Factors controlling spatio‐temporal variation in carbon dioxide efflux from surface litter, roots, and soil organic matter at four rain forest sites in the eastern Amazon

D B Metcalfe,P H L Gonçalves,A Braga,J De Athaydes,L E O C Aragão,Y Malhi,M Williams,A C L Da Costa,P Meir,S S De Almeida

doi:10.1029/2007jg000443

Abstract

This study explored biotic and abiotic causes for spatio‐temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil types in the eastern Amazon, Brazil. Estimated mean annual soil respiration varied between 13–17 t C ha−1 yr−1, which was partitioned into 0–2 t C ha−1 yr−1 from litter, 6–9 t C ha−1 yr−1 from roots, and 5–6 t C ha−1 yr−1 from soil organic matter. Litter contribution showed no clear seasonal change, though experimental precipitation exclusion over a one‐hectare area was associated with a ten‐fold reduction in litter respiration relative to unmodified sites. The estimated mean contribution of soil organic matter respiration fell from 49% during the wet season to 32% in the dry season, while root respiration contribution increased from 42% in the wet season to 61% during the dry season. Spatial variation in respiration from soil, litter, roots, and soil organic matter was not explained by volumetric soil moisture or temperature. Instead, spatial heterogeneity in litter and root mass accounted for 44% of observed spatial variation in soil respiration (p < 0.001). In particular, variation in litter respiration per unit mass and root mass accounted for much of the observed variation in respiration from litter and roots, respectively, and hence total soil respiration. This information about patterns of, and underlying controls on, respiration from different soil components should assist attempts to accurately model soil carbon dioxide fluxes over space and time.

Highlights

[1] This study explored biotic and abiotic causes for spatio-temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil types in the eastern Amazon, Brazil
[3] Rs is derived from autotrophic respiration by roots (Rr) and heterotrophic respiration by microorganisms that decompose ground surface organic litter (Rl) and soil organic matter or SOM (Rsom)
Mean Rsom contribution declined from 49% during the wet season to 32% in the dry season (Figure 1f), while Rr contribution displayed the opposite trend: increasing from 42% in the wet season to 61% during the dry season (Figure 1e)

Summary

Introduction

[1] This study explored biotic and abiotic causes for spatio-temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil types in the eastern Amazon, Brazil. Despite its clear importance for global C cycling and climate change, understanding of the processes controlling spatial and temporal variation in Rs is limited This is largely because soil is a complex and spatially heterogeneous mixture of different compounds (e.g., ground surface organic litter, live roots, and soil organic matter pools). The overall objectives of this study, were to (1) partition Rs into Rl, Rr and Rsom over one full seasonal cycle at four rain forest sites with contrasting vegetation and soil types in the eastern Amazon; (2) investigate potential biotic (roots, ground surface litter) and abiotic (soil moisture, soil temperature) causes for observed differences in respiration within and between sites and seasons; and (3) quantify the contributions of component mass and respiration per unit mass to total Rr and Rl

Methods

Results

Conclusion