Short-term succession of marine microbial fouling communities and the identification of primary and secondary colonizers

Microbial succession during the initial stages of marine biofouling has been rarely studied, especially in the Arabian Gulf. This study was undertaken to follow temporal shifts in biofouling communities in order to identify primary and secondary colonizers. Quantitative analysis revealed a significant increase in total biomass, coverage of macrofoulers, chlorophyll a concentrations, and bacterial counts with time. The relative abundance of the adnate diatoms increased with time, whereas it decreased in the case of the plocon diatoms. Non-metric multidimensional scaling (NMDS) ordination based on MiSeq data placed the bacterial communities in three distinct clusters, depending on the time of sampling. While the relative abundance of Alphaproteobacteria and Flavobacteriia decreased with time, suggesting their role as primary colonizers, the relative abundance of Actinobacteria and Planctomycetia increased with time, suggesting their role as secondary colonizers. Biofouling is a dynamic process that involves temporal quantitative and qualitative shifts in the micro- and macrofouling communities.     

Adaptive responses to drought of two Retama raetam subspecies from Tunisia

两个突尼斯细枝豆属植物亚种对干旱的适应性响应 干旱生境植物的生存和生态分布主要取决于水的可获得性以及植物抵御干旱的生理适应能力。在 本研究中，我们比较了来自突尼斯的细枝豆属植物Retama raetam的两个亚种对干旱的生理响应，其中一 种生长在沙漠气候下(raetam亚种)，另一种生长于海岸带(bovei亚种)。为了对这两个亚种进行生理表征并揭示它们耐旱性的主要机制，从受干旱胁迫最长达一个月的四月龄植株中获取了多项参数，涉及植株的萌发、生长、光合作用(净光合速率、细胞内CO₂浓度、蒸腾速率、气孔导度和水分利用效率)和渗透物(脯氨酸、甜菜碱和总可溶性糖)积累等。研究结果表明，干旱会显著抑制植株的萌发、生长，对所研究的各项光合参数也都产生很大的负面影响。经过3周的处理后，bovei亚种受到了干旱条件的显著影响，其光合作用速率与对照相比最高下降了7倍。与此同时，该亚种中出现了对脯氨酸和甜菜碱的显著积累(相较于灌溉条件下的对照)，但远低于raetam亚种；在raetam亚种中，脯氨酸和甜菜碱分别增加至相应对照的24和6倍。综上所述，相较于生长在半干旱海岸气候下的细枝豆属植物种群，生长于沙漠地区的种群对干旱胁迫表现出更强的耐性，表明这种耐性在很大程度上取决于渗透物质在体内的累积。