2.0 m·s-1. The effect of wind speed under greenhouse condition on above-ground fresh weight, under-ground fresh weight and root-shoot ratio of potted amaranth are very significant, highest at 1.0 m·s-1 and lowest at 2.0 m·s-1. Dry matter weight is obviously affected by wind speed, and is maximum at 1.0 m·s-1. The effect of wind speed on transpiration water consumption and water use efficiency is insignificant, but water use efficiency is maximum at 1.0 m·s-1 wind speed.

Transpiration and Normalized Difference Vegetation Index Response of Seashore Paspalum to Soil Drying

A consistent response has been observed among many plant species in their leaf gas exchange as soils are subjected to a drying cycle; except for one case, these studies have not included turfgrass species. The current study reports the change in transpiration rate of six genotypes of seashore paspalum (Paspalum vaginatum Swartz) during soil drying when grown on either an organic soil or sand. On organic soil, the response was consistent with results with other plant species in that there was no decline in transpiration rate until the fraction of transpirable soil water (FTSW) reached the range of 0.25 to 0.31. The decline in transpiration rate when plants were grown on sand occurred in the FTSW range of 0.10 to 0.17, which was also consistent with reports for other species when grown on sand. The lower FTSW for the decline in transpiration rate on sand appears to be a result of the greater retention of water in fully wetted sand in pot experiments as compared with field conditions. Because the decline in transpiration occurred at a higher FTSW in ‘SeaIsle Supreme’, ‘Aloha’, and ‘SeaIsle 1’ than in ‘SeaIsle 2000’, this is an indication that these genotypes are water-conserving and may be better suited to water-deficit conditions. Quality changes in these grasses were monitored daily during the drying cycle by reflectance measurements of their normalized difference vegetation index (NDVI). No change in NDVI was observed for grasses grown on either soil type until the soil had become very dry and transpiration had decreased to low rates.

Multi‐sensor plant imaging: Towards the development of a stress‐catalogue

Agricultural production is limited by a wide range of abiotic (e.g. drought, waterlogging) and biotic (pests, diseases and weeds) stresses. The impact of these stresses can be minimized by appropriate management actions such as irrigation or chemical pesticide application. However, further optimization requires the ability to diagnose and quantify the different stresses at an early stage. Particularly valuable information of plant stress responses is provided by plant imaging, i.e. non-contact sensing with spatial resolving power: (i) thermal imaging, detecting changes in transpiration rate and (ii) fluorescence imaging monitoring alterations in photosynthesis and other physiological processes. These can be supplemented by conventional video imagery for study of growth. An efficient early warning system would need to discriminate between different stressors. Given the wide range of sensors, and the association of specific plant physiological responses with changes at particular wavelengths, this goal seems within reach. This is based on the organization of the individual sensor results in a matrix that identifies specific signatures for multiple stress types. In this report, we first review the diagnostic effectiveness of different individual imaging techniques and then extend this to the multi-sensor stress-identification approach.

Impending effects of transpiration in blue light regulation of leaf growth

Light quality, drives several photomorphogenetic responses in plants such as leaf growth. A decrease in blue irradiance in the incident light leads to an increase in leaf elongation rate and final leaf length. The effects of blue light could be mediated by water flux into the growing zone since blue light has a direct effect on stomata aperture and consequently on plant transpiration. Indeed, several studies have demonstrated the effects of changes in transpiration rate on leaf elongation rate but little is known about the control of leaf elongation by water flux under low blue light conditions.

Evaluation of canopy transpiration rate by applying a plant hormone “abscisic acid”

A method for evaluation of temporal changes in canopy transpiration rate and stomatal conductance in crop fields by using a plant hormone abscisic acid (ABA) has recently been developed. The method was applied to a corn canopy at different growth stages in the upper Yellow River basin, China. Diurnal changes in the canopy transpiration rate and stomatal conductance were evaluated at the initial stage with a leaf area index (LAI) of 0.37 on June 7 and the crop development stage with an LAI of 4.39 on July 15, 2005. The proportions of the accumulated transpiration rate during daytime to the accumulated evapotranspiration were 24% and 74% at the initial and crop development stages, respectively. Stomatal conductance varied in parallel with transpiration rate in the initial stage of the crop. However, in the crop development stage with low soil water content, stomatal conductance reached the maximum value at 10:00 a.m. and thereafter decreased rapidly at around noon with high evaporative demand to corn canopy. This shows the midday stomatal closure was caused by excessive water stress to corn canopy in the crop development stage. Thus, the proposed method with ABA application is useful for evaluation of temporal changes in transpiration rate and stomatal conductance, and hence, can detect the plant water stress.

Growth and transpiration of Japanese cedar (Cryptomeria japonica) and Hinoki cypress (Chamaecyparis obtusa) seedlings in response to soil water content.

To investigate the effects of soil water content on growth and transpiration of Japanese cedar (Cryptomeria japonica D. Don) and Hinoki cypress (Chamaecyparis obtusa (Siebold et Zucc.) Endl.), potted seedlings were grown in well-watered soil (wet treatment) or in drying soil (dry treatment) for 12 weeks. Seedlings in the wet treatment were watered once every 2 or 3 days, whereas seedlings in the dry treatment were watered when soil water content (Theta; m3 m(-3)) reached 0.30, equivalent to a soil matric potential of -0.06 MPa. From Weeks 7 to 12 after the onset of the treatments, seedling transpiration was measured by weighing the potted seedlings. After the last watering, changes in transpiration rate during soil drying were monitored intensely. The dry treatment restricted aboveground growth but increased biomass allocation to the roots in both species, resulting in no significant treatment difference in whole-plant biomass production. The species showed similar responses in relative growth rate (RGR), net assimilation rate (NAR) and shoot mass ratio (SMR) to the dry treatment. Although NAR did not change significantly in either C. japonica or C. obtusa as the soil dried, the two species responded differently to the dry treatment in terms of mean transpiration rate (E) and water-use efficiency (WUE), which are parameters that relate to NAR. In the dry treatment, both E and WUE of C. japonica were stable, whereas in C. obtusa, E decreased and WUE increased (E and WUE counterbalanced to maintain a constant NAR). Transpiration rates were lower in C. obtusa seedlings than in C. japonica seedlings, even in well-watered conditions. During soil drying, the transpiration rate decreased after Theta reached about 0.38 (-0.003 MPa) in C. obtusa and 0.32 (-0.028 MPa) in C. japonica. We conclude that C. obtusa has more water-saving characteristics than C. japonica, particularly when water supply is limited.