Fertilizer-induced changes in soil nutrient supply, carbon storage and nutrient cycling

in immature pine and spruce forests

Melanie Jones2, Shannon Berch4, Rob Brockley4, Sue Grayston3 & Doug Maynard1,5

1University of Victoria

2University of British Columbia Okanagan Campus

3University of British Columbia Vancouver Campus

4Research Branch, BC Ministry of Forests and Range

5Canadian Forest Service

Dan Harrison1, Tristyn Hay2, Lori Phillips2, Roland Treu2, Val Ward2, Sophie Wertz3

Background on the Maximum Productivity Study

• Study established by Rob Brockley beginning in 1994 at representative 9-15 yr old pine and spruce stands in the SBS, ESSF and MS.

• Three treatments:

• Control: Not fertilized• Periodic: Fertilized every 6 years with 200

kg/ha N (+ P, K, S, Mg, B)

• Annual: Fertilized annually to maintain foliar N concentration at 1.3% (and other nutrients in balance with foliar N)

Sites

= PINE= SPRUCE

McKendrick Pass

Crow Creek

Crater Lake Lodi Lake

Tutu Creek

Hand Lake

Objectives of the soil study

• To determine the effect of long-term (12-14 yrs) on:

• nutrient supply rates in soil solution

• potential for leaching of N

• carbon storage in soil

• chemistry of the soil organic matter

• nutrient cycling by bacteria and fungi

• We wanted to determine whether long-term fertilization had any negative effects on nutrient cycling by soil microorganisms

Tree biomass responses by 2009

Spruce: 77 % increase with periodic fertilization

• 136 % increase with annual fertilization

Pine : 37 % increase with periodic fertilization

• 59 % increase with annual fertilization

-> How does this relate to N supply?

Supply rates of NH4+ + NO3

-

Control Periodic Annual Periodic AnnualControl

•N supply rate increases in the year of application (2008), with some carry-over to the next year.•Foliar N generally increased in year of application only

McKendrick - Pine

pH and Calcium

•Fertilization caused pH to drop if soil pH was originally < 4•At these low pH sites, both exchangeable Ca and foliar Ca decreased with fertilization

3

3.2

3.4

3.6

3.8

4

4.2

4.4

4.6

4.8

5

Control Periodic Annual

pH

a ab b

Spruce

Soil N Pools – increased in forest floor and mineral soil, relative to controls

McKendrick (Pine)

= Forest Floor

= 0-10cm

= 10-20cm

Control Periodic Annual

> 90% of N was retained on site= no evidence for major leaching or volatilization

Soil C Pools – increased in trees, forest floor and mineral soil, relative to controls

Crow (Spruce)

= Forest Floor

= 0-10cm

= 10-20cm

> 90% of N was retained on site= no evidence for major leaching or volatilization

Control Periodic Annual

= Tree

63

83 99

Why have soil C stocks increased?C inputs to soil: Roots and litter

• Root density of spruce and pine down to a depth of 10 cm was not affected by fertilization

• Fertilization increased coniferous and herbaceous litter inputs to the soil system

Litter inputs

0

500

1000

1500

2000

2500

3000

3500

4000

Control Periodic Annual

Lit

ter

Inp

uts

(k

g/h

a/y

r)

Lodi

Crow

McK

Cratera

a

ab

abbb

Soil Organic Matter (SOM)

• Soil organic matter chemistry may change with fertilization

• If so, the enzymes secreted by microbes must change in order for nutrient cycling to continue

• If this does not happen, we should be concerned that fertilization has a negative impact on SOM cycling.

Impact of fertilization on SOM cycling in forest soils

• Increased litter inputs resulted in concomitant increases in the amount of soil organic matter found in the soil system

SOM (%increase) Carbon (% increase)

Sites Treatment FH MS FH MS

Pine Periodic 5.4 6.5 5.5 14.3

Annual 19.6 37.9 18.0 54.0

Spruce Periodic 7.8 16.3 6.1 9.4

Annual 15.1 32.6 12.1 35.0

• Sugars, starches, proteins

• Cellulose, hemicellulose

• Lignin, waxes, phenols

• Humus

Increasing Recalcitrance

Impact of fertilization on SOM cycling in forest soils

0

200

400

600

Cellulose/Hemicellulose Lignin/humics

mg

/kg

dry

so

il

controlperiodicannual

Pine FH soil

Impact of fertilization on SOM cycling in forest soils

• The amount of cellulose/hemicellulose and lignin/humic fractions in the soil increased with increasing SOM

Impact of fertilization on SOM cycling in forest soils

• Enzymes involved in cellulose and hemicellulose degradation increased proportionally with those fractions

0

1000

2000

3000

4000

β-glucosidase Xylosidase Peroxidase

En

xym

e ac

tivi

ty (

nm

ol h

-1 g

-1 d

ry s

oil)

controlperiodicannual

Pine FH soil

Enzymes associated with lignin degradation increased proportionally at pine sites

Impact of fertilization on SOM cycling in forest soils

• Composition of the SOM in fertilized treatments becomes slightly enriched in recalcitrant lignin-humic fractions

Percent change in SOM composition

Sites Treatment Cellulose/hemicellulose fraction

Lignin-humic fraction

Pine Periodic -1.9 +0.9

Annual -6.4 +4.6

Spruce Periodic -5.6 +2.0

Annual -7.7 +1.7

Microorganisms involved in carbon and nutrient cycling

• Ectomycorrhizal fungi

• Secrete enzymes that solubilize nutrients in soil organic matter (SOM)

• Nitrifying bacteria

• Convert ammonium to nitrate

• Increase potential for leaching and volatilization as greenhouse gases

Ectomycorrhizal fungi

The ectomycorrhizal fungal species present on roots differed by fertilization treatment

This could explain the differences in enzyme activities

ControlPeriodicAnnual

Tutu Ck - pine

Nitrifying bacteria

• Nitrification was enhanced for up to 2 years after periodic fertilization, but generally not immediately after fertilization

•Fertilization changed the community structure of nitrifying bacteria

•Molecular data indicates that the nitrification at these sites is being carried out by Ammonium Oxidizing Bacteria, not Archaea, and by Nitrobacter-like Nitrite Oxidizing Bacteria.Wertz et al (in review)

Summary of effects of long-term fertilization on soils – a few worrying observations

• Reduced soil pH, and soil and foliar Ca at sites with pH < 4

• Reduced diversity of ectomycorrhizal fungi

• Higher rates of nitrification with periodic fertilization, increasing the potential for leaching or loss of N as greenhouse gases

But the story is mostly positive

• There is increased tree, soil and total ecosystem carbon storage, especially in recalcitrant forms – good for C sequestration

• Enzymes involved in cycling nutrients from litter responded appropriately to the changes in SOM chemistry

• The majority (>90%) of N inputs were retained on site, suggesting uptake by trees and microbes or binding to soil minerals, rather than loss by leaching or as greenhouse gases

Support Provided By:

•NSERC

•B.C. Ministry of Forests and Range

•Canadian Forest Service

•University of Victoria

•University of British Columbia

•Western Ag Innovations

•Dunkley Lumber