Open Collections

Investigation of phosphorus acquisition strategies of ectomycorrhizal fungal communities along a podzolization gradient

University of British Columbia

The role of phosphorus (P) supply in the functioning of temperate forest ecosystems is often overlooked. Yet, as temperatures and carbon dioxide rise with climate change, alongside heightened inputs of nitrogen, soil nutrient imbalances are starting to become common, leading to increasing P limitation in temperate systems. Ectomycorrhizal (EM) fungi, which form a symbiosis with tree roots, facilitate the capture of organic P that is inaccessible to trees, through the use of exogenous enzymes (exoenzymes) and low-molecular-weight organic acids. By measuring the activity of the fungal exoenzymes across a natural P gradient on Vancouver Island, I was able to further our understanding of EM fungal P acquisition in P-limited temperate rainforests. I sampled EM root-tips on Pseudotsuga menziesii var. menziesii from 12 sites across the gradient, measuring the activity of six exoenzymes and the concentration of oxalate on 10-16 EM morphotype colonies per site. The fungal DNA was then Sanger sequenced and identified using an online database. I found a negative relationship between P-specific exoenzyme activities and soil inorganic P, consistent with the literature. A negative relationship was found when exoenzyme activity was regressed against foliar P, whereas a tight, positive relationship was found with foliar N:P. These data support the concept that (i) inorganic P availability influences exoenzymatic activity both directly in the soil, and indirectly through feedback from the tree, and (ii) the exoenzymatic activities of these specific fungal communities play a vital role in support of tree growth in these temperate rainforest ecosystems. In order to test for physiological plasticity of exoenzyme activity of these EM fungi, I conducted a greenhouse study. After transplantation into a sand : vermiculite growth medium, 12 colonized Tsuga heterophylla seedlings from P-limited soils on Vancouver Island received either an organic P or an inorganic P treatment. After six months, there were no differences in exoenzyme activity between treatments and, therefore, no evidence for phenotypic plasticity. By better understanding EM P acquisition mechanisms, we can potentially manage site productivity of temperate forests more strategically, which will maintain or even enhance forest revenue and carbon sequestration.

Text

2020-05-04

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/74276

Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/