Cyanobacteria, as key biocrust components, provide a variety of ecosystem functions in drylands. In this study, to identify whether a cyanobacterial community shift is involved in biocrust succession and whether this is linked to altered ecological functions, we investigated cyanobacterial composition, total carbon and nitrogen contents of biocrusts in the Gurbantunggut Desert. Our findings showed that the biocrust cyanobacteria in the Gurbantunggut desert were mostly filamentous, coexisting with abundant unicellular colonial Chroococcidiopsis. Heterocystous Nostoc, Scytonema and Tolypothrix always represented the majority of biocrust nitrogen-fixing organisms, comprising an average of 92% of the nifH gene reads. Community analysis showed a clear shift in prokaryotic community composition associated with biocrust succession from cyanobacteria- to lichen- and moss-dominated biocrusts, and filamentous non-nitrogen-fixing cyanobacteria-dominated communities were gradually replaced by nitrogen-fixing and unicellular colonial communities. Along the succession, there were concomitant reductions in cyanobacterial relative abundance, whereas Chl-a, total carbon and nitrogen contents increased. Concurrently, distinct carbon and nitrogen stores shifts occurred, implying that the main ecological contribution of cyanobacteria in biocrusts changes from carbon- to nitrogen-fixation along with the succession. Our results suggest that any activity that reverses biocrust succession will influence cyanobacterial community composition and eventually lead to large reductions in soil carbon and nitrogen stores.

中文翻译：

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古尔班通古特沙漠中与生物结皮演替相关的蓝藻群落组成及其功能变化

蓝藻作为关键的生物结皮成分，在旱地提供多种生态系统功能。在这项研究中，为了确定蓝藻群落变化是否涉及生物结皮演替以及这是否与生态功能的改变有关，我们调查了古尔班通古特沙漠中生物结皮的蓝藻组成、总碳和氮含量。我们的研究结果表明，古尔班通古特沙漠中的生物结壳蓝细菌主要是丝状的，并与大量的单细胞菌群 Chroococcidiopsis共存。异囊念珠菌, Scytonema和Tolypothrix始终代表大多数生物结壳固氮生物，平均占 nifH 基因读数的 92%。群落分析表明，与生物结皮演替相关的原核生物群落组成发生了明显变化，从蓝藻到地衣和苔藓主导的生物结皮，并且以丝状非固氮蓝藻为主的群落逐渐被固氮和单细胞群落取代。在演替过程中，蓝藻相对丰度随之降低，而叶绿素a、总碳和氮含量增加。同时，发生了明显的碳​​和氮储存变化，这意味着蓝藻在生物结皮中的主要生态贡献随着演替从固碳转变为固氮。