Invasion by exotic grasses is a severe threat to the integrity of grassland ecosystems all over the world. Because grasslands are typically grazed by livestock and wildlife, the invasion is a community process modulated by herbivory. We hypothesized that the invasion of native South American grasslands by Eragrostis plana Nees, an exotic tussock-forming grass from Africa, could be deterred by grazing if grazers switched dietary preferences and included the invasive grass as a large proportion of their diets. Bos taurus (heifers) and Ovis aries (ewes) grazed plots with varying degrees of invasion by E. plana in a replicated manipulative experiment. Animal positions and species grazed were observed every minute in 45-min grazing session. Proportion of bites and steps in and out of E. plana tussocks were measured and used to calculate several indices of selectivity. Both heifers and ewes exhibited increasing probability of grazing E. plana as the proportion of area covered by tussocks increased, but they behaved differently. In agreement with expectations based on the allometry of dietary preferences and morphology, ewes consumed a low proportion of E. plana, except in areas that had more than 90% E. plana cover. Heifers consumed proportionally more E. plana than ewes. Contrary to our hypothesis, herbivores did not exhibit dietary switching towards the invasive grass. Moreover, they exhibited avoidance of the invasive grass and preference for short-statured native species, both of which should tend to enhance invasion. Unless invasive plants are highly palatable to livestock, the effect of grazing to deter the invasion is limited, due to the inherent avoidance of the invasive grass by the main grazers in the ecosystem, particularly sheep.
Allelopathy is an important ecological mechanism in natural and managed ecosystems. Its study is critical to understand natural plant behaviors, to isolate allelochemicals with herbicide potential, and to use the allelopathic genes in transgenic studies. Poaceae is an ecologically dominant plant family and it is economically important worldwide because its chemical diversity represents an important source to discover new molecules. From this viewpoint, Brazil is an interesting place to study, encompassing 197 genera of the Poaceae family, many of them being dominant in various biomes and some being native to Brazil. Here, we review the literature describing allelopathic activities involving grasses of the Poaceae family. We evaluate the experimental conditions used in these studies, we identify the allelochemicals involved, and, finally, we assess the applicability of allelopathy. Our main findings are (1) among the 47 Brazilian species studied for their allelopathic effects, only Bothriochloa barbinodis, Bothriochloa laguroides, Paspalum notatum, and Paspalum urvillei are native to Brazil; (2) 51% of the reviewed studies prepared extracts from the leaves and used lettuce as the target plant; and (3) 64% of the papers identified allelochemicals, of which 67% were phenolic acids. This first bibliographical survey on allelopathy in Poaceae species present in Brazil shows that less than 3% of the Brazilian species have been studied, suggesting it is an incipient research subject. Since this plant family is a valuable source of unknown natural products, refining such studies should contribute to a better understanding of the ecosystem relationships. Identification and isolation of grass allelochemicals should promote environmentally safer compounds with bioherbicide properties, in sustainable agriculture. Keywords Allelochemicals. Bioprospecting. Grasses. Native resources Contents 1. Introduction 2. Poaceae genera native to Brazil with allelopathic effect 3. Experimental conditions 3.1 Plant organs used to prepare extracts 3.2 Target species 3.3 Evaluation of allelopathic effect 4. Allelochemicals in Poaceae genera native to Brazil 5. Allelopathy and its applicability 6. Conclusion References
ISSN 0100-8358 (print) 1806-9681 (online)
Palavras-chave: bioma Pampa, campo nativo, fogo técnico, plantas invasoras.ABSTRACT -The weed South African lovegrass (Eragrostis plana) is one of the most important problems of rangelands and native pastures in southern Brazil. Several factors have limited its management in these areas. The aim of this study was to evaluate South African lovegrass control using pre-emergent herbicides safe to the native pasture by applying soil position selectivity. Two experiments were evaluated in this study. The first was conducted in a greenhouse, and South African lovegrass seeds were sown in plastic pots. The herbicides evaluated were alachlor, ametryne, ametryne + tebuthiuron, atrazine, clomazone, diuron, flumioxazin, imazaquin, mesotrione, metribuzin, oxadiazon, S-metolachlor, sulfentrazone, terbuthylazine and trifluralin. All products successfully controlled lovegrass. The second experiment was conducted on native pastures highly infested with South African lovegrass, arranged in a split-split-plot design. In the main plots, the following vegetation management methods were allocated before herbicide application: prescribed burning, and high and low cutting; in the split-plots, the herbicide doses: 75 and 100% of the label rate; and in the split-split-plots, the herbicide doses: atrazine, flumioxazin, mesotrione, S-metolachlor, sulfentrazone, trifluralin and the untreated-check control. None of the herbicides tested effectively controlled lovegrass under field conditions, likely due to the high density of South African lovegrass perennial plants. However, the herbicide effects were more pronounced when associated with prescribed burning and low cutting.
RESUMO -Objetivou-se avaliar as características morfológicas de plantas de alfafa relacionadas à aptidão ao pastejo.Foram avaliadas três populações de alfafa Crioula de diferentes regiões geográficas, sem histórico de pastejo: Chile, Roque Gonzales e Vale do Taquari, além de dois cultivares norte-americanos, ABT 805 (selecionado sob pastejo) e CUF 101 (selecionado sob cortes). O experimento foi realizado em parcelas com os diferentes materiais, mantidos sob pastejo, mantendo-se resíduo de pastejo entre 3 e 5 cm de altura durante 255 dias sob lotação contínua. Ao término do período experimental, foi determinada a porcentagem de sobrevivência das plantas, visando estratificar os genótipos quanto ao grau de aptidão ao pastejo. O cultivar ABT apresentou a maior porcentagem de sobrevivência e o cultivar CUF, a menor. As populações crioulas Chile e Vale do Taquari apresentaram sobrevivência intermediária, enquanto a Roque Gonzales teve sobrevivência similar à do cultivar CUF. Os resultados da caracterização morfológica não diferiram quanto ao crescimento contrátil da coroa, à área da coroa, à área foliar, à área foliar específica, ao número de hastes por planta e ao tipo de haste por planta (basilar ou axilar). A relação folha:caule foi melhor no cultivar ABT e foi influenciada pela menor massa de hastes por planta. A expressão do número de gemas por unidade de carbono alocada às hastes foi maior no cultivar ABT, constituindo-se um eficiente descritor funcional da aptidão ao pastejo, denominado gema específica. IntroduçãoA utilização de leguminosas forrageiras tem sido recomendada pela pesquisa, tanto para formação de pastagens cultivadas como para melhoria de pastagens naturais, embora freqüentemente a baixa persistência dos materiais sob pastejo seja o principal entrave para maior escala de utilização em sistemas de produção.Entre os fatores que contribuem para a baixa persistência das leguminosas forrageiras, destaca-se a pouca atenção dos programas de melhoramento genético à reação das plantas ao pastejo. Além disso, a maioria das avaliações R. Bras.
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