No description available.

Many areas in the arid southwestern United States depend upon ground water for irrigation and municipal water supplies. The high transpiration rates of the extensive phreatophyte tamarisk (Tamarix pentandra Pall.) cause considerable depletion of ground water in this region. Eradication of tamarisk communities would appear to be a useful method for salvaging ground water; however, the vigorous reproduction and growth of tamarisk pose economic problems because of the re-treatment and maintenance work required. Also, the removal of tamarisk thickets may adversely affect wildlife habitat, esthetic values, and the ecosystem in general. The use of antitranspirant compounds on tamarisk was investigated in the laboratory, greenhouse, and field, to determine if transpiration could be reduced significantly without damaging the plant. Athel tree (Tamarix aphylla L.) was subjected to the same analyses as tamarisk to better evaluate treatment effects. Initially, several antitranspirants were tested in greenhouse studies from which the potentially useful compounds were selected for more detailed study. Phenylmercuric acetate was toxic to both species and was not used in further experiments with tamarisk. Daily transpiration rates of tamarisk, measured gravimetrically in a greenhouse, were reduced 28 to 36 percent for 20 days with spray applications of 0.01 M 8-hydroxyquinoline sulfate (8-HQS), and the combination of 150 ppm mono-methyl (MDSA) and 150 ppm mono-glyceryl (GDSA) esters of n-decenylsuccinic acid in Triton X-100 (0.5 percent) solutions. The MDSA-GDSA combination and 8_I-[QS significantly reduced stomatal apertures of tamarisk. Stomatal measurements were not obtained for athel tree, although daily transpiration rates of athel tree were reduced 31 percent for 32 days with the MDSA-GDSA combination. The addition of the filmforming Foli-gard (10 percent) did not enhance treatment effect. Treatment effects on net photosynthesis and respiration of both species were evaluated with an infrared gas analyzer. The net photosynthesis rates of tamarisk were significantly reduced 1 to 3 days by 8-HQS and MDSA-GDSA. Respiration rates, measured in the dark, were increased significantly only by 8-HQS. Net photosynthesis rates of athel tree were significantly reduced 13 days by MDSA-GDSA, but there were no effects on respiration. MDSA-GDSA and 8-HQS reduced tamarisk growth rates for 10 to 20 days following treaLment. These growth reductions may have contributed to the decrease in transpiration rates of treated plants. Analyses of foliage samples obtained from tamarisk after treatment indicated that chlorophyll and protein contents were not affected by 8-HQS or MDSA-GDSA. Similar results were noted for athel tree treated with MDSA-GDSA and MDSA-GDSA-Foli-gard. Transpiration rates of potted tamarisk in the field were reduced significantly for only five days by 8-HQS, MDSA-GDSA, and the reflective compound, kaolinite. Rainfall after the fifth day, and phenological phenomena may have contributed to the comparatively short duration of transpiration reduction. Increased foliage temperatures of 1.5 to 2.5 C were detected with a Barnes infrared thermometer 1 and 3 days after treatment. These were obtained under conditions of intense solar radiation, and high air and soil temperatures. This study indicated that tamarisk transpiration can be reduced substantially without lethal increases in foliage temperatures, but with reductions of growth. Additional studies with these antitranspirants may provide a useful management alternative for tamarisk dominated areas to salvage ground water and yet maintain plant cover for wildlife and other uses.

No description available.

The climate, water loss, arid certain aspects of growth in semiarid-site ponderosa pine were measured from 1 February 1966 to 10 March 1967 to determine the environmental relationships governing transpiration, internal water balance, and tracheid production. Water loss from branches and from entire trees was measured by means of polyethylene enclosures. Changes In internal water status of the tree were ascertained from seasonal trends in loss of water from branches and diurnal as well as seasonal changes in the radius of the bole. The elongation of branches and needles, and the production of tracheids and their size and wall thickness were related to the coincident internal water status of the tree. The branch enclosure technique was found to be a convenient method by which the water loss process could be studied. The seasonal changes in transpiration undoubtedly were influenced by the elevated temperatures that developed within the enclosure during the day. However, the elevated temperatures did not appear to adversely influence branch and needle elongation within the chamber. Warm air temperatures and low soil moisture during June and early July increased internal water stress, reduced daytime water loss, and reduced elongation of branches and needles. Fewer tracheids were produced in the upper bole. They were small and had thick walls, Moisture from rains in July replenished soil moisture and larger, thin-walled tracheids were differentiated so that the intra-anntjlar band of small, thick-walled cells became apparent. Gradual shrinkage of the upper bole in June implied that the above changes in growth were due to changes in internal water deficits. There were no marked changes in tracheid sizes and wall thickness in the lower bole during 1966. Intra-annular bands of narrow, thick-walled tracheids occurred times during the last 10 years in the upper bole in the last 50 years in the lower bole. Graphical analysis showed that midday reductions in rates of xi transpiration during periods of low soil moisture and high air temperatures occurred in spite of steepening water vapor gradients and before stomates were closed. This evidence supports the hypothesis that reductions in water loss during midday may result directly from internal water deficits. Soil moisture, air temperature, and incident radiation appeared to influence transpiration by altering the availability of water, the vapor pressure gradient, and the energy available for evaporation.

The research described in this dissertation is predicated on the hypothesis that remotely sensed information from climatological satellites can be used to estimate the actual evapotranspiration from agricultural crops to improve irrigation scheduling and water use efficiency. The goal of the enabling research program described here was to facilitate and demonstrate the potential use of satellite data for the rapid and routine estimation of water use by irrigated crops in the Yaqui Valley irrigation scheme, an extensive irrigated area in Sonora, Mexico. The approach taken was first, to measure and model the evapotranspiration and crop factors for wheat and cotton, the most common irrigated crops in the Yaqui Valley scheme. Second, to develop and test a high-resolution (4 km x 4 km) method for determining cloud cover and solar radiation from GOES satellite data. Then third, to demonstrate the application of satellite data to calculate the actual evaporation for sample crops in the Yaqui Valley scheme by combining estimates of potential rate with relevant crop factors and information on crop management. Results show that it is feasible to provide routine estimates of evaporation for the most common crops in the Yaqui Valley irrigation scheme from satellite data. Accordingly, a system to provide such estimates has been established and the Water Users Association, the entity responsible for water distribution in Yaqui Valley, can now use them to decide whether specific fields need irrigation. A Web site (tekapucemitson. mx) is also being created which will allow individual farmers to have direct access to the evaporation estimates via the Internet.

No description available.

LD2668 .T4 1947 A2 / Master of Science

Seasonal patterns of stomatal activity, plant-temperature-based drought stress indices, growth and grain yield of two pearl millet (Pennisetum americanum (L.) Leeke) parental lines and their F₁ hybrid were studied under a sprinkler irrigation gradient system in 1985 and 1986 in Tucson, Arizona. Physiological and morphological measurements of stressed and nonstressed plants were made periodically starting at the panicle initiation stage. Well-defined trends in stomatal conductance (Cg), transpiration (Tr), and photosynthetic (Pn) rates of nonstressed plants were observed over the seasons. Tr increased from 5ug H₂O cm⁻²s⁻¹ at early panicle development stage to a peak of up to 30 ug cm⁻²s⁻¹ at flowering and declined to 10 ug cm⁻²s⁻¹ at maturity. Pn of well-irrigated plants was highest (26 uMoles CO₂ m⁻²s⁻¹) at early flag leaf appearance stage and declined slowly to 14 uMoles m⁻²s⁻¹ at maturity. In extremely stressed plants, Cg, Tr and Pn were highest early in the seasons, lowest in the middle of the seasons, and slightly increased towards the end of the seasons. The seasonal trends in stomatal response depended on the stage of plant growth and vapor pressure deficit of the air. Transpiration efficiency was highest at partial stomatal closure. Morphologically, the F₁ hybrid was more like its male than its female parent. The female parent produced less dry matter, had thinner leaves and greater ratio of leaf to stem dry matter, and yielded less grain than the other genotypes. The results indicated that leaf:stem ratio can be a useful selection criterion of drought avoiding genotypes. Plants that develop stems and heads rapidly (low leaf:stem ratio) are more desirable under stress than plants that tend to become leafy. Decreases in Tr, Pn, dry matter and grain yield due to stress could be assessed with canopy or leaf temperature, canopy minus air or leaf minus air temperature, and crop (CWSI) or leaf (LWSI) water stress indices. CWSI and LWSI were more desirable in assessing stress than the other indices. CWSI is effective in assessing the magnitude of stress in a crop stand, while LWSI may be useful in situations where use of the infrared thermometer is difficult.

Ph.D., Faculty of Science, University of the Witwatersrand, 2011 / Introduced plants will lose interactions with natural enemies, mutualists and competitors from their native ranges, and possibly gain interactions with new species, under new abiotic conditions in their new environment. The use of biocontrol agents is based on the premise that introduced species are liberated from their natural enemies, although in some cases introduced species may not become invasive because they acquire novel natural enemies. In this study I consider the potential for the biocontrol of Bryophyllum delagoense, a Madagascan endemic, and hypothesize as to why this plant is invasive in Australia and not in South Africa. Of the 33 species of insects collected on B. delagoense in Madagascar, three species, Osphilia tenuipes, Eurytoma bryophylli, and Rhembastus sp. showed potential as biocontrol agents in Australia. Surveys in southern Africa revealed that B. delagoense had acquired 14 species of insects, compared to only two in Australia, which supported the hypothesis that an introduced plant is less likely to become invasive in regions where there are many closely related species. A beetle, Alcidodes sedi, was found to be widespread and damaging in South Africa and also sufficiently host specific for release in Australia. Studies were also undertaken to determine the biology of B. delagoense and characteristics of the recipient environments in Australia and South Africa. Analysis of soils in South Africa found that B. delagoense has the ability to grow on a range of soils and is tolerant of moderate shade. Bryophyllum delagoense exhibited phenotypic plasticity by re-allocating resources to stem production in light-limited; and to root production in nutrient- or water limited, environments. Competition trials indicated that B. delagoense is a weak competitor with overgrazing and the concomitant reduction in fires facilitating invasions. The absence of damaging natural enemies and characteristics of the Australian environment may make it more prone to B. delagoense invasions than in southern Africa. The study indicates that no single trait or group of traits can completely explain the invasive ability of a plant species because the success of an invader often depends on complex interactions between the species and its recipient environment. This has widespread implications for predicting the invasibility of imported plants. Keywords: Alcidodes sedi, biological control, Bryophyllum delagoense, Crassulaceae, Eurytoma bryophylli, fire, invasions, Madagascar, Osphilia tenuipes, Rhembastus sp., soil.

No description available.