TY - JOUR
T1 - Low Redox Decreases Potential Phosphorus Limitation on Soil Biogeochemical Cycling Along a Tropical Rainfall Gradient
AU - Lin, Yang
AU - Gross, Avner
AU - Silver, Whendee L.
N1 - Funding Information:
This study was conducted in the Luquillo Experimental Forest (LEF) in northeastern Puerto Rico, part of the NSF-sponsored Long-Term Ecological Research (LTER) and Critical Zone Observatory (CZO) networks, and the DOE funded Next Generation Ecosystem Experiment (NGEE-Tropics). The Luquillo Mountains rise steeply from approximately 250 m above sea level to its highest peak, El Toro (1075 m, a.s.l.) in less than 10 km (Weaver and Murphy ). Mean annual precipitation (MAP) increases with increasing elevation. A recent assessment of the rainfall records from the LEF showed that MAP changed from approximately 3200 mm at 300 m to approximately 4800 mm at 1000 m (Murphy and others ). Estimated MAP correlated linearly with elevation (r > 0.99) (Murphy and others ). This rainfall gradient also features associated changes in soil redox conditions, with more frequent and intensive reducing events at wetter sites (Silver and others , ; Liptzin and others ; Hall and Silver ; Liptzin and Silver ). Studies have reported soil O concentrations and associated indicators of redox conditions (for example, Fe(II) concentrations, methane and nitrous oxide concentrations and production) along the Luquillo elevation gradient (Silver and others , ; Liptzin and others ; Hall and Silver ; Liptzin and Silver ), including an 8-year study by Silver and others () that found that mean monthly soil O had a strong negative correlation (R = 0.80) with mean precipitation along the elevation gradient. Mean annual temperature (MAT) decreases slightly with increasing elevation. Field measurements of MAT ranged from approximately 23 °C at 350 m to 19 °C at 930 m (Brown and others ; Weaver and Murphy ). 2 2 2
Funding Information:
We thank Summer Ahmed, Nikhil Chari, Heather Dang, Omar Gutiérrez del Arroyo, Jordan Stark, Jamarys Torres Diaz, Jesus Gomez, Jess Zimmerman, Jean Lodge, Sarah Stankavich, Grizelle Gonzalez, and Sharon Rodríguez for their support in the laboratory and in the field. Tyler Anthony, Allegra Mayer, Bill McDowell, Christine O’Connell, and Stephen Porder provided helpful advice. We thank the Subject-Matter Editor, Peter Vitousek, and two anonymous reviewers for helpful comments on this manuscript. This work was supported by an NSF Grant to WLS DEB-1457805, as well as the NSF-sponsored Luquillo CZO (EAR-1331841), and LTER (DEB-0620910). Additional support was provided by the DOE Grant TES-DE-FOA-0000749 and the USDA National Institute of Food and Agriculture, McIntire Stennis project CA-B-ECO-7673-MS to WLS. Data from this study are publicly available via Hydroshare ( https://www.hydroshare.org/resource/186d2949101f4bba8159818a97b926c5/ ).
Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
PY - 2021/7/9
Y1 - 2021/7/9
N2 - Humid tropical forests on highly weathered soils are often characterized by low bioavailable phosphorus (P) concentrations. These ecosystems also often experience low and fluctuating redox conditions. Little is known about how soil redox conditions affect P availability and how this might feedback on biogeochemical cycling. Here we used soils from a wet tropical rainfall gradient in Puerto Rico to explore the effects of redox on P bioavailability and associated biogeochemical processes. Concentrations of soil carbon (C) and poorly crystalline iron (Fe) and aluminum (Al) minerals increased at least twofold with increasing rainfall, reflecting stronger anaerobic conditions at wetter sites and associated declines in decomposition. The fraction of the total P pool in the NaOH-extractable organic form also generally increased with increasing rainfall. In a laboratory incubation experiment using three sites along the gradient, P amendment increased aerobic CO2 production. However, anaerobic processes, including anaerobic respiration, Fe reduction, and methanogenesis, increased with P amendment at the driest site only. Microbial biomass C:P ratios decreased with P amendment under anoxic conditions at the driest site, an indicator of possible microbial P limitation at this site. Both microbial biomass C and P concentrations were lower under anoxic conditions than under oxic conditions across all soils, suggesting that anoxic conditions could be a more limiting factor to microbes than P concentrations. Overall, our results demonstrate that redox conditions regulate the extent of P limitation to biogeochemical processes in tropical forest soils. Phosphorus limitation was pronounced in aerated environments with low mean annual rainfall, whereas low redox conditions or associated factors under high rainfall conditions may have a stronger impact on biogeochemical cycling than P availability.
AB - Humid tropical forests on highly weathered soils are often characterized by low bioavailable phosphorus (P) concentrations. These ecosystems also often experience low and fluctuating redox conditions. Little is known about how soil redox conditions affect P availability and how this might feedback on biogeochemical cycling. Here we used soils from a wet tropical rainfall gradient in Puerto Rico to explore the effects of redox on P bioavailability and associated biogeochemical processes. Concentrations of soil carbon (C) and poorly crystalline iron (Fe) and aluminum (Al) minerals increased at least twofold with increasing rainfall, reflecting stronger anaerobic conditions at wetter sites and associated declines in decomposition. The fraction of the total P pool in the NaOH-extractable organic form also generally increased with increasing rainfall. In a laboratory incubation experiment using three sites along the gradient, P amendment increased aerobic CO2 production. However, anaerobic processes, including anaerobic respiration, Fe reduction, and methanogenesis, increased with P amendment at the driest site only. Microbial biomass C:P ratios decreased with P amendment under anoxic conditions at the driest site, an indicator of possible microbial P limitation at this site. Both microbial biomass C and P concentrations were lower under anoxic conditions than under oxic conditions across all soils, suggesting that anoxic conditions could be a more limiting factor to microbes than P concentrations. Overall, our results demonstrate that redox conditions regulate the extent of P limitation to biogeochemical processes in tropical forest soils. Phosphorus limitation was pronounced in aerated environments with low mean annual rainfall, whereas low redox conditions or associated factors under high rainfall conditions may have a stronger impact on biogeochemical cycling than P availability.
KW - Carbon use efficiency
KW - Labile phosphorus
KW - Luquillo CZO and LTER
KW - Nutrient limitation
KW - Oxisols
UR - http://www.scopus.com/inward/record.url?scp=85110316122&partnerID=8YFLogxK
U2 - 10.1007/s10021-021-00662-4
DO - 10.1007/s10021-021-00662-4
M3 - Article
SN - 1432-9840
VL - 25
SP - 387
EP - 403
JO - Ecosystems
JF - Ecosystems
IS - 2
ER -