title: Iron controls over di-nitrogen fixation in karst tropical forest.
abstract: Limestone tropical forests represent a meaningful fraction of the land area in Central America (25%) and Southeast Asia (40%). These ecosystems are marked by high biological diversity, CO2uptake capacity, and high pH soils, the latter making them fundamentally different from the majority of lowland tropical forest areas in the Amazon and Congo basins. Here, we examine the role of bedrock geology in determining biological nitrogen fixation (BNF) rates in volcanic (low pH) vs. limestone (high pH) tropical forests located in the Maya Mountains of Belize. We experimentally test how BNF in the leaf-litter responds to nitrogen, phosphorus, molybdenum, and iron additions across different parent materials. We find evidence for iron limitation of BNF rates in limestone forests during the wet but not dry season (response ratio 3.2 ± 0.2; P = 0.03). In contrast, BNF in low pH volcanic forest soil was stimulated by the trace-metal molybdenum during the dry season. The parent-material induced patterns of limitation track changes in siderophore activity and iron bioavailability among parent materials. These findings point to a new role for iron in regulating BNF in karst tropical soils, consistent with observations for other high pH systems such as the open ocean and calcareous agricultural ecosystems.
authors.affiliation: Department of Land, Air and Water Resources, University of California, Davis, One Shields Avenue, Davis, California, 95616, USA.
authors.forename: Joy B
authors.identifier: http://orcid.org/0000-0001-8627-4835
authors.initials: JB
authors.lastname: Winbourne
authors.affiliation: Belize Foundation for Research and Environmental Education, PO Box 129 Punta Gorda, Todelo, Belize.|Copperhead Consulting, 11641 Richmond Rd., Paint Lick, Kentucky, 40461, USA.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Brewer
authors.affiliation: Department of Land, Air and Water Resources, University of California, Davis, One Shields Avenue, Davis, California, 95616, USA.
authors.forename: Benjamin Z
authors.initials: BZ
authors.lastname: Houlton
mesh_terms: D001531:Belize; D002489:Central America; D017753:Ecosystem; D065928:Forests; D007501:Iron / Q000378:metabolism*; D009584:Nitrogen; D009586:Nitrogen Fixation / Q000502:physiology*; D012987:Soil; D014197:Trees; D014329:Tropical Climate
chemical_list: D012987:Soil; D007501:Iron; D009584:Nitrogen
keywords: biological nitrogen fixation; iron; karst; limestone soil; molybdenum; trace-metal limitation; tropical forests