The most severe global warming is predicted to occur in the Amazon region of Brazil, with an estimated temperature increase of 4 to 8 °C between 2071 and 2100. Our study evaluated the effects of increased temperatures on germination success of seeds in the soil seed bank of secondary forests in Central Amazonia. Soil samples (3-cm depth) were collected in six secondary forests with different land-use histories and ages of regrowth. Soils from all sites were sieved and mixed, and germination and seedling development were assessed during 4 months of incubation in germination chambers at (1) a constant temperature of 25 °C and a 12:12 h alternating temperature regime of 20:30 °C, considered as controls; (2) a simulated 5 °C temperature increase to 30 °C and 25:35 °C and (3) a 10 °C temperature increase to 35 °C and 30:40 °C. To determine the effect of light vs. dark on germination, germination was compared for samples in light (12 h daily photoperiod) vs. continuously dark for 1 month, followed by 3 months in light. Six temperature conditions were tested with 30 subsamples each. In the mixed soil seed bank, 3640 seeds germinated, of which 18 families, 28 genera and 41 species (grouped in 20 trees, 11 shrubs, eight herbs and two lianas) could be identified. A light requirement for germination was detected for 94–97% of the species. Alternating temperatures did not stimulate germination in the dark. Seedling density m⁻² was 1.7 to 2.3 times higher at alternating (20:30 °C and 25:35 °C) than at constant temperatures (25 °C and 30 °C); but an increase of 10 °C decreased seedling density to 47% at 35 °C and 26% at 30:40 °C compared to control (100% at 25 °C and 20:30 °C); and furthermore increased seedling mortality. Thus, the secondary forest at the study area may maintain its integrity with a 5 °C but not with a 10 °C temperature increase. Species-specific sensitivities to temperature were detected. Temperature may function to fine-tune germination at a specific microsite, and the variety of germination requirements may enhance coexistence and maintenance of species diversity within the pioneer species subset. In general, seeds of tree species were more sensitive to increased temperatures than those of shrubs and herbs, supporting the hypothesis of replacement of the tropical forest by savanna-like vegetation in the Amazon region. Our results show that natural regeneration may be significantly affected by global warming and with potential to alter floristic composition.

预计最严重的全球变暖将发生在巴西的亚马逊地区，估计在2071年至2100年之间温度会升高4至8°C。我们的研究评估了温度升高对土壤种子库中种子发芽成功的影响。中亚马孙地区的次生林 土壤样本（3厘米深）收集在六个具有不同土地利用历史和再生年龄的次生林中。将所有地点的土壤过筛并混合，并在（1）恒定温度25°C和12:12 h交替温度20:30°C的发芽室内孵育4个月期间评估发芽和幼苗发育，视为对照；（2）模拟将5°C的温度升高至30°C和25:35°C，以及（3）将10°C的温度升高至35°C和30:40°C。为了确定光照与黑暗对发芽的影响，比较了光照（每天光照12小时）与持续黑暗1个月，然后光照3个月的样品的发芽率。测试了六个温度条件，每个条件有30个子样本。在混合土壤种子库中，可以鉴定出3640粒种子，其中有18科28属41种（分为20种树，11种灌木，8种药草和2种藤本植物）。94-97％的物种检测到轻度萌发的要求。交替的温度不会在黑暗中刺激发芽。幼苗密度m 在混合土壤种子库中，可以鉴定出3640粒种子，其中有18科28属41种（分为20种树，11种灌木，8种药草和2种藤本植物）。94-97％的物种检测到轻度萌发的要求。交替的温度不会在黑暗中刺激发芽。幼苗密度m 在混合土壤种子库中，可以鉴定出3640粒种子，其中有18科28属41种（分为20种树，11种灌木，8种药草和2种藤本植物）。94-97％的物种检测到轻度萌发的要求。交替的温度不会在黑暗中刺激发芽。幼苗密度m⁻²交替（20:30°C和25:35°C）时的温度比恒定温度（25°C和30°C）时高1.7至2.3倍; 但与对照相比（25°C和20:30°C为100％），温度每升高10°C，幼苗密度在35°C时降低至47％，在30:40°C时降低至26％；并且进一步增加了幼苗的死亡率。因此，研究区域的次生林可以在5°C的温度下保持其完整性，而在10°C的温度下不能保持其完整性。检测到物种对温度的敏感性。温度可以起到微调特定微场所发芽的作用，发芽要求的多样性可以增强先锋物种子集中物种的共存性和维持性。一般而言，树种的种子比灌木和草药对温度升高更为敏感，支持在亚马逊地区用热带稀树草原植被取代热带森林的假说。我们的结果表明，自然更新可能会受到全球变暖的影响，并且有可能改变植物区系。