Lepidium Latifolium Research Articles

Seed germination of Cirsium arvense and Lepidium latifolium: Implications for management of montane wetlands

Cirsium arvense and Lepidium latifolium are species that can aggressively invade wetland margins and potentially reduce biodiversity and alter ecosystem function. Although expansion of these species primarily occurs via rhizomatous growth, seeds are thought to be important in initial establishment. We conducted this study to investigate differences in seed germination of C. arvense and L. latifolium in montane wetlands of Colorado and Wyoming, USA. We used germination chambers to simulate environmental conditions (photoperiod, day/night temperature) during three periods of the growing season at each site and evaluated seed germination in relation to three soil moisture levels and two soil depths. A combination of shallow (<1 cm) seed burial and wet conditions resulted in the greatest germination probability of C. arvense (x = 63.0%), 95% CI = 41.2–80.5%), whereas deep (2–3 cm) seed burial and saturated moisture conditions resulted in almost no germination (x = 0.3%, 95% CI = 0.1–1.3%). The maximum germination probability of 44.0% (CI = 28.1–61.4%) for L. latifolium also occurred in the shallow burial and wet treatment; however, only effects of seed burial were significant (P < 0.05). The estimated mean germination probability of deeply buried seeds was < 1.0% (CI = 0.3–1.4%) compared to 32% (CI = 19.7–47.9%) for shallowly buried seeds. Our results suggest that each species has the ability to germinate at similar rates throughout the growing season and across a large portion of the moisture gradient. This suggests that management actions, including water-level manipulations, at any time during the growing season may stimulate germination. Although burial of seed to depths of 2–3 cm reduced the germination potential of both species, the use of mechanical implements may be problematic in established stands because new plants of both species easily sprout from root buds. Further, disturbance resulting from such actions diminishes the density and vigor of other plants already present, which may ultimately decrease the competitive resistance of the disturbed environment to invasion by outside species. Detection of new invasions is a critical component of any integrated weed management program. Our results indicate that the incidence of C. arvense and L. latifolium germination is most likely in areas with seeds that are within 1 cm of the soil surface and soil moisture is 75–100% of field capacity for extended periods.

Analysis of the Volatile Constituents of the Seeds, Roots, Leaves and Whole Flowering Plant of Lepidium latifolium L.

Volatile constituents of the seeds, roots, leaves and dried whole flowering plant of Lepidium latifolium L. collected after hydrolysis were analyzed by GC and GC/MS. The main volatile constituents of the seeds and the roots were allyl, benzyl and sec-butyl isothiocyanates, while the main volatile constituents of the leaves and the whole flowering plant were allyl isothiocyanate and 1-cyano-2,3-epithiopropane.

Effect of Ruminal Incubation on Perennial Pepperweed Germination

Perennial pepperweed ( Lepidium latifolium L.) is an aggressive perennial forb that is infesting much of western North America. Grazing may provide an alternative to chemical and mechanical control of perennial pepperweed. However, if livestock are used in control efforts, they may spread weeds by depositing viable seeds in fecal pats in uninfested areas. This study consisted of 2 experiments using fistulated steers to estimate the effect of ruminant digestion on germination of perennial pepperweed seeds. In Experiment 1, we tested the hypothesis that ruminal incubation (for 0, 48, and 96 hours) affects perennial pepperweed germination. In Experiment 2, we tested the hypothesis that type of incubation (no incubation, water only, or total digestive tract) affects perennial pepperweed germination. In Experiment 1, germination was 17 and 15 times greater for the 48- and 96-hour incubation treatments compared to the control, respectively. In Experiment 2, germination was 23 and 19 times greater for the water and total tract incubation treatments compared to the control, respectively. Effects were attributed to a combination of seed hydration and seed coat scarification . Results from this study suggest that grazing should occur prior to seed set or that livestock which have grazed perennial pepperweed bearing viable seed should be quarantined before being moved to uninfested areas. These results also suggest that control of perennial pepperweed is especially important where moving water may transport seeds off site . El “Perennial pepperweed” ( Lepidium latifolium L.) es una hierba perenne agresiva que esta infestando muchas áreas de Norteamérica. El apacentamiento puede ser una alternativa del control químico y mecánico del “Perennial pepperweed,” sin embargo, si el ganado es usado para el control de malezas, este puede dispersar semillas de ellas al depositar en áreas sin infestar heces fecales conteniendo semillas viables de malezas. Este estudio consistió de dos experimentos usando novillos fistulados para estimar el efecto de la digestión ruminal en la germinación de semillas de “Perennial pepperweed.” En el experimento 1 probamos la hipótesis que la incubación ruminal (0, 48, y 96 hora) afecta la germinación de las semillas de “Perennial pepperweed” y en el experimento 2 probamos la hipótesis de que el tipo de incubación (sin incubar, solo agua y el paso, a través del tracto digestivo) también afecta la germinación de las semillas de esta especie. En el experimento 1, a las 48 y 96 horas, la germinación fue 17 y 15 veces mayor que la del control respectivamente. En el experimento 2, la germinación fue 23 y 19 veces mayor para los tratamientos de agua y paso a través del tracto digestivo, respectivamente, en comparación con el tratamiento control. Los efectos fueron a atribuidos a una combinación de hidratación de la semilla y la escarificación de la cubierta de ella. Los resultados de este estudio sugieren que el apacentamiento puede ocurrir antes de la producción de semilla o que el ganado que ha apacentado el “Perennial pepperweed,” y tiene semillas viables en el tracto digestivo, debe ser cuarentenado antes de ser movido a áreas sin infestar. Estos resultados también sugieren que el control del “Perennial pepperweed” es especialmente importante donde las aguas en movimiento puede transportar las semillas de esta especie fuera de sitios infestados.

Effect of soil flooding on photosynthesis, carbohydrate partitioning and nutrient uptake in the invasive exotic Lepidium latifolium

Lepidium latifolium L. is an invasive exotic crucifer that has spread explosively in wetlands and riparian areas of the western United States. To understand the ecophysiological characteristics of L. latifolium that affect its ability to invade riparian areas and wetlands, we examined photosynthesis, chlorophyll concentration, carbohydrate partitioning and nutrient uptake in L. latifolium in response to soil flooding. Photosynthesis of flooded plants was about 60–70% of the rate of unflooded controls. Chlorophyll concentrations of flooded plants were about 60–70% of the unflooded plants during 15–50 days of flooding. Flooding resulted in an increase in leaf starch concentration, but root starch concentration was not significantly affected. However, concentrations of soluble sugar were significantly higher in both leaves and roots of flooded plants than unflooded controls. On day 50 after initial flooding, the concentrations of N, P, K and Zn in leaves of flooded plants were lower than in control plants. The concentrations of Mn and Fe in leaves of flooded plants were eight and two times those of control plants, respectively. In contrast, N, P, K and Zn concentrations of roots of flooded plants were slightly higher than in unflooded plants. The concentrations of Fe and Mn in roots of flooded plants were 15 and 150 times those of the control plants, respectively. The transport of P, K, and Zn to shoots decreased and that of Mn increased under flooding. The accumulation of N, K and Zn in roots decreased and that of Mn increased in response to flooding. The results suggested that the maintenance of relatively high photosynthesis and the accumulation of soluble sugar in roots of flooded plants are important adaptations for this species in flooded environments. Despite a reduction in photosynthesis and disruption in nutrient and photosynthate allocation in response to flooding, L. latifolium was able to survive 50 days of flooding stress. Overall, L. latifolium performed like a facultative hydrophyte species under flooding.

Dynamic Benefit–Cost Analysis for Controlling Perennial Pepperweed (Lepidium latifolium): A Case Study

Perennial pepperweed, found throughout the western United States, reduces biodiversity and causes economic losses in the form of control costs as well as decreased quantity and quality of agricultural yields. The future stream of net benefits of weed management and the future point in time at which they will have accumulated enough to equal total management costs were estimated under different land-use and expansion rate scenarios. Benefits and costs were calculated in present value terms by applying a rate of discount to future values. On land used solely for grazing, the total economic returns from management did not equal total costs until 15 yr after initial treatment. However, on land used for grazing plus hay harvest, cumulative benefits equaled and began to exceed cumulative costs after 4 to 5 yr. The costs and benefits of management efforts were also estimated for a landowner, who controls an adjacent infestation before it spreads. This landowner benefited economically from weed management in as little as 5 to 6 yr, highlighting the importance of cooperative efforts to control nearby weed infestations.

Effect of Ruminal Incubation on Perennial Pepperweed Germination

Perennial pepperweed (Lepidium latifolium L.) is an aggressive perennial forb that is infesting much of western North America. Grazing may provide an alternative to chemical and mechanical control of perennial pepperweed. However, if livestock are used in control efforts, they may spread weeds by depositing viable seeds in fecal pats in uninfested areas. This study consisted of 2 experiments using fistulated steers to estimate the effect of ruminant digestion on germination of perennial pepperweed seeds. In Experiment 1, we tested the hypothesis that ruminal incubation (for 0, 48, and 96 hours) affects perennial pepperweed germination. In Experiment 2, we tested the hypothesis that type of incubation (no incubation, water only, or total digestive tract) affects perennial pepperweed germination. In Experiment 1, germination was 17 and 15 times greater for the 48- and 96-hour incubation treatments compared to the control, respectively. In Experiment 2, germination was 23 and 19 times greater for the water and total tract incubation treatments compared to the control, respectively. Effects were attributed to a combination of seed hydration and seed coat scarification. Results from this study suggest that grazing should occur prior to seed set or that livestock which have grazed perennial pepperweed bearing viable seed should be quarantined before being moved to uninfested areas. These results also suggest that control of perennial pepperweed is especially important where moving water may transport seeds off site.

Germination of Two Noxious Range Weeds Under Water and Salt Stresses with Variable Light Regimes1

Russian knapweed and perennial pepperweed are invasive to meadow and riparian habitats in the semiarid intermountain west. Seed germination was tested to determine favored seedbed characteristics. Germination was inhibited in both species when water stress was imposed using polyethylene glycol. Knapweed achieved 60% germination after 40 d in dark and alternating light/dark environments. Pepperweed germination was greatest (30% after 14 d) in light and alternating light/ dark environments. Both species showed that germination declines when exposed to salt stress but continued to germinate under salt stress as high as 16 dSm−1. Nomenclature: Perennial pepperweed, Lepidium latifolium L. #3, LEPLA; Russian knapweed, Centaurea repens L. #3 CENRE. Additional index words: Riparian habitats, seedbed ecology.

Influence of Perennial Pepperweed (Lepidium latifolium) Biology and Plant–Soil Relationships on Management and Restoration1

Abstract Perennial pepperweed is an invasive noxious weed spreading rapidly throughout a wide range of habitats in the western United States. Shoots form dense monotypic stands with high initial leaf area, dense inflorescences, and deep litter layers that inhibit the establishment of other plant species. Roots store large amounts of carbohydrates for future growth, establish deep into the soil, and are responsible for clonal expansion of populations. In sodic soils, increases in N, Mg, and Ca were observed in invaded compared with noninvaded areas. Several management methods are effective in controlling perennial pepperweed, but success is dependent on age and density of infestations. Knowledge of many factors, including perennial pepperweed's biology and specific characteristics of the infested area, will help in the development of the most appropriate, site-specific management and restoration plans. Nomenclature: chlorsulfuron; glyphosate; 2,4-D; perennial pepperweed, Lepidium latifolium L. #3 LEPLA. Ad...

Effects of CO2enrichment on plant-soil relationships of Lepidium latifolium

The exotic crucifer Lepidium latifolium L. (perennial pepperweed) is invading wetland and riparian habitats throughout the western United States. Based on previous field studies, our working hypothesis proposed that L. latifolium elevates soil nutrient acquisition ability in response to CO2 enrichment. Replicates of L. latifolium were grown in a high fertility and low fertility soil (along with unplanted controls) in a glasshouse at ambient and elevated CO2 concentrations (360 and 699 µmol mol −1 , respectively). Plants were harvested after 81 days and numerous plant and soil attributes measured. Above-ground plant mass was influenced by a significant CO2 treatment × soil interaction ( P 20% and increased, though not significant, tissue C:N ratio by 38% in high fertility soil and by 51% in low fertility soil. For most soil attributes measured, there was a main effect or interaction with soil fertility level. Soil attributes differed between soil fertility levels and, with the exception of SO 2− 4 , were not influenced by the presence of L. latifolium. Soil attributes increased by CO2 enrichment included acetate extractable Mg 2+ (high fertility soil only), net 30 day N mineralization potential (unplanted control soils only), available N (high fertility soil), bicarbonate extractable P, soil-solution SO 2− 4 (L. latifolium planted pots only), and soil-solution Mg 2+ (high fertility control soil only). Collectively, these data tangentially support our working hypothesis that CO2 enrichment increases nutrient availability. That availability of some nutrients increases without plant growth (control soils), however, suggests an interaction of elevated CO2 with soil microflora.

INFLUENCE OF THREE WEED SPECIES ON SOIL NUTRIENT DYNAMICS

The hypotheses that weeds increase soil nutrient availability and differentially alter soil nutrient dynamics were tested in the greenhouse by comparing and contrasting plant-soil relationships among Bromus tectorum L. (cheatgrass, downy brome), Lepidium latifolium L. (perennial pep-perweed, tall whitetop), and Centaurea solstitialis L. (yellow starthistle). These species are highly invasive and produce dense stands that reduce or eliminate native species. A high resource (HR) soil and a low resource (LR) soil were evaluated. To simulate declining soil resources, individual plants were grown in the same pots, harvested, then replanted for a total of three growth cycles. Aboveground mass was greatest in the HR soil in which L. latifolium and C. solstitialis accumulated greatest biomass after the second growth cycle and B. tectorum accumulated greatest biomass after the third growth cycle. In the LR soil, all plants had the greatest aboveground mass after the third growth cycle. Overall, nutrient concentration in aboveground tissue declined significantly with growth cycle. Tissue K and P concentrations were highest in plants grown in the HR soil, whereas Ca and N were highest in plants grown in the LR soil. Nutrient uptake overall decreased with growth cycle for the HR soil and increased with growth cycle for the LR soil. Relative to unplanted controls, all three species facilitated an increase in soil-solution Ca and Mg in the HR soil, greater N-mineralization potential in both soils, and greater enzyme activity in the LR soil by the third growth cycle. The species displayed distinctly different ratios of nutrient uptake and concentration in aboveground tissue, with L. latifolium having much higher tissue Ca/Mg concentration ratios and uptake ratios of Ca/Mg, Ca/N, and Ca/P than C. solstitialis or B. tectorum. Stepwise regression suggests soils with high levels of available Mg may have a greater risk for invasion by C. solstitialis and L. latifolium. These data support the working hypotheses.

Effect of an integral suspension of Lepidium latifolium on prostate hyperplasia in rats

This paper studies the effect of an integral suspension of Lepidium latifolium on experimental induced prostate hyperplasia, in rats. Oral treatment with 0.86 mg kg −1 day −1 for 6 months, significantly reduced prostate size and volume in castrated rats where the hyperplasia were induced by steroid treatment.

Mechanism for the enhanced effect of mowing followed by glyphosate application to resprouts of perennial pepperweed (Lepidium latifolium)

Herbicides currently registered for use near water have been ineffective for control of perennial pepperweed. Previous research has demonstrated that mowing followed by an application of glyphosate at 3.33 kg ae ha−1to resprouting tissue can enhance the control of perennial pepperweed. The objectives of this study were to determine the mechanism(s) responsible for the enhanced effectiveness of glyphosate in combination with mowing. Mowing plants altered the leaf area distribution within the canopy. In mowed areas, the majority of leaf area was in the basal third of the canopy, whereas the bulk of the leaf area was in the top third of the canopy in unmowed plots. This change in plant architecture affected the deposition pattern of the spray solution. Unmowed plants retained 49 to 98% and 42 to 83% of a dye solution within the middle and top thirds of the canopy at the Colusa and Woodland sites, respectively, with only 1.9 to 6.0% dye deposited on the basal third of the canopy at both sites. In contrast, mowed plants had 18 to 34% and 26 to 70% of the dye retained in the basal third of the canopy at the Colusa and Woodland sites, respectively. Greenhouse studies showed that14C-glyphosate applied to basal leaves of mowed plants translocated significantly more to belowground tissue. Unmowed plants accumulated 0.37% of the applied14C-glyphosate in belowground tissue 48 h after labeling. In contrast, mowed plants accumulated 6.7%14C-glyphosate in the belowground tissue. In field studies, estimates of basipetal seasonal translocation rates using total nonstructural carbohydrate pools of roots indicate that mowing did not change the translocation rate. However, the delay in application timing to allow plants to resprout appeared to synchronize applications with maximal translocation of carbohydrates to belowground structures. We hypothesize that the change in the canopy structure of perennial pepperweed after mowing results in fewer aboveground sinks and greater deposition of herbicide to basal leaves where it can preferentially be translocated to the root system. Furthermore, the delay between mowing and resprouting synchronized maximal belowground translocation rates with herbicide application timing. These factors all appear to be involved in the observed enhanced control of perennial pepperweed when combining mowing and glyphosate.

Weed Invasion Susceptibility Prediction (WISP) Model for Use with Geographic Information Systems

The Weed Invasion Susceptibility Prediction (WISP) model was developed as an extension of the ArcView Geographic Information System to predict potential risk of invasion by individual weed species in rangelands. Existence potential was determined by comparing growth requirements of each weed species with respect to nine site characteristics obtained from geographic data layers: distance from water and disturbance sources, elevation, annual precipitation, soil texture and pH, aspect, slope, and land cover. Disturbance is important for predicting weed infestations; an innovative aspect of the WISP model is that we use data layers for transportation and energy development as an estimate of disturbance. Data from weed surveys conducted at the Jack Morrow Hills Study Area in southwestern Wyoming, USA, were used to test WISP model predictions for the occurrence of Hyoscyamus niger (black henbane), Cardaria draba (hoary cress), and Lepidium latifolium (perennial pepperweed). Data acquired from the U.S. Department of Interior, Bureau of Land Management were used to test model predictions for the occurrence of Euphorbia esula (leafy spurge) and Centaurea maculosa (spotted knapweed) for four counties in northwestern Wyoming, USA. The model accuracy, based on false-negative errors where a species was present but was predicted not to occur, averaged 89% for the five weed species. The WISP model allows land managers to predict more easily and accurately the potential for weed invasions in order to prioritize areas for detailed monitoring.

Notas sobre neófitas 3. Distribución de algunas Brassicaceae de reciente introducción en el centro de México

Se presenta información adicional sobre la distribución de varias especies exóticas de Brassicaceae de reciente introducción en el centro de México. Se registran tres poblaciones de Thlaspi arvense L. y de Sinapis alba L. Las especies Diplotaxis muralis (L.) DC., Hirschfeldia incana (L.) Lagrèze-Fossat y Brassica tournefortii Gouan, conocidas previamente del norte de México, ahora están naturalizadas y al parecer en expansión en varias localidades en el centro del país. Rapistrum rugosum (L.) All., Cardamine hirsuta L., Lepidium latifolium L. y Lepidium draba L. (= Cardaria draba (L.) Desv.) están extendiéndose en el Valle de México y algunas regiones vecinas.

Anaerobic metabolism in the roots of seedlings of the invasive exotic Lepidium latifolium

Lepidium latifolium is an invasive exotic crucifer that is widely distributed in riparian zones and wetlands. In this study, anoxic carbohydrate metabolism and post-anoxic injury in the roots of L. latifolium seedlings were examined. A significant increase in the activity of the fermentative enzymes alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) in roots occurred under anoxia and increased with the duration of anaerobic treatment during 7 days. However, pyruvate decarboxylase (PDC) and cytochrome c oxidase (CCO) activity was maintained at relatively stable levels under anaerobic and aerobic conditions. Soluble protein concentration in anoxic roots was two to three times that in aerobic roots throughout 7 days of anoxia. The concentration of the fermentation product ethanol in roots was two times greater under anoxia than under aerobic conditions. The concentration of lactate was much smaller than that of ethanol, but the trend was similar to that of ethanol. There was no significant difference in the concentration of malate between aerobic and anaerobic conditions for 9 days. Superoxide dismutase (SOD) activity in roots was two to three times higher under anoxia than under aerobic conditions throughout 7 days, but this increase in SOD activity decreased slightly with the duration of anoxia. Compared with aerobic conditions, the concentration of malondialdehyde (MDA), an indicator of free radical damage, increased by two to three times under anoxia. Two days after L. latifolium seedlings were returned to aerobic conditions, the concentrations of ethanol and MDA in roots were still significantly higher under the previously anoxic treatment than under continuously aerobic conditions, while no significant difference in enzyme activities or in concentrations of lactate and malate was found between treatments. The metabolism of L. latifolium roots under anoxia is characterized by the concurrent activity of both fermentative pathways and aerobic metabolism. Roots of L. latifolium have metabolically adaptive strategies to anoxia, but there is evidence of oxidative stress under anoxia and of post-anoxic injury from free radicals upon re-exposure to air. Results suggest that L. latifolium exhibit a mixture of characteristics typical of hydrophytic, facultative, and anoxia intolerant species.

INFLUENCE OF THE EXOTIC INVASIVE CRUCIFER, LEPIDIUM LATIFOLIUM, ON SOIL PROPERTIES AND ELEMENTAL CYCLING

Plant species and plant communities can alter element cycling promoting divergent pathways of soil development. We hypothesized that the exotic invasive crucifer, Lepidium latifolium, altered biogeochemical cycling relative to pre-existing vegetation such that sodium-affected subsoils are ameliorated. We tested this hypothesis at the Fleming unit within the Honey Lake Wildlife Refuge in northeastern California by comparing the distribution and cycling of various elements in paired L. latifolium invaded and noninvaded sites occupied by Elytrigia elongata. Soils are fine, smectitic, calcareous, mesic Fluvaquentic Endoaquolls. In 1998, per unit area, live biomass of L. latifolium was more than 3 times greater than that of E. elongata. Content of C, Ca, Mg, K, and S in aboveground tissue of L. latifolium was significantly (P ≤ 0.05) greater than content in E. elongata. Biogeochemical fluxes of C, N, P, Ca, Mg, and S were from 3 to 11 times greater in L. latifolium-occupied areas than in E. elongata-occupied areas. L. latifolium invasion fostered elevated soil solution levels of Mg+2 and Ca+2, thereby reducing sodium adsorption ratios that could lead to sodic soil amelioration. Invasion by L. latifolium has the potential to alter soil properties and processes, thereby altering the trajectory of soil evolution.

Lepidium latifolium : plant nutrient competition-soil interactions

Exotic weeds are invading rangelands of the western United States at unprecedented rates. Under- standing plant-soil relationships and competitive interac- tions of invasive weeds is crucial in long-term control strategies. In a greenhouse experiment, we investigated the influence of soil nutrient depletion on plant growth and plant competition between the exotic invasive weeds, Lepidium latifolium(invading wetlands) and Bro- mus tectorum (invading a multitude of habitats). Plants were grown individually and in combination until L. lati- folium flowered, then roots and aboveground mass were harvested. Soil in individual pots was homogenized, sub- samples collected for nutrient analyses, and the soil was re-planted to the same species, grown, and harvested twice more for a total of three growth cycles. As nutrient supplying capacity of the soil declined through growth cycles, aboveground mass of L. latifolium decreased sig- nificantly (P≤0.05) and growth potential of B. tectorum surpassed that of L. latifolium. Only bicarbonate-extract- able soil ortho-P positively correlated with plant mass of L. latifolium. A separate experiment demonstrated that L. latifolium has a narrow window of soil water potentials for optimal growth; greatest growth at -20 kPa with sig- nificantly declining growth at saturation and -400 kPa. Our data suggest that L. latifolium primarily invades wetlands because the high soil water content reduces tortuosity and allows efficient transport of nutrients to this sparsely rooted species. When soil moisture and/or the nutrient supplying capacity of the soil declines, plants with greater root density can out-compete L. lati- folium. Monocultural stands of L. latifolium may be self- limiting in time as available nutrients, particularly P, are biocycled to drier upper soil layers.

March JRM Erratum: Herbicide Residues and Perennial Grass on Establishment Perennial Pepperweed Sites

March JRM Erratum: Herbicide Residues and Perennial Grass on Establishment Perennial Pepperweed Sites

Adaptive responses of Lepidium latifolium to soil flooding: biomass allocation, adventitious rooting, aerenchyma formation and ethylene production

Lepidium latifolium, perennial pepperweed, is an exotic crucifer that has spread explosively in recent years in wetlands and riparian areas of the western United States. Adaptive responses of L. latifolium to different durations of 0, 3, 7, 15, 30 and 50-day soil flooding treatment were investigated. Biomass allocation, adventitious rooting, aerenchyma development and ethylene production in plants were measured. Compared with controls maintained at −20 kPa soil matric water potential, flooding stress reduced total biomass of L. latifolium. After 7 days of flooding, the total biomass and root/shoot ratio of flooded plants were significantly less than those of unflooded controls. The number of adventitious roots on the stem base increased with the duration of flooding. Root porosity was much higher in the flooded plants than in the unflooded controls after 3 days of treatment and rose to 43% after 50 days. Ethylene production in roots was higher in flooded plants than in the control throughout the 50-day duration of flooding and peaked at 7 days. The reduction in the root/shoot ratio, adventitious rooting, and aerenchyma development in flooded L. latifolium are important contributions to flood tolerance. L. latifolium resembled species adapted to standing water conditions in terms of having an initially high porosity, but it resembled species adapted to either saturated or occasionally flooded habitats in terms of the degree of increase in root porosity under flooded conditions. However, in growth of biomass, L. latifolium was more like plants that do not grow in mostly saturated conditions. Thus, L. latifolium appears to be a plant that exhibits plasticity to tolerate or survive saturated conditions, but not to grow well under these conditions. This may be an adaptation to arid or semiarid riparian habitats where spring flooding and summer drought are characteristic.

Herbicide Residues and Perennial Grass on Establishment Perennial Pepperweed Sites

Perennial pepperweed (Lepidium latifolium L.) is a creeping rooted exotic weed that has infested native hay meadows, riparian areas and agronomic fields throughout the western United States. This highly invasive species causes major losses in forage quality and creates numerous management problems. On many sites infested with perennial pepperweed, a near mono-culture exist. Sustainable suppression programs require the establishment of a competitive perennial species. You can not establish seedlings of a perennial competitive species without some initial substantial reduction in perennial pepperweed stands through weed control. Because tillage is not feasible with this creeping rooted species, herbicidal weed control is the primary option. Experience has shown, that the massive and extensive root system of perennial pepperweed can not be completely eliminated with one application of a herbicide. This means that repeated applications of a selective herbicide are required after the perennial seedlings of a competitive species are established. Perennial pepperweed is a broadleaf species that is some what susceptible to applications of 2,4-D. Therefore, the choice revegetation species is limited to a perennial grass that is resistant to 2,4-D applications at low rates as a seedlings and moderate rates once established. The saline/alkaline nature of the soils where perennial pepperweed is often found limit the adapted perennial grasses to tall wheatgrass (Elytriga elongata [Host] Nevski). The herbicide chlorsulfuron has been shown to be more effective in initially controlling perennial pepperweed than 2,4-D. We determined that applications of chlorsulfuron at rates sufficient to control perennial pepperweed resulted in herbicidal residues that severely reduced or eliminated the establishment of tall wheatgrass seedlings. Application of 2,4-D at flower budding for perennial pepperweed (June), followed by seeding tall wheatgrass in the fall (October), and application of low rates of 2,4-D over the wheatgrass seedlings the next spring (May), gave the best grass seedling establishment and suppression of the perennial weed. DOI:10.2458/azu_jrm_v55i2_young