Competition Alters Responses of Juvenile Woody Plants and Grasses to Nitrogen Addition in Brazilian Savanna (Cerrado)
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The Cerrado, Brazilian savanna, is characterized by high radiation and dystrophic soils. Seedlings of woody species must compete effectively for resources belowground in order to establish in the herbaceous matrix. Few studies focus on the dynamics of herbaceous and woody juvenile plants and their competitive strategies, especially under increasing nitrogen (N) availability. In the present study, seedlings of three woody species, Eugenia dysenterica, Magonia pubescens and Enterolobium gummiferum were grown with or without the dominant grass in Cerrado areas of central Brazil, Echinolaena inflexa. Half of the pots were exposed to N additions equivalent to a deposition of 20 kg N-NO3NH4 ha−1 year−1. The N induced responses of plants growing under intra and interspecific competition were analyzed, with special attention to plasticity of root biomass and morphology. One year after the beginning of the experiment, the fresh and dry biomass of roots and shoots were weighted. Before drying, total length, surface area and diameter of roots were determined. Interspecific competition tended to reduce root and shoot biomass of all plants. However, effects of competition with E. inflexa were more obvious on root morphology, being total root and fine root length diminished in two of the woody species in the absence of N addition. The enhancement of N availability, in general, minimized the effects of competition, increasing the potential competitiveness of some woody species due to changes in total fine root length and biomass. The results provide indication that competition between saplings of woody plants and grasses could be an important factor driving plant allometry and morphology during the first stages of development in Cerrado environments. The responsiveness of plants to N deposition seemed to depend, in part, on the type of competition (intra- or interspecific), what should be taken into account in models of vegetation dynamics in response to nutrient deposition.
KeywordsNative savannah plant species Nitrogen deposition Root morphology Sapling growth Woody plant and grass competition
We would like to thank then UnB Ecology Lab staff for valuable help. We also would like to thank the administration and staff of Experimental Station of the UnB and of the Ecological Reserve of IBGE. This study was funded by the Graduate Program in Ecology of Tropical Biomes of the Universidade Federal de Ouro Preto, CNPq (474071/2006.5) and LBA-NASA (ND-07).
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