For the majority of plants, the accumulation of snow signifies a time of dormancy. From a productivity standpoint, things really slow down when liquid water turns solid. Liquid water is the solvent that allows nutrients and plant/fungal signals to be mobile. When the forest floor dips below 0°C, water freezes, along with the processes required for plant production. Enter plant dormancy. Suspended in time, the majority of plants don’t do much at all. Some plants however have specialized in an alpine life, living thousands of feet above sea level. The snow layer in these alpine communities is vital to plant health, because the snow acts as an insulator, keeping the frigid, sub-zero temperatures away from the vulnerable roots. Some of these alpine adapted plants have evolved mechanisms to cope with the nutrient poor mountain substrates. Today, I learned that Corydalis conorhiza actually extends specialized root structures into the aboveground snow, to acquire the nutrients it contains.
Through studying this plant adaptation, I found out that the snow-beds are quite nutrient rich. Snow layers around the world are receiving more and more nitrogen deposition from a diverse array of human activities. Since these adaptations evolved even before the Anthropocene, there must have been enough pre-human N deposition to drive the evolution of specialized snow-bed roots.
Corydalis conorhiza produce two types of roots that differ morphologically. Compared to its soil-dwelling roots, C. conorhiza snow roots are very fine, like 0.1 mm fine. The snow roots also are much less differentiated, showing only a few cell rings. Additionally, the snow roots have enlarged endodermic cell walls, which suggests their main function of nutrient transport via xylem. Though without a clear differentiation of epidermal cells, and its already fragile stature, these snow roots clearly don’t invest many resources towards protection. These unprotected fine snow roots are not used throughout the year, so it makes since that the plant wouldn’t allocate many resources to ephemeral structures.
Soil-dwelling roots are significantly more robust (0.5-0.7mm) with easily more distinguished regions of root anatomy. These roots that inhabit alpine soils have densely packed exodermal and epidermal cells. These structures persist throughout the plants life, so one can see why more resources are allotted to soil-roots. Ultimately, the allocated resources are used to form exodermal and epidermal cells, which protect the roots, extending their longevity. In addition to the variance in root morphology, the soil roots maintain a symbiotic relationship with arbuscular mycorrhizal fungi (AMF).
In addition to the variance in root morphology, the soil roots maintain a symbiotic relationship with arbuscular mycorrhizal fungi (AMF). Vladimir G. Onipchenko and his team of researchers in 2009, describe the plant and its flow of alpine nutrients. This study reveals that a C. conorhiza carries out multiple strategies to access separate pools of nutrients. The snow contains nitrogen, which is retrieved by snow-roots, while the soil-roots house AMF that scavenge for phosphorus. Phosphorus is virtually absent in the snow layer, so this along with the persistence of the AMF symbiote signify that each root structure specializes in acquiring nutrients from different pools.
What is most interesting to me, is that although the snow-roots permeate large swaths of snow, they might only access snow nitrogen upon snow melt. So, throughout the cold season, snow-roots spread through the snow layer, only to acquire a subset of the snows nutrients once the icy snow melts. With snow being a solid form of liquid water, the nutrients most likely remain untapped, until conditions warm. The researchers did not record any mycorrhizae in the snow-roots, but could they possibly have a role in the snow layer? They certainty do underground.
In this modern era, although more nitrogen is being deposited in the snow layer, warming conditions may cause premature snow melt before snow roots are fully formed. This will result in much of the nitrogen migrating downslope, and may ultimately alter species distribution across this alpine gradient.