Hydropriming changes temperature thresholds for seed germination of tree species from the Caatinga, a Brazilian tropical dry forest

Joana Paula Bispo Nascimento,Bárbara França Dantas,Marcos Vinicius Meiado

doi:10.1590/2317-1545v43238649

Joana Paula Bispo Nascimento, Bárbara França Dantas + Show 1 more

Open Access

https://doi.org/10.1590/2317-1545v43238649

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Abstract

Abstract: This study evaluates the effects of hydration and dehydration cycles (HD cycles) on seed germination of four Caatinga tree species (Anadenanthera colubrina var. cebil, Enterolobium contortisiliquum, Pityrocarpa moniliformis and Pterogyne nitens) subjected to different temperatures and determine the thermal upper and lower limits of germination. For this, seeds were subjected to 0, 1, 2 and 3 HD cycles and set to germinate at temperatures of 5, 10, 15, 25, 35, 40 and 45 °C. Germinability and t50 were calculated and the differences of these parameters were compared by two-way ANOVA. In addition, germination rate (GR = 1/t50), as well as ceiling (Tc), optimum (To) and base (Tb) temperatures were calculated to estimate the limits below or above which the seeds fail to germinate. We observed that the more HD cycles, the better the seed responds, especially at extreme temperatures. Seeds of all studied species showed To between 25 and 35 °C, Tb < 10 °C, and Tc > 40 °C. The slope of regression curves for germination rate showed that submitting seeds to HD cycles expands its thermal tolerance range, revealing that this seed pre-treatment can be efficient for species as it increases their tolerance to thermal stress.

Highlights

Knowledge on the environmental conditions that interfere with seed germination is essential for understanding the establishment of plant diversity
To promote HD cycles in seeds, hydration times were set based on previous studies on hydration curves, which corresponded to two hours for A. colubrina, seven hours for E. contortisiliquum, five hours for P. moniliformis, and eight hours for P. nitens
Seeds of all species managed to germinate in a wide temperature range (10–40 °C) and failed to do so at the temperatures 5 °C and 45 °C (Table 1, Figure 1)

Summary

Introduction

Knowledge on the environmental conditions that interfere with seed germination is essential for understanding the establishment of plant diversity. Among the environmental conditions that interfere with the germination process, temperature is one of the factors that most affect germinability, germination speed, and specific biochemical and enzymatic reactions that drive the entire germination process (Bewley et al, 2013). Germination of non-dormant seeds occurs within a temperature range called cardinal temperatures, that is, ceiling (Tc), base (Tb) and optimum (To) temperatures at which a seed can germinate. The optimum temperature is considered the ideal temperature for the species to germinate since it results in the largest number of seeds germinated in a shorter period (Bewley et al, 2013). In the Caatinga, a Tropical Dry Forest occurring mainly in the Northeast region of Brazil, many species have optimum germination ranging from 30 to 35 °C, evidencing that these plants have higher tolerance to high temperatures compared to species from more humid ecosystems (Meiado et al, 2012; 2016; Nascimento et al, 2018; Dantas et al, 2020)

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