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    Presentation 210411 Presentation 210411 Presentation Transcript

    • Long-term fertilizationand soil warmingeffects on recalcitrantlitter decomposition Bas Dingemans [Faculty of Science Biology]
    • ContentsIntroduction/Recalcitrance/Warming/Nitrogen/Research questionMethods/Site description/Experimental setupResults/Incubation/Litter qualityDiscussion/Quality paradox/Interaction effect/More analysesConclusion/Neutralizing effect/Caution with quality [Faculty of Science Biology]
    • Introduction/RecalcitranceAccumulation of SOM isdetermined by the ratesof primary productionand decomposition. PP CO2Focus on the quality ofproduced material andthe decomposition ofthis material. [Faculty of Science Biology]
    • Introduction Phase 1 Phase 2 Phase 3/Recalcitrance solubles non-lignified carbohydratesMost decomposition ex- lignified carbohydratesperiments have been lignin + lignin-like compounds Remaining massdone with “fresh litter”.The recalcitrance of soilorganic matter is a lothigher.By extending my litterdecomposition experi-ments in time, I’m follow-ing the later stages in de-composition. Time Berg & Laskowski 2006 [Faculty of Science Biology]
    • a long-lasting stimulating effect on CO2-emission in subarctic short-ter peatlands. tion disp To partition the sources of increased ecosystem respiration rates, fractiona we compared the effects of OTCs during the snow-free season peat resp between intact and trenched-plus-clipped parts of plots in a com- respiratiIntroduction panion experiment. Heterotrophic respiration of peat (trenched- plus-clipped treatment) accounted for 70% of the total ecosystem Informa/Warming respiration rate (intact treatment) and both heterotrophic and plant- related (aboveground, roots, rhizosphere) respiration ratesDorrepaal et al. 2009:Soil respiration increas- 0.6 Respiration (g CO2 m–2 h–1)es with higher tempera-tures. 0.4Kirschbaum 1995: SOM 0.2decomposition increas-es more with increasing 0.0temperature than net pri- Ecosystem Rh Ramary production. respiration Figure 3 Dorrepaal et al. 2009 Figure 2 | Ecosystem respiration rates and their heterotrophic and plant- subjected related components in a subarctic bog subjected to experimental warming and summDavidson & Janssens or ambient conditions. Spring and summer warming (black bars) stimulated winter sn2006: Recalcitrant car- total ecosystem respiration (P 5 0.001), and stimulated heterotrophic (Rh) and plant-related (Ra) respiration components equally (P , 0.001; (P 5 0.03 durationbon is more sensitive to warming 3 flux-component: P 5 0.65) compared with ambient conditions effects ontemperature than labile (white bars). Response patterns remained unchanged over the first two experimental years (period 3 warming: P 5 0.41 for ecosystem respiration, ecosystem P 5 0.38)carbon. P 5 0.18 for Rh and Ra), which were averaged. Error bars represent s.e.m. of (period 3 treatments (n 5 5 plots). s.e.m. of Davidson & Janssens 2006 ©2009 Macmillan[Faculty of Science ri Publishers Limited. All Biology]
    • ng-term nutrient fertilization these inferences were based on abovegroundreduction in the thickness of the layer, because neither %C nor and surface soil measurements only. The lack of soil-profile measurements reflects affected by fertilization (Supplementary Infor- bulk density was helle C. Mack1*, Edward A. G. Schuur1*, M. Syndonia Bret-Harte2, the expectation that the large heterogeneous belowground C pool mineral soil, fertilization reduced %C by 50% us R. Shaver3 & F. Stuart Chapin III2 mation). In the upper (P ¼ 0.04), whereas the depth to the frozen soil surface and mineral partment of Botany, University of Florida, Gainesville, Florida 32611, USA titute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 75, USA Introduction e Ecosystems Center, Marine Biological Laboratory, Woods Hole, sachusetts 02543, USA /Nitrogen se authors contributed equally to this work .................................................................................................................................................................... August 2007 NUTRIENT August 2007 LIMITATION AND DECOMPOSITION NUTRIENT LIMITATION AND DECOMPOSITION 2109obal warming is predicted to be most pronounced at high tudes, and observational evidence over the past 25 years Mack et al. 2005: Nitro- gests that this warming is already under way1. One-third of global soil carbon pool is stored in northern latitudes2, so gen enrichment results re is considerable interest in understanding how the carbon ance of northern ecosystems will respond to climate warm- 3,4 in increased primary pro- . Observations of controls over plant productivity in tundrad boreal ecosystems5,6 have been used to build a conceptual duction and a stronger del of response to warming, where warmer soils and increased increase in decomposi- omposition of plant litter increase nutrient availability, ich, in turn, stimulates plant production and increases eco- tion. tem carbon storage6,7. Here we present the results of a long- m fertilization experiment in Alaskan tundra, in which Figure 1 Effect of fertilization on vascular plant aboveground net primary production (ANPP) in tundra. Fertilized plots in moist acidic tundra near Toolik Lake, Alaska, have Mack et al. 2005 reased nutrient availability caused a net ecosystem loss of received 10 g N m22 yr21 and 5 g P m22 yr21 since 1981. Values are means (^1 fertilization on tundra carbon and nitrogen pools after 20 yr of Figure 2 Effects ofmost 2,000 grams of carbon per square meter over 20 years. We standard error, s.e.); means from 1982–95 are reported in ref. fertilization. a, c, Mean (^1 s.e.) above- and belowground carbon (a) and nitrogen (c) 19; the year-2000 data Craine et al. 2006: Low nd that annual aboveground plant production doubled ing the experiment. Losses of carbon and nitrogen from are from this study (n ¼ 4). Components of ANPP (new leaves pools in unmanipulated control and fertilized treatments of moist acidic tundra near Toolik and reproductive parts, new stems and secondary growth) are shown in SupplementaryLake, 1.Fig. Alaska. Aboveground pools include shoots, standing dead plant material, and0 nitrogen availability©can Publishing Group 2004 Nature rhizomes. Belowground pools include surface litter, roots, and organic and mineral soil. NATURE | VOL 431 | 23 SEPTEMBER 2004 | www.nature.com/nature increase litter decompo- NATURE | VOL 431 | 23 SEPTEMBER 2004 | www.nature.com/nature ©2004 Nature Pub sition as microbes use labile substrates to ac- Figure 2 Effects of fertilization on tundra carbon and nitrogen pools after 20 yr of fertilization. a, c, Mean (^1 s.e.) above- and belowground carbon (a) and nitrogen (c) quire nitrogen from re- pools in unmanipulated control and fertilized treatments of moist acidic tundra near Toolik Lake, Alaska. Aboveground pools include shoots, standing dead plant material, and calcitrant organic matter rhizomes. Belowground pools include surface litter, roots, and organic and mineral soil. (microbial nitrogen min- NATURE | VOL 431 | 23 SEPTEMBER 2004 | www.nature.com/nature ©2004 Nature Pub ing). FIG. 2. Relationships between (a and b) labile-C FIG. 2. Relationships betweenandandandlabile-C pool sizeal. 2006 substrate [C] and (c and d) recalc Craine et decay rate pool size (CL) vs. substrate [C] (a (c b) d) recalcitrant-C (CL) vs. (kR) vs. substrate [N] for leaves with no nutrients added (thin line) [N] for added with no nutrients added (thin line) and N added (thick line). substrate and N leaves (thick line). [Faculty of Science followed N-mining theory with N fertilization decreas- followed N-mining theory with N fertilization decreas- ing kR (decay rate of the recalcitrant-C pool) bykR (decay rate of the recalcitrant-C pool) by 29% on ing 29% on Biology] average (Fig. 1b). Declines in kR with N average (Fig. 1b). Declines in kR with N fertilization fertilization
    • Introduction/Research questionDoes long-term fertilization amplify or neutralize the positive effect of soilwarming on the decomposition of recalcitrant litter?Is chemical composition a good predictor of decomposability of recalcitrantlitter? [Faculty of Science Biology]
    • IcelandMethods/Site descriptionField site is located nearHveragerði in Iceland.Geothermally heated val- Reykjavik Hveragerdiley with patchwork ofheated and ambient wetgrassland soils. Land age < 0.8 M y 0.8 - 3.3 M y 3.3 - 15 M y [Faculty of Science Biology]
    • Water flowMethods/Experimental Bufferzonesetup Plot C NPlots consist of two adja-cent subplots, a fertilizedand upstream its unferti-lized control. 25 Air temperature: ~10°C Ambient Warmed 20 Soil temperature (°C)Plots were layed out in2005 on warmed (~25°C) 15and ambient grass patch-es. 10 5Dead standing litter(grasses and sedges) 0from every plot was har- Fertilized Unfertilizedvested in May 2009 and Plot treatmentpouled per treatment. [Faculty of Science Biology]
    • Methods/ExperimentalsetupLitter was incubated attwo different tempera-tures (15°C and 25°C)with and without extra ni-trogen (urea)for 365 days with threeharvests (0, 175 and 365 0 days 175 days 365 daysdays).Harvested material wasused for determination ofmass loss, C:N ratio andlignin. [Faculty of Science Biology]
    • Lignin determinationMethods/Experimental dry littersetup water, methanol, lipids, sugars, chloroform soluble phenolicsLignin content wasmeasured by sequentialextraction of lipids, water hydrochlo-solubles and hydrolys- ric acid starch, fructans,able carbon. pectins, hemicel- lulose C and NBy analysing the carbon analysis,and nitrogen content of calculationthe residue the lignincontent was calculated. cellulose lignin Poorter & Villar 1997 [Faculty of Science Biology]
    • Results Mass remaining after 365 days (%)/Incubation Ambient WarmedWhen litter was incu- 55bated at plot-own situa-tion an accelerated de- 50composition was foundin litter from unfertilized,warmed plots incubated 45at 25°C without addition-al nitrogen. 40No significant tempera-ture effect was measured Fertilized Unfertilizedwithin the fertilized treat-ment. TreatmentNo significant fertiliza-tion effect was measuredwithin the ambient treat-ment. [Faculty of Science Biology]
    • 43 Ambient Litter carbon content (%) Warmed 42Results 41/Litter quality 40 39 38Initial litter C concentra- 37tion is higher and N con-centration is lower in lit- Litter nitrogen content (%) 1.6ter from warmed plots. 1.5 1.4Fertilization of the plots 1.3 1.2leads to a lower carbon 1.1and nitrogen concentra- 1.0tion in the litter. 36Initial carbon to nitrogen Litter C:N ratio (g g-1) 34ratio is higher in litter 32from warmed plots. 30 28Fertilization of the 26warmed plots leads to a Fertilized Unfertilizedhigher C:N ratio in the lit- Plot treatmentter. [Faculty of Science Biology]
    • Ambient Litter lignin content (%) WarmedResults 15/Litter quality 10Initial litter lignin concen-tration is higher in litter 5from warmed plots.Initial litter lignin concen-tration is lower in litter 12 Litter lignin:N ratio (g g-1)from fertilized plots 10 8 6 4 2 Fertilized Unfertilized Plot treatment [Faculty of Science Biology]
    • Discussion /Quality paradox Warming of plots causes a ‘time shift’, i.e. the litter from warmed plots is in a further stage in the decomposition process. Due to the loss of easily decom- posable carbon the concentration of recalcitrant carbon is higher. Spring Summer Autumn WinterAmbient SnowWarmed Harvest End growing season Fertilizing of plots causes a higher biomass production. Fertilized plants grow faster due to the production of easily composable (i.e. decomposable) plant material. The production of recalcitrant plant material takes more time and the overall recalcitrant compound concentration will be lower. [Faculty of Science Biology]
    • Discussion Mass remaining after 365 days (%)/Interaction ef- Ambientfect 55 WarmedNitrogen fertilizationmay neutralize the posi- 50tive effect of increasedtemperature on the de-composition of recalci- 45trant litter in grasslands. 40 Fertilized Unfertilized Treatment [Faculty of Science Biology]
    • Incubator treatmentDiscussion 70 Control 15°C Control 25°C/More analyses 60 Ambient WarmedIncubating without ad- 50 Mass remaining after 365 days (%)ditional nitrogen showsa clear positive effect of 40plot temperature on thedecomposition rate. 30This effect is gone whenincubating with addition- 70 Nitrogen 15°C Nitrogen 25°Cal nitrogen. 60Further discussion 50about this research atdECOlab meeting. 40 30 Fertilized Unfertilized Fertilized Unfertilized Plot treatment [Faculty of Science Biology]
    • Conclusion/Neutralizing effectNitrogen fertilization may neutralize the positive effect of increased temperatureon the decomposition of recalcitrant litter in grasslands./Caution with qualityLinking litter decomposability to the chemical composition of litter is “tricky busi-ness”. A high C:N ratio or a high lignin concentration does not necessarily meanlow decomposability. [Faculty of Science Biology]
    • Acknowledge-ments/Thanks toMariet/UUAnne/NIOOBjorn/UUPaul/NIOORiks/NIOO/UUGerrit/UUJos/UUTryggvi/UIGisli Pall/GrundRannveig/AUI [Faculty of Science Biology]