Weed interference factors that affect the growth of an atlantic forest tree species / Fatores da matointerferência determinantes no crescimento de espécie arbórea da mata atlântica

The objective of this study was to assess the possible existence of allelopathy and competition for water and nutrients of the grass Urochloa brizantha (Hochst. ex A. Rich.) Stapf cv. Marandu grown together with Schinus terebinthifolius Raddi in a greenhouse. The experimental design was completely randomized in a factorial scheme with 3 factors and the following levels: (1) one individual of the forest species with and without the presence of U. brizantha at a density of 4 individuals per pot; (2) supply of nutrients in limiting or non-limiting dose; and (3) supply of a limiting or non-limiting amount of water. We measured the height and root collar diameter of the tree seedlings, as well as the shoot and root dry weights of both species. There was competition by the grass with the tree species. The coexistence reduced the height by 30.5 cm, the root collar diameter by 1.58 mm and the shoot and root dry weights by 22.7 g and 9.5 g, respectively, of S. terebinthifolius. The greater supply of water in the pots increased the height by 18.9 cm of the S. terebinthifolius seedlings compared to the plants grown with limited water supply. Evidence was also observed of competition for nutrients, principally at the largest nutrient addition level, where the presence of the grass caused an additional decrease in the root collar diameter and shoot dry weight of the tree species, while the shoot and root dry weights of the grass increased. The results did not allow evaluating the existence of allelopathy of U. brizantha on S. terebinthifolius.

O objetivo deste estudo foi avaliar a magnitude da competição por água, nutrientes e alelopatia imposta pelo capim Urochloa brizantha (Hochst. ex A. Rich.) Stapf cv. Marandu em convivência com Schinus terebinthifolius Raddi, em casa de vegetação. O delineamento experimental foi inteiramente casualizado, em esquema fatorial completo, com 3 fatores e os seguintes níveis: (1) um indivíduo da espécie florestal na ausência ou presença de U. brizantha, plantada na densidade 4 indivíduos por vaso; (2) fornecimento de nutrientes em dose limitante ou não-limitante e (3) o fornecimento de água sob regime limitante ou não-limitante. Foram mensuradas a altura e o diâmetro do coleto das mudas, bem como a massa seca da parte aérea e radicular das espécies. Houve competição da gramínea sobre a espécie arbórea. O convívio reduziu em 30,5 cm a altura, em 1,58 mm o diâmetro do coleto e em 22,7 g e 9,5 g as massas secas da parte aérea e das raízes de S. terebinthifolius, respectivamente. O maior fornecimento de água nos vasos proporcionou crescimento em altura 18,9 cm maior nas plantas de S. terebinthifolius quando comparado às plantas com fornecimento limitado de água. Houve também evidência de competição por nutrientes, principalmente quando houve a maior adição de nutrientes, causando um decréscimo adicional no diâmetro do coleto e na massa seca da parte aérea da espécie arbórea, enquanto que a gramínea foi favorecida com aumentos nas massas secas de parte aérea e radicular. O estudo não possibilitou avaliar a existência de alelopatia de U. brizantha sobre S. terebinthifolius.

Much beyond Mantel: bringing Procrustes association metric to the plant and soil ecologist's toolbox.

The correlation of multivariate data is a common task in investigations of soil biology and in ecology in general. Procrustes analysis and the Mantel test are two approaches that often meet this objective and are considered analogous in many situations especially when used as a statistical test to assess the statistical significance between multivariate data tables. Here we call the attention of ecologists to the advantages of a less familiar application of the Procrustean framework, namely the Procrustean association metric (a vector of Procrustean residuals). These residuals represent differences in fit between multivariate data tables regarding homologous observations (e.g., sampling sites) that can be used to estimate local levels of association (e.g., some groups of sites are more similar in their association between biotic and environmental features than other groups of sites). Given that in the Mantel framework, multivariate information is translated into a pairwise distance matrix, we lose the ability to contrast homologous data points across dimensions and data matrices after their fit. In this paper, we attempt to familiarize ecologists with the benefits of using these Procrustean residual differences to further gain insights about the processes underlying the association among multivariate data tables using real and hypothetical examples.

Nitrogen-fixing legume tree species for the reclamation of severely degraded lands in Brazil.

The main challenges faced in the reclamation of severely degraded lands are in the management of the systems and finding plant species that will grow under the harsh conditions common in degraded soils. This is especially important in extremely adverse situations found in some substrates from mining activities or soils that have lost their upper horizons. Under these conditions, recolonization of the area by native vegetation through natural succession processes may be extremely limited. Once the main physical and chemical factors restrictive to plant growth are corrected or attenuated, the introduction of leguminous trees able to form symbioses with nodulating N2-fixing bacteria and arbuscular mycorrhizal fungi constitutes an efficient strategy to accelerate soil reclamation and initiate natural succession. These symbioses give the legume species a superior capacity to grow quickly in poor substrates and to withstand the harsh conditions presented in degraded soils. In this article we describe several successful results in Brazil using N2-fixing legume tree species for reclamation of areas degraded by soil erosion, construction and mining activities, emphasizing the potential of the technique to recover soil organic matter levels and restore ecosystem biodiversity and other environmental functions.