Carbon Cycle. Impacts of Agriculture: Emphasis on changes in soil

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1 Carbon Cycle. Impacts of Agriculture: Emphasis on changes in soil Roser Matamala Biosciences Division, ANL, IL, USA Team: David Cook, Julie Jastrow, Zhaosheng Fan, Sarah O Brien, Students and Postdocs

2 Soil formation and loss Geological rates: soil formation: mm y -1 soil erosion: mm y -1 Forms 2-4 x faster than lost Conventional agriculture: lost at ~ 4 mm y -1 Lost x faster than forms Alastair Fitter, University of York

3 Global Carbon Cycle Rh Rh IPCC, 2014

4 Changes in land cover has caused biodiversity loss, changes in ecosystem structure and function, loss of stored C, fragmentation.. Percent soil C Soil depth (cm) ? 75 Ag. field Remnant

5 The possibilities

6 Midwest land transformation: a case study at Fermilab Fermilab site Prairie vegetation was adapted and maintained by fires, dry seasons and droughts. Most was converted to cropland, then some was restored to prairie Risser et al., (1981)

7 Midwest, U.S. Images from Bigstock web page

8 Grassland restoration process Crop land periodical burns Tallgrass prairie Study sites: Fermi prairie, Fermi ag. Sites Flux Restoration Date Age (y) Soil BD (g cm -3 ) Rest Rest Rest Rest Rest Rest Rest Rest Rest Ag. Corn/Soy Remnant? 0.88 i) corn/soybean rotation, conservation Mollisols: tillage produced under grassland cover, wind blown loess. High organic matter layer named Mollic epipedon derived from plant roots. ii) restored prairie, biennial burns Eddy Covariance method to measure net ecosystem exchange (NEE), meteorological and soil measurements

9 Ecosystem fluxes: Eddy Covariance Method Drawing by George Burba The principle for eddy flux measurement is to measure how many molecules are moving upward and downward over time, and how fast they travel, Mathematically such vertical flux can be represented as a covariance between measurements of vertical velocity, the upward and downward movements, and the concentration of the H 2 O and CO₂, Provides net ecosystem exchange of water, heat and CO₂ fluxes using the eddy flux theory where F ρ a w' s' Baldocchi,DD. Global Change Biol. (2003); Burba, G., (2013). Eddy Covariance Method for Scientific, Industrial, Agricultural, and Regulatory Applications. LI-COR Biosciences, Lincoln, USA.

10 Ecosystem Evapotranspiration = Evaporation + Transpiration Mw / Ma LE w' e' ET crop field a ET prairie P 8 Maize Soy Maize Soy Maize Soy Maize Daily ET (mm d -1 ) years Annual and growing season ET were the same for all vegetation, ET consumed about 62% of the available energy during the growing season and 48% after, Precipitation/ET ratios ranged for crops and for the prairie.

11 Ecosystem Net Carbon Exchange Fc w' c' 10 5 NEE crops zero NEE prairie Maize Soy Maize Soy Maize Soy Maize NEE (g C m -2 d -1 ) years Carbon losses are very high for crop fields, Maize has much higher summer NEE, Large differences in phenology.

12 Number of days when NEE is negative Average #Days with negative NEE Soybean Maize Prairie The C uptake period, phenology, is one of the most important factors in sustaining C gains

13 GPP and NEP was estimated from A Q Q K max Pg ro s s f T a f T s f VPD fp SWC ets T 0 R f SWC m NEE P gross R eco R eco ref E 0 R Maize-Soy Prairie P gross R eco P gross R eco 2006M S M S M S M Mean M 1444 ± ± 156 Mean S 1035 ± ± 150 GPP = P gross + R eco Mean M&S 1268 ± ± ± ± 69 GPP 2479 ± ± 90

14 Net Ecosystem Production for Prairie and Crops 400 Maize Soy Maize Soy Maize Soy Maize 200 NEP (g C m -2 y -1 ) NEP Prairie NEP crop Years Seven-Year Average NEP: crop ~ -59 ± 107 g C m -2 y -1 prairie ~ -307 ± 42 g C m -2 y -1

15 Chronosequence studies: What pools are changing? Sites Flux Restoration Date Age (y) Soil BD (g cm -3 ) Rest Rest Rest Rest Rest Rest Rest Rest Rest Ag. Corn/Soy Remnant >

16 SOC (g m -2 ) What pools are changing? O Brien et al., Global Change Biology 16: Prairie I Prarie II Prairie III Prairie IV Brome Chronosequence Average prairie NEP rates confirmed -307 by g repeated C m -2 y -1 sampling of same sites Time since planting (years) Wet mesic prairies: 43 g C m -2 y -1 Mesic prairies: 31 g C m -2 y -1 SOC accumulations represent 10% to 14% of NEP

17 Above- and Belowground Mass (g C m -2 ) What pools are changing? and time to reach 95% of remnant stocks g C m -2 (0-15 cm belowground) Restored prairie carbon accrual SOC = (1 e [ Age] ) Leaf & stem Roots = 0.67 (1 e [ Age] ) Micro = (1 e [ Age] ) Leaf & stem 13 y Time Since Restoration (y) Root 64 y Time (years) Maize- Soy g C m -2 y -1 Prairie NEP 59 ± ± 42 Net Above Litter Net SOC Accrual Soil 444 y Net Root Accrual Net Microbial Accrual Microbial 164 y = 100% 240 = 77% - 43 = 14% - 18 = 7% - 5 = 2% Matamala et al Ecol. Appl. 18:

18 Mechanisms of Soil Organic Matter Stabilization Biochemical Recalcitrance Chemical Stabilization How do you expect to live off this stuff? Fe Ca I can t get it off. You try! Blechh!!! Tastes bad!! We already are!!! Move over. I like it!! Brrrrr! It s too cold for me Help!! I can t swim Our residues get left in all the tight places Physical Protection There s gotta be a way inside. Yuck!! Sure is gritty. Hey! There s good stuff in there. Help!! I can t breathe. I m so lonely, I could shrivel up and Nothing in the pantry again, and I can t get to the store. Aargh!! I can t get enough energy to make my enzymes. Modified from Jastrow and Miller, 1998, In Soil Processes and the Carbon Cycle, CRC Press.

19 detrital C cycling Decomposing POM becomes encrusted with organomineral particles Microaggregates form & stabilize within macroaggregates Transformation of inputs and deposition of decomposer residues creates organomineral associations Silt-sized aggregates can similarly form within microaggregates Fractions recycle when higher order aggregates destabilize Microaggregates ~ m Particulate organic matter colonized by saprophytic fungi Silt-sized aggregates with microbially derived organomineral associations Plant and fungal debris Fungal or microbial metabolites Biochemically recalcitrant organic matter Clay microstructures Sensu Golchin et al. 1994, Aust. J. Soil Res. 32: Jastrow & Miller, 1998, In Soil Processes and the Carbon Cycle, CRC Press. Jastrow et al., 2007, Climatic Change 80:5-23.

20 Changes in aggregation and organic carbon in prairie soil 100 Changes in Aggregation and Organic Carbon in a Prairie Soil (From Jastrow, 1996, Soil Biol. Biochem. 28: ) 120 Aggregates >212 m (% total soil) Macroaggregates Y = 92.3( e X ) r 2 = 0.99 Carbon recovery slower than aggregation Organic C Y = 96.6( e X ) r 2 = Organic C (g kg -1 ) Virgin 20 Complete growing seasons since last cultivation Jastrow Soil Biol. Biochem. 28:

21 Soil aggregates and the buildup and stabilization of soil carbon Most C accrued in macroaggregates, especially microaggregates stabilized within macroaggregates Silt-C in microaggregates within macroaggregates contributed greatest amount of C to whole soil Yet silt-c pool reached steady state at only 59% of its amount in remnant prairie soil (concentrations increasing) Other C pools already near that of remnant or still increasing linearly g C kg -1 soil g C kg -1 soil POM Silt Clay Microaggregates-within- Silt macroaggregates Clay Macroaggregateprotected 0 POM Remnant Remnant Time since disturbance (y) O Brien, SL, and JD Jastrow Soil Biology and Biochemistry 61:1-13.

22 Phased multi-steady-state hypothesis for carbon accrual in SOM pools Change in realized inputs to a given SOM pool, e.g. Time for plant-derived inputs to be rendered small enough to be included in pool Change in deposition of microbial residues Transformations in SOM chemistry promote binding to mineral surfaces Rearrangement of mineral and organic structures and pore-filling Even if total C inputs to soil are constant, inputs to a particular SOM pool could vary due to factors controlling intra-soil C cycling and movement among different pools O Brien, SL, and JD Jastrow Soil Biology and Biochemistry 61:1-13.

23 Soil depth (cm) Soil drivers: rhizosphere and microbial development 120 Belowground Bulk density mass (gdw(g cmdw -3 ) m -2 ) MBC (mg C g -1 soil dw) EMH Biomass ( g cm -3 soil dry wt) Soil depth increments (cm) Remnant RP > 20 y-old RP < 20 y-old Ag. Field Remnant RP > 20-y-old RP < 20-y-old Ag. Field Soil depth (cm) Remnant RP > 20-y-old RP < 20-y-old Ag. Field Matamala et al and unpublished data

24 Are these universal mechanisms? Climate change effects. Six et al., Agronomie, 22:

25 Different capacities Six et al., Agronomie, 22:

26 Soil structure, C, and nutrients in tropical soils Fonte et al., Soil Biology & Biochemistry, 68:

27 Soil as an ecosystem service: 1) water and nutrients for plant growth = Primary Production 2) regulation of the water cycle, 3) carbon storage

28 Soil as an ecosystem service: 1) water and nutrients for plant growth = Primary Production 2) regulation of the water cycle, 3) carbon storage Climate change will affect these services, largest on: Food production, plants Hydrology & C-cycle