Sequestration Rates for C and N in Soil Organic Matter at Four N-Polluted Temperate Forest Stands

Forest ecosystems can act as C sinks, thus absorbing a high percentage of atmospheric CO2. Appropriate silvicultural regimes can therefore be applied as useful tools in climate change mitigation strategies. The present study analyzed the temporal changes in the effects of thinning on soil organic matter (SOM) dynamics and on soil CO2 emissions in radiata pine ( Pinus radiata D. Don) forests. Soil C effluxes were monitored over a period of 2 years in thinned and unthinned plots. In addition, soil samples from the plots were analyzed by solid-state 13C-NMR to determine the post-thinning SOM composition and fresh soil samples were incubated under laboratory conditions to determine their biodegradability. The results indicate that the potential soil C mineralization largely depends on the proportion of alkyl-C and N-alkyl-C functional groups in the SOM and on the microbial accessibility of the recalcitrant organic pool. Soil CO2 effluxes varied widely between seasons and increased exponentially with soil heating. Thinning led to decreased soil respiration and attenuation of the seasonal fluctuations. These effects were observed for up to 20 months after thinning, although they disappeared thereafter. Thus, moderate thinning caused enduring changes to the SOM composition and appeared to have temporary effects on the C storage capacity of forest soils, which is a critical aspect under the current climatic change scenario.

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Effects of climate change on soil organic matter chemical composition and carbon content in different physical fractions

10.5194/egusphere-egu21-9216 ◽

2021 ◽

Author(s):

Moritz Mohrlok ◽

Victoria Martin ◽

Alberto Canarini ◽

Wolfgang Wanek ◽

Michael Bahn ◽

...

Keyword(s):

Climate Change ◽

Organic Matter ◽

Chemical Composition ◽

Soil Organic Matter ◽

Soil C ◽

Size Classes ◽

Soil Fractions ◽

Total Soil ◽

C And N ◽

Amp Clay

Soil organic matter (SOM) is composed of many pools with different properties (e.g. turnover times) which are generally used in biogeochemical models to predict carbon (C) dynamics. Physical fractionation methods are applied to isolate soil fractions that correspond to these pools. This allows the characterisation of chemical composition and C content of these fractions. There is still a lack of knowledge on how these individual fractions are affected by different climate change drivers, and therefore the fate of SOM remains elusive. We sampled soils from a multifactorial climate change experiment in a managed grassland in Austria four years after starting the experiment to investigate the response of SOM in physical soil fractions to temperature (eT: ambient and elevated by +3&#176;C), atmospheric CO2-concentration (eCO2: ambient and elevated by +300 ppm) and to a future climate treatment (eT x eCO2: +3&#176;C and + 300 ppm). A combination of slaking and wet sieving was used to obtain three size classes: macro-aggregates (maA, > 250 &#181;m), micro-aggregates (miA, 63 &#181;m &#8211; 250 &#181;m) and free silt & clay (sc, < 63 &#181;m). In both maA and miA, four different physical OM fractions were then isolated by density fractionation (using sodium polytungstate of &#961; = 1.6 g*cm-3, ultrasonication and sieving): Free POM (fPOM), intra-aggregate POM (iPOM), silt & clay associated OM (SCaOM) and sand-associated OM (SaOM). We measured C and N contents and isotopic composition by EA-IRMS in all fractions and size classes and used a Pyrolysis-GC/MS approach to assess their chemical composition. For eCO2 and eT x eCO2 plots, an isotope mixing-model was used to calculate the proportion of recent C derived from the elevated CO2 treatment. Total soil C and N did not significantly change with treatments.&#160; eCO2 decreased the relative proportion of maA-mineral-associated C and increased C in fPOM and iPOM. About 20% of bulk soil C was represented by the recent C derived from the CO2 fumigation treatment. This significantly differed between size classes and density fractions (p < 0.001), which indicates inherent differences in OM age and turnover. Warming reduced the amount of new C incorporated into size classes. We found that each size class and fraction possessed a unique chemical fingerprint, but this was not significantly changed by the treatments. Overall, our results show that while climate change effects on total soil C were not significant after 4 years, soil fractions showed specific effects. Chemical composition differed significantly between size classes and fractions but was unaffected by simulated climate change. This highlights the importance to separate SOM into differing pools, while including changes to the molecular composition might not be necessary for improving model predictions.&#160;&#160;&#160;&#160;

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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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Soil organic matter, C and N accumulation during natural succession and reclamation in an opencast sand quarry (southern Poland)

Archives of Agronomy and Soil Science ◽

10.1080/03650340701362516 ◽

2007 ◽

Vol 53 (5) ◽

pp. 473-483 ◽

Cited By ~ 32

Author(s):

Marcin Pietrzykowski ◽

Wojciech Krzaklewski

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

N Accumulation ◽

Natural Succession ◽

Southern Poland ◽

C And N

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Role of Crop Rotations in the Dynamic of Soil Organic Matter Pools

Journal of Agricultural Science ◽

10.5539/jas.v10n8p341 ◽

2018 ◽

Vol 10 (8) ◽

pp. 341

Author(s):

Rodrigo Santos Moreira ◽

Marcio Koiti Chiba ◽

Isabella Clerici De Maria ◽

Caio César Zito Siqueira ◽

Aildson Pereira Duarte ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Crop Rotation ◽

Light Fraction ◽

Crop Rotations ◽

Organic Matter Quality ◽

Humification Index ◽

No Till ◽

C And N ◽

Soil Organic Matter Quality

Soil organic matter is considered a key attribute for a sustainable agricultural production and is influenced by the quantity and quality of the crop residue deposited on the soil surface. Therefore, different crop rotations could change the soil organic matter pools. The objectives of this study were to evaluate the soil carbon pools obtained by chemical and physical fractionation methods and the humification index under different crop rotations in a no-till system. We test the following hypothesis: a) the distribution of C and N among the soil organic matter fractions depends on plant species rotation schemes and; b) labile fractions are more sensitive to the input of crop residues and therefore, more suitable for evaluating the impact of different crop rotations in the soil organic matter quality. We evaluated four crop sequences (corn/corn/corn; corn/wheat/corn; soybean/wheat/corn and soybean/corn/corn) in a no-till system. A five-year reforested area was used as reference. We determined the total C and N contents, the mineral-associated C and N, the light fraction of C and N, the labile carbon extracted with KMnO4 and the soil organic matter humification index. We found narrow differences between the crop rotation systems in the total C and N levels, the mineral-associated C and N fractions and the labile C extracted with KMnO4. The diversification of the agricultural system with soybean in crop rotation favored the accumulation of light fraction C and N in the soil that were more efficient to provide information about the changes in the soil organic matter quality.

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Soil organic matter as influenced by straw management practices and inclusion of grass and clover seed crops in cereal rotations

Soil Research ◽

10.1071/sr01103 ◽

2003 ◽

Vol 41 (1) ◽

pp. 95 ◽

Cited By ~ 17

Author(s):

D. Curtin ◽

P. M. Fraser

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Management Practices ◽

Degree Days ◽

Straw Management ◽

Soil C ◽

Total Soil ◽

C And N ◽

Second Year ◽

Seed Crops

In New Zealand, cereal straw has traditionally been burned to facilitate seedbed preparation for the succeeding crop. Because of concerns over the decline of organic matter and the associated deterioration in soil structure, farmers are interested in incorporating crop residues as a means of maintaining organic matter levels. In a 6-year trial on a Wakanui silt loam on the Canterbury Plains, we evaluated the effects of 3 straw management practices (i.e. straw incorporation, burning of straw, and straw removal) on total and labile soil organic matter. A fourth treatment was included to evaluate the local practice of including seed crops (grass and clover) in cereal rotations. The seed crops were grown every second year, the crop sequence being cereal–ryegrass–cereal–clover–cereal–clover. The rate of straw (wheat) decomposition was determined using a litter bag technique, with the bags being buried at a depth of 15 cm for intervals of up to 19 months. In the straw-incorporated treatment, about 25 t/ha of straw (~11 t C/ha) was returned to the soil during the trial. However, there was no significant effect (P > 0.05) of straw management treatments on total soil C (or N), or on labile organic matter pools, although there was a tendency for higher levels of mineralisable C and N where straw was incorporated. Measured straw decomposition rates were consistent with predictions of the Douglas-Rickman residue decomposition model. Under the relatively warm conditions of the Canterbury Plains (thermal time typically >4000 degree-days per year, calculated as the sum of daily degree-days above a base temperature of 0�C), about three-quarters of incorporated straw decomposed within a year. Of the 11 t C/ha of straw-C incorporated, we estimated that only about 1 t C/ha would remain in the soil at the time of sampling. An increase in soil C by this amount would not be detectable (total soil C was about 55 t/ha in the upper 15 cm). Growing seed crops every second year increased several of the labile organic pools (mineralisable C and N, light fraction C and N, microbial biomass) in the 0–7.5 and 7.5 cm soil layers and this may have beneficial effects (e.g. improved N supply) on the succeeding cereal crop. However, the seed crops did not significantly increase total soil organic matter within the 6 years.

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