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1.
Anoxic conditions should hamper the transport of sugar in the phloem, as this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks. By fumigating the shoot with N 2 or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and stationary water of the phloem were assessed by non‐invasive magnetic resonance imaging (MRI) flowmetry. Carbohydrates and δ 13C in leaves, roots and phloem saps were determined. Following flooding, volume flow and conducting area of the phloem declined and sugar concentrations in leaves and in phloem saps slightly increased. Oligosaccharides appeared in phloem saps and after 3 d, carbon transport was reduced to 77%. Additionally, the xylem flow declined and showed finally no daily rhythm. Anoxia of the shoot resulted within minutes in a reduction of volume flow, conductive area and sucrose in the phloem sap decreased. Sugar transport dropped to below 40% by the end of the N 2 treatment. However, volume flow and phloem sap sugar tended to recover during the N 2 treatment. Both anoxia treatments hampered sugar transport. The flow velocity remained about constant, although phloem sap sugar concentration changed during treatments. Apparently, stored starch was remobilized under anoxia. 相似文献
2.
Protein, amino acids and ammonium were the main forms of soluble soil nitrogen in the soil solution of a subtropical heathland (wallum). After fire, soil ammonium and nitrate increased 90- and 60-fold, respectively. Despite this increase in nitrate availability after fire, wallum species exhibited uniformly low nitrate reductase activities and low leaf and xylem nitrate. During waterlogging soil amino acids increased, particularly γ-aminobutyric acid (GABA) which accounted for over 50% of amino nitrogen. Non-mycorrhizal wallum species were significantly ( P < 0.05) 15N-enriched (0.3–4.3‰) compared to species with mycorrhizal associations (ericoid-type, ecto-, va-mycorrhizal) which were strongly depleted in 15N (-6.3 to -1.8‰). Lignotubers and roots had δ 15N signatures similar to that of the leaves of respective species. The exceptions were fine roots of ecto-, ecto/va-, and ericoid type mycorrhizal species which were enriched in 15N (0.1–2.4‰). The 5 15N signatures of δ 15N total soil N and δ 15N soil NH4+ were in the range 3.7–4.5‰, whereas δ 15N soil NO3? was significantly ( P < 0.05) more enriched in 15N (9.2–9.8‰). It is proposed that there is discrimination against 15N during transfer of nitrogen from fungal to plant partner. Roots of selected species incorporated nitrogen sources in the order of preference: ammonium > glycine > nitrate. The exception were proteoid roots of Hakea (Proteaceae) which incorporated equal amounts of glycine and ammonium. 相似文献
3.
Stable carbon isotope signatures are often used as tracers for environmentally driven changes in photosynthetic δ 13C discrimination. However, carbon isotope signatures downstream from carboxylation by Rubisco are altered within metabolic pathways, transport and respiratory processes, leading to differences in δ 13C between carbon pools along the plant axis and in respired CO 2. Little is known about the within-plant variation in δ 13C under different environmental conditions or between species. We analyzed spatial, diurnal, and environmental variations in δ 13C of water soluble organic matter (δ 13C WSOM) of leaves, phloem and roots, as well as dark-respired δ 13CO 2 (δ 13C res) in leaves and roots. We selected distinct light environments (forest understory and an open area), seasons (Mediterranean spring and summer drought) and three functionally distinct understory species (two native shrubs— Halimium halimifolium and Rosmarinus officinalis—and a woody invader— Acacia longifolia). Spatial patterns in δ 13C WSOM along the plant vertical axis and between respired δ 13CO 2 and its putative substrate were clearly species specific and the most δ 13C-enriched and depleted values were found in δ 13C of leaf dark-respired CO 2 and phloem sugars, ~?15 and ~?33 ‰, respectively. Comparisons between study sites and seasons revealed that spatial and diurnal patterns were influenced by environmental conditions. Within a species, phloem δ 13C WSOM and δ 13C res varied by up to 4 ‰ between seasons and sites. Thus, careful characterization of the magnitude and environmental dependence of apparent post-carboxylation fractionation is needed when using δ 13C signatures to trace changes in photosynthetic discrimination. 相似文献
4.
Seedlings of Ricinus communis L. were cultivated in quartz sandand supplied with media which contained either different concentrationsof nitrate or ammonium nitrogen and were treated with a lowsalt stress. The concentration of ABA was determined in tissuesand in xylem and phloem saps. Between 41 and 51 day after sowing,abscisic acid (ABA) flows between roots and shoots were modelled.Long-distance transport of ABA was not stimulated under conditionsof nitrate deficiency (0.2 mol m 3). However, when ammoniumwas given as the only N source (1.0 mol m 3), ABA transportin both xylem and phloem was increased significantly. Mild saltstress (40 mol m 3 NaCl) increased ABA transport in nitrate-fedplants, but not in ammonium-fed plants. The leaf conductancewas lowered by salt treatment with both nitrogen sources, butit was always lower in ammonium-fed compared to nitrate-fedplants. A negative correlation of leaf conductance to ABA levelsin leaves or flow in xylem was found only in comparison of ammonium-fedto nitrate-fed plants. Key words: Abscisic acid, ammonium, Ricinus communis, phloem, xylem, transport, nitrate, nitrogen nutrition 相似文献
5.
The economy of carbon, nitrogen and water during growth of nodulated, nitrogen-fixing plants of white lupin (Lupinus albus L.) was studied by measuring C, N and H 2O content of plant parts, concentrations of C and N in bleeding sap of xylem and phloem, transpirational losses of whole shoots and shoot parts, and daily exchanges of CO 2 between shoot and root parts and the surrounding atmosphere. Relationships were studied between water use and dry matter accumulation of shoot and fruits, and between net photosynthesis rate and leaf area, transpiration rate and nitrogen fixation. Conversion efficiencies were computed for utilization of net photosynthate for nitrogen fixation and for production of dry matter and protein in seeds. Partitioning of the plant's intake of C, N and H 2O was described in terms of growth, transpiration, and respiration of plant parts. An empirically-based model was developed to describe transport exchanges in xylem and phloem for a 10-day interval of growth. The model depicted quantitatively the mixtures of xylem and phloem streams which matched precisely the recorded amounts of C, N and H 2O assimilated, absorbed or consumed by the various parts of the plant. The model provided information on phloem translocation of carbon and nitrogen to roots from shoots, the cycling of carbon and nitrogen through leaves, the relationship between transpiration and nitrogen partitioning to shoot organs through the xylem, the relative amount of the plant's water budget committed to phloem translocation, and the significance of xylem to phloem transfer of nitrogen in stems as a means of supplying nitrogen to apical regions of the shoot. 相似文献
6.
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
7.
The oxygen isotope composition in leaf water and organic compounds in different plant tissues is useful for assessing the physiological performance of plants in their environment, but more information is needed on Delta(18)O variation during a diel course. Here, we assessed Delta(18)O of the organic matter in leaves, phloem and xylem in stem segments, and fine roots of Ricinus communis during a full diel cycle. Enrichment of newly assimilated organic matter in equilibrium with leaf water was calculated by applying a nonsteady-state evaporative enrichment model. During the light period, Delta(18)O of the water soluble organic matter pool in leaves and phloem could be explained by a 27 per thousand enrichment compared with leaf water enrichment. Leaf water enrichment influenced Delta(18)O of phloem organic matter during the night via daytime starch synthesis and night-time starch remobilization. Phloem transport did not affect Delta(18)O of phloem organic matter. Diel variation in Delta(18)O in organic matter pools can be modeled, and oxygen isotopic information is not biased during transport through the plant. These findings will aid field studies that characterize environmental influences on plant water balance using Delta(18)O in phloem organic matter or tree rings. 相似文献
8.
Nitrogen (N) isotope patterns are useful for understanding carbon and nitrogen dynamics in mycorrhizal systems but questions remain about how different N forms, fungal symbionts, and N availabilities influence δ 15N signatures. Here, we studied how biomass allocation and δ 15N patterns in Pinus sylvestris L. cultures were affected by nitrogen supply rate (3% per day or 4% per day relative to the nitrogen already present), nitrogen form (ammonium versus nitrate), and mycorrhizal colonization by fungi with a greater ( Laccaria laccata) or lesser ( Suillus bovinus) ability to assimilate nitrate. Mycorrhizal (fungal) biomass was greater with ammonium than with nitrate nutrition for Suillus cultures but similar for Laccaria cultures. Total biomass was less with nitrate nutrition than with ammonium nutrition for nonmycorrhizal cultures and was less in mycorrhizal cultures than in nonmycorrhizal cultures. The sequestration of available N by mycorrhizal fungi limited plant N supply. This limitation and the higher energetic cost of nitrate reduction than ammonium assimilation appeared to control plant biomass accumulation. Colonization decreased foliar δ 15N by 0.5 to 2.2‰ (nitrate) or 1.7 to 3.5‰ (ammonium) and increased root tip δ 15N by 0 to 1‰ (nitrate) or 0.6 to 2.3‰ (ammonium). Root tip δ 15N and fungal biomass on root tips were positively correlated in ammonium treatments ( r 2?=?0.52) but not in nitrate treatments ( r 2?=?0.00). Fungal biomass on root tips was enriched in 15N an estimated 6–8‰ relative to plant biomass in ammonium treatments. At high nitrate availability, Suillus colonization did not reduce plant δ 15N. We conclude that: (1) transfer of 15N-depleted N from mycorrhizal fungi to plants produces low plant δ 15N signatures and high root tip and fungal δ 15N signatures; (2) limited nitrate reduction in fungi restricted transfer of 15N-depleted N to plants when nitrate is supplied and may account for many field observations of high plant δ 15N under such conditions; (3) plants could transfer assimilated nitrogen to fungi at high nitrate supply but such transfer was without 15N fractionation. These factors probably control plant δ 15N patterns across N availability gradients and were here incorporated into analytical equations for interpreting nitrogen isotope patterns in mycorrhizal fungi and plants. 相似文献
9.
Plants of Lupinus albus were grown for 51 d under control (1.1mol m 3 NaCl) and saline (40 mol m 3 NaCl) conditions.Plants were harvested and changes of carbon, nitrogen and abscisicacid (ABA) contents of individual organs were determined 41d and 51 d after germination. In the period between the twoharvests xylem and phloem saps were collected and respirationand photosynthesis of individual organs were measured. Usingflows of carbon, C/ABA ratios and increments of ABA flows ofABA in phloem and xylem and rates of biosynthesis and degradationof ABA were calculated. Both under control and saline conditionsnet biosynthesis occurred in the root, the basal strata of leavesand in the inflorescence. Metabolic degradation of ABA tookplace in the stem internodes and apical leaf strata. Salt stress increased xylem transport of ABA up to 10-fold andphloem transport to the root up to 5-fold relative to that ofthe controls. A considerable amount of ABA in the xylem saporiginated from biosynthesis in the roots, i.e. 55% in salt-treatedand smaller than 28% in control plants. The remaining part ofABA in the xylem sap originated from the shoot: it was translocatedin the phloem from fully differentiated leaves towards the rootand from there it was recirculated back to the aerial partsof the plant. The data suggest that ABA may serve as a hormonalstress signal from the root system. Key words: Lupinus albus, salt stress, abscisic acid, long distance transport 相似文献
10.
Studies that quantify plant δ 15N often assume that fractionation during nitrogen uptake and intra-plant variation in δ 15N are minimal. We tested both assumptions by growing tomato ( Lycopersicon esculetum Mill. cv. T-5) at NH 4+ or NO ?3 concentrations typical of those found in the soil. Fractionation did not occur with uptake; whole-plant δ 15N was not significantly different from source δ 15 N for plants grown on either nitrogen form. No intra-plant variation in δ 15N was observed for plants grown with NH +4. In contrast. δ 15N of leaves was as much as 5.8% greater than that of roots for plants grown with NO ?3. The contrasting patterns of intra-plant variation are probably caused by different assimilation patterns. NH +4 is assimilated immediately in the root, so organic nitrogen in the shoot and root is the product of a single assimilation event. NO ?3 assimilation can occur in shoots and roots. Fractionation during assimilation caused the δ 15N of NO ?3 to become enriched relative to organic nitrogen; the δ 15N of NO ?3 was 11.1 and 12.9% greater than the δ 15N of organic nitrogen in leaves and roots, respectively. Leaf δ 15N may therefore be greater than that of roots because the NO ?3 available for assimilation in leaves originates from a NO ?3 pool that was previously exposed to nitrate assimilation in the root. 相似文献
11.
Key message Large variations in leaf δ 15 N in Bornean tropical rainforest trees may indicate that various tropical species have species-specific strategy for nitrogen uptake under low soil nutrient conditions, including root symbiotic microorganisms such as ectomycorrhiza. AbstractLowland tropical rainforests in Southeast Asia are characterized by high species diversity despite limited soil nutrient conditions. The plant nitrogen isotope ratio (δ15N) reflects plant uptake of soil nitrogen. We analyzed δ15N values and nitrogen content (N %) in leaves and roots of 108 woody species with different types of symbiotic microorganisms, of different life forms (emergent, canopy, sub-canopy, understory, and canopy gap species), and from different families in a Bornean lowland dipterocarp forest to gain more insight into the diversity of nitrogen uptake strategy in the rhizosphere. Leaf δ15N values in the species studied varied largely from ?7.2 to 5.0 ‰, which is comparable to the values of known Asian trees including temperate, sub-tropical, and tropical mountain forests. Leaf δ15N also varied significantly among both life forms and families, though the phylogenetically independent contrast (PIC) relationships were not statistically significant among life form, family, and symbiotic types. Some families showed specific leaf δ15N values; Dipterocarpaceae, the dominant family in the canopy layer with symbiotic ectomycorrhiza in Southeast Asia, had small intraspecific variation and higher leaf δ15N values (0.03 ‰) compared with species exhibiting arbuscular mycorrhiza, whereas several families such as Burseraceae, Euphorbiaceae, and Myrtaceae showed large interspecific variation in leaf δ15N (e.g., from ?7.2 to 5.0 ‰ in Euphorbiaceae). These variations suggest that tropical species may have family- or species-specific strategy, such as root symbiotic microorganisms, for nitrogen uptake under low-nutrient conditions in tropical rainforests in Southeast Asia. 相似文献
12.
BackgroundAnthropogenic nitrogen (N) addition has dramatically increased and significantly affected global nitrogen cycling. The natural abundance of stable N isotope ratios (δ15N) has been used as an indicator of the N status of an ecosystem. However, how plant and soil δ15N signatures would respond to N addition is still unclear. Methods and aimsHerein, we synthesized the data of 951 observations from 48 individual studies associated with responses of plant and soil δ15N values to N addition and conducted a meta-analysis to explore a general pattern of N addition effects on δ15N values of plant and soil. ResultsOur results showed that δ15N values of plant, soil total N, and soil NO3
? were significantly increased by N addition, while δ15N value of soil N2O was significantly decreased and δ15N value of soil NH4
+ was not significantly changed. The δ15N value of soil total N of different ecosystems showed similar responses to N addition, whereas δ15N values of different plant types showed different responses. Increasing treatment duration significantly increased the effects of inorganic N addition on δ15N values of shrubs and soil NH4
+ but did not affect the responses of δ15N values of soil total N and NO3
?. With increasing inorganic N addition rate, only δ15N value of plant was significantly increased, but no significant relationship was found between the effect of N addition on other components and N addition rate because of the input of isotopically depleted sources. ConclusionsOur study revealed a comprehensive picture of the effects of N addition on δ15N signatures in terrestrial ecosystems and could help us understand how plant and soil δ15N signatures change with N addition and how these signatures can be used as an indicator of ecosystem N status under increasing N deposition or fertilization. 相似文献
13.
The composition of amino acids was determined in the xylem andphloem sap of symbiotic lupins grown under a variety of treatmentsdesigned to alter the rate of nitrogen fixation. Asparaginewas the major amino acid in both xylem and phloem with glutamine,glutamate and aspartate also major components. GABA had a highconcentration in the xylem while valine was a major componentin the phloem. Exposure to combined nitrogen in the form ofeither ammonium or nitrate caused a reduction in specific nitrogenaseactivity and was associated with subsequent changes in bothof the translocated saps. Inhibiting nitrogen fixation by exposingnodules to oxygen produced a lower amide to amine ratio in thexylem sap (1.3:1) compared with control and nitrate ratios (2.6:1)and ammonium ratios (7.1:1). Similar ratios for amide aminewere also observed in the phloem sap. Labelling studies using 15N 2 to follow nitrogen fixation, ammonium assimilation andamino acid transport have shown rapid accumulation of labelinto glutamine with subsequent enrichment in glutamate, aspartate,alanine, and GABA. Asparagine was found in high concentrationsin nodules and became slowly enriched. Labelled nitrogen fixedand assimilated in nodules was detected 40 min later in stemxylem extracts, largely as the amides glutamine and asparagine.These experiments provide evidence that large amounts of nitrogenouscompounds are cycled through the root nodules of symbiotic plants(contributing approximately 50% of xylem N) and that differencesin the composition of the phloem sap may influence nodule growthand activity. Key words: Nitrogen fixation, nitrogen translocation, isotope labelling, legumes, GC-MS 相似文献
15.
Nitrogen movement through the xylem vessels and sieve tubes in rice plants was studied using xylem and phloem sap analysis in combination with stable and radioactive nitrogen isotope techniques.More than 90% of nitrogen was translocated in the sieve tubes of rice plants as amino acids. When 15N (99.6 atom%) was applied as a nitrate to the root, 15N first appeared in phloem sap of the leaf sheath within 10 minutes and increased to 37 atom% excess 5 hours after the experiment had started. In long-term experiments, 63% of nitrogen in the phloem sap of the leaf sheath and 15% in that of the uppermost internode came from nitrogen absorbed within the last 24 hours and 50 hours, respectively.To obtain information about the more rapid circulation of nitrogen in the plant, radioactive 13N was used as a tracer. A positron-emitting tracer imaging system was used to show that 13N was transferred to the leaf sheath within 8 minutes of its application to the roots. Analysis of the xylem sap of the leaf sheath showed that when the nitrate was applied to the roots, most of the nitrogen in the xylem was transported as a nitrate.These data showed that phloem and xylem sap analysis together with the stable and radioactive nitrogen techniques provide a good method for the detection of nitrogen cycles in plants. 相似文献
16.
The major findings of many years of research into plant N cycling are summarised in this review, firstly as revealed by 15N-enriched methods and secondly, in relation to natural 15N abundance (δ 15N) in plants and their metabolites. This work has mainly been done in an agricultural context. As many groups especially attempt to relate δ 15N to N cycling, atmospheric N deposition and the interactions of N with carbon budgets, we deem it useful to synthesize these major findings. Primary assimilation and distribution of N within plants were investigated from the 15N enrichment in individual plant organs and in individual amino acids after feeding them 15N-labelled compounds. In both roots and leaves, NH 4 + and NO 3 ? were assimilated into amino acids, largely by a combination of glutamine synthetase (GS) and glutamate synthase (GOGAT). In the leaves, the transfer of glutamine (amide) N to glutamic acid was accelerated in the light, and amino N in some amino acids was deaminated to ammonia in the dark, followed by its incorporation into glutamine. The N in the growing parts such as growing leaves, filling grains and growing root parts were from two sources: re-allocation (phloem supply) of reserved N (amino acids), and currently-absorbed N. The metabolites from the mature parts may perform the roles of substrates for plant growth and signals for gene expression. δ 15N values, measured for plants/soils and plant metabolites (inorganic N, amino acids, polyamines) were related with the acquisition, metabolism and distribution of N in plants. Small 15N/ 14N fractionation in the acquisition of N 2 and NO 3 ? and large 15N/ 14N fractionation in NH 4 + uptake were found. The δ 15N values of whole shoots or grains from field-grown crops were largely reflected major sources of N. In some legumes, 15N was enriched in their nodules and an extremely 15N-enriched compound was homospermidine. Nitrate reduction to ammonia (NR) and ammonia assimilation to glutamine (GS) showed large 15N/ 14N fractionations. Specific attention was paid to the δ 15N values in xylem and phloem exudates compared to those of plant organs. 相似文献
17.
Carbon and nitrogen stable isotope ratios (δ 13C and δ 15N) of macroinvertebrates inhabiting littoral zones of lakes can serve as useful indicators of material loading from the watershed. We collected snails ( Semisulcospira spp.) and bivalves ( Unio douglasiae biwae Kobelt) from 29 littoral sites in Lake Biwa near the mouths of river tributaries with various human population density (HPD) and land-use patterns. The δ 13C and δ 15N signatures were determined for three potential food sources: particulate organic matter in the pelagic zone (PPOM), riverine particulate organic matter from tributaries (RPOM) and epilithic organic matter in the littoral zone (EOM). The stable isotope mixing model revealed that snails relied mainly on EOM, and bivalves on PPOM and RPOM. Multiple regression analysis showed that intersite variation in δ 15N for snails was best explained by HPD, while variation in δ 15N of EOM and nitrate was explained to a lesser extent by HPD. Comparison with isotope signatures of their food sources and riverine nutrients revealed that snails assimilated anthropogenic nitrogen from wastewater in the watershed. Our results also showed that the δ 13C value of bivalves was marginally related to the fraction of paddy fields in the watersheds. In conclusion, the isotope signatures of macroinvertebrates inhabiting the littoral zone can be useful indicators of anthropogenic impacts from the watershed. 相似文献
18.
The distribution of NO 3? reduction between roots and shoots was studied in hydro-ponically-grown peach-tree seedlings ( Prunus persica L.) during recovery from N starvation. Uptake, translocation and reduction of NO 3?, together with transport through xylem and phloem of the newly reduced N were estimated, using 15N labellings, in intact plants supplied for 90 h with 0.5 m M NH 4+ and 0.5, 1.5 or 10 m M NO 3?. Xylem transport of NO 3? was further investigated by xylem sap analysis in a similar experiment. The roots were the main site of NO 3? reduction at all 3 levels of NO 3? nutrition. However, the contribution of the shoots to the whole plant NO 3? reduction increased with increasing external NO 3? availability. This contribution was estimated to be 20, 23 and 42% of the total assimilation at 0.5, 1.5 and 10 m M NO 3?, respectively. Both 15N results and xylem sap analysis confirmed that this trend was due to an enhancement of NO 3? translocation from roots to shoots. It is proposed that the lack of NO 3? export to the shoots at low NO 3? uptake rate resulted from a competition between NO 3? reduction in the root epidermis/cortex and NO 3? diffusion to the stele. On the other hand, net xylem transport of newly reduced N was very efficient since ca 70% of the amino acids synthesized in the roots were translocated to the shoots, regardless of the level of NO 3? nutrition. This net xylem transport by far exceeded the net downward phloem transport of the reduced N assimilated in shoots. As a consequence, the reduced N resulting from NO 3? assimilation, principally occurring in the roots, was mainly incorporated in the shoots. 相似文献
19.
Background: Plant and soil nitrogen stable isotope (δ 15N) can integrate several fundamental biogeochemical processes in ecosystem nitrogen dynamics, and reflect characteristics of ecosystem nitrogen cycling. Aims: We investigated how climate change influenced plant-soil nitrogen cycling by relating soil δ 15N, plant δ 15N and Δδ 15N (difference between soil and plant δ 15N) with climatic factors. Methods: Field investigation was conducted in temperate grasslands in Inner Mongolia during August 2015. Plant δ 15N, soil δ 15N and Δδ 15N were determined, and their relationships with climatic factors were examined by simple regression analyses and general linear models. Results: Soil δ 15N was significantly higher than plant δ 15N, and there was a positive linear correlation between them. Soil and plant δ 15N were negatively related with mean annual precipitation (MAP) and positively with mean annual temperature (MAT); conversely, Δδ 15N was positively related with MAP and negatively with MAT. Conclusion: Soil δ 15N was dominantly controlled by MAT, while it was MAP for plant δ 15N. Climate factors influenced plant δ 15N not only through their effects on soil nitrogen dynamics but also strategies of plant nitrogen acquisition. Thus, compared with plant δ 15N, soil δ 15N can more accurately reflect soil nitrogen dynamics, while plant δ 15N may integrate soil nitrogen dynamics and plant nitrogen acquisition. 相似文献
20.
Spatial variation in mean annual precipitation is the principal driver of plant water and nitrogen status in drylands. The natural abundance of carbon stable isotopes (δ 13C) in photosynthetic tissues of C3 plants is an indicator of time‐integrated behaviour of stomatal conductance; while that of nitrogen stable isotopes (δ 15N) is an indicator of the main source of plant N (soil N vs. atmospheric N 2). Previous studies in drylands have documented that plant δ 13C and δ 15N values increase with decreasing mean annual precipitation due to reductions in stomatal conductance, and soil enriched in 15N, respectively. However, evidence for this comes from studies focused on stable isotopes measurements integrated at the plant community level or on dominant plants at the site level, but little effort has been made to study C and N isotope variations within a species growing along rainfall gradients. We analysed plant δ 13C, δ 15N and C/N values of three woody species having different phenological leaf traits (deciduous, perennial and aphyllous) along a regional mean annual precipitation gradient from the central‐western Argentinian drylands. Noticeably, plant δ 13C and δ 15N values in the three woody species did not increase towards sites with low precipitation or at the start of the growing season (drier period), as we expected. These results suggest that environmental factors other than mean annual precipitation may be affecting plant δ 13C and δ 15N. The short‐term environmental conditions may interact with species‐specific plant traits related to water and nitrogen use strategies and override the predictive influence of the mean annual precipitation on plant δ 13C and δ 15N widely reported in drylands. 相似文献
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