PS 30-114 - Effect of Nitrogen Fertilizer on AM and EM Mycorrhizal Colonization for Different Temperate Forest Tree Species

Tuesday, August 16, 2022

5:00 PM – 6:30 PM EDT

Located in: ESA Exhibit Hall

Presenting Author(s)

ZS

Zachary Shortt

Undergraduate
Dartmouth College, United States

Coauthor(s)

AF

Amelia Fitch, MS

PhD candidate
Dartmouth College
Hanover, New Hampshire, United States
AV

Augustinius Vrattos

Dartmouth College, United States
SG

Sarah Goldsmith

Dartmouth College, United States
CH

Caitlin Hicks Pries

Assistant Professor
Dartmouth College
Hanover, New Hampshire, United States

Background/Question/Methods

Temperate forest soils are dominated by two main types of mycorrhizal fungi, arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF). These fungi form symbiotic relationships with trees and assist in nutrient acquisition and water uptake in exchange for photosynthate. AMF scavenge inorganic nitrogen (N) and phosphorus (P) from the soil while EMF is hypothesized to more directly mine N and P from organic matter. Some research has shown that increasing soil N availability decreases EMF root colonization, but does not change or even increases AMF colonization. Consequently, we hypothesized that adding nitrate and ammonia fertilizer to AMF and EMF-associated seedlings would lead to fewer colonized root tips in EMF, but not AMF, as plants may rely less on EMF nutrient foraging strategies with high soil nitrogen levels. To test these hypotheses, we grew eight species of trees, four AMF and four EMF-associated in a 13C-labeled CO2 atmosphere. The potting mix was 75% sand and 25% soil from an equally AMF-EMF-dominated forest plot. Seedlings received 15N-labeled NH4+-NO3- fertilizer (none, equivalent to estimated growing season N demand, and 2x that amount). Root colonization was estimated using the gridline (1cm) intersection procedure.

Results/Conclusions

Preliminary results show a negative relationship between fertilizer additions and mycorrhizal colonization for EMF. This result indicates that the addition of N to the soil reduces the plants’ need for EMF associations. Though this result is not significant, our dataset for EMF is not yet complete. We also found a negative relationship between plant biomass and colonization, which is surprising since decreased reliance on EMF for N uptake should have led to increased plant biomass. We plan to analyze plant 15N uptake in relation to biomass when these data are available in the near future, to more definitively investigate whether plants decrease EMF colonization if they take up more inorganic N. Our results for AMF colonization are pending, and we predict that there will be no relationship between AMF colonization and fertilizer.