1 Plant ecology at high elevations.- The concept of limitation.- A regional and historical account.- The challenge of alpine plant research.- 2 The alpine life zone.- Altitudinal boundaries.- Global alpine land area.- Alpine plant diversity.- Origin of alpine floras.- Alpine growth forms.- 3 Alpine climate.- Which alpine climate.- Common features of alpine climates.- Regional features of alpine climates.- 4 The climate plants experience.- Interactions of relief, wind and sun.- How alpine plants influence their climate.- The geographic variation of alpine climate.- 5 Life under snow: protection and limitation.- Temperatures under snow.- Solar radiation under snow.- Gas concentrations under snow.- Plant responses to snowpack.- 6 Alpine soils.- Physics of alpine soil formation.- The organic compound.- The interaction of organic and inorganic compounds.- 7 Alpine treelines.- About trees and lines.- Current altitudinal positions of climatic treelines.- Treeline-climate relationships.- Intrazonal variations and pantropical plateauing of alpine treelines.- Treelines in the past.- Attempts at a functional explanation of treelines.- A hypothesis for treeline formation.- Growth trends near treelines.- Evidence for sink limitation.- 8 Climatic stress.- Survival of low temperature extremes.- Avoidance and tolerance of low temperature extremes.- Heat stress in alpine plants.- Ultraviolet radiation - a stress factor.- 9 Water relations.- Ecosystem water balance.- Soil moisture at high altitudes.- Plant water relations - a brief review of principles.- Water relations of alpine plants.- Desiccation stress.- Water relations of special plant types.- 10 Mineral nutrition.- Soil nutrients.- The nutrient status of alpine plants.- Nutrient cycling and nutrient budgets.- Nitrogen fixation.- Mycorrhiza.- Responses of vegetation to variable nutrient supply.- 11 Uptake and loss of carbon.- Photosynthetic capacity of alpine plants.- Photosynthetic responses to the environment.- Daily carbon gain of leaves.- The seasonal carbon gain of leaves.- C4 and CAM photosynthesis at high altitudes.- Tissue respiration of alpine plants.- Ecosystem carbon balance.- 12 Carbon investments.- Non-structural carbohydrates.- Lipids and energy content.- Carbon costs of leaves and roots.- Whole plant carbon allocation.- 13 Growth dynamics and phenology.- Seasonal growth.- Diurnal leaf extension.- Rates of plant dry matter accumulation.- Functional duration of leaves and roots.- 14 Cell division and tissue formation.- Cell size and plant size.- Mitosis and the cell cycle.- From meristem activity to growth control.- 15 Plant biomass production.- The structure of alpine plant canopies.- Primary productivity of alpine vegetation.- Plant dry matter pools.- Biomass losses through herbivores.- 16 Plant reproduction.- Flowering and pollination.- Seed development and seed size.- Germination.- Alpine seed banks and natural recruitment.- Clonal propagation.- Alpine plant age.- Community processes.- 17 Global change at high elevation.- Alpine land use.- The impact of altered atmospheric chemistry.- Climatic change and alpine ecosystems.- References (with chapter annotation).- Taxonomic index (genera).- Geographical index.- Color plates.- Plant life forms.- The alpine life zone.- Environmental stress.- The human dimension.

Alpine plant life

A standard, based on the set of ocean water samples used by Epstein and Mayeda to obtain a reference standard for oxygen-18 data, but defined relative to the National Bureau of Standards isotopic reference water sample, is proposed for reporting both deuterium and oxygen-18 variations in natural waters relative to the same water. The range of absolute concentrations of both isotopes in meteoric-waters is discussed.

https://science.sciencemag.org/content/sci/133/3467/1833.full.pdf

Standard for Reporting Concentrations of Deuterium and Oxygen-18 in Natural Waters.

Summary
‘How are plants adapted to the low temperatures and other stresses of arctic and alpine environments ?’ At present it is not possible to answer this question completely. Much work remains to be done, particularly on low-temperature metabolism, frost resistance, and the environmental cues and requirements for flowering, dormancy, regrowth, and germination. However, in brief, we can say that plants are adapted to these severe environments by employing combinations of the following general characteristics:

1. Life form: perennial herb, prostrate shrub, or lichen. Perennial herbs have greatest part of biomass underground.

2. Seed dormancy: generally controlled by environment; seeds can remain dormant for long periods of time at low temperatures since they require temperatures well above freezing for germination.

3. Seedling establishment: rare and very slow; it is often several years before a seedling is safely established.

4. Chlorophyll content: in both alpine and arctic ecosystems not greatly different on a land-area basis from that in temperate herbaceous communities. Within a single species there is more chlorophyll in leaves of arctic populations than in those of alpine populations.

5. Photosynthesis and respiration:

(a) These are at high rates for only a few weeks when temperatures and light are favourable.

(b) Optimum photosynthesis rates are at lower temperatures than for ordinary plants; rates are both genetically and environmentally controlled with phenotypic plasticity very marked.

(c) Dark respiration is higher at all temperatures than for ordinary plants; rate is both genetically and environmentally controlled, with phenotypic plasticity very pronounced, i.e. low-temperature environment increases the rate at all temperatures.

(d) Alpine plants have higher light-saturation values in photosynthesis than do arctic or lowland plants; light saturation closely tied to temperature.

(e) There is some evidence that alpine plants can carry on photosynthesis at lower carbon dioxide concentrations than can other plants.

(f) Annual productivity is low, but daily productivity during growing season can be as high as that of most temperate herbaceous vegetation. Productivity can be increased by temperature, nutrients, or water.

6. Drought resistance: most drought stress in winter in exposed sites is due to frozen soils and dry winds. It is met by decreased water potentials, higher concentrations of soluble carbohydrates, and closed stomates. Little drought resistance in snowbank plants. Alpine plants adapted to summer drought stress can carry on photosynthesis at low water potentials; alpine or arctic plants of moist sites cannot do this.

7. Breaking of dormancy: controlled by mean temperatures near or above 0° C., and in some cases by photoperiod also.

8. Growth: very rapid even at low positive temperatures. Respiration greatly exceeds photosynthesis in early re-growth of perennials. Internal photosynthesis may occur in hollow stems of larger plants during early growth. Nitrogen and phosphorus often limiting in cold soil.

9. Food storage: characteristic of all alpine and arctic plants except annuals. Carbohydrates mostly stored underground in herbaceous perennials. Lipids in old leaves and stems of prostrate evergreen shrubs. Depleted in early growth, and usually restored after flowering.

10. Winter survival: survival and frost resistance are excellent after hardening. Cold resistance closely tied to content of soluble carbohydrates, particularly raffinose.

11. Flowering: flower buds are pre-formed the year before. Complete development and anthesis dependent upon temperature of the flowering year and also, in some cases, upon photoperiod.

12. Pollination: mostly insect-pollinated in alpine regions and even in Arctic, but to a lesser extent. Wind-pollination increasingly more important with increasing latitude. Diptera more important than bees in the Arctic and in the highest mountains.

13. Seed production: opportunistic, and dependent upon temperature during flowering period and latter half of growing season.

14. Vegetative reproduction: by rhizomes, bulbils, or layering. More common and important in Arctic than in alpine areas.

15. Onset of dormancy: triggered by photoperiod, low temperatures, and drought. Dormant plant extremely resistant to low temperatures.

The ecology of arctic and alpine plants

The application of the eddy covariance flux method to measure fluxes of trace gas and energy between ecosystems and the atmosphere has exploded over the past 25 years. This opinion paper provides a perspective on the contributions and future opportunities of the eddy covariance method. First, the paper discusses the pros and cons of this method relative to other methods used to measure the exchange of trace gases between ecosystems and the atmosphere. Second, it discusses how the use of eddy covariance method has grown and evolved. Today, more than 400 flux measurement sites are operating world-wide and the duration of the time series exceed a decade at dozens of sites. Networks of tower sites now enable scientists to ask scientific questions related to climatic and ecological gradients, disturbance, changes in land use, and management. The paper ends with discussions on where the field of flux measurement is heading. Topics discussed include role of open access data sharing and data mining, in this new era of big data, and opportunities new sensors that measure a variety of trace gases, like volatile organic carbon compounds, methane and nitrous oxide, and aerosols, may yield.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.12649

Measuring fluxes of trace gases and energy between ecosystems and the atmosphere - the state and future of the eddy covariance method.

Net CO2 assimilation (A) was analysed in situ in 12 pairs of altitudinally separated, herbaceous plant species in the Austrian Alps at 600 and 2600m. Both groups of species show a similar average response to light, saturating at quantum flux densities (400-700mm) (QFD) of more than 1200 VLmol m-2 sol. Temperature optimum of QFD-saturated A differs little (3K) and corresponds to the median of air temperature at leaf level for hours with rate-saturating light conditions and not to mean air temperature which differs by 10K. Species with an exclusive high altitude distribution show steeper initial slopes and higher levels of saturation of the response of A to internal partial pressure of CO2 (CPI) than low elevation species. Mean A at local ambient partial pressure (CPA) does not differ between sites (c. 18 VLmol m-2 s-1), despite the 21% decrease in atmospheric pressure. Plants at high altitude operate at mean CPJ of 177 debar as compared to 250 debar at low altitude. The higher ECU (efficiency of carbon dioxide uptake [linear slope of A/CPJ curve]) as well as the steeper CO2 gradient between mesophyll and ambient air of alpine plants are explained by (1) greater leaf and palisade layer thickness and (2) greater nitrogen (protein) content per unit leaf area. We hypothesize that alpine plants profit more from enhanced CO2 levels than lowland plants (Fig 7). Key-words: Microclimate, gas exchange, carboxylation, elevated CO2, nitrogen, anatomy, season, alpine

In situ photosynthetic responses to light, temperature and carbon dioxide in herbaceous plants from low and high altitude

Alpine plants of Oxyria digyna have higher apparent photosynthesis rates at various carbon dioxide concentrations than arctic, sea-level plants of the same species. The ability to utilize carbon dioxide effectively at low concentrations may be involved in the survival of plants at high elevations.

Effect of Low Concentrations of Carbon Dioxide on Photosynthesis Rates of Two Races of Oxyria.

Field measurements of photosynthesis and respiration rates of whole alpine plants in situ were made at an elevation of 3,307 m in the Medicine Bow Mountains, Wyoming, using an infrared gas analyzer. Most measurements were for periods of 30 min to 2 hr but two "whole-day" measurements lasted from before sunrise to after sunset. Maximum net photosynthesis rates ranged from 4.15 to 13.4 mg C02/dm2 two surfaces/hr with an average rate of 9.32. An all-day measurement on Geum turbinatum during somewhat cloudy weather showed net photosynthesis paralleling and responding to changes in light and temperature. Similar measurements on Polygonum bistortoides in clear, sunny weather showed a midday depression in net photosynthesis; this may be due to high leaf temperatures under intense solar radiation. Net photosynthesis of whole sod blocks averaged 6.23 mg C02/g dry wt/hr. Soil CO2 output averaged 1,846 mg C02/m2 hr which is higher than published results from lower altitudes. Rough estimates of dry weight gain as calculated from sod-block metabolic rates averaged 2.79 g dry wt/m2/day. Measurements of CO2 concentration in ambient air were made. Morning observations averaged 0.430 mg/l while afternoon measurements averaged 0.387 mg/I. The lower afternoon values probably reflect photosynthetic activity of the surrounding forest vegetation on the lower slopes.

E. E. C. Clebsch

Papers

Effect of Low Concentrations of Carbon Dioxide on Photosynthesis Rates of Two Races of Oxyria.

Photosynthesis and Respiration Rates of Rocky Mountain Alpine Plants Under Field Conditions