Research Species: Sequoiadendron giganteum (redwoods) Place: 40 miles along coast of California Course: Ecohydrology / Instructor: Dr. V. Iakovoglou http://www.google.gr/images

Research Special fog conditions when cool moist air from Pacific interacts with warm inland warm air. Tiny leaves trap moisture that condenses and falls to the forest floor. Reduces transpiration rates. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou http://www.google.gr/images

Nowadays alterations occur in a very abrupt & fast rate Research-Problem Climate change increase T that results to less fog. Redwoods endured past stressed conditions. Will they now make it under disturbance events? Nowadays alterations occur in a very abrupt & fast rate Course: Ecohydrology / Instructor: Dr. V. Iakovoglou http://www.google.gr/images

Research At 95 m to 112.3 m measured xylem pressure potential Photosynthesis, stomatal conductance and transpiration were measured in ambient conditions of light, temperature and vapor pressure. Xylem vulnerability to cavitation was also measured. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou http://www.google.gr/images

Fact: Study trees located in very moist sites Course: Ecohydrology / Instructor: Dr. V. Iakovoglou http://www.google.gr/imgres

Results Slopes of midday gradients differed during dry period, not during the wet season indicative of the increased driving force necessary to move water rapidly through the xylem. Stomatal conductance and photosynthesis during the dry season decreased by an average of 43% and 33%, respectively. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou http://www.google.gr/images

Results Stomatal conductance and photosynthesis also decreased with increase in height. No loss of hydraulic conductivity (i.e., cavitation) was observed during the dry season. Trees experienced larger soil water deficits on hill slopes and ridge tops, during very dry years and toward the southern of the species distribution. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou http://www.google.gr/images

Results Fact : high resistance to cavitation, why? Stomata conductance may decrease to reduce the risk of xylem cavitation. Not ignore the role of fog in the water relations Summer fog characterizes much of redwood's geographic distribution, “direct foliar uptake of fog in coast redwood prevent transpiration”. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Possible explanations? Could it be that foliar absorption provides a mechanism for xylem tension to relax to the point where cavitation reversal is possible? May be that the hydraulic characteristics of the extreme height growth of redwoods are related to other features (e.g., wood mechanical properties)? Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

REDWOODS Nonetheless, high cavitation resistance of redwoods is an advantage during extreme long-lasting droughts. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Evapotranspiration

Evapotranspiration (ET) Evaporation (E) The process of water changing from a liquid into a gas( in soils the upper few cm) Transpiration (T) The loss of water from a plant's leaves (stem, flowers, or roots) back into the atmosphere Evapotranspiration (ET) The sum of transpiration and evaporation. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Evapotranspitation Usually combined the E and the T into the ET. Only recently we are able to distinguish those fluxes. Recently stable isotopic technique enables the separation of the two fluxes Transpired water from leaves is more isotopic enriched

Forests? Transpiration accounts for most of the ET In Amazon Transpiration accounts for nearly all the water loss

How about arid areas? In dessert crop areas E accounted only for the 1.5-3.5% of the ET In an olive orchard E accounted for the 0 % prior irrigation to 14-31% 5 days after irrigation.

Thus Even under irrigated soils with low canopy cover, transpiration accounts the most for the air water forms.

Transpiration As long as plants can pull water from the soil as fast as it leaves from the leaves, there is no problem. When water loss exceeds water uptake, the plants will wilt as the leaves lose turgor pressure. Again, the conditions that favor wilting are hot, sunny, and windy days

Transpiration The efficiency of a plant can be measured by its transpiration-to-photosyntesis ratio The amount of water lost per gram of CO2 assimilated into organic material created by photosynthesis A typical ratio for a C3 plant is 600:1 - for a typical C4 plant it is more like 300:1 For forest trees 170-340 kg of H2O/kg of biomass accumulation (Larcher, 1975).

What controls rate of Transpiration? The driving force for water movement from the soil to the atmosphere The resistances to water movement in the plant; cuticle resistance, stomata resistance and boundary layer resistance. 1. Plant parameters, 2. Environmental conditions

Driving force Vapor Pressure Deficit (VPD) VPD is the driving force for water movement from the inside leaf to the outside air. VPD = vpsat – vpair Saturation vapor pressure (vpsat) is when the air reaches maximum water vapor content Air vapor pressure (vpair) indicates how much water vapor is in the air Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

VPD Keep in mind The greater the VPD the more water moves out of the leaf. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

VPD- Keep in mind The greater the VPD the more water moves out of the leaf. Under arid conditions this induces stress to the plants. VPD calculation is a better estimation over relative humidity (RH) because it accounts for T-effect. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

VPD As a general rule, most plants grow well at VPDs of between 0.8 to 0.95 kPa Studies showed that fungal pathogens survive best below <0.43 kPa (0.062 psi) VPD. Furthermore, disease infection is most damaging below 0.20 kPa (0.030 psi). Thus, for a greenhouse conditions should be kept above 0.20 kPa (0.030 psi) to prevent disease and crop damage.

What controls rate of Transpiration? the driving force for water movement from the soil to the atmosphere the resistances to water movement in the plant; cuticle resistance, stomata resistance and boundary layer resistance. 1. Plant parameters, 2. Environmental conditions

What controls rate of Transpiration? the driving force for water movement from the soil to the atmosphere the resistances to water movement in the plant; cuticle resistance, stomata resistance and boundary layer resistance. 1. Plant parameters, 2. Environmental conditions

Plant parameters Stomata (open, increase transpiration) Boundary layer (the larger the boundary layer the greater the transpiration) Cuticle (the thinner the cuticule the greater the transpiration) The plant species. Different plants transpire water at different rates.

Environmental conditions hot, sunny, windy days Humidity: The drier the air, the greater the transpiration rate. Temperature: The warmer the air (holds more H2O) the greater the transpiration rate. Light: Can cause the stomata to open, thus increase transpiration rate. Wind: The windier the greater the transpiration rate. Once air moves from the leaf (even at saturated conditions), it is replaced by drier (less saturated air) that can then absorb water vapor.

Factors Affecting Evapotranspiration Under moisture deficit conditions, Transpiration is reduced (closed stomata) On cloudy days stomata are closed so low transpiration At night transpiration ceases. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Factors Affecting Evapotranspiration Lack of soil moisture: plants transpire less in an effort to survive decreases evapotranspiration. Latitude & climate Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Geographic Patterns of Evapotranspiration Regions with the most solar radiation experience more evapotranspiration (more solar energy available to evaporate the water). Equator to Poles South vs North facing slopes Overstory vs understory Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Geographic Patterns of Evapotranspiration Equator to Poles Evapotranspiration rates are also highest in areas with a hot and dry climate. Southwest U. S. A., evapotranspiration is ~ 100% of yearly precipitation. Northwest U. S. A., evapotranspiration is ~ 40% of yearly precipitation. Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Geographic Patterns of Evapotranspiration South vs North facing slopes Solar radiation greater at south-facing slopes (northern hemisphere) Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

Geographic Patterns of Evapotranspiration Overstory vs understory Overstory receives the most radiation Greater radiation and lower relative humidity Course: Ecohydrology / Instructor: Dr. V. Iakovoglou

To be continued Course: Ecohydrology / Instructor: Dr. V. Iakovoglou