Hypotheses•Lower elevations have less biomass input compared to upper elevations. •Shrubs at lower elevations have higher amounts of Lignin and C:N ratios compared to higher elevations.

Soil SamplingStratified random sampling (three canopy and three Inter canopy areas(Fig.2))of soil in five plots up to 0-30cm (at 0-5, 5-10, 10-20 and 20-30 depth intervals(Fig.3)), at each elevation.

Litter TrappingLitter traps (Fig.4) are custom made for the three randomly chosen shrubs within each plot to cover the entire canopy. Litter is collected over a period of one year.

Soil FractionationSOC associated with silt and clay are higher in the degree of stabilization compared to SOC associated with CPOM and FPOM.

Percentages of these SOC will be used to determine its stability (labile or recalcitrant (Fig.5))

Laboratory IncubationsTemperature sensitivity of SOC decomposition is evaluated via exposure of the soils to a temperature gradient ((15, 20, 25, 30)oC) in controlled (constant soil moisture - 50% water holding capacity) laboratory incubations (Fig.6).

Methods

Litter Quantity and QualityCollected litter will be measured in terms of concentrations of,•biomass•total C •total N • lignin

CPOM

Recalcitrant SOC

Labile SOC

ClaySiltFPOM

Soil Sample

ShrubLitter trapsSoil sampling spot (canopy)Soil sampling spot (inter-space)

Fig.2 Soil sampling scheme

Fig.3 Soil core

Fig.6 Laboratory soil incubations

Fig.5 Schematic diagram of soil fractionation

Fig.4 Litter trap design

Soil organic carbon and its temperature sensitivity along an elevational gradient in a semi-arid ecosystem

Hasini Delvinne, Kevin Feris, Alejandro Flores, Shawn Benner, Marie-Anne de Graaff

Boise State University

Background: Semi-arid ecosystems are an important component of the global carbon (C) cycle as they store a significant amount of soil C due to large extents of land.

Rising temperatures may alter the amount of soil organic C (SOC) currently stored in these ecosystems.

A proper consensus has not yet emerged on the temperature sensitivity of SOC decomposition posing an uncertainty in predicting C cycle feedback to rising temperatures.

This study will provide improved insights to the sensitivity of SOC stores to global warming in semi arid ecosystems.

Objective: To elucidate how litter input affects soil structure and SOC quality along an elevational gradient in a semi-arid ecosystem and assess impacts of these characteristics on the temperature sensitivity of SOC decomposition.

Introduction

Acknowledgements

Fig XX

Study SiteStudy site: Reynolds Creek Experimental Watershed in the Owyhee Mountains of Southwestern Idaho (Fig.1).

Field sites : Flats, Nancy Gulch, Lower Sheep Creek , Reynolds Mountain (Table 1).

SiteDominant Vegetation

Elevation (m)

MAP (mm)

MAT (oC)

Flats

Artemisia tridentata subsp. wyomingensis

1180 240 10.22

Nancy Gulch

Artemisia tridentata subsp. wyomingensis

1417 280 8.86

Lower Sheep Creek

Artemisia arbuscula 1653 310 8.52

Reynolds Mountain

Artemisia tridentata subsp. vaseyana

2111 795 5.56

This research was supported by NSF RC CZO Cooperative Agreement #EAR 1331872 and USDA ARS. Advisors: Dr. Marie-Anne de Graaff, Dr. Kevin Feris, Dr. Alejandro Flores, Dr. Shawn Benner, all de Graaff lab members and especially Trevor Thornton, Billy Bringman, Megan Bijan and Rhet Stewart for their assistance in the field.

Question 1 Question 2 Question 3

How does the quantity and quality of SOC input change along an elevational gradient?

How does the physical distribution (silt, clay, coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM) of SOC change along an elevational gradient?

How do these changes affect soil carbon decomposition under different temperatures?

Table. 1 Field sites descriptions

Reynolds Mountain

Fig. 1 Field sites at Reynolds Creek

10m

10m

Flats

Nancy Gulch

Lower Sheep Creek

T2G

Hypotheses•More labile SOC incorporated into CPOM and FPOM fractions at upper elevations, and more recalcitrant SOC associated with silt and clay at lower elevations - less precipitation

Hypotheses•SOC pools at lower elevations: larger positive feedback to temperature rise (greater amount of CO2 emission) due to recalcitrant being more temperature sensitive than the labile SOC pools at upper elevations.