共查询到20条相似文献,搜索用时 15 毫秒
1.
Apart from a general increase of mean annual air temperature, climate models predict a regional increase of the frequency and intensity of soil frost with possibly strong effects on C cycling of soils. In this study, we induced mild soil frost (up to −5 °C in a depth of 5 cm below surface) in a Norway spruce forest soil by removing the natural snow cover in the winter of 2005/2006. Soil frost lasted from January to April 2006 and was detected down to 15 cm depth. Soil frost effectively reduced soil respiration in the snow removal plots in comparison to undisturbed control plots. On an annual basis 6.2 t C ha −1 a −1 were emitted in the control plots compared with 5.1 t C ha −1 a −1 in the snow removal plots. Only 14% of this difference was attributed to reduced soil respiration during the soil frost period itself, whereas 63% of this difference originated from differences during the summer of 2006. Radiocarbon (Δ 14C) signature of CO 2 revealed a considerable reduction of heterotrophic respiration on the snow removal plots, only partly compensated for by a slight increase of rhizosphere respiration. Similar CO 2 concentrations in the uppermost mineral horizons of both treatments indicate that differences between the treatments originated from the organic horizons. Extremely low water contents between June and October of 2006 may have inhibited the recovery of the heterotrophic organisms from the frost period, thereby enhancing the differences between the control and snow removal plots. We conclude that soil frost triggered a change in the composition of the microbial community, leading to an increased sensitivity of heterotrophic respiration to summer drought. A CO 2 pulse during thawing, such as described for arable soils several times throughout the literature, with the potential to partly compensate for reduced soil respiration during soil frost, appears to be lacking for this soil. Our results from this experiment indicate that soil frost reduces C emission from forest soils, whereas mild winters may enhance C losses from forest soils. 相似文献
2.
Throughout most of the northern hemisphere, snow cover decreased in almost every winter month from 1967 to 2012. Because snow is an effective insulator, snow cover loss has likely enhanced soil freezing and the frequency of soil freeze–thaw cycles, which can disrupt soil nitrogen dynamics including the production of nitrous oxide (N 2O). We used replicated automated gas flux chambers deployed in an annual cropping system in the upper Midwest US for three winters (December–March, 2011–2013) to examine the effects of snow removal and additions on N 2O fluxes. Diminished snow cover resulted in increased N 2O emissions each year; over the entire experiment, cumulative emissions in plots with snow removed were 69% higher than in ambient snow control plots and 95% higher than in plots that received additional snow ( P < 0.001). Higher emissions coincided with a greater number of freeze–thaw cycles that broke up soil macroaggregates (250–8000 µm) and significantly increased soil inorganic nitrogen pools. We conclude that winters with less snow cover can be expected to accelerate N 2O fluxes from agricultural soils subject to wintertime freezing. 相似文献
3.
Freezing and thawing may alter element turnover and solute fluxes in soils by changing physical and biological soil properties. We simulated soil frost in replicated snow removal plots in a mountainous Norway spruce stand in the Fichtelgebirge area, Germany, and investigated N net mineralization, solute concentrations and fluxes of dissolved organic carbon (DOC) and of mineral ions (NH 4+, NO 3−, Na +, K +, Ca 2+, Mg 2+). At the snow removal plots the minimum soil temperature was −5 °C at 5 cm depth, while the control plots were covered by snow and experienced no soil frost. The soil frost lasted for about 3 months and penetrated the soil to about 15 cm depth. In the 3 months after thawing, the in situ N net mineralization in the forest floor and upper mineral soil was not affected by soil frost. In late summer, NO 3− concentrations increased in forest floor percolates and soil solutions at 20 cm soil depth in the snow removal plots relative to the control. The increase lasted for about 2–4 months at a time of low seepage water fluxes. Soil frost did not affect DOC concentrations and radiocarbon signatures of DOC. No specific frost effect was observed for K +, Ca 2+ and Mg 2+ in soil solutions, however, the Na + concentrations in the upper mineral soil increased. In the 12 months following snowmelt, the solute fluxes of N, DOC, and mineral ions were not influenced by the previous soil frost at any depth. Our experiment did not support the hypothesis that moderate soil frost triggers solute losses of N, DOC, and mineral ions from temperate forest soils. 相似文献
4.
Short-term N 2O emission occurs in relation to snowmelt within seasonally frozen soil. To understand the effects of changing winter climates on the N 2O flux, snow cover manipulation experiments are useful. In Japan, snow cover manipulation is practiced by farmers to improve agricultural yield and is executed either by applying a broadcast of blackish agent onto the snow cover, which leads to faster snow-melting thereby extending the crop-growing season, or by snow cover removal/re-accumulation, leading to an enhanced soil frost depth for weed management. Implementation of these practices involves using an amount of fossil fuel, in addition to influencing soil-derived N 2O emissions, therefore, the load factors of snow cover management practices per unit area of agricultural field were estimated in this study. Field data including micrometeorological conditions, ground surface flux of N 2O, and amount of fossil fuel consumed during machinery operation for management practices, were obtained at two sites in Hokkaido over 2 years (2008–2010). Fuel consumption for the field spreading was found to be unexpectedly small (0.017 Mg CO 2 eq ha ?1). It was therefore suggested that acceleration of snowmelt may have the potential to reduce net greenhouse gas emissions if the agent used is a low-degradable C-rich material, such as charcoal. For soil frost control, the fossil fuel consumption during a set of snow cover removal/re-accumulation (estimated as 0.052 Mg CO 2 eq ha ?1) is discussed, together with the relationship between possible mechanisms causing stimulation of N 2O production in frozen soil and inherent large differences in N 2O flux among sites. 相似文献
5.
土壤冻融期间的温室气体排放量会显著增加,并在全年总排放量中占有重要的份额。但目前开展的土壤冻融循环模拟实验大多是在土壤冻结之前调节土壤水分含量,而忽视了雪被在整个土壤冻融过程中的作用,因此导致室内模拟研究的结果与野外原位观测的结果差异较大。为探索开展室内模拟土壤冻融实验的优化方案,采用人工浇水和覆雪两种方式调节土壤水分含量,研究了雪被和土壤水分对内蒙古典型半干旱草原土壤冻融过程中CO2和N2O排放的影响。结果表明,浇水和覆雪两种处理对冻融循环过程中土壤CO2排放影响的差异不显著,CO2排放量在消融期都会明显增加并随着冻融循环次数的增加而逐渐减小。当土壤孔隙含水率达50%左右时,浇水处理中的N2O排放量在第1次土壤冻融循环中最高并随冻融循环次数增加而降低,但在覆雪处理中,N2O在第1次冻融循环中的排放较小,而在后两次冻融循环中的排放量更为显著。造成两种处理N2O排放规律出现显著不同的原因可能是土壤剖面水分动态变化过程和微生物性状等方面的差异。土壤冻融过程中CO2和N2O排放量随土壤含水量升高而增加,但N2O在土壤含水量较低时排放不明显,这表明可能只有当土壤含水量达到一定阈值时,冻融作用才会对N2O的排放产生显著影响。这些结果显示,雪被和土壤水分显著影响土壤冻融过程中的CO2和N2O排放,室内模拟土壤冻融实验应进一步优化。 相似文献
6.
Increases in soil freezing associated with decreases in snow cover have been identified as a significant disturbance to nitrogen (N) cycling in northern hardwood forests. We created a range of soil freezing intensity through snow manipulation experiments along an elevation gradient at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains, NH USA in order to improve understanding of the factors regulating freeze effects on nitrate (NO 3 ?) leaching, nitrous oxide (N 2O) flux, potential and in situ net N mineralization and nitrification, microbial biomass carbon (C) and N content and respiration, and denitrification. While the snow manipulation treatment produced deep and persistent soil freezing at all sites, effects on hydrologic and gaseous losses of N were less than expected and less than values observed in previous studies at the HBEF. There was no relationship between frost depth, frost heaving and NO 3 ? leaching, and a weak relationship between frost depth and winter N 2O flux. There was a significant positive relationship between dissolved organic carbon (DOC) and NO 3 ? concentrations in treatment plots but not in reference plots, suggesting that the snow manipulation treatment mobilized available C, which may have stimulated retention of N and prevented treatment effects on N losses. While the results support the hypothesis that climate change resulting in less snow and more soil freezing will increase N losses from northern hardwood forests, they also suggest that ecosystem response to soil freezing disturbance is affected by multiple factors that must be reconciled in future research. 相似文献
7.
At high latitudes, winter climate change alters snow cover and, consequently, may cause a sustained change in soil frost dynamics. Altered winter soil conditions could influence the ecosystem exchange of carbon dioxide (CO 2) and, in turn, provide feedbacks to ongoing climate change. To investigate the mechanisms that modify the peatland CO 2 exchange in response to altered winter soil frost, we conducted a snow exclusion experiment to enhance winter soil frost and to evaluate its short‐term (1–3 years) and long‐term (11 years) effects on CO 2 fluxes during subsequent growing seasons in a boreal peatland. In the first 3 years after initiating the treatment, no significant effects were observed on either gross primary production (GPP) or ecosystem respiration (ER). However, after 11 years, the temperature sensitivity of ER was reduced in the treatment plots relative to the control, resulting in an overall lower ER in the former. Furthermore, early growing season GPP was also lower in the treatment plots than in the controls during periods with photosynthetic photon flux density (PPFD) ≥800 μmol m ?2 s ?1, corresponding to lower sedge leaf biomass in the treatment plots during the same period. During the peak growing season, a higher GPP was observed in the treatment plots under the low light condition (i.e. PPFD 400 μmol m ?2 s ?1) compared to the control. As Sphagnum moss maximizes photosynthesis at low light levels, this GPP difference between the plots may have been due to greater moss photosynthesis, as indicated by greater moss biomass production, in the treatment plots relative to the controls. Our study highlights the different responses to enhanced winter soil frost among plant functional types which regulate CO 2 fluxes, suggesting that winter climate change could considerably alter the growing season CO 2 exchange in boreal peatlands through its effect on vegetation development. 相似文献
8.
The release of N 2O from the snow surface in winter and the soil in summer was measured in ten types of temperate ecosystems (bare ground, grassland, forest, marsh, and crop field) in Japan. The snow-covered crop field emitted by far the largest amount of N 2O during the winter. Among the snow-covered natural ecosystems studied, marshy ecosystems showed the largest effluxes of N 2O. Based on results showing that the magnitude of the winter N 2O fluxes was not negligible compared with that of the summer N 2O fluxes and because the snow period in the areas studied area is sufficiently long, we suggest that the winter N 2O fluxes contribute significantly to the annual emission of N 2O in the study areas. 相似文献
9.
Despite growing recognition of the role that cities have in global biogeochemical cycles, urban systems are among the least understood of all ecosystems. Urban grasslands are expanding rapidly along with urbanization, which is expected to increase at unprecedented rates in upcoming decades. The large and increasing area of urban grasslands and their impact on water and air quality justify the need for a better understanding of their biogeochemical cycles. There is also great uncertainty about the effect that climate change, especially changes in winter snow cover, will have on nutrient cycles in urban grasslands. We aimed to evaluate how reduced snow accumulation directly affects winter soil frost dynamics, and indirectly greenhouse gas fluxes and the processing of carbon (C) and nitrogen (N) during the subsequent growing season in northern urban grasslands. Both artificial and natural snow reduction increased winter soil frost, affecting winter microbial C and N processing, accelerating C and N cycles and increasing soil : atmosphere greenhouse gas exchange during the subsequent growing season. With lower snow accumulations that are predicted with climate change, we found decreases in N retention in these ecosystems, and increases in N 2O and CO 2 flux to the atmosphere, significantly increasing the global warming potential of urban grasslands. Our results suggest that the environmental impacts of these rapidly expanding ecosystems are likely to increase as climate change brings milder winters and more extensive soil frost. 相似文献
10.
Fluxes of CO 2 and N 2O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge
in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic
activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and
production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C,
but there was no significant relationship between flux for either gas and temperature within this range. While early developing
snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest
CO 2 fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal
flux of CO 2
–C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO 2
–C loss ranged from 0.3 g C m −2 season −1 at sites characterized by inconsistent snow cover to 25.7 g C m −2 season −1 at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed
with C loss, a hard freeze early in the winter did not result in greater N 2O –N loss. Both mean daily N 2O fluxes and the total over-winter N 2O –N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N 2O –N loss ranged from less 0.23 mg N m −2 from the latest developing, short duration snowpacks to 16.90 mg N m −2 from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the
potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N 2O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes
suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling
in these environments.
Received: 5 April 1996 / Accepted: 25 November 1996 相似文献
11.
A snow addition experiment in moist acidic tussock tundra at Toolik Lake, Alaska, increased winter snow depths 2–3 m, and resulted in a doubling of the summer active layer depth. We used radiocarbon (? 14C) to (1) determine the age of C respired in the deep soils under control and deepened active layer conditions (deep snow drifts), and (2) to determine the impact of increased snow and permafrost thawing on surface CO 2 efflux by partitioning respiration into autotrophic and heterotrophic components. ? 14C signatures of surface respiration were higher in the deep snow areas, reflecting a decrease in the proportion of autotrophic respiration. The radiocarbon age of soil pore CO 2 sampled near the maximum mid-July thaw depth was approximately 1,000 years in deep snow treatment plots (45–55 cm thaw depth), while CO 2 from the ambient snow areas was ~100 years old (30-cm thaw depth). Heterotrophic respiration ? 14C signatures from incubations were similar between the two snow depths for the organic horizon and were extremely variable in the mineral horizon, resulting in no significant differences between treatments in either month. Radiocarbon ages of heterotrophically respired C ranged from <50 to 235 years BP in July mineral soil samples and from 1,525 to 8,300 years BP in August samples, suggesting that old soil C in permafrost soils may be metabolized upon thawing. In the surface fluxes, this old C signal is obscured by the organic horizon fluxes, which are significantly higher. Our results indicate that, as permafrost in tussock tundra ecosystems of arctic Alaska thaws, carbon buried up to several thousands of years ago will become an active component of the carbon cycle, potentially accelerating the rise of CO 2 in the atmosphere. 相似文献
12.
Based on current climate scenarios, a higher frequency of summer drought periods followed by heavy rainfall events is predicted for Central Europe. It is expected that drying/rewetting events induce an increased matter cycling in soils and may contribute considerably to increased emissions of the greenhouse gas N 2O on annual scales. To investigate the influence of drying/rewetting events on N 2O emissions in a mature Norway spruce forest in the Fichtelgebirge area (NE Bavaria, Germany), a summer drought period of 46 days was induced by roof installations on triplicate plots, followed by a rewetting event of 66 mm experimental rainfall in 2 days. Three nonmanipulated plots served as controls. The experimentally induced soil drought was accompanied by a natural drought. During the drought period, the soil of both the throughfall exclusion and control plots served as an N 2O sink. This was accompanied by subambient N 2O concentrations in upper soil horizons. The sink strength of the throughfall exclusion plots was doubled compared with the control plots. We conclude that the soil water status together with the soil nitrate availability was an important driving factor for the N 2O sink strength. Rewetting quickly turned the soil into a source for atmospheric N 2O again, but it took almost 4 months to turn the cumulative soil N 2O fluxes from negative (sink) to positive (source) values. N 2O concentration and isotope analyses along soil profiles revealed that N 2O produced in the subsoil was subsequently consumed during upward diffusion along the soil profile throughout the entire experiment. Our results show that long drought periods can lead to drastic decreases of N 2O fluxes from soils to the atmosphere or may even turn forest soils temporarily to N 2O sinks. Accumulation of more field‐scale data on soil N 2O uptake as well as a better understanding of underlying mechanisms would essentially advance our knowledge of the global N 2O budget. 相似文献
13.
Climate change may cause a decrease in snow cover in northern latitudes. This, on the other hand, may result in more severe soil frost even in areas where it is not common at present, and may lead to increased stress on the tree canopy. We studied the effects of snow removal and consequent changes in soil frost and water content on the physiology of Norway spruce ( Picea abies [L.] Karst.) needles and implications on root biomass. The study was conducted at a 47-year-old Norway spruce stand in eastern Finland during the two winters of 2005/06 and 2006/07. The treatments in three replicates were: (i) natural snow accumulation and melting (CTRL), (ii) artificial snow removal during the winter (OPEN), and (iii) the same as OPEN, but the ground was insulated in early spring to delay soil thawing (FROST). In spite of the deeper soil frost in the OPEN than in the CTRL treatment, soil warming in spring occurred at the same time, whereas soil warming in the FROST was delayed by 2 and 1.5 months in 2006 and 2007, respectively. The soil water content was affected by snow manipulations, being at a lower level in the OPEN and FROST than CTRL in spring and early summer. The physiological measurements of the needles (e.g. starch, carbon and nitrogen content and apoplastic electrical resistance) showed differences between soil frost treatments. The differences were mostly seen between the CTRL and FROST, but also in the case of the starch content in early spring 2007 between the CTRL and OPEN. The needle responses in the FROST were more evident after the colder winter of 2006. The physiological changes seemed to be related to the soil temperature and water content in the early growing season rather than to the wintertime soil temperature. No difference was found in the fine root (diameter < 2 mm) biomass between the treatments assessed in 2007. In the future, conditions similar to the OPEN treatment may be more common than at present in areas experiencing a thick snow cover. The present experiment took place over the course of two years. It is possible that whenever thin snow cover occurs yearly, the reduced starch content during the early spring may be reflected in the tree growth itself as a result of reduced energy reserves. 相似文献
14.
We exploited the natural climate gradient in the northern hardwood forest at the Hubbard Brook Experimental Forest (HBEF)
to evaluate the effects of climate variation similar to what is predicted to occur with global warming over the next 50–100 years
for northeastern North America on soil carbon (C) and nitrogen (N) cycle processes. Our objectives were to (1) characterize
differences in soil temperature, moisture and frost associated with elevation at the HBEF and (2) evaluate variation in total
soil (TSR) and microbial respiration, N mineralization, nitrification, denitrification, nitrous oxide (N 2O) flux, and methane (CH 4) uptake along this gradient. Low elevation sites were consistently warmer (1.5–2.5°C) and drier than high elevation sites.
Despite higher temperatures, low elevation plots had less snow and more soil frost than high elevation plots. Net N mineralization
and nitrification were slower in warmer, low elevation plots, in both summer and winter. In summer, this pattern was driven
by lower soil moisture in warmer soils and in winter the pattern was linked to less snow and more soil freezing in warmer
soils. These data suggest that N cycling and supply to plants in northern hardwood ecosystems will be reduced in a warmer
climate due to changes in both winter and summer conditions. TSR was consistently faster in the warmer, low elevation plots.
N cycling processes appeared to be more sensitive to variation in soil moisture induced by climate variation, whereas C cycling
processes appeared to be more strongly influenced by temperature. 相似文献
15.
No‐tillage (NT), a practice that has been shown to increase carbon sequestration in soils, has resulted in contradictory effects on nitrous oxide (N 2O) emissions. Moreover, it is not clear how mitigation practices for N 2O emission reduction, such as applying nitrogen (N) fertilizer according to soil N reserves and matching the time of application to crop uptake, interact with NT practices. N 2O fluxes from two management systems [conventional (CP), and best management practices: NT + reduced fertilizer (BMP)] applied to a corn ( Zea mays L.), soybean ( Glycine max L.), winter‐wheat ( Triticum aestivum L.) rotation in Ontario, Canada, were measured from January 2000 to April 2005, using a micrometeorological method. The superimposition of interannual variability of weather and management resulted in mean monthly N 2O fluxes ranging from − 1.9 to 61.3 g N ha −1 day −1. Mean annual N 2O emissions over the 5‐year period decreased significantly by 0.79 from 2.19 kg N ha −1 for CP to 1.41 kg N ha −1 for BMP. Growing season (May–October) N 2O emissions were reduced on average by 0.16 kg N ha −1 (20% of total reduction), and this decrease only occurred in the corn year of the rotation. Nongrowing season (November–April) emissions, comprised between 30% and 90% of the annual emissions, mostly due to increased N 2O fluxes during soil thawing. These emissions were well correlated ( r2= 0.90) to the accumulated degree‐hours below 0 °C at 5 cm depth, a measure of duration and intensity of soil freezing. Soil management in BMP (NT) significantly reduced N 2O emissions during thaw (80% of total reduction) by reducing soil freezing due to the insulating effects of the larger snow cover plus corn and wheat residue during winter. In conclusion, significant reductions in net greenhouse gas emissions can be obtained when NT is combined with a strategy that matches N application rate and timing to crop needs. 相似文献
16.
Background and aimsThe litter layer is a major source of CO2, and it also influences soil-atmosphere exchange of N2O and CH4. So far, it is not clear how much of soil greenhouse gas (GHG) emission derives from the litter layer itself or is litter-induced. The present study investigates how the litter layer controls soil GHG fluxes and microbial decomposer communities in a temperate beech forest. MethodsWe removed the litter layer in an Austrian beech forest and studied responses of soil CO2, CH4 and N2O fluxes and the microbial community via phospholipid fatty acids (PLFA). Soil GHG fluxes were determined with static chambers on 22 occasions from July 2012 to February 2013, and soil samples collected at 8 sampling events. ResultsLitter removal reduced CO2 emissions by 30 % and increased temperature sensitivity (Q10) of CO2 fluxes. Diffusion of CH4 into soil was facilitated by litter removal and CH4 uptake increased by 16 %. This effect was strongest in autumn and winter when soil moisture was high. Soils without litter turned from net N2O sources to slight N2O sinks because N2O emissions peaked after rain events in summer and autumn, which was not the case in litter-removal plots. Microbial composition was only transiently affected by litter removal but strongly influenced by seasonality. ConclusionsLitter layers must be considered in calculating forest GHG budgets, and their influence on temperature sensitivity of soil GHG fluxes taken into account for future climate scenarios. 相似文献
17.
气候变化引发的季节性雪被改变可能对高寒森林土壤氮循环产生深刻影响.以遮雪棚去除雪被,研究了雪被去除样方和对照样方在不同关键时期(雪被初期、深雪被期和雪被融化期)土壤氮库和矿化速率的变化.结果表明: 季节性雪被对土壤具有良好的保温作用,雪被去除使得5 cm深度土壤平均温度和最低温度分别降低0.33和1.17 ℃,并明显增加了土壤冻结深度和冻融循环.土壤活性氮在不同雪被时期存在显著差异.雪被去除使得冬季土壤铵态氮、硝态氮和可溶性有机氮增加38.6%、23.5%和57.3%.此外,雪被去除也促进了融化期土壤硝化和矿化速率的增加.因此,未来气候变暖引起的雪被减少可能加快川西亚高山森林冬季土壤氮循环. 相似文献
18.
Effect of removal of snow cover in winter was investigated in an 80-year-old sugar maple ( Acer saccharum Marsh.) stand in southern Quebec. We hypothesized that winter soil frost would induce some of the decline symptoms observed in sugar maple stands in southern Quebec in the early 1980's. Snow was continuously removed from around trees for a one week (partial removal) or for a four-month period (complete removal) during the 1990–1991 winter. Foliage and soils were sampled periodically during the summer of 1991. The complete snow removal treated trees showed decreased leaf water potential and increased peroxidase activity over most of the growing season. Foliar Ca was reduced in both snow removal treatments early in the growing season while foliar N was reduced in the complete snow removal trees late in the growing season. Soil NO
3
–
and K + were elevated in both snow removal treatments at various times throughout the growing season. Prolonged soil frost in a sugar maple stand can induce lower leaf water potential, higher leaf peroxidase activity and early leaf senescence during the following growing season. Soil frost may have reduced nutrient uptake without affecting significantly the leaf nutrient status. 相似文献
19.
Winter climate change may result in reduced snow cover and could, consequently, alter the soil frost regime and biogeochemical processes underlying the exchange of methane (CH 4) in boreal peatlands. In this study, we investigated the short‐term (1–3 years) vs. long‐term (11 years) effects of intensified winter soil frost (induced by experimental snow exclusion) on CH 4 exchange during the following growing season in a boreal peatland. In the first 3 years (2004–2006), lower CH 4 emissions in the treatment plots relative to the control coincided with delayed soil temperature increase in the treatment plots at the beginning of the growing season (May). After 11 treatment years (in 2014), CH 4 emissions were lower in the treatment plots relative to the control over the entire growing season, resulting in a reduction in total growing season CH 4 emission by 27%. From May to July 2014, reduced sedge leaf area coincided with lower CH 4 emissions in the treatment plots compared to the control. From July to August, lower dissolved organic carbon concentrations in the pore water of the treatment plots explained 72% of the differences in CH 4 emission between control and treatment. In addition, greater Sphagnum moss growth in the treatment plots resulted in a larger distance between the moss surface and the water table (i.e., increasing the oxic layer) which may have enhanced the CH 4 oxidation potential in the treatment plots relative to the control in 2014. The differences in vegetation might also explain the lower temperature sensitivity of CH 4 emission observed in the treatment plots relative to the control. Overall, this study suggests that greater soil frost, associated with future winter climate change, might substantially reduce the growing season CH 4 emission in boreal peatlands through altering vegetation dynamics and subsequently causing vegetation‐mediated effects on CH 4 exchange. 相似文献
20.
Fluxes of CO 2 during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the
seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow
on Niwot Ridge, Colorado, soil CO 2 fluxes were quantified with the gradient method through the snowpack in winter 2006 and 2007 and with chamber measurements
during summer 2007. The CO 2 fluxes of 0.71 μmol m −2 s −1 in 2006 and 0.86 μmol m −2 s −1 in 2007 are among the highest reported for snow-covered ecosystems in the literature. These fluxes resulted in 156 and 189 g C m −2 emitted over the winter, ~30% of the annual soil CO 2 efflux at this site. In general, the CO 2 flux increased during the winter as soil moisture increased. A conceptual model was developed with distinct snow cover zones
to describe this as well as the three other reported temporal patterns in CO 2 flux from seasonally snow-covered soils. As snow depth and duration increase, the factor controlling the CO 2 flux shifts from freeze–thaw cycles (zone I) to soil temperature (zone II) to soil moisture (zone III) to carbon availability
(zone IV). The temporal pattern in CO 2 flux in each zone changes from periodic pulses of CO 2 during thaw events (zone I), to CO 2 fluxes reaching a minimum when soil temperatures are lowest in mid-winter (zone II), to CO 2 fluxes increasing gradually as soil moisture increases (zone III), to CO 2 fluxes decreasing as available carbon is consumed. This model predicts that interannual variability in snow cover or directional
shifts in climate may result in dramatically different seasonal patterns of CO 2 flux from seasonally snow-covered soils. 相似文献
|