Dynamics in the emergence of dormant and non-dormant herbaceous species from the soil seed bank from a Brazilian dry forest

Abstract

Aims In dry tropical forests, herbaceous species may have dormancy mechanisms and form persistent and transient seed banks in the soil. Evolutionarily acquired, these mechanisms are efficient for the establishment and survival of these herbs, especially in forests with unpredictable climates, such as the Caatinga. Thus, our objective was to verify whether the studied herbaceous species adopt the physical dormancy mechanism and how these natural barriers are overcome, to understand the temporal dynamics existing in the soil seed bank from a Brazilian dry tropical forest. Methods Seeds of five native herbaceous species from the Caatinga forests were selected and submitted to pre-germinative treatments for verifying the presence of physical dormancy. We collected soil samples in the rainy and dry seasons for four consecutive years and monitored the emergence of the selected herbaceous in the greenhouse. We verified the differences in germination and seed bank emergence in the soil by generalized linear models. Important Findings The presence and absence of physical dormancy were observed in seeds from Caatinga herbaceous species. We found intraspecific and interspecific differences in the herbaceous emergence from soil seed banks between years and climatic seasons. In perennial herbs, consecutive lack of emergence between seasons and years was frequent, which suggests a direct relationship with the mechanism of physical dormancy and the environmental conditions necessary to overcome integument barriers. In these species, seed dimorphism and dormancy may confer additional advantages to their survival. Moreover, presenting intermediate levels of physical dormancy in an annual species may be an evolutionary adjustment to rainfall unpredictability. In contrast, we found that the annual herb without dormancy is more sensitive to seasonal and interannual climate changes, as evidenced by the increase and significant reduction of its emergence in the soil seed bank. These differences acquired evolutionarily are advantageous for the establishment of herbaceous populations, mainly in semiarid regions with an unpredictable climate.

Application of soil seed bank techniques to facilitate forest restoration in the Caatinga

“…This type of predominant life form is due to its permanence in the soil for a longer time, in conditions of intermediate stages of regeneration (Kunz & Martins, 2016), as found in the two collection areas, and by the type of soil fertility (Rodrigues et al, 2010). Herbaceous plant seeds can undergo dimorphism (aerial and subterranean seeds) and physical dormancy, which makes them efficient for survival in the face of the uneven climatic conditions in this ecosystem (Souza et al, 2020). They help in the interpretation of the resilience of this ecosystem, which is why they were not excluded from the accounting for species density.…”

Experimental Warming Hastens Physical Dormancy Break and Germination in Tropical Fabaceae

“…Tropical plants often avoid dry season germination by either producing dormant seeds or dispersing their seeds in the wet season ( Sautu et al, 2007 ; Salazar et al, 2011 ; Ramos et al, 2017 ; Escobar et al, 2018 ). Thus a trade-off exists, whereby species that disperse seeds during the wet season tend to be non-dormant, germinating immediately following dispersal, while species that disperse their seeds in the dry season tend to be dormant, germinating only when conditions become favorable again in the wet season ( Salazar et al, 2011 ; de Souza et al, 2020 ). Of the latter, various strategies are used to achieve seed dormancy.…”