Leveraging decadal-scale in situ experiments to examine plant, soil and ecosystem responses to climate warming

Abstract:

A major objective of ecological research is to diagnose the responses of ecosystems to warming, including potential feedbacks to the climate system. Despite this, most experiments aimed at examining warming effects on ecosystem structure and functioning take place over periods of weeks to years, and thus fall short of known lags and demographic processes in ecological systems. At the same time, in situ observations from latitudinal or elevation gradients implicitly consider several millennia of geological and evolutionary history, making them inappropriate models for the state of ecosystems following decades or centuries of temperature change. As a consequence, we know remarkably little about how ecosystems respond to warming over timescales of relevance to the climate system, leaving us unable to predict associated climate feedbacks.

Here, I present findings from a suite of in situ warming experiments to discuss the responses of plant, soil and ecosystem processes to years to centuries of climate warming. I draw from a natural geothermal warming experiment in a sub-arctic grassland ecosystem that captures both short-term (5-8 years) and very long-term (>50 years) warming to show that soil microbial physiology is intrinsically temperature sensitive, and that incorporating this information into carbon cycle models improves projections of soil carbon loss. However, by synthesising responses of 128 ecosystem pools, properties and processes to short-term versus long-term warming in the same experiment, I also show that ecosystems may overreact to the onset of warming, that this overreaction can still be present after 5-8 years and that ignoring it leads to errors of >100% per ºC for most variables when projected over a 50-year period. Finally, I draw from a global network of alpine transplant experiments encompassing different timescales of warming to examine the temporal (a)synchrony of shifts in plant and soil community composition under sustained warming, and explore the consequences for soil carbon cycle processes. From this, I discuss the challenges of making long-term ecosystem predictions from short-term observations, and provide a framework for characterising ecosystem responses to climate change over timescales of relevance to Earth’s climate system.