The seasonal pattern of N mineralization in the Bartlett

Experimental Forest

Caitlin HolmesMELNHE Shoestring

Arizona State University

Outline

Soil N mineralization research Known effects of nutrient additions Nutrient manipulations results My research Objective Methods Expected Results

Background• N mineralization: amount of organic N that is

transformed to plant usable NH4 and NO3

In the past, N mineralization has been tested at each site during the summer field season 21 days after nutrient manipulations.

Known Effects of Added Nutrients

• Net N mineralization:– Increased in N plots– Had no effect in P

plots– Decreased in N+P

plots in mineral soil only

Con N NP P0

1

2

3

4

5

6 Mineral

Net

N m

iner

aliz

ation

(mg/

g so

il/21

d) ab

a

b

c

Courtesy of Melany Fisk

Con N NP P0

50

100

150

200

250

300 Oe

Net

N m

iner

aliz

ation

(mg/

g so

il/21

d) a a

abb

Con N NP P0

1020304050607080 Oa

Net

N m

iner

aliz

ation

(mg/

g so

il/21

d) a

ab abb

Melany’s 2014 net N mineralization results

But what about before nutrient manipulations?

Seasonality of N mineralization

• Seasonal pattern of N mineralization (Ross et al., 2004)

• N mineralization in response to nutrients (Fisk and Fahey, 2001)

Is there a seasonal response of N mineralization to added N and P?

• Test N mineralization throughout the growing season to determine if there is a seasonal pattern

• Observe whether responses to N and P are the same throughout the growing season

Objective

Methods

• Collect samples from old stands: C7, C8, C9– Control, N, P, and N+P plots

• Composite Oe, Oa, and mineral soil horizons from each plot

• Test N mineralization:– Before fertilization– Twice after fertilization

• Incubations and extractions with KCl

Oe

Oa

Mineral

Expected Results

• N mineralization will respond to N and P additions in the same way throughout the growing season

• N mineralization will respond seasonally to treatments

Acknowledgements

Thank you to Melany Fisk and Shinjini Goswami for their ongoing assistance with my project.

An additional thanks to the Shoestring crew for their help in the field!

References• Fisk, M.C., and T.J. Fahey. 2001. Microbial biomass and nitrogen cycling

response to fertilization and litter removal in young northern hardwood forests. Biogeochemistry 53: 201-223.

• Ross, D.S., G.B. Lawrence, G. Fredriksen. 2004. Mineralization and nitrification patterns at eight northest USA forested research sites. Forest Ecology and Management 188: 317-335.