Carbon Sequestration in Trees and Forests Guest Lecture FOR 414 World Forestry John S. King Associate Professor of Tree Physiology Department of Forestry and Environmental Resources North Carolina State University 9 February, 2010

Outline 1. What is forest carbon (C) sequestration? 2. How do we measure it? 3. What factors affect it? 4. Why should we care?

1. What is forest carbon (C) sequestration? • In simple terms, the gain of C by a plant or forest from the environment – The starting point is photosynthetic C fixation from the atmosphere of a single leaf or plant – In a general, and increasingly common sense, refers to the storage of C by entire forest ecosystems, including soils – Strongly affected by endogenous and exogenous factors

Photosynthetic C fixation • “Net photosynthesis” refers to the balance between the photochemical fixation of C from the air, and its loss due to respiration • Occurs as a series of very fast, light-driven chemical reactions in the leaves of green plants that remove inorganic C from the air – C forms the basis of almost all energy transduction reactions and molecular structures in plants and animals. Why?

Photosynthesis • The basic reaction

Light energy 6CO2 + 12H2O Î C6H12O6 + 6O2 + 6H2O Chloroplasts

Location of Ps

Raven et al. 2005

Raven et al. 2005

Respiration and metabolism determine the fate of acquired C within the plant

Kozlowski and Pallardy 1997

Structure of sugars builds structure!

Kozlowski and Pallardy 1997

Taiz and Zeiger 1991

C Allocation

The amount of biomass produced and its biochemical composition are strongly influenced by the quality of the environment

Chung and Barnes 1977

Why care about allocation?

Chapin et al. 2002

The Forest C Cycle

GPP = 4,124 g C m-2 y-1 NPP = 2,056 g C m-2 y-1 Rsa = 2,068 g C m-2 y-1 Rsh = 694 g C m-2 y-1

Kinerson et al. 1977

Soil C Formation

2. How do we measure C assimilation and sequestration? • The basis of most modern measurement methods is infrared gas analysis (IRGA) – CO2 absorbs light at infrared wavelengths – Spectroscopic instruments are used to measure the change in CO2 concentration (absorbance) in a stream of air from a chamber enclosing plant parts • Licor 6400 Portable Photosynthesis System is the gold standard of such instruments

CO2 Light Absorbance

Gas Exchange Systems

Field 1991

At the plant and stand level, C assimilation can be estimated by changes in mass (weight) over time – Does not allow us to understand photosynthetic C gain or loss via respiration, but does provide an index of how much biomass C is going into ecosystems • Sugars, starch, cellulose, lignin, hemicellulose, proteins, nutrients, phenolics, etc.

– This is called Net Primary Production (NPP)

At the ecosystem level, we can use IRGA combined with eddy flux – Rapid response IRGAs combined with 3D micromet equipment allow calculation of landatmosphere exchanges of C (and water, and energy) – Combined with studies of physiology, NPP and soils, allows us to understand how much C is being stored by ecosystems, where, and how it is affected by changing environmental conditions

3. What factors affect C assimilation and sequestration? •

Environment (exogenous factors) – Light • Plants need adequate light • Sensitive to competition – Temperature • Not too hot, not too cold! • Length of growing season – Soil Water, Humidity • Not too much, not too little! – Soil Texture and Nutrients • Good soils produce a lot of leaf area and good photosynthetic rates • Fine soils retain more soil C – Air Quality • Like us, plants need clean air! – Disturbance!

• Endogenous factors (within plant) – Genetics • • • •

Species Varieties within a species Life history (shade tolerance) Evergreen vs. deciduous (10 vs 20 µmol m-2 s-1)

– Hormones • Balance of auxins, cytokinins and gibberellins affect leaf area and canopy development

– Leaf area display and longevity (light absorption) • Essential to productivity • Influenced by light environment, genetics, air quality, and culture, pests and pathogens

– Leaf age • “Old” and immature leaves fix less C

Light and nutrients

Temperature

Water

Air Quality

Gupta et al. 1991

Leaf Age

Leaf Area

Disturbance

Recovery of soil C in the South

Richter and Markewitz 2001

4. Why should we care about C sequestration in forest trees?

NASA, ca. 1998

Forests in the global C cycle

Griffin and Seeman 1996

Terrestrial plant carbon Ecosystem

Area (%)

Trop. Wet Forest Trop. Dry Forest Temp. Forest Boreal Forest Trop. Savannah. Temp. Steppe Desert Tundra Wetland Cultivated Total

7.2 5.3 6.3 10.3 16.9 10.4 12.5 7.5 2.0 10.9

C in Plants NPP (Pg) (Pg/yr) 156.0 49.7 73.3 143.0 48.8 43.8 5.9 9.0 7.8 21.5 558.8

8.3 4.8 6.0 6.4 11.1 4.9 1.4 1.4 3.8 12.1 60.2

NPP C in Soil (g/m2/yr) (Pg) 800 620 650 430 450 320 80 130 1300 760

255 59 142 179 56 173 101 173 137 178 1456

From Houghton and Skole 1990, Schlesinger 1977

The atmosphere is changing – Affects climate – Affects ecosystems

IPCC 2001

Things are changing very rapidly!

Scripps CO2 Program

Plants respond to changes in environment through physiology and growth (direct and indirect effects)

JCO2 = -DCO2(∂C/∂x)

Taiz and Zeiger 1991

Earth’s Temperature

Figure 3.1. Annual anomalies of global land-surface air temperature (°C), 1850 to 2005, relative to the 1961 to 1990 mean for CRUTEM3 updated from Brohan et al. (2006). The smooth curves show decadal variations (see Appendix 3.A). The black curve from CRUTEM3 is compared with those from NCDC (Smith and Reynolds, 2005; blue), GISS (Hansen et al., 2001; red) and Lugina et al. (2005; green).

IPCC, 2007

Tropospheric O3

Shriner and Karnosky 2003

The Aspen FACE Project

Harvests

Aspen FACE litter studies

Full range of biochemical analyses Field and laboratory incubations Analysis of decomposition and ecosystem-level cycling of biochemical constituents

Lab incubations

NPP response to eCO2 and eO3

Treatments: 1 = Control; 2 = +CO2; 3 = +O3; 4 = +CO2,+O3

King et al. 2005

Fine root biochemistry

Chapman et al., 2005

Leaf litter biochemistry Constituent (mg g-1) CO2 Treatment

Soluble sugars

Lipids

Tannins

Phenolics

Hemicelluose

Lignin

N

C

Ambient

15.4 ± 1.8a

56.5 ± 2.4a

18.5±1.0a

16.4±0.5a

194.6±11.0a

203.9±4.6a

11.1±0.0a

500.7±15.0a

Elevated

22.8±4.6a

59.8±4.1a

15.5±2.2a

15.9±0.8a

211.0±3.0a

200.7±13.4a

9.5±0.2b

489.2±24.0a

Liu et al. 2009

Fine root decomposition

Chapman et al. 2005

Leaf litter decomposition

Liu et al. 2009

However, microbial Rs is proportional to litter inputs

Liu et al.2009

Altered inputs will affect SOC over time

Liu et al. 2009

The major effect of atmospheric change on forest C cycling is NPP-driven litter inputs!

Liu et al. 2005

Closing remarks • Inorganic C (CO2) is the substrate for photosynthesis, forming the basis for energy flow in all ecosystems • Human activities are drastically affecting the amount of CO2 (and other greenhouse gases) in the atmosphere • It is highly likely that this is causing radiative forcing (warming) of the climate system

Closing remarks • Plants will respond to the changing environment through both direct and indirect effects • It is particularly important that we encourage widespread forest management for C sequestration – This will automatically provide many other ecosystem services

• To do this, we need to maximize productivity by limiting negative environmental factors (e.g. O3), and utilizing proactive, sophisticated management approaches

Closing remarks • Examples of this might include: – Use of drought tolerant genotypes in drought prone areas – Plant species tolerant of flooding in areas predicted to encounter sea-level rise – Reforest marginal lands to bioenergy or other forest plantations/ecosystems – Incorporate trees into all development projects, for C sequestration and efficiency in water and energy use