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1.
The net annual exchange of carbon between the atmosphere and terrestrial ecosystems is of prime importance in determining the concentration of CO2 ([CO2]) in the atmosphere and consequently future climate. Carbon loss occurs primarily through soil respiration; it is known that respiration is sensitive to the global changes in [CO2] and temperature, suggesting that the net carbon balance may change in the future. However, field manipulations of temperature and [CO2] alter many important environmental factors so it is unclear how much of the observed alterations in soil respiration is due to changes of microbial function itself instead of changes to the physical and chemical environment. Here we focus on resolving the importance of changes in the microbial community in response to warming and elevated [CO2] on carbon mineralisation, something not possible in field measurements. We took plant material and soil inocula from a long running experiment where native grassland had been exposed to both warming and elevated CO2 and constructed a reciprocal transplant experiment. We found that the rate of decomposition (heterotrophic respiration) was strongly determined by the origin of the microbial community. The combined warming + elevated CO2 treatment produced a soil community that gave respiration rates 30% higher when provided with shoot litter and 70% for root litter than elevated CO2 treatment alone, with the treatment source of the litter being unimportant. Warming, especially in the presence of elevated CO2, increased the size of the apparent labile carbon pool when either C3 or C4 litter was added. Thus, the metabolic activity of the soil community was affected by the combination of warming and elevated CO2 such that it had an increased ability to mineralise added organic matter, regardless of its source. Therefore, soil C efflux may be substantially increased in a warmer, high CO2 world. Current ecosystem models mostly drive heterotrophic respiration from plant litter quality, soil moisture and temperature but our findings suggest equal attention will need to be paid to capturing microbial processes if we are to accurately project the future C balance of terrestrial ecosystems and quantify the feedback effect on atmospheric concentrations of CO2. 相似文献
2.
Forested peatlands contain large pools of terrestrial carbon. As well as drainage, forest management such as fertilizer application can affect these pools. We studied the effect of wood ash (application rates 0, 5 and 15 t ha?1) on the heterotrophic soil respiration (CO2 efflux), cellulose decomposition, soil nutrients, biomass production and amount of C accumulated in a tree stand on a pine‐dominated drained mire in central Finland. The ash was spread 13 years before the respiration measurements. The annual CO2 efflux was statistically modelled using soil temperature as the driving variable. Wood ash application increased the amounts of mineral nutrients of peat substantially and increased soil pH in the uppermost 10 cm layer by 1.5–2 pH units. In the surface peat, the decomposition rate of cellulose in the ash plots was roughly double that in control plots. Annual CO2 efflux was least on the unfertilized site, 238 g CO2‐C m?2 year?1. The use of wood ash nearly doubled CO2 efflux to 420–475 g CO2‐Cm?2 year?1 on plots fertilized with 5–15 t ha?1 of ash, respectively. Furthermore, ash treatments resulted also in increased stand growth, and during the measurement year, the growing stand on ash plots accumulated carbon 11–12 times faster than the control plot. The difference between peat C emission and amount of C sequestered by trees on the ash plots was 43–58 g C m?2, while on the control plot it was 204 g C m?2. Our conclusion is that adding wood ash as a fertilizer increases more C sequestration in the tree stand than C efflux from the peat. 相似文献
3.
Y. Kuzyakov 《Soil biology & biochemistry》2006,38(3):425-448
Five main biogenic sources of CO2 efflux from soils have been distinguished and described according to their turnover rates and the mean residence time of carbon. They are root respiration, rhizomicrobial respiration, decomposition of plant residues, the priming effect induced by root exudation or by addition of plant residues, and basal respiration by microbial decomposition of soil organic matter (SOM). These sources can be grouped in several combinations to summarize CO2 efflux from the soil including: root-derived CO2, plant-derived CO2, SOM-derived CO2, rhizosphere respiration, heterotrophic microbial respiration (respiration by heterotrophs), and respiration by autotrophs. These distinctions are important because without separation of SOM-derived CO2 from plant-derived CO2, measurements of total soil respiration have very limited value for evaluation of the soil as a source or sink of atmospheric CO2 and for interpreting the sources of CO2 and the fate of carbon within soils and ecosystems. Additionally, the processes linked to the five sources of CO2 efflux from soil have various responses to environmental variables and consequently to global warming. This review describes the basic principles and assumptions of the following methods which allow SOM-derived and root-derived CO2 efflux to be separated under laboratory and field conditions: root exclusion techniques, shading and clipping, tree girdling, regression, component integration, excised roots and insitu root respiration; continuous and pulse labeling, 13C natural abundance and FACE, and radiocarbon dating and bomb-14C. A short sections cover the separation of the respiration of autotrophs and that of heterotrophs, i.e. the separation of actual root respiration from microbial respiration, as well as methods allowing the amount of CO2 evolved by decomposition of plant residues and by priming effects to be estimated. All these methods have been evaluated according to their inherent disturbance of the ecosystem and C fluxes, and their versatility under various conditions. The shortfalls of existing approaches and the need for further development and standardization of methods are highlighted. 相似文献
4.
Root and rhizomicrobial respiration: A review of approaches to estimate respiration by autotrophic and heterotrophic organisms in soil 总被引:2,自引:0,他引:2
Partitioning the root‐derived CO2 efflux from soil (frequently termed rhizosphere respiration) into actual root respiration (RR, respiration by autotrophs) and rhizomicrobial respiration (RMR, respiration by heterotrophs) is crucial in determining the carbon (C) and energy balance of plants and soils. It is also essential in quantifying C sources for rhizosphere microorganisms and in estimation of the C contributing to turnover of soil organic matter (SOM), as well as in linking net ecosystem production (NEP) and net ecosystem exchange (NEE). Artificial‐environment studies such as hydroponics or sterile soils yield unrealistic C‐partitioning values and are unsuitable for predicting C flows under natural conditions. To date, several methods have been suggested to separate RR and RMR in nonsterile soils: 1) component integration, 2) substrate‐induced respiration, 3) respiration by excised roots, 4) comparison of root‐derived 14CO2 with rhizomicrobial 14CO2 after continuous labeling, 5) isotope dilution, 6) model‐rhizodeposition technique, 7) modeling of 14CO2 efflux dynamics, 8) exudate elution, and 9) δ13C of CO2 and microbial biomass. This review describes the basic principles and assumptions of these methods and compares the results obtained in the original papers and in studies designed to compare the methods. The component‐integration method leads to strong disturbance and non‐proportional increase of CO2 efflux from different sources. Four of the methods (5 to 8) are based on the pulse labeling of shoots in a 14CO2 atmosphere and subsequent monitoring of 14CO2 efflux from the soil. The model‐rhizodeposition technique and exudate‐elution procedure strongly overestimate RR and underestimate RMR. Despite alternative assumptions, isotope dilution and modeling of 14CO2‐efflux dynamics yield similar results. In crops and grasses (wheat, ryegrass, barley, buckwheat, maize, meadow fescue, prairie grasses), RR amounts on average to 48±5% and RMR to 52±5% of root‐derived CO2. The method based on the 13C isotopic signature of CO2 and microbial biomass is the most promising approach, especially when the plants are continuously labeled in 13CO2 or 14CO2 atmosphere. The “difference” methods, i.e., trenching, tree girdling, root‐exclusion techniques, etc., are not suitable for separating the respiration by autotrophic and heterotrophic organisms because the difference methods neglect the importance of microbial respiration of rhizodeposits. 相似文献
5.
Jianqing Wang Xuhui Zhang Lianqing Li Kun Cheng Jufeng Zheng Jinwei Zheng Mingxing Shen Xiaoyu Liu Genxing Pan 《Journal of Soils and Sediments》2016,16(12):2666-2675
Purpose
Although micronutrients are essential to higher plants, it remains unclear whether the projected future climate change would affect their availability to plants. The objective of this study was to investigate the effect of carbon dioxide (CO2) enrichment and warming on soil micronutrient availability and plant uptake.Materials and methods
This study was conducted in an open field experiment with CO2 enrichment and plant canopy warming. Four treatments were included: (1) free-air CO2 enrichment up to 500 ppm (CE); (2) canopy warming by plus 2 °C (WA); (3) CO2 enrichment combined with canopy warming (CW), and (4) ambient condition as control. Plant and soil samples were collected, respectively, at the jointing, heading, and ripening stage over the whole wheat growing season in 2014. The micronutrient concentrations both in soil and plant were both analyzed, and the accumulated uptake by wheat harvest was assessed.Results and discussion
Both CO2 enrichment and warming increased the availability of most soil micronutrients. The availability of Fe, Mn, Cu, and Zn under CO2 enrichment increased by 47.7, 22.5, 59.8, and 114.1 %, respectively. Warming increased the availability of Fe, Cu, and Zn by 60.4, 23.8, and 15.3 %, respectively. The plant growth induced changes in soil pH and in soil microbial biomass carbon (MBC) accounted to the changes in soil micronutrient availability. The enrichment of CO2 and warming had significant effects on micronutrient uptake by wheat. The enrichment of CO2 decreased the concentration of Fe by 9.3 %, while it increased the concentrations of Mn and Zn by 18.9 and 8.1 % in plant shoot, respectively. Warming increased the concentration of Fe and Cu by 24.3 and 7.6 % in plant shoot, respectively. The increase in soil micronutrient availability did not always lead to the increase in micronutrient uptake. The element types and crop growth stage affected the uptake of micronutrients by wheat under CO2 enrichment and warming. Additionally, CO2 enrichment decreased the translocation of Fe and Zn by 25.3 and 10.0 %, respectively, while warming increased the translocation of Fe, Mn, Cu, and Zn across stages.Conclusions
Our results demonstrated that CO2 enrichment and warming would improve availability of some micronutrients and their uptake by wheat. However, it is still unclear whether a net removal of micronutrient through crop straw harvest would occur under CO2 enrichment and warming.6.
Örjan Berglund Kerstin Berglund Leif Klemedtsson 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(6):508-513
Abstract Methods used to estimate the CO2 emission from soil commonly measure the total CO2 flux. To be able to quantify the net CO2 emission from cultivated peat soils there is a need to distinguish between soil organic matter-derived CO2 respiration and plant-derived respiration. In this investigation we used the root exclusion method to separate the plant-derived respiration from total CO2 emission. The plant-derived contribution was estimated to be between 27 and 63% of total CO2 emission depending on soil type and season. We also found a relationship between soil temperature, biomass growth and CO2 efflux, which can be used to estimate plant-derived respiration. Due to the priming effect the root exclusion method is less reliable late in the season. 相似文献
7.
The presented study shows the results of measuring soil respiration in typical burozems (Dystric Cambisols) under mixed Korean pine–broadleaved forests in the southern part of the Primorskii (Far East) region of Russia growing under conditions of monsoon climate. The measurements were performed in 2014–2016 by the chamber method with the use of a portable infrared gas analyzer. Relative and total values of the CO2 efflux from the soil surface on four model plots were determined. The intensity of summer emission varied from 2.25 to 10.97 μmol/(m2 s), and the total CO2 efflux from the soils of four plots varied from 18.84 to 25.56 mol/m2. It is shown that a larger part of seasonal variability in the soil respiration is controlled by the soil temperature (R2 = 0.5–0.7); the soil water content also has a significant influence on the CO2 emission determining about 10% of its temporal variability. The daily dynamics of soil respiration under the old-age (200 yrs) forest have a significant relationship with the soil temperature (R2 = 0.51). The pyrogenic transformation of Pinus koraiensis forests into low-value oak forests is accompanied by an increase in the СО2 efflux from the soil. 相似文献
8.
Winter soil CO2 efflux and its contribution to annual soil respiration in different ecosystems of a forest-steppe ecotone, north China 总被引:1,自引:0,他引:1
Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO2 fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO2 efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO2 efflux to climate changes. In this study we measured winter soil CO2 efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO2 effluxes were 0.15-0.26 μmol m−2 s−1 and 2.65-4.61 μmol m−2 s−1, respectively, with significant differences in the growing season among the different ecosystems. Annual Q10 (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q10. Soil water content accounted for 84% of the variations in growing season Q10 and soil temperature range explained 88% of the variation in annual Q10. Soil organic carbon density to 30 cm depth was a good surrogate for SR10 (basal soil respiration at a reference temperature of 10 °C). Annual soil CO2 efflux ranged from 394.76 g C m−2 to 973.18 g C m−2 using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m−2 to 784.73 g C m−2 by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO2 efflux to annual soil respiration were 3.48-7.30% and 4.92-7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO2 efflux continues throughout the winter and winter soil respiration is an important component of annual CO2 efflux. 相似文献
9.
Increasing human demands for Earth’s resources are hastening many environmental changes and creating a need to incorporate the routine monitoring of ecosystem functions into forest management.Under global change and anthropogenic disturbances,soil carbon (C) cycling in terrestrial ecosystems is undergoing substantial changes that result in the transformation between soil C sources and sinks.Therefore,the forest C budget requires an understanding of the underlying soil C dynamic under environment... 相似文献
10.
The terrestrial biosphere component of the Integrated Model to Assess the Greenhouse Effect (IMAGE 2) uses changes in land cover to compute dynamically the C fluxes between the terrestrial biosphere and the atmosphere. The model explores the potential impact of feedback processes incorporated in the model, which are the enhancement of plant growth (CO2 fertilization) and a more efficient use of water under increased CO2 concentrations in the atmosphere; the temperature response of photosynthesis and respiration of plants; the temperature and soil water response of decomposition processes; and the climate-induced changes in vegetation and agricultural patterns with the consequent changes in land cover. In this paper we discuss the implementation and operation of the different feedback processes in the IMAGE 2 model. Results are shown for each process separately as well as the combined processes. The aim of this paper is to quantify the importance of these feedback processes geographically. The main results are that vegetation shifts due to climatic change and increased water use efficiency, CO2 fertilization decreases net C emissions, while changed decomposition rates strongly increase C emissions to the atmosphere. Changes in the global balance between photosynthesis and respiration make little net difference. With the IPPC business-as-usual scenario the terrestrial biosphere continues to emit C into the atmosphere. This behavior is governed by changes in land-use, caused by a multitude of anthropogenic processes. 相似文献
11.
Seasonal pattern of total soil respiration in undisturbed and disturbed ecosystems of Central Himalaya 总被引:1,自引:0,他引:1
Summary The rates of CO2 efflux were measured by an alkali absorption method (using 20 ml 0.5 N NaOH) from soils in four undisturbed sites [two evergreen oak forests, Quercus floribunda Lindl. (tilonj oak), Quercus leucotrichophora A Camus (banj oak), and two evergreen conifer forests, Cedrus deodara Loud. (deodar forest) and Pinus roxburghii Sarg. (chir pine forest)] and three disturbed sites. The sites were located between elevations of 1850 and 2360 m in the Central Himalaya. The seasonal pattern of soil respiration was similar in all the sites with a maximum during the rainy season, intermediate rates during the summer season and the lowest level of activity in winter. The rate of CO2 efflux was higher in broadleaf than in conifer forests, and it was lowest in the disturbed sites. Among the edaphic conditions, soil moisture, N, organic C, pH, soil porosity, and root biomass positively affected total soil respiration. The proportion of root respiration to total soil respiration was higher in the disturbed sites than the undisturbed sites in winter. Conditions in the winter season were less favourable for microbial respiration than for root respiration. 相似文献
12.
Getting a better understanding of CO2 efflux from forest soils is critical for increasing our comprehension of the global C cycle. We examined the influence of two common boreal tree species, either in pure stands (BS = black spruce; TA = trembling aspen) or in mixtures (MW = BS + TA mixedwood), on total (RS), heterotrophic (RH) and autotrophic soil respiration (RA) and their relationship with soil temperature and moisture, distance to the nearest tree, labile and total soil organic C (SOC), and root content. Stand-specific soil respiration–temperature models were developed to estimate annual soil CO2 efflux. Soil temperature was the main factor explaining RS and its components, followed by labile and total SOC. These three variables were significantly affected by forest composition, while no difference in soil moisture, distance to the nearest tree and root content was observed between stand types. A reciprocal forest floor transplant experiment showed that the influence of stand types on mineral soil temperature was due to a difference in light penetration rather than forest floor characteristics. Annual RS and RH were significantly greater in MW and TA than in BS, whereas annual RA was greater in BS and MW than in TA. Temperature sensitivity (Q10) of both RS and RH was significantly higher in BS than in MW and TA, suggesting that CO2 efflux from BS soils could be increased more under climate warming than that from the other stand types. Our results show evidence that boreal forest composition affects soil CO2 efflux and that litter quality is not the only factor explaining the differences between stand types. The influence of forest composition on soil CO2 efflux would be mediated through effects on soil temperature as well as on factors affecting the accumulation and the quality of SOC. 相似文献
13.
A natural‐13C‐labeling approach—formerly observed under controlled conditions—was tested in the field to partition total soil CO2 efflux into root respiration, rhizomicrobial respiration, and soil organic matter (SOM) decomposition. Different results were expected in the field due to different climate, site, and microbial properties in contrast to the laboratory. Within this isotopic method, maize was planted on soil with C3‐vegetation history and the total CO2 efflux from soil was subdivided by isotopic mass balance. The C4‐derived C in soil microbial biomass was also determined. Additionally, in a root‐exclusion approach, root‐ and SOM‐derived CO2 were determined by the total CO2 effluxes from maize (Zea mays L.) and bare‐fallow plots. In both approaches, maize‐derived CO2 contributed 22% to 35% to the total CO2 efflux during the growth period, which was comparable to other field studies. In our laboratory study, this CO2 fraction was tripled due to different climate, soil, and sampling conditions. In the natural‐13C‐labeling approach, rhizomicrobial respiration was low compared to other studies, which was related to a low amount of C4‐derived microbial biomass. At the end of the growth period, however, 64% root respiration and 36% rhizomicrobial respiration in relation to total root‐derived CO2 were calculated when considering high isotopic fractionations between SOM, microbial biomass, and CO2. This relationship was closer to the 50% : 50% partitioning described in the literature than without fractionation (23% root respiration, 77% rhizomicrobial respiration). Fractionation processes of 13C must be taken into account when calculating CO2 partitioning in soil. Both methods—natural 13C labeling and root exclusion—showed the same partitioning results when 13C isotopic fractionation during microbial respiration was considered and may therefore be used to separate plant‐ and SOM‐derived CO2 sources. 相似文献
14.
Temperature fluctuations are a fundamental entity of the soil environment in the temperate zone and show fast (diurnal) and slow (seasonal) dynamics. Responses of soil respiration to temperature fluctuations were investigated in a root-free soil of a mid-European beech-oak forest. First, in laboratory we analysed the efflux of CO2 from soil microcosms exposed to seasonal (±5 °C of the annual mean) and diurnal fluctuations (±5 °C of the seasonal levels) in a two-factorial design. Second, in field microcosms we investigated effects of smoothing diurnal temperature fluctuations in soil (simulating a possible global trend) on CO2 efflux. Third, the natural temperature regime was simulated in laboratory microcosms and their CO2 efflux was compared to the one in the field. The experiments lasted for 1 year to differentiate seasonal and annual responses.Dynamics of CO2 efflux, microbial basal respiration, biomass and qO2 varied with seasonal temperature regime. However, in the laboratory the annual cumulative CO2-C production did not differ between treatments and varied between 10.9% and 11.7% of the total microcosm C, disregarding seasonal and/or diurnal fluctuations. The similarity of cumulative C production suggests that the availability of microbially mobilisable carbon pools rather than the temperature regime limited soil respiration. Diurnal fluctuations generally did not affect CO2 efflux and microbial activity, though winter Q10 values were increased in their absence. Simulation of the natural temperature regime in the laboratory resulted in CO2 efflux similar to field microcosms. In the field, rates of CO2 efflux and microbial activity, seasonal and annual cumulative CO2-C production were significantly higher at smoothed than at natural temperature conditions (annually 13.1% and 11.0% of total C was respired, respectively). Facing global climate changes the mechanisms regulating responses of soil respiration to temperature fluctuations need further investigation. 相似文献
15.
Soil and detrital carbon dynamics following forest cutting in the Southern Appalachians 总被引:4,自引:0,他引:4
Summary Soil-system CO2 efflux and detrital C pools were measured in three hardwood watersheds in the Southern Appalachians, USA. On two of the watersheds (hereafter referred to as clearcuts), forests were cut via clearcut logging methods and allowed to naturally regenerate; logging residue was removed on one clearcut and was left in place on the other. The third watershed was an uncut reference watershed. There was no statistically significant difference in CO2 efflux between the two types of residue treatments on the clearcuts; however, CO2 effluxes from the clearcuts were 33% less than effluxes from the uncut watershed. Lower CO2 effluxes on the two clearcuts were associated with higher soil temperatures, smaller live-root masses, and larger forest-floor masses. No long-term (5–8 years) changes in soil C pools were apparent following forest cutting. Therefore, reductions in CO2 efflux on the clearcuts appear to be due both to fewer live roots and to slower rates of forest-floor decomposition. Cutting of these forests followed by regeneration does not appear to result in large net C transfers to the atmosphere, as has been generally assumed. 相似文献
16.
Soil carbon dioxide (CO2) flux is an integrative measure of ecosystem functioning representing both biotic and physical controls over carbon (C) balance. In the McMurdo Dry Valleys of Antarctica, soil CO2 fluxes (approximately −0.1-0.15 μmol m−2 s−1) are generally low, and negative fluxes (uptake of CO2) are sometimes observed. A combination of biological respiration and physical mechanisms, driven by temperature and mediated by soil moisture and mineralogy, determine CO2 flux and, therefore, soil organic C balance. The physical factors important to CO2 flux are being altered with climate variability in many ecosystems including arid forms such as the Antarctic terrestrial ecosystems, making it critical to understand how climate factors interact with biotic drivers to control soil CO2 fluxes and C balances. We measured soil CO2 flux in experimental field manipulations, microcosm incubations and across natural environmental gradients of soil moisture to estimate biotic soil respiration and abiotic sources of CO2 flux in soils over a range of physical and biotic conditions. We determined that temperature fluctuations were the most important factor influencing diel variation in CO2 flux. Variation within these diel CO2 cycles was explained by differences in soil moisture. Increased temperature (as opposed to temperature fluctuations) had little or no effect on CO2 flux if moisture was not also increased. We conclude that CO2 flux in dry valley soils is driven primarily by physical factors such as soil temperature and moisture, indicating that future climate change may alter the dry valley soil C cycle. Negative CO2 fluxes in arid soils have recently been identified as potential net C sinks. We demonstrate the potential for arid polar soils to take up CO2, driven largely by abiotic factors associated with climate change. The low levels of CO2 absorption into soils we observed may not constitute a significant sink of atmospheric CO2, but will influence the interpretation of CO2 flux for the dry valley soil C cycle and possibly other arid environments where biotic controls over C cycling are secondary to physical drivers. 相似文献
17.
V. N. Kudeyarov 《Eurasian Soil Science》2018,51(6):599-612
Studies on the assessment of soil respiration and ecosystem CO2 sink in the territory of Russia are reviewed over the period since the adoption of the United Nations Framework Convention on Climate Change (Rio de Janeiro, 1992). The first estimates of total soil respiration in the entire territory of Russia, made in 1995 to 1998, amount to 3.1 and 4.3 Gt C per growing season and per year, respectively. On average, soil CO2 efflux over the cold season (November–March) accounts for 20–30% of annual efflux. The contribution of heterotrophic respiration (R H ) to the total soil respiration (R S ) may reach 30–70%, depending on ecosystem type. Despite differences in methods used to measure R H , the results obtained by different authors vary within a relatively narrow range, from 2.9 to 3.5 Gt C/year at an uncertainty level of about 20%. The soil cover of Russia (11.7% of the global land area) accounts for 6.3% of global soil CO2 efflux. The data on ecosystem CO2 sink are widely scattered among publications. Estimates of carbon balance differ depending on approaches and methods used to determine its individual components and the level of uncertainty in the results. However, most of them confirm the main conclusion: the territory of Russia with its forests is an absolute CO2 sink with a potential of 200 Mt C/year. This conclusion has been corroborated in the absolute majority of studies performed by Russian and international research teams. 相似文献
18.
Soil respiration is comprised primarily of root and microbial respiration, and accounts for nearly half of the total CO2 efflux from terrestrial ecosystems. Soil acidification resulting from acid deposition significantly affects soil respiration. Yet, the mechanisms that underlie the effects of acidification on soil respiration and its two components remain unclear. We collected data on sources of soil CO2 efflux (microbial and root respiration), above- and belowground biotic communities, and soil properties in a 4-year field experiment with seven levels of acid in a semi-arid Inner Mongolian grassland. Here, we show that soil acidification has contrasting effects on root and microbial respiration in a typical steppe grassland. Soil acidification increases root respiration mainly by an increase in root biomass and a shift to plant species with greater specific root respiration rates. The shift of plant community from perennial bunchgrasses to perennial rhizome grasses was in turn regulated by the decreases in soil base cations and N status. In contrast, soil acidification suppresses microbial respiration by reducing total microbial biomass and enzymatic activities, which appear to result from increases in soil H+ ions and decreases in soil base cations. Our results suggest that shifts in both plant and microbial communities dominate the responses of soil respiration and its components to soil acidification. These results also indicate that carbon cycling models concerned with future climate change should consider soil acidification as well as shifts in biotic communities. 相似文献
19.
We used a continuous labeling method of naturally 13C-depleted CO2 in a growth chamber to test for rhizosphere effects on soil organic matter (SOM) decomposition. Two C3 plant species, soybean (Glycine max) and sunflower (Helianthus annus), were grown in two previously differently managed soils, an organically farmed soil and a soil from an annual grassland. We maintained a constant atmospheric CO2 concentration at 400±5 ppm and δ13C signature at −24.4‰ by regulating the flow of naturally 13C-depleted CO2 and CO2-free air into the growth chamber, which allowed us to separate new plant-derived CO2-C from original soil-derived CO2-C in soil respiration. Rhizosphere priming effects on SOM decomposition, i.e., differences in soil-derived CO2-C between planted and non-planted treatments, were significantly different between the two soils, but not between the two plant species. Soil-derived CO2-C efflux in the organically farmed soil increased up to 61% compared to the no-plant control, while the annual grassland soil showed a negligible increase (up to 5% increase), despite an overall larger efflux of soil-derived CO2-C and total soil C content. Differences in rhizosphere priming effects on SOM decomposition between the two soils could be largely explained by differences in plant biomass, and in particular leaf biomass, explaining 49% and 74% of the variation in primed soil C among soils and plant species, respectively. Nitrogen uptake rates by soybean and sunflower was relatively high compared to soil C respiration and associated N mineralization, while inorganic N pools were significantly depleted in the organic farm soil by the end of the experiment. Despite relatively large increases in SOM decomposition caused by rhizosphere effects in the organic farm soil, the fast-growing soybean and sunflower plants gained little extra N from the increase in SOM decomposition caused by rhizosphere effects. We conclude that rhizosphere priming effects of annual plants on SOM decomposition are largely driven by plant biomass, especially in soils of high fertility that can sustain high plant productivity. 相似文献
20.
A temporary decline in tree growth has often been observed after liming in coniferous forests poor in N but seldom in forests rich in N. To test the hypothesis that the decline was caused by decreases in N supply, C and N mineralization were estimated in incubated soil: (1) after liming in the laboratory, and (2) after earlier liming in the field. Liming increased the C mineralization rate in needle litter, nor humus and 0 to 5 cm mineral soil for a period of 40 to 100 days at 15°C. After that period, liming had no effect on the CO2 evolution rate in materials poor in N (C:N ratios 30 to 62) but increased the CO2 evolution rate in materials rich in N (C:N ratios 24 to 28). When liming induced nitrification, the CO2 evolution rate was reduced. Liming resulted in lower net N mineralization rate in needle litter and mor humus. The reduction was more pronounced when NH4 + was the only inorganic form than when NO3 ? was the predominant form. The reason is probably that chemical fixation of NH3 and amino compounds increases with increasing pH. Because of the fixation, the incubation technique most likely underestimated the mineralized N available to the roots. Taking this underestimation into consideration, liming initially reduced the N release in the litter layer. In the other soil layers, liming increased the N release in soils rich in N and had only small effects in soils poor in N. For the total N supply to the roots in the litter, humus and 0 to 5 cm mineral soil layers, liming caused a slight reduction in soils poor in N and a slight increase in soils rich in N. Data on tree growth corresponded with these results.The hypotheses that tree growth depressions can be caused by reduced N supply after liming and that tree growth increases can be caused by increased N supply after liming thus seem reasonable. 相似文献