Effect of elevated tropospheric ozone on soil carbon and nitrogen: a meta-analysis

Abstract

Elevated tropospheric ozone concentration ([O _3 ]) may substantially influence the belowground processes of the terrestrial ecosystem. Nevertheless, a comprehensive and quantitative understanding of the responses of soil C and N dynamics to elevated [O _3 ] remains elusive. In this study, the results of 41 peer-reviewed studies were synthesized using meta-analytic techniques, to quantify the impact of O _3 on ten variables associated with soil C and N, i.e. total C (TC, including soil organic C), total N (TN), dissolved organic C (DOC), ammonia N (NH _4 ^+ ), nitrate N (NO _3 ^− ), microbial biomass C (MBC) and N (MBN), rates of nitrification (NTF) and denitrification (DNF), as well as C/N ratio. The results depicted that all these variables showed significant changes ( P < 0.05) with [O _3 ] increased by 27.6 ± 18.7 nl l ^−1 (mean ± SD), including decreases in TC, DOC, TN, NH _4 ^+ , MBC, MBN and NTF, and increases in C/N, NO _3 ^− and DNF. The effect sizes of TN, NTF, and DNF were significantly correlated with O _3 fumigation levels and experimental duration ( P < 0.05). Soil pH and climate were essential in analyses of O _3 impacts on soil C and N. However, the responses of most variables to elevated [O _3 ] were generally independent of the O _3 fumigation method, terrestrial ecosystem type, and additional [CO _2 ] exposure. The altered soil C and N dynamics under elevated [O _3 ] may reduce its C sink capacity, and change soil N availability and thus, impact plant growth and enhance soil N losses.

Keywords

• elevated ozone
• meta-analysis
• soil carbon
• soil nitrogen
• microbial biomass