Litter inputs and phosphatase activity affect the temporal variability of organic phosphorus in a tropical forest soil in the Central Amazon

Karst J Schaap,Oscar J Valverde-Barrantes,Lucia Fuchslueger,Iain P Hartley,Marcel R Hoosbeek,Nathielly Pires Martins,Carlos Alberto Quesada,Laynara F Lugli,Florian Hofhansl

doi:10.1007/s11104-021-05146-x

Abstract

PurposeThe tropical phosphorus cycle and its relation to soil phosphorus (P) availability are a major uncertainty in projections of forest productivity. In highly weathered soils with low P concentrations, plant and microbial communities depend on abiotic and biotic processes to acquire P. We explored the seasonality and relative importance of drivers controlling the fluctuation of common P pools via processes such as litter production and decomposition, and soil phosphatase activity.MethodsWe analyzed intra-annual variation of tropical soil phosphorus pools using a modified Hedley sequential fractionation scheme. In addition, we measured litterfall, the mobilization of P from litter and soil extracellular phosphatase enzyme activity and tested their relation to fluctuations in P- fractions.ResultsOur results showed clear patterns of seasonal variability of soil P fractions during the year. We found that modeled P released during litter decomposition was positively related to change in organic P fractions, while net change in organic P fractions was negatively related to phosphatase activities in the top 5 cm.ConclusionWe conclude that input of P by litter decomposition and potential soil extracellular phosphatase activity are the two main factors related to seasonal soil P fluctuations, and therefore the P economy in P impoverished soils. Organic soil P followed a clear seasonal pattern, indicating tight cycling of the nutrient, while reinforcing the importance of studying soil P as an integrated dynamic system in a tropical forest context.

Highlights

The Amazon Basin contains about one third of the world’s remaining tropical forests (Mayaux et al 2005), playing an important role in the global carbon (C) cycle
We explored the seasonality and relative importance of drivers controlling the fluctuation of common P pools via processes such as litter production and decomposition, and soil phosphatase activity
We found that modeled P released during litter decomposition was positively related to change in organic P fractions, while net change in organic P fractions was negatively related to phosphatase activities in the top 5 cm

Summary

Introduction

The Amazon Basin contains about one third of the world’s remaining tropical forests (Mayaux et al 2005), playing an important role in the global carbon (C) cycle. One factor that could change the response of the forest to climate change is the CO2-fertilization effect. While in natural forest ecosystems in temperate regions nitrogen (N) is the most limiting nutrient for plant productivity (Oren et al 2001; Vitousek 1982), tropical forest ecosystems are generally considered to be constrained by phosphorus (P) availability (Hofhansl et al 2020; Turner et al 2018; Townsend et al 2011; Vitousek 1984) with feedbacks to the nitrogen cycle (Nasto et al 2014; Quesada et al 2010). The inclusion of P cycles in regional dynamic vegetation models suggest P limitation will be important in controlling forest productivity and the responses of tropical biomes to global change (Fleischer et al 2019; Terrer et al 2019). Many key processes controlling P availability in tropical forests remain poorly understood

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