TREES INCREASE SOIL CARBON

STORAGE AND BACTERIA ABUNDANCE

BUT NOT ENZYME ACTIVITIES IN

AGROFORESTRY SYSTEMS IN

CENTRAL ALBERTA, CANADA

Scott Chang, Mark Baah-Acheamfour,

Sam Banerjee, Farrah R. Fatemi, Sang-

sun Lim, Qiting Chen, Cam Carlyle and

Edward Bork

The Global Challenge

• Global temperature increased 0.6 ±0.12 °C in the 20th century and is projected to increase by 1.5 – 5.8 °C by 2100 (IPCC 2007)

• Emissions of CO2: use of fossil fuels, clearing and burning of forests, expanding and intensification of agriculture (Fearnside 2000; Lal 2002)

• Globally, agriculture accounted for 25% of CO2, 50% of CH4, and 70% of N2O emissions (Hutchinson et al. 2007)

Variations of Northern

Hemisphere Surface

Temperature and CO2

(Marian Koshland

Science Museum)

Introduction

Mitigating Climate Change: Conservation Practices

• To reduce GHG emissions and fossil fuel usage

• To decrease disturbance to soil structure

–No till + crop residue retention, cover cropping

–Perennial pastures as part of a crop rotation

–Precision farming

–Agroforestry

(Stavi & Lal 2013)

Agroforestry

• woody perennials and agricultural crops and/or animals

• deliberately used on the same land management unit

• spatial arrangement or temporal sequence

• ecological and economical interactions

(Lundgren and Raintree 1982)

Agroforestry and C Sequestration

• Area under agroforestry ~1 billion ha (Nair et al. 2009; Zomer et

al. 2009)

• C sequestration potential (CSP) in agroforestry: 0.29 - 15.21 Mg ha–1 yr–1 aboveground, 30 -300 Mg C ha-1 up to 1-m depth in the soil

What Do We Know?

(Photos: Farrah Fatemi)

Agroforestry and C Sequestration

• SOC: labile pool (MRTs ~1–2 yr), a slow pool (~25 yr), and a recalcitrant pool (~100–1000 yr) (Torn et al. 2005)

• Protection of SOC by silt and clay particles (von Lutzow et al. 2007)

• C in soil aggregates has lower decomposition rates (Six et al. 2000)

• Agroforestry reduces soil erosion and frequency of disturbance, increases C stability and biodiversity

The Effectiveness for C Sequestration Depends on

• The type of agroforestry system implemented

• Climatic regime

• Soil type/fertility

• How wood/biomass is used

• Stage of agroforestry development

• Plant species composition

Carbon Sequestration and GHG Emissions in Three Agroforestry Systems

in Central Alberta

(Photos: Qiting Chen)

Research Objectives

1. To determine soil organic C storage and distribution with depth

2. To examine the stability of soil organic C, bacterial abundance, and enzyme activities

in shelterbelt, hedgerow and grazed woodland (vs. adjacent agricultural land-use) in central Alberta

The Hypotheses

Agroforestry systems (planted shelterbelts, natural hedgerows, and grazed forests)

1) increase soil C sequestration and soil C stability

2) increase bacterial abundance and enzyme activities

as compared with agricultural land-use

Experimental Design

Across central Alberta:

Cropland or grazed pasture

Research Sites

(Credit: S. Banerjee)

EdmontonCentral

South

North

Agroforestry System

Adjacent Cropland or Pasture

15-25 m long transect

Several

tree height

(>50 m) 1 composit sample fr 10 points (e.g., 0-10 cm)

The same pattern repeated

(Credit: S. Banerjee)

Site Sampling Design

(Photos: Qiting Chen)

Basic Properties of Soils in Agroforestry Systems (Baah-Acheamfour et al. 2014)

(P<0.10)

(mg kg-1) (mg kg-1)

(mg kg-1)(mg kg-1)

Soil Organic C in Bulk Soil and Particle Size Fractions: Agroforestry Systems

(Baah-Acheamfour et al. 2014)(P<0.10)

Soil Organic C in Bulk Soil and Particle Size Fractions: Forest vs Agriculture

(Baah-Acheamfour et al. 2014)(P<0.10)

Soil Organic C in the Medium Fraction

(Baah-Acheamfour et al. 2014)(P<0.10)

Soil Organic C Density with

Depth

(Lim et al. unpublished)

Soil Organic C Stock with Depth

(Lim et al. unpublished)

(Banerjee et al. under review)

Agroforestry and the Bacterial Community

(P<0.05)

Relative Abundance of the Major Bacterial Phyla and Dominant Classes of Proteobacteria

(Banerjee et al. under review)

Relative Abundance of the 15 Most Abundant Bacterial Genera

(Banerjee et al. under review)

Connectedness between Bacterial Community and Edaphic Factors

(Banerjee et al. under review)

Blue solid line - positive linear relationship Black dashed line - negative linear relationship Red line - non-linear relationships

Enzyme Activities (nmol g soil-1 hr-1)

(Fatemi et al. unpublished)

0-10 cm soilmid-July 2013

Non-metric Multi-dimensional Scaling

(Fatemi et al. unpublished)

Conclusions

• Tree-based components of agroforestry systems had more SOC than adjacent agricultural fields, in the bulk soil and, in most cases, in the size-fractions as well;

• Greater distribution of SOC in the fine fraction in “forest” than in “agriculture” soils indicates the greater SOC stability in the “forest” soil

Conclusions

• Land-use systems had strong effects on soil bacterial communities; soil pH and C contents were the major determinants of soil bacterial community abundance; however, soil enzymes involved in C mineralization tended to be greater in “forest” soils

• The higher bacterial abundance in forests maybe linked to enhanced soil C storage in agroforestry systems

Acknowledgements

• Yuanpei (Kean) Gao, Phil Auer, Cole McCormick, Gabriel Savaris Secco, ShujieRen, Xiaopeng Li, Jinhyeob Kwak, and others for assistance in the field and lab.

• Agriculture-Agri Food Canada and NSERC (Natural Science and Engineering Council of Canada) for funding

http://www.rr.ualberta.ca/en/Research/AGGP.aspx