Dry_spells_Brazilian_savanna_seedlings

The seedling stage represents a bottleneck in plants' life cycle, particularly in savanna environments, where the rainy season is the major window of opportunity for seedling development and recruitment of new individuals. However, an increase in the duration and frequency of dry spells (days without rain during the rainy season) is expected due to climate change, which may affect species recruitment and establishment. The aim of this study was to examine the effect of simulated dry spells on the growth performance and biomass of Qualea grandiflora and Tabebuia aurea seedlings. Seedlings (60 days-old) were exposed to three irrigation treatments (daily irrigation, irrigation every 8 days, and irrigation every 15 days) for 130 days. We found no mortality in any of the irrigation treatments for both species. Although the growth parameters of Q. grandiflora were not significantly affected by the dry spells, the species invested more in shoot growth than in root growth. In contrast, there was a significant decrease in the root dry mass, root:shoot ratio, root biomass fraction, and relative growth rate of T. aurea seedlings exposed to dry spells of 15 days; but there was a significant increase in the specific taproot length and shoot biomass fraction. Overall, the plants showed species-specific responses to the dry spell treatments, and dry spells of up to 15 days did not cause seedling mortality. Further, T. aurea seedlings invested more resources in taproot growth in response to dry spells. The development of deep-reaching taproots could be an effective physiological adaptation strategy for the survival and establishment of young plants and the resilience of native tree populations under future adverse climate scenarios.幼苗期是植物生活史中的关键瓶颈阶段，在稀树草原（savanna）生境中尤为如此——雨季是幼苗发育与新个体补充定居的核心窗口期。然而，受气候变化影响，雨季内无雨的干旱期（dry spells）的持续时长与发生频率预计将上升，这可能会对物种的补充与定居过程造成不利影响。 本研究旨在探究模拟干旱期对阔裂叶离柱木（Qualea grandiflora）与黄花风铃木（Tabebuia aurea）幼苗生长表现及生物量的影响。实验选取60日龄的幼苗，分别施以三种灌溉处理（每日灌溉、每8天灌溉1次、每15天灌溉1次），处理周期为130天。 结果显示，两种供试物种在所有灌溉处理组中均未出现幼苗死亡现象。尽管干旱期并未对阔裂叶离柱木的生长参数造成显著影响，但该物种将更多资源分配至地上部生长，而非地下根系生长。与之相反，经历15天干旱期的黄花风铃木幼苗，其根系干重、根冠比、根生物量分配比例以及相对生长率均出现显著下降；但其主根比长度与地上部生物量分配比例则显著升高。 整体而言，供试植物对干旱期处理呈现出物种特异性的响应模式，且最长达15天的干旱期并未造成幼苗死亡。此外，黄花风铃木幼苗会在干旱胁迫下将更多资源投入至主根生长。在未来的恶劣气候情景下，发达的深主根可作为一种有效的生理适应策略，助力幼苗存活与定居，并提升本土树木种群的恢复能力。