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1.
To determine the effect of microbial metabolites on the release of root exudates from perennial ryegrass, seedlings were pulse labelled with [14C]-CO2 in the presence of a range of soil micro-organisms. Microbial inoculants were spatially separated from roots by Millipore membranes so that root infection did not occur. Using this technique, only microbial metabolites affected root exudation. The effect of microbial metabolites on carbon assimilation and distribution and root exudation was determined for 15 microbial species. Assimilation of a pulse label varied by over 3.5 fold, dependent on inoculant. Distribution of the label between roots and shoots also varied with inoculant, but the carbon pool that was most sensitive to inoculation was root exudation. In the absence of a microbial inoculant only 1% of assimilated label was exuded. Inoculation of the microcosms always caused an increase in exudation but the percentage exuded varied greatly, within the range of 3–34%.  相似文献   

2.
Carbon cycling responses of ecosystems to global warming will likely be stronger in cold ecosystems where many processes are temperature‐limited. Predicting these effects is difficult because air and soil temperatures will not change in concert, and will affect above and belowground processes differently. We disentangled above and belowground temperature effects on plant C allocation and deposition of plant C in soils by independently manipulating air and soil temperatures in microcosms planted with either Leucanthemopsis alpina or Pinus mugo seedlings. Daily average temperatures of 4 or 9°C were applied to shoots and independently to roots, and plants pulse‐labelled with 14CO2. We traced soil CO2 and 14CO2 evolution for 4 days, after which microcosms were destructively harvested and 14C quantified in plant and soil fractions. In microcosms with L. alpina, net 14C uptake was higher at 9°C than at 4°C soil temperature, and this difference was independent of air temperature. In warmer soils, more C was allocated to roots at greater soil depth, with no effect of air temperature. In P. mugo microcosms, assimilate partitioning to roots increased with air temperature, but only when soils were at 9°C. Higher soil temperatures also increased the mean soil depth at which 14C was allocated. Our findings highlight the dependence of C uptake, use, and partitioning on both air and soil temperature, with the latter being relatively more important. The strong temperature‐sensitivity of C assimilate use in the roots and rhizosphere supports the hypothesis that cold limitation on C uptake is primarily mediated by reduced sink strength in the roots. We conclude that variations in soil rather than air temperature are going to drive plant responses to warming in cold environments, with potentially large changes in C cycling due to enhanced transfer of plant‐derived C to soils.  相似文献   

3.
A microcosm is described in which root exudation may be estimated in the presence of microorganisms. Ryegrass seedlings are grown in microcosms in which roots were spatially separated from a microbial inoculant by a Millipore membrane. Seedlings grown in the microcosms were labelled with [14C]-CO2, and the fate of the label within the plant and rhizosphere was determined. Inoculation of the microcosms with Cladosporium resinae increased net fixation of the [14C] label compared to plants grown under sterile conditions. Inoculation also increased root exudation. The use of the microcosm was illustrated and its applications discussed.  相似文献   

4.
Kuzyakov  Y.  Kretzschmar  A.  Stahr  K. 《Plant and Soil》1999,213(1-2):127-136
Carbon rhizodeposition and root respiration during eight development stages of Lolium perenne were studied on a loamy Gleyic Cambisol by 14CO2 pulse labelling of shoots in a two compartment chamber under controlled laboratory conditions. Total 14CO2 efflux from the soil (root respiration, microbial respiration of exudates and dead roots) in the first 8 days after 14C pulse labelling decreased during plant development from 14 to 6.5% of the total 14C input. Root respiration accounted for was between 1.5 and 6.5% while microbial respiration of easily available rhizodeposits and dead root remains were between 2 and 8% of the 14C input. Both respiration processes were found to decline during plant development, but only the decrease in root respiration was significant. The average contribution of root respiration to total 14CO2 efflux from the soil was approximately 41%. Close correlation was found between cumulative 14CO2 efflux from the soil and the time when maximum 14CO2 efflux occurred (r=0.97). The average total of CO2 Defflux from the soil with Lolium perenne was approximately 21 μg C-CO2 d−1 g−1. It increased slightly during plant development. The contribution of plant roots to total CO2 efflux from the soil, calculated as the remainder from respiration of bare soil, was about 51%. The total 14C content after 8 days in the soil with roots ranged from 8.2 to 27.7% of assimilated carbon. This corresponds to an underground carbon transfer by Lolium perenne of 6–10 g C m−2 at the beginning of the growth period and 50–65 g C m−2 towards the end of the growth period. The conventional root washing procedure was found to be inadequate for the determination of total carbon input in the soil because 90% of the young fine roots can be lost. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

5.
M. Werth  Y. Kuzyakov 《Plant and Soil》2006,284(1-2):319-333
Coupling 13C natural abundance and 14C pulse labelling enabled us to investigate the dependence of 13C fractionation on assimilate partitioning between shoots, roots, exudates, and CO2 respired by maize roots. The amount of recently assimilated C in these four pools was controlled by three levels of nutrient supply: full nutrient supply (NS), 10 times diluted nutrient supply (DNS), and deionised water (DW). After pulse labelling of maize shoots in a 14CO2 atmosphere, 14C was traced to determine the amounts of recently assimilated C in the four pools and the δ13C values of the four pools were measured. Increasing amounts of recently assimilated C in the roots (from 8% to 10% of recovered 14C in NS and DNS treatments) led to a 0.3‰ 13C enrichment from NS to DNS treatments. A further increase of C allocation in the roots (from 10% to 13% of recovered 14C in DNS and DW treatments) resulted in an additional enrichment of the roots from DNS to DW treatments by 0.3‰. These findings support the hypothesis that 13C enrichment in a pool increases with an increasing amount of C transferred into that pool. δ13C of CO2 evolved by root respiration was similar to that of the roots in DNS and DW treatments. However, if the amount of recently assimilated C in root respiration was reduced (NS treatment), the respired CO2 became 0.7‰ 13C depleted compared to roots. Increasing amounts of recently assimilated C in the CO2 from NS via DNS to DW treatments resulted in a 1.6‰ δ13C increase of root respired CO2 from NS to DW treatments. Thus, for both pools, i.e. roots and root respiration, increasing amounts of recently assimilated C in the pool led to a δ13C increase. In DW and DNS plants there was no 13C fractionation between roots and exudates. However, high nutrient supply decreased the amount of recently assimilated C in exudates compared to the other two treatments and led to a 5.3‰ 13C enrichment in exudates compared to roots. We conclude that 13C discrimination between plant pools and within processes such as exudation and root respiration is not constant but strongly depends on the amount of C in the respective pool and on partitioning of recently assimilated C between plant pools. Section Editor: H. Lambers  相似文献   

6.
宋明华  陈锦  蒋婧  王枫  于飞海 《生态学报》2020,40(11):3688-3697
外源氮素(N)输入陆地生态系统后会引起植物和土壤各碳库的变化,但是对不同化学形态氮素的长期输入如何影响光合碳在植物组织、土壤、土壤呼吸中的分配及转运知之甚少,尤其是对于氮输入引起光合碳分配变化进而作用于植物和土壤碳库的机制的认识还非常匮乏。基于在青藏高原矮嵩草草甸开展的不同化学形态氮素添加的长期实验,利用~(13)C示踪方法揭示了光合碳在植物地上、地下组织的分配,及其随时间在土壤中的滞留和随土壤呼吸的释放。研究结果表明,外源氮素添加10年后,与对照未添加氮素处理相比,氨态氮处理下的地上生物量增加了49.5%,氨态氮处理下的地下生物量增加了111.3%。土壤中滞留的~(13)C整体呈下降趋势,氨态氮处理下的土壤碳库显著高于硝态氮处理下的值。不同处理下的土壤呼吸中~(13)C的滞留量随时间呈指数衰减的变化趋势,其中,硝态氮处理下的~(13)C衰减最快。~(13)C同位素标记后第1天测定植物茎和叶内的~(13)C约占刚刚标定完茎和叶内~(13)C的80%,不同处理之间没有显著性差异。直至标记后的第30天,茎和叶内~(13)C的滞留量约占初始量的30%。硝态氮处理下的值在第21天和第30天显著低于对照和氨态氮处理下的值,表明硝态氮处理下,植物光合固定的碳在短期内迅速输入地下组织和土壤中。这些结果从机理上阐明了植物光合碳分配对不同化学形态氮素长期输入的响应,进而影响到土壤呼吸CO_2的释放,以及对土壤碳库动态的贡献。加深了对高寒草甸土壤有机碳库稳定性维持机制的认识,能够为高寒草地的科学管理以及资源的可持续利用提供理论指导。  相似文献   

7.
Much of our understanding about how carbon (C) is allocated in plants comes from radiocarbon (14C) pulse‐chase labeling experiments. However, the large amounts of 14C required for decay‐counting mean that these studies have been restricted for the most part to mesocosm or controlled laboratory experiments. Using the enhanced sensitivity for 14C detection available with accelerator mass spectrometry (AMS), we tested the utility of a low‐level 14C pulse‐chase labeling technique for quantifying C allocation patterns and the contributions of different plant components to total ecosystem respiration in a black spruce forest stand in central Manitoba, Canada. All aspects of the field experiment used 14C at levels well below regulated health standards, without significantly altering atmospheric CO2 concentrations. Over 30 days following the label application in late summer (August and September), we monitored the temporal and spatial allocation patterns of labeled photosynthetic products by measuring the amount and 14C content of CO2 respired from different ecosystem components. The mean residence times (MRT) for labeled photosynthetic products to be respired in the understory (feather mosses), canopy (black spruce), and rhizosphere (black spruce roots and associated microbes) were <1, 6, and 15 days, respectively. Respiration from the canopy and understory showed significantly greater influence of labeled photosynthates than excised root and intact rhizosphere respiration. After 30 days,∼65% of the label assimilated had been respired by the canopy,∼20% by the rhizosphere, and∼9% by the understory, with∼6% unaccounted for and perhaps remaining in tissues. Maximum 14C values in root and rhizosphere respiration were reached 4 days after label application. The label was still detectable in root, rhizosphere and canopy respiration after 30 days; these levels of remaining label would not have been detectible had a 13C label been applied. Our results support previous studies indicating that a substantial portion of the C fueling rhizosphere respiration in the growing season may be derived from stored C pools rather than recent photosynthetic products.  相似文献   

8.
Turnover and distribution of root exudates of Zea mays   总被引:1,自引:0,他引:1  
Decomposition and distribution of root exudates of Zea mays L. were studied by means of 14CO2 pulse labeling of shoots on a loamy Haplic Luvisol. Plants were grown in two-compartment pots, where the lower part was separated from the roots by monofilament gauze. Root hairs, but not roots, penetrated through the gauze into the lower part of the soil. The root-free soil in the lower compartment was either sterilized with cycloheximide and streptomycin or remained non-sterile. In order to investigate exudate distribution, 3 days after the 14C labeling, the lower soil part was frozen and sliced into 15, one-mm thick layers using a microtome. Cumulative 14CO2 efflux from the soil during the first 3 days after 14C pulse labeling did not change during plant growth and amounted to about 13–20% of the total recovered 14C (41–55% of the carbon translocated below ground). Nighttime rate of total CO2 efflux was 1.5 times lower than during daytime because of tight coupling of exudation with photosynthesis intensity. The average CO2 efflux from the soil with Zea mays was about 74 g C g–1 day–1 (22 g C m–2 day–1), although, the contribution of plant roots to the total CO2 efflux from the soil was about 78%, and only 22% was respired from the soil organic matter. Zea mays transferred about 4 g m–2 of carbon under ground during 26 days of growth. Three zones of exudate concentrations were identified from the distribution of the 14C-activity in rhizosphere profiles after two labeling periods: (1) 1–2 (3) mm (maximal concentration of exudates) 2) 3–5 mm (presence of exudates is caused by their diffusion from the zone 1); (3) 6–10 mm (very insignificant amounts of exudates diffused from the previous zones). At the distance further than 10 mm no exudates were found. The calculated coefficient of exudate diffusion in the soil was 1.9 × 10–7 cm2 s–1.  相似文献   

9.
Carbon loss from the roots of tomato and pea seedlings grown in soil   总被引:2,自引:0,他引:2  
Tomato and pea seedlings were grown for 14d and 28d with shoots in constant specific activity14CO2 and the amounts and distribution of carbon within the plants and of that released into the soil from the roots were measured. The estimates of carbon loss were derived from measurements of14CO2 respired from both the root and the accompanying microbial population and from the root derived14C-labelled organic carbon compounds in the soil. The relationship between plant growth and the loss of carbon and distribution of carbon within the plants are discussed.  相似文献   

10.
The fate of carbon in pulse-labelled crops of barley and wheat   总被引:11,自引:0,他引:11  
Wheat (cv. Gutha) and barley (cv. O'Connor) were grown as field crops on a shallow duplex soil (sand over clay) in Western Australia with their root systems contained within pvc columns. At four stages during growth, the shoots were pulse-labelled for 1.5h with14CO2; immediately prior to labelling, the soil was isolated from the shoot atmosphere by pvc sheets. After labelling, the soil atmosphere was pumped through NaOH to trap respired CO2 and after 2.5, 5, 7.5 and 24 h from the start of labelling, columns were destructively sampled to recover14C from the roots, soil and shoot.Both species showed similar patterns of14C distribution and changes in distribution through the growing season. During early tillering, 15–25% of the14C recovered after 24 h had been respired by the roots and rhizosphere, 17–27% was retained in the roots, 0.4–1.8% was recovered as water-soluble14C in the soil and the remainder (45–67%) was present in the shoot. These percentages changed during growth so that during grain filling only 2–3% of the14C recovered after 24 h was as respired CO2, 2–6% was in the roots, 0.2% was in the soil and over 90% was in the shoot.The distribution of14C in components of the soil-plant system changed during the 24 h after labelling with the most rapid changes occurring generally during the first 7.5 h after labelling.Using growth measurements from adjacent plots, the amounts of C added to the soil were estimated for the whole season. Carbon input to the soil was about 48 gC m–2 for wheat and 58 gC m–2 for barley; the crops produced total shoot dry matter of 494 (wheat) and 735 g m–2 (barley). Of the C input to the soil, 27.8% (wheat) and 40.3% (barley) was as respired C and only 3.3 (wheat) and 4.1% (barley) was collected as exudate (water-soluble material).  相似文献   

11.
Radiocarbon signatures (Δ14C) of carbon dioxide (CO2) provide a measure of the age of C being decomposed by microbes or respired by living plants. Over a 2‐year period, we measured Δ14C of soil respiration and soil CO2 in boreal forest sites in Canada, which varied primarily in the amount of time since the last stand‐replacing fire. Comparing bulk respiration Δ14C with Δ14C of CO2 evolved in incubations of heterotrophic (decomposing organic horizons) and autotrophic (root and moss) components allowed us to estimate the relative contributions of O horizon decomposition vs. plant sources. Although soil respiration fluxes did not vary greatly, differences in Δ14C of respired CO2 indicated marked variation in respiration sources in space and time. The 14C signature of respired CO2 respired from O horizon decomposition depended on the age of C substrates. These varied with time since fire, but consistently had Δ14C greater (averaging ~120‰) than autotrophic respiration. The Δ14C of autotrophically respired CO2 in young stands equaled those expected for recent photosynthetic products (70‰ in 2003, 64‰ in 2004). CO2 respired by black spruce roots in stands >40 years old had Δ14C up to 30‰ higher than recent photosynthates, indicating a significant contribution of C stored at least several years in plants. Decomposition of O horizon organic matter made up 20% or less of soil respiration in the younger (<40 years since fire) stands, increasing to ~50% in mature stands. This is a minimum for total heterotrophic contribution, since mineral soil CO2 had Δ14C close to or less than those we have assigned to autotrophic respiration. Decomposition of old organic matter in mineral soils clearly contributed to soil respiration in younger stands in 2003, a very dry year, when Δ14C of soil respiration in younger successional stands dropped below those of the atmospheric CO2.  相似文献   

12.
Separating ecosystem and soil respiration into autotrophic and heterotrophic component sources is necessary for understanding how the net ecosystem exchange of carbon (C) will respond to current and future changes in climate and vegetation. Here, we use an isotope mass balance method based on radiocarbon to partition respiration sources in three mature black spruce forest stands in Alaska. Radiocarbon (Δ14C) signatures of respired C reflect the age of substrate C and can be used to differentiate source pools within ecosystems. Recently‐fixed C that fuels plant or microbial metabolism has Δ14C values close to that of current atmospheric CO2, while C respired from litter and soil organic matter decomposition will reflect the longer residence time of C in plant and soil C pools. Contrary to our expectations, the Δ14C of C respired by recently excised black spruce roots averaged 14‰ greater than expected for recently fixed photosynthetic products, indicating that some portion of the C fueling root metabolism was derived from C storage pools with turnover times of at least several years. The Δ14C values of C respired by heterotrophs in laboratory incubations of soil organic matter averaged 60‰ higher than the contemporary atmosphere Δ14CO2, indicating that the major contributors to decomposition are derived from a combination of sources consistent with a mean residence time of up to a decade. Comparing autotrophic and heterotrophic Δ14C end members with measurements of the Δ14C of total soil respiration, we calculated that 47–63% of soil CO2 emissions were derived from heterotrophic respiration across all three sites. Our limited temporal sampling also observed no significant differences in the partitioning of soil respiration in the early season compared with the late season. Future work is needed to address the reasons for high Δ14C values in root respiration and issues of whether this method fully captures the contribution of rhizosphere respiration.  相似文献   

13.
The effect of liming on the flow of recently photosynthesized carbon to rhizosphere soil was studied using 13CO2 pulse labelling, in an upland grassland ecosystem in Scotland. The use of 13C enabled detection, in the field, of the effect of a 4‐year liming period of selected soil plots on C allocation from plant biomass to soil, in comparison with unlimed plots. Photosynthetic rates and carbon turnover were higher in plants grown in limed soils than in those from unlimed plots. Higher δ13C‰ values were detected in shoots from limed plants than in those from unlimed plants in samples clipped within 15 days of the end of pulse labelling. Analysis of the aboveground plant production corresponding to the 4‐year period of liming indicated that the standing biomass was higher in plots that received lime. Lower δ13C‰ values in limed roots compared with unlimed roots were found, whereas no significant difference was detected between soil samples. Extrapolation of our results indicated that more C has been lost through the soil than has been gained via photosynthetic assimilation because of pasture liming in Scotland during the period 1990–1998. However, the uncertainty associated with such extrapolation based on this single study is high and these estimates are provided only to set our findings in the broader context of national soil carbon emissions.  相似文献   

14.
How soil carbon balance will be affected by plant–mycorrhizal interactions under future climate scenarios remains a significant unknown in our ability to forecast ecosystem carbon storage and fluxes. We examined the effects of soil temperature (14, 20, 26 °C) on the structure and extent of a multispecies community of arbuscular mycorrhizal (AM) fungi associated with Plantago lanceolata. To isolate fungi from roots, we used a mesh‐divided pot system with separate hyphal compartments near and away from the plant. A 13C pulse label was then used to trace the flow of recently fixed photosynthate from plants into belowground pools and respiration. Temperature significantly altered the structure and allocation of the AM hyphal network, with a switch from more vesicles (storage) in cooled soils to more extensive extraradical hyphal networks (growth) in warmed soils. As soil temperature increased, we also observed an increase in the speed at which plant photosynthate was transferred to and respired by roots and AM fungi coupled with an increase in the amount of carbon respired per unit hyphal length. These differences were largely independent of plant size and rates of photosynthesis. In a warmer world, we would therefore expect more carbon losses to the atmosphere from AM fungal respiration, which are unlikely to be balanced by increased growth of AM fungal hyphae.  相似文献   

15.
Distribution of net assimilated C in meadow fescue (Fectuca pratensi L.) was followed before and after cutting of the shoots. Plants were continuously labelled in a growth chamber with 14C-labelled CO2 in the atmosphere from seedling to cutting and with 13C-labelled CO2 in the atmosphere during regrowth after the cutting. Labelled C, both 14C and 13C, was determined at the end of the two growth periods in shoots, crowns, roots, soil and rhizosphere respiration. Distribution of net assimilated C followed almost the same pattern at the end of the two growth periods, i.e. at the end of the 14C- and the 13C-labelling periods. Shoots retained 71–73% of net assimilated C while 9% was detected in the roots and 11–14% was released from the roots, determined as labelled C in soil and as rhizosphere respiration. At the end of the 2nd growth period, after cutting and regrowth, 21% of the residual plant 14C at cutting (14C in crowns and roots) was found in the new shoot biomass. A minor part of the residual plant 14C, 12%, was lost from the plants. The decreases in 14C in crowns and roots during the regrowth period suggest that 14C in both crowns and roots was translocated to new shoot tissue. Approximately half of the total root C at the end of the regrowth period after cutting was 13C-labelled C and thus represents new root growth. Root death after cutting could not be determined in this experiment, since the decline in root 14C during the regrowth period may also be assigned to root respiration, root exudation and translocation to the shoots. ei]{gnH}{fnLambers} ei]{gnA C}{fnBorstlap}  相似文献   

16.
The re-sorption of carbon compounds from the rhizosphere was investigated using 14C-labelled glucose, mannose and citric acid. Uptake in roots of 5-day-old, intact Zea mays plants in sterile solution culture was determined over a period of 48 hours. Under optimal growth conditions significant re-absorption of glucose and mannose occurred with the uptake rates being 70.5 and 40.2 g compound g-1 root DW h-1, respectively. For glucose and mannose approximately 25% of the 14C label taken up by the root was recovered inside the plant as low-MW compounds and 33% polymerized into high MW compounds. 42% was respired as 14C-CO2. Citric acid by comparison showed little accumulation within plant tissues (11.4%) with most being respired and recovered as 14C-CO2 in KOH traps (88%). The uptake rate for citric acid was 34.8 g g-1 root DW h-1. Over the 48-hour period a net efflux (i.e. exudation) of labelled plus unlabelled C was observed at a rate of 608 g C g-1 root DW h-1 (equivalent to 1520 g glucose/mannose). Of the C released as root exudates, a minimum estimate of the amount of C taken back into the plant was therefore 9.5%. The two main C fluxes within the rhizosphere, namely release of C by the root and uptake by the microorganisms, have been well documented in recent years. It is now apparent however that a third flux term, re-sorption of C by roots, can also be identified. This may play an important but previously overlooked role within the rhizosphere, and further work is needed to determine its significance.A comparison between exudate release in static (permitting accumulation of C) and flowing culture (C removed as it is released) was also made with the respective rates being 15.36 and 45.18 mg C g-1 root DW in 2 days. The relative important of re-sorption in natural environments and laboratory experiments is discussed.  相似文献   

17.
Mineral-associated organic matter (MAOM) is a key component of the global carbon (C) and nitrogen (N) cycles, but the processes controlling its formation from plant litter are not well understood. Recent evidence suggests that more MAOM will form from higher quality litters (e.g., those with lower C/N ratios and lower lignocellulose indices), than lower quality litters. Shoots and roots of the same non-woody plant can provide good examples of high and low quality litters, respectively, yet previous work tends to show a majority of soil organic matter is root-derived. We investigated the effect of litter quality on MAOM formation from shoots versus roots using a litter-soil slurry incubation of isotopically labeled (13C and 15N) shoots or roots of Big Bluestem (Andropogon gerardii) with isolated silt or clay soil fractions. The slurry method minimized the influence of soil structure and maximized contact between plant material and soil. We tracked the contribution of shoot- and root-derived C and N to newly formed MAOM over 60 days. We found that shoots contributed more C and N to MAOM than roots. The formation of shoot-derived MAOM was also more efficient, meaning that less CO2 was respired per unit MAOM formed. We suggest that these results are driven by initial differences in litter chemistry between the shoot and root material, while results of studies showing a majority of soil organic matter is root-derived may be driven by alternate mechanisms, such as proximity of roots to mineral surfaces, greater contribution of roots to aggregate formation, and root exudation. Across all treatments, newly formed MAOM had a low C/N ratio compared to the parent plant material, which supports the idea that microbial processing of litter is a key pathway of MAOM formation.  相似文献   

18.
Abstract Young willow plants (Salix‘aquatica gigantea’) were grown in hydroponic culture media, and 14C–labelled sodium bicarbonate was fed to the roots. Uptake of 14C-label in the leaves and shoots was assayed after two different feeding periods (6 h, 48 h). Even during the shortest feeding period, 14C-label had been transferred to the leaves and shoots. Compared with the longer feeding period, after the 6 h feeding period more label was in the form of acid-labile products, whereas after the 48 h feeding period most of the label was in acid-stable products. A second experiment was designed to test whether carbon uptake by roots affects the growth of young willow plants. Uniform rooted cuttings were grown in hydroponic cultures at five different levels of bicarbonate: 0, 0.015, 0.147 0.737, and 1.473 mol m?3 NaHCO3. After a 4-week growing period we determined the biomass of leaves, shoots, roots and cuttings. Production of total dry matter (shoots, leaves and roots) increased with increasing bicarbonate concentration. Saturation of dry matter production was reached at 0.737 mol m?3 NaHCO3, but a higher concentration of NaHCO3 (1.470 mol m?3) caused a slight decrease in the dry matter production. At 0.737 mol m?3 NaHCO3 the total dry weight increased by 31.1%, which suggests that uptake of dissolved carbon dioxide through the roots might affect carbon budgeting in young willow plants.  相似文献   

19.
Gorissen  A.  Cotrufo  M.F. 《Plant and Soil》2000,224(1):75-84
Leaf and root tissue of Lolium perenne L., Agrostis capillaris L. and Festuca ovina L. grown under ambient (350 μl l-1 CO2) and elevated (700 μl l-1) CO2 in a continuously 14C-labelled atmosphere and at two soil N levels, were incubated at 14°C for 222 days. Decomposition of leaf and root tissue grown in the low N treatment was not affected by elevated [CO2], whereas decomposition in the high N treatment was significantly reduced by 7% after 222 days. Despite the increased C/N ratio (g g-1) of tissue cultivated at elevated [CO2] when compared with the corresponding ambient tissue, there was no significant correlation between initial C/N ratio and 14C respired. This finding suggests that the CO2-induced changes in decomposition rates do not occur via CO2-induced changes in C/N ratios of plant materials. We combined the decomposition data with data on 14C uptake and allocation for the same plants, and give evidence that elevated [CO2] has the potential to increase soil C stores in grassland via increasing C uptake and shifting C allocation towards the roots, with an inherent slower decomposition rate than the leaves. An overall increase of 15% in 14C remaining after 222 days was estimated for the combined tissues, i.e., the whole plants; the leaves made a much smaller contribution to the C remaining (+6%) than the roots (+26%). This shows the importance of clarifying the contribution of roots and leaves with respect to the question whether grassland soils act as a sink or source for atmospheric CO2. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

20.
Kuzyakov  Y.  Domanski  G. 《Plant and Soil》2002,239(1):87-102
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   

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