Abstract：
Detecting changes in the phenological responses of herbaceous species as a function of predicted climate change is important for forecasting future scenarios for the functioning of dry tropical forests, especially when predicting an increase in the frequency and intensity of extreme droughts. Because of the sensitivity of plants to water availability, our study hypothesizes that if years become drier or wetter, herbaceous plants will synchronously change the onset, duration, and intensity of their vegetative phenophases. We used a historical series of 60 years of precipitation observations for the Caatinga vegetation to define daily average of precipitation for rainy (Twet), median (Tcontrol), and dry (Tdry) years. We simulated past average daily rainfall (Twet, Tcontrol, and Tdry) while growing two herbaceous perennials and two herbaceous annuals. We monitored plant growth and measured the activity (absence or presence) and intensity of vegetative phenophases. We used circular statistical analysis to assess differences between treatments. Our results revealed that leaf production was seasonal but relatively uniform for perennial species and highly seasonal (wet season) for annual species. Simulated dry years induced lower leaf emergence concentrated over a few months in annual species, but this effect was more strongly significant in one of the two perennial species. Both annual and perennial species can experience delayed and less intense leaf abscission during the rainy season in years with below-average precipitation. In contrast, large voluminous rains in years with above-average precipitation can accelerate and intensify the process of leaf renewal. If future precipitation reductions occur, the changes in phenological response indicate that the cover of annual and perennial herbaceous species in this study will likely decrease, altering the landscape and functioning of dry tropical forests. However, the potential trade-offs observed may help populations of these species to persist during years of severe drought in the Caatinga.
摘要：
检测作为预测的气候变化的函数的草本物种的物候响应的变化对于预测干燥的热带森林的功能的未来情景很重要。特别是在预测极端干旱的频率和强度增加时。由于植物对水的敏感性，我们的研究假设，如果年份变得更干燥或更潮湿，草本植物会同步改变发病，持续时间,以及它们的营养物候期的强度。我们使用了Caatinga植被的60年降水观测的历史系列来定义雨天（Twet）的日平均降水量，中位数（Tcontrol），和干（Tdry）年。我们模拟了过去的平均日降雨量(Twet，Tcontrol,和Tdry），同时种植两个多年生草本植物和两个草本一年生植物。我们监测了植物生长，并测量了营养物候期的活性（不存在或存在）和强度。我们使用循环统计分析来评估治疗之间的差异。我们的结果表明，多年生物种的叶片产量是季节性的，但相对均匀，而一年生物种的叶片产量则是高度季节性的（雨季）。模拟的干旱年份诱导的下部叶片出苗集中在一年生物种中的几个月内，但是这种影响在两个多年生物种之一中更为明显。在降水量低于平均水平的年份，一年生和多年生物种在雨季期间都会经历延迟和较少的叶片脱落。相比之下,降水量高于平均水平的年份大量降雨可以加速和加剧叶片更新过程。如果未来降水减少，物候响应的变化表明，本研究中一年生和多年生草本物种的覆盖率可能会降低，改变干旱热带森林的景观和功能。然而,观察到的潜在权衡可能有助于这些物种的种群在卡廷加严重干旱的年份中持续存在。
