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TOBIAS RÜTTING TIM J. CLOUGH CHRISTOPH MÜLLER MARK LIEFFERING PAUL C. D. NEWTON 《Global Change Biology》2010,16(9):2530-2542
The increasing concentration of atmospheric carbon dioxide (CO2) is expected to lead to enhanced competition between plants and microorganisms for the available nitrogen (N) in soil. Here, we present novel results from a 15N tracing study conducted with a sheep‐grazed pasture soil that had been under 10 years of CO2 enrichment. Our study aimed to investigate changes in process‐specific gross N transformations in a soil previously exposed to an elevated atmospheric CO2 (eCO2) concentration and to examine indicators for the occurrence of progressive nitrogen limitation (PNL). Our results show that the mineralization–immobilization turnover (MIT) was enhanced under eCO2, which was driven by the mineralization of recalcitrant organic N. The retention of N in the grassland was enhanced by increased dissimilatory NO3? reduction to NH4+ (DNRA) and decreased NH4+ oxidation. Our results indicate that heterotrophic processes become more important under eCO2. We conclude that higher MIT of recalcitrant organic N and enhanced N retention are mechanisms that may alleviate PNL in grazed temperate grassland. 相似文献
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Mineral nitrogen cycling through earthworm casts in a grazed pasture under elevated atmospheric CO2 总被引:1,自引:0,他引:1
ALEXIS J. T. CHEVALLIER † MARK LIEFFERING R. A. CARRAN P. C. D. NEWTON 《Global Change Biology》2006,12(1):56-60
We used the New Zealand grazed pasture free air CO2 enrichment experiment to determine the effects of elevated CO2 on earthworm (Aporrectodea caliginosa and Lumbricus rubellus) cast production and mineral nitrogen (N) concentration over a 5‐week period in the spring. Elevated CO2 did not affect earthworm biomass or the amount of cast material produced. However, cast mineral N concentrations were 18% lower, resulting in 27% less mineral N being deposited on the soil surface under elevated CO2. An analysis of the earthworms' potential diet showed that a reduction in the N content of sheep dung at elevated CO2 was the most likely cause of the lower cast N concentrations. Earthworm casts made only a small contribution to mineral N cycling in our system; however, their quality may act as a sensitive indicator of reduced N availability under elevated CO2 which is consistent with the hypothesised process of progressive N limitation. 相似文献
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Relationships between nitrate (NO-3) supply, uptake and assimilation,water uptake and the rate of mobilization of seed reserves wereexamined for the five main temperate cereals prior to emergencefrom the substrate. For all species, 21 d after sowing (DAS),residual seed dry weight (d.wt) decreased while shoot plus rootd.wt increased (1530%) with increased applied NO-3concentrationfrom 0 to 520 mM . Nitrogen (N) uptake and assimilationwere as great with addition of 5 mM ammonium (NH+4) or 5 mMNO-3but NH+4did not affect the rate of mobilization of seedreserves. Chloride (Cl-) was similar to NO-3in its effect onmobilization of seed reserves of barley (Hordeum vulgare L.).Increased rate of mobilization of seed reserves with additionalNO-3or Cl-was associated with increases in shoot, root and residualseed anion content, total seedling water and residual seed watercontent (% water) 21 DAS. Addition of NH+4did not affect totalseedling water or residual seed water content. For barley suppliedwith different concentrations of NO-3or mannitol, the rate ofmobilization of seed reserves was positively correlated (r >0.95)with total seedling water and residual seed water content. Therate of mobilization of seed reserves of barley was greaterfor high N content seed than for low N content seed. Seed watercontent was greater for high N seed than for low N seed, 2 DAS.Additional NO-3did not affect total seedling water or residualseed water content until 1014 DAS. The effects of seedN and NO-3on mobilization of seed reserves were detected 10and 14 DAS, respectively. It is proposed that the increasedrate of mobilization of seed reserves of temperate cereals withadditional NO-3is due to increased water uptake by the seedlingwhile the seed N effect is due to increased water uptake bythe seed directly. Avena sativa L.; oat; Hordeum vulgare L.; barley; Secale cereale L.; rye; xTriticosecale Wittm.; triticale; Triticum aestivum L.; wheat; nitrate; seed; germination; seed reserve mobilization 相似文献
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The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses 总被引:2,自引:1,他引:1
Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO-3) content of root and shoot and NO-3 and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO-3 concentrations (0·120mol m3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m3 NO-3 For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO-3 concentration on the partitioning of NO-3 assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m3 NO-3 and that for all cereals, shoot assimilationincreased in importance as applied NO-3 concentration increasedfrom 1.0 to 20 mol m3 At 5.020 mol m3 NO3,the data indicated that the shoot played an important if notmajor role in NO-3 assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO-3 assimilation at 0.5 mol m3NO-3 but shoot assimilation was predominant at 5.0 mol m3NO-3 Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m3 NO-3 Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap 相似文献
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