Abstract

Soils from humid forests undergo spatial and temporal variations in moisture and oxygen (O₂) in response to rainfall, and induce changes in iron (Fe) and carbon (C) biogeochemistry. We hypothesized that high rainfall periods stimulate Fe and C cycling, with the greatest effects in areas of high soil moisture. To test this, we measured Fe and C cycling across three catenas at valley, slope, and ridge positions every two days for a two-month period in a rainforest in Puerto Rico. Over 12 days without rain, soil moisture, Fe^II, rapidly reducible Fe oxides (Fe^III_RR), and dissolved organic C (DOC) declined, but Eh and O₂ increased; conversely, during a 10-day period of intense rain (290 mm), we observed the opposite trends. Mixed-effects models suggest precipitation predicted soil moisture, soil redox potential (Eh), and O₂, which in turn influenced Fe reduction/oxidation, C dissolution, and mineralization processes. The approximate turnover time for HCl-extractable Fe^II was four days for both production and consumption, and may be driven by fluctuations in Fe^III_RR, which ranged from 42% to 100% of citrate–ascorbate-extractable Fe^III (short-range order (SRO)-Fe^III) at a given site. Our results demonstrated that periods of high precipitation (hot moments) influenced Fe and C-cycling within day-to-week timescales, and were more pronounced in humid valleys (hot spots)

Citation

Diego Barcellos, Christine S. O’Connell, Whendee Silver, Christof Meile, Aaron Thompson (2018): Hot Spots and Hot Moments of Soil Moisture Explain Fluctuations in Iron and Carbon Cycling in a Humid Tropical Forest Soil . Soil Systems. DOI: 10.3390/soilsystems2040059

This Paper/Book acknowledges NSF CZO grant support.