Colorado State University Extension
Tri River Area
Tamarisk Symposium
September 26 & 27, 2001
Holiday Inn - Grand Junction, CO

Abstract
Saltcedar (Tamarix) Physiology - a Primer

Saltcedar (Tamarix)was introduced into the United States as an ornamental in the early 1800's. Since then it has been classified as a noxious weed in many parts of the Southwest due to its invasiveness. Reports indicate an upstream spread of 12 miles a year is possible.

A variety of environmental attributes control the populational and ecological relationships between floodplain species. Species competitively superior under both wet years and drought will persist as the sole species through successional time. Tamarix, a floodplain species, has the ability to grow rapidly in wet years, tolerate or avoid extreme water and heat stress in drought years, tolerate salinization of surface soils, and develop deep roots. This woody plant is a prolific seeder - a mature tamarisk tree produces 600,000 seeds each year - and spreads rapidly by layering. Tamarisk also is hardy enough to withstand floods by stabilizing the underlying surface and trapping sediments.

Tamarisk is capable of absorbing deep water and releasing it at or near the soil surface. This allows shallower roots to absorb nutrients. Obligate phreatophytes, such as cottonwood and willow, require uninterrupted access to saturated soil with roots in the water table or capillary fringe. Tamarisk, a facultative phreatophyte, is able to use water from the water table and capillary fringe, and able to extract water and survive indefinitely in unsaturated soil.

Tamarix twigs transpire a weight of water greater than their own fresh leaf weight each hour, a rate common to many herbaceous plants. Salix on the other hand, transpires more water per unit leaf surface area. Recent research indicates Tamarix has a higher water use efficiency (photosynthesis vs transpiration) than Salix or Populus species.

Its ability to absorb and regulate salts gives Tamarix the ability to maintain turgor and high leaf conductance as tissue water potential declines; other plants are required to close stomata to maintain turgor reducing their ability to photosynthesize. Salts are controlled by Tamarix through extrusion and cellular compartmentation; salts also are utilized for osmoregulation. While some plants excrete salts into glands that then burst, salts absorbed by Tamarix are excreted through pores in their salt glands. Salts detected in high concentrations in and on leaf tissue closely represent the ion concentration in the soil and solution. Tamarix secretes actively even under low salt conditions. Bicarbonates, metabolically produced, also are excreted in large amounts (60%) even when not in the soil solution.

Leaf tissue of Tamarix is light saturated at 44% of full sunlight (1100 E m-2 s-1) allowing it to photosynthesize under low light conditions. Photosynthesis is optimal at a temperature between 23 and 28 degrees C. At higher temperatures, Tamarix stomata close. The waxy coating on the leaf surface thickens throughout the season further increasing the plant's resistance to water loss. These capabilities insure seedling survival under low light situations, high temperatures and drought conditions. As a result of these physiological capabilities, Tamarix is competitively superior to many other floodplain species.

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