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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"altering soil microbial community due to a greater C use efficiency which accelerates the mineralization of native organic matter (Derrien et al., 2014; Kuzyakov, 2010; Manzoni et al., 2008). Thus, given the short-term nature of our experiment (i.e. 6 years), we could hypothesize that this effect could have played a major role in the turnover of the initial SOC in the GL1 and GL2 treatments. "
[Show abstract][Hide abstract] ABSTRACT: Inserting legumes in low-input innovative cropping systems can represent a good strategy to reduce
current N fertilizer dependency while enhancing ecosystem services. However, although the impact of
the use of legumes as cover crops has been broadly studied, very little is known about the effects of grain
legume-based rotations on soil organic carbon (SOC) and nitrogen (SON). A cropping system experiment
with three 3-year rotations with different levels of inclusion of grain legumes: GL0, GL1 and GL2 (none,
one, and two grain legumes, respectively), with (CC) or without (BF, bare fallow) cover crops was
established in SW France (Auzeville) under temperate climate. Durum wheat was present in all the
rotations to act as an indicator of their performance. Soil organic C and SON were quantified before the
beginning of the experiment and after 3 and 6 years (i.e., after one and two complete 3-yr rotations).
Aboveground C and N inputs to the soil, and C and N harvest indexes and grain yield of the cash crops
were also measured. Inserting grain legumes in the rotations significantly affected the amount of C and N
inputs and consequently SOC and SON. After two cycles of the 3-yr rotation, the GL1 and GL2 treatments
showed a greater decrease in SOC and SON when compared to GL0. However, the inclusion of cover crops
in the rotations led to mitigate this loss. Durum wheat produced significantly greater grain yields in
GL1 when compared to GL0, while GL2 presented intermediate values. In turn, the incorporation of cover
crops did not reduce C and N harvest indexes or the grain yield of the different cash crops. We concluded
that, in such conventionally-tilled grain legume-based rotations, the use of cover crops was efficient to
mitigate SOC and SON losses and then increase N use efficiency at the cropping system level without
Full-text · Article · Oct 2016 · Soil and Tillage Research
"We integrate Davidson et al.'s  conceptual framework of quantifying concentration of soluble C substrates that are directly accessible for microbial assimilation, thus building a direct linkage between environmental factors with microbial state transitions. Substrate quality is also reflected in the model through a generic index of soil C:N ratio [Manzoni et al., 2008], and the assimilation of substrate by microorganisms is assumed to be regulated by the C:N ratio of microbial biomass and that of the soil. We apply the model to simulate the top 30 cm of the soil due to data availability for site validation. "
[Show abstract][Hide abstract] ABSTRACT: Soil carbon dynamics of terrestrial ecosystems play a significant role in the global carbon cycle. Microbial-based decomposition models have seen much growth recently for quantifying this role, yet dormancy as a common strategy used by microorganisms has not usually been represented and tested in these models against field observations. Here we developed an explicit microbial-enzyme decomposition model and examined model performance with and without representation of microbial dormancy at six temperate forest sites of different forest types. We then extrapolated the model to global temperate forest ecosystems to investigate biogeochemical controls on soil heterotrophic respiration and microbial dormancy dynamics at different temporal-spatial scales. The dormancy model consistently produced better match with field-observed heterotrophic soil CO2 efflux (RH) than the no dormancy model. Our regional modeling results further indicated that models with dormancy were able to produce more realistic magnitude of microbial biomass (<2% of soil organic carbon) and soil RH (7.5±2.4PgCyr-1). Spatial correlation analysis showed that soil organic carbon content was the dominating factor (correlation coefficient=0.4-0.6) in the simulated spatial pattern of soil RH with both models. In contrast to strong temporal and local controls of soil temperature and moisture on microbial dormancy, our modeling results showed that soil carbon-to-nitrogen ratio (C:N) was a major regulating factor at regional scales (correlation coefficient=-0.43 to -0.58), indicating scale-dependent biogeochemical controls on microbial dynamics. Our findings suggest that incorporating microbial dormancy could improve the realism of microbial-based decomposition models and enhance the integration of soil experiments and mechanistically based modeling.
Full-text · Article · Dec 2015 · Journal of Geophysical Research: Biogeosciences
"Climate, litter quality and soil organisms have been identified as the key variables controlling C turnover and nutrient mineralization of surface litter in terrestrial ecosystems (Meentemeyer 1978; Swift, Heal & Anderson 1979; Hobbie 1992; Co^ uteaux, Bottner & Berg 1995). More recently, the complex interactions among these variables have demonstrated several global scale patterns: litter characteristics determined by plant traits including leaf mass per area (LMA), recalcitrant C (lignin) and initial litter nutrient content appear to cross ecosystems as general controls on mass loss (Parton et al. 2007; Cornwell et al. 2008; Manzoni et al. 2008); changes in allocation and growth strategies within and across species can have large impacts on decomposition (Vivanco & Austin 2006; Orwin et al. 2010; Freschet et al. 2013; Hobbie 2015); and litter-soil biota interactions and their interaction with climate are increasingly recognized as an important factor in determining the first stages of C and nitrogen turnover (Garc ıa-Palacios et al. 2013; van der Putten et al. 2013; Austin et al. 2014; Bradford et al. 2014). As such, there is much current interest in understanding the importance of these interactive controls on litter decomposition in the context of ecosystems altered by human impact and predicted climate change. "
[Show abstract][Hide abstract] ABSTRACT: Our understanding of the principal controls on litter decomposition is critical for our capacity to predict how global changes will impact terrestrial ecosystems. Although climate, litter quality and soil organisms clearly modulate carbon (C) and nutrient turnover, land-use change affecting plant species composition and structure can alter the relative importance of such controls. We took advantage of prior land-use changes of intentional planting of exotic forest species along a broad precipitation gradient [250–2200 mm mean annual precipitation (MAP)] in Patagonia, South America, where we established five paired sites in natural vegetation and adjacent 35-year-old pine plantations. We explored direct and interactive effects of precipitation and plant community structure on litter decomposition with in situ decomposition, common litters and reciprocal transplants, in addition to an evaluation of microenvironmental changes. Surface litter decomposition in natural vegetation (NV) was similar in all sites along the gradient, independent of litter quality, MAP or soil characteristics, while mass loss demonstrated a significant positive linear relationship with MAP in pine plantations (PP). Decomposition of common litters in PP was markedly reduced with respect to NV, which was > 50% faster at the arid extreme of the gradient. C:N ratios predicted decomposition only in PP, and differences in decomposition were highly correlated with impacts of vegetative cover on incident solar radiation. Synthesis. Concurrent changes in plant cover in NV with increasing MAP resulted in reduced incident solar radiation at the soil surface and decreased the relative importance of photodegradation as a control on surface mass loss. These changes eclipsed direct effects of water availability, litter quality and soil nutrients. In contrast, increased shade and recalcitrant litter with afforestation in PP sites combined such that photodegradation was entirely eliminated as a control and biotic decomposition was much reduced. While afforestation projects are promoted as a strategy to mitigate increased atmospheric carbon dioxide due to human activity, our results highlight that primary controls of litter decomposition were substantially altered with unexpected consequences for the C balance of these ecosystems.
Full-text · Article · Nov 2015 · Journal of Ecology