Freeze-thaw cycles change the physiological sensitivity of Syntrichia caninervis to snow cover

Insights into the adaptive response of extremotolerant desert moss Syntrichia caninervis to extreme high temperature

Moss has remarkable abilities to survive harsh environmental conditions, making it a key species in habitat restoration following disturbances such as fire, exploring these abilities informs efforts to improve stress tolerance in other plants and enhances our understanding of the evolution of stress tolerance. Here, we report a new record of thermal tolerance for the dried moss Syntrichia caninervis. Dry moss cuttings survived 60 min at 120 °C, exceeding the previous record of 30 min at 120 °C. We also investigated the morphology and gene expression profile of the shoots from dried S. caninervis shoots exposed to 80, 100, 110, and 120 °C for 10, 20, 30, or 60 min, using 20 °C as the control temperature. Shoots were allowed to regenerate on native sand under recovery conditions, after which we examined them daily for 56 days. Over this period, our observations indicated that lethal time-temperature combinations abolished shoot regeneration potential, whereas sub-lethal combinations lengthened the emergence time of protonema and new shoots, and led to decreased protonema emergence area. In addition, we determined that the transcript levels of nine genes (ScHSP70-3, ScHSP70-12, ScHSP70-15, ScELIP1, ScELIP2, ScABA1, ScABA3, ScNCED, and ScDREB) were induced upon temperature stress, as assessed following 120 °C 30 min of heat stress exposure. Few extant desert mosses encounter temperatures this high in nature, suggesting that the observed tolerance is unlikely to be the result of adaptation to current or recent climate conditions. We hope that the results of this study will help us understand the mechanisms by which organisms such as mosses survive thermal stress and how these mechanisms evolved.

ScDREBA5 Enhances Cold Tolerance by Regulating Photosynthetic and Antioxidant Genes in the Desert Moss Syntrichia caninervis

Extreme cold events, becoming more frequent, affect plant growth and development. Much is known about C-repeat binding transcription factor (CBF)-dependent cold-signaling pathways in plants. However, the CBF-independent regulatory pathway in angiosperms is unclear, and the cold-signaling pathways in non-angiosperms lacking CBFs, such as the extremely cold-tolerant desert moss Syntrichia caninervis, are largely unknown. In this study, we determined that fully hydrated S. caninervis without cold acclimation could tolerate a low-temperature of -16°C. Transcriptome analysis of S. caninervis under 4°C and -4°C treatments revealed that sugar and energy metabolism, lipid metabolism and antioxidant activity were altered in response to cold stress, and surprisingly, most photosynthesis-related genes were upregulated under cold treatment. Transcription factors analysis revealed that A-5 DREB genes, which share a common origin with CBFs, are the hubs in the freezing-stress response of S. caninervis, in which ScDREBA5 was upregulated ~1000-fold. Overexpressing ScDREBA5 significantly enhanced freezing tolerance in both S. caninervis and Physcomitrium patens by upregulating genes involved in photosynthetic and antioxidant pathways. This is the first study to uncover the mechanism regulating the cold-stress response in S. caninervis. Our findings increase our understanding of different cold-stress response strategies in non-angiosperms and provide valuable genetic resources for breeding cold-tolerant crops.

Exogenous γ-aminobutyric acid (GABA) effectively alleviates the synergistic inhibitory effect of freeze-thaw and copper combined stress on rye seedling growth

Rye (Secale cereale L.) may suffer from combined stress due to freeze-thaw cycles and copper (Cu) pollution during cultivation in grasslands. This study aims to investigate the effects of combined freeze-thaw and Cu stress on the physiological characteristics of rye seedlings and to assess the potential of exogenous GABA in mitigating these effects. The results indicated that root length, shoot length, fresh weight, and dry weight of rye seedlings were significantly reduced under combined stress, indicating synergistic inhibition. Combined stress impaired photosynthesis, increased MDA and H2O2 levels, and reduced endogenous GABA, thereby exacerbating physiological damage in rye seedlings. Treatment with exogenous GABA effectively alleviated growth inhibition and enhanced photosynthesis. Furthermore, exogenous GABA underscores its role in adaptation to combined stress by increasing soluble protein content, activating the antioxidant system, regulating GABA metabolism, and enhancing metal detoxification capacity, thereby improving stress tolerance. This finding not only contributes to enhancing the stability of grassland ecosystems but also provides a theoretical foundation for the future application of GABA in agricultural production, particularly in crop protection under environmental pollution and extreme climatic conditions.

Bryophytes adapt to open-pit coal mine environments by changing their functional traits in response to heavy metal-induced soil environmental changes

Plants have unique adaptability to heavy metal pollution. However, the adaptation strategies of bryophytes are still unclear. In order to better understand the response of bryophytes to different heavy metal and the adaptation mechanisms of different species to heavy metal pollution, we studied soil physicochemical properties, distribution of heavy metal elements, ecological risk assessment and the community structure, functional characteristics of bryophytes in large open-pit coal mines in Inner Mongolia. The results indicate that: (1) The soil in three open-pit mining areas currently does not pose an ecological risk from the heavy metal pollution, but high concentrations of Zn and Hg are found in most parts of the study area; (2) The presence of a single heavy metal drives the distribution of specific taxa of bryophytes. Apart from Hg, Pb, and Zn, all the other heavy metals significantly impact the community structure of bryophytes; (3) With the exception of Pb and Hg, all the other heavy metals have an influence on the functional traits of bryophytes; 4) Different taxa of bryophytes will adapt to changes in soil environments caused by heavy metal pollution by altering their functional traits (blades, leaf cells, or plant size).

Expression Profiling Analysis of the SWEET Gene Family in In Vitro Pitaya Under Low-Temperature Stress and Study of Its Cold Resistance Mechanism

Pitaya (Hylocereus undatus) fruit is an attractive, nutrient-rich tropical fruit with commercial value. However, low-temperature stress severely affects the yield and quality of pitaya. The relevant mechanisms involved in the response of pitaya to low-temperature stress remain unclear. To study whether the SWEET gene family mediates the response of H. undatus to low-temperature stress and the related mechanisms, we performed genome-wide identification of the SWEET gene family in pitaya, and we used 'Baiyulong' tissue-cultured plantlets as material in the present study. We identified 28 members of the SWEET gene family from the H. undatus genome and divided these family members into four groups. Members of this gene family presented some differences in the sequences of introns and exons, but the gene structure, especially the motifs, presented relatively conserved characteristics. The promoter regions of most HuSWEETs have multiple stress- or hormone-related cis-elements. Three duplicated gene pairs were identified, including one tandem duplication gene and two fragment duplication gene pairs. The results revealed that the SWEET genes may regulate the transport and distribution of soluble sugars in plants; indirectly regulate the enzyme activities of CAT, POD, and T-SOD through its expression products; and are involved in the response of pitaya to low-temperature stress and play vital roles in this process. After ABA and MeJA treatment, the expression of HuSWEETs changed significantly, and the cold stress was also alleviated. This study elucidated the molecular mechanism and physiological changes in the SWEET gene in sugar metabolism and distribution of pitaya when it experiences low-temperature stress and provided a theoretical basis for cold-resistant pitaya variety breeding.

The extremotolerant desert moss Syntrichia caninervis is a promising pioneer plant for colonizing extraterrestrial environments

Many plans to establish human settlements on other planets focus on adapting crops to growth in controlled environments. However, these settlements will also require pioneer plants that can grow in the soils and harsh conditions found in extraterrestrial environments, such as those on Mars. Here, we report the extraordinary environmental resilience of Syntrichia caninervis, a desert moss that thrives in various extreme environments. S. caninervis has remarkable desiccation tolerance; even after losing >98% of its cellular water content, it can recover photosynthetic and physiological activities within seconds after rehydration. Intact plants can tolerate ultra-low temperatures and regenerate even after being stored in a freezer at -80°C for 5 years or in liquid nitrogen for 1 month. S. caninervis also has super-resistance to gamma irradiation and can survive and maintain vitality in simulated Mars conditions; i.e., when simultaneously exposed to an anoxic atmosphere, extreme desiccation, low temperatures, and intense UV radiation. Our study shows that S. caninervis is among the most stress tolerant organisms. This work provides fundamental insights into the multi-stress tolerance of the desert moss S. caninervis, a promising candidate pioneer plant for colonizing extraterrestrial environments, laying the foundation for building biologically sustainable human habitats beyond Earth.

ROS scavenging enzyme-encoding genes play important roles in the desert moss Syntrichia caninervis response to extreme cold and desiccation stresses

Abiotic stress is one of the major environmental constraints limiting plant growth. Syntrichia caninervis is one of the unique plant models that can cope with harsh environments. Reactive oxygen species (ROS) are a vital signaling molecule for protecting plants from oxidative stress, but research on ROS in S. caninervis is limited. Here, we identified 112 ROS genes in S. caninervis, including 40 GSTs, 51 PODs, 9 SODs, 6 CATs, 3 GPXs and 3 APXs families. GO and KEGG analyses showed that ROS genes are involved in responses to various stimuli and phenylpropanoid biosynthesis. ROS genes contain many stress-responsive and hormonal cis-elements in their promoter regions. More ROS genes were induced by cold stress than desiccation stress, and both conditions changed the transcript abundances of several ROS genes. CAT and POD, H2O2, MDA, and GSH were also induced under biotic stress, specifically CAT activity. The results indicated that the ScCAT genes and their activities could be strongly associated with the regulation of ROS production. This is the first systematic identification of ROS genes in S. caninervis and our findings contribute to further research into the roles of ScROS adjustment under abiotic stress while also providing excellent genetic resources for plant breeding.

Artemisinin and Ambrosia trifida extract aggravate the effects of short freeze-thaw stress in winter rye (Secale cereale) seedlings

The freeze-thaw and allelopathy from alien giant ragweed (Ambrosia trifida L.) and artemisinin have led to a serious stress to plants, influencing the agricultural quality and crop yield in north-east China. Yet, little is known how allelopathy affect plants under the freeze-thaw process. In this study, the characteristics in winter rye (Secale cereale L.) seedlings were investigated by laboratory simulation. The results showed that during the freezing process, application of artemisinin and A. trifida extract significantly increased the soluble protein content and accelerated lipid peroxidation, while they significantly inhibited antioxidant enzymes, photosynthesis and respiration (P <0.05). During the thawing process, the freezing pressure decreased, and activities of antioxidant enzymes were significantly improved to mitigate artemisinin and A. trifida extract induced stress (P <0.05). In addition, the sensitivity of the investigated metabolic processes in winter rye seedlings were highest to artemisinin and A. trifida extract in the freezing process. This study suggested that the stress response induced by artemisinin and A. trifida extract on winter rye seedlings in the freezing process was greater than that in the thawing process.

A Na+/H+ antiporter-encoding salt overly sensitive 1 gene, LpSOS1, involved in positively regulating the salt tolerance in Lilium pumilum

Lilium pumilum has a strong salt tolerance. However, the molecular mechanism underlying its salt tolerance remains unexplored. Here, LpSOS1 was cloned from L. pumilum and found to be significantly enriched at high NaCl concentrations (100 mM). In tobacco epidermal cells, localization analysis showed that the LpSOS1 protein was primarily located in the plasma membrane. Overexpression of LpSOS1 resulted in up-regulation of salt stress tolerance in Arabidopsis, as indicated by reduced malondialdehyde levels and Na⁺/K⁺ ratio, and increased activity of antioxidant reductases (including superoxide dismutase, peroxidase, and catalase). Treatment with NaCl resulted in improved growth, as evidenced by increased biomass, root length, and lateral root growth, in both sos1 mutant (atsos1) and wild-type (WT) Arabidopsis plants that overexpressed LpSOS1,Under NaCl treatment,atsos1 and WT Arabidopsis plants overexpressing LpSOS1 exhibited better growth, with higher biomass, root length, and lateral root quantity, whereas in the absence of LpSOS1 overexpression, the plants of both lines were wilted and chlorotic and even died under salt stress. When exposed to salt stress, the expression of stress-related genes was notably upregulated in the LpSOS1 overexpression line of Arabidopsis as compared to the WT. Our findings indicate that LpSOS1 enhances salt tolerance in plants by regulating ion homeostasis, reducing Na⁺/K⁺ ratio, thereby protecting the plasma membrane from oxidative damage caused by salt stress, and enhancing the activity of antioxidant enzymes. Therefore, the increased salt tolerance conferred by LpSOS1 in plants makes it a potential bioresource for breeding salt-tolerant crops. Further investigation into the mechanisms underlying lily's resistance to salt stress would be advantageous and could serve as a foundation for future molecular improvements.

Differentiate responses of soil nutrient levels and enzymatic activities to freeze-thawing cycles in different layers of moss-dominated biocrusts in a temperate desert

Introduction

The biological soil crust, a widespread phenomenon in arid and semi-arid regions, influences many ecological functions, such as soil stability, surface hydrology, and biogeochemical cycling. Global climate change has significantly altered winter and spring freeze-thaw cycles (FTCs) in mid and high-latitude deserts. However, it is unclear how these changes will affect the biological soil crust and its influence on nutrient cycling and soil enzyme activity.

Methods

We conducted this study in the Gurbantunggut Desert, a typical temperate desert, using the moss crust as an example of an evolved biological soil crust. Simulating the effects of different FTC frequencies (0, 5, and 15 times) on soil carbon, nitrogen, phosphorus-related nutrients, and extracellular enzyme activities allowed us to understand the relationship between soil environmental factors and nutrient multifunctionality during FTC changes.

Results

The results showed that recurrent FTCs significantly increased the accumulation of carbon and phosphorus nutrients in the soil and decreased the effectiveness of nitrogen nutrients. These changes gradually stabilized after 15 FTCs, with available nutrients showing greater sensitivity than the previous full nutrient level. FTCs inhibited carbon, nitrogen, and phosphorus cycle-related hydrolase activities and promoted carbon cycle-related oxidase activities in the crust layer. However, in the 0-3 cm layer, the carbon and phosphorus cycle-related hydrolase activities increased, while peroxidase and urease activities decreased. Overall, the nutrient contents and enzyme activities associated with the carbon, nitrogen, and phosphorus cycles were lower in the 0-3 cm layer than in the crust layer. In addition, the multifunctionality of nutrients in the soil decreased after 15 FTCs in the crust layer and increased after 5 FTCs in the 0-3 cm layer. Structural equation modeling showed that FTC, soil water content, pH, available nutrients, and extracellular enzyme activity had opposite effects on nutrient multifunctionality in different soil layers. The change in nutrient multifunctionality in the crust layer was primarily caused by changes in total nutrients, while soil water content played a greater role in the 0-3 cm layer. Regardless of the soil layer, the contribution of total nutrients was much higher than the contribution of available nutrients and extracellular enzyme activity. In conclusion, it is essential to consider different soil layers when studying the effects of global climate change on the nutrient cycling of the biological soil crust.

Sub-arctic mosses and lichens show idiosyncratic responses to combinations of winter heatwaves, freezing and nitrogen deposition

Arctic ecosystems are increasingly exposed to extreme climatic events throughout the year, which can affect species performance. Cryptogams (bryophytes and lichens) provide important ecosystem services in polar ecosystems but may be physiologically affected or killed by extreme events. Through field and laboratory manipulations, we compared physiological responses of seven dominant sub-Arctic cryptogams (three bryophytes, four lichens) to single events and factorial combinations of mid-winter heatwave (6°C for 7 days), re-freezing, snow removal and summer nitrogen addition. We aimed to identify which mosses and lichens are vulnerable to these abiotic extremes and if combinations would exacerbate physiological responses. Combinations of extremes resulted in stronger species responses but included idiosyncratic species-specific responses. Species that remained dormant during winter (March), irrespective of extremes, showed little physiological response during summer (August). However, winter physiological activity, and response to winter extremes, was not consistently associated with summer physiological impacts. Winter extremes affect cryptogam physiology, but summer responses appear mild, and lichens affect the photobiont more than the mycobiont. Accounting for Arctic cryptogam response to multiple climatic extremes in ecosystem functioning and modelling will require a better understanding of their winter eco-physiology and repair capabilities.

Impact of repeated freeze-thaw cycles environment on the allelopathic effect to Secale cereale L. seedlings

Allelopathy, as environmental stress, plays a prominent role in stress ecotoxicity, and global warming directly increases freeze-thaw cycles (FTCs) frequency in the winter. Yet, the effect between FTCs environment and allelopathy stress is rarely known, and the interaction of allelopathy stresses lacks consideration. Here, we addressed interactions between artemisinin stress (AS) and A. trifida extract stress (AES) under Non-FTCs and FTCs environments. The results found that AS and AES had an antagonistic relation under Non-FTCs environment, while a strong synergism and cooperation under FTCs environment affect the growth and physiology in S. cereale seedlings. Besides, AS and AES under FTCs environment had more inhibition on the growth of roots and shoots, chlorophylls, photosynthetic parameters, and relative water content; while more promotion on malondialdehyde, soluble sugar, and soluble protein. Moreover, the antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) were increased by AS and AES, showing a good resistance of S. cereale seedlings to allelopathy stress, but FTCs environment significantly weakened this resistance. Thus, the allelopathic effect of AS and AES on S. cereale seedlings was significantly emphasized by FTCs environment.

Long-term snow alters the sensitivity of nonstructural carbohydrates of Syntrichia caninervis to snow cover: Based on a 7-year experiment

The dynamics of nonstructural carbohydrates (NSC) profoundly affect productivity and ecological adaptability to adversity in plants. Global warming induced the frequent occurrence of extreme precipitation events that altered the winter snow pattern in deserts. However, there is a lack of understanding of how desert mosses respond to long-term snow cover change at the NSC level. Therefore, in this study, long-term (7-years) winter snow removal (-S), ambient snow (CK), and double snow (+S) experiments were set in the field to investigate the content of NSC and its component in Syntrichia Caninervis. Our results showed that changes in snow depth, snow years, and their interaction significantly affected NSC and its component of Syntrichia caninervis. Compared to snow removal, NSC, soluble sugar, and starch significantly decreased with the increasing snow depth. The ratio of soluble sugar to starch significantly increased, while NSC and soluble sugar gradually returned to the normal level with an increase in snow years. It is worth mentioning that snow removal significantly reduced the soluble sugar to starch ratio compared to ambient snow depth, whereas the double snow experiment significantly increased the ratio of soluble sugar to starch during winter. This indicated an obvious trade-off between carbon utilization and carbon storage in Syntrichia caninervis. Snow removal stimulated Syntrichia caninervis to store sufficient carbon sources by starch accumulation for its future growth, while double snow promoted its current growth by soluble sugar accumulation. The variance in decomposition showed that soil physical and chemical properties, snow cover, and their interaction explained 83% of the variation in NSC and its components, with soil and plant water content, pH, and electrical conductivity (P-WC, S-WC, S-pH, and S-EC) as significant predictors. This highlights that snow indirectly affected NSC and its component contents by changing soil physical and chemical properties; however, long-term changes in snow cover could slow down its sensitivity to snow.

Do freeze-thaw cycles affect the cadmium accumulation, subcellular distribution, and chemical forms in spinach (Spinacia oleracea L.)?

To date, although there are many studies investigating the toxicity of heavy metal to plant, little research exists in the seasonal freeze-thaw (FT) regions where FT cycles often happen during the plant growing process. To reveal the adaptive mechanisms of plants to the combination stresses of cadmium (Cd) and FT, the Cd accumulation, subcellular distribution, chemical forms, and antioxidant enzyme activity (peroxidase (POD)) were investigated in spinach (Spinacia oleracea L.) growing under different soil Cd levels (i.e., 0.10 mg Cd kg-1 soil (low), 1.21 mg Cd kg-1 soil (medium), and 2.57 mg Cd kg-1 soil (high)). Compared to the non-freeze-thaw (NFT) treatments, higher Cd concentrations in the root and lower translocation factors from root to leaf were found for the plants experiencing FT cycles. FT significantly decreased the Cd concentrations in the leaves under the low- and medium-Cd treatments, while similar values were found for the high-Cd treatments. Generally, FT could decrease the concentrations and proportions of Cd stored in the cell wall and soluble fractions and increase them in the organelle fractions for the medium- and high-Cd treatments, while opposite tendency was found for the low-Cd treatments. Moreover, larger Cd amounts in the inorganic and water-soluble forms were found for the low- and medium-Cd treated plants under FT, while lower values were found for the high-Cd treatments. Additionally, POD, which presented higher activities at the low- and medium-Cd treatments and lower activities at the high-Cd treatments under FT, were also significantly influenced by the Cd × FT interaction. This study indicated that FT could significantly change the accumulations of Cd in plant, and it provided a new insight into the Cd accumulation by plants in the seasonal FT region.