Variation In Soil CO2 Efflux Research Articles

Variação temporal do efluxo de CO2do solo em sistemas agroflorestais com palma de óleo na Amazônia Oriental

RESUMOA dinâmica do efluxo de dióxido de carbono (CO2) do solo e seus fatores controladores em sistemas agroflorestais da Amazônia são pouco compreendidas. O objetivo deste estudo foi avaliar a variação temporal do efluxo de CO2 do solo em sistemas agroflorestais onde a palma de óleo é a cultura principal e sua relação com fatores bióticos (carbono microbiano do solo, carbono total do solo, respiração microbiana do solo, raízes finas do solo, indivíduos componentes dos sistemas agroflorestais (SAFs) ) e abióticos (umidade e temperatura do solo). As medições foram realizadas nos períodos menos chuvoso (dezembro de 2010) e chuvoso (maio de 2011). O efluxo de CO2do solo foi mais alto no período chuvoso, provavelmente, devido à maior atividade microbiana nesse período influenciada por fatores climáticos aliados a fatores bióticos. O efluxo de CO2do solo se correlacionou positivamente com umidade do solo e carbono da biomassa microbiana e negativamente com temperatura do solo e quociente metabólico, porém as correlações foram fracas. O efluxo de CO2do solo foi sensível ao tipo de sistema agroflorestal e a sazonalidade da precipitação.

Variability of soil organic carbon stocks and soil CO2 efflux across urban land use and soil cover types

Urban soils are an important soil organic carbon (SOC) store, but soils are also a natural source of carbon dioxide (CO2) due to soil CO2 efflux derived from decomposition and root related respiration. Little is known about the temporal and spatial variability of SOC stocks and soil CO2 efflux in urban areas, in particular in the southern hemisphere. The objectives of our study were to quantify SOC stocks and soil CO2 efflux in tree (urban forests) and grass dominated (parklands) urban ecosystems and to investigate the underlying processes which determine urban SOC stocks and soil CO2 efflux. Soil organic C stocks were quantified to 30cm depth and soil CO2 efflux was determined using a closed chamber technique at 16 sites across Auckland, New Zealand. Vegetation and soil characteristics were measured to 30cm depth at each study plot. In addition, the diurnal and seasonal variability in soil CO2 efflux was assessed at six sites. Median soil organic C stocks (0–10cm) were significantly higher in parkland soils (4.8kgm−2, IQR: 0.9) compared to urban forest soils (2.7kgm−2, IQR: 0.1), which was largely due to higher bulk densities in parkland soils. In contrast, median soil CO2 efflux was not significantly different between parklands (5.2μmolm−2s−1, IQR: 0.8) and urban forests (4.5μmolm−2s−1, IQR: 1.9) sites. This suggests that increasing soil bulk densities without restricting root growth may enhance SOC stocks without increasing soil CO2 efflux. Soil temperature and soil water content explained 54% (urban parkland) and 71% (urban forests) of the temporal variation in soil CO2 efflux. Urban SOC stocks and soil CO2 efflux were similar to non-urban forests and grasslands in New Zealand, highlighting the importance of considering urban soils when assessing SOC stocks and soil CO2 efflux.

Measurement of environmental parameters in polar regions based on a ubiquitous sensor network

To estimate the spatial variation of soil CO2 flux in a permafrost region, major environmental parameters were measured and analyzed using the proposed ubiquitous sensor network-based remote monitoring system (U-RMS). The use of techniques for power-efficient operation and network scalability that enable long-term use of a wireless sensor network (WSN) that can be deployed reliably and widely is described. The temporal and spatial variations in air temperature (Ta) and relative humidity (RH) near the surface at 16 locations and soil temperature (Ts) and soil water content (SWC) at 10 locations were measured to monitor the active permafrost layer in Alaska from September 2012 to January 2013 and from July to September 2013. The temporal variations in environmental parameters in the soil and near the surface depended on the thawing and freezing of the snow cover in the permafrost regions. The spatial patterns of Ts in the three periods were not similar because of the heterogeneous distribution of snow coverage and depth in winter. On the other hand, the spatial patterns of Ts and SWC had a negative relationship during summer. The spatial variations in Ts and SWC showed a high coefficient of variation (CV) that ranged from 20% to 40%, while the CV of Ta and RH was within 5% except in winter due to the spatially heterogeneous snow cover. The relationship between CO2 efflux and Ts or SWC in 2012, which had a high CV, was examined to estimate the soil CO2 efflux in 2013. The Ts explained ~60% (soil CO2 efflux=0.066×exp0.1443×Ts, R2 0.59) of the variation in soil CO2 efflux in a temperature range of 3 to 8°C. Therefore, the soil CO2 efflux in 2013 was estimated in the range of 0.08mgm−2s−1 to 0.47mgm−2s−1, and average CV was 25%. Using the camera sensor, the growth of vegetation and the operating appearance of the remote WSN were also monitored. In the long term, measurement of temporal and spatial variations in environmental parameters, based on U-RMS, is expected to contribute to the understanding of the carbon and water cycles in permafrost.

CO2 efflux from the biological soil crusts of the High Arctic in a later stage of primary succession after deglaciation, Ny-Ålesund, Svalbard, Norway

The CO2 efflux from representative tundra ecosystems in the high Arctic should be monitored in order to evaluate the potential future sensitivity of the carbon cycle to climate change. However, studies on the soil CO2 efflux from them are still limited, especially deglaciated area due to the Arctic warming. The ecosystem in Ny-Ålesund, Svalbard, Norway (∼79°N) has gradually undergone substantial alterations due to deglaciation induced by climate change, where biological soil crusts (BSCs, mainly consisting of cyanobacteria, algae, lichen, and bryophytes, etc. on the soil surface) are widely formed in the glacier foreland and further developed especially in the later stages of primary succession. In this study, soil CO2 efflux from partly or totally covered with black-colored BSCs (BSCs-B) was measured from 2007 to 2009 using portable dynamic chamber system. The objectives of this study were (i) to quantify the CO2 efflux from the soil, (ii) to examine the controlling factors which affect the temporal and spatial variation of soil CO2 efflux, (iii) to examine the contribution of BSCs-B to soil CO2 efflux, and (iv) to estimate the relationship between soil CO2 efflux and microbial activity to evaluate its role on the surface carbon budget at deglaciated area. It was found that the emission of soil CO2 from BSCs-B was consistent through the long-term in situ measurement in the high arctic tundra. Soil CO2 efflux ranged from 0.3 to 0.7μmolm−2s−1 with means of 0.56 (±0.07)μmolm−2s−1 in 2007, 0.54 (±0.13)μmolm−2s−1 in 2008, and 0.51 (±0.09)μmolm−2s−1 in 2009. The soil temperature (Ts) explained 50–70% of the temporal variation of the soil CO2 efflux when temperature ranged from 6 to 12°C, whereas Ts is not controlling factor for spatial variation of soil CO2 efflux considering the low coefficient of variation (CV). In the meanwhile, soil water content (SWC) was not a main controlling factor for temporal variation of soil CO2 efflux. Even though CV of SWC was not low, spatial variation of SWC could not explain that of soil CO2 efflux. The soil CO2 efflux was spatially affected by BSCs-B coverage, amount of pebble, and the nearby vegetation distribution. All enzyme activities exhibited significantly higher values in BSCs-B than in mineral soil of BSCs (p<0.01). The activities of enzymes in BSCs-B generally exhibited positive correlations with the soil CO2 efflux except for humic substances (R2=0.52). It can be concluded that the magnitude of the soil CO2 efflux from BSCs-B is comparable to those from moss and vascular plants in the surface carbon budget.

A multisite analysis of temporal random errors in soil CO2 efflux

AbstractAn important component of the terrestrial carbon balance is the efflux of CO2 from soils to the atmosphere, which is strongly influenced by changes in soil moisture and temperature. Continuous measurements of soil CO2 efflux are available around the world, and there is a need to develop and improve analyses to better quantify the precision of the measurements. We focused on random errors in measurements, which are caused by unknown and unpredictable changes such as fluctuating environmental conditions. We used the CO2 gradient flux method with two different algorithms to study the temporal variation of soil CO2 efflux and associated random errors at four different ecosystems with wide ranges in mean annual temperature, soil moisture, and soil CO2 efflux. Our results show that random errors were better explained by a double‐exponential distribution, had a mean value close to zero, were nonheteroscedastic, and were independent of soil moisture conditions. Random errors increased with the magnitude of soil CO2 efflux and scale isometrically (scaling exponent ≈ 1) within and across all sites, with a single relation common to all data. This isometric scaling is unaffected by ecosystem type, soil moisture conditions, and soil CO2 efflux range (maximum and minimum values within an ecosystem). These results suggest larger uncertainty under extreme events that increase soil CO2 efflux rates. The accumulated annual uncertainty due to random errors varied between ±0.38 and ±2.39%. These results provide insights on the scalability of the sensitivity of soil CO2 efflux to changing weather conditions across ecosystems.

Spatial variability at different scales and sampling requirements for in situ soil CO2 efflux measurements on an arable soil

The experimental determination of soil CO2 efflux and the investigation of the effect of different treatments require several replicates. However, the required number depends on various factors (soil properties, spatial heterogeneity, etc.). Moreover, the spatial and temporal scales have an impact on the uncertainty of CO2 efflux determination. Here, we characterize the spatial variability of soil CO2 efflux at different scales, analyze the drivers of CO2 efflux, and assess the required number of samples for obtaining CO2 efflux determinations. In situ CO2 efflux measurements were made in situ at an agricultural site with different treatments of organic manures from biogas plants at 21 dates during the growing season of 2years. Overall variability of CO2 efflux was characterized by CV values of about 27%, with a range between 10 and 57%. Small-scale variability (within plots) was on average larger than large-scale variability between the blocks. All variability components showed a pronounced seasonal variability. Consequently, spatial variability patterns determined at a site for one date and at a specific scale are not representative for all measurement dates and for larger or smaller scales. The spatial variation in CO2 efflux seems to be driven by soil temperature, soil water content, year, C/N ratio, treatment and block. The estimated numbers of required replicates based on statistical considerations were often larger than the actual number of replicates (n=16). Monte Carlo type simulations showed that deviations from an estimated reference value largely depend on the variability and number of (sub)samples.

Contribution of soil moisture to seasonal and annual variations of soil CO2 efflux in a humid cool‐temperate oak‐birch forest in central Japan

AbstractTo quantify the contribution of soil moisture to seasonal and annual variations in soil CO2 efflux in a cool‐humid deciduous broadleaf forest, we measured soil CO2 efflux during the snow‐free seasons of 2005–2008 using an automated chamber technique. This worked much better than manual chambers employing the same steady‐state through‐flow method. Soil CO2 efflux (g C m−2 period−1) during the snow‐free season ranged from 979.8 ± 49.0 in 2005 to 1131.2 ± 56.6 in 2008 with a coefficient variation of 6.4 % among the 4 years. We established two‐parameter (soil temperature and moisture) empirical models, finding that while soil temperature and moisture explained 69–86 % and 10–13 % of the temporal variability, respectively. Soil moisture had the effect of modifying the temporal variability of soil CO2 efflux, particularly during summer and early fall after episodic rainfall events; greater soil moisture enhanced soil CO2 efflux in the surface soil layers. High soil moisture conditions did not suppress soil CO2 efflux, leading to a positive correlation between normalized soil CO2 efflux (ratio of the measured to predicted efflux using a temperature‐dependent Q10 function) and soil moisture. Therefore, enhanced daily soil CO2 efflux following heavy rainfall events could significantly reduce net ecosystem exchange (i.e. daily net ecosystem production) by 32 % on some days. Our results highlight the importance of precisely estimating the response of soil CO2 efflux to changes in soil moisture following rainfall events when modeling seasonal carbon dynamics in response to climate change, even in humid monsoon regions.

English

Forest biomass is a major component in carbon sequestration and a driver of heterotrophy and autotrophy soil CO2 efflux, as it accumulation increases carbon organic nutrients, root growth and microbial activity. Understanding forest biomass rational to ascertain the forest ecosystems productivity is important. A study has been conducted in a 70-year-old forest of mixed tree species, Sungai Menyala Forest, Port Dickson, Peninsular Malaysia, measuring the total above ground biomass (TAGB), below ground biomass (BGB), total forest carbon (SOCs), soil organic carbon stock (SOCstoc) and soil CO2 efflux from 1 February to 30 June 2013. The aim was to determine the effect of forest biomass, litter fall and influence of environmental factors on soil CO2 efflux. Multiple regression analysis has been conducted on the relationship between the variables and the soil CO2 efflux. Soil CO2 efflux was found to range from 92.09-619.67 mg m-2 h-1, with the amount of the tropical forest biomass estimated at 1.9×106, 7.7×106 and 9.2×105 kg for TAGB, BGB and SOCs, respectively. The analysis showed a strong correlation between soil CO2 efflux and soil temperature, soil moisture, water potential and forest carbon input with R2 more than 0.89 at p<0.01. The findings showed a strong contribution from forest biomass as drivers of heterotrophy and autotrophy soil CO2 efflux. We can conclude that the forest biomass and environmental factors are responsible for the remarkable variation in soil CO2 efflux, as climate change can cause increase in temperature as well as deforestation decreases forest biomass.

Factors responsible for spatial and temporal variation of soil CO2 efflux in a 50 year recovering tropical forest, Peninsular Malaysia

Environmental abiotic and biotic factors are important in controlling soil CO2 efflux in forest ecosystems of different ages, as they play an important role in soil respiration. In understanding the spatial and temporal variation of soil CO2 efflux after several years of forest logging, there is a need to quantify the changing soil properties, environmental factors, and the total above and below ground biomass. This study was conducted in a 50-year old recovering tropical lowland forest in Peninsular Malaysia, measuring soil CO2 efflux using the continuous open flow chambers technique connected to a multi gas-handling unit and infrared gas analyser. The aim of this study was to determine the spatial and temporal variation of soil CO2 efflux in relation to changes in soil properties, environmental factors and forest carbon in a recovering forest. The efflux rates of about 389.20, 634.78, 564.81, 537.92 and 428.72 mg m−2 h−1, respectively, varied across the days and months, increasing from February and attaining the maximum in March and then gradually decreasing from April to June. The soil properties revealed a considerable amount of soil organic carbon, total organic carbon, and soil organic carbon stock, while the total above ground biomass, below ground biomass, soil pH, nitrogen to carbon ratio were found to provide nutrients for microbial activities in soil and to emit soil CO2. The multiple linear regression model indicated that the soil temperature and moisture explained the spatial and temporal variation in soil CO2 efflux; likewise, the changes in the soil properties and forest carbon significantly increased the soil CO2 efflux indicating a strong positive correlation (R 2 = 0.93).

The effects of an induced short-term drought period on the spatial variations in soil respiration measured around emergent trees in a typical bornean tropical forest, Malaysia

Our previous studies documented how soil CO2 efflux, one of the main carbon pathways in forest ecosystems, is affected by soil moisture and forest structure in an aseasonal tropical rainforest in Borneo, Malaysia. In this study, we clarify the effect of short-term drought treatment on the spatial variation of soil CO2 efflux in a forest, and to interpret the changes in soil CO2 efflux caused by root activities. Experimental plots (15 m radius) were established around six emergent trees and a drought treatment was conducted for three of the six plots. Soil CO2 efflux was measured along with environmental factors and root biomass, respiration and production in each plot. Soil CO2 efflux at 0.5 m of the emergent trees was nearly three times higher than at 5 and 10 m away from the trees. Root respiration and biomass had no correlation with the spatial variation. Soil water content decreased by nearly 30 % during the drought treatment, although soil CO2 efflux was unchanged between drought and control plots. Our result suggests a strong spatial variation exists in soil CO2 efflux around emergent trees, but short-term severe drought has little effect on it.

Hot spots, hot moments, and spatio-temporal controls on soil CO2 efflux in a water-limited ecosystem

Soil CO2 efflux is the primary source of CO2 emissions from terrestrial ecosystems to the atmosphere. The rates of this flux vary in time and space producing hot moments (sudden temporal high fluxes) and hot spots (spatially defined high fluxes), but these high reaction rates are rarely studied in conjunction with each other. We studied temporal and spatial variation of soil CO2 efflux in a water-limited Mediterranean ecosystem in Baja California, Mexico. Soil CO2 efflux increased 522% during a hot moment after rewetting of soils following dry summer months. Monthly precipitation was the primary driver of the seasonal trend of soil CO2 efflux (including the hot moment) and through changes in soil volumetric water content (VWC) it influenced the relationship between CO2 efflux and soil temperature. Geostatistical analyses showed that the spatial dependence of soil CO2 efflux changed between two contrasting seasons (dry and wet). During the dry season high soil VWC was associated with high soil CO2 efflux, and during the wet season the emergence of a hot spot of soil CO2 efflux was associated with higher root biomass and leaf area index. These results suggest that sampling designs should accommodate for changes in spatial dependence of measured variables. The spatio-temporal relationships identified in this study are arguably different from temperate ecosystems where the majority of soil CO2 efflux research has been done. This study provides evidence of the complexity of the mechanisms controlling the spatio-temporal variability of soil CO2 efflux in water-limited ecosystems.

Spatial heterogeneity of soil CO2 efflux after harvest and prescribed fire in a California mixed conifer forest

Spatial variability is a key factor when quantifying soil CO2 efflux and punctual measurements need to be extended to larger stand, ecosystem, or regional scales. Spatial variation also affects comparisons among ecosystems, as when quantifying effects of disturbances on ecosystem carbon dynamics. However, spatial variability of soil CO2 efflux is still unknown and difficult to predict. We quantified the effects of silvicultural practices (prescribed fire and harvesting) on spatial variability of soil CO2 efflux in a mixed conifer forest from the central Sierra Nevada in California, USA. Soil CO2 efflux was measured using a portable chamber system, on 20–29 locations in four treatment sites: an untreated control, a prescribed fire site (burned in 2002 and 2009) and two clear cut sites harvested in 2010. In one of the harvested sites the soils were mechanically ripped to reduce soil compaction, a common practice done on industrial timber forest lands in the Sierra Nevada. Results showed that disturbance increased spatial variability of soil CO2 efflux. Coefficient of variability increased from an annual average of 32% at the control site to 37% at the burned site, and 49–51% at the harvested sites (without and with soil ripping, respectively), mirroring post-disturbance increases in spatial variability of soil temperature and soil water content. Because of the post-harvest increase in spatial variability, the ability to detect differences became lower, and the number of samples needed to obtain a value representative of the full population mean (within a 10% range) increased by 100%, from 60 to 120 samples. To reduce uncertainty in our soil CO2 efflux treatment estimates, more than 10–15 randomly selected locations per study site were necessary. Spatial variability of soil CO2 efflux at our sites was not affected by distance between measurement locations, was correlated to fine root and litter biomass at the control site, negatively correlated to soil bulk density at the fire site, and un-correlated to soil temperature and water content at all sites. The increase of spatial variability in soil CO2 efflux after disturbance and the requirement for a sufficient number of measurement locations should be considered when quantifying carbon dynamics of disturbed ecosystems, or assessing effects of different forest management practices.

Response of soil CO2 efflux to water addition in temperate semiarid grassland in northern China: the importance of water availability and species composition

Knowledge of the effects of water addition and the composition of plant species on soil CO2 efflux (SCE) and its temperature sensitivity (Q10) in temperate semiarid grassland is essential for understanding carbon (C) cycles and for evaluating future C balance. Our objective was to examine the seasonal variability of SCE and its sensitivity to temperature in response to water addition in four grasslands on the northern Loess Plateau. SCE was measured during the growing seasons (April–October) in 2010 and 2011 in the four grasslands dominated by different species: purple alfalfa (ALF), bunge needlegrass (BNE), degraded alfalfa (DALF), and fallow land for the recovery of natural vegetation (NAF), in two treatments: water addition (50 mm year−1) and a control. Water addition consistently increased mean seasonal SCE by 8.4–33.8 % across the four communities, attributable to enhanced plant growth, root and microbial activities, and respiration. The magnitudes of the positive effects, however, varied with plant community and measuring period. Soil temperature was primarily responsible for the seasonal changes in SCE in both the control (37–63 %) and the watered (40–75 %) plots. The addition of water increased the Q10 of SCE by 11.0 %, 14.4 %, and 13.4 % for ALF, DALF, and NAF, respectively, but had no significant effect on the Q10 for BNE. We therefore conclude that water addition can significantly increase SCE and may stimulate the sensitivity to temperature in semiarid grassland. The composition of plant species may regulate the dependence of SCE on water and temperature.

Variation in Soil CO2 Efflux in Pinus Wallichiana and Abies Pindrow Temperate Forests of Western Himalayas, India

Soil CO2 efflux was measured by alkali absorption method from April to December 2012 in two different forest types, i.e., Pinus wallichiana and Abies pindrow, with three replicate plots in each forest type. Soil CO2 efflux was found maximum in July and minimum in December in both the forest types. Significantly (P<0.001) greater soil CO2 efflux was measured in Pinus wallichiana forest compared to Abies pindrow forest throughout the study period. The range of soil CO2 efflux (mg CO2 m-2 hr-1) from the soil was 126-427 in Abies pindrow forest and 182-646 in Pinus wallichiana forest. Soil CO2 efflux showed greater values in Pinus wallichiana forest than Abies pindrow forest, which could be attributed to greater tree density, tree biomass, shrub density, shrub biomass, forest floor litter and moisture. Soil CO2 efflux also showed significant positive relationship with air temperature. In addition to that the altitudinal difference may be one of the reasons for variation in soil CO2 efflux between the two forest types. This result also indicates that at higher altitude even a small difference in elevation (100 m) alter the functional attributes of the ecosystem.

Variations in soil carbon dioxide efflux across a thaw slump chronosequence in northwestern Alaska

Warming of the arctic landscape results in permafrost thaw, which causes ground subsidence or thermokarst. Thermokarst formation on hillslopes leads to the formation of thermal erosion features that dramatically alter soil properties and likely affect soil carbon emissions, but such features have received little study in this regard. In order to assess the magnitude and persistence of altered emissions, we use a space-for-time substitution (thaw slump chronosequence) to quantify and compare peak growing season soil carbon dioxide (CO2) fluxes from undisturbed tundra, active, and stabilized thermal erosion features over two seasons. Measurements of soil temperature and moisture, soil organic matter, and bulk density are used to evaluate the factors controlling soil CO2 emissions from each of the three chronosequence stages. Soil CO2 efflux from the active slump is consistently less than half that observed in the undisturbed tundra or stabilized slump (1.8 versus 5.2 g CO2−C m−2 d−1 in 2011; 0.9 versus 3.2 g CO2−C m−2 d−1 in 2012), despite soil temperatures on the floor of the active slump that are 10–15 °C warmer than the tundra and stabilized slump. Environmental factors such as soil temperature and moisture do not exert a strong control on CO2 efflux, rather, local soil physical and chemical properties such as soil organic matter and bulk density, are strongly and inversely related among these chronosequence stages (r2 = 0.97), and explain ∼50% of the variation in soil CO2 efflux. Thus, despite profound soil warming and rapid exposure of buried carbon in the active slump, the low organic matter content, lack of stable vegetation, and large increases in the bulk densities in the uppermost portion of active slump soils (up to ∼2.2 g−1 cm−3) appear to limit CO2 efflux from the active slump. Future studies should assess seasonal fluxes across these features and determine whether soil CO2 fluxes from active features with high organic content are similarly low.

Temporal Variations in Soil CO2 Efflux Under Different Land Use Types in the Black Soil Zone of Northeast China

The quantification of soil CO2 efflux is crucial for better understanding the interactions between driving variables and C losses from black soils in Northeast China and for assessing the function of black soil as a net source or sink of atmospheric CO2 depending upon land use. This study investigated responses of soil CO2 efflux variability to soil temperature interactions with different soil moisture levels under various land use types including grassland, bare land, and arable (maize, soybean, and wheat) land in the black soil zone of Northeast China. The soil CO2 effluxes with and without live roots, defined as the total CO2 efflux (FtS) and the root-free CO2 efflux (FrfS), respectively, were measured from April 2009 to May 2010 using a static closed chamber technique with gas chromatography. The seasonal soil CO2 fluxes tended to increase from the beginning of the measurements until they peaked in summer and then declined afterwards. The mean seasonal FtS ranged from 20.3±7.8 to 58.1±21.3 mg CO2-C m−2 h−1 for all land use types and decreased in the order of soybean land > grassland > maize land > wheat land > bare land, while the corresponding values of FrfS were relatively lower, ranging from 20.3±7.8 to 42.3±21.3 mg CO2-C m−2 h−1. The annual cumulative FtS was in the range of 107–315 g CO2-C m−2 across all land uses types. The seasonal CO2 effluxes were significantly (P < 0.001) sensitive to soil temperature at 10 cm depth and were responsible for up to 62% of the CO2 efflux variability. Correspondingly, the temperature coefficient Q10 values varied from 2.1 to 4.5 for the seasonal FtS and 2.2 to 3.9 for the FrfS during the growing season. Soil temperature interacting with soil moisture accounted for a significant fraction of the CO2 flux variability for FtS (up to 61%) and FrfS (up to 67%) via a well-defined multiple regression model, indicating that temperature sensitivity of CO2 flux can be mediated by water availability, especially under water stress.

Temporal patterns of soil CO2 efflux in a temperate Korean Larch (Larix olgensis Herry.) plantation, Northeast China

There is little information available regarding seasonal and annual variations in soil CO2 efflux from Korean Larch plantations, which are an important component of forests’ carbon balance in temperate China. In this study, the soil respiration rate (R s), soil temperature (T 10) and soil moisture (SM10) at 10 cm depth were observed in a Korean Larch (Larix olgensis Herry.) plantation in Northeast China from 2008 to 2012. Mean R s in growing season (GS) varied greatly, ranged from 2.32 ± 0.08 to 3.88 ± 0.09 μmol CO2 m−2 s−1 (mean ± SE) over the period of 2008–2012. In comparison with T-model, the increase of explained variability by applying both T 10 and SM10 to the T-M model is very small. It is indicated that R s was controlled largely by T 10 in the present study. By accounting for 22.2 and 17.7 % of the total soil CO2 emissions in 2010/2011 and 2011/2012, respectively, the soil CO2 efflux in dormant season (DS) was an essential component of the total soil CO2 efflux. The Q 10 value in the study period was always smaller for GS than DS, suggesting that soil carbon cycling may be more sensitive to the temperature changes at low than at high temperature range. These results indicated that climate changes may have great potential impacts on temperate Larch plantations in Northeast China, owing to soil carbon emissions of Larch plantation during the long period of DS being more sensitive to T 10 than in GS, and played a significant role in the annual forest ecosystems carbon budget.

Non-growing season soil CO2 efflux and its changes in an alpine meadow ecosystem of the Qilian Mountains, Northwest China

Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative, non-growing season soil CO2 fluxes are reported to be a significant component of these systems’ annual carbon budgets. However, little information exists on soil CO2 efflux during the non-growing season from alpine ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of estimating ecosystem carbon budgets, as well as predicting the response of soil CO2 efflux to climate changes. In this study, we measured soil CO2 efflux and its spatial and temporal changes for different altitudes during the non-growing season in an alpine meadow located in the Qilian Mountains, Northwest China. Field experiments on the soil CO2 efflux of alpine meadow from the Qilian Mountains were conducted along an elevation gradient from October 2010 to April 2011. We measured the soil CO2 efflux, and analyzed the effects of soil water content and soil temperature on this measure. The results show that soil CO2 efflux gradually decreased along the elevation gradient during the non-growing season. The daily variation of soil CO2 efflux appeared as a single-peak curve. The soil CO2 efflux was low at night, with the lowest value occurring between 02:00–06:00. Then, values started to rise rapidly between 07:00–08:30, and then descend again between 16:00–18:30. The peak soil CO2 efflux appeared from 11:00 to 16:00. The soil CO2 efflux values gradually decreased from October to February of the next year and started to increase in March. Non-growing season Q10 (the multiplier to the respiration rate for a 10°C increase in temperature) was increased with raising altitude and average Q10 of the Qilian Mountains was generally higher than the average growing season Q10 of the Heihe River Basin. Seasonally, non-growing season soil CO2 efflux was relatively high in October and early spring and low in the winter. The soil CO2 efflux was positively correlated with soil temperature and soil water content. Our results indicate that in alpine ecosystems, soil CO2 efflux continues throughout the non-growing season, and soil respiration is an important component of annual soil CO2 efflux.

Spatial and temporal variability of soil CO2 efflux in three proximate temperate forest ecosystems

Abstract The magnitude of CO2 flux from soil (Fsoil) varies with primary productivity and environmental drivers of respiration, soil temperature (Tsoil) and moisture, all of which vary temporally and spatially. To quantify the sources of Fsoil variability, we first compared Fsoil of three proximate forests within 30 km of one another, ranging in age, composition, soil, and environment and, thus, productivity. We collected data with automated soil respiration chambers during a 10-year period in a mid-rotation Pinus taeda plantation (PP), for three-years in a mature P. taeda stand (OP), and for five-years in a mature, mixed-species hardwood (HW) stand; PP and HW were on clay-loam soil and OP on a sandy soil. Among stands, Fsoil sensitivity to Tsoil was lowest in OP and highest in PP, reflected in mean annual Fsoil (±standard deviation) of 1033 ± 226 (OP), 1206 ± 99 (HW), and 1383 ± 152 (PP) g C m−2; both Fsoil sensitivity to Tsoil and annual Fsoil increased with leaf litterfall. For the second portion of our study, we established an additional three plots at PP for a six-year period to examine within-stand variability. Within PP, sensitivity of Fsoil to Tsoil was similar, yet higher leaf area was correlated with a combination of lower soil temperature and belowground carbon flux, resulting in lower Fsoil. Temporally, diurnal to seasonal Fsoil followed Tsoil whereas annual values were driven by soil moisture. Spatially, among the three stands Fsoil increased with leaf production, whereas within a stand (PP) Fsoil decreased with increasing leaf production.

Forest Management Influence on the Carbon Flux of Cupressus lusitanica Plantation in the Munessa Forest, Ethiopia

The effect of plantation forests on the global carbon balance is controversially discussed in recent times. As soil respiration is a decisive component in the carbon exchange between terrestrial ecosystems and atmosphere, effects of forest management measures (e.g. thinning) in the context of driving parameters of soil CO2 efflux is a key issue in optimizing carbon friendly land management. In the present study, we report the effects of thinning, soil temperature and soil moisture, and biotic parameters on soil CO2 efflux rate. Soil CO2 efflux was measured by using an Infrared Gas Analyzer. We selected thinned and un-thinned stands within six years old Cupressus lusitanica plantation forest. Soil respiration rate ranged from 1.47 to 6.92 µmol m-2s-1 (thinned) and 1.31 to 5.20 µmol m-2s-1 (control stand). Generally higher soil respiration rates were measured during wet than in dry season. Seasonal variability of soil CO2 efflux was significantly (p<0.05) correlated with soil moisture, but poorly correlated with soil temperature. Soil respiration increased with increasing soil moisture and reached maximum at 31% but after this threshold it start to decline. In general, soil CO2 efflux rate in the first and second year after thinning was 24% and 14% higher in the thinned stand. Increased soil temperature at the thinned stand contributed minor to the larger soil CO2 efflux, the more important reason appeared to be the trees’ direct response. Higher fine root production together with larger microbial concentrations representing different groups infers a higher autotrophic respiration by roots and associated mycorrhizal fungi as well as by heterotrophic respiration. Despite the higher CO2 losses with soil respiration, the organic C and total N concentrations in soil rather tended to increase, indicating higher organic matter input to soil at the thinned stand.