Modelling seed dormancy cycling and seedling emergence of <i>Thlaspi arvense</i> in field soils and a global warming scenario

Thlaspi arvense (field pennycress; Brassicaceae) is a competitive and invasive weed which causes significant yield reductions in crops. It is also a target for domestication as an oil seed crop. Here we investigate its dormancy cycling and seedling emergence behaviour to understand how it will adapt to climate change. Seed dormancy cycling was monitored in the field. Germination at alternating temperatures was modelled to understand the field response. Seedling emergence timing in response to increasing soil temperature was studied in field experiments and in a thermogradient tunnel to evaluate the impact of global warming. Thlaspi arvense displays winter annual dormancy cycling. However, the thermal germination window (TGW) of this species does not close during winter, resulting in a small opportunistic spring emergence window, in contrast to the dominant autumn window which coincides with falling soil temperatures. Thermal alternations >8°C contribute to dormancy release, consistent with increasing germination in seeds recovered from field soils in late summer. Soil temperatures >10°C promote emergence in both windows, which correlates with accumulated thermal time. Because of TGW, T. arvense has evolved independent high-risk spring and low-risk autumn seedling emergence windows. The opportunistic spring window exploits temperate summers, while the low-risk autumn window exploits falling soil temperature to maximize seedling emergence success by avoiding hot dry conditions. This indicates T. arvense is highly adapted to survive in soils disturbed in spring and autumn by agricultural practices.