Drought can lead to important shifts in population dynamics if it occurs during seedling establishment. With the aim of elucidating the underlying mechanisms of drought tolerance and resilience, here we monitored the survival of seedlings of the Mediterranean shrub Cistus albidus L. throughout a year growing in the natural Park of the Montserrat Mountains (Spain) and, additionally, we studied the response to severe drought and subsequent recovery after rewatering of seedlings grown in growth chambers. To find possible mechanisms explaining how seedlings respond to drought, growth and survival together with physiological-related parameters such as chlorophyll contents, vitamin E and stress-related phytohormones were measured. We found that survival decreased by 30% at the end of summer and that the main proxy of seedling survival was total chlorophyll. This proxy was further confirmed in the growth chambers, where we found that seedlings that recovered from drought had higher levels of total chlorophyll compared with the seedlings that did not recover. Furthermore, modulation of vitamin E and jasmonates contents appeared to be crucial in the drought response of C. albidus seedlings. We propose a prediction model of survival that includes total chlorophyll height, leaf mass area and maximum photosystem II efficiency with chlorophyll contents being a good long-term predictor of C. albidus seedling survival under severe stress, which, in turn, could help to better foresee population fluctuations in the field.

中文翻译：

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白岩蔷薇幼苗的生死阈值：耐旱性和恢复力的机制

如果干旱发生在幼苗建立期间，它会导致种群动态发生重大变化。为了阐明耐旱性和恢复力的潜在机制，我们在这里监测了地中海灌木Cistus albidus幼苗的存活情况L. 在蒙特塞拉特山脉（西班牙）的自然公园中全年生长，此外，我们研究了对生长室中生长的幼苗重新浇水后对严重干旱的反应和随后的恢复。为了找到解释幼苗如何响应干旱、生长和存活的可能机制，以及测量了叶绿素含量、维生素 E 和压力相关植物激素等生理相关参数。我们发现夏末成活率下降了 30%，幼苗成活率的主要指标是总叶绿素。这一代表在生长室中得到了进一步证实，我们发现从干旱中恢复的幼苗与未恢复的幼苗相比具有更高水平的总叶绿素。此外，C. albidus幼苗。我们提出了一种生存预测模型，其中包括叶绿素总高度、叶质量面积和最大光系统 II 效率，叶绿素含量是严重胁迫下C. albidus幼苗存活的良好长期预测因子，反过来，这有助于更好地预见该领域的人口波动。