Fertilizer-induced changes in soil nutrient supply, carbon storage and nutrient cycling in immature pine and spruce forests Melanie Jones 2, Shannon Berch 4, Rob Brockley 4, Sue Grayston 3 & Doug Maynard 1,5 1 University of Victoria 2 University of British Columbia Okanagan Campus 3 University of British Columbia Vancouver Campus 4 Research Branch, BC Ministry of Forests and Range 5 Canadian Forest Service Dan Harrison 1, Tristyn Hay 2, Lori Phillips 2, Roland Treu 2, Val Ward 2, Sophie Wertz 3

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 NH NO 3 - Control Periodic AnnualPeriodicAnnualControl 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 aabb Spruce

Soil N Pools – increased in forest floor and mineral soil, relative to controls McKendrick (Pine) = Forest Floor = 0-10cm = 10-20cm ControlPeriodicAnnual > 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 ControlPeriodic Annual = Tree

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

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) SitesTreatmentFHMSFHMS PinePeriodic Annual SprucePeriodic Annual

Sugars, starches, proteins Cellulose, hemicellulose Lignin, waxes, phenols Humus Increasing Recalcitrance Impact of fertilization on SOM cycling in forest soils

The amount of cellulose/hemicellul ose 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 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 SitesTreatmentCellulose/hemicellulose fraction Lignin-humic fraction PinePeriodic Annual SprucePeriodic Annual

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 Control Periodic Annual 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