Frank B. Salisbury

Leaf temperatures of alpine plants in the field

Summary1.Leaf temperatures of Colorado alpine plants on Mount Evans (4300 m) and near the Trail Ridge Road (3800 m) were measured along with air temperature, wind velocity, maximum and zenith light intensities, net radiation, and in one study humidity.2.When skies were clear above Mount Evans, plant temperatures were clearly dependent upon insolation, being as much as 22° C above ambient. Under uniformly cloudy skies, plant temperatures did not deviate far from air temperatures.3.Under typically fluctuating alpine conditions, correlations between leaf temperature and certain environmental factors are imperfect. Failure of the correlation is ascribed to factors not measured, mechanics of the analysis, changing environment, and position effects.4.Application of these findings to controlled environment (growth chamber) studies poses an interesting and inherently difficult problem.Zusammenfassung1.Auf dem Mount Evans (4300 m ü.d.M.) und in der Nähe der Trail Ridge Road (3800 m) in den Rocky Mountains des Staates Colorado wurden an Hochgebirgspflanzen Blatt-Temperaturen und parallel dazu auf dem Standort die Lufttemperatur, die Windstärke, die maximale und zenithale Beleuchtungsstärke und die Strahlungsbilanz gemessen. In einem Versuch (Abb. 1) wurde außerdem auch die relative Luftfeuchtigkeit bestimmt.2.Bei wolkenlosem Wetter (Mt. Evans) hängen die Blatt-Temperaturen, die dann bis zu 22° C über die Lufttemperatur ansteigen können, eindeutig von der Einstrahlung ab. Bei bedecktem Himmel weichen die Blatt-Temperaturen kaum von der Lufttemperatur ab.3.Bei dem für das Hochgebirge typischen Wechselwetter hingegen ergab die rechnerische Auswertung keine klare Korrelation zwischen den Blatt-Temperaturen und bestimmten Umweltfaktoren. Als Gründe dafür kommen in Frage: Nicht erfaßte Standortsfaktoren, die Art der Korrelationsanalyse, zu rasch sich ändernde Standortsfaktoren bei nachhinkender Messung und der Einfluß der Hangneigung.4.Ein sehr interessantes aber an sich schwieriges Problem ist die Anwendung der vorliegenden Ergebnisse auf Versuche unter willkürlich gesteuerten Bedingungen (wie z. B. in Klimakammern).

Leaf temperatures in controlled environments

ConclusionsThe extent to which our results can be explained by assuming that the leaf is a purely physical body, showing virtually no physiological changes in response to changing environment, is rather impressive. Two results seemed, at first glance, to be exceptions to this conclusion: the temperature of irradiated leaves rose less above air temperature when the air temperature was highest; and transpiration of irradiated leaves decreased steeply with increasing wind velocity. The analysis of these results indicated, however, that even these reactions were primarily physical. Physiological adaptations became apparent only at unnaturally high radiation intensities and at high wind velocities.The correlation between leaf-air-temperature difference and transpiration can also be explained on a purely physical basis. In the one exception (Fig. 5) more than one environmental variable changed, and the failure of correlation might be expected on theoretical grounds.The relatively minor importance of convection as a mechanism of heat transfer as revealed by calculation of the energy budget (Table 4) is also of interest, as is the strong response of plant temperature to light quality (Fig. 7).

Growth regulators and flowering

I t seems clear tha t transformation of the vegetative bud of eocklebur (Xanthium pennsylvanicum WALL.) to the reproductive condition occurs in response to a hormone which is synthesized in the leaf starting about 8 hours after the beginning of darkness (e.g. SALISBURY 1961, 1963). The present paper describes the results of one indirect approach used to gain insight into the physiology and biochemistry of flowering hormone synthesis, translocation, and action at the bud. Antimetabolites which are known to inhibit specific metabolic steps in other systems are applied. I f flowering is inhibited, the suspected step is implicated in a preliminary way in the flowering process. The participation of this suspected step can be further tested by a t tempts to reverse the effects of the antimetabolite by simultaneous application of a suspected corresponding metabolite or the product of the blocked step. The time of effectiveness of the antimetabolite can also be determined. A related approach using conventional growth regulators has shown tha t measurement of the critical 8 hour 20 minute dark period (critical night) is metabolically different from the subsequent synthesis of flowering hormone, and tha t ATP synthesis is an essential par t of hormone synthesis (SALISBURY 1957). Thus cobaltous ion inhibits flowering only when applied during time measurement, while 2,4-dinitrophenol inhibits during hormone synthesis. Auxins inhibit during the translocation period, and 2,2-dichloropropionic acid, 2,4-diehlorophenoxyacetie acid, and maleic hydrazide inhibit development of the floral bud.

Time measurement and the light period in flowering

SummaryTime measurement during the light period in the photoperiodic induction of flowering in Xanthium pennsylvanicum has been studied, primarily by one type of experiment: a subcritical dark period (7.5 hours) is terminated by a brief but saturating interruption of light; and varlous conditions (light periods) are then given to discover treatments which will result in optimum flowering in response to a second inductive dark period (typically 12 hours).1.Experiments with applied sucrose, as well as the general tenor of most of the experiments in this paper, indicate that the High Intensity Light Process is more than photosynthesis. Sucrose, for example, will not overcome the inhibitory effect of a light interruption during a dark period.2.Following the first subcritical dark period (optimally 7.0 to 7.5 hours), a light period of 8 to 12 hours will result in maximum flowering in response to a second, test-dark period (12 hours). There is little if any response to light intensity during this intermediate light period. This is true for low intensities on the order of those required for saturation of the phytochrome pigment system (intensities comparable to those effective in the inhibition of the dark period) to intensities which might saturate photosynthesis.3.Red light is most promotive of flowering during the intervening light period, and far-red light is inhibitory. Thus the light process is apparently a phytochrome response, opposite in direction to the Pfr inhibition of the dark period.4.Time measurement during the light period is apparently quite temperature intensitive from 15° to 38°C.5.As the light period is lengthened, the critical dark period is shorted. With a 12-hour light period, the critical dark period has been shortened to less than 8 hours. As the light period is lengthened beyond 12 hours, the critical dark period increases towards its usual “lower” limit of 8.3 hours.6.If time measurement is studied by determination of the time during the dark period when the flowering process is maximally sensitive to a red light interruption, it can be seen that the process is considerably slowed during dark periods which follow a very short light interruption. After a 12-hour light interruption, the time of maximum sensitivity is reached even earlier (ca. 6 hours) than under “normal” conditions (ca. 8 hours).7.Results are discussed according to the concepts of catenary steps in the flowering process or rhythmical changes in the plants sensitivity to light. It is concluded that both approaches have merit, and that some blending of the two ideas probably comes closest to description of the true state of affairs. The plant seems to clearly go through a diurnal cycle, during half of which red light (Pfr) is promotive, even essential to flowering, and during the other half of which red light (Pfr) is inhibitory. Yet catenary steps in the process are also discernible, such as a conversion of the phytochrome pigment system by light or metabolically in the dark, coupling through this system to the timing mechanism, synthesis and translocation of flowering hormone after a sufficient period of time, and synthesis of an inhibitor (apparently an inhibitor of time measurement during the critical dark period) during light periods longer than about 12 hours.

Eco-Physiology of Geum turbinatum and Implications Concerning Alpine Environments

Field and controlled-environment studies were made of Geum turbinatum Rydb. This perennial herb, though almost ubiquitous throughout the Rocky Mountain alpine, is seldom encountered below timberline. High viability among the seeds tested indicated that sexual reproduction may be important in the dispersal and maintenance of the species, but there were no apparent environmental requirements for germination which would restrict Geum to the alpine. Vegetative growth was favored by low average temperatures (<15 C)-particularly soil-temperature conditions. No treatment consistently caused Geum plants to initiate flowering-shoot primordia at lower elevations. Development of alpine-initiated flowers continued, however, if temperatures averaged 10-14 C, but above 15 C development was almost completely inhibited. Dormancy in Geum seems to be regulated by relative changes in soil temperatures with at least 5 weeks of freezing temperatures required to break dormancy completely. It is suggested that the dormancy response is primarily regulated by the roots. Because of its importance to Geum-functioning, low soil temperature is probably an essential factor in the distribution of this species and consequently may also operate in determining the lower limits of western American alpine tundra. Low soil temperature may likewise be important in setting the upward limit of tree distribution, that is, in the formation of alpine timberlines.

Biological timing and hormone synthesis in flowering ofXanthium

The flowering response of short-day plants, such as Xanthium occurs after they have been exposed to a period of darkness which exceeds some minimum duration. We suspect the participation of at least three fundamental processes during this dark period: the action of the photo morphogenetic pigment system (phytochrome), biological time measure ment, and the synthesis of flowering hormone. Action of the phyto chrome system probably combines with some other time measuring mechanism to determine the critical night : the period of darkness which is just infinitesimally too short for the initiation of flowers. Following the critical night, flowering hormone is synthesized in the leaves and subsequently exported to the buds (for reviews, see Hilt .man 1962; Salisbuey 1961, 1963A). Time measurement is especially interesting. At present we have virtually no information about the process except that it is relatively temperature independent (Long 1939, see review in Hillman 1962), and that it may be slowed by the presence of the cobaltous ion (Salis bury 1959 and 1963B). It has been suggested by workers at Beltsville, Maryland (e.g. Borthwick and Hendricks 1960, and Hendricks and Borthwick 1963) that time measurement results from the metabolic conversion of one form of the pigment phytochrome (F-phytochrome, sensitive to far-red light) to the other form (R-phytochrome, sensitive to red light). After darkness begins, the time required for this conversion might constitute the critical night. Some degree of temperature insen sitivity could be achieved by a feed-back between the rate of phyto chrome conversion and the effectiveness of phytochrome in a given process, as both are influenced by temperature. Thus F-phytochrome may inhibit the flowering process most effectively at higher temperatures but also convert most rapidly at higher temperatures. It has been suggested by Bunning (e.g. 1960) and others (e.g. Hamner, 1960, 1963) that time measurement in flowering is related to an internal oscillator such as that apparently in control of other bio

Analysis of an Alpine Environment

If plant physiological approaches are to be applied to the solution of ecological problems, it is essential that the field environment and the response of plants to it be described and understood, even to the level of the microenvironment surrounding the responding constituents of the cell. We have studied the environment of the alpine zone on the northern border of Rocky Mountain National Park since 1960, and results of these studies are summarized here. The approach attempts to emphasize the time factor, considering the periods and amplitudes of cyclical changes in environmental parameters at four levels of cycle lengths: short cycles (seconds to hours), diurnal cycles, secular cycles (several days), and annual cycles. In addition to this analysis of change, the usual averages must also be considered in any environmental description. Light intensity, measured continuously with a pyrheliograph, was analyzed primarily from the standpoint of total daily incoming radiation and number of fluctuations (due to clouds) per day, but the temperature records, obtained with a hygrothermograph in a special dome-shaped weather shelter near the ground, were analyzed more intensively. Total daily temperature fluctuations and number of cycles were measured, and these values were considered as a function of location, time during the season, and year. Diurnal cycles were also described, and changes in these constituted secular weather cycles having periods of about 10-22 days. A temperature index was derived from the daily short-cycle variations, the diurnal temperature amplitude, and the daily average temperature. This index proved valuable in detection of secular cycles, differences between various locations, etc. For the summer of 1965, a comparison was made between the station in Rocky Mountain National Park and a new station placed on Independence Pass in central Colorado. Other factors of the environment were also studied, including wind velocity, precipitation, atmospheric humidity, and various soil factors. These parameters were not emphasized in the present study, but they should be an important part of any future attempt to understand the physiological ecology of the alpine tundra. Implications of these environmental studies in the field for future (and current) laboratory studies using controlled environments are briefly considered.

Ratio of Blue to Red Light: A Brief Increase Following Sunset

Visible spectra of solar radiation were recorded during sunset. With the development of twilight, there was an expected decrease in the blue-to-red ratio; but directly upon setting of the sun there was a sharp rise in this ratio (due to the predominance of sky-light) which attenuated rapidly to follow the pattern that it had previously taken.

Martian Biology: Accumulating evidence favors the theory of life on Mars, but we can expect surprises

Of all the proposals put forth to account for the observed Martian phenomena, the idea of life on Mars seems to be the most tenable. And if this idea is accepted, we are immediately drawn to the conclusion that this life is a very well-adapted and flourishing one—not the struggle for existence so often suggested in light of the obvious difficulties earthly organisms would have in living on Mars. The suggested criteria seem to eliminate all the known life forms, but of all these forms, a higher plant would require the least modification in order to meet the criteria. The basic shape of the leaf of a higher plant seems suited to conditions on Mars, but the lower gravity might well result in some interesting modifications in morphology. Some life forms on Mars might resemble our own higher plants, but we should be prepared to encounter some interesting surprises in biochemistry.

Soil Formation and Vegetation on Hydrothermally Altered Rock Material in Utah

In the south-central part of Utah near Marysvale, exposed cross sections of ancient hot springs support vegetation strikingly different from the surrounding semi-desert plant communities. A similar situation in Nevada has been studied by Billings (1950), and chemical and biological investigations of the hot-spring material in Utah have been described earlier (Salisbury 1954). The present paper bears on the ecology of the hotspring areas, especially in relation to soil formation on the material derived from hydrothermally altered rock.