TY - JOUR

T1 - Aluminum cycling in a tropical montane forest ecosystem in southern Ecuador

AU - Rehmus, Agnes

AU - Bigalke, Moritz

AU - Boy, Jens

AU - Valarezo, Carlos

AU - Wilcke, Wolfgang

N1 - Funding information: We thank Jürgen Homeier and Ingeborg Haug for their support in determining plant species, Thorsten Peters, Paul Emck, Rütger Rollenbeck, Jörg Bendix, and Michael Richter for providing climate data, Jaime Arturo García Ochoa for providing nutrient concentrations in leaves from the investigated study site, Daniel Kübler for providing maps for the localization of specific tree species in the forest, Alexander Hermann for the illustration of the Al fluxes, the AE Prof. van Groening and three anonymous reviewers for helpful suggestions and comments, which improved the manuscript, Nature and Culture International in Loja, Ecuador, for providing the study area and the research station, Ecuadorian authorities for the research permit, and the German Research Foundation (DFG) for funding (FOR 816, Wi 1601/8-2).

PY - 2017/2/15

Y1 - 2017/2/15

N2 - Growth limitation induced by Al toxicity is believed to commonly occur in tropical forests, although a direct proof is frequently lacking. To test for the general assumption of Al toxicity, Al, Ca, and Mg concentrations in precipitation, throughfall, stemflow, organic layer leachate, mineral soil solutions, stream water, and the leaves of 17 native tree species were analyzed. We calculated Al fluxes and modeled Al speciation in the litter leachate and mineral soil solutions. We assessed potential Al toxicity based on soil base saturation, Al concentrations, Ca:Al and Mg:Al molar ratios and Al speciation in soil solution as well as Al concentrations and Ca:Al and Mg:Al molar ratios in tree leaves. High Al fluxes in litterfall (8.77 ± 1.3 to 14.2 ± 1.9 kg ha − 1 yr − 1, mean ± SE) indicated a high Al circulation through the ecosystem. The fraction of exchangeable and potentially plant-available Al in mineral soils was high, being a likely reason for a low root length density in the mineral soil. However, Al concentrations in all solutions were consistently below critical values and Ca:Al molar and the Ca 2 +:Al inorganic molar ratios in the organic layer leachate and soil solutions were above 1, the suggested threshold for Al toxicity. Except for two Al-accumulating and one non-accumulating tree species, the Ca:Al molar ratios in tree leaves were above the Al toxicity threshold of 12.5. Our results demonstrate high Al cycling through the vegetation partly because of the presence of some Al accumulator plants. However, there was little indication of an Al toxicity risk in soil and of acute Al toxicity in plants likely reflecting that tree species are well adapted to the environmental conditions at our study site and thus hardly prone to Al toxicity.

AB - Growth limitation induced by Al toxicity is believed to commonly occur in tropical forests, although a direct proof is frequently lacking. To test for the general assumption of Al toxicity, Al, Ca, and Mg concentrations in precipitation, throughfall, stemflow, organic layer leachate, mineral soil solutions, stream water, and the leaves of 17 native tree species were analyzed. We calculated Al fluxes and modeled Al speciation in the litter leachate and mineral soil solutions. We assessed potential Al toxicity based on soil base saturation, Al concentrations, Ca:Al and Mg:Al molar ratios and Al speciation in soil solution as well as Al concentrations and Ca:Al and Mg:Al molar ratios in tree leaves. High Al fluxes in litterfall (8.77 ± 1.3 to 14.2 ± 1.9 kg ha − 1 yr − 1, mean ± SE) indicated a high Al circulation through the ecosystem. The fraction of exchangeable and potentially plant-available Al in mineral soils was high, being a likely reason for a low root length density in the mineral soil. However, Al concentrations in all solutions were consistently below critical values and Ca:Al molar and the Ca 2 +:Al inorganic molar ratios in the organic layer leachate and soil solutions were above 1, the suggested threshold for Al toxicity. Except for two Al-accumulating and one non-accumulating tree species, the Ca:Al molar ratios in tree leaves were above the Al toxicity threshold of 12.5. Our results demonstrate high Al cycling through the vegetation partly because of the presence of some Al accumulator plants. However, there was little indication of an Al toxicity risk in soil and of acute Al toxicity in plants likely reflecting that tree species are well adapted to the environmental conditions at our study site and thus hardly prone to Al toxicity.

KW - Al speciation

KW - Aluminum fluxes

KW - Aluminum toxicity

KW - Molar Ca:Al ratios

KW - Tropical forest ecosystems

UR - http://www.scopus.com/inward/record.url?scp=84995785245&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2016.11.002

DO - 10.1016/j.geoderma.2016.11.002

M3 - Article

VL - 288

SP - 196

EP - 203

JO - GEODERMA

JF - GEODERMA

SN - 0016-7061

ER -