ABSTRACT Salinity is one of the major obstacles to agriculture in semi-arid regions, as it affects the physiological processes, growth, and yield of numerous crops. Hence, the application of salt stress attenuators is of paramount importance, as it enables the use of saline water for agricultural purposes. Among these, humic acid promotes the growth as well as water and nutrient uptake of plants. To this end, the present study evaluated the effects of humic acid on the growth and physiology of Carica papaya seedlings irrigated with saline water. The experiment followed the randomized block design with five levels of electrical conductivity (0.5, 1.15, 2.75, 4.35, and 5.0 dS m-1) and five concentrations of humic acid (0.5, 0.94, 2.0, 3.06, and 3.5 mL L-1). Growth, gas exchange, chlorophyll content, and chlorophyll a fluorescence were evaluated. Irrigation with 4.9 dS m-1 water and application of 3.05 mL L-1 humic acid promoted the growth of papaya seedlings. Irrigation with high-salinity water (4.96 and 3.09 dS m-1) coupled with the application of 3.05 and 2.21 mL L-1 humic acid increased internal CO2 concentration, transpiration, instantaneous water use efficiency, carboxylation efficiency, and chlorophyll b content. Overall, humic acid (3.5 mL L-1) attenuated the deleterious effects of salt stress, promoting the growth and improving the performance of papaya seedlings under moderate salinity (4 dS m-1).

RESUMO A salinidade é um dos grandes entraves na agricultura em regiões semiáridas, pois afeta os processos fisiológicos, crescimento e produção de diversas culturas. Assim, o uso de atenuadores do estresse salino é de extrema importância, pois permite o uso de águas salinas para fins agrícolas. Dentre estes, destacam-se os ácidos húmicos que promovem o crescimento e a absorção de água e nutrientes. Assim, o objetivo deste trabalho foi avaliar o efeito do ácido húmico sob o crescimento e a fisiologia de mudas de mamão irrigadas com água salina. O delineamento experimental utilizado foi em blocos casualizados com cinco níveis de condutividade elétrica (0,5; 1,15; 2,75; 4,35 e 5,0 dS m-1), e cinco concentrações de ácido húmico (0,5; 0,94; 2,0; 3,06 e 3,5 mL L-1). Foram avaliados o crescimento, trocas gasosas, índice de clorofilas e fluorescência da clorofila a. A irrigação com água de 4,9 dS m-1 e aplicação de 3,05 mL L-1 de ácido húmico proporcionou maior crescimento das mudas de mamoeiro. A irrigação de mudas de mamoeiro com alta salinidade (4,96 e 3,09 dS m-1) aliada à aplicação de 3,05 e 2,21 mL L-1 de ácido húmico proporcionou aumento da concentração interna de CO2, taxa de transpiração, eficiência instantânea do uso da água, eficiência de carboxilação e teor de clorofila b. O ácido húmico (3,5 mL L-1) atenua os efeitos deletérios da salinidade no mamoeiro, sendo capaz de aumentar o crescimento e melhorar o desempenho das mudas de mamão em salinidade moderada (4 dS m-1).

Energy substrate used by workers of leaf-cutting ants during nest excavation. In this study we aimed to ascertain whether leaf-cutting ant workers lose body reserves (fat or sugars) as a function of nest excavation. For each treatment, we isolated 10 workers of Atta sexdens into two experimental groups, Control (C- without excavation) and Soil (S- with excavation), which were kept for different time intervals (0, 24, 48 or 72 hours), totaling 700 tested workers. We then determined the concentration of soluble carbohydrates and total lipid content in them. The total carbohydrates were determined colorimetrically, based on the reaction between carbohydrates and sulfuric acid-phenol. For determination of lipids, the insects were immersed in organic solvent until they reached a constant weight. Our results showed that carbohydrates are consumed during nest excavation activities. In the experimental groups S24, S48 and S72, there was an average reduction of 5.82 (20.42%), 14.31 (44.96%) and 13.27 (43.96%) µ.mg-1 in soluble sugar when compared with the experimental groups that did not excavate. Furthermore, the lipids were not used during this activity. With respect to dry mass of the workers, their values were C0 = 8%, C24 = 10.4%, C48 = 9.2%, C72 = 10%, S24 = 9.2%, S48 = 8.7% and S72 = 8.5%. Our results show experimentally that the source of energy for nest excavation is carbohydrates, whereas lipids are conserved for other activities.

Energetic cost of digging behavior in workers of the leaf-cutting ant Atta sexdens (Fabricius). During nest excavation, leaf-cutting ant workers undergo reduction in their body reserve, particularly carbohydrates. In order to estimate the energetic cost of digging, groups of 30 workers of the leaf-cutting ant Atta sexdens were sealed in a hermetic chamber for 24, 48 and 72 hours, with and without soil for digging, and had the CO2 concentration measured using respirometric chambers as well as volume of soil excavated (g). As expected, the worker groups that carried out soil excavation expelled more carbon dioxide than the groups that did not excavate. Therefore, a worker with body mass of 9.65 ± 1.50 mg dug in average 0.85 ± 0.27 g of soil for 24 hours, consuming ca. 0.58 ± 0.23 J. In this study, we calculate that the energetic cost of excavation per worker per day in the experimental set-up was ca. 0.58 J.

Os ninhos adultos das formigas cortadeiras (gênero Atta e Acromyrmex) são compostos de milhares de câmaras subterrâneas, as quais abrigam o jardim de fungo, lixo e a população desses insetos. Entretanto, como as câmaras são construídas? Para responder essa questão, nós hipotetizamos que o jardim de fungo atua como um molde para a construção das câmaras. Assim, foram utilizadas 20 colônias de 6 meses de idade, divididas em quatro séries experimentais: padrão (quantidade normal de jardim de fungo); metade de jardim de fungo; dobro de jardim de fungo e sem jardim de fungo (Testemunha). As variáveis estudadas foram: parâmetros morfológicos das estruturas (túneis e câmara formada); fluxo das atividades das operárias; volume de solo escavado. Como se esperava, o jardim de fungo atua como um molde para a construção das câmaras em formigas cortadeiras. Os resultados foram: o tratamento sem jardim de fungo não apresentou nenhuma câmara, apenas túneis, em contraposição às demais séries experimentais que apresentaram no mínimo 2 câmaras, com dimensões similares; o fluxo das operárias carregando pellet de solo por minuto durante as 72 horas diferiu estatisticamente entre as séries experimentais e, finalmente, o volume do solo escavado foi resultado da taxa de escavação das operárias, diferindo estatisticamente entre as séries experimentais. Os resultados corroboram a hipótese de que o jardim de fungo atua como um molde para a construção da câmara. A ausência de uma estrutura funcional como uma câmara, quando o jardim de fungo está ausente, comprova a hipótese.

Adult nests of leaf cutting ants (genus Atta and Acromyrmex) are composed of thousands of underground chambers, which harbor the fungus garden, garbage and their population. However, how the chambers are constructed? To answer this question, we hypothesized that the fungus garden acts as a template for the chambers construction. Thus, we used 20 colonies of 6 months of age, divided into four treatments: Normal (Control); Half fungal symbiont; Double symbiont fungus and No symbiotic fungus. The variables studied were: morphology, (tunnels and chamber formed); flow of activities of workers and volume of soil excavated. As expected, treatment no symbiotic fungus did not have any cameras, just tunnels, as opposed to other treatments that showed at least two chambers, with similar dimensions. The flow of workers carrying pellet of soil per minute for 72 hours, it differed between treatments. Thus, the volume of excavated soil was the result of the excavation rate of workers, differences among the treatments. The results confirm the hypothesis that the symbiotic fungus acts as a template for the construction of the chamber. The absence of a functional structure as a chamber when is absent of symbiont fungus proves the hypothesis.

As formigas cortadeiras apresentam uma sofisticada divisão de trabalho durante o forrageamento, cultivo do jardim de fungo e devolução dos materiais forrageados. Materiais com diferentes graus de hidratação e dureza (esponja floral, isopor, plástico e argila) foram oferecidos a duas colônias de laboratório de Acromyrmex subterraneus brunneus Forel, 1911. As diferentes categorias de tamanho de operárias foram observadas durante a execução de 14 subtarefas. Probabilidade relativa de desempenho e as curvas aloéticas foram usadas para verificar a flexibilidade comportamental e os padrões comportamentais estereotipados das operárias. Os padrões comportamentais possibilitaram estabelecer papeis dentro de prováveis subcastas.

Leaf cutting-ants present a sophisticated division of labor during foraging, fungus-garden cultivation and devolution of foraged materials. Material with different degrees of moisture and hardness (floral sponge, polystyrene, plastic and clay) were offered to two Acromyrmex subterraneus brunneus Forel, 1911 laboratory colonies. The different size categories of workers were observed during the execution of 14 subtasks. Relative probability performance and alloethic curves were used to verify behavioral flexibility and behavioral stereotyped patterns in the workers. The behavioral patterns could establish roles within probable subcastes.