The indirect effects of rising atmospheric carbon dioxide (CO2) levels, such as changes in soil moisture and plant structure, can have a bigger impact on ecosystems than previously thought.
Understanding the importance of these indirect effects, in comparison to the direct effects, will improve our understanding of how ecosystems respond to climate change
A study, involving researchers
from the University of Southampton, found that water-limited ecosystems in arid and semi-arid regions, such as The Great Plains and South-West United States
and some in Australia
and Mediterranean Europe
, were particularly impacted by these indirect effects. For those ecosystems, the importance of the indirect effects was as much as or in some cases, greater than, the direct effects.
Co-author Dr Athanasios Paschalis
, a New Frontiers Fellow in the Water
and Environmental Engineering
group at the University of Southampton, said: “These results have major implications for our understanding of the CO2
response of ecosystems, the future of water resources and for global
projections of CO2 fertilisation. This is because, although direct effects are typically understood and easily reproducible in models, simulations of indirect effects are far more challenging and difficult to quantify.”
Rising CO2 levels affect a lot of plants directly by stimulating photosynthesis and reducing the loss of water (plant transpiration) by reducing the opening of the small pores
in the leaves, known as ‘stomata’. This triggers several more subtle, indirect effects. For example, when plants close their stomata, they use less soil water, changing the amount of soil water available to other plants. At the same time, altered water availability and enhanced photosynthesis can change
the amount of leaf, root and below ground microbial biomass, resulting in changes to ecosystem functioning.