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Transcript
2/18/2016 Background i) Cropping management Controls soil OM gain vs. loss mainly through: • Amount and quality of litter • Soil disturbance • Fertilization Management History, Soil Porosity, and Litter Quality Interact to Regulate Organic Matter Stabilization and Greenhouse Gas Emission Ehsan Toosi: Jing Yu: ii) Litter quality (i.e. crop residue) Affects decomposition, particularly at early stages Michigan State University Hubei University, China Andrey Guber: Michigan State University Timothy Doane: Mark Rivers: ii) How about Pore characteristics? University of California, Davis An important, but overlooked aspect in soil organic matter research The University of Chicago Terence Marsh: • Pore size distribution Michigan State University Alexandra Kravchenko: • Pores connectivity Michigan State University • Total porosity (%) • Pore shapes 500 µm Importance of pore characteristics is soil OM processes Pore characteristics specifically regulate decomposition of fresh OM (vs. native soil OM) (Juarez et al., 2013; Negassa et al., 2015) • Providing micro-habitats for microbes against predators • Spatial accessibility of microbes to substrate (OM) Decomposition • Transport of gases and solutes • Oxidation-reduction status Regulatory effect of pores characteristics on the soil matrix-pores interacting zone • Activity of fine roots and fungi Regulatory effect of pore characteristics ? Decomposition of fresh OM GHGs efflux Pore characteristics regulate the rate at which biotic and abiotic processes occur in the “hotspots” Priming effect Accelerated decomposition of native soil C following supply of fresh C Decomposition of soil native OM Materials & Methods The broad research question: How interactions of contrasting pore characteristics, crop residue quality, land management history, and soil moisture status regulate efflux of GHGs and C stability? Soil preparation Site and sampling 1-2 mm soil fraction was separated and used as i) Coarse fraction, and ii) To generate the Fine fraction • Kellogg Biological Station (Long Term Ecological Research Site) • Long term management (since 1989) • 11 land management systems Coarse (1-2 mm) SOM loss vs. gain GHGs emission Conventional Cover Crop ? ? Management Fertilization Cover Crop Cover Crop-N Conventional NPK fertilizer Vegetation Wheat N Decomposition of plant residue Clover Corn Rye Fine (0.05-0.1 mm) Belowground biodiversity Soybean Soil OM Wheat Crop residue quality Pore characteristics Soil moisture status Cropping management Corn Soybean Soil: fine-loamy, mixed, mesic Typic Hapludalf 1 2/18/2016 Materials & Methods Materials & Methods Plant materials: • 13C-labeled corn and Components of the experiment soybean Analyses Incubation experiment: • 110 days • 4 replicates - Residue quality: Soybean (C/N: 7.4) > Corn (C/N: 13) - Common crop residues across the Midwest Independ variable • Leaf disks were used as a source of plant residue Level Porosity 2 Substrate quality 2 Management history 2 Soil moisture status 2 i) Headspace gas analyses • 110 days • 11 sampling events • 13C-CO2 and GHGs (CO2, CH4, N2O) • 420 samples Treatment i) Large (1-2 mm) soil fraction ii) Small (0.05-0.1 mm) soil fractions Syringe tube i) Corn ii) Microbial community structure • Sampling events: day 7, 14, 24 • 16S-18SrRNA analysis ii) Soybean i) Cover cropping ii) Conventional cropping Leaf disk Soil (1 g) i) Field Capacity ii) Image analysis X-ray computed micro-tomography • Sampling events: day 7, 14, 24 • 3.2 µm resolution Teflon support ii) Capillary Break Point Argonne National Lab, IL 6.5 mm Large (1-2 mm) soil fraction Pore characteristics of the large and small soil fractions Connectivity of air-filled (large) pores mm cm3 cm-3 μm % 1.0–2.0 0.562 104 99 0.05–0.1 0.566 10 <1 960 µm Start day size 1-2 mm 2.E-03 size 0.05-0.1 mm 2.E-03 Water Soil Air 1.E-03 5.E-04 0.E+00 Leaf loss at day 24 (% of original) Pore medial axes voxels as a fraction of total image voxels Small (0.05-0.1 mm) soil fraction Abundance of pore sizes 3.E-03 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 10 100 ** 1 900 800 Primed C (Day 24) Large pores Small pores * ** 700 600 500 400 300 200 140 120 100 100 2 Large pores Small pores * 60 40 20 0 0 Corn ** 80 Soy -20 Corn Soy Corn -40 **: P≤0.01 Findings Findings Decomposition: Cumulative CO2 efflux during the incubation (110 d) 600 300 0 Soy *: P≤0.05 Corn 1200 * Capillary break point 1500 * 900 600 300 0 1200 * * 900 600 300 0 Soy Corn Soy Large pores Small pores * 6 5.5 5 Corn Corn Soy 6.5 Effect of soil moisture 6.5 Cover crop Conventional * 6 5.5 Log cumulative N2O (ug-N/Kg soil) 900 1500 6.5 Log cumulative N2O (ug-N/Kg soil) * Cumulative CO2 (ug C/g) * Field capacity Effect of management history Effect of pore characteristics Effect of soil moisture Cover crop Conventional Log cumulative N2O (ug-N /kg soil) Effect of management history Large pores Small pores 1500 Cumulative N2O efflux during the incubation (110 d) Cumulative CO2 (ug C/g) Effect of pore characteristics Cumulative CO2 (ug C/g) Small pores 1000 Equivalent pore size, mm 1200 Day 7 Decomposed C (Day 24) Large pores Soy 1 Start day Day 7 Loss of leaf (Day 24) Negassa et al., 2015 3.E-03 Soy leaf Corn leaf Primed C (ug-C/g) Total Average pore porosity diameter Image analysis – Enabled to visualize and quantify loss leaf Cumulative CO2 (ug C/g soil) Fraction size Findings Water Soil Air Field capacity Capillary break point * 6 5.5 5 5 Corn Soy Corn Soy *: P≤0.05 * (P≤0.1) 2 2/18/2016 Research highlights: Acknowledgement: 1- Combined application of labeled plant materials and X-ray µ tomography allowed us to quantify the rate of substrate and soil OM decomposition, under contrasting soil pore characteristics. Under the experimental conditions: 2- In soils with dominance of large pores the rate of leaf loss was greater, primarily due to better aeration. However, the loss of soil native C (primed C) was lower due to limited movement of substrate (decomposing leaf) to the ambient soil. 3- Contrary to CO2, emission of N2O tended to be greater from soils with abundance of the large pores. Questions: 3