Influence of current and future climate on the seed germination of Cenostigma microphyllum (Mart. ex G. Don) E. Gagnon & G. P. Lewis

Abstract

Seasonally tropical dry forests are among the most threatened environments by climate change. However, these forests, which are at risk of desertification, are still poorly studied and conserved. Seeds of several species endemic to the Caatinga, a Brazilian dry forest, are also understudied, mainly regarding their ability to cope with a hotter and drier climate predicted for the future. For the first time in seeds of Cenostigma microphyllum (Leguminosae), we aimed to study the presence of physical dormancy, temperature and salt tolerance to ascertain the effects of current and future climate on seed germination. Intact and scarified seeds were investigated by incubating at constant temperatures (15 to 40°C) or in NaCl solutions (−0.2 to −1.0 MPa) at 25 and 30°C. Thermal and osmotic thresholds, as well as thermal time and hydrotime constants, were calculated using linear regressions between the germination conditions and germination rate. To predict germination in the future, a heat sum model based on thermal time and hydrotime was applied to current and future climate scenarios. Seeds of C. microphyllum were permeable to water and did not have physical dormancy. The results indicated that increases in temperature are unlikely to affect germination, despite greater sensitivity to salinity presented at higher temperatures. In a future climate, the reduction in the number of weeks with at least 15 mm rainfall will affect the germination timing for the seeds. Thus, we can conclude that under the most pessimistic climate scenario predicted for the future, the seed germination of C. microphyllum may be restricted, likely leading to low seedling recruitment and establishment.Keywords temperature . salt stress . climate change . thermal time model . hydrotime model

Germination Functional Traits in Seeds of Halophytes

“…Consistent with this, germination of Suaeda maritima was three times more tolerant to NaCl at 5°C (maximum threshold of 1279 mM) than at 25°C (maximum threshold of 447 mM; Seal et al 2018). This was also observed in the non-halophyte Cenostigma microphyllum which had a higher tolerance to salt at 25°C than at 30°C (Gomes et al 2019).…”

“…Thermal time and hydro time models were initially developed on crop species but have since been applied to the germination of hundreds of wild and domesticated species, of different life-forms (e.g., trees, shrubs, herbs) and from different habitats (see Dürr et al 2015 for a review). These models have also been applied to species to describe dormancy loss (Porceddu et al 2017) and field emergence (Porceddu et al 2013) and to assess the germination risk of species to climate change (Seal et al 2017;Gomes et al 2019;Dantas et al 2020). With such broad applications, population-based germination models have become powerful and popular tools to characterize seed functional traits.…”

“…Even if precipitation/ evapotranspiration is not altered, measured soil salinity increases by 0.249 dS/m for each 1°C increase in maximum monthly temperature (Dasgupta et al 2015). A general model describing germination events (based on heat sum and seed thermal requirements and thresholds), and its relationship with precipitation reduction in a future climate (adapted from Dantas et al 2020 andGomes et al 2019), is presented in Fig. 3.…”

“…3 Germination events during a year of a hypothetical tropical dryland specialist species in response to rainfall volume in current and future climate. (Adapted from Dantas et al 2020;Gomes et al 2019). Germination events (gray columns) are based on available heat sum for germination (i. e., the temperature accumulated by the seed per day, above the minimum or base temperature threshold), which in tropical areas is not usually limiting.…”

“…This includes the importance of the thermal memory, representing phenotypic plasticity that has arisen in response to thermal environments previous generations have experienced (Fernández-Pascual et al 2019). Understanding and quantifying the germination niche of a species can also highlight its sensitivity to environmental perturbation, such as experienced through climate change (Porceddu et al 2013;Seal et al 2017;Gomes et al 2019;Dantas et al 2020).…”