Ronald E. Sosebee

The characteristics of Na+, K+ and free proline distribution in several drought-resistant plants of the Alxa Desert, China

The distribution characteristics of Na+, K+ and free proline were investigated in succulent xerophytes-Haloxylon ammodendron and Zygophyllum xanthoxylum; xerophytes-Artemisia sphaerocephala and Caragana korshinskii; and mesophytes-Agriophyllum squarrosum and Corispermum mongolicum in the Alxa Desert of China. The results showed that mesophytes and xerophytes were salt excluding species, and the concentrations of Na+ in these species were 1.5% to 3.8% of those in succulent xerophytes. Concentrations of K+ in Agriophyllum squarrosum and Corispermum mongolicum were 1.3-2.7 times those in Artemisia sphaerocephala and Caragana korshinskii. Concentrations of K+ in the stems of Agriophyllum squarrosum and Corispermum mongolicum were 1.8 and 2.2 times those in their roots, respectively, For mesophytes, accumulating large quantities of K+ in their stems may facilitate water movement along a soil-plant gradient. The xerophytes accumulated large quantities of K+ and free proline. Their proline concentrations in the whole plant were 6.0-16.0 times higher than those of mesophytes, and were 1.8-25.0 times higher than those of succulent xerophytes. In Artemisia sphaerocephala, the concentrations of proline increased by 3.1- and 10.5-fold from roots to stems, and from stems to leaves, respectively. A similar trend was observed in Caragana korshinskii. Therefore, accumulating K+ and free proline may play a role in drought adaptation in xerophytes. Succulent xerophytes Haloxylon ammodendron and Zygophyllum xanthoxylum were identified as salt diluting species that absorbed much Na+ by roots, and the Na+ was transported to the leaves and photosynthesizing branches. The succulent xerophytes accumulated larger quantities of Na+ than K+ for osmotic adjustment even at low soil salinities, resulting in the lowest values of selective absorption and selective transport capacities of the root systems. Our data suggest that Na+ accumulation rather than exclusion may be one of the most effective strategies for adaptation of succulent xerophytes to and environments

Hydraulic lift in drought-tolerant and -susceptible maize hybrids.

Hydraulic lift was investigated in a greenhouse study involving two drought-tolerant maize (Zea mays L.) hybrids (TAES176 and P3223) and a drought-susceptible hybrid (P3225) during the flowering stage. Root systems were grown in two soil compartments – a drier upper soil and a wetter deep soil. The plants were shaded for 3 h during the daytime. Soil volumetric water content (Øv) in the upper pots was measured with time domain reflectometry (TDR) before and after shading. An increase in Øv in the upper pot was detected with TDR in the drought-tolerant hybrids following 3 h of shading, but not in the drought-susceptible hybrid. Furthermore, water exuded from roots in the top soil layers was greater in the more drought-tolerant TAES176 than in P3223 (489 vs. 288 g per pot in 3 h, P<0.005). The sizable amount of water from hydraulic lift allowed TAES176 to reach a peak transpiration rate 27–42% higher than the drought-susceptible hybrid P3225 on the days when the evaporative demand was high. To our knowledge, this is the first experiment that reveals a significant surge of transpiration due to hydraulic lift following midday shading. Hydraulic lift also prevented soil moisture depletion in the upper pots with TAES176, but not with P3223 or P3225. Root characteristics may be responsible for differences in hydraulic lift of the three maize hybrids. There were 2.3–3.3-fold more primary roots in the deep moist soil in P3223 and TAES176 than in P3225 that may enable these hybrids to absorb and transport water at faster rates. Therefore, more water can be exuded into the upper drier soil when transpiration is suppressed by shading. Larger primary roots (20–28% larger diameter) and a higher root volume in the upper soil in TAES176 and P3223 than in P3225 may contribute to higher root hydraulic conductance and greater water efflux from the roots. The negligible hydraulic lift in P3225 may also relate to higher night-time transpiration of the hybrid. This report has documented, for the first time, the existence of genetic variations in hydraulic lift among maize hybrids and links between hydraulic lift and drought tolerance within maize plants. It appears that one of drought tolerance mechanisms in maize may lie in the extent of hydraulic lift.

Tillering responses to red:far-red light ratio during different phenological stages in Eragrostis curvula

Abstract Tillering responses to light quality in different phenological stages of a perennial warm-season grass Eragrostis curvula were investigated in controlled environments. In vegetative plants, the tillering rate was greater (P

Does hydraulic lift exist in shallow-rooted species? A quantitative examination with a half-shrub Gutierrezia sarothrae

Hydraulic lift occurs in some deep-rooted shrub and herbaceous species. In this process, water taken up by deep roots from the moist subsoil is delivered to the drier topsoil where it is later reabsorbed by shallow roots. However, little is known about the existence of hydraulic lift in shallow-rooted xeric species. The objectives of this study were 1) to ascertain whether hydraulic lift exists in Gutierrezia sarothrae (broom snakeweed), a widespread North American desert species with a shallow root system, grown in pot and field conditions and 2) if it does, how much water can be transferred from the subsoil to the 30 cm topsoil during the night. Snakeweed seedlings were transplanted in buried pots allowing the deeper roots to grow into the subsoil 30 cm below the surface. Soil water content inside and outside of the pot was measured seasonally and diurnally with time domain reflectometry technique (TDR). An increase in water content was detected in the pot after the plant was covered for 3 h by an opaque plastic bag during the day, suggesting hydraulic lift from deeper depths and exudation of water into the drier topsoil. Root exudation was also observed on native range sites dominated by snakeweed. Water efflux in the pot was 271 g per plant per night. which was equivalent to 15.3% of the extrapolated, porometer-derived whole-plant daily transpiration. Hydraulic lift observed in Gutierrezia improved water uptake during the day when evaporative demand is high and less water is available in the topsoil. We concluded that hydraulic lift might help snakeweed to alleviate the effect of water stress.

Physiological impacts of biosolids application in desert grasses

Abstract Although some studies have demonstrated that application of biosolids enhances biomass production of desert grasses, there is a lack of information regarding the physiological mechanisms of this enhanced production. The main objective of this study was to evaluate how gas exchange and leaf area production of blue grama ( Bouteloua gracilis ) and tobosagrass ( Hilaria mutica ) are affected by different rates and seasons of biosolids application and irrigation regimes. Plants of both species were transplanted in pots and maintained under a rain-out shelter. Pots were treated either in the spring or summer with biosolids at rates of 0, 7, 18, 34 and 90 dry Mg ha −1 and irrigated at either 40 or 80% field capacity soil water content. The increase in biosolids rates produced increases in leaf area that did not always correspond with increases in photosynthetic rates ( P n ). This suggests that achieving a well-developed canopy was more important than increasing P n per se. However, plant responses to biosolids application varied with irrigation regimes and between species. A decrease in P n of blue grama treated with 34 Mg ha −1 of biosolids was, in part, due to stomatal closure to modulate water loss and possibly to relocation of N for root growth. Under 80% field capacity, tobosagrass seemed to have a less conservative strategy in regulating g s than blue grama. Spring application of biosolids resulted in higher P n than summer application. Photosynthetic rates of blue grama and tobosagrass were not always related to tissue N concentrations.

Water relations and transpiration of honey mesquite on 2 sites in west Texas.

Transpiration rates and internal water relationships of honey mesquite (Prosopis glandulosa) were investigated weekly during May through September 1986 on sandy loam and clay loam, both upland sites in west Texas. Average transpiration rates peaked at approximately 7 mmol m-2 s-1 at 1100 hr during wet periods and reached a plateau between 4 and 5 mmol m-2 s-1 between 1200 and 1400 hr. During dry periods, the average transpiration rates reached their maximum plateau of 2 mmol m-2 s-1 at 1000 hr and declined between 1200 and 1600 hr. The transpiration rates ranged from an average of 3.28 +/- 2.05 mmol m-2 s-1 for trees on a sandy loam site to an average of 3.85 +/- 1.94 mmol m-2 s-1 for those on a clay loam site. Stomatal closure in midsummer caused a substantial increase in leaf temperature. Mesquite has developed other means, such as leaf orientation, wax accumulation, and reduction in canopy development, to avoid drought. Stomatal conductance of mesquite is very responsive to soil water availability and dryness of the air, and is less responsive to internal water status. This research further substantiates that mesquite behaves like a facultative phreatophyte in west Texas.

Forage Response of a Mesquite-Buffalograss Community Following Range Rehabilitation.

The influence of different range rehabilitation methods on honey mesquite control, herbage production, and grazing capacity were evaluated on a depleted clay loam range site in west Texas. Mesquite control by foliar application of 2,4,5-T + picloram, shredding, mechanical grubbing, mechanical grubbing and seeding to kleingrass, and mechanical grubbing and vibratilling increased herbage production and grazing capacity. Shredding increased soil cover by adding plant litter, but significantly controlled mesquite competition for only 2 years. Seeding to kleingrass resulted in a productive stand with a high estimated grazing capacity. Foliar spraying doubled grass production compared to no treatment and resulted in 76% mesquite mortality 3 years after treatment. Deferment from grazing was important in increasing herbage production during the study period; however, for maximum grazing capacity both mesquite control and proper grazing would be

Soil water extraction and photosynthesis in Gutierrezia sarothrae and Sporobolus cryptandrus.

Broom snakeweed (Gutierrezia sarothrae Shinners), a C3 evergreen half-shrub, is a formidable competitor of grasses in the semiarid southwestern rangelands. Sand dropseed (Sporobolus cryptandrus (Toff.) Gray), perennial C4 bunchgrass, is the most drought resistant species in the short-grass prairie. A comparative study on soil water extraction patterns, photosynthesis, and canopy development in both species during spring-summer growing season of 1991 was conducted in pot- and field-grown plants. Sand dropseed extracts water at depths between 0 and 30 cm more effectively than broom snakeweed. In contrast, broom snakeweed can take up more water from the subsoil (30-60 cm) than sand dropseed. Photosynthesis in sand dropseed was more affected by soil water deficit than was broom snakeweed, which was related to their water extraction patterns. Leaf area accumulation of broom snakeweed was not affected by spring drought, but that of sand dropseed was reduced. Because of greater water extraction from the wetter subsoil by broom snakeweed during drought, it can assimilate more carbon and, therefore, prevail in a competitive relationship with sand dropseed.

Influence of soil-water potential on the water relationships of honey mesquite.

Highlight: Thermocouple psychrometry was used to measure soil and plant water potentials of honey mesquite growing under irrigated and nonirrigated field conditions. The trees growing on the irrigated area experienced more internal stress {average minimum water potential, -30.9 bars) than trees growing under nonirrigated conditions (average minimum water potential, - 19.4 bars). The water potential in the trees and transpiration rates adhered to a very distinct daily pattern. Minimum water potential occurred about noon in the trees growing on both sites. During the growing season, the average transpiration rate of the trees on the irrigated area was 9.59 X lo-’ g crne2 min-‘, while the average transpiration rate for those trees growing on the nonirrigated area .was 7. I.5 X 1 O-’ g cmm2 min-‘. The trees growing under irrigation produced 2 times more foliage than the trees growing without irrigation. Consequently, the greatest amount of soil water depletion occurred under irrigation. The results of this study indicated that water loss via transpiration in honey mesquite growing in shallow soils or on upland sites (relatively dry situations) is not as great as the amount lost from trees growing on bottomland and on riparian sites.

Total nonstructural carbohydrate trends in Chinese tallow roots.

Chinese tallow (Sapium sebiferum L. Roxb.) was introduced to the United States from China in the mid to late 1800s and has since naturalized throughout much of the southern U. S. Tallow continues to invade a wide variety of habitats, but control efforts have been inconsistent. We related root total nonstructural carbohydrate (TNC) levels and phenological development in Chinese tallow over an annual cycle to determine optimal timing for control treatments. Six phenological stages were recorded; (1) dormancy, (2) bud break, (3) leaf development, (4) seed formation, (5) seed maturation, and (6) leaf fall. Tallow root TNC concentrations varied by phenological stage (P<0.001), where concentrations were highest (P <0.05) during leaf fall (60.72%) and lowest during leaf development (41.11%) and seed formation (36.71%). Chinese tallow root TNC concentrations increased during the period of seed maturation until leaf fall. If foliar applied herbicides are delivered during this period of downward translocation, effective tallow control may be observed.