Physical fractionation of soil organic matter: Destabilization of deep soil carbon following harvesting of a temperate coniferous forest

In boreal forest ecosystems fire, fungi and bacteria, and their interactions, have a pronounced effect on soil carbon dynamics. In this study we measured enzymatic activities, litter decomposition rates, carbon stocks and fungal and microbial biomasses in a boreal subarctic coniferous forest on a four age classes of non-stand replacing fire chronosequence (2, 42, 60 and 152 years after the fire). The results show that microbial activity recovered slowly after fire and the decomposition of new litter was affected by the disturbance. The percent mass loss of Scots pine litter increased with time from the last fire. Slow litter decomposition during the first post-fire years accelerates soil organic matter accumulation that is essential for the recovery of soil biological activities. Fire reduced the enzymatic activity across all the enzyme types measured. Carbon-degrading, chitin-degrading and phosphorus-dissolving enzymes showed different responses with the time elapsed since the fire disturbance. Microbial and enzymatic activity took decades before recovering to the levels observed in old forest stands. Our study demonstrates that slower post-fire litter decomposition has a pronounced impact on the recovery of soil organic matter following forest fires in northern boreal coniferous forests.

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Vegetation Effects on Soil Properties in the Monteagle Sandy Loam Series: Implications for Land‐use Change

Inquiry@Queen's Undergraduate Research Conference Proceedings ◽

10.24908/iqurcp.7470 ◽

2017 ◽

Author(s):

Allison Neil

Keyword(s):

Land Use ◽

Organic Matter ◽

Land Use Change ◽

Soil Properties ◽

Soil Carbon ◽

Sugar Maple ◽

Agricultural Land ◽

Deciduous Forest ◽

Coniferous Forest ◽

The Impact

Soil properties are strongly influenced by the composition of the surrounding vegetation. We investigated soil properties of three ecosystems; a coniferous forest, a deciduous forest and an agricultural grassland, to determine the impact of land use change on soil properties. Disturbances such as deforestation followed by cultivation can severely alter soil properties, including losses of soil carbon. We collected nine 40 cm cores from three ecosystem types on the Roebuck Farm, north of Perth Village, Ontario, Canada. Dominant species in each ecosystem included hemlock and white pine in the coniferous forest; sugar maple, birch and beech in the deciduous forest; grasses, legumes and herbs in the grassland. Soil pH varied little between the three ecosystems and over depth. Soils under grassland vegetation had the highest bulk density, especially near the surface. The forest sites showed higher cation exchange capacity and soil moisture than the grassland; these differences largely resulted from higher organic matter levels in the surface forest soils. Vertical distribution of organic matter varied greatly amongst the three ecosystems. In the forest, more of the organic matter was located near the surface, while in the grassland organic matter concentrations varied little with depth. The results suggest that changes in land cover and land use alters litter inputs and nutrient cycling rates, modifying soil physical and chemical properties. Our results further suggest that conversion of forest into agricultural land in this area can lead to a decline in soil carbon storage.

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Towards a representation of priming on soil carbon decomposition in the global land biosphere model ORCHIDEE (version 1.9.5.2)

Geoscientific Model Development ◽

10.5194/gmd-9-841-2016 ◽

2016 ◽

Vol 9 (2) ◽

pp. 841-855 ◽

Cited By ~ 15

Author(s):

Bertrand Guenet ◽

Fernando Esteban Moyano ◽

Philippe Peylin ◽

Philippe Ciais ◽

Ivan A Janssens

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Soil Carbon ◽

Global Scale ◽

Soil Incubation ◽

First Order ◽

Carbon Decomposition ◽

Litter Manipulation ◽

Global Land ◽

Biosphere Model

Abstract. Priming of soil carbon decomposition encompasses different processes through which the decomposition of native (already present) soil organic matter is amplified through the addition of new organic matter, with new inputs typically being more labile than the native soil organic matter. Evidence for priming comes from laboratory and field experiments, but to date there is no estimate of its impact at global scale and under the current anthropogenic perturbation of the carbon cycle. Current soil carbon decomposition models do not include priming mechanisms, thereby introducing uncertainty when extrapolating short-term local observations to ecosystem and regional to global scale. In this study we present a simple conceptual model of decomposition priming, called PRIM, able to reproduce laboratory (incubation) and field (litter manipulation) priming experiments. Parameters for this model were first optimized against data from 20 soil incubation experiments using a Bayesian framework. The optimized parameter values were evaluated against another set of soil incubation data independent from the ones used for calibration and the PRIM model reproduced the soil incubations data better than the original, CENTURY-type soil decomposition model, whose decomposition equations are based only on first-order kinetics. We then compared the PRIM model and the standard first-order decay model incorporated into the global land biosphere model ORCHIDEE (Organising Carbon and Hydrology In Dynamic Ecosystems). A test of both models was performed at ecosystem scale using litter manipulation experiments from five sites. Although both versions were equally able to reproduce observed decay rates of litter, only ORCHIDEE–PRIM could simulate the observed priming (R2 = 0.54) in cases where litter was added or removed. This result suggests that a conceptually simple and numerically tractable representation of priming adapted to global models is able to capture the sign and magnitude of the priming of litter and soil organic matter.

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Predicting decadal trends and transient responses of radiocarbon storage and fluxes in a temperate forest soil

Biogeosciences ◽

10.5194/bg-9-3013-2012 ◽

2012 ◽

Vol 9 (8) ◽

pp. 3013-3028 ◽

Cited By ~ 19

Author(s):

C. A. Sierra ◽

S. E. Trumbore ◽

E. A. Davidson ◽

S. D. Frey ◽

K. E. Savage ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Soil Carbon ◽

Empirical Model ◽

Temperate Forest ◽

Global Environmental Change ◽

Carbon Dynamics ◽

Co2 Efflux ◽

Soil C ◽

Soil Carbon Dynamics

Abstract. Representing the response of soil carbon dynamics to global environmental change requires the incorporation of multiple tools in the development of predictive models. An important tool to construct and test models is the incorporation of bomb radiocarbon in soil organic matter during the past decades. In this manuscript, we combined radiocarbon data and a previously developed empirical model to explore decade-scale soil carbon dynamics in a temperate forest ecosystem at the Harvard Forest, Massachusetts, USA. We evaluated the contribution of different soil C fractions to both total soil CO2 efflux and microbially respired C. We tested the performance of the model based on measurable soil organic matter fractions against a decade of radiocarbon measurements. The model was then challenged with radiocarbon measurements from a warming and N addition experiment to test multiple hypotheses about the different response of soil C fractions to the experimental manipulations. Our results showed that the empirical model satisfactorily predicts the trends of radiocarbon in litter, density fractions, and respired CO2 observed over a decade in the soils not subjected to manipulation. However, the model, modified with prescribed relationships for temperature and decomposition rates, predicted most but not all the observations from the field experiment where soil temperatures and nitrogen levels were increased, suggesting that a larger degree of complexity and mechanistic relations need to be added to the model to predict short-term responses and transient dynamics.

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Changes in soil carbon under long-term maize in monoculture and legume-based rotation

Canadian Journal of Soil Science ◽

10.4141/s00-041 ◽

2001 ◽

Vol 81 (1) ◽

pp. 21-31 ◽

Cited By ~ 142

Author(s):

E G Gregorich ◽

C F Drury ◽

J A Baldock

Keyword(s):

Nuclear Magnetic Resonance ◽

Organic Matter ◽

Soil Organic Matter ◽

Magnetic Resonance ◽

Soil Carbon ◽

Crop Residues ◽

Cropping Systems ◽

Natural Abundance ◽

Organic C ◽

Soil C

Legume-based cropping systems could help to increase crop productivity and soil organic matter levels, thereby enhancing soil quality, as well as having the additional benefit of sequestering atmospheric C. To evaluate the effects of 35 yr of maize monoculture and legume-based cropping on soil C levels and residue retention, we measured organic C and 13C natural abundance in soils under: fertilized and unfertilized maize (Zea mays L.), both in monoculture and legume-based [maize-oat (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa] rotations; fertilized and unfertilized systems of continuous grass (Poa pratensis L.); and under forest. Solid state 13C nuclear magnetic resonance (NMR) was used to chemically characterize the organic matter in plant residues and soils. Soils (70-cm depth) under maize cropping had about 30-40% less C, and those under continuous grass had about 16% less C, than those under adjacent forest. Qualitative differences in crop residues were important in these systems, because quantitative differences in net primary productivity and C inputs in the different agroecosystems did not account for observed differences in total soil C. Cropping sequence (i.e., rotation or monoculture) had a greater effect on soil C levels than application of fertilizer. The difference in soil C levels between rotation and monoculture maize systems was about 20 Mg C ha-1. The effects of fertilization on soil C were small (~6 Mg C ha-1), and differences were observed only in the monoculture system. The NMR results suggest that the chemical composition of organic matter was little affected by the nature of crop residues returned to the soil. The total quantity of maize-derived soil C was different in each system, because the quantity of maize residue returned to the soil was different; hence the maize-derived soil C ranged from 23 Mg ha-1 in the fertilized and 14 Mg ha-1 in the unfertilized monoculture soils (i.e., after 35 maize crops) to 6-7 Mg ha-1 in both the fertilized and unfertilized legume-based rotation soils (i.e., after eight maize crops). The proportion of maize residue C returned to the soil and retained as soil organic C (i.e., Mg maize-derived soil C/Mg maize residue) was about 14% for all maize cropping systems. The quantity of C3-C below the plow layer in legume-based rotation was 40% greater than that in monoculture and about the same as that under either continuous grass or forest. The soil organic matter below the plow layer in soil under the legume-based rotation appeared to be in a more biologically resistant form (i.e., higher aromatic C content) compared with that under monoculture. The retention of maize residue C as soil organic matter was four to five times greater below the plow layer than that within the plow layer. We conclude that residue quality plays a key role in increasing the retention of soil C in agroecosystems and that soils under legume-based rotation tend to be more “preservative” of residue C inputs, particularly from root inputs, than soils under monoculture. Key words: Soil carbon, 13C natural abundance, 13C nuclear magnetic resonance, maize cropping, legumes, root carbon

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CO2-C losses and carbon quality of selected Maritime Antarctic soils

Antarctic Science ◽

10.1017/s0954102012000648 ◽

2012 ◽

Vol 25 (1) ◽

pp. 11-18 ◽

Cited By ~ 9

Author(s):

Juliana Vanir De Souza Carvalho ◽

Eduardo De Sá Mendonça ◽

Newton La Scala ◽

César Reis ◽

Efrain Lázaro Reis ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Soil Temperature ◽

Soil Carbon ◽

Humic Substances ◽

Microbial Activity ◽

Chemical Characteristics ◽

Maritime Antarctic ◽

Antarctic Soils ◽

Humification Degree

AbstractPolar Regions are the most important soil carbon reservoirs on Earth. Monitoring soil carbon storage in a changing global climate context may indicate possible effects of climate change on terrestrial environments. In this regard, we need to understand the dynamics of soil organic matter in relation to its chemical characteristics. We evaluated the influence of chemical characteristics of humic substances on the process of soil organic matter mineralization in selected Maritime Antarctic soils. A laboratory assay was carried out with soils from five locations from King George Island. We determined the contents of total organic carbon, oxidizable carbon fractions of soil organic matter, and humic substances. Two in situ field experiments were carried out during two summers, in order to evaluate the CO2-C emissions in relation to soil temperature variations. The overall low amounts of soil organic matter in Maritime Antarctic soils have a low humification degree and reduced microbial activity. CO2-C emissions showed significant exponential relationship with temperature, suggesting a sharp increase in CO2-C emissions with a warming scenario, and Q10 values (the percentage increase in emission for a 10°C increase in soil temperature) were higher than values reported from elsewhere. The sensitivity of the CO2-C emission in relation to temperature was significantly correlated with the humification degree of soil organic matter and microbial activity for Antarctic soils.

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