Recruitment stages play a particularly important role for species distribution by creating different opportunities for new plant establishment in changing environment (Fraaije et al. 2015). The early recruitment stages of clonal plants was mainly dominated by vegetative reproduction (including radicle emergence, ramet survival and growth) (Vazquez-Ramirez and Venn 2021), and this process was influenced by a variety of environmental factors (Huang et al. 2015). Associated with global change, there has been a rapid increase in frequency and intensity of extreme climatic events (Abernathy et al. 2019). Temperature and flooding, two of the changing environmental factors, are the major determinants of the early life-history stages of plants (Walck et al. 2011). Therefore, understanding the influence of these two factors on the early recruitment stages might allow to predict, and mitigate the effect of future environmental changes on wetland vegetation distribution.
Temperature is a major limiting factor for plant establishment and survival in recruitment stages (Campbell et al. 2018). The response of germination to temperature has three cardinal temperatures: base, optimal, and ceiling temperature. At both, the base and ceiling temperatures germination is zero, whereas, at the optimum temperature, the highest germination rate occurs (Zaferanieh et al. 2020). Generally, the propagules of varied species could not sprout at the temperatures lower than 5°C or higher than 50°C, and the tubers sprouted at the optimum temperature range of 15 ~ 35°C (Hossain et al. 2001, Loddo et al. 2018). These parameters are the basis for models used to predict the timing of sprouting (Kamkar et al. 2012). So more studies on the early plant recruitment stages are required to provide information to maximize the possibilities of their application.
Flooding regime has long been considered as crucial for individual propagule sprouting rates (Greet et al. 2020). Flooding depth is an important occurrence of flooding regime (Mauchamp et al. 2001). At low flooding depth, propagule and ramet can utilize resources, especially carbon dioxide and oxygen in the atmosphere (Vervuren et al. 2003, Deegan et al. 2007). At deep flooding depth, plants can suffer from hypoxia or anoxia because the ability of oxygen to diffuse through the water to the soil is extremely low (Ejiri et al. 2020). Many studies found that sprouting percentage of rhizome of many plants increased first and then decreased with the increasing of flooding depth (Zhan et al. 2010, Dong et al. 2012). However, the effects of flooding on the vegetative structure of wetland plants are very limited and need further study.
Bolboschoenus planiculmis, a perennial helophyte with tuber propagation, is distributed in East Asia, Central Asia and Central Europe (Ding et al. 2021). It forms a monodominant or mixed community in salt marshes, reclaimed paddy fields and lagoons (Yang et al. 2020). Meanwhile, this species provides food for endangered migratory birds like swan geese (Anser cygnoides) and cranes (Grus leucogeranus) (Yang et al. 2020, 2021). Generally, B. planiculmis lives at low elevations, and it is one of the most vulnerable species to seasonal flooding conditions and temperature (Kim et al. 2013). The effects of temperature, flooding state, salinity, and interspecific interactions on B. planiculmis have been discovered by several scholars (Kim et al. 2013, Liu et al. 2018, Yang et al. 2020). However, there were few studies on the response of the early plant recruitment stages to environmental factors.
The study was to investigate how the tubers of B. planiculmis adapt to the environment of temperature and flooding depth change during the early plant recruitment. The purposes of the current study were (1) to investigate the effects of different temperatures and flooding depths on B. planiculmi tuber sprouting performance, and (2) to estimate the temperature and flooding depth thresholds for bud sprouting of B. planiculmi.