RESUMO Objetivou-se avaliar características morfofisiológicas e produtivas em quatro cultivares semieretas de feijão-caupi submetidas a cinco populações de plantas. O experimento foi conduzido no campo experimental da Embrapa Meio-Norte, em Teresina-PI. Utilizou-se o delineamento experimental de blocos completos casualizados com quatro repetições, em arranjo fatorial 4x5 sendo avaliadas quatro cultivares (BRS Guariba, BRS Novaera, BRS Potengi e BRS Tumucumaque) e cinco populações de plantas (105, 2x105, 3x105, 4x105 e 5x105 plantas ha-1). Houve diferenças significativas entre as cultivares para o comprimento do ramo principal (CRP), número de ramos laterais (NRL), massa de cem grãos (MCG) e rendimento de grãos secos (REND). O CRP máximo de 58,5 cm foi obtido com 300 mil plantas ha-1, correspondendo a um aumento de 11,5% quando comparado com 100 mil plantas ha-1. Entretanto, houve redução de 91,2% no NRL quando comparadas às populações de 100 e 500 mil plantas ha-1. Os aumentos de 188% obtidos no índice de área foliar (IAF) no intervalo de 100 e 500 mil plantas ha-1, explicam o aumento linear da taxa de crescimento da cultura (TCC) em função da maior produção de área foliar, bem como, os decréscimos obtidos na taxa de assimilação líquida (TAL), notadamente no intervalo de 100 a 300 mil plantas ha-1, devido ao consequente autossombreamento, que foi intensificado nas maiores populações. O IAF, a interceptação de luz e a TCC das cultivares aumentam em resposta às maiores densidades. O MCG e o REND não são afetados significativamente pelas diferentes populações.

ABSTRACT The aim of this study was to evaluate morpho-physiological and productive characteristics in four semi-erect cultivars of the cowpea under five plant populations. The experiment was conducted in the experimental area of Embrapa Meio-Norte in Teresina in the State of Piauí, Brazil (PI). The experimental design was of randomised complete blocks with four replications, in a 4 x 5 factorial scheme, for evaluating four cultivars (BRS Guariba, BRS Novaera, BRS Potengi and BRS Tumucumaque) and five plant populations (105, 2x105, 3x105, 4x105 and 5x105 plants ha-1). There were significant differences between cultivars for primary branch length (PBL), number of lateral branches (NLB), 100-grain weight (HGW), and dry-grain yield (GY). The maximum PBL of 58.5 cm was obtained with 300 thousand plants ha-1, corresponding to an increase of 11.5% when compared to 100 thousand plants ha-1. However, there was a reduction of 91.2% in NLB when compared to the populations of 100 and 500 thousand plants ha-1. The increases of 188% obtained in the leaf area index (LAI) in the range of 100 to 500 thousand plants ha-1 explain the linear increase in the crop growth rate (CGR) as being due to the greater production of leaf area; also, the decreases seen in the net assimilation rate (NAR), especially in the range of 100 to 300 thousand plants ha-1, are explained as due to the consequent self-shading, which was intensified in the larger populations. LAI, light interception, and CGR in the cultivars increase in response to higher densities. HGW and GY are not significantly affected by the different populations.

Mercury (Hg) occurs in the environment as a natural and anthropogenic element, and through the years the accumulation of mercury has affected the integrity of ecosystems and human health. This study presents a screening of microorganisms resistant to organic and inorganic mercury, the determination of the minimum inhibitory concentration of Hg, the estimation of the mercury volatilization by selected microorganisms and the dynamics of volatilization. Eight Gram-negative bacteria resistant to high concentrations of mercury (60 to 210 mg L-1) were selected, and these isolates showed ability to volatilize the metal. The dynamics of the volatilization of the Proteus mirabilis M50C demonstrated that in only 4 h of incubation it was possible to volatilize 72% of the mercury present in the culture. The results showed promising application for bioremediation strategies.

This work evaluated the kinetics as well as the retention capacity of Cu, Zn, Cd, and Pb by arbuscular mycorrhizal fungi (AMF) mycelium. The metal retention is a fast process with Cu being retained 3, 30, and 60 times faster than Zn, Cd, and Pb, respectively. Metal retention capacity varied amongst the different tested AMF species and decreased in the following order: Cu>Zn>>Cd>Pb. The Glomus clarum mycelium showed the highest retention capacity for Cu, Cd and Pb, whereas Zn was mostly retained by Gigaspora gigantea mycelium. The simultaneous application of all tested metals in solution decreased Cu and Zn retention by AMF mycelium. The high retention capacity of Cu and Zn by mycelium of G. clarum and G. gigantea suggests a promising use of these isolates in phytoremediation.