Abstract
Based on regional-scale studies, aboveground production and litter decomposition are thought to positively covary, because they are driven by shared biotic and climatic factors. Until now we have been unable to test whether production and decomposition are generally coupled across climatically dissimilar regions, because we lacked replicated data collected within a single vegetation type across multiple regions, obfuscating the drivers and generality of the association between production and decomposition. Furthermore, our understanding of the relationships between production and decomposition rests heavily on separate meta-analyses of each response, because no studies have simultaneously measured production and the accumulation or decomposition of litter using consistent methods at globally relevant scales. Here, we use a multi-country grassland dataset collected using a standardized protocol to show that live plant biomass (an estimate of aboveground net primary production) and litter disappearance (represented by mass loss of aboveground litter) do not strongly covary. Live biomass and litter disappearance varied at different spatial scales. There was substantial variation in live biomass among continents, sites and plots whereas among continent differences accounted for most of the variation in litter disappearance rates. Although there were strong associations among aboveground biomass, litter disappearance and climatic factors in some regions (e.g. U.S. Great Plains), these relationships were inconsistent within and among the regions represented by this study. These results highlight the importance of replication among regions and continents when characterizing the correlations between ecosystem processes and interpreting their global-scale implications for carbon flux. We must exercise caution in parameterizing litter decomposition and aboveground production in future regional and global carbon models as their relationship is complex.
Highlights
It is a long-held tenet of ecosystem ecology that regional variation in production and decomposition processes are positively correlated with both temperature and precipitation and production and decomposition processes should be coupled at regional scales, e.g. [1,2,3]
There were no strong correlations between site-level averages of aboveground biomass, litter, or litter disappearance and most climate variables (Table 2) at the site scale
Aboveground biomass, litter stocks, and litter disappearance varied depending on spatial scales, with aboveground biomass varying at plot, site and continent scales, litter varying strongly among sites and litter disappearance varying strongly among continents
Summary
It is a long-held tenet of ecosystem ecology that regional (i.e., areas bounded by sub-continental scale geographic features) variation in production and decomposition processes are positively correlated with both temperature and precipitation and production and decomposition processes should be coupled at regional scales, e.g. [1,2,3]. Carbon cycling models (e.g., CENTURY model [8], [9]), motivated by such results, assume a coupling between net primary production (NPP) and litter loss, driven by parallel responses to temperature and precipitation. A challenge to understanding and quantifying the productiondecomposition relationship is considering the covarying influence of other regulatory factors. Biotic drivers such as vegetation type, vegetation chemistry, and trophic interactions can significantly affect rates of plant growth or organic matter decay, even within the same climatic region Testing for regional variation in the relationship between production and decomposition is crucial to climate change research globally because it may require revisions to ecosystem response projections that inform Earth system models
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