The Hidden Value of Bud Banks

We tend to assume that plants come from seeds. However, not all that we see has come from seeds as explained in a new paper by Jacqueline Ott and colleagues, “The Ecology and Significance of Belowground Bud Banks in Plants“. It’s a paper that promises to be useful for anyone studying perennial plants.

Speaking to Botany One, Dr Ott said: “Perennial plants use aboveground buds, like buds in leaf axils, to produce new branches. In temperate regions, plants use these aboveground buds to overwinter and resprout in the spring. Plants can use belowground buds in a similar fashion. Belowground buds can enable a plant to go dormant over an adverse seasonal period, like winter. Then they grow back when conditions are more favorable. They can also be used to resprout after disturbance, such as grazing, fire, or ploughing, injures a plant.”

Bud banks can lead to clonal plants. Dr Ott said: “When a perennial plant uses belowground buds to produce new stems, and these new stems could eventually separate from their parent plant and operate independently, they would be considered clonal plants. Clonal plant species exist throughout the world. Belowground buds are what enable a lot of plants to be clonal.”

The bud banks act, some ways, like a seed bank. There are some differences. Dr Ott explained: “Similar to a soil seed bank, buds can accumulate and be stored in the soil for varying lengths of time. However, buds are attached to a plant organ (rhizome, tuber, root) that helps support them while they are dormant and helps provide resources as they grow out into new stems. Plants may have both a seed and bud bank and use these under different circumstances or for different purposes.”

It’s this similarity to seed banks that is important to ecosystem and community ecologists and land managers. Dr Ott said: “Bud banks will interest anyone seeking a mechanistic understanding of patterns of species composition or productivity in herbaceous and shrub communities. The bud bank is one of the mechanisms driving the process producing the patterns we observe. For example, grassland productivity is largely driven by precipitation but the bud bank could introduce lag effects affecting annual net primary productivity in these systems.” For this reason, Dr Ott sees managing the bud bank a similar problem to managing a seed bank in conserving plants.

It’s the productivity of bud banks that makes them so important. Dr Ott said: “Belowground buds rather than seeds can be responsible for >99% of stem production in some plant communities. They are important for seasonal regeneration of plants as well as resprouting of plants following injury. Belowground bud banks play a large role in plant response to disturbance and climate. They can also be involved in the spread of weeds in agricultural systems. If a species produces a lot of buds following injury from a plough cutting through their bud-bearing organ (root, rhizome, tuber), this species may increase in abundance in agricultural settings.”

Dr Ott added that while both bud banks and seed banks produce stems to regenerate plants, the genetic content is quite different. “Seeds are a source of genetic novelty whereas bud banks are assumed to use the same genotype as their parents. However, recent work in epigenetics may show that other factors than genetic diversity can affect the flexibility of a plant population to respond to environmental fluctuations. The bud bank tends to reflect the aboveground plant species composition whereas the seed bank often has little similarity to aboveground species composition. Bud dormancy can be influenced by the parent plant directly whereas parental control of seed dormancy is limited. Both have the same potential to buffer population dynamics and be a source of new vegetation if the aboveground plant is destroyed. Both seed and bud banks enable dispersal through time.”

Dr Ott also explained how a bud bank opens opportunities that a seed bank does not. “Belowground bud banks enable plant populations to persist without relying heavily on successful seed production and germination. A stem produced from a bud has the whole support system of the parent plant helping it to succeed whereas a seed only relies on its own reserves. Oftentimes multiple buds are connected through the parent plant organs. A bud bank enables a plant to operate and respond to environmental factors and disturbances as an integrated unit.”

Anyone looking for research problems should find plenty of opportunities with bud banks, Dr Ott said. “Data on bud banks is relatively scarce, and the largest bud bank dataset is focused on the flora of Central Europe. In addition to studying the bud bank traits of more species, it will be necessary to standardize methodologies for bud classifications in order to facilitate comparisons among studies. More research is needed to examine the response of bud banks to environmental variables and disturbance. The ecological implications of maintaining a bud bank needs to be tested explicitly in future studies.”