Abstract
Humid tropical forest soils are characterized by warm temperatures, abundant rainfall, and high rates of biological activity that vary considerably in both space and time. These conditions, together with finely textured soils typical of humid tropical forests lead to periodic low redox conditions, even in well‐drained upland environments. The relationship between redox and biogeochemical processes has been studied for decades in saturated environments like wetlands and sediments, but much less is known about redox dynamics in upland soils. The goal of this study was to understand the spatial variability of redox sensitive biogeochemistry within and across two forest types at the ends of a high rainfall gradient (3500 to 5000 mm y−1) in the Luquillo Experimental Forest, Puerto Rico. The two sites differed significantly in average soil chemical and physical properties, but the scale of variability was similar across sites, with greater variability in soil gas concentrations than extractable Fe and P. Soil P and Fe pools and trace gas concentrations were more strongly correlated with each other and exhibited more spatial structure at the wetter site. While the within‐site relationships among these redox sensitive variables were typically weak, the relationships across sites were much stronger. We provide a conceptual model that elucidates how the strength of the relationships between indicators of redox‐sensitive biogeochemical processes depends on the spatial scale of analysis.
Highlights
The reduction and oxidation potential in soils is a strong driver of biogeochemical cycling in terrestrial ecosystems
Our results suggest that soil redox can have effects at smaller spatial scales in upland wet tropical forests
Soil redox is an important driver of biogeochemical processes in upland tropical forest soils
Summary
The reduction and oxidation potential (redox) in soils is a strong driver of biogeochemical cycling in terrestrial ecosystems. Redox dynamics are well studied in flooded environments, where patterns in water movement and the distribution of electron donors and acceptors create strong spatial gradients in redox (Chapelle et al 1995). Redox gradients occur at the scale of a single soil aggregate, where oxygen (O2) concentrations typically decrease from the surface towards the center, providing a reducing environment even in seemingly well-aerated soils (Sexstone et al 1985, Hojberg et al 1994). Redox can vary across topographic gradients as factors such as soil texture, degree of saturation, and soil depth influence gaseous diffusion and drainage (McKeague 1965, Silver et al 1999, Yu et al 2006). Redox status varies along climate gradients at landscape and regional scale, where redox potential tends
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