Thermal Time and Cardinal Temperatures for Germination of Cedrela odorata L.

Abstract

Thermal time models are useful to determine the thermal and temporal requirements for seed germination. This information may be used as a criterion for species distribution in projected scenarios of climate change, especially in threatened species like red cedar. The objectives of this work were to determine the cardinal temperatures and thermal time for seeds of Cedrela odorata and to predict the effect of increasing temperature in two scenarios of climate change. Seeds were placed in germination chambers at constant temperatures ranging from 5 ± 2 to 45 ± 2 °C. Germination rate was analyzed in order to calculate cardinal temperatures and thermal time. The time required for germination of 50% of population was estimated for the current climate, as well as under the A2 and B2 scenarios for the year 2050. The results showed that base, optimal and maximal temperatures were −0.5 ± 0.09, 38 ± 1.6 and 53.3 ± 2.1 °C, respectively. Thermal time (θ1(50)) was 132.74 ± 2.60 °Cd, which in the current climate scenario accumulates after 5.5 days. Under the A2 scenario using the English model, this time is shortened to 4.5 days, while under scenario B2, the time is only 10 hours shorter than the current scenario. Under the German model, the accumulation of thermal time occurs 10 and 6.5 hours sooner than in the current climate under the A2 and B2 models, respectively. The seeds showed a wide range of temperatures for germination, and according to the climate change scenarios, the thermal time accumulates over a shorter period, accelerating the germination of seeds in the understory. This is the first report of a threshold model for C. odorata, one of the most important forest species in tropical environments.

Thermal Niche for Seed Germination and Species Distribution Modelling of Swietenia macrophylla King (Mahogany) under Climate Change Scenarios

“…For the intermediate future (2050) and distant future (2070), the French (CNRMCM5), American (GFDL-CM3), English (HADGEM2-ES) and German (MPI-ESM-LR) models predict an increase in temperature due to the high emissions of greenhouse gases, which will lead to the thermal sum ( • Cd) accumulating in less time for S. macrophylla. This coincides with previous report for C. odorata [34]. According to Rajjou et al [37] optimal temperatures tend to be higher for tropical trees, were germination speed increases, and faster germination ensures the establishment of individuals to compete for space [47].…”

“…The seed germination of S. macrophylla was influenced by temperature. The highest germination percentage was recorded in the range of 25-35 • C, which coincides with Sol-Sánchez et al [30], who obtained 100% germination in seeds of this species at 30 • C. The highest germination percentages occurred below the optimal temperature (sub-optimal range), which coincides with results reported by Sampayo-Maldonado et al [34] for Cedrela odorata. Calzada-López et al [32] mentioned that the temperature at which the germination percentage is the highest does not always coincide with the temperature at which the fastest germination speed occurs (optimal temperature).…”

“…According to Rajjou et al [37], temperature has an effect on the enzymes that regulate the speed of the biochemical reactions that occur within the seeds after rehydration. The fastest germination speed occurred at 35 ± 2 • C, which coincides with results reported for C. odorata [34].…”

“…This is the first time that to our knowledge the thermal time has been reported for S. macrophylla. In this study, the thermal time for S. macrophylla (θ 1 (50)) in the sub-optimal temperature range was 189.091 ± 4.239 • Cd, which is higher than that, reported for Cedrela fissilis of 157 ± 20 • Cd [39], and much more than the thermal time for C. odorata of 132.74 ± 2.6 • Cd [34]. According to Parra-Coronado et al [33] and Normand and Léchaudel [49], the late-successional tropical trees require shorter times to reach different phenological stages than the climax trees.…”

“…The optimal temperature was 37.3 ± 1.3 • C and is directly related with a faster germination speed, which is very similar to C. odorata (38 ± 1.6 • C), that share the same environmental niche [34]. This coincides with Daibes et al [39], since they mention that the optimal temperature for tropical trees is between 20 and 40 • C. According to Gilbertson et al [40]; Dürr et al [41] and Caroca et al [36], this is the temperature at which germination is fastest and a seedling is obtained in the least amount of time; which could be an advantage of the species to compete in high density forests.…”