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Author(s): John N. Klironomos (corresponding author) [1]; Michael F. Allen [2]; Matthias C. Rillig [3]; Jeff Piotrowski [3]; Shokouh Makvandi-Nejad [1]; Benjamin E. Wolfe [1]; Jeff R. Powell [1] Attempts [...]

Author(s): John N. Klironomos (corresponding author) Understanding the relative abundance of species in plant communities is an unsolved problem[sup. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]] . [...]

Mechanisms controlling plant biodiversity continue to be debated. There has been little attention paid to the effects of microbe-plant interactions, such as mycorrhizal symbiosis, on plant biodiveristy, and ecosystem variability. Arbuscular mycorrhizal fungi (AMF) are plentiful in most ecosystems and their presence increases plant biodiversity. It has been shown that AMF richness plays an important part in plant species composition, biodiversity, and productivity in artificial microcosms and macrocosms.

Attempts to understand the ecological effect of increasing atmospheric CO2 concentration, [CO2], usually involve exposing today's ecosystems to expected future [CO2] levels. However, a major assumption of these approaches has not been tested-that exposing ecosystems to a single-step increase in [CO2] will yield similar responses to those of a gradual increase over several decades. We tested this assumption on a mycorrhizal fungal community over a period of six years. [CO2] was either increased abruptly, as is typical of most [CO2] experiments, or more gradually over 21 generations. The two approaches resulted in different structural and functional community responses to increased [CO2]. Some fungi were sensitive to the carbon pulse of the abrupt [CO2] treatment. This resulted in an immediate decline in fungal species richness and a significant change in mycorrhizal functioning. The magnitude of changes in fungal diversity and functioning in response to gradually increasing [CO2] was smaller, and not significantly different to those with ambient [CO2]. Our results suggest that studies may overestimate some community responses to increasing [CO2] because biota may be sensitive to ecosystem changes that occur as a result of abrupt increases. [ABSTRACT FROM AUTHOR]