Recruitment from seeds is among the most vulnerable stage for plants as global temperatures change. While germination is the means by which the vast majority of the world's flora regenerate naturally, a framework for accurately predicting which species are at greatest risk of germination failure during environmental perturbation is lacking. Taking a physiological approach, we assess how one family, the Cactaceae, may respond to global temperature change based on the thermal buffering capacity of the germination phenotype. We selected 55 cactus species from the Americas, all geo-referenced seed collections, reflecting the broad environmental envelope of the family across 70° of latitude and 3700 m of altitude. We then generated empirical data of the thermal germination response from which we estimated the minimum (T ), optimum (T ) and ceiling (T ) temperature for germination and the thermal time (θ ) for each species based on the linearity of germination rate with temperature. Species with the highest T and lowest T germinated fastest, and the interspecific sensitivity of the germination rate to temperature, as assessed through θ , varied tenfold. A left-skewed asymmetry in the germination rate with temperature was relatively common but the unimodal pattern typical of crop species failed for nearly half of the species due to insensitivity to temperature change at T . For 32 fully characterized species, seed thermal parameters correlated strongly with the mean temperature of the wettest quarter of the seed collection sites. By projecting the mean temperature of the wettest quarter under two climate change scenarios, we predict under the least conservative scenario (+3.7°C) that 25% of cactus species will have reduced germination performance, whilst the remainder will have an efficiency gain, by the end of the 21st century.
Collaea argentina (Fabaceae) and Abutilon pauciflorum (Malvaceae) are of high medicinal and ornamental value and are collected for pharmaceutical and ornamental purposes. However, one obstacle for plant production is the occurrence of seed dormancy. Here, we confirmed the occurrence of dormancy in these species, identified possible methods for breaking dormancy and assessed the dormancy condition after seed storage. Wet heat, physical and acid scarification were effective methods for breaking physical dormancy in both species. After four years of dry storage, a high proportion of C. argentina seeds were able to germinate (i.e. physical dormancy levels had reduced), whereas A. pauciflorum seeds continued to be dormant but were more sensitive to dormancybreaking treatments. These results should aid plant production and seed conservation of these two species.
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