Measuring and Modeling Tree and Stand Level Transpiration

Abstract

Transpiration is a key process in the application of phytoremediation 'to soil or groundwater pollutants. To be successful, vegetation must transpire . enough water from the soil or groundwater to control or take up the,cdntam-in&. Transpiration is driven by a combination of abiotic (climate, soil water availability, and groundwater depth) and biotic (leaf area, stomatal functions, root amount and distribution, and hydraulic characteristies) that need to be evaluated when considering appropriate site and species combinations. The protocols are not trivial, but transpiration can be measured at a variety of scales using techniques such as direct measurements of sap flow on individual trees, eddy flux gradient analyses, or gauged watersheds. Alternatively, models can be used to estimate transpiration, but these usually require on-site calibration or parameterization to produce accurate predictions. Case study analyses across a range of site conditions and species indicate a maximum transpiration capacity of approximately 7.5 x lo6 liters of water per hectare per year (8 x IO5 gallons of water per acre per year), with a range of 1.5x lo6 to 7.5x lo6 liters per hectare per year (1.6 x 105 to 8x lti gallons per acre per year). Variation among sites is related to species, tree size, and .stocking (i.e., vegetation density) differences. Application of a physiologically based and site-specific parameterized model suggests reasonable agreement between . measured and predicted transpiration estimates for the Air Force Plant 4 site in central Texas.

Transpiration in 15 Tree Species Grown on a Phytocapped Landfill Site

“…Trees grown on phytocaps varied significantly (P<0.01) in their transpiration rates ( Figure 8) and this can be attributed to differing performances of these species in different seasons associated with variations in soil moisture regimes [17], leaf area [20], leaf biomass [25,26] solar radiation [4,61], and root development. Although all species experienced the same climatic conditions and seasonal change, they differed largely in their LAI, leaf biomass and root development.…”

“…Trees generally transpire water during the day as part of photosynthesis [3]. The transpiration rates vary between species due to variation in stomatal density and climatic conditions [4]. Transpiration has been expressed in a number of ways and most scientists and hydrologists express transpiration as mm d -1 [3], as this takes into consideration the area covered by the tree.…”

“…Transpiration rates of whole plants are also influenced by the soil moisture potential [19], the extent of soil volume explored by the root system [20], the architecture of the tree [21], and anatomical and physiological features of the tree [22]. Transpiration rates vary among species [23], season [17], soil water availability, leaf area [24], leaf biomass [25], climatic conditions, root development, the age of plantation [26] and geographical region [4]. It is also influenced by shallow water tables [27].…”

Use of Phytohormones for Strengthening Metal(loid) Phytoextraction: Limitations and a Case Study

“…The rate of transpiration is also directly related to whether the stomata are open or closed, and it accounts for the movement of water from roots to shoots by subsequent water loss as vapor through the stomata. An increase in transpiration rate has been observed from 20 to 40 % when stomata are wide open (Vose et al 2003 ). The chemical regulation of stomatal behavior is one strategy for improving water and contaminant uptake, since water absorbed at the roots by osmosis carries any dissolved mineral nutrients and/or soluble contaminants through the xylem.…”

Phytomanagement: Phytoremediation and the Production of Biomass for Economic Revenue on Contaminated Land

“…During dry periods vegetation also protects the soil surface against desiccation, so that the soil surface is stabilized by capillary cohesion of the soil particles against wind erosion. Soil water consumption for transpiration also reduces contaminant leaching (Pilon-Smits 2005 ; Robinson et al 2003b ;Vose et al 2003 ). How effective vegetation is in controlling leaching also depends on climate.…”