Surprisingly decomposition of leaf litter in nature is not affected by temperature when reciprocally transplanted!

Matthew A. Krna, Kevin R. Tate, Surinder Saggar, Hannah L. Buckley, Gillian L. Rapson

This is a plain language summary of a Functional Ecology research article which can be found here.

Combatting climate change is a big issue for the planet. One obvious approach is to better understand what happens to carbon as it progresses from the atmosphere through plants and into the soils. A critical process here is the rate at which litter from plants decomposes. Some evidence indicates that this is temperature-dependent, implying litter decomposes at a higher rate as temperatures warm.

            In our experiment we studied the rate of leaf litter decomposition from a dominant tussock grass over an 800 m altitudinal gradient as a proxy for temperature changes. We collected litter from 8 plots along this gradient, bagged it in open-weave fabric, and placed that litter back into all 8 plots we collected it from, replicated this 6 times, and recorded decomposition rates over each of 4 years. This generates a reciprocal transplant, allowing us to separate environmental effects from effects of litter quality.

Segmenting and pooling litter samples per plot after detaching achlorophyllous leaves of Chionochloa at Plot 3, and still cheerful! (credit: Jill Rapson)

Cancelling out random environmental variation via the reciprocal transplant design, we found that there were only very weak signs of differences in litter quality (which affects digestibility to decomposers). Cancelling out random differences in litter quality, there was only weak and implausible evidence of differences in decomposition rates between the plots along the gradient. More importantly we found no evidence at all that different litters decompose at different rates at the different plots. So there is no temperature-dependence of decomposition in a properly-controlled experimental setup.

            We conclude that warming temperatures will not affect litter decomposition rates, so future searches for temperature dependence are futile. Any changes in carbon storage (sequestration) in soils will be due to other processes, such as changes in plant productivity, or soil moisture or in microbial community composition.

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