Abstract
Exposure to high-temperature stress (HTS) during early regeneration in plants can profoundly shape seed germination, seedling growth, and development, thereby providing stress resilience. In this study, we assessed how the timing of HTS, which was implemented as 8 h in 40°C, could affect the early regeneration stages and phytohormone concentration of four hemiepiphytic (Hs) and four non-hemiepiphytic (NHs) Ficus species. Their seed germination, seedling emergence, and seedling survival probabilities and the concentrations of three endogenous phytohormones, abscisic acid (ABA), indole-3-acetic acid (IAA), and salicylic acid (SA) were assessed after HTS imposed during imbibition, germination, and emergence. In both groups, seeds were more sensitive to HTS in the early regeneration process; stress experienced during imbibition affected emergence and survival, and stress experienced during germination affected subsequent emergence. There was no effect from HTS when received after emergence. Survival was highest in hemiepiphytes regardless of the HTS treatment. The phytohormones showed growth form- and regeneration stage-specific responses to HTS. Due to the HTS treatment, both SA and ABA levels decreased in non-hemiepiphytes during imbibition and germination; during germination, IAA increased in hemiepiphytes but was reduced in non-hemiepiphytes. Due to the HTS treatment experienced during emergence ABA and IAA concentrations were greater for hemiepiphytes but an opposite effect was seen in the two growth forms for the SA concentration. Our study showed that the two growth forms have different strategies for regulating their growth and development in the early regeneration stages in order to respond to HTS. The ability to respond to HTS is an ecologically important functional trait that allows plant species to appropriately time their seed germination and seedling development. Flexibility in modulating species regeneration in response to HTS in these subtropical and tropical Ficus species could provide greater community resilience under climate change.
Highlights
Temperatures above the normal optimum are sensed as temperature stress by all living organisms
The assessment of the effect of temperature stress during seed imbibition, seed germination, seedling emergence on the early regeneration stages of the eight Ficus species showed that Ficus microcarpa had the highest survival under all temperature stress treatments (Supplementary Figure 2)
Seedling survival was highest for hemiepiphytic species (47.35 ± 0.27%) when the temperature stress treatment was experienced during seedling emergence and seedling survival was lowest for the same treatment for non-hemiepiphytic species (26.18 ± 0.16%)
Summary
Temperatures above the normal optimum are sensed as temperature stress by all living organisms. Among suitable microsite conditions appropriate for seed germination, the temperature is one of the most critical drivers that alter seed viability and shape seed germination success (Walck et al, 2011). Temperature changes can affect seed dormancy and persistence in soil, preventing, delaying, or enhancing the processes and mechanisms of seed germination, seedling development, and seedling establishment (Walck et al, 2011; Chen et al, 2021). Due to abrupt variation in climate, which is driven by anthropogenic activities, suitable temperature conditions for successful seed development and germination have been significantly altered in natural landscapes (Liu et al, 2018; Uriarte et al, 2018; Wan et al, 2018). Most often temperature stress goes hand in hand with severe drought further impeding the regeneration process due to low levels or lack of water
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