Controls on the Stability of Soils
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1) The document presents a hypothesis that the stability of soil food webs and their functioning depends on two energy channels - a fast bacterial channel and a slow fungal channel. 2) Long-term intensive management is found to reduce plant diversity, fungal dominance, and soil organic matter. Higher fungal biomass is associated with increased nitrogen retention and microbial immobilization of nitrogen. 3) An experimental approach is proposed to examine how soil food webs and their functions respond to and recover from drought and flood disturbances, both individually and in sequence, to develop models predicting impacts of land use and climate change.
Controls on the Stability of Soils
- 1. Controls on the stability of soils and their functioning and under land use and climate change Richard D Bardgett Dave Johnson Tancredi Caruso Franciska De Vries Liz Baggs Mark Emmerson Project Partners: Peter de Ruiter (Amsterdam) and Kevin McCann (Guelph, Canada)
- 3. Hypothesis: soils ability to perform multiple functions under global change is controlled by the structure and asymmetry of the soil food web. (Moore and Hunt 1988, Rooney et al. 2006) Stability of soil food webs and their functioning depends on two distinct, but coupled energy channels The ‘fast’ bacterial channel which cycles nutrients rapidly, and recovers quickly from disturbances The ‘slow’ fungal channel which cycles nutrients slowly, and dampens responses to perturbations Intensive agriculture, disturbance, climate change
- 5. 0 0.02 0.04 0.06 0.08 0.1 Low Medium High F:BBiomass c a b 0 20000 40000 60000 80000 100000 120000 140000 Low Medium High TotalC(µgg-1 ) b a ab 0 5 10 15 20 25 Low Medium High Speciesrichness c a b Long-term intensive management of grasslands reduce plant diversity, fungal dominance and soil organic matter Species richness Fungal-bacteria ratio Soil carbon
- 6. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 0.05 0.1 0.15 15Nleached(kgha-1) F/B ratio Improved Unimproved Increased N retention with higher fungal biomass in extensive grasslands 0 1 2 3 4 5 6 7 0 2 4 6 8 10 Microbial15N(kgha-1) Fungal PLFA (nmol g-1) 15N leached reduced with higher F/B ratio Microbial immobilization of 15N increase with fungal biomass De Vries et al. (2012)
- 7. • N leaching and respiration more resistant to drought in grassland soil with fungal- based food web than arable soil with bacterial based food web • N and C losses mitigated by soil food web and fungal energy channel Microarthropod diversity F/B channel ratio Microbial diversity Respiration N2O production Total N leached R2 =0.30 R2 =0.26 R2 =0.03 R2 <0.01 0.03 -0.14 P = 0.04 -0.26 P =0.03 0.54P<0.001-0.40P<0.001 -0.07 One day after rewetting Response Time Disturbance Resilience: Magnitude and speed of return to initial state Resistance: Immediate response to disturbance
- 8. What controls the ability of soils and their functions to withstand, recover and potentially adapt to disturbance events in a rapidly changing world? H1: Intensive grassland management reduces the stability of food webs, decreasing their ability to resist and recover from extreme drought, resulting in oscillations in soil functioning and greater loss of C and nutrients from soil. H2: Effects of intensive management on the stability of soil food webs and their functioning are context dependent and vary spatially with vegetation and soil abiotic properties. H3: Negative effects of land use intensity on the stability of food webs and their functioning under drought are driven by changes in soil resource supply and physical disturbance, which destabilize the food web and its functioning under drought. H4: Changes in the stability of soil food webs and their functioning are driven by disruption of key components of the soil food web, especially mycorrhizal fungi and higher trophic levels, which couple bacterial and fungal energy channels and their complementary functions.
- 9. Combined theoretical-experimental approach at different scales: MODULE 1: Land use and soil food web stability at landscape scales: Acid grassland (James Hutton) Mesotrophic grassland (BBSRC BB/I009000/1) Calcareous grassland (NERC NE/J014729/1); Response Time Disturbance Paired intensive/extensive systems (n = 5 each site) with bacteria and fungal food webs • Food webs • Nutrient and C • Greenhouse gas
- 10. Combined theoretical-experimental approach at different scales: MODULE 2: Mechanisms underpinning stability to multiple disturbances Response Time Disturbance (a) Field manipulations food webs Nutrient addition/disturbance matrix Cole et al. (2004)
- 11. Combined theoretical-experimental approach at different scales: MODULE 2: Mechanisms underpinning stability to multiple disturbances (b) Experimental manipulation food webs Manipulation of top down (predation) and bottom up (resource supply) via soil animals and mycorrhizal fungi
- 12. Combined theoretical-experimental approach at different scales: MODULE 3/4: Development of a soil food web model ensemble to predict how land use/climate change impact soil functioning
- 13. Proof-of-concept experiment • How do soil food webs and their functioning respond to drought and flood? • Does exposure to one perturbation modify food web responses to a subsequent perturbation? • Use data to inform cutting- edge models of soil community dynamics
- 14. Experimental design Control Precipitation Time Experimental drought mean Current mean Drought Precipitation Time Current mean Experimental flood mean Flood Precipitation Time Current mean Experimental flood mean Flood Precipitation Time Experimental drought mean Current mean Drought Control
- 15. Trt3 1Week Drought 2 3 4 5 6 7 8 9 10 11 12 13 14 Sampling Point Time 0 Recovery Flood Recovery Control Flood Recovery Control Flood Recovery Drought Recovery Drought RecoveryControl Does previous drought affect response to flood? Does previous flood affect response to drought? How do food webs respond to flood vs. drought? (temporal aspect for modelling) Post perturbation 1 (1d) Post recovery 1 (32d) 2d 8d 16d Post perturbation 2 (1d) Post recovery 2 (32 d) 4d 2d 8d 16d4d 2d 8d 16d4d 14d 32d 14d 32dTrt1 Trt2 Trt4 Control Experimental design
- 16. Microbial responses to drought Bacteria Fungi De Vries et al., in prep
- 17. Theoretical food webs: response to perturbation Resistance = the maximum difference in the biomass of a species before and after a perturbation is applied Microarthropod diversity F/B channel ratio Microbial diversity Respiration N2O production Total N leached R2 =0.30 R2 =0.26 R2 =0.03 R2 <0.01 0.03 -0.14 P = 0.04 -0.26 P =0.03 0.54P<0.001-0.40P<0.001 -0.07 Relationships between food web parameters and ecosystem functions
- 18. What have we done so far: • A team of theoretical and empirical soil ecologists • Initiated proof-concept-study to inform models on response food webs and their functioning to multiple perturbations • Establish network of field sites for experimental studies to commence spring 2016