African Grasses Research Articles

Impact of invasive grasses on Cerrado under natural regeneration

Cerrado is the Brazilian neotropical savanna threatened by invasive African grasses. We aimed to quantify the impact of invasive Melinis minutiflora and Urochloa brizantha on the cover of different functional groups (native graminoids, forbs, shrubs) and the structure (bare soil and the cover of natives’ and invasives’ dead biomass) of regenerating plant communities. We hypothesized that the impact of invasives would be negative and more pronounced in the rainy period, given the great influence of seasonality in savannas. In three community types (non-invaded, invaded by M. minutiflora and invaded by U. brizantha) we evaluated the cover of functional groups and structural components by sampling 120 1 m × 1 m plots, four times a year. Using the Cohen’s D impact index, we showed that both invasive species reduced the cover of all native functional groups, decreased bare soil and increased total dead cover. Greatest effects occurred when M. minutiflora was present. M. minutiflora’s impact on total graminoids varied from positive in the Early-Dry season to negative in the Mid-Dry season, while the negative impact of U. brizantha on bare soil became more pronounced from the dry to the rainy season. Differences in the impacts caused by the invasive species are probably due to the large biomass produced by M. minutiflora versus the fast colonization and soil occupancy by U. brizantha. Overall, invaded versus non-invaded communities differed in structure, as well as both invaded communities differed from each other. Our results demonstrate the need to control these species for conservation and restoration of Cerrado ecosystems.

Allelopathy of a native shrub can help control invasive grasses at sites under ecological restoration in a Neotropical savanna

ABSTRACTBackground: African C4 grasses threatens newly restored areas in Neotropical savannas. Allelopathy exhibited by some native species may contribute to ecological restoration.Aims: To establish the potential use of Lepidaploa aurea (Asteraceae) in ecological restoration of invaded savannas, we evaluated its allelopathic effects on two invasive grasses, a native grass, and two native trees (one savanna and one riparian forest species).Methods: We tested the allelopathic effects of the leaves and roots of L. aurea in a growth chamber, a greenhouse, and in field experiments.Results: Leaf extracts reduced the growth of all other species in the growth chamber experiment. Root extracts reduced growth in one invasive grass and promoted root growth in the savanna tree. The invasive grass and riparian forest tree were negatively affected when planted in soil where L. aurea had grown, whereas the savanna tree showed increased growth. Lepidaploa aurea litter reduced growth in one invasive grass species and increased root biomass accumulation in the native grass species.Conclusions: Lepidaploa aurea negatively affected the growth of invasive grasses, through plant extracts, litter and through soil. These patterns could explain its ability to colonise abandoned pasturelands and its high success of establishing in restoration areas.

Effects of initial disturbances and grazing regime on native grassland invasion by Eragrostis plana in southern Brazil

Extensive invasion of the Campos grasslands of southern Brazil by the South African grass, Eragrostis plana, is a serious conservation problem due to its low palatability and ability to quickly spread. Here, we experimentally evaluated the effects of grazing management and initial disturbance on invasibility of native grassland community by E. plana. The experiment, a split-plot complete block design with three replications, was established in 2004 in non-invaded native grassland. Grazing management treatments were assessed in main plots (continuous grazing, rotational grazing, and grazing exclusion). The initial disturbance treatments (light grazing, heavy grazing, and heavy grazing plus soil scarification) were applied in subplots before the sowing of standard amounts of E. plana seeds. The initial disturbances heavy grazing and heavy grazing plus soil scarification simulated the introduction of exotic forage species. We monitor plant species composition and diversity along six years after the experiment starting. The effects of grazing management and initial disturbance on community invasibility were significant and showed interaction. Heavy grazing plus soil scarification increased the rate of E. plana invasion and produced more pronounced changes in species composition than the other treatments. Plots under grazing exclusion, rotational or continuous grazing without soil scarification had low levels of invasion (<10% cover). But exclusion also changed community composition and decreased diversity, while rotational and continuous grazing maintained community structure. The invasion can be largely prevented on undisturbed grassland by employing either rotational or continuous grazing management. If the livestock producers want to introduce another forage species in their natural grasslands and, at the same time, do not run the risk of opening space for E. plana should avoid the use of soil scarification.

Pre-breeding studies in &lt;i&gt;Panicum coloratum&lt;/i&gt; var. &lt;i&gt;coloratum&lt;/i&gt;: Characterization using agro-morphological traits and molecular markers

Panicum coloratum var. coloratum is a native African perennial C4 grass, introduced to Argentina. It is tolerant of salinity and cold and has good forage production. The scarce genotypic and phenotypic information about this grass limits its breeding in order to satisfy market demands. The aim of this study was to evaluate the variability in a collection of Panicum coloratum var. coloratum formed by 8 accessions and grown at EEA INTA Rafaela during the summer of 2011, based on 15 ISSR molecular markers and 17 morphological characters. For all morphological characters, the distribution of variability observed in the collection was high and not homogenous. The characters that showed greater variation were related to forage and seed production. Eight ISSRs, selected according to their reproducibility, showed 127 bands with 100% polymorphism and allowed grouping of populations according to their site of collection. AMOVA study indicated that more than 58% of the molecular variation existed within accessions; this would be consistent with the predominant allogamous form of reproduction. The results showed that the combined use of molecular and morphological markers offer complementary information. The high variability detected in this collection will allow for the initiation of a breeding program to improve important characters like those related to DM yield and seed production.

Diurnally active rodents for laboratory research.

Although inbred domesticated strains of rats and mice serve as traditional mammalian animal models in biomedical research, the nocturnal habits of these rodents make them inappropriate for research that requires a model with human-like diurnal activity rhythms. We conducted a literature review and recorded locomotor activity data from four rodent species that are generally considered to be diurnally active, the Mongolian gerbil ( Meriones unguiculatus), the degu ( Octodon degus), the African (Nile) grass rat ( Arvicanthis niloticus), and the antelope ground squirrel ( Ammospermophilus leucurus). Our data collected under 12-hour light/dark cycles confirmed and expanded the existing literature in showing that the activity rhythms of antelope ground squirrels and African grass rats are stronger and more concentrated in the light phase of the light/dark cycle than the activity rhythms of Mongolian gerbils and degus, making the former two species preferable and more reliable as models of consistent diurnal activity in the laboratory. Among the two more strongly diurnal species, antelope ground squirrels are more exclusively diurnal and have more robust activity rhythms than African grass rats. Although animals of these two species are not currently available from commercial suppliers, African grass rats are indigenous to a wide area across the north of Africa and thus available to researchers in the eastern hemisphere, whereas antelope ground squirrels can be found throughout much of western North America's desert country and, therefore, are more easily accessible to North American researchers.

The increase of current atmospheric CO2 and temperature can benefit leaf gas exchanges, carbohydrate content and growth in C4 grass invaders of the Cerrado biome

Leaf gas exchanges, carbohydrate metabolism and growth of three Brazilian Cerrado invasive African grasses were evaluated after growing for 75 days under doubled CO2 concentration and temperature elevated by 3 °C. Results showed that although the species presented photosynthetic C4 metabolism, they all had some kind of positive response to increased CO2. Urochloa brizantha and Megathyrsus maximus showed increased height for all induced environmental conditions. Urochloa decumbens showed only improvement in water use efficiency (WUE), while U. brizantha showed increased CO2 assimilation and M. maximus presented higher biomass accumulation under doubled CO2 concentration. The most significant improvement of increased CO2 in all three species appears to be the increase in WUE. This improvement probably explains the positive increase of photosynthesis and biomass accumulation presented by U. brizantha and M. maximus, respectively. The increase in temperature affected leaf carbohydrate content of M. maximus by reducing sucrose, glucose and fructose content. These reductions were not related to thermal stress since photosynthesis and growth were not harmed. Cellulose content was not affected in any of the three species, just the lignin content in U. decumbens and M. maximus. All treatments promoted lignin content reduction in U. brizantha, suggesting a delay in leaf maturation of this species. Together, the results indicate that climate change may differentially promote changes in leaf gas exchanges, carbohydrate content and growth in C4 plant species studied and all of them could benefit in some way from these changes, constituting a threat to the native Cerrado biodiversity.

Characterization of the Nile Grass Rat as a Unique Model for Type 2 Diabetic Polyneuropathy.

Type 2 diabetes (T2D) has reached pandemic proportions worldwide. Almost half of T2D patients suffer from polyneuropathy that can present as paresthesia, hyperalgesia, allodynia, or hypoesthesia. Therapeutic treatment options are largely incomplete, suggesting new avenues of research are needed. Herein, we introduce the African Nile Grass rat (NGR), which develops T2D solely by diet manipulation, as a novel T2D polyneuropathy model. The purpose of this study was to first characterize T2D-induced polyneuropathy in the NGRs before highlighting their strength as a potential prediabetic model of T2D. NGRs with long-term T2D exhibit hallmark features of polyneuropathy such as decreased motor nerve conduction velocity, intraepidermal denervation, and hyposensitivity to noxious mechanical and thermal stimulation. At the dorsal root ganglia, T2D neurons have altered sodium channel expression, specifically increased Nav1.7 and Nav1.9, and their surrounding satellite glial cells express glial fibrillary acidic protein. Now that these T2D NGRs have been characterized and shown to have a similar presentation to human and other animal models of T2D, the strength of this diet-induced model can be exploited. The prediabetic changes can be observed over their long progression to develop T2D which may allow for a therapeutic window to prevent T2D before permanent damage occurs.

Exotic grass invasion alters microsite conditions limiting woody recruitment potential in an Australian savanna

Andropogon gayanus Kunth. is a large African tussock grass invading Australia’s tropical savannas. Invasion results in more intense fires which increases the mortality rate of adult woody plants. Invasion may also affect community structure by altering the recruitment potential of woody plants. We investigated the effects of A. gayanus invasion on ground-level microclimate, and the carbon assimilation potential and recruitment potential of two Eucalyptus species. We compared microclimatic variables from the early wet-season and into the mid-dry season to coincide with the period of growth of A. gayanus. We assessed Eucalyptus recruitment by monitoring seedling establishment, growth and survival of experimentally sown seed, and estimating seedling density resulting from natural recruitment. A. gayanus invasion was associated with increased grass canopy height, biomass and cover. Following invasion, the understorey microclimate had significantly reduced levels of photon flux density, increased air temperatures and vapour pressure deficit. The conditions were less favourable for woody seedling with aboveground biomass of seedlings reduced by 26% in invaded plots. We estimated that invasion reduced daily carbon assimilation of woody seedlings by ~30% and reduced survivorship of Eucalyptus seedlings. Therefore, A. gayanus invasion reduces recruitment potential, contributing to the transformation of savanna to a grassland ecosystem.

First record of Ehrharta longiflora Sm. (Poaceae, Ehrharteae) for South America

Ehrharta longiflora Sm. (Poaceae) is recorded for the first time in South America. A few naturalized populations were located in disturbed areas of Valparaíso (Central Chile). A brief taxonomic discussion, images and a location map of the new record of this African grass are provided here.

All-cellulose composite films with cellulose matrix and Napier grass cellulose fibril fillers

Diverse move has been attempted to use biomass as a filler for the production of biodegradable all-cellulose composites. In this study, cellulose fibrils (CFs) extracted from native African Napier grass (NG) fibres were used as fillers in cellulose matrix and made all-cellulose composites. Napier Grass Cellulose fibrils (NGCFs) loading was varied from 5 to 25 wt% in cellulose matrix in random orientation and the all cellulose composites were made by regeneration process. These composites were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, thermogravimetric analysis, optical microscopy, and tensile testing. The FTIR spectra indicated not only the presence of minute amounts of hemicelluloses and lignin in the filler but also the possible interaction between the matrix and NGCFs. The crystallinity of the all-cellulose composites was found to be lower than that of the cellulose matrix. The thermal stability of the all-cellulose composites was found to be higher than that of the cellulose matrix and increased with NGCFs filler content. The tensile strength of the all-cellulose composites though was lower than that of the cellulose matrix but still was higher than for commodity polymers. The all-cellulose composites can be considered for wrapping and mulching applications.

Extraction and characterization of cellulose single fibers from native african napier grass

With increasing awareness of protecting the environment, the demand for renewable and environmental materials is increasing. In this work, the cellulose single fibers (CSFs) were extracted from the African native Napier grass fibers (NGFs) by chemical process. NGFs and CSFs were characterized for their chemical composition, structure, morphology, crystallinity and thermal properties using, chemical analysis, FTIR, 13C CP/MAS NMR, SEM, XRD and TGA techniques. The resulted CSFs had higher α-cellulose content, crystallinity and thermal stability than the pristine NGFs. SEM images showed cleaner and rough surfaces for the CSFs when compared to those of NGFs. About 69% of the extracted CSFs showed a diameter range between 4 and 10 μm. FTIR and 13C CP/MAS NMR spectra confirmed the removal of lignin and hemicellulose components after chemical treatments.

Seed longevity and seedling emergence rate of Urochloa decumbens as influenced by sowing depth in a Cerrado soil

AbstractUrochloa decumbens (Signal grass) is an African grass species that is widely used in Brazil for pasture formation, and it has a high potential for invading natural areas. This study evaluated the longevity of U. decumbens seeds in the soil seed bank and the emergence rates of seedlings from different depths. In the greenhouse (natural light; ~25°C), seeds were sown at depths of 0, 1, 2 or 3 cm, in trays filled with sterile soil, to assess seedling emergence. Seeds sowed on the soil surface began to germinate 3 days after sowing. Seeds sowed at depths of 2 and 3 cm germinated 5 days after sowing. No seedlings emerged after 15 days. The seedling emergence rate was 74 ± 7% with no significant difference between sowing depths. In the field, seed longevity was evaluated by burying 60 replicates of 100 seeds at a soil depth of 2–3 cm, in a Cerrado area in the IBGE Ecological Reserve, Brasília. From September 2016 to April 2017, five samples were retrieved monthly to assess seed viability. In September, the viability was 68%, declining to 3% in October; by February, viable seeds were no longer recorded. As U. decumbens flowers in several episodes throughout the year, a soil survey may result in a misleading interpretation of the formation of a permanent soil seed bank.

Invasive Andropogon gayanus (Gamba grass) alters litter decomposition and nitrogen fluxes in an Australian tropical savanna

The African grass Andropogon gayanus Kunth. is invading Australian savannas, altering their ecological and biogeochemical function. To assess impacts on nitrogen (N) cycling, we quantified litter decomposition and N dynamics of grass litter in native grass and A. gayanus invaded savanna using destructive in situ grass litter harvests and litterbag incubations (soil surface and aerial position). Only 30% of the A. gayanus in situ litter decomposed, compared to 61% of the native grass litter, due to the former being largely comprised of highly resistant A. gayanus stem. In contrast to the stem, A. gayanus leaf decomposition was approximately 3- and 2-times higher than the dominant native grass, Alloteropsis semilata at the surface and aerial position, respectively. Lower initial lignin concentrations, and higher consumption by termites, accounted for the greater surface decomposition rate of A. gayanus. N flux estimates suggest the N release of A. gayanus litter is insufficient to compensate for increased N uptake and N loss via fire in invaded plots. Annually burnt invaded savanna may lose up to 8.2% of the upper soil N pool over a decade. Without additional inputs via biological N fixation, A. gayanus invasion is likely to diminish the N capital of Australia’s frequently burnt savannas.

How scattered trees matter for biodiversity conservation in active pastures

Large areas of Tropical Forest have been cleared and deeply modified aiming at growing crops and producing livestock. Many of these areas are transformed in pastures with scattered trees. We investigated an area of 618.59ha in Southeastern Brazil composed of active pastures of an African grass, Urochloa decumbens, with scattered trees and forest patches. We surveyed all the scattered trees in the active pastures and in 60 plots of 200m2 within eight forest patches. To identify the ecosystem services and the history of scattered trees we applied a semi-structured survey to the landowners. We assessed regeneration, distance of propagules source, grass cover, microclimate, seed rain, and soil compaction under scattered tree crowns and in samples in the pasture without scattered trees. We found the scattered tree community highly diverse and associated this to apparent lack of preference for species showed by farmers during the clearing process for pasture, choosing the trees only by their shading capability (size). We also found that the scattered trees strongly affect seed rain and sapling regeneration in the pastures, improving microclimate and attracting dispersers, although this last effect is strongly dependent of the forest proximity. We found that the major difference between the scattered tree community and forest patches is associated with small trees lost during forest clearing and not to the largest trees left in the pastures. We see the scattered trees as key factors for promoting forest recovery, as well as an important biodiversity pool per si in highly fragmented landscapes.

De novo assembly and annotation of the retinal transcriptome for the Nile grass rat (Arvicanthis ansorgei).

Cone photoreceptors are required for color vision and high acuity vision, and they die in a variety of retinal degenerations, leading to irreversible vision loss and reduced quality of life. To date, there are no approved therapies that promote the health and survival of cones. The development of novel treatments targeting cones has been challenging and impeded, in part, by the limitations inherent in using common rodent model organisms, which are nocturnal and rod-dominant, to study cone biology. The African Nile grass rat (Arvicanthis ansorgei), a diurnal animal whose photoreceptor population is more than 30% cones, offers significant potential as a model organism for the study of cone development, biology, and degeneration. However, a significant limitation in using the A. ansorgei retina for molecular studies is that A. ansorgei does not have a sequenced genome or transcriptome. Here we present the first de novo assembled and functionally annotated transcriptome for A. ansorgei. We performed RNA sequencing for A. ansorgei whole retina to a depth of 321 million pairs of reads and assembled 400,584 Trinity transcripts. Transcriptome-wide analyses and annotations suggest that our data set confers nearly full length coverage for the majority of retinal transcripts. Our high quality annotated transcriptome is publicly available, and we hope it will facilitate wider usage of A. ansorgei as a model organism for molecular studies of cone biology and retinal degeneration.

Restoring Brazilian savanna ground layer vegetation by topsoil and hay transfer

AbstractTropical grassy biomes have been widely neglected for conservation and, after unplanned land use conversion, ecological restoration becomes urgent. The majority of interventions have been based on the misapplication of forest restoration techniques, because there are no validated techniques to restore the species‐rich ground layer. In search for innovative techniques to restore the herbaceous layer of the cerrado vegetation, we carried out an experiment based upon topsoil and hay transfer, in the state of São Paulo, Brazil. The restoration treatments were: (1) transfer of topsoil collected at the end of the dry season; (2) topsoil collected at the end of the rainy season; (3) transfer of hay collected at the end of the dry season; (4) topsoil + hay collected at the end of the dry season; and (5) control. We used an old‐growth grassland as source of material and as reference ecosystem to assess the efficacy of the restoration techniques applied to an area severely degraded after invasion by African grasses. After 211 days, hay transfer apparently inhibited germination and did not contribute to grassland vegetation recovery. Topsoil transfer, however, was effective at reintroducing herbaceous plants, including target species. The season of topsoil collection mattered: material collected at the end of the rainy season provided better results in terms of density and richness of the restored community than that from the dry season. The remaining challenge is to find sources of topsoil not invaded by exotic grasses in large enough amounts to support restoration initiatives without jeopardizing the source ecosystems.

Sweet vernal grasses (Anthoxanthum) colonized African mountains along two fronts in the Late Pliocene, followed by secondary contact, polyploidization and local extinction in the Pleistocene.

High tropical mountains harbour remarkable and fragmented biodiversity thought to a large degree to have been shaped by multiple dispersals of cold-adapted lineages from remote areas. Few dated phylogenetic/phylogeographic analyses are however available. Here, we address the hypotheses that the sub-Saharan African sweet vernal grasses have a dual colonization history and that lineages of independent origins have established secondary contact. We carried out rangewide sampling across the eastern African high mountains, inferred dated phylogenies from nuclear ribosomal and plastid DNA using Bayesian methods, and performed flow cytometry and AFLP (amplified fragment length polymorphism) analyses. We inferred a single Late Pliocene western Eurasian origin of the eastern African taxa, whose high-ploid populations in one mountain group formed a distinct phylogeographic group and carried plastids that diverged from those of the currently allopatric southern African lineage in the Mid- to Late Pleistocene. We show that Anthoxanthum has an intriguing history in sub-Saharan Africa, including Late Pliocene colonization from southeast and north, followed by secondary contact, hybridization, allopolyploidization and local extinction during one of the last glacial cycles. Our results add to a growing body of evidence showing that isolated tropical high mountain habitats have a dynamic recent history involving niche conservatism and recruitment from remote sources, repeated dispersals, diversification, hybridization and local extinction.

Ungulate grazing drives higher ramet turnover in sodium‐adapted Serengeti grasses

AbstractQuestionsUngulate grazers requiring sodium (Na) will preferentially graze in areas with Na‐accumulating forage grasses (i.e. many saline soils with high NaCl). Given that high‐Na conditions necessitate specific adaptations in plants, the mechanisms allowing plants to persist under combined herbivory and Na stress are unclear. Has adaptation to soil salinity in East African grasses modified the evolution of grazing tolerance, leading to plants that are susceptible to defoliation? Does grazing differentially impact the survivorship of plants with different tolerances to Na? Finally, can species traits that confer salinity and herbivory tolerances help to explain the presence of mosaic structure in high salinity regions?LocationShort‐grass plains of Serengeti National Park, Tanzania, East Africa.MethodsWe tracked the fate of 836 individuals of 26 grass species, over an entire growing season, in the short‐grass plains using a network of 41 quadrats (0.25 m2). We investigated the impact of soil properties (e.g., electrical conductivity [EC], bulk density, clay), ungulate herbivory and grass species identity on patterns of composition and turnover. Finally, we linked plant leaf Na and leaf palatability data to species environmental responses.ResultsUnder comparable levels of grazing pressure, grass species known to accumulate Na have much higher levels of turnover compared to low‐Na species. These Na accumulators were generally short, highly palatable and clonal species.ConclusionsHerbivory most affects turnover (of ‘ramets’) of species with the highest tolerance to Na, suggesting that Na tolerance ability interacts with defoliation response in Serengeti grasses. As a result, spatial heterogeneity in soil EC produces high‐turnover communities that overlay high‐EC soil adjacent to more stable communities composed of Na‐intolerant species. While Na‐intolerant grasses in Serengeti range from short and palatable to taller and less palatable species, grasses that accumulate Na tend to be short and palatable, a likely result of the grazing pressure they experience.

The Invasive Legacy of Forage Grass Introductions into Florida

Exotic African warm-season forage grasses were first introduced into the Americas in the 16th century, and have become invasive in many areas. In Florida, 16 exotic grasses are considered invasive, with the majority originating in Africa and introduced as forages. The high propensity of Africa warm-season grasses to become invasive may be related to the same characteristics that are associated with their value as forages, including adaptability to a wide range of abiotic conditions, rapid establishment, persistence in the environment with minimal husbandry, high productivity under grazing pressure, and adaptation to disturbance. The majority of African warm-season grasses in Florida reproduce vegetatively, a trait known to be associated with invasiveness, and many have been widely planted leading to high propagule pressure and opportunities to invade a variety of niches. In spite of a long history of introduction and promotion in Florida, few African forage grasses are in use today, while many have become invasive. The benefit/cost ratio appears to be tilted in the direction of environmental and economic costs, with minimal benefits. We support newly enacted restrictions on the importation of potentially invasive plants into the USA, and suggest the establishment of a more comprehensive and transparent system for tracking past and future introductions.

Phytochemical and Antimicrobial Studies of Crude extract of Cow Sandbur and African Foxtail Grasses of Thar Desert

Phytochemical and Antimicrobial Studies of Crude extract of Cow Sandbur and African Foxtail Grasses of Thar Desert