Regional Contingencies in the Relationship Between Aboveground Biomass and Litter in the World’s Grasslands
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.
Citation:
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:
References: 1. 1. Meentemeyer V (1978) Macroclimate and lignin control of litter decomposition rates. Ecology 59: 465–472. doi: 10.2307/1936576. * CrossRef 2. 2. Swift MJ, Heal OW, Anderson JM (1979) Decomposition in Terrestrial Ecosystems. University of California Press, Berkeley, California, USA. 3 7. 7. Del Grosso SJ, Parton WJ, Stohlgren T, Zheng D, Bachelet D, et al. (2008) Global Net Primary Production Predicted from Vegetation Class, Precipitation, and Temperature. Ecology 89: 2117–2126. doi: 10.1890/07-0850.1. * CrossRef 16. 16. Aerts R (1997) Climate, leaf litter chemistry and leaf litter decomposition in terrestrial ecosystems: a triangular relationship. Oikos 79: 439–449. doi: 10.2307/3546886. * CrossRef 17. 17. Silver WL, Miya RK (2001) Global patterns in root decomposition: comparisons of climate and litter quality effects. Oecologia 129: 407–419. * CrossRef 18. 18. Hobbie SE, Vitousek PM (2000) Nutrient limitation of decomposition in Hawaiian forests. Ecology 81: 1867–1877. doi: 10.1890/0012-9658(2000)081[1867:NLODIH]2.0.CO;2. * CrossRef 19. 19. Parton W, Silver WL, Burke IC, Grassens L, Harmon M, et al. (2007) Global-scale similarities in nitrogen release patterns during long-term decomposition. Science 315: 361–364. doi: 10.1126/science.1134853. * CrossRef 20. 20. LeBauer DS, Treseder KK (2008) Nitrogen limitation of net primary productivity in terrestrial ecosystems is globally distributed. Ecology 89: 371–379. doi: 10.1890/06-2057.1. * CrossRef 21. 21. Austin A, Vivanco L (2006) Plant litter decomposition in a semi-arid ecosystem controlled by photodegradation. Nature 442: 555–558. doi: 10.1038/nature05038. * CrossRef 22. 22. White R, Muray S, Rohweder M (2000) Pilot Analysis of Global Ecosystems: Grassland Ecosystems Technical Report. World Resources Institute, Washington, DC. 23