Abstract. Although bromeliads are believed to obtain nutrients from debris deposited by animals in their rosettes, there is little evidence to support this assumption. Using stable isotope methods, we found that the Neotropical jumping spider Psecas chapoda (Salticidae), which lives strictly associated with the terrestrial bromeliad Bromelia balansae, contributed 18% of the total nitrogen of its host plant in a greenhouse experiment. In a one-year field experiment, plants with spiders produced leaves 15% longer than plants from which the spiders were excluded. This is the first study to show nutrient provisioning in a spider-plant system. Because several animal species live strictly associated with bromeliad rosettes, this type of facultative mutualism involving the Bromeliaceae may be more common than previously thought.

RESUMOCom o objetivo de avaliar a produção da cana-de-açúcar (cana-planta) e a utilização do N da uréia aplicada no plantio, com incorporação de restos culturais ao solo (raízes, rizomas, colmos, ponteiro e folhas secas), desenvolveu-se um experimento em vasos (220 L) que continham terra de textura arenosa. Os fatores de estudo foram: doses de N no plantio 0, 30, 60 e 90 kg ha -1 de N-uréia marcada com 15 N e restos culturais de cana-de-açúcar incorporados ao solo, com ou sem folhas secas. O delineamento experimental foi o de blocos ao acaso, com três repetições, sendo o experimento levado a efeito em Piracicaba (SP), de janeiro a dezembro de 1996. A cana-planta respondeu à adubação nitrogenada em produção de colmos e rendimento em açúcar, independentemente do tipo de resto cultural incorporado ao solo. A adubação nitrogenada, associada à incorporação de resíduos culturais ao solo, fez com que a cana-planta acumulasse maior quantidade total de N. Independentemente da dose de N-uréia aplicada, a planta utilizou 54 % desse N, contribuindo as raízes e rizomas com 10 % dessa recuperação. A fertilização nitrogenada no plantio favoreceu o crescimento das raízes e o estoque de N no sistema radicular.Termos para indexação: técnica isotópica, 15 N, uréia, restos culturais.(1) Recebido para publicação em janeiro de 2001 e aprovado em abril de 2002.

No abstract

No abstract

Current limitations on the use of conventional N fertilizers on sugarcane (Saccharum spp.) in Brazil require the search for alternative sources with adequate N use efficiency. Field experiments were conducted in Typic Hapludox (TH) and Typic Eutrustox (TE) soils in São Paulo State, Brazil, to evaluate the dynamics of soil mineral N, N uptake, and sugarcane yield in response to N amendments including Ajifer‐8, ammonium chloride, ammonium nitrate, calcium ammonium nitrate (CAN), and urea applied on sugarcane ratoon at 100 kg N ha−1. The experiments were arranged in randomized complete block design, with four replications. The treatments were applied at 105 and 122 days after harvest of plant cane (DAH) in the TH and TE soil. Ajifer‐8 exhibited higher NH4+–N availability in the 0‐ to 20‐cm soil layer 139 DAH in the TH soil. Ammonium nitrate and CAN resulted in the highest NO3−–N values in the soil within the same period. In the TE soil, the soil mineral N content remained unaltered during all of the sampling dates. The high values of accumulated N uptake by sugarcane in both soils indicates that a good portion of the soil mineral N was take up by the plants. The Ajifer‐8 and CAN fertilizers resulted in higher sugarcane yield in both experiments, and may be used as replacement for conventional N sources. In contrast, the use of ammonium chloride resulted in low values of soil mineral N and accumulated N uptake.