Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

Abstract. Heterotrophic soil respiration is an important component of the global terrestrial carbon (C) cycle, driven by environmental factors acting from local to continental scales. For tropical Africa, these factors and their interactions remain largely unknown. Here, using samples collected along topographic and geochemical gradients in the East African Rift Valley, we study how soil chemistry and fertility drive soil respiration of soils developed from different parent materials even after many millennia of weathering. To address the drivers of soil respiration, we incubated soils from three regions with contrasting geochemistry (mafic, felsic and mixed sediment) sampled along slope gradients. For three soil depths, we measured the potential maximum heterotrophic respiration under stable environmental conditions and the radiocarbon content (Δ14C) of the bulk soil and respired CO2. Our study shows that soil fertility conditions are the main determinant of C stability in tropical forest soils. We found that soil microorganisms were able to mineralize soil C from a variety of sources and with variable C quality under laboratory conditions representative of tropical topsoil. However, in the presence of organic carbon sources of poor quality or the presence of strong mineral-related C stabilization, microorganisms tend to discriminate against these energy sources in favour of more accessible forms of soil organic matter, resulting in a slower rate of C cycling. Furthermore, despite similarities in climate and vegetation, soil respiration showed distinct patterns with soil depth and parent material geochemistry. The topographic origin of our samples was not a main determinant of the observed respiration rates and Δ14C. In situ, however, soil hydrological conditions likely influence soil C stability by inhibiting decomposition in valley subsoils. Our results demonstrate that, even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks and the turnover of C in soil. Soil parent material and its control on soil chemistry need to be taken into account to understand and predict C stabilization and rates of C cycling in tropical forest soils.

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Controls on heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

10.5194/soil-2020-96 ◽

2021 ◽

Author(s):

Benjamin Bukombe ◽

Peter Fiener ◽

Alison M. Hoyt ◽

Sebastian Doetterl

Keyword(s):

Soil Respiration ◽

Tropical Forest ◽

Forest Soils ◽

Soil Chemistry ◽

Poor Quality ◽

Parent Material ◽

Soil C ◽

Soil Parent Material ◽

C Stocks ◽

Heterotrophic Soil Respiration

Abstract. Heterotrophic soil respiration is an important component of the global terrestrial carbon (C) cycle, driven by environmental factors acting from local to continental scales. For tropical Africa, these factors and their interactions remain largely unknown. Here, using samples collected along strong topographic and geochemical gradients in the East African Rift Valley, we study how soil chemistry and soil fertility, derived from the geochemical composition of soil parent material, can drive soil respiration even after many millennia of weathering and soil development. To address the drivers of soil respiration, we incubated soils from three regions with contrasting geochemistry (mafic, felsic, and mixed sedimentary) sampled along slope gradients. For three soil depths, we measured the potential maximum heterotrophic respiration under stable environmental conditions as well as the radiocarbon content (Δ14C) of the bulk soil and respired CO2. We found that soil microbial communities were able to mineralize C from fossil as well as other poor quality C sources under laboratory conditions representative of tropical topsoils. Furthermore, despite similarities in terms of climate, vegetation, and the size of soil C stocks, soil respiration showed distinct patterns with soil depth and parent material geochemistry. The topographic origin of our samples was not a main determinant of the observed respiration rates and Δ14C. In situ, however, soil hydrological conditions likely influence soil C stability by inhibiting decomposition in valley subsoils. Our study shows that soil fertility conditions are the main determinant of C stability in tropical forest soils. Further, in the presence of organic carbon sources of poor quality or the presence of strong mineral related C stabilization, microorganisms tend to discriminate against these sources in favor of more accessible forms of soil organic matter as energy sources, resulting in a slower rate of C cycling. Our results demonstrate that even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks, and the turnover of C in soil. Soil parent material and its lasting control on soil chemistry need to be taken into account to understand and predict C stabilization and rates of C cycling in tropical forest soils.

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Carbon release from tropical forest soils informed by soil chemistry, fertility, and carbon quality derived from geochemistry of the parent material

10.5194/egusphere-egu21-14344 ◽

2021 ◽

Author(s):

Benjamin Bukombe ◽

Peter Fiener ◽

Alison M. Hoyt ◽

Sebastian Doetterl

Keyword(s):

Organic Carbon ◽

Soil Respiration ◽

Tropical Forest ◽

Forest Soils ◽

Soil Chemistry ◽

Poor Quality ◽

Parent Material ◽

Soil C ◽

Soil Parent Material ◽

C Stocks

Tropical forest soils are a vital component of the global carbon (C) cycle and their response to environmental change will determine future atmospheric carbon dioxides (CO2). For example, increasing biomass productivity in tropical forests suggests a potential sink for C. However, its storage and stability are driven by factors acting from small to large scale. For tropical Africa, these factors are not well known and documented.&#160; Predicting tropical soil C dynamics ultimately depends on our understanding and the ability to determine the primary environmental controls on soil organic carbon content and respiration.Here, using samples collected along strong geochemical gradients in the East African Rift Valley, we demonstrate how soil chemistry and soil fertility, derived from the geochemical composition of soil parent material, can drive soil respiration even in deeply weathered soils.&#160;To address the drivers of soil respiration, we incubated soils from three regions with contrasting geochemistry (mafic, felsic, and mixed sedimentary). For three soil depths, we measured the potential maximum heterotrophic respiration as well as the radiocarbon isotopic signature (&#916;14C) of the bulk soil and respired CO2 under stable environmental conditions.&#160;We found that soil microbial communities were able to mineralize C from fossil as well as other poor quality C sources under laboratory conditions representative of tropical topsoils. Despite similarities in terms of climate, vegetation, and the size of soil C stocks, soil respiration showed distinct patterns with soil depth and parent material geochemistry. Our study shows that soil fertility conditions are the main determinant of C stability in tropical forest soils. Further, in the presence of organic carbon sources of poor quality or the presence of strong mineral-related C stabilization, microorganisms tend to discriminate against these sources in favor of more accessible forms of soil organic matter as energy sources, resulting in a slower rate of C cycling.&#160;Our results demonstrate that even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks, and the turnover of C in soil. Soil parent material and its lasting control on soil chemistry need to be taken into account to understand and predict C stabilization and rates of C cycling in tropical forest soils.&#160;

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Impact of temperature and moisture on heterotrophic soil respiration along a moist tropical forest gradient in Australia

Soil Research ◽

10.1071/sr14217 ◽

2015 ◽

Vol 53 (3) ◽

pp. 286 ◽

Cited By ~ 5

Author(s):

M. Zimmermann ◽

K. Davies ◽

V. T. V. Peña de Zimmermann ◽

M. I. Bird

Keyword(s):

Soil Respiration ◽

Tropical Forest ◽

Tropical Forests ◽

Mean Annual Temperature ◽

Soil Cores ◽

Site Specific ◽

Soil C ◽

Respiration Rates ◽

C Stocks ◽

Specific Temperature

Tropical forests represent the largest store of terrestrial carbon (C) and are potentially vulnerable to climatic variations and human impact. However, the combined influence of temperature and precipitation on aboveground and belowground C cycling in tropical ecosystems is not well understood. To simulate the impact of climate (temperature and rainfall) on soil C heterotrophic respiration rates of moist tropical forests, we translocated soil cores among three elevations (100, 700 and 1540 m a.s.l.) representing a range in mean annual temperature of 10.9°C and in rainfall of 6840 mm. Initial soil C stocks in the top 30 cm along the gradient increased linearly with elevation from 6.13 kg C m–2 at 100 m a.s.l. to 10.66 kg C m–2 at 1540 m a.s.l. Respiration rates of translocated soil cores were measured every 3 weeks for 1 year and were fitted to different model functions taking into account soil temperature, soil moisture, mean annual temperature and total annual rainfall. Measured data could be best fitted to the model equation based on temperature alone. Furthermore, Akaike’s information criteria revealed that model functions taking into account the temperature range of the entire translocation gradient led to better estimates of respiration rates than functions solely based on the site-specific temperature range. Soil cores from the highest elevation revealed the largest temperature sensitivity (Q10 = 2.63), whereas these values decreased with decreasing elevation (Q10 = 2.00 at 100 m a.s.l.) or soil C stocks. We therefore conclude that increased temperatures will have the greatest impact on soil C stocks at higher elevations, and that best projections for future soil respiration rates of moist tropical forest soils can be achieved based on temperature alone and large soil cores exposed to temperatures above site-specific temperature regimes.

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Soil carbon respiration in tropical forest soils along geomorphic and geochemical gradients

10.5194/egusphere-egu2020-13609 ◽

2020 ◽

Author(s):

Benjamin Bukombe ◽

Laurent Kidinda ◽

Alison Hoyt ◽

Cordula Vogel ◽

Marijn Bauters ◽

...

Keyword(s):

Soil Respiration ◽

Tropical Forest ◽

Soil Carbon ◽

Nutrient Availability ◽

Soil Depth ◽

Sedimentary Rocks ◽

Parent Material ◽

Congo Basin ◽

Geochemical Background ◽

Soil C

Tropical ecosystems and the soils therein have been reported as one of the most important and largest terrestrial carbon (C) pools and are considered important climate regulator. Carbon stabilization mechanisms in these ecosystems are often complex, as these mechanisms crucially rely on the interplay of geology, topography, climate, and biology. Future predictions of the perturbation of the soil carbon pool ultimately depend on our mechanistic understanding of these complex interactions.Using laboratory incubation experiments, we investigated if carbon release from soils through heterotrophic respiration in the African highland forests of the Eastern Congo Basin follows predictable patterns related to topography, soil depth or geochemical soil properties that can be described at the landscape scale and ultimately be used to improve the spatial accuracy of soil C respiration in mechanistic models. In general, soils developed on basalt and granite parent material (mafic and felsic geochemistry of parent material) showed significantly (p <0.05) higher specific respiration than soils developed on sedimentary rocks (mixed geochemistry) with highest rates measured for soils developed on granite. For soils developed on basalt, specific respiration decreased two-fold with soil depth, but not for soils developed on granite or sedimentary rocks. No significant differences in respiration under tropical forest were found in relation to topography for any soil and geochemical background.Using a non-linear, &#160;stochastic gradient boosting machine learning approach we show that soil biological, physical and chemical properties can predict the pattern of specific soil respiration (R2=0.41, p<0.05). An assessment of the relative importance of the included predictors for soil respiration resulted in 43 % of the model being driven by geochemistry (pedogenic oxides, nutrient availability), 12 % driven by soil texture and clay mineralogy, 34 % by microbial biomass, C:N, and C:P ratios and 11 % by topographic indices.&#160;We conclude that, in order to explain soil C respiration patterns in tropical forests, a complex set of variables need to be considered that differs depending on the local bedrock chemistry. Its effect is likely related to the varying strength of C stabilization with minerals as well as nutrient availability that might drive C input patterns and microbial turnover.

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Short- and Long-term Influence of Litter Quality and Quantity on Simulated Heterotrophic Soil Respiration in a Lowland Tropical Forest

Ecosystems ◽

10.1007/s10021-016-0104-x ◽

2017 ◽

Vol 20 (6) ◽

pp. 1190-1204 ◽

Cited By ~ 8

Author(s):

Laëtitia Bréchet ◽

Valérie Le Dantec ◽

Stéphane Ponton ◽

Jean-Yves Goret ◽

Emma Sayer ◽

...

Keyword(s):

Soil Respiration ◽

Tropical Forest ◽

Litter Quality ◽

Lowland Tropical Forest ◽

Heterotrophic Soil Respiration ◽

Short And Long Term

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Carbon and nitrogen in the silt-size fraction and its HCl-hydrolysis residues from coarse-textured Canadian boreal forest soils

Canadian Journal of Soil Science ◽

10.4141/cjss2013-082 ◽

2014 ◽

Vol 94 (2) ◽

pp. 157-168 ◽

Cited By ~ 4

Author(s):

Caroline M. Preston ◽

Charlotte E. Norris ◽

Guy M. Bernard ◽

David W. Beilman ◽

Sylvie A. Quideau ◽

...

Keyword(s):

Boreal Forest ◽

Soil Carbon ◽

Forest Soils ◽

Mineral Soil ◽

Size Fraction ◽

Soil C ◽

Carbon And Nitrogen ◽

Total Soil ◽

C Stocks ◽

Canadian Boreal Forest

Preston, C. M., Norris, C. E., Bernard, G. M., Beilman, D. W., Quideau, S. A. and Wasylishen, R. E. 2014. Carbon and nitrogen in the silt-size fraction and its HCl-hydrolysis residues from coarse-textured Canadian boreal forest soils. Can. J. Soil Sci. 94: 157–168. Improving the capacity to predict changes in soil carbon (C) stocks in the Canadian boreal forest requires better information on the characteristics and age of soil carbon, especially more slowly cycling C in mineral soil. We characterized C in the silt-size fraction, as representative of C stabilized by mineral association, previously isolated in a study of soil profiles of four sandy boreal jack pine sites. Silt-size fraction accounted for 13–31% of the total soil C and 12–51% of the total soil N content. Solid-state 13C nuclear magnetic resonance spectroscopy showed that silt C was mostly dominated by alkyl and O,N-alkyl C, with low proportions of aryl C in most samples. Thus, despite the importance of fire in this region, there was little evidence of storage of pyrogenic C. We used HCl hydrolysis to isolate the oldest C within the silt-size fraction. Consistent with previous studies, this procedure removed 21–74% of C and 74–93% of N, leaving residues composed mainly of alkyl and aryl C. However, it failed to isolate consistently old C; 11 out of 16 samples had recent 14C ages (fraction of modern 14C > 1), although C-horizon samples were older, with Δ14C from –17 to –476‰. Our results indicate relatively young ages for C associated with the silt-size fractions in these sites, for which mineral soil C storage may be primarily limited by good drainage and coarse soil texture, exacerbated by losses due to periodic wildfire.

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Reviews and syntheses: Field data to benchmark the carbon cycle models for tropical forests

Biogeosciences ◽

10.5194/bg-14-4663-2017 ◽

2017 ◽

Vol 14 (20) ◽

pp. 4663-4690 ◽

Cited By ~ 12

Author(s):

Deborah A. Clark ◽

Shinichi Asao ◽

Rosie Fisher ◽

Sasha Reed ◽

Peter B. Reich ◽

...

Keyword(s):

Tropical Forest ◽

Tropical Forests ◽

Field Data ◽

Reference Level ◽

Field Observations ◽

Current Effort ◽

C Cycling ◽

C Cycle ◽

Starting Point ◽

C Stocks

Abstract. For more accurate projections of both the global carbon (C) cycle and the changing climate, a critical current need is to improve the representation of tropical forests in Earth system models. Tropical forests exchange more C, energy, and water with the atmosphere than any other class of land ecosystems. Further, tropical-forest C cycling is likely responding to the rapid global warming, intensifying water stress, and increasing atmospheric CO2 levels. Projections of the future C balance of the tropics vary widely among global models. A current effort of the modeling community, the ILAMB (International Land Model Benchmarking) project, is to compile robust observations that can be used to improve the accuracy and realism of the land models for all major biomes. Our goal with this paper is to identify field observations of tropical-forest ecosystem C stocks and fluxes, and of their long-term trends and climatic and CO2 sensitivities, that can serve this effort. We propose criteria for reference-level field data from this biome and present a set of documented examples from old-growth lowland tropical forests. We offer these as a starting point towards the goal of a regularly updated consensus set of benchmark field observations of C cycling in tropical forests.

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Biodegradation of low molecular weight organic compounds and their contribution to heterotrophic soil respiration in three Japanese forest soils

Plant and Soil ◽

10.1007/s11104-010-0398-y ◽

2010 ◽

Vol 334 (1-2) ◽

pp. 475-489 ◽

Cited By ~ 34

Author(s):

Kazumichi Fujii ◽

Chie Hayakawa ◽

Patrick A. W. Van Hees ◽

Shinya Funakawa ◽

Takashi Kosaki

Keyword(s):

Molecular Weight ◽

Soil Respiration ◽

Organic Compounds ◽

Forest Soils ◽

Low Molecular Weight ◽

Heterotrophic Soil Respiration ◽

Japanese Forest

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Seasonal Soil Respiration Dynamics and Carbon-Stock Variations in Mountain Permanent Grasslands Compared to Arable Lands

Agriculture ◽

10.3390/agriculture9080165 ◽

2019 ◽

Vol 9 (8) ◽

pp. 165 ◽

Cited By ~ 1

Author(s):

Matteo Francioni ◽

Paride D’Ottavio ◽

Roberto Lai ◽

Laura Trozzo ◽

Katarina Budimir ◽

...

Keyword(s):

Land Use ◽

Land Use Change ◽

Soil Respiration ◽

Soil Temperature ◽

Land Use Changes ◽

Soil C ◽

Permanent Grassland ◽

Heterotrophic Soil Respiration ◽

C Stock ◽

Soil C Stock

Permanent grasslands provide a wide array of ecosystem services. Despite this, few studies have investigated grassland carbon (C) dynamics, and especially those related to the effects of land-use changes. This study aimed to determine whether the land-use change from permanent grassland to arable lands resulted in variations in the soil C stock, and whether such variations were due to increased soil respiration or to management practices. To address this, seasonal variations of soil respiration, sensitivity of soil respiration to soil temperature (Q10), and soil C stock variations generated by land-use changes were analyzed in a temperate mountain area of central Italy. The comparisons were performed for a permanent grassland and two adjacent fields, one cultivated with lentil and the other with emmer, during the 2015 crop year. Soil respiration and its heterotrophic component showed different spatial and temporal dynamics. Annual cumulative soil respiration rates were 6.05, 5.05 and 3.99 t C ha−1 year−1 for grassland, lentil and emmer, respectively. Both soil respiration and heterotrophic soil respiration were positively correlated with soil temperature at 10 cm depth. Derived Q10 values were from 2.23 to 6.05 for soil respiration, and from 1.82 to 4.06 for heterotrophic respiration. Soil C stock at over 0.2 m in depth was 93.56, 48.74 and 46.80 t C ha−1 for grassland, lentil and emmer, respectively. The land-use changes from permanent grassland to arable land lead to depletion in terms of the soil C stock due to water soil erosion. A more general evaluation appears necessary to determine the multiple effects of this land-use change at the landscape scale.

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Temporal changes in global soil respiration since 1987

Nature Communications ◽

10.1038/s41467-020-20616-z ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jiesi Lei ◽

Xue Guo ◽

Yufei Zeng ◽

Jizhong Zhou ◽

Qun Gao ◽

...

Keyword(s):

Soil Respiration ◽

Temporal Variations ◽

Global Scale ◽

Future Climate ◽

Climate Projections ◽

Microbial Decomposition ◽

Soil C ◽

Modeling Analysis ◽

C Stocks ◽

Global Soil

AbstractAs the second-largest terrestrial carbon (C) flux, soil respiration (RS) has been stimulated by climate warming. However, the magnitude and dynamics of such stimulations of soil respiration are highly uncertain at the global scale, undermining our confidence in future climate projections. Here, we present an analysis of global RS observations from 1987–2016. RS increased (P < 0.001) at a rate of 27.66 g C m−2 yr−2 (equivalent to 0.161 Pg C yr−2) in 1987–1999 globally but became unchanged in 2000–2016, which were related to complex temporal variations of temperature anomalies and soil C stocks. However, global heterotrophic respiration (Rh) derived from microbial decomposition of soil C increased in 1987–2016 (P < 0.001), suggesting accumulated soil C losses. Given the warmest years on records after 2015, our modeling analysis shows a possible resuscitation of global RS rise. This study of naturally occurring shifts in RS over recent decades has provided invaluable insights for designing more effective policies addressing future climate challenges.

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