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Abstract Plants in dryland ecosystems experience extreme daily and seasonal fluctuations in light, temperature, and water availability. We used an in situ field experiment to uncover the effects of natural and reduced levels of ultraviolet radiation (UV) on maximum PSII quantum efficiency (Fv/Fm), relative abundance of photosynthetic pigments and antioxidants, and the transcriptome in the desiccation-tolerant desert moss Syntrichia caninervis. We tested the hypotheses that: (i) S. caninervis plants undergo sustained thermal quenching of light [non-photochemical quenching (NPQ)] while desiccated and after rehydration; (ii) a reduction of UV will result in improved recovery of Fv/Fm; but (iii) 1 year of UV removal will de-harden plants and increase vulnerability to UV damage, indicated by a reduction in Fv/Fm. All field-collected plants had extremely low Fv/Fm after initial rehydration but recovered over 8 d in lab-simulated winter conditions. UV-filtered plants had lower Fv/Fm during recovery, higher concentrations of photoprotective pigments and antioxidants such as zeaxanthin and tocopherols, and lower concentrations of neoxanthin and Chl b than plants exposed to near natural UV levels. Field-grown S. caninervis underwent sustained NPQ that took days to relax and for efficient photosynthesis to resume. Reduction of solar UV radiation adversely affected recovery of Fv/Fm following rehydration. 

Abstract Plant functional trait analyses have focused almost exclusively on vascular plants, but bryophytes comprise ancient and diverse plant lineages that have widespread global distributions and important ecological functions in terrestrial ecosystems. We examined a diverse clade of dryland mosses,Syntrichia, and studied carbon balance during a precipitation event (C‐balance), a functional trait related to physiological functioning, desiccation tolerance, survival, and ecosystem carbon and nitrogen cycling. We examined variability in C‐balance among 14 genotypes ofSyntrichiaand measured an additional 10 physiological and 13 morphological traits at the cell, leaf, shoot, and clump level. C‐balance varied 20‐fold among genotypes, and highest C‐balances were associated with long, narrow leaves with awns, and small cells with thick cell walls, traits that may influence water uptake and retention during a precipitation event. Ordination analyses revealed that the axis most strongly correlated with C‐balance included the maximum chlorophyll fluorescence,F_m, indicating the importance of photosystem II health for C exchange. C‐balance represents a key functional trait in bryophytes, but its measurement is time intensive and not feasible to measure on large scales. We propose two models (using physiological and morphological traits) to predict C‐balance, whereby identifying simpler to measure traits for trait databases. 

Summary With global climate change, water scarcity threatens whole agro/ecosystems. The desert mossSyntrichia caninervis, an extremophile, offers novel insights into surviving desiccation and heat. The sequencedS. caninervisgenome consists of 13 chromosomes containing 16 545 protein‐coding genes and 2666 unplaced scaffolds. Syntenic relationships within theS.caninervisandPhyscomitrellapatensgenomes indicate theS. caninervisgenome has undergone a single whole genome duplication event (compared to two forP. patens) and evidence suggests chromosomal or segmental losses in the evolutionary history ofS. caninervis. The genome contains a large sex chromosome composed primarily of repetitive sequences with a large number ofCopiaandGypsyelements. Orthogroup analyses revealed an expansion ofELIPgenes encoding proteins important in photoprotection. The transcriptomic response to desiccation identified four structural clusters of novel genes. The genomic resources established for this extremophile offer new perspectives for understanding the evolution of desiccation tolerance in plants.