The old growth remnant forests in Stebbins Gulch are locations at Holden Arboretum that David Burke and his lab have been studying for years. Burke first began hiking to the old growth portions of Stebbins Gulch back in 2006. One thing that he and Charlotte Hewins noticed every spring was the immense cover of wild leek (Allium tricoccum) on the forest floor. “Come April when the leeks are fully emerged, there is nowhere to step that isn’t completely covered in them,” Hewins once told me. In April of 2008, I saw it for myself and it took my breath away. Forest floors were supposed to be brown and covered in decaying leaves. But, the forest floor of Stebbins Gulch that April (and every April after) was green due to numerous wild leek leaves unfurling toward the sun!
Photo: Wild Leek covering the forest floor of Stebbins Gulch in May
Wild leek plants are small compared to their woody counterparts in forests. “But, there are just so many of them that they have to be important for the overall function of this forest!” Burke told me back on that April day. Wild leek are spring ephemerals; their leaves emerge in early spring for a short window before the trees leaf-out at a time when light levels are high on the forest floor. Because wild leek leaves emerge well before tree leaves do, these plants, like other spring ephemerals, are actively fixing carbon through photosynthesis at this time of high light availability before the canopy closes. This fixed carbon is then stored in the bulb belowground. The wild leek leaves disappear in late spring, but are still active through their bulbs belowground. Even when their leaves are no longer visible, wild leek bulbs send up flower stalks in early summer, which set seed by late summer. Therefore, wild leek plants are still active when they are flowering and fruiting, even though light levels are much lower in June, July, and August. Wild leek go dormant in the fall and the bulbs are believed to remain dormant throughout the winter. We wondered, though, if the roots could still be active belowground even when the aboveground structures are resorbed.
In the spring of 2011, we measured the nutrient content of wild leek bulbs and the association of their roots with beneficial fungi (arbuscular mycorrhizal fungi) over one year. These were measured during leaf emergence, vegetative state, leaf senescence, flower emergence, seed set, and dormancy. Carbon content of the bulb showed a predictable pattern; it was highest just after leaf senescence when the leaves had finished their months of photosynthesis. Carbon content declined as the flower emerged and seeds set; these are costly processes for the plant. Nitrogen and phosphorus content of the bulbs showed a similar pattern to carbon, but also increased during the winter months and dormant season. This suggests that the roots are still active during the dormant season in acquiring these essential soil nutrients! Interestingly, the dormant roots were also colonized by arbuscular mycorrhizal fungi. These fungi are known to acquire nitrogen and phosphorus for plants. Our data suggests that wild leek and their symbiotic fungi are active belowground, even when the plants are not producing aboveground structures!
Photo: Wild Leek in Stebbins Gulch in April
Sometimes when I am walking in Stebbins Gulch in the winter, I think about the many, many wild leek bulbs belowground actively acquiring nutrients and getting ready to emerge in the spring. Now that we are in March, I am anxiously awaiting the emergence of the wild leek leaves that turn the forest floor green for a few months!
Results from our wild leek study are published here: https://link.springer.com/article/10.1007/s00572-015-0628-5.
Photo: Wild Leek shortly after emergence in March
Sarah Kyker, PhD
Postdoctoral Research Associate
I am a microbial ecologist interested in the influence of human-induced and natural environmental changes on microbial communities. Because microorganisms are small in size, they are environmentally sensitive. Despite their small size, microorganisms can have a large impact on the overall health of a habitat due to their role in ecosystem processes. Consequently, environmental changes that alter microbial communities can have a large effect on the overall health of the habitat. My research focuses on deciduous forest soils, which harbor a tremendous diversity of microorganisms. For example, just a teaspoon of uncontaminated soil is estimated to contain millions of microbial species and billions of individual microbial cells. I primarily study bacteria and fungi, as these groups make up a large portion of the microbial diversity in soil. I use molecular techniques to study the community composition of microorganisms and functional genes possessed by microorganisms. The goal of my research is to help elucidate the importance of environmental changes to the health of a habitat or an ecosystem when these changes affect the smallest inhabitants.