Marques M C M, Oliveira P E A M
Laboratório de Ecologia Vegetal, Departamento de Botânica, Universidade Federal do Paraná, Curitiba, Brazil.
Plant Biol (Stuttg). 2008 Sep;10(5):596-603. doi: 10.1111/j.1438-8677.2008.00061.x.
Seasonal tropical forests show rhythms in reproductive activities due to water stress during dry seasons. If both seed dispersal and seed germination occur in the best environmental conditions, mortality will be minimised and forest regeneration will occur. To evaluate whether non-seasonal forests also show rhythms, for 2 years we studied the seed rain and seedling emergence in two sandy coastal forests (flooded and unflooded) in southern Brazil. In each forest, one 100 x 30-m grid was marked and inside it 30 stations comprising two seed traps (0.5 x 0.5 m each) and one plot (2 x 2 m) were established for monthly monitoring of seed rain and a seedling emergence study, respectively. Despite differences in soil moisture and incident light on the understorey, flooded and unflooded forests had similar dispersal and germination patterns. Seed rain was seasonal and bimodal (peaks at the end of the wetter season and in the less wet season) and seedling emergence was seasonal and unimodal (peaking in the wetter season). Approximately 57% of the total species number had seedling emergence 4 or more months after dispersal. Therefore, both seed dormancy and the timing of seed dispersal drive the rhythm of seedling emergence in these forests. The peak in germination occurs in the wetter season, when soil fertility is higher and other phenological events also occur. The strong seasonality in these plant communities, even in this weakly seasonal climate, suggests that factors such as daylength, plant sensitivity to small changes in the environment (e.g. water and nutrient availability) or phylogenetic constraints cause seasonal rhythms in the plants.
季节性热带森林由于旱季的水分胁迫而呈现出生殖活动的节律。如果种子传播和种子萌发都发生在最佳环境条件下，死亡率将降至最低，森林更新将会发生。为了评估非季节性森林是否也有节律，我们在巴西南部的两片沿海沙地森林（水淹和未水淹）中对种子雨和幼苗出土情况进行了为期两年的研究。在每片森林中，划定了一个100×30米的网格，在网格内分别设立了30个监测站，其中包括两个种子收集器（每个0.5×0.5米）和一个样地（2×2米），分别用于每月监测种子雨和进行幼苗出土研究。尽管林下土壤湿度和入射光存在差异，但水淹森林和未水淹森林的种子传播和萌发模式相似。种子雨具有季节性且呈双峰模式（在较湿润季节末期和较干燥季节出现峰值），而幼苗出土具有季节性且呈单峰模式（在较湿润季节达到峰值）。约57%的物种总数在种子传播4个月或更长时间后出现幼苗出土。因此，种子休眠和种子传播时间共同驱动了这些森林中幼苗出土的节律。萌发高峰出现在较湿润的季节，此时土壤肥力较高，其他物候事件也会发生。这些植物群落中强烈的季节性，即使是在这种季节性较弱的气候条件下，表明诸如日照长度、植物对环境微小变化（如水和养分供应）的敏感性或系统发育限制等因素导致了植物的季节性节律。
