Dryland biological soil crust cyanobacteria show unexpected decreases in abundance under long‐term elevated CO₂

Abstract

Biological soil crusts (biocrusts) cover soil surfaces in many drylands globally. The impacts of 10 years of elevated atmospheric CO2 on the cyanobacteria in biocrusts of an arid shrubland were examined at a large manipulated experiment in Nevada, USA. Cyanobacteria-specific quantitative PCR surveys of cyanobacteria small-subunit (SSU) rRNA genes suggested a reduction in biocrust cyanobacterial biomass in the elevated CO2 treatment relative to the ambient controls. Additionally, SSU rRNA gene libraries and shotgun metagenomes showed reduced representation of cyanobacteria in the total microbial community. Taxonomic composition of the cyanobacteria was similar under ambient and elevated CO2 conditions, indicating the decline was manifest across multiple cyanobacterial lineages. Recruitment of cyanobacteria sequences from replicate shotgun metagenomes to cyanobacterial genomes representing major biocrust orders also suggested decreased abundance of cyanobacteria sequences across the majority of genomes tested. Functional assignment of cyanobacteria-related shotgun metagenome sequences indicated that four subsystem categories, three related to oxidative stress, were differentially abundant in relation to the elevated CO2 treatment. Taken together, these results suggest that elevated CO2 affected a generalized decrease in cyanobacteria in the biocrusts and may have favoured cyanobacteria with altered gene inventories for coping with oxidative stress.

Climate Change and Physical Disturbance Manipulations Result in Distinct Biological Soil Crust Communities

“…Cyanobacteria qPCR measured the abundance of Cyanobacteria 16S rRNA genes, acting as a secondary measure of cyanobacterial biomass. The Cyanobacteria qPCR was performed with primers that target the V2 to V4 variable regions, using CYA 359 (5=-GGGGAATYTTCCGCAATGGG-3=) and an equimolar mixture of CYA-781RA (5=-GACTACTGGGGTATCT AATCCCATT-3=) and CYA-781RB (5=-GACTACAGGGGTATCTAATC CCTTT-3=) with reaction mixtures, standards, and thermocycling conditions as previously described (27,28). Analysis of variance (ANOVA) was used for treatment comparisons of the DNA, chlorophyll a, and qPCR data sets, followed by pairwise t tests (Arches or ISKY, where two treatments were performed) or Tukey's honestly significant difference (HSD) mean separation procedure (CV experiment, where four treatments were performed) using the JMP software package.…”

Biocrusts in the Context of Global Change

“…At the same Desert FACE site, molecular and metagenomic analyses of the biocrust bacterial community showed that cyanobacteria exhibited reduced total biomass and constituted a lower proportion of the biocrust bacterial community after 10 years of elevated CO 2 relative to the ambient CO 2 controls (Haimovich-Dayan et al 2011;Steven et al 2012). Functional analyses of biocrust metagenomes showed that cyanobacterial genes related to oxidative stress responses were higher in biocrusts exposed to elevated CO 2 conditions compared to ambient conditions, suggesting that increased oxidative stress may play a role in the cyanobacterial response (Steven et al 2012). Thus, the photosynthetic cyanobacteria in biocrusts responded negatively to long-term elevated CO 2 conditions in the field, highlighting the complexity of biocrust community responses to changing CO 2 concentrations.…”

Nitrogen inputs and losses in response to chronic CO<sub>2</sub> exposure in a subtropical oak woodland

“…Growth and N 2 fixation in N 2 -fixing plants can respond positively to elevated CO 2 (Cernusak et al, 2011), but in many cases these responses are absent, e.g., N-fixers in temperate grasslands (Garten et al, 2008;Zhang et al, 2011), Alnus (Temperton et al, 2003;Millett et al, 2012), and ocean cyanobacteria (Czerny et al, 2009;Law et al, 2012). Chronic CO 2 exposure was found to reduce cyanobacterial abundance in desert crusts (Steven, 2012). Our finding that nonsymbiotic 3332 B.…”