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Rising atmospheric CO2 concentrations have highlighted the importance of being able to understand and predict C fluxes in plant-soil systems. We
investigated the responses of the two fluxes contributing to below-ground efflux of plant root-dependent CO2, root respiration and rhizomicrobial respiration of root exudates. Wheat (Triticum aestivum L., var. Consort) plants were grown in hydroponics at 20°C, pulse-labelled with 14CO2 and subjected to two regimes of temperature and light (12 h photoperiod or darkness at either 15°C or 25°C), to alter plant
C supply and demand. Root respiration was increased by temperature with a Q
10 of 1.6. Root exudation was, in itself, unaltered by temperature, however, it was reduced when C supply to the roots was reduced
and demand for C for respiration was increased by elevated temperature. The rate of exudation responded much more rapidly
to the restriction of C input than did respiration and was approximately four times more sensitive to the decline in C supply
than respiration. Although temporal responses of exudation and respiration were treatment dependent, at the end of the experimental
period (2 days) the relative proportion of C lost by the two processes was conserved despite differences in the magnitude
of total root C loss. Approximately 77% of total C and 67% of 14C lost from roots was accounted for by root respiration. The ratio of exudate specific activity to CO2 specific activity converged to a common value for all treatments of 2, suggesting that exudates and respired CO2were not composed of C of the same age. The results suggest that the contributions of root and rhizomicrobial respiration
to root-dependent below-ground respiration are conserved and highlight the dangers in estimating short-term respiration and
exudation only from measurements of labelled C. The differences in responses over time and in the age of C lost may ultimately
prove useful in improving estimates of root and rhizomicrobial respiration. 相似文献
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Phuy-Chhoy Vong Séverine Piutti Emile Benizri Sophie Slezack-Deschaumes Christophe Robin Armand Guckert 《Plant and Soil》2007,294(1-2):19-29
Investigating the impact of plant species on sulphur (S) availability in the rhizosphere soil is agronomically important to
optimize S fertilization. Bulk, rhizosphere soils and the roots of field-grown rape and barley were sampled 7 times (every
fortnight), from March to June, at plant maturity. Root carbon (C) and nitrogen (N) in water extract, along with soil SO42−-S, labile soil organic-C (HWC) and -N (HWN) in hot water extract, as well as soil arylsulphatase activity were then monitored.
The average concentrations of both HWC and HWN were observed in the following decreasing order: rape rhizosphere soil >barley
rhizosphere soil >bulk soil. In parallel, the average contents of water extractable-C and -N in rape roots were higher than
those in barley roots. These results suggest that soil C and N contents in hot water extract (including rhizodeposition) were
correlated with C and N released by roots. Great ARS activities found in rape rhizosphere soil were accompanied by great SO42−-S mineralization over time. Finally, bulk and rhizosphere soils of rape and barley were pooled from the seven samplings and
incubated with the corresponding pooled root water-soluble C of both plant species and glucose-C. After 1 and 9 weeks, a greater
net S mineralization (gross mineralization - immobilization) was observed with rape root water-soluble C than with barley
root water-soluble C and glucose-C. Conjointly, we found a higher average value of ARS activity in rape rhizosphere than in
barley rhizosphere soil. Our findings suggest that plant species, via their rhizodeposition, determine the dynamic of S in
soil. 相似文献
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Contribution of plant photosynthates to dissolved organic carbon in a flooded rice soil 总被引:1,自引:0,他引:1
Dissolved organic C (DOC) plays important roles in nutrient cycling and methane production in flooded rice ecosystem. The microcosm experiment was carried out to measure directly the contribution of photosynthates to DOC by using a 13C pulse-chase labeling technique. DOC was operationally divided into water-extractable organic C (WEOC) and salt-extractable organic C (SEOC) by successive extraction firstly with deionized water and then with 0.25 M K2SO4. Total WEOC increased with plant growth, whereas SEOC concentration did not change significantly over the growing season. About 0.037–0.36% (mean 0.16%) of the assimilated 13C was incorporated into WEOC immediately after 13CO2 assimilation (Day 0), but only 0–0.025% (mean 0.01%) was incorporated into SEOC. At the end of the growing season, the 13C amounts of WEOC substantially decreased, while those of SEOC slightly increased. The estimated net plant C contribution was 21 mg C plant–1 to WEOC and 6 mg C plant–1 to SEOC, corresponding to 33.8% of total WEOC and 20.2% of total SEOC at the end of the growing season, respectively. The results suggest that the incorporation and decomposition of the photosynthesized C occurred rapidly in rice soil which significantly affected the WEOC dynamics, but SEOC appeared to be in equilibrium with the native soil organic matter, receiving less effect from the plant growth. 相似文献
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Root exudate components change litter decomposition in a simulated rhizosphere depending on temperature 总被引:3,自引:0,他引:3
The release of root exudates into the rhizosphere is known to enhance soil biological activity and alter microbial community structure. To assess whether root exudates also stimulated litter decomposition, in a rhizosphere model system we continuously injected solutions of glucose, malate or glutamate through porous Rhizon® soil solution samplers into the soil at rhizosphere concentrations. The effect of these substances on the decomposition of 14C-labelled Lolium perenne shoot residues present in the soil was evaluated by monitoring 14CO2 evolution at either 15°C or 25°C. The incorporation of the 14C into the microbial biomass and appearance in the dissolved organic matter (DOM) pool was estimated after 32 d incubation. The presence of malate and glutamate increased the mineralization of L. perenne residues by approximately 20% relative to the soil without their addition at 15°C, however, no significant effects on residue decomposition were observed at 25°C. The incorporation of the 14C-label into the microbial biomass and DOM pool was not affected by the addition of either glucose, malate or glutamate. Although nearly the same amount of L. perenne residues were mineralized at either temperature after 32 d, less 14C was recovered in the microbial biomass and DOM pools at 25°C compared to 15°C. Alongside other results, this suggests that the rate of microbial turnover is greater at 25°C compared to 15°C. We conclude that the addition of labile root exudate components to the rhizosphere induced a small but significant increase on litter decomposition but that the magnitude of this effect was regulated by temperature. 相似文献
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Consequences of including adapted white clover in northern European grassland: transfer and deposition of nitrogen 总被引:1,自引:0,他引:1
The interspecific transfer of nitrogen (N) between white clover (Trifolium repens) and smooth meadow grass (Poa pratensis) in legume-based grasslands was assessed under North European field conditions using 15N individual plant leaf labelling. On average 50% of N in the grass was transferred from the white clover and about 6% of
N in white clover was transferred from the grass. This corresponds to 2.5 and 0.3 g N m−2 being transferred over the growing season between the two species, respectively, and demonstrates that a significant part
of the total N of the grass is coming through interspecific transfer. The majority of the 15N transferred was within a period of 20 days at relatively low soil temperatures. This implies that there is a need for a
new focus on direct transfer pathways or exudation and transfer of organic N sources. Rhizodeposition in the top 10 cm of
the soil was found to be 2.98 g N m−2 on average over the growing season for the grass and white clover mixture. Inclusion of adapted white clover varieties in
the low-input grassland systems of northern Europe will lead to a substantial contribution of N.
Responsible Editor: Euan K. James. 相似文献
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Influence of plant roots on C and P metabolism in soil 总被引:7,自引:1,他引:6
Summary A technique for studying the modification of soil by plant roots is described. Using it, soil zones differently affected by plant roots can be separated for subsequent analysis. With this method, the transfer of C from roots of14C-labelled maize plants into soil and the change in soil C and P fractions were investigated.The results show that the C released from roots to soil was 13% of the total assimilated C. The remaining root-derived C in soil was relatively small (15%). Maize roots induced a decrease in organic soil C and in both total and isotopically exchangeable soil P. On the other hand they increased the microbial biomass C, phosphatase activity, bicarbonate extractable organic P and phospholipid P and enhanced the incorporation of32P into organic P fractions. Both root C and root influences were detectable outside the immediate root zone.These results demonstrate an intensive C turnover and P mobilization in the rhizosphere soil, including some organic P fractions, and suggest that the actual rhizosphere may be greater than is generally assumed. 相似文献
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Injection of hydrogen gas stimulates acid mine drainage treatment in laboratory‐scale hydroponic root mats 下载免费PDF全文
Juliane Richter Arndt Wiessner Andreas Zehnsdorf Jochen A. Müller Peter Kuschk 《Engineering in Life Science》2016,16(8):769-776
The environmentally benign disposal of acid mine drainage (AMD) is still a technical challenge. In the present study, artificial AMD was treated in a laboratory‐scale floating hydroponic root mat of soft rush, Juncus effusus. This ecotechnological system was operated with hydrogen injection and water recirculation but without an external carbon supply. It achieved a mean increase of ΔpH = 3.3 up to pH ≈ 8.2, high sulfate removal of up to 87%, and efficient removal of iron (100%), aluminum (99.8%), manganese (97.4%), and zinc (99.6%). Sulfide was not detected in the outflow. Treatment performance correlated with the amount of hydrogen loading. Daily oscillations of the redox potential up to amplitudes of ΔEh ≈ 450 mV in a mean range of Eh ≈ ?150 to +300 mV indicated a correlation of plant physiology and removal processes. Apparently, sulfate and metal removal were the result of chemolithotrophic microbial sulfate reduction supported by the externally provided H2 and chemoorganotrophic sulfate reduction driven by rhizodeposits. Bicarbonate generated in the microbial transformation of such plant‐derived organic carbon contributed to pH neutralization. The effluent's pH increase was governed further by recirculation of the treated AMD. The flow regime and the injection of hydrogen at the ground of the root mat caused concentration gradients where the most efficient removal occurred in the deepest zone of the root mat. Further investigations should target long‐term stability, plant growth dynamics, load variations, balances of carbon and sulfur, the removal of H2S and metal precipitates from the system as well as efficient hydrogen supply. 相似文献
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Francesca Scandellari Giustino Tonon Martin Thalheimer Christian Ceccon Paola Gioacchini John D. Aber Massimo Tagliavini 《Trees - Structure and Function》2007,21(5):499-505
The mass transfer from root to soil by means of rhizodeposition has been studied in grasses and forest trees, but its role
in fruit trees is still unknown. In this study, N fluxes from roots to soil were estimated by applying a 15N mass balance technique to the soil–tree system. Apple (Malus domestica) trees were pre-labelled with 15N and then grown outdoors in 40 L pots for one vegetative season in (1) a coarse-textured, low organic matter soil, (2) a
coarse-textured, high organic matter soil, and (3) a fine-textured, high organic matter soil. At tree harvest the 15N abundance of the soils was higher than at transplanting, but the total amount of 15N present in the tree–soil system was similar at transplanting and tree harvest. The soils had a strong effect on N fluxes
from and to the soil. In the fine-textured soil, 11% of the total plant-derived nitrogen was transferred to the soil, compared
with 2–5% in the two coarse-textured soils. Rhizodeposition was higher in the fine soil (18% of the primary production) than
in the coarse-textured soils, whereas higher soil organic matter depressed rhizodeposition. Nitrogen uptake was almost double
in the coarse-textured, high organic matter soil versus the other soils. Our results indicate that belowground primary productivity
is significantly underestimated if based on root production data only. Rhizodeposition represents a major process, whose role
should not be underestimated in carbon and nitrogen cycles in orchard ecosystems. 相似文献
10.
Combined effects of atmospheric CO<Subscript>2</Subscript> and N availability on the belowground carbon and nitrogen dynamics of aspen mesocosms 总被引:1,自引:0,他引:1
It is uncertain whether elevated atmospheric CO2 will increase C storage in terrestrial ecosystems without concomitant increases in plant access to N. Elevated CO2 may alter microbial activities that regulate soil N availability by changing the amount or composition of organic substrates
produced by roots. Our objective was to determine the potential for elevated CO2 to change N availability in an experimental plant-soil system by affecting the acquisition of root-derived C by soil microbes.
We grew Populus tremuloides (trembling aspen) cuttings for 2 years under two levels of atmospheric CO2 (36.7 and 71.5 Pa) and at two levels of soil N (210 and 970 μg N g–1). Ambient and twice-ambient CO2 concentrations were applied using open-top chambers, and soil N availability was manipulated by mixing soils differing in
organic N content. From June to October of the second growing season, we measured midday rates of soil respiration. In August,
we pulse-labeled plants with 14CO2 and measured soil 14CO2 respiration and the 14C contents of plants, soils, and microorganisms after a 6-day chase period. In conjunction with the August radio-labeling
and again in October, we used 15N pool dilution techniques to measure in situ rates of gross N mineralization, N immobilization by microbes, and plant N uptake.
At both levels of soil N availability, elevated CO2 significantly increased whole-plant and root biomass, and marginally increased whole-plant N capital. Significant increases
in soil respiration were closely linked to increases in root biomass under elevated CO2. CO2 enrichment had no significant effect on the allometric distribution of biomass or 14C among plant components, total 14C allocation belowground, or cumulative (6-day) 14CO2 soil respiration. Elevated CO2 significantly increased microbial 14C contents, indicating greater availability of microbial substrates derived from roots. The near doubling of microbial 14C contents at elevated CO2 was a relatively small quantitative change in the belowground C cycle of our experimental system, but represents an ecologically
significant effect on the dynamics of microbial growth. Rates of plant N uptake during both 6-day periods in August and October
were significantly greater at elevated CO2, and were closely related to fine-root biomass. Gross N mineralization was not affected by elevated CO2. Despite significantly greater rates of N immobilization under elevated CO2, standing pools of microbial N were not affected by elevated CO2, suggesting that N was cycling through microbes more rapidly. Our results contained elements of both positive and negative
feedback hypotheses, and may be most relevant to young, aggrading ecosystems, where soil resources are not yet fully exploited
by plant roots. If the turnover of microbial N increases, higher rates of N immobilization may not decrease N availability
to plants under elevated CO2.
Received: 12 February 1999 / Accepted: 2 March 2000 相似文献
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