Article

The Global Stoichiometry of Litter Nitrogen Mineralization

Civil and Environmental Engineering Department, Duke University, Durham, NC 27708, USA.
Science (Impact Factor: 31.48). 09/2008; 321(5889):684-6. DOI: 10.1126/science.1159792
Source: PubMed

ABSTRACT Plant residue decomposition and the nutrient release to the soil play a major role in global carbon and nutrient cycling.
Although decomposition rates vary strongly with climate, nitrogen immobilization into litter and its release in mineral forms
are mainly controlled by the initial chemical composition of the residues. We used a data set of ∼2800 observations to show
that these global nitrogen-release patterns can be explained by fundamental stoichiometric relationships of decomposer activity.
We show how litter quality controls the transition from nitrogen accumulation into the litter to release and alters decomposers'
respiration patterns. Our results suggest that decomposers lower their carbon-use efficiency to exploit residues with low
initial nitrogen concentration, a strategy used broadly by bacteria and consumers across trophic levels.

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    • "Recently, modeling work has linked the N enrichment response of R soil to microbial physiology through C and N stoichiometry (Schimel and Weintraub, 2003; Parton et al., 2007; Manzoni et al., 2008). These studies suggest microbes adjust respiration rates based on external C and N availability to meet internal stoichiometric requirements. "
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    ABSTRACT: The response of soil CO 2 fluxes (R soil) to interactions between carbon (C) and nitrogen (N) availability or C and temperature conditions is not well understood, but may increasingly affect future C storage under the combined anthropogenic impacts of N deposition and climate change. Here we addressed this uncertainty through a series of laboratory incubation experiments using soils from three contrasting ecosystems to investigate how changes in C, N, and temperature regulate R soil through changes to MichaeliseMenten parameters (i.e. V max and K m). Results of this study demonstrate that R soil response to N enrichment and changes in temperature are dependent on the C availability of soil substrates. N addition influenced R soil through both the maximum rate (V max) and the half saturation constant (K m). The increase in K m corresponded to a decrease in R soil when C was limited. Alternatively, when C was abundant, N enrichment increased R soil , which corresponded to an increase in V max. Regulation of temperature sensitivity through V max and K m was also dependent on C availability. Both V max and K m demonstrated positive temperature responses, supporting the hypothesis of a canceling effect at low C concentrations. While temperature sensitivity was influenced by both C quantity and C complexity, our results suggested that C quantity is a stronger predictor. Despite strong differences in climate, vegetation, and management of our soils, CeN and C-temperature interactions were markedly similar between sites, highlighting the importance of C availability in the regulation of R soil and justifying the use of MichaeliseMenten kinetics in biogeochemical modeling.
    Soil Biology and Biochemistry 06/2015; 88. DOI:10.1016/j.soilbio.2015.05.014 · 4.41 Impact Factor
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    • "This challenges the current paradigm that links elemental ratios to the decomposability of below-ground plant tissues (Hobbie et al., 2010). This disconnect could be attributable to differences in the chemical construct of the root tissues, as highlighted by the compound-specific decomposition of aboveground tissues (Manzoni et al., 2008; Suseela et al., 2013, 2014a). Despite their lower abundance compared with polysaccharides, phenolic compounds exert a disproportionate influence in conferring recalcitrance to plant tissues. "
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    ABSTRACT: Fine roots constitute a significant source of plant productivity and litter turnover across terrestrial ecosystems, but less is known about the quantitative and qualitative profile of phenolic compounds within the fine root architecture, which could regulate the potential contribution of plant roots to soil organic matter pool. To understand the linkage between traditional macro-elemental and morphological traits of roots with its molecular-level carbon chemistry, we analyzed the seasonal variations in monomeric yields of the free-, bound-, and lignin-phenols in fine roots (distal five orders) and leaves of Ardisia quinquegona. Fine roots contained two-fold higher levels of bound-phenols and three-fold higher levels of lignin-phenols than leaves. Within fine roots, the levels of free- and bound-phenols decreased with increasing root order, and seasonal variation in phenolic profile was more evident in the lower-order than in higher-order roots. The morphological and macro-elemental root-traits were decoupled from the quantity, composition and tissue-association of phenolic compounds, revealing the potential inability of these traditional parameters to capture the carbon quality within the fine root architecture and between fine roots and leaves. Our results highlight the molecular-level heterogeneity in carbon composition within the fine root architecture, and imply that traits that capture molecular identity of the root-construct might better predict the decomposition dynamics within fine root orders.
    New Phytologist 02/2015; 206:1261-1273. DOI:10.1111/nph.13385 · 7.67 Impact Factor
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    • "In the past, experimental investigations into effects on decomposition caused by plant litter diversity focused on litter mass loss only (Gartner and Cardon 2004, Ha¨ttenschwiler et al. 2005, Gessner et al. 2010, Cardinale et al. 2011). However, litter decomposition also involves nutrient transformations (immobilization and mineralization [Parton et al. 2007, Manzoni et al. 2008]), which can have important ecosystem consequences beyond the decomposition process (e.g., altered nutrient cycling in streams [Webster et al. 2009]). In addition, decomposing leaf litter is an important site of microbial biomass production, which can be extraordinarily high in streams (up to 280 g dry massÁm À2 Áyr À1 [Suberkropp et al. 2010]). "
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    ABSTRACT: Biodiversity and ecosystem functioning theory suggests that litter mixtures composed of dissimilar leaf species can enhance decomposition due to species trait complementarity. Here we created a continuous gradient of litter chemistry trait variability within species mixtures to assess effects of litter dissimilarity on three related processes in a natural stream: litter decomposition, fungal biomass accrual in the litter, and nitrogen and phosphorus immobilization. Litter from a pool of eight leaf species was analyzed for chemistry traits affecting decomposition (lignin, nitrogen, and phosphorus) and assembled in all of the 28 possible two-species combinations. Litter dissimilarity was characterized in terms of a range of trait diversity measures, using Euclidean and Gower distances and dendrogram-based indices. We found large differences in decomposition rates among species, but no significant relationships between decomposition rate of individual leaf species and litter trait dissimilarity, irrespective of whether decomposition was mediated by microbes alone or by both microbes and litter-consuming invertebrates. Likewise, no effects of trait dissimilarity emerged on either fungal biomass accrual or changes during decomposition of nitrogen or phosphorus concentrations in individual leaf species. In line with recent meta-analyses these results provide support for the contention that litter diversity effects on decomposition, at least in streams, are less pronounced than effects on terrestrial primary productivity.
    Ecology 02/2015; DOI:10.1890/14-1151.1 · 5.00 Impact Factor
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