Dirt was one of my first friends. My earliest days were spent collecting worms from the backyard and trying to convince my parents I hadn’t done any dirt taste testing that day (I probably had, but for purely scientific reasons). I was fascinated by what seemed like an entirely different world in the soil of my parent’s garden. I could find all kinds of goodies from insects to plant roots.
At university I was introduced to the truly magical world in soil: microbes. Although not visible to the naked eye, the tiny worlds inhabited by fungi, bacteria, viruses, and other unbelievably small things, should not be overlooked. These tiny worlds are called the microbial community and they have important roles in New Zealand forests.
A good place to start thinking about microbial communities is our own bodies. Most people have heard of their gut microbiome. The microbes in our digestive system are important for our health from immune function to digestion (especially for dirt tasters). However, some microbes, such as the COVID-19 virus, can make us sick. Soil microbes in forests are not so different.
Forests are dependent on microbes that cycle nutrients, decompose waster, and aid plants in nutrient uptake. Like humans and the common cold, some soil microbes hurt their associated plants. An example of this is kauri dieback disease, a disease spread by a spore in the soil that attacks tree roots and trunks. This disease hinders the tree’s ability to uptake and transport nutrients, essentially starving and killing the tree. Kauri dieback is incurable and fatal for kauri.
Kauri dieback is named after the tree it infects, New Zealand’s mighty kauri tree. The Department of Conservation explains that kauri can grow up to 16 m in circumference and live over 2000 years. The legendary status of kauri is clear in the language used to describe them. The largest surviving kauri is called Tāne Mahuta, which means ‘lord of the forest’. If you were to visit Tāne Mahuta today, you would find boot cleaning stations, warning signs, and only be able to view the great tree from a platform. Moreso, entire trails have been shutdown to stop people from spreading soil around kauri. Why?
A soil microbe, Phytophthora agathidicida, travels under the name of kauri dieback. This microbe cannot be seen with the naked eye but has the power to kill tremendously large kauri trees. In humans, the heroic microbes of our immune system save us when nasty microbes make us sick. Are there unseen heroes hiding in the soil that can help kauri?
During a PhD project at Lincoln University, Dr. Alexa Byers studied soil microbial communities under kauri to find out. The goal was to identify microbes that suppress kauri dieback and can aid in kauri conservation.
The first step was to understand how microbial communities under kauri react to kauri dieback disease. Alexa infected kauri seedlings with kauri dieback and looked for changes in the soil microbial community. When humans are attacked by illness causing microbes, our immune system amps up to protect us. When soils were infected, Alexa found bacteria that were involved in disease suppression. This was a promising result suggesting that heroic soil microbes could build up their numbers to fight off kauri dieback.
Next, Alexa looked into how specific strains of bacteria from kauri soil impacted the development of kauri dieback. She identified Paraburkholderia and Penicillium microbes that inhibited the growth of kauri dieback in soils. Paraburkholderia are known to enhance plant growth and fix nitrogen. Penicillium are fungi that can kill or stop growth of other bacteria. We officially have some heroic contenders!
The battles between heroic microbes and kauri dieback in the soil could determine the fate of the kauri above them. Hopefully, researchers can find a way to rig microbial battles in favour of these unseen heroes. More research is needed to determine their true potential, but these soil microbes could be called to action in the near future.
The world under kauri is just one example of fascinating soil microbes. Soil microbes have been found to be key for carbon storage, impact the taste of tea, and reduce nitrogen runoff from agriculture, among many other amazing things. This is your reminder to appreciate the little things, even the things so little you cannot see them. Next time you play in a garden or walk through a forest, I hope you take a moment to think about all the tiny microbes working away in the soil to help (or hinder) plants and make the natural world work.
This article was prepared by Master of International Nature Conservation student Jodie Wiltse as part of the ECOL608 Research Methods in Ecology course.
Research Paper: Byers, A.K. (2021). The soil microbiota associated with New Zealand’s kauri (Agathis australis) forests under threat from dieback disease: A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University. Lincoln University. https://hdl.handle.net/10182/13887
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