Automated measurements of greenhouse gases fluxes from tree stems and soils: magnitudes, patterns and drivers

Josep Barba,Rafael Poyatos,Rodrigo Vargas

doi:10.1038/s41598-019-39663-8

Josep Barba, Rafael Poyatos + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-39663-8

Copy DOI

Abstract

Tree stems exchange CO2, CH4 and N2O with the atmosphere but the magnitudes, patterns and drivers of these greenhouse gas (GHG) fluxes remain poorly understood. Our understanding mainly comes from static-manual measurements, which provide limited information on the temporal variability and magnitude of these fluxes. We measured hourly CO2, CH4 and N2O fluxes at two stem heights and adjacent soils within an upland temperate forest. We analyzed diurnal and seasonal variability of fluxes and biophysical drivers (i.e., temperature, soil moisture, sap flux). Tree stems were a net source of CO2 (3.80 ± 0.18 µmol m−2 s−1; mean ± 95% CI) and CH4 (0.37 ± 0.18 nmol m−2 s−1), but a sink for N2O (−0.016 ± 0.008 nmol m−2 s−1). Time series analysis showed diurnal temporal correlations between these gases with temperature or sap flux for certain days. CO2 and CH4 showed a clear seasonal pattern explained by temperature, soil water content and sap flux. Relationships between stem, soil fluxes and their drivers suggest that CH4 for stem emissions could be partially produced belowground. High-frequency measurements demonstrate that: a) tree stems exchange GHGs with the atmosphere at multiple time scales; and b) are needed to better estimate fluxes magnitudes and understand underlying mechanisms of GHG stem emissions.

Highlights

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the most important greenhouse gases, contributing 60, 20 and 10% to global warming, respectively[1]
CH4 emissions decreased with height along the tree stem (0.46 ± 0.03 and 0.28 ± 0.02 nmol m−2 s−1 for LowerStem and UpperStem, respectively), but the soil was a clear sink of this gas (−0.66 ± 0.06 nmol m−2 s−1)
Mean N2O uptake was higher in soil (−0.046 ± 0.011 nmol m−2 s−1) and decreased with stem height (−0.017 ± 0.008 and −0.014 ± 0.006 nmol m−2 s−1 for LowerStem and UpperStem, respectively)

Summary

Introduction

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the most important greenhouse gases, contributing 60, 20 and 10% to global warming, respectively[1]. Several studies in the last 2 years have reported stem CH4 emissions in upland forests where adjacent soils are not a source but a sink of CH412,16–23. A second issue deals with the origin (i.e., production and transport) of stem CH4 and N2O emissions in upland forests Are these gases largely produced in the soil and transported upwards through the stem or are they mainly locally produced within the heartwood? If a diurnal pattern is consistent across tree stems and throughout the growing season, manual measurements may bias estimates of daily total emissions[33] and the net impact of stem CH4 emissions for the ecosystem carbon balance. There is no information based on automated measurements of stem N2O fluxes

Objectives

Methods

Results

Conclusion