Articles | Volume 12, issue 22
Biogeosciences, 12, 6529–6571, 2015
Biogeosciences, 12, 6529–6571, 2015

Research article 18 Nov 2015

Research article | 18 Nov 2015

Edaphic, structural and physiological contrasts across Amazon Basin forest–savanna ecotones suggest a role for potassium as a key modulator of tropical woody vegetation structure and function

J. Lloyd2,1, T. F. Domingues3, F. Schrodt5,4, F. Y. Ishida2, T. R. Feldpausch6, G. Saiz7, C. A. Quesada8, M. Schwarz9, M. Torello-Raventos10, M. Gilpin11, B. S. Marimon12, B. H. Marimon-Junior12, J. A. Ratter13, J. Grace14, G. B. Nardoto15, E. Veenendaal16, L. Arroyo17, D. Villarroel18, T. J. Killeen19, M. Steiningera, and O. L. Phillips11 J. Lloyd et al.
  • 1Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, Berkshire SL5 7PY, UK
  • 2Centre for Tropical Environment and Sustainability Sciences (TESS) and College of Marine and Environmental Sciences, James Cook University, Cairns, 4870, Qld, Australia
  • 3Universidade de São Paulo, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Av Bandeirantes, 3900, CEP 14040-901, Bairro Monte Alegre, Ribeirão Preto, São Paulo, Brazil
  • 4Max Planck Institute for Biogeochemistry, Postfach 10 0164, 07701 Jena, Germany
  • 5iDiv, German Centre for Integrative Biodiversity Research, Halle-Jena-Leipzig, Deutscher Platz 5e, 04103 Leipzig, Germany
  • 6Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4RJ, UK
  • 7Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, 82467, Garmisch-Partenkirchen, Germany
  • 8Instituto Nacional de Pesquisas da Amazonia, Manaus, Cx Postal 2223 – CEP 69080-971, Brazil
  • 9Fieldwork Assistance, PSF 101022, 07710, Jena, Germany
  • 10Centre for Tropical Environment and Sustainability Sciences (TESS) and College of Science Technology and Engineering, James Cook University, Cairns, Qld, Australia
  • 11School of Geography, University of Leeds, LS2 9JT, Leeds, UK
  • 12Universidade do Estado de Mato Grosso, Br 158, Km 655, Antiga FAB, Nova Xavantina, MT. CEP 78690-00, Brazil
  • 13Royal Botanic Garden, Edinburgh, EH3 5NZ, Scotland, UK
  • 14School of Geosciences, University of Edinburgh, EH8 9XP, Scotland, UK
  • 15Campus Darcy Ribeiro – Prédio da FACE Brasília, Distrito Federal, 70910-900, Brazil
  • 16Centre for Ecosystem Studies, University of Wageningen, P.O. Box 47, 6700AA, Wageningen, the Netherlands
  • 17Universidad Autonoma Gabriel Rene Moreno, Avenidas Centenario, Venezuela y Av. 26 de Febrero 56 Santa Cruz de la Sierra, Bolivia
  • 18Museo Noel Kempff Mercado, Av. Irala no 565 – casilla 2489, Santa Cruz, Bolivia
  • 19Agrotecnologica Amazonica, Santa Cruz, Bolivia
  • aformerly at: Conservation International, Washington D.C., USA

Abstract. Sampling along a precipitation gradient in tropical South America extending from ca. 0.8 to 2.0 m a−1, savanna soils had consistently lower exchangeable cation concentrations and higher C / N ratios than nearby forest plots. These soil differences were also reflected in canopy averaged leaf traits with savanna trees typically having higher leaf mass per unit area but lower mass-based nitrogen (Nm) and potassium (Km). Both Nm and Km also increased with declining mean annual precipitation (PA), but most area-based leaf traits such as leaf photosynthetic capacity showed no systematic variation with PA or vegetation type. Despite this invariance, when taken in conjunction with other measures such as mean canopy height, area-based soil exchangeable potassium content, [K]sa , proved to be an excellent predictor of several photosynthetic properties (including 13C isotope discrimination). Moreover, when considered in a multivariate context with PA and soil plant available water storage capacity (θP) as covariates, [K]sa also proved to be an excellent predictor of stand-level canopy area, providing drastically improved fits as compared to models considering just PA and/or θP. Neither calcium, nor magnesium, nor soil pH could substitute for potassium when tested as alternative model predictors (ΔAIC > 10). Nor for any model could simple soil texture metrics such as sand or clay content substitute for either [K]sa or θP. Taken in conjunction with recent work in Africa and the forests of the Amazon Basin, this suggests – in combination with some newly conceptualised interacting effects of PA and θP also presented here – a critical role for potassium as a modulator of tropical vegetation structure and function.

Short summary
Across tropical South America, forest soils are typically of a higher cation status than their savanna equivalents with soil exchangeable potassium a key soil nutrient differentiating these two vegetation types. Differences in soil water storage capacity are also important – interacting with both potassium availability and precipitation regimes in a relatively complex manner.
Final-revised paper