Steven P. McLaughlin

Effects of Wildfire on A Sonoran Desert Plant Community

Fires occur frequently in desert grassland at the eastern margin of the Sonoran Desert (Wright 1980), but fires in the desert proper are reported to be very infrequent and of low intensity (Humphrey 1974). Wildfires require both an adequate fuel load and an agent of ignition. While lightning storms are common during the summer in both desert and desert grassland, production of annual and perennial herbs in the desert is generally far too low to provide a fuel load capable of sustaining fire. Unusually heavy precipitation during the winter of 1978-1979 did result in high production of winter annuals and several fires occurred the following spring and summer in the desert regions of Arizona. One of the largest was the Granite Burn, which was started on 29 June 1979 by a lightning strike and covered 11 500 ha south of Florence, Arizona. This paper describes the effects of the Granite Burn on the perennial vegetation. The study area is located 20 km southeast of Florence at an elevation of 670 m. Topography is level with typic haplargid soils developed from acid igneous alluvium (Buol 1966). Vegetation is typical of the Arizona Upland subdivision of the Sonoran Desert as defined by Shreve (1964). The dominant species are bursage (Ambrosia deltoidea), paloverde (Cercidium microphyllum), and creosote bush (Larrea tridentata). Cacti are visually conspicuous, including saguaro (Carnegiea gigantea), buckhorn cholla (Opuntia acanthocarpa), hedgehog (Echinocereus fasciculatus), barrel (Ferocactus wislizenii), and prickly pear (Opuntia phaeacantha).

Survey of biocrude-producing plants from the southwest

One hundred ninety-five species of plants native to the southwestern United States and northwestern Mexico were surveyed for potential feedstocks for biocrude production in arid lands. Biocrude is the hydrocarbon and hydrocarbonlike chemical fraction of plants which may be extracted by organic solvents and upgraded to liquid fuels and chemical feedstocks. Plants were evaluated using a set of models which provide estimates of oil and energy production costs. Plants producing either latex or resinous exudates had the highest percentage of high energy extracts. Total extracts were highest in smaller, potentially less productive plants. The optimum combination of percentage biocrude and potential yield occurred in plants of intermediate size having higher than average extractables. High biomass yields do not appear necessary for the economic production of biocrude in irrigated, arid regions. Several desert plants might produce biocrude for between

POTENTIAL ANTIMICROBIAL ACTIVITY OF PLANTS FROM THE SOUTHWESTERN UNITED STATES

10–15 per million BTU without by-product credits.

2,3-Dihydrowithaferin A-3β-O-sulfate, a new potential prodrug of withaferin A from aeroponically grown Withania somnifera

Organic solvent extracts of 300 southwestern U.S.A. plant species in 69 families were evaluated against four microorganisms in an agar-streak bioassay. The dichloromethane extract of Guardiola platyphylla and ethanol extracts of Plumbago scandens, Acacia angustissima and Salvia sonomensis demonstrated the best spectrum of activity by completely inhibiting the growth of Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae and Candida albicans. Of the 300 species, 12 completely inhibited the growth of the gram-negative K. pneumoniae and 36 inhibited the yeast C. albicans. B. subtilis proved to be very susceptible with 188 species either completely inhibiting or slowing the growth of this gram-positive organism. S. aureus proved to be more selective with only 107 species affecting its growth. Ninety-one species demonstrated no inhibitory effects on any test organisms.

Biocrude production in arid lands

Preparations of the roots of the medicinal plant Withania somnifera (L.) Dunal commonly called ashwagandha have been used for millennia in the Ayurvedic medical tradition of India as a general tonic to relieve stress and enhance health, especially in the elderly. In modern times, ashwagandha has been shown to possess intriguing antiangiogenic and anticancer activity, largely attributable to the presence of the steroidal lactone withaferin A as the major constituent. When cultured using the aeroponic technique, however, this plant was found to produce a new natural product, 2,3-dihydrowithaferin A-3beta-O-sulfate (1), as the predominant constituent of methanolic extracts prepared from aerial tissues. The characteristic bioactivities exhibited by 1 including inhibition of cancer cell proliferation/survival, disruption of cytoskeletal organization and induction of the cellular heat-shock response paralleled those displayed by withaferin A (2). The delayed onset of action and reduced potency of 1 in cell culture along with previous observations demonstrating the requirement of the 2(3)-double bond in withanolides for bioactivity suggested that 1 might be converted to 2 in cell culture media and this was confirmed by HPLC analysis. The abundant yield of 1 from aeroponically cultivated plants, its good aqueous solubility and spontaneous conversion to 2 under cell culture conditions, suggest that 1 could prove useful as a readily formulated prodrug of withaferin A that merits further evaluation in animal models.

Grindelia camporum: Potential cash crop for the arid southwest

Recent research in the development of bioenergy crops for arid and semiarid regions has stressed the objective of increasing biomass productivity in order to improve energetic and economic returns. However, an examination of the constraints on arid-adapted plant species indicates that a preferable approach to biocrude feedstock development is one that emphasizes quality, rather than quantity, of biomass. This conclusion is illustrated by economic and energetic comparisons of 4 potential biocrude feedstocks. The species with the greatest economic potential are those with high biocrude contents and moderate or low annual yields.

Economic prospects for new crops in the Southwestern United States

Grindelia camporum is a conspicuously resinous, herbaceous perennial found in the Central Valley area of California. The resin is produced in multicellular glands, which occur on the surfaces of stems, leaves, and involucres. The resin is composed of grindelic acid and several of its derivatives. These labdane diterpenes are similar to the resin acids that constitute rosin, a principal product of the naval stores industry, and it seems likely that resin extracted from Grindelia would have uses similar to those of rosin. If improved varieties of Grindelia camporum can be developed that yield a higher proportion of resin, this species would be suitable for domestication as a new crop for arid lands.

Production of Resins by Arid-Adapted Astereae

Agriculture in the Southwest is productive but expensive. High yields of traditional crops depend on extensive irrigation. As water costs increase and water availability is reduced, production of traditional crops will decline. New crops with low water use (and consequently lower yields) will be needed if agriculture is to persist in the region. The best candidates will be drought-tolerant species with high value products. Plants producing botanochemicals will probably be favored over those yielding pulp, energy, commodity foods, or fiber.

Grindelia chiloensis resin and biomass production in its native environment

The arid regions of the world and their native flora remain a largely unexplored frontier in the search for new plant chemicals. This search has been revived in recent years because, in addition to the scientific gains to be made through the study of the production and ecological significance of plant secondary metabolites, many of these compounds have practical value as well.

Properties of paper made from fibers of Hesperaloe funifera (Agavaceae.

Preliminary studies have shown that Grindelia chiloensis has higher resin contents than Grindelia camporum which has been previously evaluated as a new resin crop for arid environments. G. chiloensis may provide an additional source of germplasm variability from which to improve resin content and adaptation to cold, arid environments. A number of studies were conducted to evaluate several native populations of G. chiloensis growing in its native environment in southern Argentina. Three native stands of G. chiloensis from northeastern Patagonia were evaluated. All three sites are located around 42 S latitude, within 200 m from the seacoast, and receive an average precipitation below 160 mm/year. Native cover of G. chiloensis ranged between 8% and 11% and was not significantly different among populations. Average individual plant net primary productivity (NPP) was estimated with a single harvest at the end of the growing season (April 1995) and ranged between 92 g and 168 g dry weight (DW). No significant difference in NPP was found among populations. Plant density was significantly different among populations (P < 0.01) and ranged between 2.8 and 0.16 plants/m2. Crude resin (CR) content of the years biomass (stems, leaves, and flowers) was significantly different among populations (P < 0.01); CR content was 23.4%, 17.4%, and 16.7% for the three populations studied. Refined resin (RR, an estimate of resin acids content) was significantly different among populations and ranged between 16.3% and 11.5% for these samples. The ratio RRCR was around 69% and was not different among populations. Capitula and leaves did not differ in resin CR and RR contents, but these were significantly higher than those found in stems. This contrasts with what has been found in G. camporum in which capitula have significantly higher resin contents than leaves. This characteristic will influence the ideotype used in the selection of high productivity germplasm.