COS 218-4 - CANCELLED - Belowground storage in grassland systems: the impact of seasonal fires on non-structural carbohydrate reserves in native forbs

Abstract: Fire is a primary driver for the maintenance and restoration of grassland systems. However, invasive species, fire staff availability, and other management constraints, like drought timing, have led to variable timing of wildland and prescribed grassland fires. While it is known that high fuel loads with their greater energy release lead to increased air temperatures, soils, where rooting systems are located, are less impacted by these temperatures. However, high temperatures and complete consumption of aboveground plant material require aboveground recovery from belowground meristems (i.e., bud banks). As soil heating is minimal, belowground bud death may be minimal; plant responses are likely driven by indirect effects, such as fire or season of fire have on outgrowth. Therefore, fire effects on aboveground regrowth are likely constrained by belowground meristem response, specifically the supply of carbohydrates that will support their outgrowth. To understand how native belowground plant tissues respond to experimentally manipulated seasonal fires, soil cores (6 in diameter) with native species were extracted from Buffalo Gap National Grassland in South Dakota during the early (nearly pre-emergent individuals) and late Spring (mature individuals) of 2021. To simulate seasonal wildland fires, samples were burned in Spring or Summer via fire tables at fuel loads mimicking 3 tons per acre. An additional treatment of carbon starvation (watered yet kept in darkness) was introduced, alongside seasonal burns, in order to determine extreme impacts on belowground storage (via non-structural carbohydrates; NSCs). At species senescence, we measured starch content at the root and crown (bud bank) level of all samples to compare across treatments and with pre-emergent NSC levels. Initial results indicate that while air temperatures may be extremely high, there is a significantly precipitous decrease in temperature at the soil surface and subsequent depths ( < 1cm) which reflect minimal soil heating even at high fuel loads. While species and treatment type (i.e., seasonal burns) have variable impacts on non-structural carbohydrates, individuals with more time to recover following a disturbance were more likely to possess more stored energy (i.e., starch). Therefore, timing of wildland fires can impact stored carbohydrate reserves available to the plant in subsequent growing seasons.