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
Soil and Tillage Research 10/2016; 156:33-43. DOI:10.1016/j.still.2015.09.021 · 2.62 Impact Factor
"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.
Journal of Ecology 11/2015; 103(6):1408-1420. DOI:10.1111/1365-2745.12433 · 5.52 Impact Factor
"During this process , the release of N as ammonium and nitrate from a given plant residue only occurs when the C:N ratio of remaining plant litter reaches a critical threshold value (*25 g g -1 ), below which net immobilization of N by microorganisms subsides (Manzoni et al. 2008). Soil C–N coupling is differentiated between grassland ecosystems having low versus high litter C:N ratio: high C:N ratio corresponding to low intensification and low net N mineralization, while low C:N ratio corresponding to high intensification and greater net N mineralization (Soussana and Lemaire 2014). "
[Show abstract][Hide abstract] ABSTRACT: A need to increase agricultural production across the world to ensure continued food security appears to be at odds with the urgency to reduce the negative environmental impacts of intensive agriculture. Around the world, intensification has been associated with massive simplification and uniformity at all levels of organization, i.e., field, farm, landscape, and region. Therefore, we postulate that negative environmental impacts of modern agriculture are due more to production simplification than to inherent characteristics of agricultural productivity. Thus by enhancing diversity within agricultural systems, it should be possible to reconcile high quantity and quality of food production with environmental quality. Intensification of livestock and cropping systems separately within different specialized regions inevitably leads to unacceptable environmental impacts because of the overly uniform land use system in intensive cereal areas and excessive N-P loads in intensive animal areas. The capacity of grassland ecosystems to couple C and N cycles through microbial-soil-plant interactions as a way for mitigating the environmental impacts of intensive arable cropping system was analyzed in different management options: grazing, cutting, and ley duration, in order to minimize trade-offs between production and the environment. We suggest that integrated crop-livestock systems are an appropriate strategy to enhance diversity. Sod-based rotations can temporally and spatially capture the benefits of leys for minimizing environmental impacts, while still maintaining periods and areas of intensive cropping. Long-term experimental results illustrate the potential of such systems to sequester C in soil and to reduce and control N emissions to the atmosphere and hydrosphere.