Carbon turnover in the rhizosphere and why plants release carbon in soil

Transcription

1 Elevated CO Global C cycle Carbon turnover in the rhizosphere and why plants release carbon in soil Yakov Kuzyakov kuzyakov@gwdg.de Soil Science of Temperate Ecosystems Georg-August-University Göttingen Units: Petagrams (Pg) = gc Pools: Pg Fluxes: Pg/year 3 Element O Si Al Fe C (total) Ca Mg K a Mn Zn Mo i Cu P S Element contents in soils (mg/kg), the Earth crust and sediments (Sparks 3) Soils Sediments Median Range 49, - 33,,-4, 7,,-3, 4,,-,, 7,-,, 7-,, 4-9, 4, 8-37,, -,, -, , -, 8 3-,3 7 3-,6 Earth crust (mean) 474, 77, 8, 4, 48 4, 3,, 3, , 6 (mean) 486, 4, 7, 4, 9,4 66, 4,,, , 4 Main differences between soils and soil parent material High C and content biophilic elements High content of chemical energy available for microorganisms High activity of microorganisms utrients are available for plants Fertility! the ability of soil to maintain plant growth: Water utrients Oxygen

2 Haplic Phaeozem Very high C and content! Fertility! Importance of roots Plants ( > 99%) Dead / Litter: Above ground Leaves Shoots Below ground Roots Sources of organic C in soils Contribution of root-c to soil-c is ~. times higher than of shoot-c (Rasse et al. Plant and Soil) Living: Rhizodeposition (organic C released by living roots) Other sources ( << %) Algae CaCO 3 Organic C of some rocks (shist) 6 7 Functions of root C in the rhizosphere Modification of soil chemistry ph and redox Organic acids composition Chelating substances for nutrient solubilizaiton Detoxication of Al 3+ and Fe 3+ (at low ph) Symbiosis with soil microbes fixing bacteria: Symbiotic: Rhizobia, Frankia,... Associated: Klebsiella,... Free-living: Azospirillum,... Mycorrhiza fungi Rhizosphere microorganisms Plant growth promoting bacteria Substrate and energy for symbiosis Defense against pathogens (allelopathics) Improving of soil structure Lubricator to decrease soil impendance... Trade: C for Plants provide C as energy for Rhizobia and Frankia to fix atmospheric Associative bacteria to fix atmospheric Mycorrhizal fungi to acquire and P from soil Rhizospheric bacteria to accelerate SOM mineralization for min release C costs of aquisition 9

3 Trade: C for Symbiotic fixation g ~.-4 g C Warembourg & Roumet 989 g ~ 6 g C Mol ~ 7 Mol C Vance & Heichel 99 Legumes: fixation and shoot dry matter kg / Mg DM g DM for g g C for g Trade: C for Plants provide C as energy for Rhizobia and Frankia to fix atmospheric Associative bacteria to fix atmospheric Mycorrhizal fungi to acquire and P from soil Rhizospheric bacteria to accelerate SOM mineralization for min release kg / Mg DM Herridge et al., Plant & Soil 8 Mycorrhiza of young pine Trade: C for Plants provide C as energy for Rhizobia and Frankia to fix atmospheric Associative bacteria to fix atmospheric Mycorrhizal fungi Rhizospheric bacteria to acquire and P from soil to accelerate SOM mineralization for min release C and cycles in the rhizosphere Smith & Read 3 4

4 Rhizosphere: Elevated CO Opposite directions of C and fluxes Labeling: Approach to study processes under steady state C release uptake C and fluxes in opposite directions Yaalon C input and turnover of organics in the rhizosphere 3CO 4CO Pulse labeling Limitations for microorganisms: in root-free soil: available C in rhizosphere: available Pulse addition of a tracer (3C, 4C,, ) Chasing of the tracer in various pools Parameters Trade C for Time lag between assimilation and any flux C and flow rates through any pools Residence time in pools Dynamics of C,, in individual pools: turnover times flux rates modelling Continuous input = continuous decomposition 3C 4C C/ known C input sensitivity C budget, high resolution & 6 Bangor, Wales, UK 9 7 Drought effects on C fluxes in the rhizosphere microorganisms of spruce Foto: S Heinrich Fichtelgebirge 9

5 Budget of assimilated C for some grasses and crops in % of total assimilated C Above ground: Shoots % Shoot respiration 3% Below ground: Roots 3% Root respiration 3 6% Soil organic matter 3% Microorganisms % Rhizodeposition % Available substrate for microorganisms! Kuzyakov & Domanski JPSS 3 Budget of assimilated C for trees in % of total assimilated C Time scale of the links between above and below? Janssens et al. Forest Ecol & Management 4 C C/ CO Photosynthesis is the main source of available substrates in soil Time lag vs. height and age of plants Species savanna Fagus sylatica Picea abies Picea abies Liquidambar styraciflua Populus eumericana Populus tremuloides Picea mariana Loblolly pine Pinus sylvestris Picea abies Pinus taeda Mixed diverse Mixed coniferous Pseudotsuga menziesii Pseudotsuga menziesii Pinus ponderosa Juniperus occidentalis Pinus taeda Mixed broadleaf decid. Mixed temperate Picea abies Fagus sylatica Time-lag d.; ;9 3; Height, m , Average age, yr ,, 68 Reference Baldocchi et al., 6 Moyano et al., 8 Ekblad et al., 4 Liu et al., 6 Horwath et al., 994 Mikan et al., Carbone et al., 7 Johnsen et al. 7 B.Singh et al., 3 Olsson et al., Andrews et al., 999 Keel et al., 6 Ekblad & Hogberg, Bowling et al., Mortazavi et al., Steinmann et al., 4 Ekblad et al., 4 Knohl et al., Time lag (hours) Very short link between aboveand belowground Localization of C input Time lag (days) 6 3 Grasses Herbs ~ hours DAS, d R =.3 R =.48 Time lag between photosynthesis and soil CO for trees and grasses depending on age Trees ~ 4 days R =.7 R =. TSA of CO Labeling Interruption 3C natural Age, yr Kuzyakov & Gavrichkova Global Change Biology 6

6 Autoradiogramm Ryegrass -% of total assimilated C Maize Elevated CO 6 hours after assimilation 4C Localization of root exudates = -% of netassimilated C of - C availability - microbial activity 7 8 Maize Elevated CO Life time of Relative 4C activity Localization of root exudates Time after 4C labeling Life time of hotspots? 6 hours days Changes of hotspots on Lolium roots after days 4C labeling: 6 h, d, d. What are these? 9 Pausch & Kuzyakov JPSS 3

7 Soil volume Microbial in soil: Rhizosphere Detritusphere Drilosphere in soil are small soil volumes with much higher process rates and intensive interactions compared to the average soil conditions Dead soil Mean Relat. volume Process rate Dead soil Process rate (h - ) Rich in: carbon, energy, and nutrients compared to the surrounding soil prefered habitat for microorganisms 3 Group Bacteria Fungi Protozoa Ammonifiers Denitrifiers Organism abundances in the rhizosphere Rhizosphere (R) Properties of hotspots CFU g - Activity of microorganisms Rates of SOM decomposition utrient mobilization Rouatt et al. 96, Kennedy 996 Soil (S) R/S 4 6 Rhizosphere effect Carex riparia - root cap Magnification 63 Fluorescens staining green: living bacteria red: dead bacteria Photo: E. Jüschke 3 µgco-c*g - *h Respiration and growth rates of microorganisms rhizosphere soil root free soil h 8 Higher input + higher mineralization faster turnover priming effects nutrient mobilization µ (h - ) =.38±. µg CO-C*g - * h - µ =.3±. Microorganisms in the rhizosphere specific growth rates increase for > %, shift to r strategists Mineralization potential K max >. times µg C glucose S O M -d e riv e d C effect O e fflu (kg x C (k ha g C - d h - a ) - d - ) effects: changes of SOM decomposition by addition of available substrates effects in rooted soil Faster turnover of soil C in rooted soil Lolium Wheat Maize Lettuce plant age (days) -3 re ta rd a tio n a c c e le ra tio n Additional nutrient mobilization Release of by microbes (for plants) Blagodatskaya et al. 8 Applied Soil Ecology 33 Kuzyakov JPSS 34

8 Elevated CO Chain of. Release of C substrate processes:. Triggering?. Competition for min: Live cycle 3- days MO shortterm winners MO Microorganisms slow SOM P Elevated CO 4. mineralization from SOM C Soil: Gleyic Cambisol 9% sand, 69% silt, % clay; ph ppm CO canola, wheat - MO short-term winners, but... - Plants long-term winners SOM MO FACE in Hohenheim 3. Microbial activation () longterm winners 3- months Plants slow fast CO = -8. δ3c CO Elevated CO, (+ ppm CO) δ3cco = -. = -8. min Importance of rhizosphere hotspots and priming effects in future? 3 MiniFACE Hohenheim Prof. A. Fangmeier 37 Fotos: S. Marhan Elevated CO Elevated CO C and turnover under elevated CO Microbail growth rates C and turnover under elevated CO Ambient CO Control δ3c 3 FACE experiments o changes of pools: SOM fractions microbial biomass FACE CO plant Changes of microbial activity: Growth rates Enzyme activities: β-glucosidase, Acceleration of element cycles Chitinase Amb 4 Elev - - Activity (nmol g h ) Higher C input by plants in the soil Activation of microbial biomass Faster C and turnover Higher nutrient mobilization Biosphere +4/+8 ppm CO poplar Braunschweig + ppm CO sugar beet, wheat Aggregate classes Chitinase, Sulphatase, Phosphotase Elevated CO leads to: Hohenheim + ppm CO canola, wheat bulk Dorodnikov et al. 7 Soil Biology Biochemistry > mm.-mm <.mm 9 Global Change Biology 38 39

9 Specific growth rate (h - ).4.3 R =.76 Braunschweig, Beta vulgaris. Braunschweig, Triticum aestivum Hohenheim, Brassica napus Biosphere-, Populus deltoides Atmospheric CO (ppm).4 Rhizosphere hotspots and priming will be more important in future because of acceleration of biogeochemical cycles Ratio: µ elevated CO / µ ambient CO.. Microbial growth rates depending on CO concentration Brassica napus 4 ppm Rhizosphere soil Root free soil Triticum aestivum ppm Beta vulgaris ppm Elevated CO Populus deltoides 8 ppm Blagodatskaya et al. Global Change Biology Populus deltoides ppm 4 % Relative increase of fluxes & pools in soil: no changes of pools strong increase of fluxes De Graaff et al. 6 Global Change Biology Kuzyakov ature Climate Change 4 Microbial respiration C sequestration in soil C sequestration in soil after ( ), ( ), and ( ) months. Means for 6 plants expressed as % of ambient CO with no added nutrients -month harvest, added nutrients C sequestration in soil decreases Soil microbial respiration after months. Means for 6 species expressed as % of the ambient CO control with no added nutrients. no added nutrients; added nutrients 4 Conclusions C C/ P Release of C in soil by living roots: ecological importance for symbiosis with microbes Photosynthesis: is the main source of available substrates in soil links above ground and C turnover in soil affects belowground processes in short time trees: days grasses: hours initiation of hotspots : especially in the rhizosphere life time: few days increase of microbial activity acceleration of SOM turnover priming effect : mobilization of extra nutrients for plants Rhizodeposition is the most important process linking: above and belowground processes plants and soils roots and microorganisms nutrients and C Thanks! 43