Thermal buffering capacity of the germination phenotype across the environmental envelope of the Cactaceae

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 (Tb), optimum (To) and ceiling (Tc) temperature for germination and the thermal time (θ50) for each species based on the linearity of germination rate with temperature. Species with the highest Tb and lowest Tc germinated fastest, and the interspecific sensitivity of the germination rate to temperature, as assessed through θ50, 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 To. 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.Fil: Seal, Charlotte E.. Royal Botanic Gardens; Reino UnidoFil: Daws, Matthew I.. Royal Botanic Gardens; Reino UnidoFil: Flores, Joel. Instituto Potosino de Investigación Científica y Tecnológica; MéxicoFil: Ortega Baes, Francisco Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; Argentina. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Escuela de Agronomía. Laboratorio de Investigaciones Botánicas; ArgentinaFil: Galindez, Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Salta. Estación Experimental Agropecuaria Salta; ArgentinaFil: León Lobos, Pedro. Instituto de Investigaciones Agropecuaria; ChileFil: Sandoval, Ana. Instituto de Investigaciones Agropecuaria; ChileFil: Ceroni Stuva, Aldo. Universidad Nacional Agraria La Molina; PerúFil: Ramírez Bullón, Natali. Universidad Nacional Agraria La Molina; PerúFil: Dávila-Aranda, Patricia. Universidad Nacional Autónoma de México; MéxicoFil: Ordoñez Salanueva, Cesar A.. Universidad Nacional Autónoma de México; MéxicoFil: Yáñez Espinosa, Laura. Universidad Autónoma de San Luis Potosí; MéxicoFil: Ulian, Tiziana. Royal Botanic Gardens; Reino UnidoFil: Amosso, Cecilia. Università di Padova; ItaliaFil: Zubani, Lino. Università di Padova; ItaliaFil: Torres Bilbao, Alberto. Empresa Nacional para la Protección de la Flora y la Fauna; CubaFil: Pritchard, Hugh W.. Royal Botanic Gardens; Reino Unid