干旱与重吸水对人工藻结皮光合特性的影响

通过接种蓝藻构建人工藻结皮促进荒漠地区生物结皮的生长发育以及整个荒漠生态系统的恢复,被认为是一种行之有效的荒漠化控制方法。在构建藻结皮过程中,接种的蓝藻以及形成的藻结皮,经常遭受干旱等环境条件的胁迫。本研究通过室内人工构建藻结皮,对形成的藻结皮进行干旱及重吸水处理,在此过程中监测结皮光合生物量、多糖含量以及结皮光合特性的变化规律。结果发现,干旱处理1d后,结皮蓝藻胞外多糖的分泌明显增加(p0.05);当结皮完全进入干燥状态后,结皮蓝藻停止所有代谢活动,结皮生物量及胞外多糖含量保持在一个相对稳定的水平。在结皮重吸水后,结皮初始荧光Fo能够迅速恢复,并在10 min内达到最大;之后Fo逐渐下降,同时结皮光合活性(Fv/Fm)按照函数y=ax/(b+x)逐渐上升并达到稳定。此外,在不同水分条件下,结皮光合活性随着水分的增加逐渐增加;然而结皮净光合速率(Pn)却随着水分的增加先增加后又下降,呈现单峰变化模式。该研究表明结皮蓝藻的代谢调节在人工藻结皮适应荒漠干旱环境中具有重要的作用,这对于进一步理解蓝藻乃至蓝藻结皮对干旱胁迫的适应,以及荒漠化防治中人工藻结皮的构建、维护、管理具有重要的理论与实践意义。

Effects of drought and rehydration on photosynthetic characteristics of artificial algal crusts

Constructing artificial algal crusts by means of cyanobacterial inoculation could promote growth and development of biological crusts on sand dunes in desert regions and restoration of the whole desert ecosystem, and hence is considered as an effective approach to desertification control. However, in the course of constructing artificial algal crusts, the inoculated cyanobacteria or formed crusts are susceptible to various environmental stresses, mainly drought in the desert regions. An in-lab experiment was carried out to have artificial algal crusts exposed to drought and rehydration, and to explore their effects on crust biomass, exopolysaccharides and photosynthesis of the crusts. It was found that drought for one day could provisionally promote secretion of crust cyanobacterial exopolysaccharides (p<0.05). Once the crusts were completely dried, cyanobacteria of the crusts stopped all their metabolic activities, and biomass and exopolysaccharides content of the crusts remained at a certain relatively steady level. After rehydration, crust original fluorescence Fo got recovered quickly and reached the maximum within 10 min. Afterwards, Fo decreased gradually and crust photosynthetic activity (Fv/Fm) increased and leveled off steadily in line with the function y = ax/(b x). In addition, under different water conditions, crust photosynthetic activity increased with the increasing crust water content, but crust net photosynthesis (Pn) first increased and then decreased with the increasing crust water content, showing a unimodal variation pattern. This study suggests that the regulation of crust cyanobacteria in metabolism plays an important role in the adaptation of artificial algal crusts to arid desert environmental conditions. The findings may help us further understand how crust cyanobacteria or biological soil crusts adapt to drought stress, and provide theoretical basis and practical lessons for construction, maintenance and management of artificial algal crusts in desertification control.