scholarly journals Top-down and bottom-up controls on soil carbon and nitrogen cycling with repeated burning across four ecosystems

2019 ◽  
Author(s):  
Adam F. A. Pellegrini ◽  
Sarah E. Hobbie ◽  
Peter B. Reich ◽  
Ari Jumpponen ◽  
E. N. Jack Brookshire ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Carbon ◽  
Fire History ◽  
Tree Cover ◽  
Top Down ◽  
Bottom Up ◽  
Soil C ◽  
Soil C And N ◽  
C And N

AbstractFires shape the biogeochemistry and functioning of many ecosystems, but fire frequencies are changing across large areas of the globe. Frequent fires can change soil carbon (C) and nitrogen (N) storage through both “top-down” pathways, by altering inputs through shifting plant composition and biomass, and “bottom-up” ones, by altering losses through decomposition and turnover of soil organic matter. However, the relative importance of these different pathways and the degree to which they regulate ecosystem responses to decades of changing fire frequencies is uncertain. Here, we sampled soils and plant communities in four North American and African sites spanning tropical savanna, temperate coniferous savanna, temperate broadleaf savanna, and temperate coniferous forest that each contained multiple plots repeatedly burned for 33-61 years and nearby plots that were protected from fire over the same period. The sites varied markedly in temperature, precipitation, species composition, fire history and soil chemistry; thus they represent a broad test for the generality of fire impacts on biogeochemical cycling. For all four sites, bulk soil C and N by were 25-180% higher in unburned vs. frequently burned plots, with greater soil losses occurring in areas with greater declines in tree cover and biomass inputs into soils. Fire reduced the activity of soil extracellular enzymes that hydrolyze labile C and N from soil organic matter by two- to ten-fold, whereas tree cover was the predominant control on the oxidation of recalcitrant C compounds. C-acquisition enzyme activity tended to decline with decreasing soil N, suggesting that N losses may contribute to limited decomposition, buffering systems against increased losses of soil C with fire. In conclusion, variability in how fire alters soil C and N across ecosystems can be explained partly by fire-driven changes in tree cover and biomass, but the slower turnover of organic matter we observed may offset some of the reduction of C inputs from plants after fire.

Soil aggregate stability and soil organic matter fractions under agropastoral systems established in native savanna

Soil Research ◽  
1996 ◽  
Vol 34 (6) ◽  
pp. 891 ◽  
Author(s):  
AJ Gijsman
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Aggregate Stability ◽  
Aggregate Size ◽  
Soil Disturbance ◽  
N Content ◽  
Soil C ◽  
Size Classes ◽  
Soil C And N ◽  
C And N

An area of native savanna on an Oxisol in the Eastern Plains of Colombia was opened and sown to various rotations of grass or grass-legume pasture with rice. After 4.5 years, the soil was sampled for studying the effect of land conversion on soil aggregation and on the distribution of total and particulate soil organic matter across the aggregate size classes. The size distribution of undisturbed aggregates did not vary among treatments. Five different methods were used to measure wet aggregate stability (WAS). The choice of method affected the WAS average across treatments as well as the differences among treatments. The only consistent observation was the lower WAS under monocropped rice compared with the other treatments. Inclusion of a legume in a pasture hardly affected aggregate stability. In contrast to the WAS measurements, which were carried out with soil aggregates of 1-2 mm, wet sieving of whole-soil samples revealed additional differences among treatments: large macroaggregates (>2 mm) proved less stable under those treatments that involved soil disturbance through ploughing and harvesting. Total soil C and N content did not vary among treatments, despite considerable differences in plant production levels. The C concentration, but not the N concentration, declined with decreasing aggregate size. The distribution of whole-soil C and N content across aggregate size classes depended more on the amount of soil in a certain size class than on the size class's C or N concentration. Those treatments that involved frequent soil disturbance had a smaller fraction of large macroaggregates (>2 mm) and, as a consequence, less C and N in the large macroaggregate fraction. The particulate organic matter (POM) fraction accounted for only 6.2-8.5% of total soil carbon. The small size of this pool makes it unlikely that POM can serve in these Oxisols for estimating the amount of soil organic matter with medium turnover rate, as suggested by others.

scholarly journals Soil organic matter in fire-affected pastures and in an Araucaria forest in South-Brazilian Leptosols

2012 ◽  
Vol 47 (5) ◽  
pp. 707-715 ◽  
Author(s):  
Mariana da Luz Potes ◽  
Deborah Pinheiro Dick ◽  
Graciele Sarante Santana ◽  
Michely Tomazi ◽  
Cimélio Bayer
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Grazing Intensity ◽  
Soil C ◽  
Araucaria Forest ◽  
Physical Fractionation ◽  
C Stocks ◽  
Native Pasture ◽  
Soil C And N ◽  
C And N

The objective of this work was to evaluate the distribution pattern and composition of soil organic matter (SOM) and its physical pools of Leptosols periodically affected by fire over the last 100 years in South Brazil. Soil samples at 0-5, 5-10, and 10-15 cm depths were collected from the following environments: native pasture without burning in the last year and grazed with 0.5 livestock per hectare per year (1NB); native pasture without burning in the last 23 years and grazed with 2.0 livestock per hectare per year (23NB); and an Araucaria forest (AF). Physical fractionation was performed with the 0-5 and 5-10 cm soil layers. Soil C and N stocks were determined in the three depths and in the physical pools, and organic matter was characterized by infrared spectroscopy and thermogravimetry. The largest C stocks in all depths and physical pools were found under the AF. The 23NB environment showed the lowest soil C and N stocks at the 5-15 cm depth, which was related to the end of burning and to the higher grazing intensity. The SOM of the occluded light fraction showed a greater chemical recalcitrance in 1NB than in 23NB. Annual pasture burning does not affect soil C stocks up to 15 cm of depth.

Effects of organic matter removal and soil compaction on fifth-year mineral soil carbon and nitrogen contents for sites across the United States and Canada

2006 ◽  
Vol 36 (3) ◽  
pp. 565-576 ◽  
Author(s):  
Felipe G Sanchez ◽  
Allan E Tiarks ◽  
J Marty Kranabetter ◽  
Deborah S Page-Dumroese ◽  
Robert F Powers ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Carbon ◽  
Treatment Effects ◽  
Mineral Soil ◽  
The United States ◽  
Organic Matter Removal ◽  
Soil C ◽  
Competition Control ◽  
Soil C And N ◽  
C And N

This study describes the main treatment effects of organic matter removal and compaction and a split-plot effect of competition control on mineral soil carbon (C) and nitrogen (N) pools. Treatment effects on soil C and N pools are discussed for 19 sites across five locations (British Columbia, Northern Rocky Mountains, Pacific Southwest, and Atlantic and Gulf coasts) that are part of the Long-Term Soil Productivity (LTSP) network and were established over 5 years ago. The sites cover a broad range of soil types, climatic conditions, and tree species. Most sites showed increased soil C and N levels 5 years after study establishment; however, the rate and magnitude of the changes varied between sites. Organic matter removal, compaction, or competition control did not significantly affect soil C and N contents at any site, except for the Northern Rocky Mountain site, where competition control significantly affected soil C and N contents. The observation that, after 5 years, the soil C and N contents were not negatively affected by even the extreme treatments demonstrates the high resiliency of the soil, at least in the short term, to forest management perturbations.

scholarly journals Spatially Related Sampling Uncertainty in the Assessment of Labile Soil Carbon and Nitrogen in an Irish Forest Plantation

2021 ◽  
Vol 11 (5) ◽  
pp. 2139
Author(s):  
Junliang Zou ◽  
Bruce Osborne
Keyword(s):  
Spatial Variability ◽  
Soil Carbon ◽  
Sampling Effort ◽  
Limited Information ◽  
Sampling Area ◽  
Soil C ◽  
Distribution Maps ◽  
Soil C And N ◽  
C And N ◽  
Highly Correlated

The importance of labile soil carbon (C) and nitrogen (N) in soil biogeochemical processes is now well recognized. However, the quantification of labile soil C and N in soils and the assessment of their contribution to ecosystem C and N budgets is often constrained by limited information on spatial variability. To address this, we examined spatial variability in dissolved organic carbon (DOC) and dissolved total nitrogen (DTN) in a Sitka spruce forest in central Ireland. The results showed moderate variations in the concentrations of DOC and DTN based on the mean, minimum, and maximum, as well as the coefficients of variation. Residual values of DOC and DTN were shown to have moderate spatial autocorrelations, and the nugget sill ratios were 0.09% and 0.10%, respectively. Distribution maps revealed that both DOC and DTN concentrations in the study area decreased from the southeast. The variability of both DOC and DTN increased as the sampling area expanded and could be well parameterized as a power function of the sampling area. The cokriging technique performed better than the ordinary kriging for predictions of DOC and DTN, which are highly correlated. This study provides a statistically based assessment of spatial variations in DOC and DTN and identifies the sampling effort required for their accurate quantification, leading to improved assessments of forest ecosystem C and N budgets.

Post-thinning soil organic matter evolution and soil CO2 effluxes in temperate radiata pine plantations: impacts of moderate thinning regimes on the forest C cycle

2012 ◽  
Vol 42 (11) ◽  
pp. 1953-1964 ◽  
Author(s):  
Irene Fernandez ◽  
Juan Gabriel Álvarez-González ◽  
Beatríz Carrasco ◽  
Ana Daría Ruíz-González ◽  
Ana Cabaneiro
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Radiata Pine ◽  
Soil Samples ◽  
Mitigation Strategies ◽  
Change Scenario ◽  
Soil C ◽  
C Storage ◽  
C Cycle ◽  
C And N

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.

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

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

<p>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°C), atmospheric CO<sub>2</sub>-concentration (eCO<sub>2</sub>: ambient and elevated by +300 ppm) and to a future climate treatment (eT x eCO<sub>2</sub>: +3°C and + 300 ppm). A combination of slaking and wet sieving was used to obtain three size classes: macro-aggregates (maA, > 250 µm), micro-aggregates (miA, 63 µm – 250 µm) and free silt & clay (sc, < 63 µm). In both maA and miA, four different physical OM fractions were then isolated by density fractionation (using sodium polytungstate of ρ = 1.6 g*cm<sup>-3</sup>, 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 eCO<sub>2</sub> and eT x eCO<sub>2 </sub>plots, an isotope mixing-model was used to calculate the proportion of recent C derived from the elevated CO<sub>2 </sub>treatment. Total soil C and N did not significantly change with treatments.  eCO<sub>2</sub> 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 CO<sub>2</sub> 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.    </p>

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

2012 ◽  
Vol 9 (8) ◽  
pp. 3013-3028 ◽  
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.

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

2001 ◽  
Vol 81 (1) ◽  
pp. 21-31 ◽  
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

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

Soil Research ◽  
2003 ◽  
Vol 41 (1) ◽  
pp. 95 ◽  
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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