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1.
Shawn A. Steffan Kent M. Daane Daniel L. Mahr 《Entomologia Experimentalis et Applicata》2001,98(2):173-180
New techniques are presented on the use of 15N to mark insects. 15N, a stable isotope of nitrogen, was enriched above natural abundance in plant and insect tissues. Two laboratory studies demonstrated that enriched 15N-concentrations could be tracked from plant to insect using mass spectrometry. In the first study, adult Cotesia plutellae (Kurdjimov) (Hymenoptera: Braconidae) and Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae) were allowed to feed at the flowers of rapid-cycling Chinese cabbage plants that had been fertilized with 15N-enriched potassium nitrate (KNO3-15NO3). Both insect groups were found to have significantly elevated 15N levels after visiting the flowers of the 15N-enriched plants for 48 hours. In the second study, 15N-enriched bean plant (Phaseolus vulgaris L.) tissue was incorporated into an insect diet and fed to navel orangeworms, Amyelois transitella (Walker) (Lepidoptera: Pyralidae). When the navel orangeworm larvae were 4th instars, they were removed from the diet and exposed to the parasitoid, Goniozus legneri Gordh (Hymenoptera: Bethylidae). Results indicated that the enriched 15N-concentration of the bean plants was transferred to the navel orangeworms and, subsequently, to the parasitoids. This work may provide useful techniques to help establish whether agriculturally important entomophaga visiting 15N-enriched flowers or parasitizing enriched sentinel larvae in the field can be effectively marked with 15N. 相似文献
2.
Effects of aluminium on growth and root reactions of phosphorus stressed Betula pendula seedlings 总被引:1,自引:0,他引:1
The impact of two constant non-toxic levels of Al stress (0.2 and 0.4 mM) on growth and 32P uptake capacity on sub-optimal (P-limited) Betula pendula seedlings grown in sand culture was examined.Seedling growth was under optimum controlled conditions in a growth chamber where nutrient additions were made at a predetermined relative addition rate (RA) of 10% day-1. Three treatment groups of seedlings 0, 0.2 and 0.4 mM Al were harvested at 15, 29 and 42 days. The excised roots were exposed to a 32P-labelled solution for 15 minutes to measure their capacity for P uptake. Growth was determined by weighing the roots, stems and leaves of the seedlings.Growth data showed that relative growth rate (RG) should equal the RA of P the most limiting nutrient, which was supplied at P/N 3% instead of an optimal 15%. Therefore, Ingestad's theory can also be used succesfully in sand culture and this may be particularly important for future studies of root and rhizosphere exudates. Low levels of Al (< 0.2 mM) in combination with low P supply significantly lowered the RG of the birch seedlings by further reducing P supply. However, previous studies of birch seedling growth and nutrient uptake using Ingestad's solution culture technique with optimumal P supply did not show any effect of Al on growth untill the Al was in excess of 3 mM. Aluminium was not directly toxic to the plants and therefore roots could respond to the 32P bioassay. 相似文献
3.
Mark B. Peoples Brian Palmer Dianne M. Lilley Lam Minh Duc David F. Herridge 《Plant and Soil》1996,182(1):125-137
The apparently diminished capacity for N2 fixation by the shrub legume Calliandra calothyrsus (Calliandra) relative to other woody perennial legumes was investigated in a field experiment in northern Queensland, Australia. In this trial, (i) the proportion of plant nitrogen (N) derived from symbiotic N2 fixation (%Pfix) and the amounts of N2 fixed were compared in Calliandra, Gliricidia sepium (Gliricidia) and Codariocalyx gyroides (Codariocalyx), (ii) variations in N2 fixation due to season or tree age were determined, (iii) estimates of Pfix derived with the 15N natural abundance technique were compared with values obtained from 15N enrichment or xylem sap ureide procedures to determine whether the previous conclusions about Calliandra's ability to fix N had resulted from specific problems with the natural abundance methodology used in the earlier studies.Inoculated seedlings of each of the three shrub legume species were planted in dense stands (1.5 m rows, 0.5 m between trees) in two randomised blocks. The northern block was used solely for natural abundance measurements, while 15N-enriched KNO3 (10 atom % 15N excess) was applied four times over a 52 week period to plots in the southern block. The non-nodulating tree legume Senna spectabilis (formally Cassia spectabilis) was used as a non-N2-fixing reference for the 15N-based procedures, with Guinea grass (Panicum maximum) included as an additional non-fixing check. Growth by the trees above 75 cm was first cut and removed after 22 weeks and regrowth was subsequently pruned periodically for another 95 weeks. Sampling for dry matter production, N yield and estimates of Pfix were restricted to the central four of the 32 plants which constituted each replicate plot. Information generated during the 117 week study indicated that estimates of Pfix by 15N natural abundance were closely similar to values derived with 15N-enrichment or sap ureides. The data indicated that Calliandra had a reduced reliance upon N2 fixation relative to Gliricidia and Codariocalyx for the first 65 weeks after establishment. This appeared to be due to more prolifc root growth by Calliandra than either of the other N2-fixing species and an ability to extract a greater proportion of its N requirements from soil mineral N. However, after week 65 and for the remainder of the experiment, estimates of Pfix for Calliandra were similar to the other shrub legumes. Over 117 weeks, prunings from Calliandra and Gliricidia had removed 52–58 t dry matter ha-1, and between 1471 and 1678 kg N ha-1, of which 1026–1063 kg N ha-1 was estimated to have been derived from N2 fixation. At the time of final harvest, 65–73% of the fixed N was present in shoot regrowth of the N2 fixing shrubs, 9–18% in the roots, 15% in the trunk, and 2–6% in fallen leaves. 相似文献
4.
Two treatments were employed to influence the amount of amino nitrogen (N) transport in phloem. In walnut trees (Juglans regia L.), developing fruit significantly reduced the efflux of foliar-applied 15N-enriched urea from treated spurs over a 33-day period in comparison with similarly-treated defruited spurs. Those data suggest
that local aboveground demand for N influences vascular transport of amino N. In another experiment, a 1% urea solution was
applied foliarly to 5-year old `Mission' almond trees [Prunus dulcis (Mill.) D. A. Webb] to increase the concentration of amino N in the phloem. The effect of foliar N treatments on a) the transport
and distribution of labelled urea N within the trees over the experimental period and b) the uptake of soil-applied labelled
N were determined by replicated whole tree excavation, fractionation into various tree components and mass spectrometric analyses
of the 14N/15N ratios. Concentrations and composition of amino acids in the phloem and xylem saps of control trees and trees receiving
foliar-applied urea were also determined. In foliar urea-treated trees, the amino acid concentrations increased significantly
in leaf and bark phloem exudate, within 24 and 96 h, respectively. Foliar-applied urea N was translocated to the roots of
almond trees over the experimental period and decreased soil N uptake. The results of these experiments are consistent with
the hypothesis that aboveground N demand affects the amount of amino N cycling between shoots and roots, and may be involved
in the regulation of soil N uptake.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
Uptake of nitrogen from prey and substrate and partitioning of prey-derived nitrogen were studied in the carnivorous plant species Pinguicula alpina, P. villosa, P. vulgaris and Drosera rotundifolia in a subarctic environment. Efficiency in nitrogen uptake from prey was evaluated by tracing 15N from 15N-enriched Drosophila flies fed to the plants. The in situ uptake efficiency differed somewhat between species and ranged from 29 to 41% of prey N. This efficiency was not affected by different feeding levels or plant reproductive status (flowering or non-flowering). A test of the amount of N absorbed from prey caught on flower stalks of Pinguicula villosa and P. vulgaris showed that both species took up little of what was available in prey (2.5% or less). The uptake efficiency found in greenhouse grown plants was higher than in plants in situ (40–50% vs. 30–40% respectively). This could probably best be explained by the absence of rain and a higher temperature in the greenhouse. The prey-derived 15N was traced to reproductive organs and winter buds. Non-flowering individuals allocated 58–97% of the N derived from prey to their winter buds. Flowering individuals allocated 17–43% of the N income from prey to reproduction, while 34–71% were allocated to buds. Root uptake of nitrogen was stimulated by increased prey capture. This increase in uptake of nitrogen from the substrate was larger than the potential direct uptake of nitrogen from captured prey. 相似文献
6.
Although a high proportion of fertilizer N may be immobilized in organic forms in the soil, no studies have examined the long-term
availability of residual fertilizer 15N in forestry situations. We investigated this by growing lodgepole pine (Pinus contorta) seedlings in surface (0–10 cm) soil sample eight years after application of 15N-urea, 15NH4NO3 and NH4
15NO3 to lodgepole pine in interior British Columbia. After nine months of growth in the greenhouse, seedlings took up an average
of 8.5% of the 15N and 4.6% of the native N per pot. Most of the mineral N in the pots without seedlings was in the form of nitrate, while
pots with seedlings had very low levels of mineral N. In contrast to the greenhouse study, there was no significantuptake
of 15N by trees in the field study after the first growing season, although half of the soil organic 15N was lost between one and eight years after fertilization. This indicates the need to understand the mechanisms which limit
the uptake of mineral N by trees in the field, and the possible mismatch of tree demand and mineral N availability. 相似文献
7.
Little information is known on what the magnitude of nitrogen (N) processed by ectomycorrhizal (ECM) fungal species in the
field. In a common garden experiment performed in a northern California oak woodland, we investigated transfer of nitrogen
applied as 15NH4 or 15NO3 from leaves to ectomycorrhizal roots of three oak species, Quercus agrifolia, Q. douglasii, and Q. garryana. Oak seedlings formed five common ectomycorrhizal morphotypes on root tips. Mycorrhizal tips were more enriched in 15N than fine roots. N transfer was greater to the less common morphotypes than to the more common types. 15N transfer from leaves to roots was greater when , not , was supplied. 15N transfer to roots was greater in seedlings of Q. agrifolia than in Q. douglasii and Q. garryana. Differential N transfer to ectomycorrhizal root tips suggests that ectomycorrhizal morphotypes can influence flows of N
from leaves to roots and that mycorrhizal diversity may influence the total N requirement of plants. 相似文献
8.
Hans Göransson Ulrika Rosengren Håkan Wallander Ann-Mari Fransson Gunnar Thelin 《Trees - Structure and Function》2006,20(3):292-298
Eight oak trees (Quercus robur L.) received 32P at a soil depth of 50 cm and 33P at a soil depth of 15 cm at the end of June 2002 through plastic tubes inserted into the mineral soil. The phosphorus uptake from different soil depths was estimated by analysing the concentration of 32P and 33P in the foliage of oak growing in a mixed stand in southern Sweden. 32P and 33P were recovered in the leaves/needles after 21 and 39 days. The recovery of labelled P in oak was higher from 15 cm soil depth than from 50 cm, however, more than 4% of the total amount of labelled P was taken up from 50 cm. This indicates that oak can utilize deep soil layers for nutrient uptake. A study on the uptake of Cs (as an analogue to K) and 15N into the leaves was performed on the same trees and detectable amounts of 15N and Cs were recovered in leaves and buds. This indicates that 15N and Cs can be used to study nutrient uptake of mature trees from the mineral soil. 相似文献
9.
Summary The technique of15N isotope dilution was used to verify that nitrogen was fixed and transferred to the plant byKlebsiella pneumoniae strain Pp in association withPoa pratensis orTriticum aestivum. Surface sterilized, sprouting seeds were inoculated withK. pneumoniae and grown in sand in modified Leonard jars. Potassium nitrate enriched with15N was used to provide N concentrations ranging from 10–40 mg Nl–1 nutrient solution. After 10–18 weeks the shoots and roots were analyzed separately for dry matter, N content, total N, and atom %15N excess. The acetylene reduction technique was used to test for the presence of N2-fixing organisms on the roots. The data from15N isotope dilution demonstrated that up to 33.8% of N in the shoots ofP. pratensis and 15.9% in those ofT. aestivum were derived from associative N2 fixation byK. pneumoniae. In most experiments the dry matter yield, N content, and total N yield of the shoots ofP. pratensis were increased byK. pneumoniae inoculation, whereas inoculation had no significant effect on the dry matter yield, N content or total N of the shoots ofT. aestivum. 相似文献
10.
R. W. Ruess 《Oecologia》1988,77(4):550-556
Summary
Sporobolus kentrophyllus, a grazing-tolerant C4 grass from the southeastern Serengeti Plains, was grown in solution culture to examine the effects of clipping on the uptake, preference and subsequent transport of varying nitrogen forms. Clipping reduced offtake mass, crown mass ane root mass, resulting in a 58% decline in plant mass. Proportional biomass allocation to roots decreased with clipping, while tillering rates increased. Clipping also increased the nitrogen concentrations of all tissues, and plant nitrogen uptake (nitrogen accumulated throughout the experiment per gram root). The 15N concentrations (% atom excess) of all tissues were higher in clipped compared with unclipped plants, and the average 15N uptake rate of clipped plants was twice that of unclipped plants. The relative 15N allocation to aboveground mass, a measure of canopy sink strength, was higher in clipped plants. Plants fed 15N-ammonium or 15N-nitrate during the 15N pulse experiment had greater 15N tissue concentrations compared with urea-fed plants, and 15N uptake rates were higher in ammonium-fed and nitrate-fed plants, compared with urea-fed plants. The relative magnitudes of these differences were higher when plants were clipped. Clipped plants had higher uptake rates for potassium, phosphorus and sodium, while differences between clipping treatments for calcium, iron, and magnesium were indistinguishable. Rapid uptake rates for species on the southeastern Serengeti plains, particularly during grazing periods, have important implications for nutrient cycling in this system. 相似文献
11.
Summary The leaf and root nitrate reductase activities were measured in 7 day-old barley seedlings by anoxic nitrite accumulation in darkness, during 48h after the transfer from a N-starved medium to a 1.5 mM K15NO3 medium. Thisin situ nitrate reduction was compared with the15N incorporation in the reduced N fraction of the whole seedlings.The nitrate reduction integrated fromin situ measurements was lower than the reduced15N accumulation. The rootin situ nitrate reductase activity seemed to account for only the third of the real root nitrate reduction, which may have been responsible for the overall underestimation. This discrepancy was partly explained by the ability of the root to reduce nitrite in an anoxic environment.These results suggest that, after correction of thein situ estimation of the nitrate reduction. the roots contribute to about 50% of the total assimilation. 相似文献
12.
A. W. Bevan G. C. K. Roberts J. Feeney L. Kuyper 《European biophysics journal : EBJ》1985,11(4):211-218
The binding of trimethoprim and [1,3,2-amino-15N3]-trimethoprim to Lactobacillus casei dihydrofolate reductase has been studied by 15N and 1H NMR spectroscopy. 15N NMR spectra of the bound drug were obtained by using polarisation transfer pulse sequences. The 15N chemical shifts and 1H-15N spin-coupling constants show unambiguously that the drug is protonated on N1 when bound to the enzyme.The N1-proton resonance in the complex has been assigned using the 15N-enriched molecule. The temperature-dependence of the linewidth of this resonance has been used to estimate the rate of exchange of this proton with the solvent: 160±10s-1 at 313 K, with an activation energy of 75 (±9) kJ·mole-1. This is considerably faster than the dissociation rate of the drug from this complex, demonstrating that there are local fluctuations in the structure of the complex. 相似文献
13.
Cultivating dinitrogen-fixing legume trees with crops in agroforestry is a relatively common N management practice in the
Neotropics. The objective of this study was to assess the N2 fixation potential of three important Neotropical agroforestry tree species, Erythrina poeppigiana, Erythrina fusca, and Inga edulis, under semi-controlled field conditions. The study was conducted in the humid tropical climate of the Caribbean coastal plain
of Costa Rica. In 2002, seedlings of I. edulis and Vochysia guatemalensis were planted in one-meter-deep open-ended plastic cylinders buried in soil within hedgerows of the same species. Overall
tree spacing was 1 × 4 m to simulate a typical alley-cropping design. The 15N was applied as (NH4)2SO4 at 10% 15N atom excess 15 days after planting at the rate of 20 kg [N] ha−1. In 2003, seedlings of E. poeppigiana, E. fusca, and V. guatemalensis were planted in the same field using the existing cylinders. The 15N application was repeated at the rate of 20 kg [N] ha−1 15 days after planting and 10 kg [N] ha−1 was added three months after planting. Trees were harvested 9 months after planting in both years. The 15N content of leaves, branches, stems, and roots was determined by mass spectrometry. The percentage of atmospheric N fixed
out of total N (%Nf) was calculated based on 15N atom excess in leaves or total biomass. The difference between the two calculation methods was insignificant for all species.
Sixty percent of I. edulis trees fixed N2; %Nf was 57% for the N2-fixing trees. Biomass production and N yield were similar in N2-fixing and non-N2-fixing I. edulis. No obvious cause was found for why not all I. edulis trees fixed N2. All E. poeppigiana and E. fusca trees fixed N2; %Nf was ca. 59% and 64%, respectively. These data were extrapolated to typical agroforestry systems using published data on N recycling
by the studied species. Inga edulis may recycle ca. 100 kg ha−1 a−1 of N fixed from atmosphere to soil if only 60% of trees fix N2, E. poeppigiana 60–160 kg ha−1 a−1, and E. fusca
ca. 80 kg ha−1 a−1. 相似文献
14.
Katja Pörtl Sophie Zechmeister-Boltenstern Wolfgang Wanek Per Ambus Torsten W. Berger 《Plant and Soil》2007,295(1-2):79-94
Natural 15N abundance measurements of ecosystem nitrogen (N) pools and 15N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ15N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure
spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ15N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ15N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand:
5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in 15N of all soil N pools. Denitrification represented the main N2O-producing process in the mixed forest stand as we detected a significant 15N enrichment of its substrate NO3− (3.6 ± 4.5‰) compared to NH4+ (−4.6 ± 2.6‰) and its product N2O (−11.8 ± 3.2‰). In a 15N-labelling experiment in the spruce stand, nitrification contributed more to N2O production than denitrification. Moreover, in natural abundance measurements the NH4+ pool was slightly 15N-enriched (−0.4 ± 2.0 ‰) compared to NO3− (−3.0 ± 0.6 ‰) and N2O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N2O. The more positive δ15N values of N2O in the spruce stand than in the mixed stand point to extensive microbial N2O reduction in the spruce stand. Combining natural 15N abundance and 15N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately. 相似文献
15.
Mata Catarina van Vemde Nicole Clarkson David T. Martins-Loução Maria Amélia Lambers Hans 《Plant and Soil》2000,221(1):25-32
Nitrate influx, efflux and net nitrate uptake were measured for the slow-growing Quercus suber L. (cork-oak) to estimate the N-uptake efficiency of its seedlings when grown with free access to nitrate. We hypothesise
that nitrate influx, an energetically costly process, is not very efficiently controlled so as to avoid losses through efflux,
because Q. suber has relatively high respiratory costs for ion uptake. Q. suber seedlings were grown in a growth room in hydroponics with 1 mM NO3
-. Seedlings were labelled with 15NO3
- in nutrient solution for 5 min to measure influx and for 2 h for net uptake. Efflux was calculated as the difference between
influx and net uptake. Measurements were made in the morning, afternoon and night. The site of nitrate reduction was estimated
from the ratio of NO3
- to amino acids in the xylem sap; the observed ratio indicated that nitrate reduction occurred predominantly in the roots.
Nitrate influx was always much higher than net acquisition and both tended to be lower at night. High efflux occurred both
during the day and at night, although the proportion of 15NO3
- taken up that was loss through efflux was proportionally higher during the night. Efflux was a significant fraction of influx.
We concluded that the acquisition system is energetically inefficient under the conditions tested.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
干旱胁迫下胡杨实生幼苗氮素吸收分配与利用 总被引:5,自引:0,他引:5
胡杨(Populus euphratica)是塔里木河流域荒漠河岸林的建群种,水分和氮素是限制胡杨幼苗的存活及早期生长的主要因子。利用~(15)N同位素示踪技术分析水和氮素的交互作用对胡杨幼苗不同生长阶段氮素的吸收分配利用及幼苗生长的影响,进一步探究氮素对胡杨实生苗早期形态建成的作用及对干旱胁迫的缓解效应,以期提高幼苗的存活率。实验以一年生胡杨实生幼苗为研究对象,采用温室内盆栽实验,设置4个干旱处理(D_1、D_2、D_3、D_4,土壤相对含水量为:20%—25%、40%—45%、60%—65%、80%—85%)和3种氮素水平(N_0、N_1、N_2:0、3、6 g/盆)测定胡杨幼苗的生长指标和各部分的Ndff、分配率及利用率。结果表明:胡杨幼苗在土壤相对含水量60%—65%(D_3)、氮素添加量3 g/盆(N_1)时,其生长表现为最佳状态;干旱胁迫下,不同氮素添加量对胡杨幼苗各部分的Ndff值存在显著差异,N_2低于N_1;随干旱胁迫减弱(D_3、D_4),植株在生长早期(25 d)根部吸收的~(15)N优先向地上部分转运,生长后期(75 d)植株Ndff最高,其中以根系中Ndff最高;不同生长期幼苗各部分的~(15)N分配存在显著差异,根系~(15)N分配率较高,但不同氮量处理间差异不显著;随生长期的推移,植株对~(15)NH_4~(15)NO_3的利用率表现为粗根最大,各处理中D_3N_1处理均显著高于其他处理。结论:轻度干旱胁迫下添加适量的氮素能够增强植株对氮素的吸收征调能力,优化水资源获取以维持生存的重要机制。 相似文献
17.
Estimation of root distributions in natural systems remains challenging due to the difficulties in excavation and easy breakage of fine roots. Identifying lateral fine root distribution is necessary to determine the potential exploitation of spatially and temporally variable nutrient supplies that characterize most arid ecosystems. We estimated this potential by taking field measurements of lateral root distribution of the small herbaceous perennial Cryptantha flava (A. Nels.) Payson using 15N-enriched nutrient solutions wicked into the soil at various distances from study plants. Leaves were subsequently harvested from these plants and analyzed for N isotopic ratios. C. flava plants were capable of N uptake at distances of greater than 1.0 m from the outer edge of their aboveground canopy. The considerable lateral root neighborhood area of C. flava increases the amount of spatially variable N that is exploitable in these low-N soils. The ability to acquire spatially variable N and rapidly translate N uptake into photosynthetic carbon gain are traits that aid C. flava in maintaining its position as a successful subordinate competitor in a community dominated by larger, woody perennials. 相似文献
18.
Fotelli Mariangela N. Rienks Michael Rennenberg Heinz Geßler Arthur 《Trees - Structure and Function》2004,18(2):157-166
We investigated the effect of (a) different local climate and (b) thinning of the forest canopy on growth and N status of naturally regenerated European beech seedlings in a beech forest on shallow rendzina soil in southern Germany. For this purpose, a 15N-tracing experiment was conducted during the growing season of the year 2000 with beech seedlings growing on a warm, dry SW-exposed site and a cooler, moist NE-exposed site, and in a thinned and a control stand at each site. Biomass, 15N uptake and partitioning and total N concentrations of beech seedlings were determined. Site and thinning produced clear differences, particularly at the end of the growing season. Biomass and cumulative 15N uptake of beech seedlings then increased due to thinning on the NE site and decreased on the SW site. Total N concentrations in leaves, roots and stems of beech seedlings responded similarly. Therefore, growth and N status of beech seedlings are found to be favoured by thinning under cool-moist conditions. However, under higher temperature and reduced water availability—conditions that are prognosticated in the near future—thinning reduces N uptake and plant N concentration and, thus, impairs N balance and growth of beech regeneration. 相似文献
19.
M. A. Topa 《Plant and Soil》1996,182(2):259-265
Short-term 32P uptake experiments were conducted with intact seedlings of loblolly pine (Pinus taeda L.) to examine possible seed source variation in net accumulation of 32P in roots and shoots, and in rates of unidirectional influx. Seed source had a highly significant effect on biomass and P concentrations of shoots and roots. Seedlings from two seed sources representing fast-growing populations (a broadly-adapted and wet-site seed source) accumulated over 60% more total seedling P than smaller seedlings from a drought-hardy seed source, reflecting higher biomass and root P concentrations. Rates of unidirectional 32P influx in seedlings from the drought-hardy seed source were more than twice the rates of the seedlings from the broadly-adapted seed source. However, after 24 h in labeled uptake solution, net accumulation of 32P was similar, suggesting that rates of unidirectional efflux from roots of the drought-hardy seed source were also high. Although there were no significant differences in biomass and tissue P concentrations between the two fast-growing seed sources, rates of unidirectional influx in seedlings from the broadly-adapted seed source were 42% lower than rates in seedlings from the wet-site source. Yet, after 24 h in labeled uptake solution, net accumulation of 32P in seedlings from the broadly-adapted seed source was 50% higher. Unidirectional efflux out of the root may regulate net uptake of P as much, if not more, than influx in loblolly pine seedlings-at least under high-P growth conditions. The results in this study do not support previous studies with herbaceous plants suggesting that fast-growing species typically exhibit higher rates of nutrient uptake than slow-growing species. 相似文献
20.
Summary Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO2 and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO2 partial pressures of 350 and 650 bar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO2 when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO2 enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO2 enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO2. In seedlings supplied with soil N, elevated CO2 increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf 15N). While CO2 enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO2 partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO2 will depend greatly on plant and soil nutrient status. 相似文献