Investigation of Plant Interactions Across Common Mycorrhizal Networks Using Rotated Cores

Summary

Most plants within communities likely are interconnected by arbuscular mycorrhizal (AM) fungi, but mediation of plant interactions by them has been investigated primarily by growing plants with versus without mycorrhizas. We present a method to manipulate common mycorrhizal networks among mycorrhizal plants to investigate their consequences for plant interactions.

Abstract

Arbuscular mycorrhizal (AM) fungi influence plant mineral nutrient uptake and growth, hence, they have the potential to influence plant interactions. The power of their influence is in extraradical mycelia that spread beyond nutrient depletion zones found near roots to ultimately interconnect individuals within a common mycorrhizal network (CMN). Most experiments, however, have investigated the role of AM fungi in plant interactions by growing plants with versus without mycorrhizal fungi, a method that fails to explicitly address the role of CMNs. Here, we propose a method that manipulates CMNs to investigate their role in plant interactions. Our method uses modified containers with conical bottoms with a nylon mesh and/or hydrophobic material covering slotted openings, ¹⁵N fertilizer, and a nutrient-poor interstitial sand. CMNs are left either intact between interacting individuals, severed by rotation of containers, or prevented from forming by a solid barrier. Our findings suggest that rotating containers is sufficient to disrupt CMNs and prevent their effects on plant interactions across CMNs. Our approach is advantageous because it mimics aspects of nature, such as seedlings tapping into already established CMNs and the use of a suite of AM fungi that may provide diverse benefits. Although our experiment is limited to investigating plants at the seedling stage, plant interactions across CMNs can be detected using our approach which therefore can be applied to investigate biological questions about the functioning of CMNs in ecosystems.

Introduction

Arbuscular mycorrhizal (AM) fungi assisted plants in the colonization of land 460 million years ago¹ and today, they are ubiquitous symbionts of most plants², providing them with vital mineral nutrients for growth. The thin, thread-like hyphae of AM fungi forage for mineral nutrients beyond nutrient depletion zones near roots, often encountering and colonizing root systems of neighboring plants in a “common mycorrhizal network” (CMN). Common mycorrhizal networks also may form when fungal germlings join established networks³, or when AM hyphae fuse (anastomose) with conspecific hyphae

Protocol

 1. Construction and assembly of rotatable cores

1. Modify commercial tubular seedling containers (subsequently called ‘containers’; Table of Materials) to have 19 mm wide x 48 cm length openings.
   1. Using a drill-press with a 19 mm hole saw without a central, pilot twist drill, cut two holes, one above the other, in the sides of a container (2.5 cm diameter x 12.1 cm length) so that the holes are about 1 cm apart. Hold the container against a fence on the drill press and have a stop with a short dowel that will fit inside the container to help hold it in place while drilling. Use a container with flexible plastic to prevent cracking....

Results

To determine how CMNs may influence plant performance through nutrient partitioning, we grew Andropogon gerardii Vitman, a dominant prairie grass, in a target plant experiment with 6 equally spaced neighbors and intact, severed, or no CMNs. We found that severing or preventing CMNs diminished targets’ aboveground dry weights (Figure 2), suggesting that intact CMNs promoted plant growth. Plants with severed CMNs and prevented CMNs responded notably si.......

Discussion

Our results affirm that our rotated core method can sharply focus on the role of CMNs in belowground plant interactions. There are several critical steps in the protocol, however, that if altered, have potential to influence the ability to detect CMN effects. It is critical to fill the interstitial area surrounding containers with a nutrient-poor medium. In our unsuccessful, rotated-core target plant experiment with guava tree seedlings, although there was a marked reduction of target growth in the presence of any number.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Commercial tubular seedlings container (called 'containers' in the manuscript)	Stuewe and Sons, Inc	Ray Leach Cone-tainer ™	RLC3U
Course glass beads	Industrial Supply, Inc.	12/20 sieve	Size #1
Course silica sand	Florida Silica Sand	6/20 50lb bags	None
Fine glass beads	Black Beauty	Black Beauty FINE Crushed Glass Abrasive (50 lbs)	BB-Glass-Fine
Hydrophobic membrane	Gore-tex	None	None
Large commercial tubular seedling containers	Stuewe and Sons, Inc.	Deepot ™	D16L
Medium silica sand	Florida Silica Sand	30/65 50 lb bags	None
Nylon mesh	Tube Lite Company, Inc.	Silk screen	LE7-380-34d PW YEL 60/62 SEFAR LE PECAP POLYESTER
Soil and foliar nutrient analysis facility	Kansas State University Soil Testing Lab	None	None
Stable isotope core facility	University of Miami	None	None