Larkspur poisoning: toxicology and alkaloid structure–activity relationships

Systematic approaches to taxonomic classifications of the tall larkspur spp. have been developed using traditional chemical methods to profile alkaloids, comparison of relative toxicity of individual alkaloids, plant morphology/taxonomy and molecular genetics. Using these methods (papers published in this series) toxicology of three distinct species of tall larkspurs including Delphinium glaucum, Delphinium barbeyi and Delphinium occidentale is described. Tall larkspurs (Delphinium spp.) continue to be the most serious cause of cattle losses on mountain rangelands in the western US. Over 40 norditerpenoid alkaloids have been reported in species of larkspurs and toxicology data on 25 of these have been reported by the authors. These alkaloids can be classified into three general types based on their structural characteristics and toxicity: the N-(methylsuccinyl) anthranoyl lycoctonine (MSAL)-type, having high toxicity; the lycoctonine-type, with moderate toxicity; and the 7,8-methylenedioxylycoctonine (MDL)-type, of low toxicity. The structural importance of the methylsuccinimido anthranilic acid ester group at the C18 position is evident in the high toxicity of MSAL alkaloids, particularly methyllycaconitine (MLA), Nudicauline (NUD) and 14-deacetylnudicauline (14-DAN). Other structural aspects of these alkaloids such as the C14 functionality are also important, as demonstrated by the reduced toxicity of barbinine. MLA is the alkaloid of most importance in toxicity of larkspurs on mountain rangelands because of its prevalence in most larkspurs and high toxicity. While NUD and 14-DAN also possess high toxicity, they are relatively minor components in few larkspur species (generally the plains and low larkspurs), but when present at concentrations approaching 1 mg/g dry weight they contribute significantly to overall toxicity. Deltaline (DLT) is often found in high concentrations in many larkspurs but because of low toxicity, its contribution to larkspur poisoning in the field is relatively minor and it will probably not cause toxicosis in the absence of the MSAL-type alkaloids.     

Taxonomic implications of diterpene alkaloids in three toxic tall larkspur species (Delphinium spp.)

The diterpene alkaloid content was used to assess the chemical taxonomic diversity in three larkspur species. Samples (n=163) were collected from 18 different locations in five western states, extracted and analyzed for diterpene alkaloids using electrospray mass spectrometry. The data were statistically analyzed using canonical discriminant analysis and analysis of variance. Delphinium glaucum samples were easily grouped and were significantly different from all other groups (P<0.005) for two compounds. Delphinium barbeyi and Delphinium occidentale were found to be distinct groups, but more closely related. Samples representing a putative hybrid between D. barbeyi and D. occidentale were found to be closely related to D. occidentale, but were significantly different from all other groups. These data support the classification of D. glaucum, D. barbeyi, and D. occidentale as distinct species and suggest that a possible hybrid is more similar to D. occidentale than D. barbeyi.     

Norditerpene alkaloid concentrations in tissues and floral rewards of larkspurs and impacts on pollinators

Plant secondary compounds mediate interactions with insects and other animals. The norditerpene alkaloids are significant secondary compounds in Delphinium (larkspur) species which are divided into two classes: the 7, 8-methylenedioxylycoctonine (MDL-type) and N-(methylsuccinimido) anthranoyllycoctonine (MSAL-type), and are known to be toxic to herbivorous insects and livestock. Alkaloid concentrations were measured in a whole plant context in vegetative and floral tissues as well as rewards (pollen and nectar) in Delphinium barbeyi and Delphinium nuttallianum. Alkaloid concentrations differed between vegetative tissues, floral tissues and floral rewards. Alkaloid concentrations in floral parts were consistent with optimal defense theory, with tissues more closely tied to plant fitness, such as fruits, being more heavily defended than foliage. However, alkaloid concentrations were significantly lower in nectar compared to other tissues. The norditerpene alkaloids influenced the activity of bumble bees, the dominant pollinator of larkspur, but the effects were concentration dependent. Alkaloids in nectar are found at concentrations that have no effect on bee activity; however, if alkaloid concentrations in nectar were similar to those in foliage bee activity would be reduced significantly. These results suggest that nectar with low alkaloid concentrations may be beneficial to plant fitness by limiting adverse effects on pollinator activity.     

Two Delphinium ramosum chemotypes,their biogeographical distribution and potential toxicity

Larkspurs (Delphinium, Ranunculaceae) are poisonous plants found on rangelands throughout Western North America. Two main structural groups of norditerpene alkaloids, the N-(methylsuccinimido) anthranoyllycoctonine type (MSAL-type) and the non-MSAL type, are responsible for larkspur-induced poisoning. Information on the alkaloid composition is lacking for a number of Delphinium species, including D. ramosum. Delphinium ramosum grows throughout parts of Colorado and northern New Mexico. The objective of this study was to profile the alkaloid composition of D. ramosum throughout its geographical distribution using both field and herbarium specimens. Two alkaloid profiles were identified, one that contained significantly greater concentrations of the MSAL-type alkaloids than the other. Plants containing each respective alkaloid profile were unique in their geographical distribution. Populations of these two chemotypes will likely differ in their toxic potential and consequently pose different risks of poisoning when grazed by livestock species. This information has important implications in grazing management decisions on D. ramosum-infested rangelands and demonstrates that botanical classification alone is not an adequate indicator of relative risk of toxicity.     

Seasonal variation in the secondary chemistry of foliar and reproductive tissues of Delphinium nuttallianum

Plant secondary compounds are critical in affecting interactions between plants and their herbivores. The norditerpene alkaloids are secondary compounds in Delphinium (larkspur) species which are divided into two classes: the N-(methylsuccinimido) anthranoyllycoctonine (MSAL-type) and non MSAL-type, and are known to be toxic to herbivorous insects and livestock. Alkaloid concentrations were measured in a whole plant context in vegetative and reproductive tissues in Delphinium nuttallianum at different stages of plant maturity at two locations to explore how plant maturity affected alkaloid concentrations within a growing season. Alkaloid concentrations differed between vegetative and reproductive tissues, with vegetative tissues having significantly lower alkaloid concentrations than reproductive tissues. However, no systematic differences in alkaloid concentrations were observed at different plant maturity stages across the growing season. Based on the data we suggest that alkaloid allocation in different plant parts of D. nuttallianum is influenced by life history of the plant, consistent with plant defense theory. At one location, as pods mature the qualitative alkaloid composition changed through structural diversification of the alkaloids present. The ecological significance of this structural diversification awaits further exploration.     

Seasonal variation in toxic steroidal alkaloids of foothill death camas (Zigadenus paniculatus)

Death camas (Zigadenus spp.) is a common poisonous plant in North America with plants occurring in a wide variety of habitats with species of toxic concern occurring primarily in meadows, grasslands, shrublands, and mountains. The toxicity of Zigadenus species has been attributed to a series of steroidal alkaloids. The objective of this study was to evaluate zygacine and total steroidal alkaloid concentrations in different plant tissues of Zigadenus paniculatus as a function of plant maturity. Death camas plants were collected at two locations at different developmental growth stages representing vegetative, flower, seed pod, and shattered seed pod stages. Zygacine represented greater than 50% of the total steroidal alkaloids at all developmental stages. In bulbs, total steroidal alkaloid and zygacine concentrations did not change significantly as a function of plant phenology, and concentrations were lower than what were observed in above ground plant parts. Total steroidal alkaloid and zygacine concentrations in above ground parts were highest at early vegetative growth stages and decreased over the growing season. In plant reproductive parts, total steroidal alkaloid and zygacine concentrations increased until maturity and then decreased as the plant senesced. The concentrations of steroidal alkaloids reported here suggest that the toxic risk associated with death camas is greatest in the early vegetative growth stages followed by the flower and pod stages. There is a toxic risk to livestock as long as the plant is present, and caution should be taken when grazing livestock in areas with death camas until the plant senesces.     

Cattle grazing and conservation of a meadow-dependent amphibian species in the Sierra Nevada

World-wide population declines have sharpened concern for amphibian conservation on working landscapes. Across the Sierra Nevada''s national forest lands, where almost half of native amphibian species are considered at risk, permitted livestock grazing is a notably controversial agricultural activity. Cattle (Bos taurus) grazing is thought to degrade the quality, and thus reduce occupancy, of meadow breeding habitat for amphibian species of concern such as the endemic Yosemite toad (Anaxyrus [ = Bufo] canorus). However, there is currently little quantitative information correlating cattle grazing intensity, meadow breeding habitat quality, and toad use of meadow habitat. We surveyed biotic and abiotic factors influencing cattle utilization and toad occupancy across 24 Sierra Nevada meadows to establish these correlations and inform conservation planning efforts. We utilized both traditional regression models and Bayesian structural equation modeling to investigate potential drivers of meadow habitat use by cattle and Yosemite toads. Cattle use was negatively related to meadow wetness, while toad occupancy was positively related. In mid and late season (mid July–mid September) grazing periods, cattle selected for higher forage quality diets associated with vegetation in relatively drier meadows, whereas toads were more prevalent in wetter meadows. Because cattle and toads largely occupied divergent zones along the moisture gradient, the potential for indirect or direct negative effects is likely minimized via a partitioning of the meadow habitat. During the early season, when habitat use overlap was highest, overall low grazing levels resulted in no detectable impacts on toad occupancy. Bayesian structural equation analyses supported the hypothesis that meadow hydrology influenced toad meadow occupancy, while cattle grazing intensity did not. These findings suggest cattle production and amphibian conservation can be compatible goals within this working landscape.     

Nectar Yeasts in the Tall Larkspur Delphinium barbeyi (Ranunculaceae) and Effects on Components of Pollinator Foraging Behavior

Microorganisms frequently colonize the nectar of angiosperm species. Though capable of altering a suite of traits important for pollinator attraction, few studies exist that test the degree to which they mediate pollinator foraging behavior. The objective of our study was to fill this gap by assessing the abundance and diversity of yeasts associated with the perennial larkspur Delphinium barbeyi (Ranunculaceae) and testing whether their presence affected components of pollinator foraging behavior. Yeasts frequently colonized D. barbeyi nectar, populating 54–77% of flowers examined depending on site. Though common, the yeast community was species-poor, represented by a single species, Metschnikowia reukaufii. Female-phase flowers of D. barbeyi were more likely to have higher densities of yeasts in comparison to male-phase flowers. Pollinators were likely vectors of yeasts, as virgin (unvisited) flowers rarely contained yeasts compared to flowers open to pollinator visitation, which were frequently colonized. Finally, pollinators responded positively to the presence of yeasts. Bombus foragers both visited and probed more flowers inoculated with yeasts in comparison to uninoculated controls. Taken together, our results suggest that variation in the occurrence and density of nectar-inhabiting yeasts have the potential to alter components of pollinator foraging behavior linked to pollen transfer and plant fitness.     

Control of nematode parasites by grazing management—II. Decontamination of sheep and cattle pastures by varying periods of grazing with the alternate host

Commencing in December 1970, paddocks of a uniform series of sheep pastures were grazed for 6, 12 or 24 weeks by either yearling steers is or yearling ewes. Cattle pastures were treated similarly. All ewes and steers were pre-dosed with anthelmintic.At the conclusion of alternate grazing the effectiveness of the grazing treatments was evaluated by grazing each paddock for 1 month with either ten worm-free lambs (sheep pastures) or three wormfree calves (cattle pastures). The test animals were then slaughtered for total worm counts. The grazing of sheep pastures with cattle for 6, 12 or 24 weeks from December onwards resulted in reductions in numbers of Haemonchus contortus and Trichostrongylus colubriformis in test lambs. In comparison with continuous grazing by sheep, Nematodirus spp was only reduced after 24 weeks grazing by cattle. Cattle pastures grazed by sheep for 6 weeks showed no reduction in numbers of Ostertagia ostertagi or Cooperia oncophora in test calves. However after 12 weeks with sheep, numbers of O. ostertagi though not C. oncophora were reduced and after 24 weeks of alternate grazing both these species were reduced.Calves following the 6 week sheep treatments acquired both Haemonchus contortus and Trichostrongylus colubriformis and the calves from the 12 week sheep treatment paddock also carried H. contortus. For sheep the only evidence of cross-transmission was the occurrence of small numbers of Cooperia oncophora in test lambs from the 24 week cattle grazing treatment.The results provide evidence that sequential stocking with cattle and sheep in conjunction with anthelmintic treatment is an effective management strategy for preparing parasitologically safer pastures, but further information is required to determine the optimum timing of sequential stocking in farming situations.     

Alkaloid levels in Duncecap (Delphinium occidentale) and Tall larkspur (D. barbeyi) grown in reciprocal gardens: separating genetic from environmental influences

The objective of this study was to determine whether differences in toxicity between Tall larkspur (Delphinium barbeyi) and Duncecap larkspur (D. occidentale) were genetically inherent within the species, or due to environmental influences unique to the different regions where they grow. There was no difference in the concentration of the toxic alkaloids between the two species when grown in common gardens. However, both species had higher concentration of toxic alkaloids when grown in the southern Rocky Mountain region which is characterized by summer monsoonal thunderstorms, compared to summer drought in the north. In a unique occurrence where Duncecap larkspur grew beside Tall larkspur, toxic alkaloids were very low in Duncecap larkspur, but total alkaloid concentration was often higher than in Tall larkspur.     

Herbivory of clonal populations: cattle browsing affects reproduction and population structure of Yucca elata

The hypothesis that cattle browsing on inflorescences of the soaptree Yucca elata reduces reproductive success was investigated by comparing recruitment and population structure in six populations protected from grazing, six grazed during the flowering season and five grazed outside the flowering season. Cattle consumed 98% of inflorescences, which were found to be highly nutritious. Reduced recruitment in flower-grazed populations could not be attributed to reduced flower survival, as recruitment in non-flower grazed populations was also reduced. Changes in population structure were due to cattle browsing small caudices, including both genets and ramets. An alternate hypothesis of limited germination in soils compacted by cattle was not supported. Cattle browsing of inflorescences reduced reproductive effort, which may be due to the inability of the plants to resorb nutrients after flowering. Browsing also increased branching, probably through lack of apical dominance, whereas physical trampling increased procumbency. Cattle browsing implies a lack of genetic recruitment, possible local extinction of the yucca moth Tegeticula yuccasella, the exclusive pollinator of Y. elata, and local reduction in insect and bird biodiversity.     

Water Quality Conditions Associated with Cattle Grazing and Recreation on National Forest Lands

There is substantial concern that microbial and nutrient pollution by cattle on public lands degrades water quality, threatening human and ecological health. Given the importance of clean water on multiple-use landscapes, additional research is required to document and examine potential water quality issues across common resource use activities. During the 2011 grazing-recreation season, we conducted a cross sectional survey of water quality conditions associated with cattle grazing and/or recreation on 12 public lands grazing allotments in California. Our specific study objectives were to 1) quantify fecal indicator bacteria (FIB; fecal coliform and E. coli), total nitrogen, nitrate, ammonium, total phosphorus, and soluble-reactive phosphorus concentrations in surface waters; 2) compare results to a) water quality regulatory benchmarks, b) recommended maximum nutrient concentrations, and c) estimates of nutrient background concentrations; and 3) examine relationships between water quality, environmental conditions, cattle grazing, and recreation. Nutrient concentrations observed throughout the grazing-recreation season were at least one order of magnitude below levels of ecological concern, and were similar to U.S. Environmental Protection Agency (USEPA) estimates for background water quality conditions in the region. The relative percentage of FIB regulatory benchmark exceedances widely varied under individual regional and national water quality standards. Relative to USEPA’s national E. coli FIB benchmarks–the most contemporary and relevant standards for this study–over 90% of the 743 samples collected were below recommended criteria values. FIB concentrations were significantly greater when stream flow was low or stagnant, water was turbid, and when cattle were actively observed at sampling. Recreation sites had the lowest mean FIB, total nitrogen, and soluble-reactive phosphorus concentrations, and there were no significant differences in FIB and nutrient concentrations between key grazing areas and non-concentrated use areas. Our results suggest cattle grazing, recreation, and provisioning of clean water can be compatible goals across these national forest lands.     

Tracking gastrointestinal nematode risk on cattle farms through pasture contamination mapping

Gastrointestinal nematode (GIN) parasites in grazing cattle are a major cause of production loss and their control is increasingly difficult due to anthelmintic resistance and climate change. Rotational grazing can support control and decrease reliance on chemical intervention, but is often complex due to the need to track grazing periods and infection levels, and the effect of weather on larval availability. In this paper, a simulation model was developed to predict the availability of infective larvae of the bovine GIN, Ostertagia ostertagi, at the level of individual pastures. The model was applied within a complex rotational grazing system and successfully reproduced observed variation in larval density between fields and over time. Four groups of cattle in their second grazing season (n = 44) were followed throughout the temperate grazing season with regular assessment of GIN faecal egg counts, which were dominated by O. ostertagi, animal weight and recording of field rotations. Each group of cattle was rotationally grazed on six group-specific fields throughout the 2019 grazing season. Maps and calendars were produced to illustrate the change in pasture infectivity (density of L3 on herbage) across the 24 separate grazing fields. Simulations predicted differences in pasture contamination levels in relation to the timing of grazing and the return period. A proportion of L3 was predicted to persist on herbage over winter, declining to similar intensities across fields before the start of the following grazing season, irrespective of contamination levels in the previous year. Model predictions showed good agreement with pasture larval counts. The model also simulated differences in seasonal pasture infectivity under rotational grazing in systems that differed in temperature and rainfall profiles. Further application could support individual farm decisions on evasive grazing and refugia management, and improved regional evaluation of optimal grazing strategies for parasite control. The integration of weather and livestock movement is inherent to the model, and facilitates consideration of climate change adaptation through improved disease control.     

Light grazing of saltmarshes is a direct and indirect cause of nest failure in Common Redshank Tringa totanus

The Common Redshank Tringa totanus breeding population on British saltmarshes has declined by over 50% since 1985, with declines linked to changes in grazing management. Conservation initiatives have encouraged low‐intensity grazing of less than one cattle per hectare, but Redshank have continued to decline, even in regions where light grazing was predominant. This study quantified effects of grazing intensity on Redshank nest survival over six lightly grazed saltmarshes with livestock densities between 0 and 0.82 cattle per hectare, in the Ribble Estuary, northwest England. We assessed whether grazing resulted in nest mortality directly through cattle trampling and/or indirectly through grazer modification of habitat that accelerates predation risks. Cattle density was recorded both during the Redshank breeding season and for 1 year prior to the study, to account for both short‐term trampling effects and the longer term effects on vegetation. Results showed that risk of nest loss to trampling increased from 16% at 0.15 cattle per hectare to 98% at 0.82 cattle per hectare in the breeding season. The risk of a nest being predated increased from 28% with no grazing to 95% at 0.55 cattle per hectare based on all year grazing data. These results suggest that even light conservation grazing at less than one cattle per hectare can reduce Redshank nest survival rates to near zero. It may therefore be appropriate to reduce saltmarsh grazing intensities, or change the timing of saltmarsh grazing to reduce the number of livestock present during the Redshank breeding season.     

Methane emissions from beef cattle grazing on semi-natural upland and improved lowland grasslands

In ruminants, methane (CH₄) is a by-product of digestion and contributes significantly to the greenhouse gas emissions attributed to agriculture. Grazed grass is a relatively cheap and nutritious feed but herbage species and nutritional quality vary between pastures, with management, land type and season all potentially impacting on animal performance and CH₄ production. The objective of this study was to evaluate performance and compare CH₄ emissions from cattle of dairy and beef origin grazing two grassland ecosystems: lowland improved grassland (LG) and upland semi-natural grassland (UG). Forty-eight spring-born beef cattle (24 Holstein–Friesian steers, 14 Charolais crossbred steers and 10 Charolais crossbred heifers of 407 (s.d. 29), 469 (s.d. 36) and 422 (s.d. 50) kg BW, respectively), were distributed across two balanced groups that grazed the UG and LG sites from 1 June to 29 September at stocking rates (number of animals per hectare) of 1.4 and 6.7, respectively. Methane emissions and feed dry matter (DM) intake were estimated by the SF₆ tracer and n-alkane techniques, respectively, and BW was recorded across three experimental periods that reflected the progression of the grazing season. Overall, cattle grazed on UG had significantly lower (P<0.001) mean daily DM intake (8.68 v. 9.55 kg/day), CH₄ emissions (176 v. 202 g/day) and BW gain (BWG; 0.73 v. 1.08 kg/day) than the cattle grazed on LG but there was no difference (P>0.05) in CH₄ emissions per unit of feed intake when expressed either on a DM basis (20.7 and 21.6 g CH₄ per kg DM intake for UG and LG, respectively) or as a percentage of the gross energy intake (6.0% v. 6.5% for UG and LG, respectively). However, cattle grazing UG had significantly (P<0.001) greater mean daily CH₄ emissions than those grazing LG when expressed relative to BWG (261 v. 197 g CH₄/kg, respectively). The greater DM intake and BWG of cattle grazing LG than UG reflected the poorer nutritive value of the UG grassland. Although absolute rates of CH₄ emissions (g/day) were lower from cattle grazing UG than LG, cattle grazing UG would be expected to take longer to reach an acceptable finishing weight, thereby potentially off-setting this apparent advantage. Methane emissions constitute an adverse environmental impact of grazing by cattle but the contribution of cattle to ecosystem management (i.e. promoting biodiversity) should also be considered when evaluating the usefulness of different breeds for grazing semi-natural or unimproved grassland.     

Influence of Endophyte and Water Regime Upon Tall Fescue Accessions. II. Pyrrolizidine and Ergopeptine Alkaloids

Alkaloids, along with specific environmental conditions, havebeen associated with both detrimental and beneficial aspectsof endophyte (Acremonium coenophialum Morgan-Jones et Gams)infected tall fescue (Festuca arundinacea Schreb.) associations.Benefits to the plant accrue through reduced herbivory, whereasdetriment to the animal occurs as altered grazing behaviourand reduced productivity. A controlled environment study wasconducted to examine pyrrolizidine and ergopeptine alkaloidconcentration of four tall fescue accessions as influenced byendophyte status and water regime. Endophyte-free plants weredevoid of ergopeptine alkaloid and contained little, if any,pyrrolizidine alkaloid. Leaf blade tissue of endophyte-infectedisolines contained a range of both ergopeptine (256 to 1633ng g^–1) and pyrrolizidine (92 to 450 µg g^–1)alkaloid concentrations. Water deficit generally increased alkaloidconcentration. Alkaloid yield, based upon concentration andtissue d. wt, showed that significant increase in ergopeptineand pyrrolizidine alkaloid in leaf tissue was associated withwater deficit and was due to actual increased synthesis andnot simply decreased phytomass. Leaf and pseudostem (leaf sheathand stem base) tissue alkaloid concentrations indicated differentaccumulation patterns for ergopeptine and pyrrolizidine alkaloids.Ergopeptine alkaloid yield increased in water-stressed pseudostem,whereas pyrrolizidine alkaloid yield decreased in some, butnot all accessions. The range of host genotype/endophyte biotyperesponse offers the possibility to select associations whichproduce few deleterious effects in animals yet maintain highforage productivity and persistence. Festuca arundinacea, Acremonium coenophialum, tall fescue genotypes, water stress, N-formyl and N-acetyl loline, ergovaline     

Effects of livestock exclusion on density,survival and biomass of the perennial sagebrush grass Hymenachne pernambucense (Poaceae) from a temperate fluvial wetland

In Argentina, the intensification of soybean production has displaced a substantial proportion of cattle ranching to fluvial wetlands such as those in the Delta of the Paraná River. Cattle grazing affects structure and dynamics of native forage plants but there is little information on this impact in populations from fluvial wetlands. This study addresses the effect of cattle ranching on density, survival, mean life-span and aerial biomass of Hymenachne pernambucense (Poaceae), an important forage species in the region. The study was carried out monthly for one year in permanents plots subject to continuous grazing and plots excluded from grazing in the Middle Delta of the Paraná River. In plots excluded from grazing, tillers showed significantly higher population density and survival, and a two-fold increase in mean life-span, while continuous grazing decreased survival of cohorts. The largest contribution to tiller density in ungrazed and grazed populations was made by spring and summer cohorts, respectively. Total and green biomass were significantly higher in the ungrazed population, with highest differences in late spring-early summer. Cattle grazing affected the relationship between tiller density and green biomass suggesting that cattle prefer sprouts because they are more palatable and nutritious than older tissue.     

Accumulation of Ergopeptide Alkaloids in Symbiotic Tall Fescue Grown under Deficits of Soil Water and Nitrogen Fertilizer

The fungus Acremonium coenophialum is endophytically associated with tall fescue (Festuca arundinacea Schreber). Within this symbiotum the fungus produces ergopeptide alkaloids, which are associated with livestock toxicoses. Environmental effects on the production of ergot alkaloids within the symbiotum are unknown. We conducted a greenhouse study of the effects of flooding, nitrogen rate during fertilization (11, 73, and 220 mg of N per pot weekly), nitrogen form (3.4 and 34 mg of N as NH₄⁺ or NO₃^- per pot), and drought stress (-0.03, -0.05, and -0.50 MPa) on ergopeptide alkaloid concentrations in one genotype of nonsymbiotic and symbiotic tall fescue grown in plastic pots. It was determined that the concentration of ergovaline, the major type of ergopeptide alkaloid, was increased but was not as high as that in nonflooded controls. Total ergopeptide and ergovaline concentrations in plants receiving high (220 mg of N per pot) and low (11 mg of N per pot) levels of NH₄NO₃ fertilization were not affected by flooding. The form of nitrogen was important since all concentrations of NO₃^--N increased ergopeptide alkaloid content, as opposed to the effects of NH₄⁺-N, which was effective only at high concentrations (34 mg of N per pot). Ergopeptide concentrations were highest in drought-stressed plants grown at -0.50 MPa and fertilized at the moderate or high N rate. The results suggest that within this genotype, ergopeptide alkaloid biosynthesis by the fungus is not appreciably affected by flooding but is greatly increased by high rates of N fertilization and moderate water deficit.     

Nutrient concentrations in two savannah grass species and their implications for grazers

The diversity of grazers on savannahs exerts pressure on the grass to provide nutrition. In this study the concentrations of major and trace animal nutrients in above ground grass tissue as influenced by grazing were examined. Two palatable grass species grazed by both livestock and wild grazers were sampled: Brachiaria nigropedata and Eragrostis lehmanniana. Samples of grass tissue were collected from widely spread sampling sites in both livestock and wildlife grazing sites, at the end of the growing season. Although B. nigropedata had higher nutrient concentrations, there was general covariance in nutrient levels in the two grasses. The covariance indicated that the respective sites generally had location context-dependent low or high nutrient concentrations in all grasses. The adequacy of the nutrient concentrations for grazer nutrition was assessed using literature-sourced minimum and maximum tolerable limit requirements of cattle and the high population gazelle-like species as illustration. The results showed that, in these nitrogen-limited savannahs, the grass generally met grazer requirements in terms of crude protein, potassium, molybdenum, nickel and zinc but that it had deficiencies in phosphorous, sodium, and boron, as well as grazing intensity-related localised toxic levels of potassium, phosphorous, magnesium, iron and manganese. The deficiencies and toxicities were inferred to result in abnormalities in grazer physical condition and reproduction. Given the importance of livestock in semiarid savannahs, these effects on livestock grazers were inferred as threatening human food security. The study shows that high grazing intensity can raise the concentrations of some animal nutrients in above ground grass tissue to levels above grazer tolerable limits. Grazing rotation to reduce grazing intensity is recommended as a proactive grazing management strategy to limit the effects.