Gutierrezia Sarothrae Research Articles

Hydraulic Properties of Shallow vs. Deep Lateral Roots in a Semiarid Shrub, Gutierrezia sarothrae

-Hydraulic conductivity of the deep and shallow lateral roots in the xerophyte Gutierrezia sarothrae Shinners (broom snakeweed) was measured for plants grown under two soil-water regimes. Hydraulic conductivity was 3.4-fold greater in the white, nonsuberized deep roots than in the brown, suberized shallow roots in dry soil; but was only 67% higher under favorable soil moisture conditions. Deep roots had 40% more large xylem vessels (diameters -20 ,tm) than shallow roots in the plants growing in the field during the normal summer dry season. This may result in lower axial resistance to water flow in the xylem conduits in deep roots, but theoretical axial resistances calculated with the PoiseuilleHagen equation could only explain 23% of the difference in hydraulic conductivity between deep and shallow roots. Apparently, increased radial resistance in the suberized shallow roots was mainly responsible for the low hydraulic conductivity observed during the dry season. Suberized roots of G. sarothrae regained high hydraulic conductivity 1 day after soil rewetting. This indicates a rectifier-like behavior of root systems in this half-shrub, as has been documented for desert succulents.

Overstory-Understory Relationships for Broom Snakeweed-Blue Grama Grasslands

Data collected over a 11-year period at 2 study areas near Vaughn and Roswell, N.M. were used to define equations that relate grass biomass to the amount of broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) occupying blue grama (Bouteloua gracilis [H.B.K. Lag]) rangeland over time. A 5 parameter sigmoidal growth equation and a negative exponential equation best expressed the relationship between understory grass biomass and overstory broom snakeweed biomass. Explanatory variables included realized precipitation during the second April to June) and third (July to September) quarters, which coincides primarily with warm-season grass growth. Minimum suppression of grass biomass occurred with complete elimination of broom snakeweed, suggesting control strategies with high overstory mortality will likely be most beneficial to understory production.

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.

Broom Snakeweed Responses to Drought: I. Photosynthesis, Conductance, and Water-Use Efficiency

The effects of water deficit on photosynthesis, transpiration, stomatal conductance, canopy development, and water-use efficiency of broom snakeweed (Gutierrezia sarothrae (Pursh) Britt and Rusby) were studied during the spring-summer growing season in pot-grown plants subjected to 5 soil water regimes. Stomatal conductance was proportionately more reduced by a mild water stress (soil water potential = -0.2 MPa) than were canopy development and photosynthesis. However canopy development was most affected by moderate to severe soil water deficit (< -1.1 MPa), followed by photosynthesis; transpiration and leaf conductance were least affected. When subjected to severe water stress, broom snakeweed controlled its water loss mainly through reduced canopy development rather than stomatal closure. Photosynthesis was more limited by mesophyll conductance than by stomatal conductance. Water-use efficiency was not affected by mild water stress. As soil water deficit developed, water-use efficiency declined, which was a response to nonstomatal limitation to photosynthesis and less sensitive stomata to severe water deficit. Broom snakeweed maintained positive net photosynthesis at soil water potential as low as -3.4 MPa and leaf water potential of -8.19 MPa. Waterspending behavior (low water-use efficiency) and high degree of drought tolerance were the main physiological characteristics of broom snakeweed subjected to water stress.

Broom Snakeweed Responses to Drought: II. Root Growth, Carbon Allocation, and Mortality

The effects of soil water deficit on root growth, carbon allocation, and plant mortality of broom snakeweed (Gutierrezia sarothrae (Pursh) Britt and Rusby) were studied during the spring-summer growing season in plants subjected to different soil water regimes. As soil water deficit developed, root length density decreased, indicating that water deficit reduced root proliferation. Root/shoot ratio remained unchanged (p > 0.05) as soil water potential decreased from -0.023 Mpa to -2 MPa; but it became higher (P < 0.05) in extremely stressed plants (-3.4 MPa), indicating that root growth was favored over shoot growth. Root length density was more closely correlated with green tissue dry weight/-stem dry weight ratio (r = 0.82, p < 0 .0001) than with root/shoot ratio (r = 0.52, p < 0 .05). This suggests that (1) expansion of photosynthetic area was more sensitive than stem growth to water deficit and (2) carbon allocation within the shoot was more sensitive to water deficit than allocation between root and shoot. Plants died when gravimetric soil water decreased to around 0.03 g g-1 (equivalent to a soil water potential of -7.5 MPa). The leaf relative water content just before death was about 0.50. Soil water content in the top 20 or 30 cm of the profile is the single most important factor determining mortality of the snakeweed plant and can be used in making decisions in snakeweed control programs.

Range Condition Influences on Chihuahuan Desert Cattle and Jackrabbit Diets

Knowledge of comparative diet selection by cattle and black-tailed jackrabbits (Lepus californicus) would permit better estimation of grazing capacity on Chihuahuan desert ranges. Cattle and black-tailed jackrabbit diets were evaluated seasonally on good and fair condition ranges over a 2-year period. Fecal samples analyzed by the microhistological technique were used to determine diets of both animals. Key forage species in cattle diets were dropseeds (Sporobolus sp.), black grama (Bouteloua eriopoda Torr.), leatherweed croton (Croton pottsii Lam.), and bush muhly (Muhlenbergia porteri Scribn.). Key forage species in jackrabbit diets were honey mesquite (Prosopis glandulosa Torr.), cactus (Opuntia sp.), dropseed, broom snakeweed (Gutierrezia sarothrae Pursh.), and black grama. Overall diet botanical composition data showed cattle consumed 58% grass compared to 22% for jackrabbits (P < 0.05). Forb consumption was similar between the 2 animals and averaged about 31%. Shrub consumption averaged 47% and 12% for jackrabbits and cattle, respectively (P < 0.05). Range condition did not influence total grass consumption by either animal. Both animals, however, had lower forb and higher shrub consumption on fair compared to good condition range. Overall dietary overlaps between jackrabbits and cattle were 40 and 42% on good and fair condition ranges, respectively. Poisonous plants contributed up to 14 and 36% of cattle and jackrabbit diets, respectively. Data from this study show little forage competition occurs between cattle and jackrabbits when stocking rates and jackrabbit numbers are moderate. Several plants poisonous and unpalatable to cattle were important jackrabbit foods. These plants were more prevalent on the fair compared to the good condition range.

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.

Drought-induced changes in water relations in broom snakeweed ( Gutierrezia sarothrae) under greenhouse- and field-grown conditions

Pressure-volume analyses were done on a half-shrub broom snakeweed ( Gutierrezia sarothrae) subjected to different soil water regimes under pot- and field-grown conditions. Under pot and field conditions, water deficit decreased water and osmotic potentials. In the severely droughted pot-grown, osmotic potential at full turgor (П 100) decreased by 0.44 MPa due to reduced symplastic volume, the result of a decreased leaf turgid to dry weight ( TW/DW) ratio. A reduction of 0.86 MPa in П 100 was observed in the field-grown plants subjected to the first drought cycle, but increased cell wall elasticity occurred in the second drought cycle. The lowered П 100 was attributed to osmotic adjustment and reduced symplastic volume. High cell wall elasticity in the second drought cycle led to a greater water loss and tissue desiccation. It is concluded that osmotic adjustment, increased apoplastic water fraction and more rigid tissue are important dehydration-avoidance mechanisms in broom snakeweed.

Growth, Photosynthesis, and Stomatal Conductance in Gutierrezia sarothrae Associated with Hydraulic Conductance and Soil Water Extraction by Deep Roots

We hypothesize that predominance of Gutierrezia sarothrae in the rangeland plant community depends on its ability to take up water more effectively from soil depths below 30 cm. Gutierrezia seedlings grown in 30-cm-deep pots were allowed to develop deep lateral roots out of pots into subsoil. The deep laterals were then excised and photosynthesis and stomatal conductance of the test plants measured before and after root pruning. Photosynthesis (A) and stomatal conductance (g) were at least 49% greater (P < .05) before than after root pruning. Photosynthesis and g were more affected by the removal of four deep roots 30 cm below the surface than by the removal of four shallow roots in the top 30 cm of soil. The soil water extraction patterns in Gutierrezia plants grown in 60-cm soil columns were determined for the upper 30 cm and 30 to 60 cm of soil. Water extraction was significantly greater (P < .05) from the wetter, lower section of the soil column than from the drier, upper column. Higher photosynthesis...

Remote Sensing of Broom Snakeweed (Gutierrezia Sarothrae) with Noaa-10 Spectral Image Processing

Low-spatial resolution satellite imagery from the NOAA-10 polar-orbiting meteorological satellite was analyzed to determine if central New Mexico grasslands infested by broom snakeweed could be discriminated from unaffected areas. Distinctive phenological characteristics of broom snakeweed, including an early season growth flush and late season flowering, enable moderate to heavily infested areas to be separated from grasslands having few or no weeds present. The procedure used shows promise as a tool for locating and monitoring brown snakeweed and other weeds growing on shortgrass prairie.

Picloram Absorption by Broom Snakeweed (Gutierrezia sarothrae) Leaf Tissue

Foliar absorption of picloram by broom snakeweed, a rangeland shrub, was investigated. Picloram uptake into leaf, axillary bud, and stem tissues was similar. In addition, picloram uptake by leaf tissue from greenhouse- and field-grown broom snakeweed did not differ. Picloram accumulated rapidly and absorption saturated between 15 min and 1 h of application; no further absorption occurred through 72 h with maximum uptake ca. 15% of applied picloram. Picloram content increased linearly with increasing external picloram concentration, implying that movement of the herbicide across the cuticle is via diffusion. Absorption was dependent on relative humidity and temperature with the greatest uptake at 94% relative humidity and 35 C, respectively. Absorption was pH dependent; picloram absorption was greatest at pH 4 and least at pH 8. In addition, picloram absorption was less at pH 3 compared to pH 4. These results provide evidence that picloram is absorbed across the cuticle via simple diffusion and absorption is dependent on environmental conditions and solution pH at and following application.

A comparison of 14C, 86Rb, and total excavation for determination of root distributions of individual plants

Individual grass (Bouteloua gracilis) and shrub (Gutierrezia sarothrae) plants were either excavated as monoliths on nail boards, exposed to 14CO2, or stem-injected with 86Rb to compare the ability of the techniques to determine horizontal and vertical distribution of roots. The vertical distribution or roots directly under plant centers obtained by coring most closely correlated with monolith root length. 14C activity greatly overestimated near-surface roots and underestimated deep roots. 86Rb activity did not follow the pattern of geometric decrease in root biomass with depth. Comparisons of both isotopes with monolith root length, over both horizontal and vertical axes, indicated that 14C activity was consistently concentrated near the soil surface, and 86Rb activity was highly variable and randomly distributed. 14C may better represent root activity than root mass, and stem-injection methods can result in nonuniform labeling of roots. Caution should be exercised when using tracers to infer root biomass distributions. Resource partitioning between shrubs and grasses is discussed in relation to soil water dynamics in this semiarid grassland.

Estimating the Life of Short-lived, Cyclic Weeds with Markov Processes

Some annual weeds, perennial herbs, and suffrutescent half shrubs are unique in that their populations are cyclic in nature and relatively short-lived. This variability presents a confounding factor that makes management decisions about control of these weeds difficult. This paper presents a procedure, using Markov processes, that gives additional information for managing cyclic weed populations. The Markov chain model is used to evaluate the interyear patterns of broom snakeweed survival when growing on New Mexico rangeland.

Economics of Broom Snakeweed Control on the Southern Plains

Revenues associated with controlling broom snakeweed (Xanthocephalum sarothrae) on 6 soils with heavy, moderate, and light infestations of snakeweed were estimated. The analysis considered economic returns associated with grass yield response and those from livestock efficiency gains. Results indicate that control of moderate and heavy infestations is generally economically feasible, but treatment of light infestations does not pay. The economic benefits from livestock efficiency gains are generally greater than the value of increased grass production.

PICLORAM-INDUCED ETHYLENE PRODUCTION BY BROOM SNAKEWEED

Broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. &amp; Rusby] is a suffrutescent shrub that is a problem in rangeland production areas because it interferes with forage growth and is potentially dangerous to livestock. Picloram, an auxin-like herbicide, is used for broom snakeweed control. Picloram-induced ethylene production may be important to its efficacy, therefore, studies were conducted to characterize ethylene production and phytotoxicity. Picloram, applied as individual drops, induced a linear increase in ethylene production (r= 0.738***) between 0 and 72 hr after treatment. When plants were sprayed with 0.125, 0.25 and 0.50 lb ae/A, ethylene production increased linearly through 120 hr then leveled off and began to decrease for all three concentrations. The highest rate of ethylene production was induced by 0.25 lb ae/A followed by 0.50 and 0.125, respectively. Epinasty was evident 24 hr after treatment and chlorosis 3 to 4 days after treatment. Both were more severe with increasing picloram concentration. It appears that picloram-induced ethylene production is an important component in picloram activity.

Influence of Insect Herbivory on Photosynthetic Area and Reproduction in Gutierrezia Species

(1) Larvae of the two tortricid lepidopterans, Synnoma lynosyrana and Synalocha gutierreziae, form silk cases that tie together a significant proportion of the photosynthetic stems and leaves of the common rangeland perennial, Gutierrezia sarothrae, which are toxic to cattle. (2) These insects were significantly more abundant in cattle-grazed plots than in ungrazed plots of the Sevilleta National Wildlife Refuge, located in central New Mexico, USA. (3) Using these herbivores as the experimental manipulation of the plant, measurements were made of photosynthetic area and proximate reproduction of plants with both tied and control (non-tied) branches. In within-plant comparisons, tied branches had significantly less photosynthetic area than control branches. The number of flowers/ branch, flowers/capitulum, seeds/branch and seeds/capitulum were all significantly greater for control than for tied branches. However, seeds produced by tied branches germinated more rapidly and at a higher percentage than seeds from control branches over the same time period. (4) The onset of senescence occurred on smaller volume plants in the ungrazed, high larval abundance plots than in the grazed, low larval abundance plots. (5) The results suggest that, at natural levels of tissue loss, Synnoma and Synalocha can seriously affect both the photosynthetic area and the reproduction of individual plants, and can thus potentially affect Gutierrezia population dynamics.

Growth of Gutierrezia sarothrae Seedlings in the Field

Growth of Gutierrezia sarothrae Seedlings in the Field

Broom Snakeweed (Gutierrezia sarothrae) Control with Picloram and Metsulfuron

Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) and metsulfuron {2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] amino] sulfonyl] benzoic acid} were applied to broom snakeweed (Gutierrezia sarothrae[Pursh.] Britt. and Rusby # GUESA) on two spring dates and three fall dates from October 1983 to 1985. Applications of picloram and metsulfuron in the fall more effectively controlled broom snakeweed than applications in the spring. Lower herbicide rates were necessary for 90% or greater control on a sandy loam than on a silty clay loam. Grass yield increased significantly the first, second, and third growing seasons when a majority of the broom snakeweed were killed by either herbicide, but was not different from untreated rangeland when less than 50% of the plants were killed. Reduction in broom snakeweed densities of 90% or greater following applications of picloram or metsulfuron resulted in 3- to 5-fold increases in the estimated carrying capacity of rangeland in east-central New Mexico.

Soil Seed Banks Associated with Individual Broom Snakeweed Plants

Soil Seed Banks Associated with Individual Broom Snakeweed Plants

Remote Sensing of Broom Snakeweed (Gutierrezia sarothrae) and Spiny Aster (Aster spinosus)

Field spectroradiometric plant canopy measurements showed that broom snakeweed [Gutierrezia sarothrae(Pursh.) Britt. and Rusby # GUESA] and spiny aster (Aster spinosusBenth. # ASTSN) had lower near-infrared (0.85-μm) reflectance than did other associated rangeland shrubs and herbaceous vegetation. The low near-infrared reflectances of both species were attributed to their erectophile (erect leaf/stem) canopy structures. These low near-infrared reflectance values caused broom snakeweed to have a dark-brown to black image on color-infrared aerial photos (0.50- to 0.90-μm), whereas spiny aster had a dark reddish-brown to black image. Other rangeland plant species had light-brown, red, or magenta images. Computer-based image analyses of color-infrared film positive transparencies showed that broom snakeweed and spiny aster infestations could be quantitatively differentiated from associated rangeland species. Computer analyses can permit “percent land area infested” estimates of broom snakeweed and spiny aster infestations on rangelands.