This past Memorial Day, I had the privilege of picking the brain of a local farmer from Warsaw NY about the world of agriculture. Warren Goodenow has been farming his entire life. Without any degree, you might think these hardworking folks are ill-informed, not knowing the underlying processes of the natural world; you couldn’t be more wrong. Like an ecologist, Warren sees the patterns in nature. Making a living from the land, he knows when to plant, when to harvest and what to do throughout the duration of the growing season. Crops need water, sunlight, and nutrients to grow, sounds simple enough, but climate change is altering these variables. He’s already witnessed 4 tornadoes and a handful of other extreme natural phenomena. With more random weather patterns, and a more challenging climate, Warren’s job is more difficult than ever.
The people of our nation, regardless of their ability to understand climate change need to eat. We depend on our crops to feed us, so the department of agriculture is constantly researching ways to maximize plant production. We aren’t the only ones trying the maximize the crop potential of our land either. All over the world, billions of dollars are being dumped into the agricultural sciences so we as a species can become more self-sustainable. A main factor in maximizing the potential of an agricultural field is water availability. Like us, the crops we eat require water.
If there’s too much of it, anoxic roots can’t function. Too little, the stomata close, and photosynthesis ceases. In a perfect world, it rains systematically over our crop lands at precisely the right time, maximizing NPP (net primary production). Obviously, this is not the case. We water our crops regularly, but this is becoming increasingly difficult and expensive. I mean to ensure our crops get watered, there are outlandish campaigns to implement water pipelines from the great lakes to the west coast! This would not be remotely considered if there was an adequate water supply nationwide. Sometimes even when there is enough water, plant can’t access this resource pool efficiently because of soil type, or when they are associated with a less functional soil community.
Some soils with a high sand ratio have excellent drainage and hold onto less water. Plants rooted in these soil types need to be watered more frequently. Constant watering washes away nutrients like soluble nitrogen fertilizers; products that are increasingly expensive to synthesize. To maximize water and nutrient acquisition, farmers are now looking for help from beneficial mycorrhizal fungi. By inoculating specific communities of mycorrhizal fungi to soils, many crops have increased their NPP, and require less watering and fertilizer.
Fungal hyphae are finer than plant roots by an order of magnitude. These fine networks can squeeze into tiny pockets of soils that are inaccessible to crops. Agricultural land with a dense fungal community help hold the soil together and limits the amount of erosion. We can utilize the ecosystem services fungi provide to maximize water and nutrient scavenging, and maintain the structural integrity of the soil, but we still fall short on being entirely sustainable. Like I said earlier, fertilizer production is an expensive, highly industrious process that isn’t very energy efficient. Another farming technique to cut back on applying synthetic fertilizer is the use of green manure crops.
Seeds of green manure crops are sowed when field become limited by nutrients. These plants grow and are not harvested as the field requires a growing season off. Insects lay their eggs in the vegetation where they hatch and break down the vegetation. The insects along with the decomposing vegetation increase crop yield/sustainability through the accumulation of soil nutrients, and the prevention of soil erosion and nutrient leaching. One of the most used green manure plants are in the broccoli family (Brassicaceae). Crops from the genus Brassica are widely used, non-mycorrhizal species that are often utilized as bio-fumigants. Although these plants reduce fungal pathogens, these same species compete with plants that require mycorrhizae by decreasing the viability of fungal spores. Although they enhance field nutrient load, these plants reduce the ecosystem services provided by beneficial mycorrhizal fungi. Many non-mycorrhizal plants reduce AMF diversity in present soils both passively, by not allocating photosynthate to the rhizosphere, and actively, by releasing noxious allelochemicals that target fungi. The most sustainable agricultural processes plant green manure plants that enhance soil diversity, not limit it.
Right now, you might be thinking that there is a disconnect here as this is not an agricultural blog. These interactions however are directly related to the forest floor. With 90% of terrestrial plants using mycorrhizal fungi, the hyphae of these organisms provide several ecosystem services that are vital to maintain in a warming world. Invasive non-mycorrhizal plants similar to Brassica green manures diminish the soil fungal community, thereby reducing the nutrient and water services they provide. This agriculture correlation is occurring on the forest floor in North America because of a relentless invasive species.
Garlic mustard (Alliaria petiolata) is a highly invasive species in North America that comes from a lineage of plants that do not require mycorrhizae for germination or nutrient acquisition. In turn, A. petiolata root exudates inhibit fungal spore germination by up to 57% and, as a result, the number of mycorrhizal soil propagules decrease when this plant is present. The lowered mycorrhizal potential in invaded soils gives A. petiolata a competitive edge against mycorrhizal dependent individuals by creating a fungal inhibitory zone.
Like Brassica green manures, non-mycorrhizal invasive plants reduce fungal communities most plants require to access water and nutrients. Maintaining soil diversity will help crops and forest species diversity persevere on a changing planet. Diverse soil communities have a higher degree of ecological functioning, as more soil water and nutrients make it into the plant, and becomes translated to plant production. We need to utilize these soil fungi to maintain the services they provide in both an agricultural and natural setting. We also need to learn more from farmers that have been working the land for their entire life.