SRS 2017-034 - PowerPoint Presentation

Slide1

SRS 2017-034

ABSTRACTSoils are the largest terrestrial carbon sink, therefore increasing soil carbon stability has implications for atmospheric CO2 and climate change. Adding C to soils from plant residue could increase soil C, however increasing soil C pools requires understanding the response of soil microbes that have a major role in C transformations. In an attempt to understand the C pool stability in arid environments, we added extracts of native prickly pear (Opuntia spp.) as a carbon amendment to soils from two sites and determined CO2 flux and soil aggregate size as evidence of microbial impact on soil C. Extracts were added to both desert and agricultural soils to test for differences in C cycling between important Chihuahuan Desert soil types. Microbial activities were found to increase macroaggregates (>250 µm) from sieved microaggregate (<250 µm) soils indicating the use of added C as a binding agent by-product of microbial processes. To analyze microbial activity, CO2 flux was measured weekly from incubating soils. After two weeks, soils with the cactus amendment showed 57% and 144% greater CO2 flux than controls from agricultural and desert soils, respectively. The increase in desert flux suggests microbial processes are more C limited in these soils. Total CO2 flux was higher from agricultural soils, possibly due to relaxed water and nutrient limitations on microbes. These results suggest limited capacity for C storage in arid land soil in short-term experiments, but highlight important differences between soil types (C limitation differences) that could be important for long-term soil C storage.

METHODS AND MATERIALSSite Description:10 soil cores per site were collected in late JanuaryDesert soil: Box Canyon; 8 mi from NMIMT soil was relatively undisturbed desert soilsAgricultural soil: Private agricultural land; 2 mi from NMIMT with land use history of fertilization (urea) and flood-irrigationPretreatment:Both soil types were wet-sieved using a 2000 µm, 250 µm, and 53 µm sieve then oven-dried at 60oC for 24 hrsAggregate size-classes were weighed and recorded when dried Incubation:40 g of soil, ground to <250 µm, was combined with either 6.5 ml of water (control) or 5 ml of cactus extract (C addition) and 1.5 ml of water in specimen cupsSpecimen cups were then placed in jars with 40 ml of water and sealed tightlySoil Respiration:For one month, gas emissions were measured weekly and recorded using a Gasmet FTIR Gas AnalyzerMacroaggregate Formation:Following incubation, samples were wet-sieved as before and aggregate size-classes were determined and weighed

FURTHER RESEARCH

We aim to predict organic C flux in arid soils in response to climate change. Understanding will require new lines of research, including:

new field experiments focused on long-term, controlled manipulations of entire soil profilesidentification of the long-term drivers of microbial-cell and microbial-product decomposition

NEGATIVE FEEDBACK

POSITIVE FEEDBACK

Organic C

CO

2

O

rganic C

Soil Organic C

Increased microbial metabolism

Expressed by increased CO

2

flux

Soils are p

otential

C source

Unlikely terrestrial C storage

Microbial

waste (polysaccharides?) act to bind microaggregatesIncrease in macroaggregates Increase terrestrial C pool

Acknowledgments

Thank you to Dr. Thomas and Sandy Kieft for providing access to their agricultural land for soil core collection. Huge thanks to Dr. Duval for his continual support and expertise on soil science while conducting this project. I would also like to thank Natalie Herrera for her assistance sieving.

Addition

Released to Atmosphere

Stored in

Macroaggregates

Agricultural or Desert Soil

Figure 1

CO

2 flux plotted against 29 day incubation period with addition of organic carbon (Opuntia spp.). Flux decreased over time, most likely due to decreased labile organic carbon in the system. With standard deviation error bars.

Figure 2

Resampled effect size of C additions on Rh. Initial measurements had a 400% increase from control to addition for agricultural soil and a 175% increase for desert soils. Error bars = resampled 95% CI.

Figure 3

S

oils were sieved to less than 250 µm before being incubated. After incubation, the aggregate size-class for samples was measured.Microaggregates (< 250 µm) decreased in mass proportion while macroaggregates (> 250 µm) increased in mass fraction. Desert macroaggregates increased by 72% while Agricultural macroaggregates increased by 99%.

CHANGES IN SOIL ORGANIC MATTER CYCLING IN RESPONSE TO NATIVE

OPUNTIA

EXTRACT ADDITIONS

Faith

Simitz and Benjamin D. Duval

Department of Biology,

New Mexico Institute of Mining and

Technology, Socorro, New Mexico