Coupling of soil carbon, organic phosphorus, and amorphous minerals along wet tropical forest rainfall gradient

Y. Lin, A. Gross, W. L. Silver

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


Carbon cycling in wet tropical forests on highly weathered soils is often limited by low plant-available phosphorus (P) concentrations. The soil P cycle in these ecosystems is controlled by interactions with soil organic matter (SOM), and iron (Fe) and aluminum (Al) minerals. Changes in rainfall regimes associated with climate change are likely to affect these interactions and alter P cycling. We used a well-defined high rainfall gradient in wet tropical forests in Puerto Rico to test the following hypotheses: 1) anoxic conditions under high rainfall regimes drive the accumulation of organic P associated with increased SOM, and 2) loss of amorphous Fe and Al minerals via leaching will increase with mean annual rainfall, decreasing the importance of sorbed and occluded inorganic P fractions in wetter sites. We measured inorganic and organic soil P fractions, soil organic C (SOC), and Fe and Al concentrations from parallel transects of mixed forests and monodominant palm forests. Along both transects, soil NaOH-extractable organic P and SOC concentrations were higher at wetter sites, supporting our first hypothesis. Contrary to our second hypothesis, high rainfall did not reduce the concentrations of amorphous Fe and Al minerals. Instead, we found a concurrent accumulation of these minerals with SOC and organic P concentrations at wetter sites, suggesting that high rainfall promoted the formation of organo-Fe/Al complexes that were protected from leaching. With increasing rainfall, the NaOH-extractable inorganic P fraction was depleted relative to soil total P concentrations. However, the ratio of NaOH-extractable total P or residual P to soil total P concentrations remained unchanged. These results highlight the importance of organic matter accumulation and the associated P concentrations in retaining P in soils under high rainfall conditions. The coupling of SOC, organic P, and amorphous minerals were found along both transects, indicating that vegetation did not impose a strong control on these biogeochemical patterns along the gradients. Overall, our results demonstrate that rainfall affected soil P fractions mainly by altering organic matter accumulation. The coupling of SOC, organic P, and amorphous minerals is likely central to predicting the responses of soil biogeochemical cycling to climate change.
Original languageEnglish GB
Title of host publicationAmerican Geophysical Union, Fall Meeting 2018
StatePublished - 1 Dec 2018
Externally publishedYes


  • 0414 Biogeochemical cycles
  • processes
  • and modeling
  • BIOGEOSCIENCESDE: 0428 Carbon cycling
  • BIOGEOSCIENCESDE: 0470 Nutrients and nutrient cycling
  • BIOGEOSCIENCESDE: 0486 Soils/pedology


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