A Rare Opportunity to Get Dirty -- BLM Idaho and BSU Partner to Study Mulford’s Milkvetch

It’s just dirt.  No, it’s not!

A dirt sample collected from BLM Idaho rangeland under a microscope, reveals that the soil is a metropolis with millions of microscopic organisms. This soil is a fundamental part of the ecosystem. In fact the living soil is the foundation for all plants. Just like our human bodies contain a living system of “flora and fauna” integral to our health so too does the soil. As the soil provides nutrients plants need to survive. For example:

• In humans, bacteria digest food and produce essential nutrients like vitamin K and certain B vitamins, which our bodies cannot produce on their own. 

• Similarly soil contains bacteria used by plants to breakdown nutrients. In plant roots a nitrogen-fixing bacteria called rhizobia  forms nodules on roots of some plant species. Rhizobia is taken up from the soil into the roots. For Mulford’s milkvetch (also known as ASMU) the rhizobia allows ASMU to - “breath” and converts nitrogen gas into ammonia compounds plants use.

Mulford’s milkvetch, a rare plant across it’s range, occurs in Idaho primarily on the Snake River Plain.  Ancient Lake Idaho, once spanned much of the Snake River Plain in southwestern Idaho more than 6.5 million years ago. This ancient lake is a hotspot for ASMU.  The species thrives in a specific band of sandy soils on the ancient lake’s shorelines. These soils are found in the hills surrounding Boise, the Owyhee Mountains in Idaho, and in Malheur County, Oregon.

The image shows a dormant Mulford’s plant before root excavation.

Mulford’s milkvetch is also listed as a Special Status Species (SSS) for both Idaho and Oregon BLM. The small range (about 100 miles by 100 miles) and it’s rarity make it a potential candidate to be Federally listed as either a threatened or endangered species. The BLM is taking steps to conserve this rare and special plant species.

Managing SSS plants provides challenges on BLM Idaho rangelands, particularly in areas where the urban space meets public lands. Whenever possible the BLM will leave SSS plant occurrences undisturbed. However, a recent plan for a transmission line in the Boise foothills will disturb a portion of one of the occurrences of Mulford’s milkvetch.  To conserve as much of the occurrence as possible from the transmission line disturbance the BLM partnered with Boise State University (BSU). Dr. Serpe and Dr. Buerki at BSU will do research to better understand this understudied rare plant.

 Dr. Serpe and Dr. Buerki’s research will look at:

• population genetics
• planting methods (seeding/pug planting) and the benefits of root symbionts for nutrient acquisition via rhizobia
• arbuscular mycorrhizae, and other associated fungi (these organisms are otherwise known as plant growth promoters (PGP).  

Knowledge gained from the partnership between the BLM and BSU will improve establishment of ASMUU during future restoration and rehabilitation activities.

Although ASMU rises no more than 12 inches above the ground, under normal field conditions, individual plants often grow a taproot that can extend 40 inches below the surface. This enables ASMU to reach the water table. Allowing for the plants to access water in this dry environment. BLM botanists got dirty at the excavation at the Boise foothills research site, they were fascinated by small statured plant’s network of roots.

According to BLM Idaho botanists and ecologists working at this location, the taproots of this desert species only reached 18 inches.  The lateral root system spanned a 3.5-foot radius from the mother plant, branching and turning but maintaining a horizontal spread below ground. It may be puzzling that the taproot of this desert species only reached a depth of 18 inches, but given the area is a powerline right-of-way the taproot was likely discouraged from penetrating the hardpacked soil and grew out laterally to compensate.

The image above shows the Mulford’s plant and the exposed roots.

The image above shows the area excavated to collect the Mulford’s roots.

The excavated plant is in the custody of BSU researchers where they will examine it for rhizobia and other root symbionts that may be useful during restoration.  They hope to capture rhizobia, small nitrogen-fixing bacteria that live in nodules of root tissue the plant grows to protect itself.  If discovered, rhizobia will be increased in the laboratory. Allowing teams  to  apply it during restoration activities. This allows for  the enhancement of nitrogen acquisition which can increase out-planting success.

The image above shows fine roots with soil attached.

Picture A: a dry dormmate root with a withered and broken nodule.   1 mm black reference scale. Picture B: a growing healthy root with rhizobia nodule. 3 mm black reference scale bar.

The rhizobia promote a living soil biome, a system that is constantly changing, growing, and moving slowly; a complex soil ecosystem and life blood for our above ground world. So the next time you get dirty digging a hole, reflect upon how the below ground world affects the above ground world. It is a dance of balanced interactions which shape desert ecosystems and provide food, clean water, and air for all creatures.

Image shows Dr. Serpe evaluating the Mulford’s roots collected.