Reduction of soil carbon formation by tropospheric ozone under increased carbon dioxide levels

Abstract

In the Northern Hemisphere, ozone levels in the troposphere have increased by 35 per cent over the past century, with detrimental impacts on forest and agricultural productivity, even when forest productivity has been stimulated by increased carbon dioxide levels. In addition to reducing productivity, increased tropospheric ozone levels could alter terrestrial carbon cycling by lowering the quantity and quality of carbon inputs to soils. However, the influence of elevated ozone levels on soil carbon formation and decomposition are unknown. Here we examine the effects of elevated ozone levels on the formation rates of total and decay-resistant acid-insoluble soil carbon under conditions of elevated carbon dioxide levels in experimental aspen (Populus tremuloides) stands and mixed aspen-birch (Betula papyrifera) stands. With ambient concentrations of ozone and carbon dioxide both raised by 50 per cent, we find that the formation rates of total and acid-insoluble soil carbon are reduced by 50 per cent relative to the amounts entering the soil when the forests were exposed to increased carbon dioxide alone. Our results suggest that, in a world with elevated atmospheric carbon dioxide concentrations, global-scale reductions in plant productivity due to elevated ozone levels will also lower soil carbon formation rates significantly.

Large but decreasing effect of ozone on the European carbon sink

“…O3 exposure such as litter quality and composition, reduced litter quantity also has significant detrimental 570 consequences for soil carbon stocks (Andersen, 2003;Lindroth, 2010;Loya et al, 2003). Results from this study 571 therefore suggest that increasing tropospheric O3 may be a contributing factor to the declining soil carbon stocks 572 observed across Europe as a result of reduced litter input to the soil carbon pool consistent with reduced NPP.…”

“…Field studies show that in some regions of Europe, soil carbon stocks are decreasing (Bellamy et al, 558 2005;Capriel, 2013;Heikkinen et al, 2013;Sleutel et al, 2003). The study of Bellamy et al (2005), for example, carbon content in more stable soil organic matter pools, and Loya et al (2003) showed that the fraction of soil 567 carbon formed in forest soils over a 4 year experimental period when fumigated with both CO2 and O3 was reduced…”

Concentration of sugars, phenolic acids, and amino acids in forest soils exposed to elevated atmospheric CO2 and O3

“…Elevated atmospheric CO 2 (around 560 ml l À1 ) has been shown to increase carbon (C) inputs into the soil (Jastrow et al, 2005), while current levels of O 3 in many parts of the world are capable of directly altering belowground processes by reducing C inputs (Anderson, 2003;Loya et al, 2003). A significant portion of net primary production is allocated to root systems, resulting in large fluxes of organic compounds into the soil (King et al, 2004).…”

Mycorrhizal Hyphal Turnover as a Dominant Process for Carbon Input into Soil Organic Matter

“…In the EUROFACE system, pure CO 2 is released at high velocity into the atmosphere through a very large number of small gas jets. Such FACE systems allow estimation of C accumulation in forest soils over a number of years (Loya et al, 2003;Hoosbeek et al, 2004). To increase the applicability of our system to natural forest ecosystems, where poplar and aspen are major components of boreal forests, we used three species of poplar with contrasting ecological and physiological characteristics, and exposed the trees from the outset to elevated CO 2 , thus avoiding an unrealistic stepwise change in CO 2 concentration.…”