RESUMO
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.
Assuntos
Conservação dos Recursos Naturais , Plantas Daninhas , Alelopatia , PoaceaeRESUMO
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.