Fine root growth and nutrient release in decomposi

Authors: Regina C C Luizão Flávio J Luizão John Proctor

Publish Date: 2007/06/16

Volume: 192, Issue: 2, Pages: 225-236

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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 ovendried 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 nutrientsWe wish to thank Cilene Soares for helping with sample analyses and data management Professor Peter Grubb an anonymous reviewer and Laszlo Nagy provided helpful comments to improve the manuscript This study was supported by the Instituto Nacional de Pesquisas da Amazônia—INPA Conselho Nacional de Pesquisas—CNPq and by the Overseas Development Administration —ODA through the Bionte Project in Manaus

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