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About one-third of organic agriculture production in Brazil is carried out by smallholders, who seek to use low-cost organic fertilizers in their crops. In this study, we evaluated the nest refuse of leaf-cutting ants (NR) in the formulation of growing substrates for lettuce (Lactuca sativa) and arugula (Eruca sativa) seedlings. A completely randomized design with six treatments and four repetitions was applied. The treatments were basis growing substrate (CONT), commercial substrate (TropstratoHT®—TROP), and four formulations using NR of two species of leaf-cutting ants associated with 75 or 85% (volume fraction) of CONT. Substrates were submitted to chemical analysis for determination of macro- and micronutrients while plant vigor was evaluated considering plant height (PH), root length (RL), stem diameter (SD), dry mass (DM), and number of leaves (NL) at 15, 20, 25, and 30 days after sowing. The data were submitted to a chemometric evaluation by means of principal component analysis (PCA). Treatments with 25% of NR resulted in lettuce seedlings from 42 to 53% higher and with a twofold increase of dry mass compared to the commercial substrate (TROP) (P

The accumulation and spatial distribution of arsenic and phosphorus in the As-hyperaccumulator fern Pityrogramma calomelanos were investigated by micro-energy dispersive X-ray fluorescence spectrometry (μ-EDXRF). Ferns were grown in half-strength Hoagland nutrient solution without and with 1.0, 10 or 30 × 10−3 mol L−1 As during three weeks. Microchemical As and P maps in different areas of the pinna were obtained by μ-EDXRF, and the same elements were also determined in pelletized powdered samples from the pinna, stipe and root. The reference method for the determination of As and P in the fern samples was a validated method based on microwave-assisted acid digestion followed by ICP OES analysis. Correlations between X-ray characteristic emission intensities and the corresponding As and P mass fractions obtained from the analysis of pelletized test samples exhibited linear correlation coefficients higher than 0.98 (n = 42). Better root mean square errors of prediction (RMSEPs) were obtained when different calibration models were built with pinna, stipe and root test samples separately. Arsenic was accumulated mainly in the pinna midrib, secondary veins, and apical and marginal regions of the pinnule of P. calomelanos, causing alterations in the P distribution. The proposed μ-EDXRF method is an appropriate analytical tool for simultaneously mapping As and P in P. calomelanos. In addition, useful information for either environmental monitoring or phytoremediation studies regarding As contamination is properly obtained.

Leaf-cutting ants are responsible for carrying out an important ecological process in neotropical ecosystems: the cycling of elements. However, although several studies have demonstrated the accumulation of organic matter inside colonies, little is known about the dynamics of nutrients and its residence time in nest refuse compared to the leaf material harvested by ants. This study compares the nutrient content of nest refuse and leaf material of the leaf-cutting ant Atta sexdens during states of decomposition in a transitional environment between forest and shrub vegetation in Northeastern Brazil. The decomposition rate of the refuse material was two-fold faster than the substrate harvested. In addition, there was a substantial difference in chemical and structural characteristics between both substrates. Refuse material showed higher contents of Ca whereas leaf fragments had a higher P content, more organic carbon (OC), and a higher lignin/cellulose ratio. During the period of decomposition in the field, only OC content decreased simultaneously in both substrates, indicating that changes had occurred mainly in the structure of the substrates with a low transference rate of most nutrients to the surrounding soil. A higher lignin/cellulose ratio in the leaf material may explain the higher residence time of this substrate in the environment. Results indicate that colonies of A. sexdens accelerate the decomposition of organic matter, perhaps due to reduced lignin–cellulose ratio. Organic carbon may be mineralized in the first days after the disposal of the refuse material into the nest chambers.

Leaf-cutting ants perform a vital role in the cycling of carbon and nutrients in tropical ecosystems. Nests have high levels of organic matter and refuse dumps host up to two times more soil micro-organisms than non-nest soil. The increased levels of organic matter in the soil of nests, however, can affect CO2 emissions from soil and alter the balance of atmospheric CO2. We aimed at assessing the effect of nests of the leaf-cutting ant Acromyrmex balzani on CO2 emissions in a coastal area of Northeast Brazil. Results show that A. balzani nests emitted up to four times more CO2 than the surrounding soil and emissions were positively correlated with soil moisture and soil organic matter (SOM) content. In addition, field experiments demonstrated that refuse material has a lower residence time than the leaf material brought to the colonies. Despite the high density of nests and high content of SOM compared to adjacent control soil, CO2 emissions by A. balzani nests represent only 0.3% of the total CO2 efflux by the studied ecosystem. Although these effluxes account for a relative small portion of the total soil CO2 emission, they are still important for the understanding of C balance, especially when one considers the thousands of tons of CO2 emitted each day, across entire Neotropical regions where leaf-cutting ants occur.

As formigas cortadeiras (Atta e Acromyrmex) são consideradas importantes pragas na agricultura e silvicultura, mas pouco se sabe sobre os reais danos dessas espécies. Uma forma bastante difundida de avaliação do dano é por meio do cálculo da taxa de conversão, dividindo-se o peso do material cortado pelo peso de lixo produzido pelas colônias. Foi levantada a hipótese de que a qualidade do substrato cortado pode influenciar no forrageamento das operárias, alterando a taxa de conversão e dificultando as estimativas de dano. A taxa de conversão de oito colônias de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) foi calculada com duas espécies vegetais com diferentes concentrações de lignina e celulose, para testar essa hipótese. Colônias mantidas com folhas de baixa qualidade (razão lignina/celulose elevada) tiveram maior forrageamento e produziram mais lixo. Entretanto, a taxa de conversão das colônias foi semelhante com essas duas plantas (média = 1,54). Esse valor está dentro da variação encontrada para outras espécies no campo (1,5-1,8), indicando um fator semelhante de conversão entre os gêneros Atta e Acromyrmex. O consumo médio de material vegetal, em termos de pesos seco e fresco, de uma colônia de A. sexdens rubropilosa com 4.500 operárias, foi estimado em 520 e 1.100 g/ano, respectivamente. Leaf-cutting ants (Atta and Acromyrmex) are important pests in agriculture and forestry, although few data exist on the actual damage caused by these species. A model used to evaluate damage by leaf-cutting ants are estimates of the conversion factor, which is the ratio between the weight of material cut by the ants and the refuse produced by the colonies. The hypothesis that substrate quality influences foraging by workers, modifying the conversion factor and impairing damage estimates was put forward. To test this hypothesis, the conversion factor was calculated for eight colonies of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae), using two plant species, with different lignin and cellulose concentrations. Colonies maintained with low quality leaves (high lignin/cellulose ratio) presented higher foraging activity and produced more refuse than colonies maintained with high quality leaves. However, the conversion factors obtained for the two groups of leaf-cutting ant colonies (average = 1.54) was within the variation found for other species in the field (1.5 – 1.8), indicating a similar conversion factor in Atta and Acromyrmex. The average consumption in both dry and fresh weight of plant material of a colony of Atta sexdens rubropilosa with 4,500 workers was estimated as 520 and 1,100 g/year, respectively.

The soils developed under High Altitude Rocky Complexes in Brazil are generally of very low chemical fertility, with low base saturation and high exchangeable aluminium concentration. This stressful condition imposes evolutionary pressures that lead to ecological success of plant species that are able to tolerate or accumulate high amounts of aluminium. Several analytical methods are currently available for elemental mapping of biological structures, such as micro-X-ray fluorescence (μ-EDX) and histochemical tests. The aim of this study was to combine μ-EDX analysis and histochemical tests to quantify aluminium in plants from High Altitude Rocky Complexes, identifying the main sites for Al-accumulation. Among the studied species, five showed total Al concentration higher than 1000 mg kg−1. The main Al-hyperaccumulator plants, Lavoisiera pectinata, Lycopodium clavatum and Trembleya parviflora presented positive reactions in the histochemical tests using Chrome Azurol and Aluminon. Strong positive correlations were observed between the total Al concentrations and data obtained by μ-EDX analysis. The μ-EDX analysis is a potential tool to map and quantify Al in hyperaccumulator species, and a valuable technique due to its non-destructive capacity. Histochemical tests can be helpful to indicate the accumulation pattern of samples before they are submitted for further μ-EDX scrutiny. Solos associados aos Complexos Rupestres de Altitude no Brasil destacam-se pela baixa fertilidade química, baixa saturação de bases e elevados teores de alumínio trocável. Esta condição estressante impõe pressões evolutivas que determinam o sucesso ecológico de espécies capazes de tolerar ou acumular grandes quantidades de alumínio. Vários métodos analíticos são utilizados para mapeamento de elementos químicos em estruturas biológicas, como microfluorescência de raios-X (μ-EDX) e testes histoquímicos. O objetivo do presente trabalho foi combinar a μ-EDX e testes histoquímicos para quantificar o teor de Al em espécies vegetais de Complexos Rupestres de Altitude, e identificar os principais sítios de bioacumulação de Al. Cinco das espécies investigadas apresentaram concentração total de Al maior que 1000 mg kg−1. As principais hiperacumuladoras de Al, Lavoisiera pectinata, Lycopodium clavatum e Trembleya parviflora, apresentaram reação positiva nos testes histoquímicos com Chrome Azurol e Aluminon. Alta correlação positiva foi observada entre as concentrações totais de Al e as magnitudes de sinal obtidas por μ-EDX. A análise com o uso da μ-EDX mostrou-se uma ferramenta promissora para mapear e quantificar Al em espécies hiperacumuladoras, constituindo uma importante técnica não destrutiva. Testes histoquímicos podem ser úteis na identificação de padrões de acumulação de Al em amostras vegetais antes de serem submetidas a uma minuciosa análise com a μ-EDX.

As saúvas (Atta spp.) estão amplamente distribuídas pelo continente Sul-Americano e são consideradas importantes componentes do ecossistema neotropical. Diversos estudos têm demonstrado o efeito de formigueiros no enriquecimento do solo e na facilitação ao estabelecimento de espécies vegetais. Possivelmente o enriquecimento do solo seja devido ao acúmulo de matéria orgânica decomposta em câmaras de descarte (lixo) no interior das colônias. Entretanto, pouco se sabe sobre a composição química do lixo de formigas cortadeiras. O objetivo do presente trabalho foi comparar os teores de nutrientes do lixo produzido por colônias de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae), em laboratório, mantidas com folhas de duas espécies de plantas. Os tratamentos foram dois tipos de substrato (Acalypha sp. ou Bauhinia sp.), repetidos quatro vezes. Oito colônias foram divididas em dois grupos (n = 4), e cada grupo foi mantido com apenas um tratamento. Após 30 dias de experimento, as amostras de folhas e lixo foram secas em estufa (70 ºC) e submetidas à digestão ácida, para determinação das concentrações de N, P, K, S, Ca e Mg. Diferenças nas concentrações dos macronutrientes entre os tratamentos (lixo ou folha) foram comparadas por meio de ANOVA e teste T. As concentrações de nutrientes no lixo foram sempre maiores do que nas folhas, independentemente da espécie cortada. Folhas de Acalypha sp. apresentaram concentrações significativamente maiores do que folhas de Bauhinia sp. com relação aos teores de P, Ca, Mg e S; entretanto, as concentrações do lixo em todos os formigueiros foram muito próximas, indicando incorporação adicional de nutrientes por meio do fungo, excreções e, ou, cadáveres no lixo. Esses resultados indicam que, independentemente do substrato cortado, o lixo produzido apresenta maiores concentrações de nutrientes do que as folhas, sendo importante locus de reciclagem de nutrientes no ecossistema. O lixo pode ser uma das principais razões para o aumento da concentração de nutrientes em solos de formigueiros. Leaf-cutting ants (Atta spp.) are widely distributed in South America, and are considered to be important components of the neotropical ecosystems. Several studies have demonstrated the effect of ant-nesting in soil enrichment, thus facilitating vegetation succession. Possibly, this enrichment is due to decomposed organic matter concentration after disposal of nest refuse in the deep soil by the colonies. However, little is known about the chemical composition of refuse material produced by leaf-cutting ants. The present work aimed to compare the macronutrient concentration in nest refuse and leaves of two different harvested plants (Acalypha sp. or Bauhinia sp.) in colonies of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) maintained in laboratory. Eight colonies were divided into two groups (n = 4), and each one was maintained with only one feed type. After 30 days of experiment, samples of leaves and refuse were oven-dried at 70 ºC and subjected to acid digestion for chemical determination of total N, P, K, S, Ca and Mg. Differences in concentrations of macronutrients in both leaves and refuse were compared using ANOVA and T test. Nutrient concentration in the refuse material was consistently higher than in leaves, for both plants. Acalypha sp. leaves showed greater nutrient concentration than those of Bauhinia sp., while the concentration of all refuses were very similar. This indicates an additional enrichment of nutrients in the refuse material by either ant carcasses, fungus cycling or excretions. Results suggest that nests of leaf-cutting ant are important loci of nutrient recycling of the ecosystem. Moreover, the refuse may represent an important factor for chemical enrichment in soils influenced by leaf-cutting ants.