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1.
On the assessment of root and soil respiration for soils of different textures: interactions with soil moisture contents and soil CO2 concentrations 总被引:10,自引:0,他引:10
Estimates of root and soil respiration are becoming increasingly important in agricultural and ecological research, but there
is little understanding how soil texture and water content may affect these estimates. We examined the effects of soil texture
on (i) estimated rates of root and soil respiration and (ii) soil CO2 concentrations, during cycles of soil wetting and drying in the citrus rootstock, Volkamer lemon (Citrus volkameriana Tan. and Pasq.). Plants were grown in soil columns filled with three different soil mixtures varying in their sand, silt
and clay content. Root and soil respiration rates, soil water content, plant water uptake and soil CO2 concentrations were measured and dynamic relationships among these variables were developed for each soil texture treatment.
We found that although the different soil textures differed in their plant-soil water relations characteristics, plant growth
was only slightly affected. Root and soil respiration rates were similar under most soil moisture conditions for soils varying
widely in percentages of sand, silt and clay. Only following irrigation did CO2 efflux from the soil surface vary among soils. That is, efflux of CO2 from the soil surface was much more restricted after watering (therefore rendering any respiration measurements inaccurate)
in finer textured soils than in sandy soils because of reduced porosity in the finer textured soils. Accordingly, CO2 reached and maintained the highest concentrations in finer textured soils (> 40 mmol CO2 mol−1). This study revealed that changes in soil moisture can affect interpretations of root and soil measurements based on CO2 efflux, particularly in fine textured soils. The implications of the present findings for field soil CO2 flux measurements are discussed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Effects of elevated atmospheric CO2 on protozoan abundance in soil planted with wheat and on decomposition of wheat roots 总被引:1,自引:1,他引:0
The effect of elevated CO2 on growth of wheat plants (Triticum aestivum cv. Minaret) and soil protozoan and bacterial populations was investigated in soil pots placed in open top chambers fumigated with ambient air or air enriched with CO2 (ambient + 320 l L–1 CO2). We harvested plants two times during the growing season and measured the biomass and the C and N content of roots and shoots. The soil was divided into bulk and rhizosphere soil and the number of bacteria (colony-forming units, CFU) and protozoa was determined. There was no effect of atmospheric CO2 content on the number of bacteria, but the total number of bacterivorous protozoa was higher in pots from the elevated CO2 treatment. This increase was mainly due to an increase in the number of protozoa in the bulk soil. Density of protozoa in the rhizosphere was not affected by elevated CO2. This suggests that the increase in protozoan numbers was a result of a general increase in rhizodeposition, presumably caused by increased root production, and not to an increased root exudation per root mass. After harvest, soil from the two treatments was incubated with and without roots and the respiration rate was estimated at intervals for 200 days. During the first 55 days, the specific root induced respiration rate was not affected by the CO2 level at which the plants had been grown, indicating that the quality of the easily decomposable components of the roots was not affected by CO2 level. 相似文献
3.
Taiji Kou Jianguo Zhu Zubin Xie Toshihiro Hasegawa Katia Heiduk 《Plant and Soil》2007,299(1-2):237-249
Soil respiration in a cropland is the sum of heterotrophic (mainly microorganisms) and autotrophic (root) respiration. The
contribution of both these types to soil respiration needs to be understood to evaluate the effects of environmental change
on soil carbon cycling and sequestration. In this paper, the effects of free-air CO2 enrichment (FACE) on hetero- and autotrophic respiration in a wheat field were differentiated and evaluated by a novel split-root
growth and gas collection system. Elevated atmospheric pCO2 of approximately 200 μmol mol−1 above the ambient pCO2 significantly increased soil respiration by 15.1 and 14.8% at high nitrogen (HN) and low nitrogen (LN) application rates,
respectively. The effect of elevated atmospheric pCO2 on root respiration was not consistent across the wheat growth stages. Elevated pCO2 significantly increased and decreased root respiration at the booting-heading stage (middle stage) and the late-filling stage
(late stage), respectively, in HN and LN treatments; however, no significant effect was found at the jointing stage (early
stage). Thus, the effect of increased pCO2 on cumulative root respiration for the entire wheat growing season was not significant. Cumulative root respiration accounted
for approximately 25–30% of cumulative soil respiration in the entire wheat growing season. Consequently, cumulative microbial
respiration (soil respiration minus root respiration) increased by 22.5 and 21.1% due to elevated pCO2 in HN and LN, respectively. High nitrogen application significantly increased root respiration at the late stage under both
elevated pCO2 and ambient pCO2; however, no significant effects were found on cumulative soil respiration, root respiration, and microbial respiration.
These findings suggest that heterotrophic respiration, which is influenced by increased substrate supplies from the plant
to the soil, is the key process to determine C emission from agro-ecosystems with regard to future scenarios of enriched pCO2. 相似文献
4.
Hiroshi Koizumi Toshie Nakadai Youzou Usami Mitsumasa Satoh Masae Shiyomi Takehisa Oikawa 《Ecological Research》1991,6(3):227-232
In order to assess the validity of conventional methods for measuring CO2 flux from soil, the relationship between soil microbial respiration and ambient CO2 concentration was studied using an open-flow infra-red gas analyser (IRGA) method. Andosol from an upland field in central
Japan was used as a soil sample. Soil microbial respiration activity was depressed with the increase of CO2 concentration in ventilated air from 0 to 1000 ppmv. At 1000 ppmv, the respiration rate was less than half of that at 0 ppmv.
Thus, it is likely that soil respiration rate is overestimated by the alkali absorption method, because CO2 concentration in the absorption chamber is much lower than the normal level. Metabolic responses to CO2 concentration were different among groups of soil microorganisms. The bacteria actinomycetes group cultivated on agar medium
showed a more sensitive response to the CO2 concentration than the filamentous fungi group. 相似文献
5.
Increased atmospheric carbon dioxide (CO2) concentration will likely cause changes in plant productivity and composition that might affect soil decomposition processes.
The objective of this study was to test to what extent elevated CO2 and N fertility-induced changes in residue quality controlled decomposition rates. Cotton (Gossypium hirsutum L.) was grown in 8-l pots and exposed to two concentrations of CO2 (390 or 722 μmol mol-1) and two levels of N fertilization (1.0 or 0.25 g l-1 soil) within greenhouse chambers for 8 wks. Plants were then chemically defoliated and air-dried. Leaf, stem and root residues
were assayed for total non-structural carbohydrates (TNC), lignin (LTGA), proanthocyanidins (PA), C and N. Respiration rates
of an unsterilized sandy soil (Lakeland Sand) mixed with residues from the various treatments were determined using a soda
lime trap to measure CO2 release. At harvest, TNC and PA concentrations were 17 to 45% higher in residues previously treated with elevated CO2 compared with controls. Leaf and stem residue LTGA concentrations were not significantly affected by either the elevated
CO2 or N fertilization treatments, although root residue LTGA concentration was 30% greater in plants treated with elevated CO2. The concentration of TNC in leaf residues from the low N fertilization treatment was 2.3 times greater than that in the
high N fertilization treatment, although TNC concentration in root and stem residues was suppressed 13 to 23% by the low soil
N treatment. PA and LTGA concentrations in leaf, root and stem residues were affected by less than 10% by the low N fertilization
treatment. N concentration was 14 to 44% lower in residues obtained from the elevated CO2 and low N fertilization treatments. In the soil microbial respiration assay, cumulative CO2 release was 10 to 14% lower in soils amended with residues from the elevated CO2 and low N fertility treatments, although treatment differences diminished as the experiment progressed. Treatment effects
on residue N concentration and C:N ratios appeared to be the most important factors affecting soil microbial respiration.
The results of our study strongly suggest that, although elevated CO2 and N fertility may have significant impact on post-harvest plant residue quality of cotton, neither factor is likely to
substantially affect decomposition. Thus, C cycling might not be affected in this way, but via simple increases in plant biomass
production.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
区分土壤呼吸组分并揭示其与环境因素的相关关系,对于准确评估土壤碳过程及其环境影响机制至关重要。根据底物来源和作用机制的差异,土壤呼吸主要包括根系呼吸、根际微生物呼吸、凋落物分解、自然条件下和激发效应下土壤有机质(SOM)分解。现有土壤呼吸组分拆分方法可以分为基于植物源CO2测定或土壤有机质源CO2测定的差分拆分方法,以及基于土壤呼吸组分同位素信号差异的拆分方法。土壤呼吸组分拆分研究可以解决不同土壤呼吸组分对环境变化的响应机制、植物光合碳输入与地下土壤呼吸组分的交互作用、土壤呼吸组分变化对土壤碳库周转的影响机制等科学问题,但其理论假设、观测技术方法、潜在的误差来源等仍需要继续关注并系统研究。 相似文献
7.
Effects of soil water content on soil respiration in forests and cattle pastures of eastern Amazonia 总被引:78,自引:0,他引:78
Eric A. Davidson Louis V. Verchot J. Henrique Cattânio Ilse L. Ackerman J.E.M. Carvalho 《Biogeochemistry》2000,48(1):53-69
The effect of soil water content on efflux of CO2 from soils has been described by linear, logarithmic, quadratic, and parabolic functions of soil water expressed as matric potential, gravimetric and volumetric water content, water holding capacity, water-filled pore space, precipitation indices, and depth to water table. The effects of temperature and water content are often statistically confounded. The objectives of this study are: (1) to analyze seasonal variation in soil water content and soil respiration in the eastern Amazon Basin where seasonal temperature variation is minor; and (2) to examine differences in soil CO2 emissions among primary forests, secondary forests, active cattle pastures, and degraded cattle pastures. Rates of soil respiration decreased from wet to dry seasons in all land uses. Grasses in the active cattle pasture were productive in the wet season and senescent in the dry season, resulting in the largest seasonal amplitude of CO2 emissions, whereas deep-rooted forests maintained substantial soil respiration during the dry season. Annual emissions were 2.0, 1.8, 1.5, and 1.0 kg C m-2 yr-1 for primary forest, secondary forest, active pasture, and degraded pasture, respectively. Emissions of CO2 were correlated with the logarithm of matric potential and with the cube of volumetric water content, which are mechanistically appropriate functions for relating soil respiration at below-optimal water contents. The parameterization of these empirical functions was not consistent with those for a temperate forest. Relating rates of soil respiration to water and temperature measurements made at some arbitrarily chosen depth of the surface horizons is simplistic. Further progress in defining temperature and moisture functions may require measurements of temperature, water content and CO2 production for each soil horizon. 相似文献
8.
Fine root litter derived from birch (Betula pendula Roth.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) plants grown under two CO2 atmospheric concentrations (350 ppm and 600 ppm) and two nutrient regimes was used for decomposition studies in laboratory
microcosms. Although there were interactions between litter type, CO2/fertiliser treatments and decomposition rates, in general, an increase in the C/N ratio of the root tissue was observed for
roots of both species grown under elevated CO2 in unfertilized soil. Both weight loss and respiration of decomposing birch roots were significantly reduced in materials
derived from enriched CO2, whilst the decomposition of spruce roots showed no such effect.
A parallel experiment was performed using Betula pendula root litter grown under different N regimes, in order to test the relationship between C/N ratio of litter and root decomposition
rate. A highly significant (p<0.001) negative correlation between C/N ratio and root litter respiration was found, with an r2=0.97. The results suggest that the increased C/N ratio of plant tissues induced by elevated CO2 can result in a reduction of decomposition rate, with a resulting increase in forest soil C stores. 相似文献
9.
The aim of this study was to evaluate a measuring technique for determining soil CO2 efflux from large soil samples having undisturbed structure under controlled laboratory conditions. Further objectives were
to use the developed measuring method for comparing soil CO2 efflux from samples, collected in three different soil management systems at various soil water content values. The experimental
technique was tested and optimised for timing of sampling by taking air samples after 1, 3 and 6 hours of incubation. Based
on the results, the incubation time was set to three hours. The CO2 efflux measured for different soil management systems was the highest in the no-till and the lowest in the ploughing treatment,
which was in accordance with measurements on accessible organic carbon for microbes. An increase in CO2 efflux with increasing soil water content was found in the studied soil water content range. Our results indicate that soil
respiration rates, measured directly after tillage operations, can highly differ from those measured long after. 相似文献
10.
Non-phototrophic CO
2
fixation by soil microorganisms 总被引:1,自引:0,他引:1
Anja Miltner Frank-Dieter Kopinke Reimo Kindler Draženka Selesi Anton Hartmann Matthias Kästner 《Plant and Soil》2005,269(1-2):193-203
Although soils are generally known to be a net source of CO2 due to microbial respiration, CO2 fixation may also be an important process. The non-phototrophic fixation of CO2 was investigated in a tracer experiment with 14CO2 in order to obtain information about the extent and the mechanisms of this process. Soils were incubated for up to 91 days
in the dark. In three independent incubation experiments, a significant transfer of radioactivity from 14CO2 to soil organic matter was observed. The process was related to microbial activity and could be enhanced by the addition
of readily available substrates such as acetate. CO2 fixation exhibited biphasic kinetics and was linearly related to respiration during the first phase of incubation (about
20–40 days). The fixation amounted to 3–5% of the net respiration. After this phase, the CO2 fixation decreased to 1–2% of the respiration. The amount of carbon fixed by an agricultural soil corresponded to 0.05% of
the organic carbon present in the soil at the beginning of the experiment, and virtually all of the fixed CO2 was converted to organic compounds. Many autotrophic and heterotrophic biochemical processes result in the fixation of CO2. However, the enhancement of the fixation by addition of readily available substrates and the linear correlation with respiration
suggested that the process is mainly driven by aerobic heterotrophic microorganisms. We conclude that heterotrophic CO2 fixation represents a significant factor of microbial activity in soils. 相似文献
11.
Examination of the method for measuring soil respiration in cultivated land: Effect of carbon dioxide concentration on soil respiration 总被引:7,自引:1,他引:6
Toshie Nakadai Hiroshi Koizumi Youzou Usami Mitsumasa Satoh Takehisa Oikawa 《Ecological Research》1993,8(1):65-71
An acceleration of soil respiration with decreasing CO2 concentration was suggested in the field measurements. The result supporrs that obtained in laboratory experiments in our
previous study. The CO2 concentrations in a chamber of the alkali absorption method (the AA-method) were about 150–250 parts/106 lower than that in the atmosphere (about 350 parts/106), while those observed in the open-flow IRGA method (the OF-method) were nearly equal to the soil surface CO2 levels. The AA-method at such low CO2 levels in the chamber appears to overestimate the soil respiration. Our results showed that the rates obtained by the AA-method
were about twice as large as those by the OF-method in field and laboratory measurements. This finding has important consequences
with respect to the validity of the existing data obtained by the AA-method and the estimation of changes in the terrestrial
carbon flow with elevated CO2 相似文献
12.
Sands Roger Nugroho Putranto B. Leung David W.M. Sun Osbert J. Clinton Peter W. 《Plant and Soil》2000,225(1-2):213-225
This study examined the reciprocal effects of growing ryegrass, lotus and other weed species in competition with radiata pine
on soil CO2 and O2 concentrations and on the growth and root respiration of the radiata pine. Soil O2 concentrations decreased and soil CO2 concentrations increased with increasing soil depth. Radiata pine plus competing species slightly reduced soil O2 concentrations and markedly increased soil CO2 concentrations (up to 40 mmol mol−1) compared with radiata pine alone. The dry weights of shoots and roots, and the root respiration rates of radiata pine grown
with competing vegetation were much less than those for radiata pine alone. This probably was not solely caused by competition
for nutrients water or light since adequate water and nutrients were supplied to all treatments and the radiata pine overtopped
the competing vegetation. When radiata pine roots were raised in NaHCO3 solutions equivalent to a range of CO2 concentrations, succinate dehydrogenase activity (a metabolic indicator of mitochondrial respiration) and elongation rates
of roots decreased as CO2 concentrations increased from 0 to 40 mmol mol−1. This suggests that the elevated CO2 concentrations found in the experiments in soil was the cause, at least in part, of the reduced growth of radiata pine in
competition with other species.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
Our investigations of diurnal variations of the 13C/12C ratio and CO2 content in soil air were carried out in three environments during periods of high biosphere activity. It has been observed that diurnal variation of CO2 concentration is negatively correlated 13. Particularly great variations occurred at shallow soil depths (10–30 cm) when the plant cover activity was high while the soil temperature was rather low. Under such conditions the 13 variations had the magnitude of 4, while the CO2 concentration varied more than doubly. The maximum of the 13C/12C ratlo and the minimum of the CO2 concentration in a cultivated field with winter wheat took place in the afternoon, whereas in deciduous forest similar patterns were observed at dawn. In these cases soil temperatures at 10 cm depths varied less than 2°C. Hence, under wheat the variation in root respiration rate seem to be the main reason of the recorded varations. In an uncultivated grass-field during the hottest period in summer we did not measure any distinct variations of CO2 properties in spite of the fact that soil temperature varied up to 5°C. This might be due to dominant microbial respiration at the high soil temperature, which exceeded 20°C. 相似文献
14.
The strength of coupling between canopy gas exchange and root respiration was examined in ~15-yr-old ponderosa pine (Pinus ponderosa Doug. Ex Laws.) growing under seasonally drought stressed conditions. By regularly watering part of the root system to reduce tree water stress and measuring soil CO2 efflux on the dry, distant side of the tree, we were able to determine the strength of the relationship between soil autotrophic (root and rhizosphere) respiration and changes in canopy carbon uptake and water loss by comparison with control trees (no watering). After ~40 days the soil CO2 efflux rate, relative to pre-treatment conditions, was twice that of the controls. This difference, attributable to root and rhizosphere respiration, was strongly correlated with differences in transpiration rates between treatments (r2 = 0.73, p<0.01). By the end of the period, transpiration of the irrigated treatment was twice that of controls. Periodic measurements of photosynthesis under non-light limited conditions paralleled the patterns of transpiration and were systematically higher in the irrigated treatment. We observed no evidence for a greater sensitivity of soil autotrophic respiration to temperature compared to the response of heterotrophic respiration to temperature; the Q10 for total soil respiration was 1.6 (p>0.99) for both treatments. At the ecosystem scale, daily soil CO2 efflux rate was linearly related to gross primary productivity (GPP) as measured by eddy-covariance technique (r2 = 0.55, p<0.01), suggesting patterns of soil CO2 release appear strongly correlated to recent carbon assimilation in this young pine stand. Collectively the observed relationships suggest some consideration should be given to the inclusion of canopy processes in future models of soil respiration. 相似文献
15.
The [CO2] in the xylem of tree stems is typically two to three orders of magnitude greater than atmospheric [CO2]. In this study, xylem [CO2] was experimentally manipulated in saplings of sycamore (Platanus occidentalis L.) and sweetgum (Liquidambar styraciflua L.) by allowing shoots severed from their root systems to absorb water containing [CO2] ranging from 0.04% to 14%. The effect of xylem [CO2] on CO2 efflux to the atmosphere from uninjured and mechanically injured, i.e., wounded, stems was examined. In both wounded and unwounded stems, and in both species, CO2 efflux was directly proportional to xylem [CO2], and increased 5-fold across the range of xylem [CO2] produced by the [CO2] treatment. Xylem [CO2] explained 76–77% of the variation in pre-wound efflux. After wounding, CO2 efflux increased substantially but remained directly proportional to internal stem [CO2]. These experiments substantiated our previous finding that stem CO2 efflux was directly related to internal xylem [CO2] and expanded our observations to two new species. We conclude that CO2 transported in the xylem may confound measurements of respiration based on CO2 efflux to the atmosphere. This study also provided evidence that the rapid increase in CO2 efflux observed after tissues are excised or injured is likely the result of the rapid diffusion of CO2 from the xylem, rather than an actual increase in the rate of respiration of wounded tissues. 相似文献
16.
Model for rhizodeposition and CO2 efflux from planted soil and its validation by 14C pulse labelling of ryegrass 总被引:4,自引:0,他引:4
A model for rhizodeposition and root respiration was developed and parameterised based on 14C pulse labelling of Lolium perenne. The plants were grown in a two-compartment chamber on a loamy Haplic Luvisol under controlled laboratory conditions. The dynamics of 14CO2 efflux from the soil and 14C content in shoots, roots, micro-organisms, dissolved organic carbon (DOC) and soil were measured during the first 11 days after labelling. Modelled parameters were estimated by fitting on measured 14C dynamics in the different pools. The model and the measured 14C dynamics in all pools corresponded well (r
2=0.977). The model describes well 14CO2 efflux from the soil and 14C dynamics in shoots, roots and soil, but predicts unsatisfactorily the 14C content in micro-organisms and DOC. The model also allows for division of the total 14CO2 efflux from the soil in 14CO2 derived from root respiration and 14CO2 derived from rhizomicrobial respiration by use of exudates and root residues. Root respiration and rhizomicrobial respiration amounted for 7.6% and 6.0% of total assimilated C, respectively, which accounts for 56% and 44% of root-derived 14CO2 efflux from the soil planted with 43-day-old Lolium perenne, respectively. The sensitivity analysis has shown that root respiration rate affected the curve of 14CO2 efflux from the soil mainly during the first day after labelling. The changes in the exudation rate influenced the 14CO2 efflux later than first 24 h after labelling. 相似文献
17.
Indirect partitioning of soil respiration in a series of evergreen forest ecosystems 总被引:1,自引:0,他引:1
A simple estimation of heterotrophic respiration can be obtained analytically as the y-intercept of the linear regression between soil-surface CO2 efflux and root biomass. In the present study, a development of this indirect methodology is presented by taking into consideration
both the temporal variation and the spatial heterogeneity of heterotrophic respiration. For this purpose, soil CO2 efflux, soil carbon content and main stand characteristics were estimated in seven evergreen forest ecosystems along an elevation
gradient ranging from 250 to 1740 m. For each site and for each sampling date the measured soil CO2 efflux (R
S) was predicted with the model R
S = a × S
C + b × R
D ± ε, where S
C is soil carbon content per unit area to a depth of 30 cm and R
D is the root density of the 2–5 mm root class. Regressions with statistically significant a and b coefficients allowed the indirect separation of the two components of soil CO2 efflux. Considering that the different sampling dates were characterized by different soil temperature, it was possible to
investigate the temporal and thermal dependency of autotrophic and heterotrophic respiration. It was estimated that annual
autotrophic respiration accounts for 16–58% of total soil CO2 efflux in the seven different evergreen ecosystems. In addition, our observations show a decrease of annual autotrophic respiration
at increasing availability of soil nitrogen.
Section Editor: A. Hodge 相似文献
18.
Separating root and soil microbial contributions to soil respiration: A review of methods and observations 总被引:131,自引:12,他引:119
Forest soil respiration is the sum of heterotrophic (microbes, soil fauna) and autotrophic (root) respiration. The contribution of each group needs to be understood to evaluate implications of environmental change on soil carbon cycling and sequestration. Three primary methods have been used to distinguish hetero- versus autotrophic soil respiration including: integration of components contributing to in situ forest soil CO2 efflux (i.e., litter, roots, soil), comparison of soils with and without root exclusion, and application of stable or radioactive isotope methods. Each approach has advantages and disadvantages, but isotope based methods provide quantitative answers with the least amount of disturbance to the soil and roots. Published data from all methods indicate that root/rhizosphere respiration can account for as little as 10 percent to greater than 90 percent of total in situ soil respiration depending on vegetation type and season of the year. Studies which have integrated percent root contribution to total soil respiration throughout an entire year or growing season show mean values of 45.8 and 60.4 percent for forest and nonforest vegetation, respectively. Such average annual values must be extrapolated with caution, however, because the root contribution to total soil respiration is commonly higher during the growing season and lower during the dormant periods of the year. 相似文献
19.
T. J. BOUMA K. L. NIELSEN D. M. EISSENSTAT J. P. LYNCH 《Plant, cell & environment》1997,20(12):1495-1505
Contrasting effects of soil CO2 concentration on root respiration rates during short-term CO2 exposure, and on plant growth during long-term CO2 exposure, have been reported. Here we examine the effects of both short- and long-term exposure to soil CO2 on the root respiration of intact plants and on plant growth for bean (Phaseolus vulgaris L.) and citrus (Citrus volkameriana Tan. & Pasq.). For rapidly growing bean plants, the growth and maintenance components of root respiration were separated to determine whether they differ in sensitivity to soil CO2. Respiration rates of citrus roots were unaffected by the CO2 concentration used during the respiration measurements (200 and 2000 μmol mol−1), regardless of the soil CO2, concentration during the previous month (600 and 20 000 μmol mol−1). Bean plants were grown with their roots exposed to either a natural CO2 diffusion gradient, or to an artificially maintained CO2 concentration of 600 or 20 000 μmol mol−1. These treatments had no effect on shoot and root growth. Growth respiration and maintenance respiration of bean roots were also unaffected by CO2 pretreatment and the CO2 concentration used during the respiration measurements (200–2000 μmol mol−1). We conclude that soil CO2 concentrations in the range likely to be encountered in natural soils do not affect root respiration in citrus or bean. 相似文献
20.
Vincent J. Pacific Brian L. McGlynn Diego A. Riveros-Iregui Daniel L. Welsch Howard E. Epstein 《Biogeochemistry》2008,91(1):51-70
The spatial and temporal controls on soil CO2 production and surface CO2 efflux have been identified as outstanding gaps in our understanding of carbon cycling. We investigated both across two riparian-hillslope transitions in a subalpine catchment, northern Rocky Mountains, Montana. Riparian-hillslope transitions provide ideal locations for investigating the controls on soil CO2 dynamics due to strong, natural gradients in the factors driving respiration, including soil water content (SWC) and soil temperature. We measured soil air CO2 concentrations (20 and 50 cm), surface CO2 efflux, soil temperature, and SWC at eight locations. We investigated (1) how soil CO2 concentrations differed within and between landscape positions; (2) how the timing of peak soil CO2 concentrations varied across riparian and hillslope zones; and (3) whether higher soil CO2 concentrations necessarily resulted in higher efflux (i.e. did surface CO2 efflux follow patterns of subsurface CO2)? Soil CO2 concentrations were significantly higher in the riparian zones, likely due to higher SWC. The timing of peak soil CO2 concentrations also differed between riparian and hillslope zones, with highest hillslope concentrations near peak snowmelt and highest riparian concentrations during the late summer and early fall. Surface CO2 efflux was relatively homogeneous at monthly timescales as a result of different combinations of soil CO2 production and transport, which led to equifinality in efflux across the transects. However, efflux was 57% higher in the riparian zones when integrated to cumulative growing season efflux, and suggests higher riparian soil CO2 production. 相似文献