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

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 harpophylia 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 degrees 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,, likely contributed to an increase in biomass, especially root biomass, resulting in the net increase in SOC stocks. Furthermore, SIN stocks increased by 057 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 N-2 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 semiarid subtropical regions. Crown Copyright (C) 2021 Published by Elsevier B.V. All rights reserved.

Automated summary

Climate change and associated factors have significant impacts on soil organic carbon and soil total nitrogen stocks. A study on subtropical soil showed an increase in both organic carbon and total nitrogen stocks over the past three decades, with a significant correlation with the increasing trend of mean annual temperatures. Additionally, the rise in CO2 and atmospheric nitrogen deposition also contributed to the net increase in soil organic carbon and nitrogen stocks.