A study over 33 years shows that carbon and nitrogen stocks in a subtropical soil are increasing under native vegetation in a changing climate

Ram C Dalal; Craig M Thornton; Diane E Allen; Peter M Kopittke

doi:10.1016/j.scitotenv.2021.145019

A study over 33 years shows that carbon and nitrogen stocks in a subtropical soil are increasing under native vegetation in a changing climate

Sci Total Environ. 2021 Jun 10:772:145019. doi: 10.1016/j.scitotenv.2021.145019. Epub 2021 Feb 2.

Authors

Ram C Dalal¹, Craig M Thornton², Diane E Allen³, Peter M Kopittke⁴

Affiliations

¹ The University of Queensland, School of Agriculture and Food Sciences, St Lucia, Qld 4072, Australia. Electronic address: r.dalal@uq.edu.au.
² Department of Natural Resources, Mines and Energy, Rockhampton, Qld 4700, Australia. Electronic address: Craig.Thornton@dnrme.qld.gov.au.
³ The University of Queensland, School of Agriculture and Food Sciences, St Lucia, Qld 4072, Australia; Department of Environment and Science, Dutton Park, Qld 4102, Australia. Electronic address: diane.allen@des.qld.gov.au.
⁴ The University of Queensland, School of Agriculture and Food Sciences, St Lucia, Qld 4072, Australia. Electronic address: p.kopittke@uq.edu.au.

PMID: 33578168
DOI: 10.1016/j.scitotenv.2021.145019

Abstract

Soil plays a critical role in the global carbon (C) cycle. However, climate change and associated factors, such as warming, precipitation change, elevated carbon dioxide (CO₂), and atmospheric nitrogen (N) deposition, will affect soil organic carbon (SOC) stocks markedly - a decrease in SOC stocks is predicted to drive further planetary warming, although whether changes in climate and associated factors (including atmospheric N deposition) will cause a net increase in SOC or a net decrease is less certain. Using a subtropical soil, we have directly examined how changes over the last three decades are already impacting upon SOC stocks and soil total nitrogen (STN) in a Vertisol supporting native brigalow (Acacia harpophylla L.) vegetation. It was observed that SOC stocks increased under native vegetation by 5.85 Mg C ha^-1 (0.177 ± 0.059 Mg C ha^-1 y^-1) at a depth of 0-0.3 m over 33 years. This net increase in SOC stocks was not correlated with change in precipitation, which did not change during the study period. Net SOC stocks, however, were correlated with an increasing trend in mean annual temperatures, with an average increase of 0.89 °C. This occurred despite a likely co-occurrence of increased decomposition due to higher temperatures, presumably because the increase in the SOC was largely in the stable, mineral-associated fraction. The increases in CO₂ from 338 ppm_v to 395 ppm_v likely contributed to an increase in biomass, especially root biomass, resulting in the net increase in SOC stocks. Furthermore, STN stocks increased by 0.57 Mg N ha^-1 (0.0174 ± 0.0041 Mg N ha^-1 y^-1) at 0-0.3 m depth, due to increased atmospheric N deposition and potential N₂ fixation. Since SOC losses are often predicted in many regions due to global warming, these observations are relevant for sustainability of SOC stocks for productivity and climate models in semi-arid subtropical regions.

Keywords: Atmospheric nitrogen deposition; C(3) vegetation; Elevated CO(2) fertilization; Global warming.