Melinis Minutiflora Research Articles

The presence of invasive grasses affects the soil seed bank composition and dynamics of both invaded and non-invaded areas of open savannas

One of the major threats to tropical savannas globally is the invasion by alien grasses. In systems frequently disturbed, individuals can be recruited from the seed bank, and areas under natural regeneration can be more easily invaded when exotic newcomers are in the system, including the presence of invasive propagules in the soil seed bank. This study analyzed the dynamics of the soil seed bank in invaded and non-invaded areas of open savannas elucidating the potential of grass regeneration from the seed bank. Soil samples were collected in areas with different invasive grasses: Urochloa brizantha (Hochst. ex A. Rich.) R.D.Webster – synonym Brachiaria brizantha (Hochst. ex A. Rich.) Stapf, Melinis minutiflora Beauv. and areas with native vegetation. Soil seed bank was assessed using two techniques: seed counting and seedling emergence. Dominant species in each area influenced the seed bank composition, showing the highest densities from April to September. In invaded areas, the seed bank was composed mainly of invasive grasses that contributed to 98% (670 ± 382 seeds.m−2) of total seeds. In non-invaded areas, the soil seed bank presented the highest density (65%, 135 ± 38 seeds.m−2) of native species. However, the presence of invasive grasses was significant, with 35% of the total seeds belonging to U. brizantha. Although non-invaded areas have a higher potential for regeneration by native grasses, the presence of invasive grasses in the seed bank is an indication that the invasive species is already in the system and changes in the aboveground cover could accelerate the invasion process. Early management efforts towards establishing and/or established invasive species before seed dispersal could help reduce the soil seed bank load and should be carried out to control and avoid the establishment of African grasses, since they can dominate the seed bank in non-invaded areas if they are present in neighboring areas, affecting the dynamics of plant communities.

Species richness both impedes and promotes alien plant invasions in the Brazilian Cerrado

Worldwide, alien plant invasions have been intensively studied in the past decades, but mechanisms controlling the invasibility of native communities are not fully understood yet. The stochastic niche hypothesis predicts that species-rich plant communities are less prone to alien plant invasions than species-poor communities, which is supported by some but not all field studies, with some very species-rich communities such as the Brazilian Cerrado becoming heavily invaded. However, species-rich communities potentially contain a greater variety of facilitative interactions in resource exploitation than species-poor communities, from which invasive plants might benefit. This alternative hypothetical mechanism might explain why nutrient-poor, species-rich ecosystems are prone to invasion. Here we show that a high species richness both impedes and promotes invasive plants in the Brazilian Cerrado, using structural equation modelling and data from 38 field sites. We found support for the stochastic niche hypothesis through an observed direct negative influence of species richness on abundance of alien invasive species, but an indirect positive effect of species richness on invasive alien plants through soil phosphatase activity that enhances P availability was also found. These field observations were supported with results from a mesocosm experiment. Root phosphatase activity of plants increased with species richness in the mesocosms, which was associated with greater community P and N uptake. The most prominent alien grass species of the region, Melinis minutiflora, benefited most from the higher N and P availability in the species mixtures. Hence, this study provides a novel explanation of why species-richness may sometimes promote rather than impede invasion, and highlights the need to perform facilitation experiments in multi-species communities.

Atributos físicos do solo em diferentes sistemas de manejo de agroecossistemas no Território do Caparaó

Comprehending impacts of soil management and use on its physical attributes is essential to develop sustainable agricultural systems. This study evaluated the behavior of soil physical properties under different types of use and management in “Caparao Capixaba” territory, state of Espirito Santo. This study was performed in eight different agroecosystems: Molasses grass pasture (PCG); Signalgrass pasture (PBR); Arabic coffee plantation (CA1 and CA2); Horticulture (HOR); Citrus culture (FRU); Eucalyptus forest (EUC) and Native vegetation (VEN). Gravimetric moisture (GM), bulk density (Bd), particle density (Pd), total porosity (Tp) and soil penetration resistance (PR) were evaluated at 0–10 cm, 10–20 cm and 20–40 cm depths. The highest GM was found in HOR and VEN. The highest Bd were found in the CA2, PCG and FRU management system. At a surface depth (0–10 cm), PBR presented the lowest PT value, statistically equal to CA2 and FRU. The highest values of RP were observed in PBR at all evaluated depths (5.28, 8.32 and 10.68 Mpa). CA1 and CA2 were similar in RP, even when in different places. PCG, PBR, FRU e EUC showed RP higher than 4.0 MPa, which is beyond the critical limit for root system growth. The results indicate that different soil management approaches for the existing crops and vegetation in the agroecosystems can cause significant changes in soil physical attributes.

Fire cues and germination of invasive and native grasses in the Cerrado

Fire-related cues may enhance seed recruitment in flammable ecosystems and differences in fire-germination responses of invasive vs. native species can drive the invasion process. We evaluated the effects of heat shock and smoke water solution treatment on seed germination of invasive (Melinis minutiflora, Urochloa decumbens, U. brizantha) and native grasses (Axonopus pressus, Aristida setifolia, Gymnopogon foliosus) of the Cerrado. The effect of fire temperature was tested by exposing seeds to heat shock treatments of 60, 100, and 200 °C for one minute, comparing them to untreated seeds. The effect of smoke was tested by soaking seeds for 24-h in an aqueous smoke comparing them to seeds soaked in distilled water. Differences among treatments were evaluated by ANOVA and randomization tests. None of the tested species had germination stimulated by the temperature or smoke. Both species of Urochloa experienced decreased viability with increasing temperature, while seeds of native species and M. minutiflora tolerated heat shock up to 200 °C. The invasive grasses usually germinated faster than the native grasses. Germination time is therefore a crucial trait driving the invasion process, irrespective of fire-related cues. Other seed traits (e.g. dormancy) and higher resprouting capacity may help invasive species to persist in frequently burned savannas.

Push-Pull Strategy: an integrated approach to manage insect-pest and weed infestation in cereal cropping systems

The “Push–Pull” strategy is an effective, efficient, and powerful tool in integrated pest management (IPM) that is combining several behaviour-modifying stimuli to control cereal stem borers and the noxious weed Striga in cereal-based farming systems in Africa. This technology involves driving away from the cereal stemborers from the main crop by using stimuli of repellent intercrops (push) that mask host apparency and simultaneously stemborers are attracted by highly apparent and attractive stimuli from trap plants (pull). The fodder legume, Desmodium (D. uncinatum and D. intortum), and Molasses grass (Melinis minutiflora) are used as the repellent intercrop, which is repugnant to stemborer moths. On the other hand, Napier grass (Pennisetum purpureum) and Sudangrass (sorghum vulgare sudanese) is planted as a border crop used as the trap plant (pull). Chemicals that are released by the roots of the Desmodium intercrop induce abortive germination of seeds of noxious Striga weeds, providing very effective control of this weed. Napier grass and Molasses grass also provide high-value animal fodder that facilities milk production, diversifying sources of farmers’ income. Besides, this technology helps to improve soil fertility and prevent soil erosion that leads to increased grain yield in the future. Chemicals that are released by the roots of the Desmodium intercrop induce abortive germination of seeds of noxious Striga weeds, providing very effective control of this weed.

Molasses Grass Induces Direct and Indirect Defense Responses in Neighbouring Maize Plants.

Plants have evolved intricate defence strategies against herbivore attack which can include activation of defence in response to stress-related volatile organic compounds (VOCs) emitted by neighbouring plants. VOCs released by intact molasses grass (Melinis minutiflora), have been shown to repel stemborer, Chilo partellus (Swinhoe), from maize and enhance parasitism by Cotesia sesamiae (Cameron). In this study, we tested whether the molasses grass VOCs have a role in plant-plant communication by exposing different maize cultivars to molasses grass for a 3-week induction period and then observing insect responses to the exposed plants. In bioassays, C. partellus preferred non-exposed maize landrace plants for egg deposition to those exposed to molasses grass. Conversely, C. sesamiae parasitoid wasps preferred volatiles from molasses grass exposed maize landraces compared to volatiles from unexposed control plants. Interestingly, the molasses grass induced defence responses were not observed on hybrid maize varieties tested, suggesting that the effect was not simply due to absorption and re-emission of VOCs. Chemical and electrophysiological analyses revealed strong induction of bioactive compounds such as (R)-linalool, (E)-4,8-dimethyl-1,3,7-nonatriene and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene from maize landraces exposed to molasses grass volatiles. Our results suggest that constitutively emitted molasses grass VOCs can induce direct and indirect defence responses in neighbouring maize landraces. Plants activating defences by VOC exposure alone could realize enhanced levels of resistance and fitness compared to those that launch defence responses upon herbivore attack. Opportunities for exploiting plant-plant signalling to develop ecologically sustainable crop protection strategies against devastating insect pests such as stemborer C. partellus are discussed.

Effects of Aqua-Dispersing Nano-Binder on Clay Conductivity at Different Temperatures

Soil nutrients are the basis of ecological remediation. Soil amendments can form a reticular membrane structure on the soil surface to increase nutrient storage and alleviate nutrient imbalances, and are affected by the environmental temperature. At present, the qualitative evaluation of the effect of soil amendment is mainly based on vegetative growth. However, with the increasing use of soil amendments, how to conveniently and quantitatively evaluate the impact of soil amendments on ecological restoration under different temperature conditions from the perspective of soil urgently needs to be solved. Therefore, a new soil amendment named aqua-dispersing nano-binder (ADNB) and silty clay that is commonly used for ecological restoration in South China were used as research subjects, and the important soil nutrient storage capacity—soil conductivity index—was used as the starting point to find solutions to the above problems. We independently developed a multifunctional instrument to measure the soil amendment concentration. Clay conductivity measurements were used by adding different concentrations of ADNB within the range of 0 to 50 °C, and the mechanism by which temperature and ADNB affect the conductivity of clay was revealed. In addition, the quantitative relationship between the clay conductivity, ambient temperature and concentration of ADNB was elucidated. According to the growth conditions of melinis minutiflora and pigeon pea under different concentrations of ADNB, the optimal ADNB concentration needed to improve ecological restoration was obtained, which provided a new way to evaluate the effects of the large-scale use of soil modifiers on ecological restoration.

South American and African Grass Species Cope Differently With Soil Water Availability

African grasses pose a serious threat to the integrity and conservation of the Cerrado biome (Brazilian savanna). This study evaluated the responses of an invasive (Melinis minutiflora) and a native (Schizachyrium microstachyum) grass species to water availability, simulating natural situations. Individuals of the two species were submitted to different soil moisture levels, simulating from drought to flood, for four weeks in a climate-control chamber. Several morphological and physiological parameters were assessed: shoot height, biomass, number of leaves, tillers, leaf area, leaf gas exchange and chlorophylla fluorescence parameters, photosynthetic pigments and MDA concentration and GST, G-POX, APX and CAT activities. Significant differences were observed between species and among soil moisture levels, being drought more detrimental to both. Although both species were able to cope with water stress conditions and performed best at 80% soil moisture, the invasive species grew more rapidly, showed higher net photosynthetic rates in all circumstances and showed less evidence of stress. Variations in soil moisture levels promoted a stronger response in the native species, reducing biomass accumulation and triggering a stronger biochemical response than in the invasive species.

The N-fixing legume Periandra mediterranea constrains the invasion of an exotic grass (Melinis minutiflora P. Beauv) by altering soil N cycling

Melinis minutiflora is an invasive species that threatens the biodiversity of the endemic vegetation of the campo rupestre biome in Brazil, displacing the native vegetation and favouring fire spread. As M. minutiflora invasion has been associated with a high nitrogen (N) demand, we assessed changes in N cycle under four treatments: two treatments with contrasting invasion levels (above and below 50%) and two un-invaded control treatments with native vegetation, in the presence or absence of the leguminous species Periandra mediterranea. This latter species was considered to be the main N source in this site due to its ability to fix N2 in association with Bradyrhizobia species. Soil proteolytic activity was high in treatments with P. mediterranea and in those severely invaded, but not in the first steps of invasion. While ammonium was the N-chemical species dominant in plots with native species, including P.mediterranea, soil nitrate prevailed only in fully invaded plots due to the stimulation of the nitrifying bacterial (AOB) and archaeal (AOA) populations carrying the amoA gene. However, in the presence of P. mediterranea, either in the beginning of the invasion or in uninvaded plots, we observed an inhibition of the nitrifying microbial populations and nitrate formation, suggesting that this is a biotic resistance strategy elicited by P. mediterranea to compete with M. minutiflora. Therefore, the inhibition of proteolytic activity and the nitrification process were the strategies elicited by P.mediterranea to constrain M.munitiflora invasion.

Olfactory response of Mahanarva spectabilis (Hemiptera: Cercopidae) to volatile organic compounds from forage grasses

Several herbivorous insects utilize plant chemical cues to identify hosts for feeding. The role of smell in host plant detection by Mahanarva spectabilis (Distant) remains largely unknown. In this study, assays were applied to assess M. spectabilis olfactory responses to forage grasses (Pennisetum purpureum cvs. Roxo Botucatu and Pioneiro; Panicum maximum cvs. Makueni and Tanzânia; Hyparrhenia rufa cv. Jaraguá; Melinis minutiflora; Cynodon dactylon cv. Tifton; Brachiaria brizantha cv. Marandú; and Brachiaria decumbens cv. Basilisk). Bioassays were performed using a Y-olfactometer to evaluate the behavior of adult M. spectabilis to forage damaged and undamaged by insects. M. spectabilis preferred volatiles of undamaged Basilisk and Pioneiro. Repellent behavior by M. spectabilis to cospecifics was recorded for plant volatiles from damaged Marandú. The mixture of volatiles from undamaged forage grasses differed from that of forage grasses damaged by insects. Forage grasses showed a greater diversity of compounds after damage, including menthone, eucalyptol and camphor, which are compounds likely to cause loss of attractiveness or repellence. Our results demonstrate that M. spectabilis employs plant chemical cues in its choice of hosts. This fact may contribute to strategies of integrated management against this pest.

Uso de mantas geotêxteis na revegetação de um fragmento de mata de galeria no Jardim Botânico de Brasília - DF: sobrevivência e desenvolvimento de mudas

Atividades antrópicas têm causado danos ao Cerrado, segundo maior bioma do Brasil. Entre as formações vegetais mais ameaçadas do bioma Cerrado, destaca-se a Mata de Galeria. Programas de recuperação tentam restaurar essa ftofsionomia, mas ervas invasoras difcultam o estabelecimento e o desenvolvimento de espécies nativas lenhosas. Nesse cenário, cerca de 2 ha da Mata de Galeria do Córrego Cabeça de Veado, na área do Jardim Botânico de Brasília, fora desmatada para a prática de agricultura de subsistência e, posteriormente, a área foi dominada por Melinis minutiflora Beauv. (capim-gordura). Algumas tentativas de restauração do local falharam devido à competição dessa erva com as mudas arbóreas plantadas. Dessa forma, este trabalho visou avaliar o efeito do uso de mantas geotêxteis na sobrevivência e desenvolvimento de mudas de espécies arbóreas plantadas em um trecho de Mata de Galeria infestado por capim-gordura. Na área de estudo foram plantadas mudas arbóreas de trinta espécies nativas do Cerrado. Metade das mudas recebeu manta geotêxtil e a outra metade das mudas não recebeu essa proteção. Quatro levantamentos foram efetuados, quando se mediram a sobrevivência, a altura e o diâmetro das mudas. Os resultados indicaram que as mantas geotêxteis aumentaram em 19,6% a sobrevivência de plantas e que sete das trinta espécies apresentaram maior incremento alométrico com o uso de mantas geotêxte is. Duas espécies se desenvolveram mais sem a presença de mantas geotêxteis e o incremento de metade das espécies não foi signifcativamente afetado pelo uso desse protetor.

Spatial pattern of invasive and native graminoids in the Brazilian cerrado

Invasive grasses are an important threat in tropical savannas and grasslands and may be affected by natural and anthropogenic features of the environment. They may affect native species at a variety of scales, but a spatially explicit assessment of their effects is lacking. We studied the spatial pattern of native and invasive graminoids in Brazilian cerrado in southeastern Brazil and assessed the effects of vegetation type, elevation, and edges. We sampled native grasses, native sedges, and two invasive grass species (Urochloa decumbens and Melinis minutiflora) along three 301- to 1334-m-long transects encompassing grassland, forest, and savanna. We used wavelet transforms, generalized additive models, and null model simulations for analysis. Invasive grasses were mostly found in open vegetation. Neither native nor invasive species were consistently affected by elevation or edges. Much of the spatial variation could be explained by small-scale autocorrelation, but M. minutiflora had a more heterogeneous pattern than U. decumbens. Invasive grasses were negatively related to native ones at a variety of scales, from 1 to 66 m, and we observed both positive and negative relations between the two invasive species, with positive ones a finer scales. We hypothesize that spatial pattern characteristics of different invasive species may be related to their invasion potential.

Phenological and reproductive traits and their response to environmental variation differ among native and invasive grasses in a Neotropical savanna

Phenology is a key component of the life-history of plants, and non-native plant species with distinctive phenological traits may have an advantage over native species. In tropical savannas, water and light availability are often spatially and temporally heterogeneous, so that non-native species capable of changing their phenology in response to these factors are more likely to succeed in these ecosystems. We compared flowering onset and flowering period among African and native grasses in a Brazilian Neotropical savanna and assessed if these traits and the production of flowering tillers differ between two consecutive years and respond to spatial heterogeneity in water table depth and canopy closure. Non-native species showed multiple flowering patterns; Urochloa decumbens flowered from the mid-rainy season to the mid-dry season, Melinis minutiflora flowered during the dry season and Mepens repens flowered throughout the year. In addition, they were responsive to annual and abiotic variation, as U. decumbens also showed longer flowering period and produced more flowering tillers in the second year, except over shallow groundwater and high canopy closure, whereas M. minutiflora produced fewer flowering tillers under high canopy closure and M. repens showed large reproductive decline in the second year. Native grasses flowered in the middle of the rainy season regardless of annual and abiotic variation, although in the second year one species produced more flowering tillers in seasonally flooded sites. The phenology of M. repens is consistent with a ruderal life-history, so that it is only likely to become dominant under repeated disturbances. By contrast, the ability of changing flowering period and reproductive output according to growing conditions showed by U. decumbens and the distinct flowering timing showed by M. minutiflora may favour these species over less plastic native grasses, suggesting that phenological attributes contribute to the dominance of African grasses in Neotropical savannas.

Residues of Invasive Forage Species Inhibits the Growth of Caryocar brasiliense

ABSTRACT: Native species seedling growth may be affected by allelopathic substances released by invasive forage species, mainly in natural regrowth areas. Thus, this research aimed to evaluate the growth characteristics of pequi trees influenced by concentrations of plant residues of different forage species (Urochloa decumbens, Melinis minutiflora and Paspalum notatum). A randomized block experimental design was arranged in a factorial 3 x 4 + 1, with four replications. Treatments consisted of incorporating plant shoot residues of three forage species to pequi seedling substrate (soil + fertilizer) at four concentrations (1%, 2%, 3%, and 4% mass/mass), plus pequi seedlings grown in a residue-free substrate (control). Pequi plant height, stem diameter, and leaf number were evaluated at fortnightly intervals. Leaf area, root/shoot ratio, leaf area ratio, specific leaf area, and leaf mass ratio were determined 100 days after transplanting. Forage residues added to substrate inhibited pequi growth, and with increasing residue concentration, this inhibition was intensified. Pequi leaf characteristics proved to be more sensitive to allelopathic effect, especially from U. decumbens residues.

O uso do <em>software</em> Imagej na estimativa de substrato exposto pós controle de gramíneas invasoras

Espécies de gramíneas (Poaceae) têm sido recomendadas em processos iniciais de recuperação. Entretanto, necessitam de um controle posterior, para evitar competição com espécies de interesse, especialmente arbóreas. Neste contexto, objetivou-se, por meio do software ImageJ, quantificar o substrato exposto em uma área degradada em Diamantina, MG, sobre a qual foram aplicados distintos métodos de capina para o controle das gramíneas exóticas Urochloa decumbes (Stapf) RD, Wabster e Melinis minutiflora P. Beauv.. Foi realizado o controle das gramíneas por meio da aplicação de diferentes métodos (químico, manual e mecânico), distribuídos em 4 blocos, subdivididos em parcelas e subparcelas. Após 100 dias, por meio de imagens processadas pelo ImajeJ, observou-se que método químico proporcionou a menor exposição do substrato e maior presença de biomassa superficial, diferentemente do método manual, onde houve menor cobertura vegetal. Foi possível quantificar o substrato exposto em ambiente com controle de gramíneas permitindo, de modo eficaz, o planejamento das técnicas de recuperação. O uso do ImageJ se mostrou eficiente, representando uma alternativa para a quantificação de substrato, e diversos estudos inerentes à análise de cobertura vegetal de ambientes degradados.

Invasive Melinis minutiflora outperforms native species, but the magnitude of the effect is context-dependent

Impacts of invasive species are context-dependent owing to genetic differences in the invasive species, in the abiotic environment or the recipient biotas. Here, we tested how these factors affected the invasive grass Melinis minutiflora and its impacts on native plants in Hawai’i (USA) and in the Brazilian Cerrado under four environmental conditions. We sampled M. minutiflora and three native species from each studied region and conducted two equivalent greenhouse experiments. In each experiment, we manipulated shade, irrigation, soil nutrients, and interspecific competition. We found that M. minutiflora had low genetic polymorphism, and two distinct genetic clusters exist. Both clusters exist in Hawai’i and Brazil. Melinis minutiflora biomass was three-times greater in Brazil compared to Hawai’i. Both in Brazil and Hawai’i, M. minutiflora was affected by shade, irrigation, and competition. While in Brazil the identity of the competing native species did not matter for M. minutiflora, in Hawai’i the identity of the native species affected M. minutiflora when shade was applied. Brazilian native species were all affected by shading, two of them by competition with M. minutiflora, and one of them by fertilization. Two Hawaiian native plants were affected by shade and competition with M. minutiflora, whereas one native species was not affected by any of the experimental factors. In summary, both biotic and abiotic factors affected native and invasive species. However, in all cases native species were outperformed by the invader.

English

The objective of this study was to evaluate the efficiency of different methods of exotic grass control in a degraded area in the urban area of Diamantina, state of Minas Gerais, Brazil. The experiment was carried out in a randomized block design, with the following methods of control of invasive grasses: T1) manual; T2) mechanical; T3) chemical; and T4) chemical + mechanical. After one hundred days, regenerants of alien invasive species biomass were sampled for the quantification of fresh biomass and dry biomass. The results found fresh biomass vary among the control methods, with higher values from mechanical control, followed by the combination of mechanical + chemical control. Chemical and manual methods had the lowest fresh biomass production, indicating that they were more effective in controlling the invasive grasses. The production of dry matter did not differ significantly among the methods of exotic grass control, on Tukey test, at 5% significance. Key words: Urochloa decumbes, Melinis minutiflora, biomass, restauration.

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.

Weeds Interference in Pequi Plants

ABSTRACT: Pequi plants are native fruit species of the Cerrado and is at risk of extinction due to the destruction of native vegetation and the extraction of their fruits. Because this species has a long juvenile period, it becomes susceptible to the interference of weeds, mainly forage grass. This research aimed to evaluate the effects of forage grass species coexisting with small seedlings. The treatments, arranged in a factorial scheme, consisted of three weed species(Melinis minutiflora, Paspalum notatumandUrochloa decumbens)coexisting in four densities (1, 2, 3, and 4 plants per pot) with pequi plants. As an additional treatment a pequi plant was cultivated free of coexistence. The physiological variables photosynthetic rate (A), stomatal conductance (gs), transpiration rate (E) Ci/Ca relation, the effective quantum yield of PS II, transport rate of electrons and non-photochemical quenching, and growth variables: height (PH), Leaf area (LA) and dry matter (DM) were affected by weed coexistence.U. decumbenspromoted greater intensity interference with pequi plants. The degree of interference was greater with increasing density of weeds, with linear decreasing behavior for the variables A, gs, E, PH, LA, MD, stem diameter and number of leaves of pequi plants.

RESIDUES OF FORAGE SPECIES AFFECT PHOTOSYNTHETIC CHARACTERISTICS OF THE PEQUIZEIRO

ABSTRACT Some forages release allelopathic substances into the environment, and may prevent consortium with arboreal species in pastures. The objective of this work was to evaluate photosynthetic characteristics of pequizeiro plants (hereafter pequi) influenced by concentrations of residues of the forage species Urocholoa decumbens, Melinis minutiflora and Paspalum notatum. The treatments consisted of pequi cultivation under aerial residues of the three forage species mixed to the substrate in four concentrations (1, 2, 3 and 4% mass/mass), plus an additional treatment (comparative control) with pequi cultivated on the substrate without waste. The following parameters were evaluated: photosynthetic rate, stomatal conductance, transpiration rate, relationship between internal and external CO2 concentration (Ci/Ca), maximum quantum yield, effective quantum yield of FS II, electron transport rate, nonchemical quenching and chlorophyll index, concerning the content of chlorophyll a, b and total in pequi plants at 50 and 100 days after transplanting (DAT), and the relative production of dry matter at 100 DAT. At 50 DAT, the following photosynthetic variables were affected in pequi plants: A, gs, chlorophyll a, chlorophyll b and total chlorophyll when cultivated in the presence of forage residues. At 100 DAT, the following photosynthetic variables were affected in pequi plants: A, Fv/Fm, ETR, NPQ, chlorophyll a, chlorophyll b and total chlorophyll, when cultivated in the presence of forage residues. Pequi plants had reduced relative dry matter yield when grown in the presence of U. decumbens. This variable was also affected when pequi was grown in increasing concentrations of residues of the species U. decumbens, M. minutiflora and P. notatum.