Decreasing Soil Water Potential Research Articles

Field Response of Photosynthesis to CO"2 Enhancement in Ponderosa Pine

Net photosynthesis was determined by CO2 analysis for Pinus ponderosa Laws. in situ in the San Bernardino Mountains of southern California. Leafy shoots were maintained in cuvettes under ambient and enhanced levels of CO2 on successive days. Carbon dioxide enhancement was up to 150 ppm above ambient levels. Mean response of net photosynthesis increased 84%. Responsiveness to CO2 enhancement was not altered by high temperature or decreasing soil water potential during the months June—October. The added CO2 compensated for reduction of 50% in light intensity. Severe damage from oxidant air pollution reduced but did not eliminate the response to CO2 enhancement. The evidence suggests that net photosynthesis will increase in linear relation to rising atmospheric CO2 during the next few decades.

Effects of drought and salinity on some growth-contributing parameters in wheat and barley

This study is mainly concerned with some parameters contributing to growth as indicators of difference in drought resistance and salt tolerance of wheat and barley cultivars. Parameters made use of are: transpiration efficiency (‘dry matter/transpiration’ ratio), ‘leaf/root’ ratio, chlorophyll content, chlorophyll stability to heat and anatomical modifications. The results revealed that transpiration efficiency is much higher in mexican ‘super-x’ wheat than in the egyptian ‘Giza-155’ cultivar under reduced soil water matric- or osmotic potentials. Chlorophyll content increased in super-x with decreasing soil water potential while chlorophyll heat stability decreased. The reverse is true in Giza-155 cultivar. Decreased leaf/root ratio in super-x is interpretted in favour of more beneficial water balance in this cultivar. Development of more sclerenchyma in its stems supports this judgement. Of barley cultivars tested, Borg El-Arab is favoured for drought resistance and Giza-117 for salt tolerance. re]19751014

Stomatal Response to Leaf Water Potential as Affected by Preconditioning Water Stress in the Field1

AbstractPrevious research has shown that stomatal response to decreasing soil water potential of chamber‐grown sorghum (Sorghum bicolor L. Moench. ‘Oro’) and cotton (Gossypium hirsutum L. ‘Stoneville 213’) is altered by exposure to previous water stress. This work was undertaken to determine if stomatal response of field‐grown plants is also altered by previous water stress.Stoneville 213 cotton was grown in the field under movable rainshelters and was subjected to three treatments: control — well watered, one period of water stress, and two periods of water stress. After this preconditioning period, all plants underwent a final stress during which stomatal response to leaf water potential was measured.The periods of preconditioning water stress were characterized by decreased cumulative growth as measured by leaf area per plant. Leaf areas for the control, one soil water stress plants, and two soil water stress plants were 5,200, 2,200, and 1,200 cm2, respectively. Lower stomates of preconditoned field‐grown plants remained open to lower leaf water potentials (—28 to —30 bars) during the final stress than those of plants which were not preconditioned (—22 bars). These results were similar to those found previously on chamber‐grown plants which had been exposed to more frequent but shorter stresses. The 6 to 8 bar adjustment in leaf water potential vs. stomatal resistance as a result of previous water stress indicates a need for caution in interpreting data from plants of unknown water stress history.

Effect of Abscisic Acid at Different Levels of Soil Water Potential on the Transpiration of Zea mays

AbstractThe effect of different levels of both exogenous abscisic acid (ABA) and soil water potential on transpiration from intact maize leaves was studied in growth chamber experiments. The transpiration rate showed a more consistent decrease with decreasing soil water potential than with increasing concentration of applied ABA. The effect of exogenous ABA on the transpiration rate was markedly lower at low than at high levels of soil water potential.

Response of Root and Shoot Growth of Three Grass Species to Decreases in Soil Water Potential

Highlight: Native grass species show differences in leaf and root growth response to soil water potential. Soil water potential developed by blue grama at the time of leaf growth stoppage ranged from <-80.0 bars at 5 cm depths to -8.4 bars at 35 cm depths, while corresponding values for little bluestem were 24.3 and 3. 0 bars, and 30. 0 and -15.3 bars for western wheatgrass. Soil water potentials at the time of root growth cessation were somewhat lower with a minimum of -16.6 bars at the 5 cm depth of blue grama and a maximum of -5. 0 bars at the 25 cm and 35 cm depths of little bluestem. The R2 values indicate a lower level of correlation between soil water potential and root growth than between soil water potential and leaf growth. In ranking the three mixed prairie grass species as to their growth tolerance to decreasing soil water potential, blue grama ranks the highest followed by western wheatgrass and little bluestem, respectively.

Soybean and Corn Rooting in Southwestern Minnesota: II. Root Distributions and Related Water Inflow

AbstractRoot length density (RLD) of corn (Zea mays L.) and two isolines (determinate and indeterminate) of Harosoy soybean (Glycine max. L. Merr.) in a Nicollet soil were measured from 1 July to 15 Aug. 1971. These measurements, along with water uptake sinks in these vertically developing root systems, were used to evaluate water relations of these three crops.Both soybean isolines had about 0.2 cm/cm3 RLD in the Ap layer with values &lt; 0.1 below the Ap layer. This RLD distribution persisted with depth as the root system expanded vertically. Corn RLD were about 0.3 initially in the Ap layer, and as the root system expanded vertically, maximum RLD of about 0.3 was produced even to the 100‐cm depth on 9 Aug. Vertical extension rates of corn after 1 July were 1.3 cm/day as compared with 1.7 for soybeans, but maximum rooting depths on 9 Aug. were 145 and 120 cm, respectively.Modal specific water inflows were 0.03 cm3/cm root per day—maximal values for soybeans were 0.2; maximal values for corn were about 0.05. Maximum soybean rooting depths coincided with maximum depth of water uptake sink, but corn rooting depths ranged 15 to 30 cm deeper than the water uptake sink.Specific water inflow generally increased as soil hydraulic conductivity increased and RLD decreased, which agrees with models for steady‐state water flow into single roots. At low RLD, specific water inflows were either constant or increased as hydraulic conductivity decreased. This increased root resistance to water flow at the lower fringes of rooting may have resulted from low soil temperatures. Soybean root conductivities decreased with decreasing soil water potential. Corn root conductivities were largest at about −700 mbars and decreased as soil water potential decreased. Decreases of corn root conductivity resulted from potentials &gt; −700 mbars when soil temperatures were low.

Gas exchange of four arctic and alpine tundra plant species in relation to atmospheric and soil moisture stress.

Gas exchange measurements of two arctic tundra plants, Dupontia fischeri and Carex aquatilis, and two alpine tundra species, Deschampsia caespitosa and Geum rossii, were conducted under a range of atmospheric and soil moisture stress conditions to determine if photosynthetic adaptations to water stress may play a role in the local distributions of these species. Under low soil moisture stress, the species which are normally restricted to wet sites, Dupontia and Deschampsia, exhibited higher net photosynthetic rates than Carex and Geum which are more widely distributed. However, photosynthetic of the wider ranging species was not so abruptly curtailed as that of the wet site species when the plants were exposed to increasing atmospheric or soil moisure stress. Although the depression of photosynthesis with water stress in these tundra species could be partially attributed to reduced stomatal aperture, with decreased soil water potential most of the decline of photosynthesis was due to a greater non-stomatal or residual resistance, indicating a direct impact of water stress on the photosynthetic apparatus. Dark respiration did not increase with enhanced water stress. Stomata of the wet site species did not appear to undergo a closing response until the bulk leaf water potential decreased. However, at high soil water potential reduced stomatal aperture of the more widely distributed species was noted before leaf water potential dropped. Therefore, stomata of these species may respond directly to the vapor pressure gradient between the leaf and the atmosphere when soil moisture potential is high. The wet site species typically exhibited higher photosynthesis/transpiration ratios at low soil moisture stress; however, as soil moisture stress increased, the photosynthesis/transpiration ratios of the wider ranging species generally exceeded those of the wet site species.

Effect of Aerial Environment and Soil Water Potential on the Transpiration and Energy Status of Water in Wheat Plants1

AbstractWater stress is an important factor limiting wheat (Triticum aestivum L.) growth on the Canadian prairies. To determine the effect of evaporative demand and soil water potential on transpiration and leaf water status, Thatcher wheat was grown under four combinations of air temperature and relative humidity in a loam and a clay soil. Transpiration rate, leaf water potential, leaf water content, and soil water potential were determined. The relationship between transpiration rate and soil water potential depended on evaporative demand and soil texture. The decline in the transpiration rate from its maximum commenced at higher soil water potentials under conditions of higher evaporative demand and was more gradual on the clay than on the loam soil, presumably due to the higher capillary conductivity of the former. Permanent wilting occurred at soil water potentials of —20 to —25 bars on the loam soil and at —45 to —50 bars on the clay soil. At these potentials the capillary conductivities of both soils were about equal. Resistance to Water flow in the plant decreased with increased temperature, while changes in relative humidity had no consistent effect. The total resistance to water movement in the plant and the soil increased with decreasing soil water potential and decreasing air temperature. The relationship between leaf water potential and relative water content was affected by aerial environment and soil texture.

Resting Roots of Pinus halepensis: Structure, Function, and Reaction to Water Stress

Metacutization is a special chemical process of lignification and suberization occurring in particular cells of the cortex and the dormant root cap (Muller 1906). The resting root of Pinus halepensis Mill. had a greatly reduced and heterogeneous meristematic region compared with that of the growing root. Cells of the peripheral zone of the apical meristem, unlike those of the central zone, were filled with dark phenolic compounds. Metacutization developed regularly in the outer cells of the peripheral, phenol-containing zones, forming a boundary between the meristematic and mature tissues. The value of the metacutis as a protective sheath for the growing point was found to be negligible. The formation of the metacutis in the resting root tip could be induced by decreasing soil water potential to about -7 bars. The quiescent state of the roots in the dry summer could be altered by irrigation.

Photosynthesis, Transpiration, Leaf Temperature, and Stomatal Activity of Cotton Plants under Varying Water Potentials

Cotton plants, Gossypium hirsutum L. were grown in a growth room under incident radiation levels of 65, 35, and 17 Langleys per hour to determine the effects of vapor pressure deficits (VPD's) of 2, 9, and 17 mm Hg at high soil water potential, and the effects of decreasing soil water potential and reirrigation on transpiration, leaf temperature, stomatal activity, photosynthesis, and respiration at a VPD of 9 mm Hg.Transpiration was positively correlated with radiation level, air VPD and soil water potential. Reirrigation following stress led to slow recovery, which may be related to root damage occurring during stress. Leaf water potential decreased with, but not as fast as, soil water potential.Leaf temperature was usually positively correlated with light intensity and negatively correlated with transpiration, air VPD, and soil water. At high soil water, leaf temperatures ranged from a fraction of 1 to a few degrees above ambient, except at medium and low light and a VPD of 19 mm Hg when they were slightly below ambient, probably because of increased transpirational cooling. During low soil water leaf temperatures as high as 3.4 degrees above ambient were recorded. Reirrigation reduced leaf temperature before appreciably increasing transpiration. The upper leaf surface tended to be warmer than the lower at the beginning of the day and when soil water was adequate; otherwise there was little difference or the lower surface was warmer. This pattern seemed to reflect transpiration cooling and leaf position effects.Although stomata were more numerous in the lower than the upper epidermis, most of the time a greater percentage of the upper were open. With sufficient soil water present, stomata opened with light and closed with darkness. Fewer stomata opened under low than high light intensity and under even moderate, as compared with high soil water. It required several days following reirrigation for stomata to regain original activity levels.Apparent photosynthesis of cotton leaves occasionally oscillated with variable amplitude and frequency. When soil water was adequate, photosynthesis was nearly proportional to light intensity, with some indication of higher rates at higher VPD's. As soil water decreased, photosynthesis first increased and then markedly decreased. Following reirrigation, photosynthesis rapidly recovered.Respiration was slowed moderately by decreasing soil water but increased before watering. Respiration slowed with increasing leaf age only on leaves that were previously under high light intensity.