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1.
Gerd Johansson 《Plant and Soil》1993,151(1):11-20
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
2.
The allocation of carbon to shoots, roots, soil and rhizosphere respiration in barrel medic (Medicago truncatulaGaertn.) before and after defoliation was determined by growing plants in pots in a labelled atmosphere in a growth cabinet.
Plants were grown in a 14CO2-labelled atmosphere for 30 days, defoliated and then grown in a 13CO2-labelled atmosphere for 19 days. Allocation of 14C-labelled C to shoots, roots, soil and rhizosphere respiration was determined before defoliation and the allocation of 14C and 13C was determined for the period after defoliation. Before defoliation, 38.4% of assimilated C was allocated below ground,
whereas after defoliation it was 19.9%. Over the entire length of the experiment, the proportion of net assimilated carbon
allocated below ground was 30.3%. Of this, 46% was found in the roots, 22% in the soil and 32% was recovered as rhizosphere
respiration. There was no net translocation of assimilate from roots to new shoot tissue after defoliation, indicating that
all new shoot growth arose from above-ground stores and newly assimilated carbon. The rate of rhizosphere respiration decreased
immediately after defoliation, but after 8 days, was at comparable levels to those before defoliation. It was not until 14
days after defoliation that the amount of respiration from newly assimilated C (13C) exceeded that of C assimilated before defoliation (14C).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
Wheat and maize were grown in a growth chamber with the atmospheric CO2 continuously labelled with 14C to study the translocation of assimilated carbon to the rhizosphere. Two different N levels in soil were applied. In maize 26–34% of the net assimilated 14C was translocated below ground, while in wheat higher values (40–58%) were found. However, due to the much higher shoot production in maize the total amount of carbon translocated below ground was similar to that of wheat. At high N relatively more of the C that was translocated to the root, was released into the soil due to increased root respiration and/or root exudation and subsequent microbial utilization and respiration. The evolution rate of unlabelled CO2 from the native soil organic matter decreased after about 25 days when wheat was grown at high N as compared to low N. This negative effect of high N in soil was not observed with maize. 相似文献
4.
Roots of annual crop plants are a major sink for carbon particularly during early, vegetative growth when up to one-half of all assimilated carbon may be translocated belowground. Flowering marks a particularly important change in resource allocation, especially in determinate species, with considerably less allocation to roots and, depending on environmental conditions, there may be insufficient for maintenance. Studies with 14C indicate the rapid transfer belowground of assimilates with typically 50% translocated in young cereal plants of which 50% is respired; exudation/rhizodeposition is generally <5% of the fixed carbon. Root: total plant mass decreases through the season and is affected by soil and atmospheric conditions. Limited water availability increased the allocation of 13C to roots of wheat grown in columns so that at booting 0.38 of shoot C (ignoring shoot respiration) was belowground compared to 0.31 in well-watered plants. Elevated CO2 (700 mol CO2 mol–1 air) increased the proportion of root:total mass by 55% compared with normal concentration, while increasing the air temperature by a mean of 3 °C decreased the proportion from 0.093 in the cool treatment to 0.055 in the warm treatment. 相似文献
5.
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.
Interspecific variations in carbon (C) allocation and partitioning in the rhizosphere were investigated on 12 Mediterranean species belonging to different family groups (grasses, legumes, non-legume forbs) and having different life cycles. Plants grown individually in artificial soil, in a greenhouse and inoculated with rhizosphere microflora were labelled with 14CO2 for 3 h at the vegetative stage. Rhizosphere respiration was measured during 6 days after which labelled C partitioning between shoots, roots, soil, root washing solution and respiration was estimated. The percentage of assimilated 14C allocated below ground differed significantly between species (41 – 76%) but no significant difference was found between grasses, legumes and non-legume forbs. When expressed as percentage of below-ground 14C, rhizosphere respiration was significantly smaller for non-legume forbs (42%) than for grasses (46%) and legumes (51%). Consequently more 14C was incorporated into root biomass in the former. Half-life of 14CO2 evolution through respiration ranged from 23 h in legumes to 27 h for non-legume forbs and 37 h for grasses. This suggested differences in microbial activities due to quantities and quality of root exuded C. Rhizosphere respiration was positively correlated with the amount of 14C in the solution used to wash the roots on one hand, and root N concentration on the other hand. This led to a functional hierarchy between plant family groups of the overall rhizosphere activity. It went from non-legume forbs being the less active (except Crepis sancta)in terms of respiration and exudation, to grasses and then legumes, the most active but also the richest in nitrogen. 相似文献
7.
Forest soil respiration rate and δ13C is regulated by recent above ground weather conditions 总被引:1,自引:0,他引:1
Soil respiration, a key component of the global carbon cycle, is a major source of uncertainty when estimating terrestrial carbon budgets at ecosystem and higher levels. Rates of soil and root respiration are assumed to be dependent on soil temperature and soil moisture yet these factors often barely explain half the seasonal variation in soil respiration. We here found that soil moisture (range 16.5–27.6% of dry weight) and soil temperature (range 8–17.5°C) together explained 55% of the variance (cross-validated explained variance; Q2) in soil respiration rate (range 1.0–3.4 mol C m–2 s–1) in a Norway spruce (Picea abies) forest. We hypothesised that this was due to that the two components of soil respiration, root respiration and decomposition, are governed by different factors. We therefore applied PLS (partial least squares regression) multivariate modelling in which we, together with below ground temperature and soil moisture, used the recent above ground air temperature and air humidity (vapour pressure deficit, VPD) conditions as x-variables. We found that air temperature and VPD data collected 1–4 days before respiration measurements explained 86% of the seasonal variation in the rate of soil respiration. The addition of soil moisture and soil temperature to the PLS-models increased the Q2 to 93%. 13C analysis of soil respiration supported the hypotheses that there was a fast flux of photosynthates to root respiration and a dependence on recent above ground weather conditions. Taken together, our results suggest that shoot activities the preceding 1–6 days influence, to a large degree, the rate of root and soil respiration. We propose this above ground influence on soil respiration to be proportionally largest in the middle of the growing season and in situations when there is large day-to-day shifts in the above ground weather conditions. During such conditions soil temperature may not exert the major control on root respiration. 相似文献
8.
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
9.
Willow is often used in bio-energy plantations for its potential to function as a renewable energy source, but knowledge about its effect on soil carbon dynamics is limited. Therefore, we investigated the temporal variation in carbon dynamics in willow, focusing on below-ground allocation and sequestration to soil carbon pools. Basket willow plants (Salix viminalis L.) in their second year of growth were grown in pots in a greenhouse. At five times during the plants growth, namely 0, 1, 2, 3 and 4 months after breaking winter dormancy, a subset of the plants were continuously labelled with 14CO2 in an ESPAS growth chamber for 28 days. After the labelling, the plants were harvested and separated into leaves, first and second year stems and roots. The soil was analysed for total C and 14C content as well as soil microbial biomass. Immediately after breaking dormancy, carbon stored in the first year stems was relocated to developing roots and leaves. Almost half the newly assimilated C was used for leaf development the first month of growth, dropping to below 15% in the older plants. Within the second month of growth, secondary growth of the stem became the largest carbon sink in the system, and remained so for the older age classes. Between 31 and 41% of the recovered 14C was allocated to below-ground pools. While the fraction of assimilated 14C in roots and root+soil respiration did not vary with plant age, the amount allocated to soil and soil microbial biomass increased in the older plants, indicating an increasing rhizodeposition. The total amount of soil microbial biomass was 30% larger in the oldest age class than in an unplanted control soil. The results demonstrate a close linkage between photosynthesis and below-ground carbon dynamics. Up to 13% of the microbial biomass consisted of carbon assimilated by the willows within the past 4 weeks, up to 11% of the recovered 14C was found as soil organic matter. 相似文献
10.
Summary
14CO2 at ambient concentration was administered to a section of an upper branch of 8-year-old Scots pines and the import of radiocarbon into the stem and roots was determined after various chase periods. 14CO2 fixation was performed in October when export of carbon into the stems and roots was maximal. In the short-term experiments the trees were harvested 1 h, 2 days and 5 days after a 3-h 14C pulse, while chase periods of 5 or 8 months were used in the long-term experiments. Loss of 14C was initially substantial, and even after a 5-day chase had not come down to a rate which indicated decrease only by respiration. After 5 days, more than 10% of the recovered radiocarbon (53% of the 14C translocated into the stem) had entered the roots and approximately the same amount was found in the stem. Extension of the chase period beyond 5 months did not result in a further significant loss of 14C by respiration, and the bulk of the label could be localized in the cell-wall fraction. No substantial redistribution of radiocarbon prior and subsequent to the formation of the new shoots could be observed, thus indicating that the stored material was utilized for thickening the stem and roots. Radioautography of stem cross-sections revealed a narrow helical strip of 14C from the feeding branch to the root in the phloem region. In the tree harvested after bud break the utilization of the 14C-labelled material stored in the stem for the production of the first layers of earlywood and the corresponding phloem was apparent. 相似文献
11.
Erick Zagal 《Plant and Soil》1994,160(1):21-31
A pot experiment was conducted in a 14C-labelled atmosphere to study the influence of living plants on organic-N mineralization. The soil organic matter had been labelled, by means of a 200-days incubation, with 15N. The influence of the carbon input from the roots on the formation of microbial biomass was evaluated by using two different light intensities (I). Mineralization of 15N-labelled soil N was examined by following its fate in both the soil biomass and the plants. Less dry matter accumulated in shoots and roots at the lower light intensity. Furthermore, in all the plant-soil compartments examined, with the exception of rhizosphere respiration, the proportion of net assimilated 14C was lower in the low-I treatment than in the high-I treatment. The lower rates of 14C and 15N incorporation into the soil biomass were associated with less root-derived 14C. During the chamber period (14CO2-atmosphere), mineralized amounts of 15N (measured as plant uptake of 15N) were small and represented about 6.8 to 7.8% of the initial amount of organic 15N in the soil. Amounts of unlabelled N found in the plants, as a percentage of total soil N, were 2.5 to 3.3%. The low availability of labelled N to microorganisms was the result of its stabilization during the 210 days of soil incubation. Differences in carbon supply resulted in different rates of N mineralization which is consistent with the hypothesis that roots induce N mineralization. N mineralization was higher in the high-I treatment. On the other hand, the rate of mineralization of unlabelled stable soil N was lower than labelled soil 15N which was stabilized. The amounts of 15N mineralized in planted soil during the chamber period (43 days) which were comparable with those mineralized in unplanted soil incubated for 210 days, also suggested that living plants increased the turnover rate of soil organic matter. 相似文献
12.
Erick Zagal 《Plant and Soil》1994,166(1):63-74
To examine the influence of plant-microorganism interactions on soil-N transformations (e.g. net mineralization, net immobilization) a pot experiment was conducted in a14C-labelled atmosphere by using different (two annuals, one perennial) plants species. It was assumed that variation in below-ground, microorganism-available C would influence N transformations in soil. Plant species were fertilized (low rate) with15N-labelled nitrogen and grown, during days 13 and 62 after germination, in a growth chamber with a14C-labelled atmosphere. Nitrification was inhibited by using nitrapyrin (N-Serve). During the chamber period, shoots were harvested, and associated roots and soil were collected on two sampling occasionm, e.g. after 4 and 7 weeks in the growth chamber.The distribution of net (%) assimilated14C was significantly affected by both plant and time factors, and there was a significant plant × time interaction. There were significant differences between plants in all plant-soil compartments examined as well as in the degree of the plant × time interaction.Differences in the14C distribution between plants were due to both interspecific and developmental variation. In general, when comparing15N and14C quantities between species, many of the differences found between plants can be explained by the differences determined in the weight of shoot or root parts. Despite the fact that amounts of C released were greater in ryegrass than in the other plant-treatments no unequivocal evidence was found to show that the effects of plant-microorganism interactions on soil-N mineralization were greater under ryegrass. Possible mechanisms accounting for the partitioning of N found among plant biomass, soil biomass and soil residues are discussed. 相似文献
13.
Using a 14C pulse-labelling technique, we studied the seasonal changes in assimilation and partitioning of photoassimilated C in the plant–root–soil components of a temperate pasture. Pasture and soil samples were taken after 4-h, and 35-day chase periods, to examine these seasonal 14C fluxes. Total C and 14C were determined in the shoot, root and soil system. The amounts of C translocated annually to roots and soil were also estimated from the seasonal 14C distribution and pasture growth. The in situ field decomposition of newly formed roots during different seasons, also using 14C-labelling, was studied for one year in undisturbed rhizosphere soil. The 14C-labelled roots were sampled five times and decomposition rates were calculated assuming first-order decomposition.Annual pasture production at the site was 16 020 kg DM ha–1, and pasture growth varied with season being highest (75–79 kg ha–1 d–1) in spring and lowest (18–20 kg ha–1 d–1) in winter. The above- and below-ground partitioning of 14C also varied with the season. The respiratory 14C–CO2 losses, calculated as the difference between the total amounts of 14C recovered in the soil-plant system at 4 h and 35 days, were high (66–70%) during the summer, autumn and winter season, and low (37–39%) during the spring and late-spring season. Pasture plants partitioned more C below-ground during spring compared with summer, autumn and winter seasons. Overall, at this high fertility dairy pasture site, 18 220 kg C/ha was respired, 6490 kg remained above-ground in the shoot, and 6820 kg was translocated to roots and 1320 kg to soil. Root decomposition rate constant (k) differed widely with the season and were the highest for the autumn roots. The half-life was highest (111 days) for autumn roots and lowest (64 days) for spring roots. About one-third of the root label measured in the spring season disappeared in the first 5 weeks after the initial 35 Day of allocation period. The late spring, summer, late summer and winter roots had intermediate half-lives (88–94 days). These results indicate that seasonal changes in root growth and decomposition should be accounted for to give a better quantification of root turnover. 相似文献
14.
Weixin Cheng 《Plant and Soil》1996,183(2):263-268
Due to the limitations in methodology it has been a difficult task to measure rhizosphere respiration and original soil carbon decomposition under the influence of living roots. 14C-labeling has been widely used for this purpose in spite of numerous problems associated with the labeling method. In this paper, a natural 13C method was used to measure rhizosphere respiration and original soil carbon decomposition in a short-term growth chamber experiment. The main objective of the experiment was to validate a key assumption of this method: the 13C value of the roots represents the 13C value of the rhizosphere respired CO2. Results from plants grown in inoculated carbon-free medium indicated that this assumption was valid. This natural 13C method was demonstrated to be advantageous for studying rhizosphere respiration and the effects of living roots on original soil carbon decomposition. 相似文献
15.
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
16.
The use of C14O2 canopy techniques for measuring carbon transfer through the plant-soil system 总被引:1,自引:0,他引:1
Summary Methods for labelling growing plants by exposing them to C14O2 under a cellulose acetate-butyrate canopy have been developed for laboratory and field use. The length of labelling ranged from 2 to 33 days and the C14O2 content of the atmosphere was automatically controlled. This made it possible to measure carbon assimilation by the plants, transfer of photosynthates beneath ground and respiration of the roots.In the laboratory, root respiration of wheat plants was measured by separating the above and beneath ground plant parts using a RTV rubber partition. Half to two thirds of the assimilated carbon was found above ground, 15 to 25 per cent in the roots and shoot bases below the partition and 17 to 25 per cent was lost by underground respiration. The variability of these proportions was related to the stage of maturity of the plants.On native grassland, the relative above and beneath ground productivity was 50 per cent. The time required for the photosynthates to reach the roots at various depths ranged from 1 to 5 days and the amount of material deposited in the roots changed with time and soil moisture content. The use of tubes inserted at various depths beneath the canopy permitted sampling of soil air for C14 and CO2 measurements. The soil C14O2 flux indicated that root respiration during 8 days accounted for 24 per cent of the labelled carbon translocated to the roots after a two days labelling period. 相似文献
17.
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
18.
Herbivore-induced changes in plant carbon allocation: assessment of below-ground C fluxes using carbon-14 总被引:10,自引:0,他引:10
Effects of above-ground herbivory on short-term plant carbon allocation were studied using maize (Zea mays) and a generalist lubber grasshopper (Romalea guttata). We hypothesized that above-ground herbivory stimulates current net carbon assimilate allocation to below-ground components, such as roots, root exudation and root and soil respiration. Maize plants 24 days old were grazed (c. 25–50% leaf area removed) by caging grasshoppers around individual plants and 18 h later pulse-labelled with14CO2. During the next 8 h,14C assimilates were traced to shoots, roots, root plus soil respiration, root exudates, rhizosphere soil, and bulk soil using carbon-14 techniques. Significant positive relationships were observed between herbivory and carbon allocated to roots, root exudates, and root and soil respiration, and a significant negative relationship between herbivory and carbon allocated to shoots. No relationship was observed between herbivory and14C recovered from soil. While herbivory increased root and soil respiration, the peak time for14CO2 evolved as respiration was not altered, thereby suggesting that herbivory only increases the magnitude of respiration, not patterns of translocation through time. Although there was a trend for lower photosynthetic rates of grazed plants than photosynthetic rates of ungrazed plants, no significant differences were observed among grazed and ungrazed plants. We conclude that above-ground herbivory can increase plant carbon fluxes below ground (roots, root exudates, and rhizosphere respiration), thus increasing resources (e.g., root exudates) available to soil organisms, especially microbial populations. 相似文献
19.
Frédéric Henry Christophe Nguyen Eric Paterson Allan Sim Christophe Robin 《Plant and Soil》2005,269(1-2):181-191
The objective of this work was to determine if the impact of nitrogen (N) on the release of organic carbon (C) into the soil
by roots (rhizodeposition) correlated with the effect of this nutrient on some variables of plant growth. Lolium multiflorum Lam. was grown at two levels of N supply, either in sterile sand percolated with nutrient solution or in non-sterile soil.
The axenic sand systems allowed continuous quantification of rhizodeposition and accurate analysis of root morphology whilst
the soil microcosms allowed the study of 14C labelled C flows in physico-chemical and biological conditions relevant to natural soils. In the axenic sand cultures, enhanced
N supply strongly increased the plant biomass, the plant N content and the shoot to root ratio. N supply altered the root
morphology by increasing the root surface area and the density of apices, both being significantly positively correlated with
the rate of organic C release by plant roots before sampling. This observation is consistent with the production of mucilage
by root tips and with mechanisms of root exudation reported previously in the literature, i.e. the passive diffusion of roots
solutes along the root with increased rate behind the root apex. We proposed a model of root net exudation, based on the number
of root apices and on root soluble C that explained 60% of the variability in the rate of C release from roots at harvest.
The effects of N on plant growth were less marked in soil, probably related to the relatively high supply of N from non-fertiliser
soil-sources. N fertilization increased the shoot N concentration of the plants and the shoot to root ratio. Increased N supply
decreased the partitioning of 14C to roots. In parallel, N fertilisation increased the root soluble 14C and the 14C recovered in the soil per unit of root biomass, suggesting a stimulation of root exudation by N supply. However, due to
the high concentration of N in our unfertilised plants, this stimulation was assumed to be very weak because no significant
effect of N was observed on the microbial C and on the bacterial abundance in the rhizosphere. Considering the difficulties
in evaluating rhizodeposition in non sterile soil, it is suggested that the root soluble C, the root surface area and the
root apex density are additional relevant variables that should be useful to measure along with the variables that are commonly
determined when investigating how plant functioning impacts on the release of C by roots (i.e soil C, C of the microbial biomass,
rhizosphere respiration). 相似文献
20.
Jukka Sakari Pumpanen Jussi Heinonsalo Terhi Rasilo Kaj-Roger Hurme Hannu Ilvesniemi 《Trees - Structure and Function》2009,23(3):611-621
Carbon dioxide is released from the soil to the atmosphere in heterotrophic respiration when the dead organic matter is used
for substrates for soil micro-organisms and soil animals. Respiration of roots and mycorrhiza is another major source of carbon
dioxide in soil CO2 efflux. The partitioning of these two fluxes is essential for understanding the carbon balance of forest ecosystems and for
modelling the carbon cycle within these ecosystems. In this study, we determined the carbon balance of three common tree species
in boreal forest zone, Scots pine, Norway spruce, and Silver birch with gas exchange measurements conducted in laboratory
in controlled temperature and light conditions. We also studied the allocation pattern of assimilated carbon with 14C pulse labelling experiment. The photosynthetic light responses of the tree species were substantially different. The maximum
photosynthetic capacity (P
max) was 2.21 μg CO2 s−1 g−1 in Scots pine, 1.22 μg CO2 s−1 g−1 in Norway spruce and 3.01 μg CO2 s−1 g−1 in Silver birch seedlings. According to the pulse labelling experiments, 43–75% of the assimilated carbon remained in the
aboveground parts of the seedlings. The amount of carbon allocated to root and rhizosphere respiration was about 9–26%, and
the amount of carbon allocated to root and ectomycorrhizal biomass about 13–21% of the total assimilated CO2. The 14CO2 pulse reached the root system within few hours after the labelling and most of the pulse had passed the root system after
48 h. The transport rate of carbon from shoot to roots was fastest in Silver birch seedlings. 相似文献