scholarly journals Soil CO<sub>2</sub> efflux from two mountain forests in the Eastern Himalayas Bhutan: components and controls

2016 ◽  
Author(s):  
Norbu Wangdi ◽  
Mani Prasad Nirola ◽  
Mathias Mayer ◽  
Norbu Zangmo ◽  
Karma Orong ◽  
...  
Keyword(s):  
Soil Respiration ◽  
Soil Temperature ◽  
Monsoon Season ◽  
Coniferous Forest ◽  
High Elevation ◽  
Co2 Efflux ◽  
Mountain Forests ◽  
Eastern Himalayas ◽  
Soil C ◽  
C Stocks

Abstract. The biogeochemistry of mountain forests in the Hindu Kush-Himalaya range is poorly studied although climate change is expected to disproportionally affect the region. We measured the soil CO2 efflux (Rs) at a high elevation (3260 m) coniferous, and a lower elevation (2460 m) broadleaved forest in Bhutan, eastern Himalayas, during 2014 and 2015. Both sites experienced typical monsoon weather (cold-dry winters, warm-wet summers) during the study. Trenching was applied to estimate the contribution of autotrophic (Ra) and heterotrophic (Rh) soil respiration. The temperature (Q10) and the moisture sensitivities of Rh were determined under controlled laboratory conditions and were used to model Rh in the field. The higher elevation coniferous forest had a higher standing tree stock, reflected in higher soil C stocks and basal soil respiration (R10). Rs was similar between the two forests (2015: 14.5 ± 1.2 t C yr−1 broadleaved; 12.8 ± 1.0 t C yr−1 coniferous). Modelled annual contribution of Ra was ~ 45 % at both forests with a low autotrophic contribution during winter and high contribution during the monsoon season. Ra, estimated from trenching, was lower and highly variable, indicating that trenching poorly performed at these forests/soils. Rs neatly followed the annual course of soil temperature (field Q10 between 4 and 5) at both sites. Co-variation between soil temperature and moisture likely was the main cause for the high Q10 obtained from field Rs. Temperature sensitivity of Rh was lower (Q10 ~ 2.3 at both sites). Under the preceding weather conditions, a simple temperature-driven model was able to explain more than 90 % of the temporal variation in Rs. To predict and understand how Rs responds to infrequently occurring extreme climate conditions such as monsoon failures, however, longer Rs time series are required for a better integration of interactions between soil temperature, moisture, Ra and Rh.

scholarly journals Soil CO<sub>2</sub> efflux from two mountain forests in the eastern Himalayas, Bhutan: components and controls

2017 ◽  
Vol 14 (1) ◽  
pp. 99-110 ◽  
Author(s):  
Norbu Wangdi ◽  
Mathias Mayer ◽  
Mani Prasad Nirola ◽  
Norbu Zangmo ◽  
Karma Orong ◽  
...  
Keyword(s):  
Soil Respiration ◽  
Soil Temperature ◽  
Mixed Forest ◽  
Co2 Efflux ◽  
Measured Temperature ◽  
Mountain Forests ◽  
Broadleaf Forest ◽  
Eastern Himalayas ◽  
Forest Sites ◽  
C Stocks

Abstract. The biogeochemistry of mountain forests in the Hindu Kush Himalaya range is poorly studied, although climate change is expected to disproportionally affect the region. We measured the soil CO2 efflux (Rs) at a high-elevation (3260 m) mixed forest and a lower-elevation (2460 m) broadleaf forest in Bhutan, eastern Himalayas, during 2015. Trenching was applied to estimate the contribution of autotrophic (Ra) and heterotrophic (Rh) soil respiration. The temperature (Q10) and the moisture sensitivities of Rh were determined under controlled laboratory conditions and were used to model Rh in the field. The higher-elevation mixed forest had a higher standing tree stock, reflected in higher soil C stocks and basal soil respiration. Annual Rs was similar between the two forest sites (14.5 ± 1.2 t C ha−1 for broadleaf; 12.8 ± 1.0 t C ha−1 for mixed). Modelled annual contribution of Rh was  ∼  65 % of Rs at both sites with a higher heterotrophic contribution during winter and lower contribution during the monsoon season. Rh, estimated from trenching, was in the range of modelled Rh but showed higher temporal variability. The measured temperature sensitivity of Rh was similar at the mixed and broadleaf forest sites (Q10 2.2–2.3) under intermediate soil moisture but decreased (Q10 1.5 at both sites) in dry soil. Rs closely followed the annual course of field soil temperature at both sites. Covariation between soil temperature and moisture (cold dry winters and warm wet summers) was likely the main cause for this close relationship. Under the prevailing weather conditions, a simple temperature-driven model was able to explain more than 90 % of the temporal variation in Rs. A longer time series and/or experimental climate manipulations are required to understand the effects of eventually occurring climate extremes such as monsoon failures.

scholarly journals Soil CO<sub>2</sub> efflux from mountainous windthrow areas: dynamics over 12 years post-disturbance

2014 ◽  
Vol 11 (21) ◽  
pp. 6081-6093 ◽  
Author(s):  
M. Mayer ◽  
B. Matthews ◽  
A. Schindlbacher ◽  
K. Katzensteiner
Keyword(s):  
Soil Temperature ◽  
Initial Phase ◽  
Forest Disturbance ◽  
Mixed Forest ◽  
Tree Regeneration ◽  
Forest Site ◽  
Co2 Efflux ◽  
Soil C ◽  
C Stocks ◽  
Atmospheric Co2 Concentrations

Abstract. Windthrow-driven changes in carbon (C) allocation and soil microclimate can affect soil carbon dioxide (CO2) efflux (Fsoil) from forest ecosystems. Although Fsoil is the dominant C flux following stand-replacing disturbance, the effects of catastrophic windthrow on Fsoil are still poorly understood. We measured Fsoil at a montane mixed-forest site and at a subalpine spruce forest site from 2009 until 2012. Each site consisted of an undisturbed forest stand and two adjacent partially cleared (stem-fraction-harvested) windthrow areas, which differed with regard to the time since disturbance. The combination of chronosequence and direct time-series approaches enabled us to investigate Fsoil dynamics over 12 years post-disturbance. At both sites Fsoil rates did not differ significantly from those of the undisturbed stands in the initial phase after disturbance (1–6 years). In the later phase after disturbance (9–12 years), Fsoil rates were significantly higher than in the corresponding undisturbed stand. Soil temperature increased significantly following windthrow (by 2.9–4.8 °C), especially in the initial phase post-disturbance when vegetation cover was sparse. A significant part (15–31%) of Fsoil from the windthrow areas was attributed to the increase in soil temperature. According to our estimates, ~500–700 g C m−2 year−1 are released via Fsoil from south-facing forest sites in the Austrian Calcareous Alps in the initial 6 years after windthrow. With a high browsing pressure suppressing tree regeneration, post-disturbance net loss of ecosystem C to the atmosphere is likely to be substantial unless forest management is proactive in regenerating such sites. An increase in the frequency of forest disturbance by windthrow could therefore decrease soil C stocks and feed back positively on rising atmospheric CO2 concentrations.

scholarly journals Warming increases soil respiration in a carbon-rich soil without changing microbial respiratory potential

2020 ◽  
Author(s):  
Marion Nyberg ◽  
Mark J. Hovenden
Keyword(s):  
Soil Respiration ◽  
Community Composition ◽  
Plant Community ◽  
Climate Feedback ◽  
Co2 Efflux ◽  
Plant Community Composition ◽  
Soil C ◽  
Incubation Experiments ◽  
C Stocks ◽  
Respiratory Potential

Abstract. Increases in global temperatures due to climate change threaten to tip the balance between carbon (C) fluxes, liberating large amounts of C from soils. Evidence of warming-induced increases in CO2 efflux from soils has led to suggestions that this response of soil respiration (Rs) will trigger a positive land C–climate feedback cycle, ultimately warming the earth further. Currently, there is little consensus about the mechanisms driving the warming-induced Rs response, and there are relatively few studies from ecosystems with large soil C stores. Here, we investigate the impacts of experimental warming on Rs in the C-rich soils of a Tasmanian grassy sedgeland, and whether alterations of plant community composition or differences in microbial respiratory potential could contribute to any effects. In situ, warming increased Rs on average by 28 % and this effect was consistent over time and across plant community composition treatments. In contrast, warming had no impact on microbial respiration in incubation experiments. Plant community composition manipulations did not influence Rs or the Rs response to warming. Processes driving the Rs response in this experiment were, therefore, not due plant community effects and are more likely due to increases in belowground autotrophic respiration and the supply of labile substrate through rhizodeposition and root exudates. CO2 efflux from this high-C soil increased by more than a quarter in response to warming, suggesting inputs need to increase by at least this amount if soil C stocks are to be maintained. These results indicate the need for comprehensive investigations of both C inputs and losses from C-rich soils if efforts to model net ecosystem C exchange of these crucial, C-dense systems are to be successful.

scholarly journals Warming increases soil respiration in a carbon-rich soil without changing microbial respiratory potential

2020 ◽  
Vol 17 (17) ◽  
pp. 4405-4420
Author(s):  
Marion Nyberg ◽  
Mark J. Hovenden
Keyword(s):  
Soil Respiration ◽  
Community Composition ◽  
Plant Community ◽  
Climate Feedback ◽  
Co2 Efflux ◽  
Plant Community Composition ◽  
Soil C ◽  
C Stocks ◽  
Below Ground ◽  
Respiratory Potential

Abstract. Increases in global temperatures due to climate change threaten to tip the balance between carbon (C) fluxes, liberating large amounts of C from soils. Evidence of warming-induced increases in CO2 efflux from soils has led to suggestions that this response of soil respiration (RS) will trigger a positive land C–climate feedback cycle, ultimately warming the Earth further. Currently, there is little consensus about the mechanisms driving the warming-induced RS response, and there are relatively few studies from ecosystems with large soil C stores. Here, we investigate the impacts of experimental warming on RS in the C-rich soils of a Tasmanian grassy sedgeland and whether alterations of plant community composition or differences in microbial respiratory potential could contribute to any effects. In situ, warming increased RS on average by 28 %, and this effect was consistent over time and across plant community composition treatments. In contrast, warming had no impact on microbial respiration in incubation experiments. Plant community composition manipulations did not influence RS or the RS response to warming. Processes driving the RS response in this experiment were, therefore, not due to plant community effects and are more likely due to increases in below-ground autotrophic respiration and the supply of labile substrate through rhizodeposition and root exudates. CO2 efflux from this high-C soil increased by more than a quarter in response to warming, suggesting inputs need to increase by at least this amount if soil C stocks are to be maintained. These results indicate the need for comprehensive investigations of both C inputs and losses from C-rich soils if efforts to model net ecosystem C exchange of these crucial, C-dense systems are to be successful.

scholarly journals Soil CO<sub>2</sub> efflux from mountainous windthrow areas: dynamics over 12 years post-disturbance

2014 ◽  
Vol 11 (5) ◽  
pp. 6383-6417 ◽  
Author(s):  
M. Mayer ◽  
B. Matthews ◽  
A. Schindlbacher ◽  
K. Katzensteiner
Keyword(s):  
Soil Temperature ◽  
Vegetation Cover ◽  
Initial Phase ◽  
Forest Disturbance ◽  
Mixed Forest ◽  
Forest Site ◽  
Co2 Efflux ◽  
Soil C ◽  
C Stocks ◽  
Later Phase

Abstract. Windthrow driven changes in carbon (C) allocation and soil microclimate can affect soil carbon dioxide (CO2) efflux (Fsoil) of forest ecosystems. Although Fsoil is the dominant C flux following stand-replacing disturbance, the effects of catastrophic windthrow on Fsoil are still poorly understood. We measured Fsoil at a montane mixed forest site and at a subalpine spruce forest site from 2009 until 2012. Both sites consisted of undisturbed forest stands and two adjacent windthrow areas which differed in time since disturbance. The combination of chronosequence and direct time-series approaches enabled us to investigate Fsoil dynamics over 12 years post-disturbance. In the initial phase after disturbance (1–6 years), Fsoil rates did not differ significantly from those of the undisturbed stands, but in the later phase (9–12 years after disturbance) Fsoil rates were significantly higher than corresponding undisturbed stand values. The higher Fsoil rates in the later phase post-disturbance are likely explained by a dense vegetation cover and correspondingly higher autotrophic respiration rates. Soil temperature increased significantly following windthrow (by 2.9–4.8 °C) especially in the initial phase post-disturbance when vegetation cover was sparse. A significant part (20–36%) of Fsoil from the windthrow areas was thus attributed to disturbance induced changes in soil temperature. According to our estimates, ~500 to 700 g C m−2yr−1 are released via Fsoil from south-facing forest sites in the Austrian Calcareous Alps in the initial 6 years after windthrow. With high game pressure suppressing primary production in these areas, post-disturbance loss of ecosystem C to the atmosphere is likely to be substantial unless management is proactive in regenerating such sites. An increase in the frequency of forest disturbance by windthrow could therefore decrease soil C stocks and positively feedback on rising atmospheric CO2 concentrations.

scholarly journals Distinct patterns in the diurnal and seasonal variability in four components of soil respiration in a temperate forest under free-air CO<sub>2</sub> enrichment

2011 ◽  
Vol 8 (10) ◽  
pp. 3077-3092 ◽  
Author(s):  
L. Taneva ◽  
M. A. Gonzalez-Meler
Keyword(s):  
Soil Respiration ◽  
Seasonal Variability ◽  
Ecosystem Respiration ◽  
Co2 Efflux ◽  
Diurnal Variability ◽  
Soil C ◽  
Free Air ◽  
C Cycle ◽  
Strong Control ◽  
Average Contribution

Abstract. Soil respiration (RS) is a major flux in the global carbon (C) cycle. Responses of RS to changing environmental conditions may exert a strong control on the residence time of C in terrestrial ecosystems and in turn influence the atmospheric concentration of greenhouse gases. Soil respiration consists of several components oxidizing soil C from different pools, age and chemistry. The mechanisms underlying the temporal variability of RS components are poorly understood. In this study, we used the long-term whole-ecosystem 13C tracer at the Duke Forest Free Air CO2 Enrichment site to separate forest RS into its autotrophic (RR) and heterotrophic components (RH). The contribution of RH to RS was further partitioned into litter decomposition (RL), and decomposition of soil organic matter (RSOM) of two age classes – up to 8 yr old and SOM older than 8 yr. Soil respiration was generally dominated by RSOM during the growing season (44% of daytime RS), especially at night. The contribution of heterotrophic respiration (RSOM and RL) to RS was not constant, indicating that the seasonal variability in RR alone cannot explain seasonal variation in RS. Although there was no diurnal variability in RS, there were significant compensatory differences in the contribution of individual RS components to daytime and nighttime rates. The average contribution of RSOM to RS was greater at night (54%) than during the day (44%). The average contribution of RR to total RS was ~30% during the day and ~34% during the night. In contrast, RL constituted 26% of RS during the day and only 12% at night. About 95% of the decomposition of soil C older than 8 yr (Rpre-tr) originated from RSOM and showed more pronounced and consistent diurnal variability than any other RS component; nighttime rates were on average 29% higher than daytime rates. In contrast, the decomposition of more recent, post-treatment C (Rpre-tr) did not vary diurnally. None of the diurnal variations in components of RH could be explained by only temperature and moisture variations. Our results indicate that the variation observed in the components of RS is the result of complex interaction between dominant biotic controls (e.g. plant activity, mineralization kinetics, competition for substrates) over abiotic controls (temperature, moisture). The interactions and controls among roots and other soil organisms that utilize C of different chemistry, accessibility and ages, results in the overall soil CO2 efflux. Therefore understanding the controls on the components of RS is necessary to elucidate the influence of ecosystem respiration on atmospheric C-pools at different time scales.

scholarly journals Soil respiration on an aging managed heathland: identifying an appropriate empirical model for predictive purposes

2013 ◽  
Vol 10 (5) ◽  
pp. 3007-3038 ◽  
Author(s):  
G. R. Kopittke ◽  
E. E. van Loon ◽  
A. Tietema ◽  
D. Asscheman
Keyword(s):  
Soil Respiration ◽  
Soil Temperature ◽  
Cultural Landscapes ◽  
Plant Biomass ◽  
Model Fit ◽  
Selection Procedures ◽  
Soil C ◽  
Experimental Planning ◽  
Improve Model ◽  
Level Model

Abstract. Heathlands are cultural landscapes which are managed through cyclical cutting, burning or grazing practices. Understanding the carbon (C) fluxes from these ecosystems provides information on the optimal management cycle time to maximise C uptake and minimise C output. The interpretation of field data into annual C loss values requires the use of soil respiration models. These generally include model variables related to the underlying drivers of soil respiration, such as soil temperature, soil moisture and plant activity. Very few studies have used selection procedures in which structurally different models are calibrated, then validated on separate observation datasets and the outcomes critically compared. We present thorough model selection procedures to determine soil heterotrophic (microbial) and autotrophic (root) respiration for a heathland chronosequence and show that soil respiration models are required to correct the effect of experimental design on soil temperature. Measures of photosynthesis, plant biomass, photosynthetically active radiation, root biomass, and microbial biomass did not significantly improve model fit when included with soil temperature. This contradicts many current studies in which these plant variables are used (but not often tested for parameter significance). We critically discuss a number of alternative ecosystem variables associated with soil respiration processes in order to inform future experimental planning and model variable selection at other heathland field sites. The best predictive model used a generalized linear multi-level model with soil temperature as the only variable. Total annual soil C loss from the young, middle and old communities was calculated to be 650, 462 and 435 g C m−2 yr−1, respectively.

scholarly journals Significance of soil respiration from biological activity in the degradation processes of different types of organic matter

2020 ◽  
Vol 1 (2) ◽  
pp. 171-179
Keyword(s):  
Climate Change ◽  
Organic Matter ◽  
Soil Moisture ◽  
Soil Respiration ◽  
Soil Temperature ◽  
Temperature Sensitivity ◽  
Soil Co2 Efflux ◽  
Co2 Efflux ◽  
Soil Co2 ◽  
Total Soil

Soil respiration is a major component of global carbon cycle. Therefore, it is crucial to understand the environmental controls on soil respiration for evaluating potential response of ecosystems to climate change. In a temperate deciduous forest (located in Northern-Hungary) we added or removed aboveground and belowground litter to determine total soil respiration. We investigated the relationship between total soil CO2 efflux, soil moisture, and soil temperature. Soil CO2 efflux was measured at each plot using soda-lime method. Temperature sensitivity of soil respiration (Q10) was monitored via measuring soil temperature on an hourly basis, while soil moisture was determined monthly. Soil respiration increased in control plots from the second year after implementing the treatment, but results showed fluctuations from one year to another. The effect of doubled litter was less significant than the effect of removal. Removed litter and root inputs caused substantial decrease in soil respiration. We found that temperature was more influential in the control of soil respiration than soil moisture. In plots with no litter Q10 varied in the largest interval. For treatment with doubled litter layer, temperature sensitivity of CO2 efflux did not change considerably. The effect of increasing soil temperature is more conspicuous to soil respiration in litter removal treatments since lack of litter causes greater irradiation. When exclusively leaf litter was considered, the effect of temperature on soil respiration was lower in treatments with added litter than with removed litter. Our results reveal that soil life is impacted by the absence of organic matter, rather than by an excess of organic matter. Results of CO2 emission from soils with different organic matter content can contribute to sustainable land use, considering the changed climatic factors caused by global climate change.

scholarly journals Spatial and temporal variation of CO<sub>2</sub> efflux along a disturbance gradient in a <i>miombo</i> woodland in Western Zambia

2011 ◽  
Vol 8 (1) ◽  
pp. 147-164 ◽  
Author(s):  
L. Merbold ◽  
W. Ziegler ◽  
M. M. Mukelabai ◽  
W. L. Kutsch
Keyword(s):  
Soil Respiration ◽  
Soil Temperature ◽  
Temporal Variation ◽  
Carbon Content ◽  
Ecosystem Respiration ◽  
Spatial And Temporal Variation ◽  
Co2 Efflux ◽  
Forest Reserve ◽  
Disturbance Gradient ◽  
Total Ecosystem Respiration

Abstract. Carbon dioxide efflux from the soil surface was measured over a period of several weeks within a heterogeneous Brachystegia spp. dominated miombo woodland in Western Zambia. The objectives were to examine spatial and temporal variation of soil respiration along a disturbance gradient from a protected forest reserve to a cut, burned, and grazed area outside, and to relate the flux to various abiotic and biotic drivers. The highest daily mean fluxes (around 12 μmol CO2 m−2 s−1) were measured in the protected forest in the wet season and lowest daily mean fluxes (around 1 μmol CO2 m−2 s−1) in the most disturbed area during the dry season. Diurnal variation of soil respiration was closely correlated with soil temperature. The combination of soil water content and soil temperature was found to be the main driving factor at seasonal time scale. There was a 75% decrease in soil CO2 efflux during the dry season and a 20% difference in peak soil respiratory flux measured in 2008 and 2009. Spatial variation of CO2 efflux was positively related to total soil carbon content in the undisturbed area but not at the disturbed site. Coefficients of variation of efflux rates between plots decreased towards the core zone of the protected forest reserve. Normalized soil respiration values did not vary significantly along the disturbance gradient. Spatial variation of respiration did not show a clear distinction between the disturbed and undisturbed sites and could not be explained by variables such as leaf area index. In contrast, within plot variability of soil respiration was explained by soil organic carbon content. Three different approaches to calculate total ecosystem respiration (Reco) from eddy covariance measurements were compared to two bottom-up estimates of Reco obtained from chambers measurements of soil- and leaf respiration which differed in the consideration of spatial heterogeneity. The consideration of spatial variability resulted only in small changes of Reco when compared to simple averaging. Total ecosystem respiration at the plot scale, obtained by eddy covariance differed by up to 25% in relation to values calculated from the soil- and leaf chamber efflux measurements but without showing a clear trend.

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

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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