Fine root growth and nutrient release in decomposing leaf litter in three contrasting vegetation types in central Amazonia |
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Authors: | Regina C C Luizão Flávio J Luizão John Proctor |
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Institution: | 1.Departamento de Ecologia,Instituto Nacional de Pesquisas da Amaz?nia,Manaus,Brasil;2.Department of Biological Sciences,Stirling University,Stirling,Scotland, UK |
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Abstract: | We tested the hypothesis that the growth of fine roots upward into the leaf litter, forming a ‘surface root mat’, found widely
in Amazonian forests, is of adaptive value for plants of poor soils because it makes possible more rapid uptake of limiting
nutrients. We assessed the effect of invasion by fine roots on the rates of loss of dry mass and nutrient content of leaf
litter over 1 year in three plots in each of three contrasting forest types in central Amazonia: the stunted facies of heath
forest known as campina (SHF), the taller facies of heath forest known as campinarana (THF), both on spodosols, and the surrounding lowland evergreen rain forest (LERF) on ultisol. Pairs of bags filled with
freshly fallen leaves from the trees of Clitoria fairchildiana (Fabaceae) were placed on the litter layer; in order to prevent roots entering the control bag in each pair that bag was
lifted from the forest floor and turned over each week, while the treatment bag was left undisturbed. From each plot, four
pairs of litter bags were retrieved after 30, 60, 120, 180, 270 and 360 d, and all roots that had grown into the litterbags
were carefully removed. The leaves and roots from each bag were oven-dried for nutrient analysis. In no forest type was there
a significant difference in the rate of loss of dry matter from the litter between the bags with and without roots. The amounts
of roots invading the litter bags increased significantly in the sequence SHF < THF < LERF. In no forest did the presence
of roots have a significant effect on the rate of disappearance of N or P from the leaf material, or on the rate of accumulation
of Fe and Al. In the SHF there was no significant effect of invasion by roots on the rates of disappearance of Ca, Mg, Mn
or Zn, but in the THF, the rates of disappearance of these four elements between 270 and 360 d were significantly greater
in the presence of roots. In the LERF the results were similar, but the effects of roots started earlier—the rates of disappearance
of Ca and Mg were significantly enhanced between 120 and 360 d. The results from the SHF may be interpreted to suggest that
the growth of fine roots (and their fungal associates) upward into leaf litter is unlikely to be explained wholly by their
role in the efficient recovery of mineral nutrients. |
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Keywords: | Amazon rainforest Campinarana Campina Heath forest Leaf litter decomposition Fine roots Nutrient capture |
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