Pennsylvania is the fourth largest wine producer in the United States, according to the Pennsylvania Department of Agriculture. The industry supports nearly 11,000 jobs and directly contributes $1.77 billion to the state economy annually. In an effort to produce more and better grapes at a lower cost and with less environmental impact, vineyard growers have increasingly planted grass between rows of vines. These "groundcovers" root shallowly, but can benefit vineyard soils and reduce the need for herbicide applications.
Now, a team of plant scientists in Penn State's College of Agricultural Sciences has found that implementing this practice impacts far more than previously thought. It not only alters the biology and ecology at the surface, where the grasses are planted, but also alters the system far below the surface, the researchers reported in a new study published in Phytobiomes Journal.
The team compared how vineyards with and without groundcover in the vine row impacted the soil microbiome - the community of bacteria and fungi associated with soil - across a soil profile about three feet deep over two growing seasons. They concluded that grass groundcover changed the soil microbiome far beyond the depth of its own root system.
"The grass roots are primarily growing within the top six to 12 inches of soil, and the grape roots are going from the soil surface to a meter-plus deep," said Hayden Bock, assistant professor of landscape sustainability in the Department of Plant Science and co-lead author of the paper. "What is interesting is that at deeper soil depths, up to a meter deep, the community of microorganisms that were there responded to the grass roots growing far above them. What we do at one point of the soil can cascade to other deeper parts of the soil."
Bock explained that vineyard growers have traditionally grown grasses between their rows - up to about two to three feet from the planted vine row - as a way of suppressing weeds and providing a travel path for harvest and maintenance equipment.
The vine row has traditionally been left vegetation-free with herbicide to minimize competition between groundcovers and grapevines. But previous research site has shown that grapevines can successfully co-exist with groundcovers planted across the entire vineyard floor by deepening their root system. The deeper grapevine roots avoid the shallower grass roots and access deeper soils that usually have more available water and consistent supply of nutrients. It's also thought that deeper rooted grapevines may be more resistant to weather extremes, Bock said.
However, Bock said little is known about how the soil changes when groundcover is introduced, and how those changes might influence the vines.
This project took place in the research vineyard at Penn State's Russell E. Larson Agricultural Research Center at Rock Springs. The research vineyard and this experiment were initiated by co-author Michela Centinari, associate professor of viticulture. Bock began to examine the soils in this vineyard as an undergraduate student, working with co-lead author Suzanne Fleishman, who graduated with a doctorate in ecology from Penn State in 2022 and is now an assistant professor of root biology.
The team planted the first vines and groundcovers in 2016, giving them time to become established before sampling the soil at different depths during peak growth seasons in the summer of 2019 and again in the summer of 2020.
While bacterial and fungal diversity varied year-to-year, overall, the researchers found that vines with groundcover had a unique microbiome signature with the abundance of bacteria and fungi species shifting across the soil profile under groundcovers. Based on the life history of these microbes, Bock said that there is reason to suspect that these microbial changes could also change the health and functioning of vineyard soils.
More research is needed to understand how this shift translates to vine health, Bock cautioned, but he explained that this first step in understanding a change exists could eventually help vineyard growers more strategically care for their crops.
"In this study, we show the effects of groundcover extend below the surface rooting zone and may have widespread implications for below-ground ecological trajectories," he said. "Because vineyard soil microbes influence vine health, performance and can operate as a reservoir of microbes for above-ground tissues - the stems, leaves and grapes - adopting under-vine groundcovers may provide a biology-driven means for combining production goals with soil-health stewardship."
Bock said growers may spend extra effort getting groundcovers established in their vineyards, but the long-term payoff comes in less erosion, less weed management and improved nutrient management. Beyond vineyards, he said the same benefits of groundcovers could potentially be seen in other horticultural crops grown in Pennsylvania.
"The novelty of this research is that we don't often think about deep soil health, as far as the community of microorganisms and nutrients that are there, but many horticultural crops, especially grapes and apples, have very deep roots," he said. "So, thinking about deep soils are crucial to the long-term sustainability and management of these systems."
In addition to Bock, Centinari and Fleishman, co-authors include Terrence Bell, assistant professor of soil microbiology and ecology; David Eissenstat, professor of woody plant physiology; and William King, previously a researcher with Penn State who is now a lecturer in plant-microbe interactions at the University of Southampton in the U.K.
This work was supported by the U.S. Department of Agriculture's National Institute of Food and Agriculture.
