New Jackson lab manuscript on plant-associated soil microbes

The Randy Jackson lab has released a new manuscript titled “Bioenergy cropping systems that incorporate native grasses stimulate growth of plant-associated soil microbes in the absence of nitrogen fertilization”.


The choice of crops and their management can strongly influence soil microbial communities and their processes. We used lipid biomarker profiling to characterize how soil microbial composition of five potential bioenergy cropping systems diverged from a common baseline five years after they were established. The cropping systems we studied included an annual system (continuous no-till corn) and four perennial crops (switchgrass, miscanthus, hybrid poplar, and restored prairie). Partial- and no-stover removal were compared for the corn system, while N-additions were compared to unfertilized plots for the perennial cropping systems. Arbuscular mycorrhizal fungi (AMF) and Gram-negative biomass was higher in unfertilized perennial grass systems, especially in switchgrass and prairie. Gram-positive bacterial biomass decreased in all systems relative to baseline values in surface soils (0–10 cm), but not subsurface soils (10–25 cm). Overall microbial composition was similar between the two soil depths. Our findings demonstrate the capacity of unfertilized perennial cropping systems to recreate microbial composition found in undisturbed soil environments and indicate how strongly agroecosystem management decisions such as N addition and plant community composition can influence soil microbial assemblages.

You can read the manuscript here (PDF).

Study Suggests Perennial Crop Yields Can Compete with Corn Stover

A six-year Great Lakes Bioenergy Research Center (GLBRC) study on the viability of different bioenergy feedstocks recently demonstrated that perennial cropping systems such as switchgrass, giant miscanthus, poplar, native grasses, and prairie can yield as much biomass as corn stover.

The study is significant for beginning to address one of the biofuel industry’s biggest questions: can environmentally beneficial crops produce enough biomass to make their conversion to ethanol efficient and economical?

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“Second generation” Feedstocks Reduce Greehouse Gas Emissions

Left photo by James Tesmer, Right photo by Gregg Sanford.

Left photo by Andrew Dean, Right photo by Gregg Sanford.

Scientists at the University of Wisconsin–Madison and Michigan State University (MSU) report today that emissions of the potent greenhouse gas nitrous oxide (N2O) can be reduced significantly by replacing annual biofuels feedstocks, such as corn, with second-generation, perennial feedstocks such as switchgrass.

“If we are going to add second-generation biofuel crops to the landscape, we need a better sense of how they’ll impact ecosystem processes such as greenhouse gas emissions,” says Gary Oates, research scientist in the Great Lakes Bioenergy Research Center (GLBRC) Sustainability group and the paper’s lead author.

The study, published in the journal Global Change Biology–Bioenergy, compares eight different biofuel cropping systems planted at both UW–Madison’s Arlington Agricultural Research Station and MSU’s Kellogg Biological Research Station.

So-called “first-generation” biofuel crops in the study include corn, soybean, and canola, which need to be replanted each year. Second-generation crops include switchgrass, miscanthus, poplar, a mixture of native grasses, and a prairie mix. These perennial crops require an “establishment phase” after planting, a few years during which they settle into a “production phase.”

“We understand annual systems like corn really well but, up till now, little research has been done on perennial N2O emissions during that establishment phase, when farmland has just been converted to a perennial system,” says Oates.

Emissions data collected during the first three years of the long-term experiment indicate that cumulative N2O emissions from fertilized second-generation cropping systems were 57% lower than emissions from first-generation systems. In addition, cumulative N2O emissions from unfertilized second-generation cropping systems were 85% lower compared to first-generation systems.

If second-generation biofuel crops can meet productivity needs with fewer fertilizer inputs, the study suggests, they have the potential to dramatically reduce N2O emissions compared to the first–generation crops used for almost all of today’s biofuel production.

But the researchers also conclude that the relationship between N2O flux and environmental conditions is not generalizable across numerous and varied cropping systems, indicating that the computer models currently used to predict N2O emissions, especially for perennials, need improvement.

“We’ve definitely gained a better understanding of biofuel cropping systems, but the underlying mechanisms driving N2O production remain elusive,” says Randy Jackson, co-leader of GLBRC’s Sustainability research group. “The amounts of water, nitrogen, and carbon in the soil are clearly important but we have more work to do.”

The first phase of the analysis used data collected between 2009 and 2011. Researchers are now in the process of analyzing an additional three years of data collected during the production phase of the perennial systems. A primary focus of the current work is gaining a better understanding of the genetic make-up of the soil’s microbial community and how knowledge of that genetic make-up might be used to predict N2O emissions for biofuel cropping systems.

Switchgrass Trials Show Promise For Alternative Biofuels

 The switchgrass nitrogen fertility trial at Kellogg Biological Research Center in Hickory Corners, MI (left), and GLBRC researcher Laura Smith collecting switchgrass tissue samples at Chiwaukee Prairie in Kenosha City, WI (right). Photos by Laura and Matt Smith.

By now most of us are accustomed to filling our cars with fuels that are part ethanol, and we know that corn is not only in our tortillas but also in our gas tanks. Great Lakes Bioenergy Research Center (GLBRC) researchers, however, are moving beyond corn and other first-generation biofuel feedstocks in an attempt to fill our tanks with environmentally sustainable biofuels.

Randy Jackson, GLBRC’s sustainability research group co-leader, says “the focus of agricultural biofuel research has changed recently from ‘agronomic intensification’ to ‘ecological intensification.’ In other words, it’s not just about how much money you can make growing a crop anymore…it’s about how we can grow what we need and nurture the land at the same time.”

“One way to move towards a system of ecological intensification,” Jackson continues, “is to move from fields of corn, which need to be planted annually and require lots of fertilizer, to mixed varieties of perennial grasses such as switchgrass.”

Perennial grasses dramatically reduce soil erosion, provide protective cover and food for wildlife, encourage bird populations and insect pollination, foster methane-consuming microbes, and suppress the invasion of agricultural pests. Perennial grasses also use nitrogen more efficiently than annual monocultures such as corn, which could mean less nitrogen fertilizer in our fields.

Reducing the use of nitrogen fertilizer, in addition to saving farmers time and money, is a big plus for the environment. Most crops are unable to retain the majority of applied nitrogen. Some is lost in run-off where it contributes to nitrate contamination of ground water, streams, and rivers. At the same time, a significant amount of excess nitrogen ends up in the soil, where microbes convert it to the greenhouse gas (GHG) nitrous oxide (N2O).

N2O is a highly potent greenhouse gas — the atmospheric-warming impact of a single pound of N2O is more than 300 times that of a pound of carbon dioxide. In addition, N2O is the most significant ozone-depleting chemical resulting from human activity. And currently, N2O accounts for about 6% of GHG emissions resulting from human activities, with 75% of those emissions coming from the agricultural use of synthetic fertilizers.

Although the ideal field of biofuel feedstock, from an ecological standpoint, would contain a variety of perennial grasses, studying switchgrass, a native prairie grass, is an important step toward realizing that ideal.

Laura Smith

“Switchgrass is a promising biofuel feedstock and represents a kind of halfway point between agronomic intensification and ecological intensification,” says GLBRC doctoral researcher David Duncan, “It has the downside of being a single species, but it’s perennial so you don’t have to replant it every year. And it doesn’t require as many inputs, such as nitrogen, as a crop like corn.”

Switchgrass also has the advantages of being fast-growing, productive, and able to grow on marginal land unsuited for food crops.

But it’s a major transition for farmers accustomed to tending monoculture crops such as corn to add perennial cropping systems to their crop selections. In a corn field, every plant is genetically identical and the varieties have become so predictable that farmers know, almost to the day, how long they will take to mature.

In a switchgrass field, on the other hand, you find many genetic differences within a single variety, and the time required for crop maturation varies significantly depending on weather, light conditions, moisture, and nutrient availability.

Moving biofuel cropping systems toward long-term sustainability and profitability will thus require a better understanding of how perennial grasses develop under differing conditions. GLBRC doctoral researcher Laura Smith, for example, is trying to determine the relationship between biomass productivity and nitrogen uptake in switchgrass fields.

“We are trying to understand the ways that perennial grasses such as switchgrass use nitrogen so we can reduce the use of nitrogen fertilizer and still maximize biomass harvest,” Smith explains. “A significant challenge to the use of these grasses as biofuel feedstocks is the inefficiency of harvest — currently, if we wait until fall to harvest, we are only able to collect about 60% of harvestable biomass from switchgrass plants and we need to figure out how to improve on that.”

One important factor limiting maximum biomass harvest is harvest timing. Plants typically reach peak biomass in August. Yet the long-term health of perennial plant systems depends on their having the chance to senesce, or let the plant system’s nutrients return to the roots, before harvest.

“The time of peak biomass yield is also the time when plants have the highest nutrient content.” Smith says.  “If that’s when you harvest, you’re pulling huge amounts of nutrients off the field. You are losing a whole lot of nitrogen and that means you’ll have to use more fertilizer for next year’s crop.”

But waiting for senescence significantly compromises biomass yield, as plants recycle carbohydrates and leaf litter falls to the ground.

“Finding the balance point where we can maximize yield and still ensure nutrient resorption moves us toward ecological intensification,” Smith says. “Some of our work indicates that fertilized switchgrass plants take longer to resorb nitrogen than unfertilized plants. If we can reduce added fertilizer and get the same amount of biomass off a field, it’s good for the farmer and very good for the environment.”

In focusing on ecological intensification, GLBRC researchers are tackling a central challenge of “second generation” biofuel feedstocks: promoting highly productive harvests that also nurture the environment.  – Leslie Shown

Originally seen on the GLBRC website, here: