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. Citation: O’Halloran LR, Borer ET, Seabloom EW, MacDougall AS, Cleland EE, et al. (2013) Regional Contingencies in the Relationship between Aboveground Biomass and Litter in the World’s Grasslands. PLoS ONE 8(2): e54988. doi:10.1371/journal.pone.0054988 Editor: Han YH. Chen, Lakehead University, Canada
Received: September 13, 2012; Accepted: December 17, 2012; Published: February 6, 2013 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Funding: This work was generated using data from the Nutrient Network collaborative experiment, funded at the site-scale by individual researchers and coordinated through Research Coordination Network funding from National Science Foundation (NSF) to ETB and EWS (NSF-DEB-1042132). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors declare that no competing interests exist. Introduction
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 hence, production and decomposition processes should be coupled at regional scales, e.g. –. This assumption is supported by recent meta-analyses and models that suggest climate strongly influences plant production and decomposition rates of terrestrial foliage –. Carbon cycling models (e.g., CENTURY model , ), motivated by such results, assume a coupling between net primary production (NPP) and litter loss, driven by parallel responses to temperature and precipitation. Given predicted scenarios of climate change, these carbon models predict significant changes to the way that...
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