The Climate Near the Ground

Microbiotic crusts are biological soil crusts composed of lichens, cyanobacteria, algae, mosses, and fungi. The biodiversity of these crusts is poorly understood; several cosmopolitan species dominate in most areas, but many species are confined to one or a few sites. Nitrogen fixation by organisms within the crust can be the dominant source of nitrogen input into many ecosystems, although rates of nitrogen input are limited by water availability, temperature, and nitrogen loss from the crust. Photosynthetic rates of the microbiotic crust can be 50% of those observed for higher plants, but the contribution of crusts to carbon cycling is not known. The microbiotic crust binds soil particles together, and this significantly increases soil surface stability and resistance to erosion. Greenhouse studies have found that crusts can enhance seed germination, seedling survivorship, and plant nutrient status, but further experiments are needed under field conditions. Crusts are extremely susceptible to surface dis...

Microbiotic Crusts and Ecosystem Processes

Desiccation-tolerance, the ability to revive from the air-dried state, is found in prokaryotes, algae and bryophytes, and occasionally in pteridophytes, but is very rare in the vegetative tissues of angiosperms or in animal tissues. However, the vast majority of lichens are desiccation-tolerant. Under natural conditions, the life of most lichens is characterized by rapidly changing water contents, and correspondingly rapidly changing physiological activity such as respiration and photosynthesis. Taken to the extreme, some lichens can revive after being desiccated under controlled laboratory conditions for many months. As a result of their desiccation-tolerance, lichens are extremophiles and can live in places no higher plant can. They may be the predominant life-form in ecosystems characterized by severe environmental stresses such as Arctic, Antarctic and alpine regions, as well as deserts. This review critically assesses our current knowledge about desiccation-tolerance in lichens, concentrating on mechanisms that protect from desiccation-induced damage. Evidence available from other desiccation-tolerant life-forms suggests that desiccation-tolerance is a multifaceted trait involving a suite of interacting mechanisms. The majority of recent studies on mechanisms of lichen desiccation-tolerance have focused on the scavenging of reactive oxygen species, which therefore forms a major part of this review. It is argued that effective control of reactive oxygen species and mutual up-regulation of protective mechanisms was critically important for the evolution of lichens, facilitating the transition from free-living fungi and green algae or cyanobacteria to the lichenized state. Recently developed tools of molecular biology, particularly from the -omics disciplines, have only just started to be applied to lichens. There remain many unsolved questions as to how lichens survive desiccation and the authors hope to encourage more scientists to investigate this intriguing phenomenon.

Desiccation-Tolerance in Lichens: A Review

1. Introduction.- Basic Vegetation Science Contributions.- 2. Plant synecology in the service of rangeland management.- 3. Ecophysiology of range plants.- 4. Rangeland plant taxonomy.- 5. New plant development in range management.- 6. Successional concepts in relation to range condition assessment.- 7. A role for nonvascular plants in management of arid and semiarid rangelands.- 8. Seedbeds as selective factors in the species composition of rangeland communities.- 9. Modelling rangeland ecosystems for monitoring and adaptive management.- Vegetation Distribution and Organization.- 10. Vegetation-soil relationships on arid and semiarid rangelands.- 11. Vegetation attributes and their applications to the management of Australian rangelands.- 12. The ecology of shrubland/woodland for range use.- 13. Tundra vegetation as a rangeland resource.- 14. Forest rangeland relationships.- 15. Ecological principles and their application to rangeland management practice in South Africa.- 16. Range management from grassland ecology.- 17. Riparian values as a focus for range management and vegetation science.- Vegetation Science Rangeland Applications.- 18. Rangeland vegetation productivity and biomass.- 19. Rangeland vegetation - hydrologic interactions.- 20. Grazing management and vegetation response.- 21. Understanding fire ecology for range management.- 22. Reclamation of drastically disturbed rangelands.- 23. Rangeland vegetation as wildlife habitat.- 24. Revegetation of arid and semiarid rangelands.

Vegetation science applications for rangeland analysis and management.

CO2-concentrating mechanisms based on active inorganic C influx across a membrane (or membranes) are widespread in aquatic phototrophs. They are apparently absent from, or poorly developed in, taxa...

Implications of inorganic carbon utilization: ecology, evolution, and geochemistry

SUMMARY
The control of the net photosynthetic rate in Peltigera canina var. praetextata and P. polydactyla by temperature, light and moisture has been examined on a seasonal basis. Mean optimum values of 6 mg CO2 g−1·h−1 are achieved by young lobes of either species during late spring, summer and early winter. However, under full winter conditions optimum net photo-synthetic rates fall to 3 mg CO2 g−1·h−1. Light saturation is approximately 500 μE m−2 s−1 at all times of the year, but the temperature at which maximum rates of net photosynthesis are achieved changes markedly throughout the year in both species. In winter, maximum rates occur at an experimental thallus temperature of 5°C but by mid-summer, the optimum temperature for net photosynthesis is c. 30°C, which corresponds to equivalent ambient temperature levels in the field. This temperature acclimation of net photosynthetic optima is achieved without any significant change in respiration rate and shows a remarkable degree of homeostasis during spring, summer and early winter. The results strongly emphasize the unsatisfactory nature of the univariate experimental design which has often been used in lichen physiological ecology. The extreme importance of a controlled storage temperature for experimental lichen material is also clearly evident. The low net photosynthetic rates in winter show the same pattern in both Peltigera species during these low temperature and short day conditions.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1981.tb03210.x

Physiological-environmental interactions in lichens

Summary

Little attention has been paid to the potential importance of light in the ecology of lichens. Data is presented which shows that Peltigera canina var. praetextata from a woodland floor can rapidly acclimate to low or high light levels and thus maintain a given level of photosynthesis irrespective of the leaf canopy status. This photosynthetic adjustment takes place naturally in the field during leaf fall in October. P. scabrosa shows a similar response to low light and furthermore, acclimation to low levels of illumination can readily take place in air-dry material. In contrast populations of Peltigera aphthosa collected from the dense shade of spruce in northern Ontario are extremely sensitive to quite modest levels of ‘high’ light, with pronounced damage occurring under 350 μE m-3 8-1 illumination. Contrasting populations of P. aphthosa collected from open habitats are not affected by this level of illumination.



The maintenance of the correct day length during air-dry storage is also very important since a rapid alteration of daylength produces a marked although temporary photosynthetic decline. On the other hand continuous daylight induces a rapid and continuous decline of photosynthesis probably leading eventually to the death of the phycobiont.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1980.tb04781.x

Physiological‐environmental interactions in lichens x. light as an ecological factor

Lichens are believed to be extremely resistant to high-temperature stress when desiccated. Results from a reexamination of this concept indicate that some air-dry lichen thalli can be extremely sensitive to even moderate levels of heat stress whereas others exhibit a considerable degree of heat resistance. These differential levels of thermal resistance correlate exactly with the ecology of these populations.

Thermal sensitivity in lichens.

Summary
The nitrogenase activity in Peltigera polydactyla was examined during varying periods of darkness and after re-illumination. There was an immediate decrease in activity of about 50% when the lichen was darkened, followed by a progressive further decrease of activity with time. Recovery to the original level of activity on re-illumination showed an increasing lag as the dark period was extended. The effect of an external carbon source on nitrogenase activity was also examined and very large increases in activity were induced in the light, by both 2% glucose and mannitol. The decrease during a dark period was, however, still very marked.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1976.tb04664.x

Environmental‐physiological interactions in lichens

Summary
The influence of a long term snowcover on the rates of nitrogenase activity in the lichens Peltigera canina var. praetextata and P. canina var. rufescens has been investigated. In accordance with the existing literature, only very low rates of nitrogenase activity could be detected after several months of snowcover. These low rates of activity result from prolonged darkness rather than an inactivation of the nitrogenase enzyme by low temperature. The subsequent recovery of nitrogenase activity after snowmelt is very largely controlled by the presence of radiant energy with temperature playing a subordinate role.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1980.tb04782.x

Physiological‐environmental interactions in lichens xi. snowcover and nitrogenase activity

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