Humidity and Plants PDF

Humidity and Plants Author(s): Theodore W. Tibbitts Source: BioScience, Vol. 29, No. 6 (Jun., 1979), pp. 358-363 Published by: Oxford University Press on behalf of the American Institute of Biological Sciences Stable URL: http://www.jstor.org/stable/1307692. Accessed: 18/06/2014 10:40 Your use of t...

Humidity and Plants Author(s): Theodore W. Tibbitts Source: BioScience, Vol. 29, No. 6 (Jun., 1979), pp. 358-363 Published by: Oxford University Press on behalf of the American Institute of Biological Sciences Stable URL: http://www.jstor.org/stable/1307692. Accessed: 18/06/2014 10:40 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at. http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected].. Oxford University Press and American Institute of Biological Sciences are collaborating with JSTOR to digitize, preserve and extend access to BioScience. http://www.jstor.org This content downloaded from 62.122.79.81 on Wed, 18 Jun 2014 10:40:32 AM All use subject to JSTOR Terms and Conditions  Humidity and Plants Theodore W. Tibbitts Humidity(atmosphericmoisture)is an and metabolic changes that result from ter transpirationrates. This is shown in importantfactor of the environmentfor the responses. However, these may be Table 1 for the growth of cotton over a plant growth and development. The sig- very significant, as evidenced by inter- 14-weekperiod(Hoffmanet al. 1971)un- nificance of humidityfor plants was ig- node elongation in normally rosette der carefully controlled conditions. nored for many years by physiologists plants and differencesin the amountand Moreover, if plants are grown and main- who were intent on assessing the more type of cuticle development that can be tained undera low vaporpressuredeficit dramatic effects of radiation, temper- triggered under certain humidity condi- and then placed in an environmentwith a ature, soil moisture, and mineral nutri- tions (Bairdand Webster 1978). Further- larger vapor pressure deficit, they will tion on growth of plants. However, dur- more, I will not here discuss the biotic transpiremore water per unit area than ing the last decade there has been a interactions controlled by humidity, plants maintained continuously under significantamountof humidityresearch, such as disease organism entry into large vapor pressuredeficits (Mitchellet leading to a recognitionand acceptance plantsand controlof insect infestations. al. 1976). of the importantrole that humidity has Transpirationtends to increase with upon plant growth. This recent research increases in temperaturebecause the va- TRANSPIRATION has been stimulatedby the need to im- por pressure difference between the prove the efficiency of water use in The most obvious direct effect of hu- plant and the air increases with increas- plantsand to understandthe role that hu- midity is the control of the rate of trans- ing temperatures. Thus, over a sunny midityplays in controllingthe sensitivity piration or evaporation from the leaf. day transpiration increases as the air of plants to pollution. Decreases in atmospheric moisture in- warms. Transpirationcan also be accel- The influenceof humidityupon plants crease the vaporpressuredifference(Ae) erated with highertemperaturesbecause is apparent by examining the different between the air and moist leaf surfaces stomatalopening will increase with tem- patterns of naturalvegetation that have and increase water loss from the leaves. perature increases until excessive plant evolved in different areas of the world The vapor pressure of the air within the water stress results (Forde et al. 1977, and the species that grow and maturein leaf is considered to be at saturation Mitchellet al. 1976,Schulze et al. 1974). differentseasons. Certainvegetationpat- (100%relative humidity)at the leaf tem- terns are closely linkedwith atmospheric perature. Thus, the vapor pressure dif- STOMATAL REGULATION moisture levels. Home owners and ference is determinedby subtractingthe greenhouse managers have long recog- vapor pressure of the air from the satu- Atmosphericmoisture has a direct ef- nized the importance of increased hu- rated vapor pressure of the leaf. fect also in regulationof stomatal open- midity for better plant growth. They Waterloss per unit of leaf surface has ing. Stomata close when the difference have developed procedures to increase been proportionalto changes in air hu- between the vapor pressure of the air or decrease humidityfor certainplantsat miditywhen Ae is not largeand when de- and the vapor pressureof the cells lining particulartimes of the year. terminationsare madeover shortperiods the substomatalchamberof the leaf ex- Transpirationalwater loss and stoma- (Aston 1976, Elgawharyet al. 1972, Mel- ceeds a critical level (Cowan 1977, Hall tal opening are two physiological activi- lor et al. 1964, O'Leary 1975,Rawson et and Hoffman 1976, Kaufmann 1976, ties of plants that are directly regulated al. 1977,Swalls and O'Leary 1975).With Raschke 1975, Schulze et al. 1974, by atmosphericmoisturelevel. Otherre- large Ae levels, water loss has not been 1975b,Sheriff1977).The moistureon the sponses that are regulatedas a result of proportionalto the atmospherichumidi- surface of the cells in the substomatal changes in transpiration and stomatal ty (Drake et al. 1970, Swalls and opening include water potential, photo- O'Leary 1975) because stomata tend to TABLE 1. Transpiration of cotton synthesis, nutrient translocation, plant close and slow the transpirationalwater plantsgrownfor 14 weeks underdifferent temperature, and moisture condensa- loss. When plants are grown and main- atmospheric moisturedeficits. (Adapted tion. Although I will discuss these ac- tained under particularhumidity levels from Hoffmanet al. 1971) tivities in this paper, I will not attempt for extended periods, transpirationhas to review the many possible structural not been directly proportional to Ae Atmospheric moisture Transpiration deficit (mb) (mLldm2/day) (Forde et al. 1977, Hoffmanet al. 1971, Mitchell et al. 1976, Rawson et al. 1977) 39 69 The author is with the HorticultureDepartment, for soil moisture levels, plant water po- 32 66 University of Wisconsin, Madison, WI 53706. ? 16 51 1979AmericanInstituteof Biological Sciences. All tential, and other physiological factors 7 41 rightsreserved. within the plants provide feedback to al- 358 BioScience Vol. 29 No.6 This content downloaded from 62.122.79.81 on Wed, 18 Jun 2014 10:40:32 AM All use subject to JSTOR Terms and Conditions TABLE2. Species response to an increase in vaporpressure differencebetween the dioxide diffuses throughthe open stoma- plant leaves and the air. (AdaptedfromSheriff1977) ta and saturatesthe photosynthetic sys- tem, stomatalclosure occurs in response Stomatal aperture* Stomatal aperture Stomatal aperture Stomatal aperture to the high Ae. decreased; tran- decreased; tran- unaffected; tran- increased; tran- spiration decreased spiration increased spiration increased Stomata of plants maintained under spiration increased low levels of photosynthetically active Avenasativa L. Acacia aneura Banksiaserratifolia Eucalyptus radiation(PAR) respond more rapidlyto Citrussinensis F.v.M. Salisb. paucifloraSieb. Osbeck. Acacia sudden Ae increases and decreases than Citrullusvulgaris Pelargoniumzonale Eremophila brachystachya Schrad. L. under high PAR levels (Davies and Koz- macgillivrayi Benth. Clianthusformosus lowski 1974, Kaufmann1976).Apparent- Black Atriplexhastata L. G. Don. ly, under low PAR levels, stomatalregu- Geijeraparviflora Atriplexnumularia Gossypium lation by radiant energy and carbon Lindl. Lindl. hirsutum L. Myoporum Tradescantia Hederahelix L. dioxide flux is weakened so that the reg- floribundum virginianaL. Populusalba L. ulation by Ae is strengthened. Cunn. Zea mays L. Taraxacum Adaxial (upper) stomata of sunflower Myoporum officinaleWeber were found to respond more to changes platycarpumR. Viciafaba L. in Ae than abaxial(lower) ones, but both Br. Nicotianaglauca adaxial and abaxial stomata showed a Grah. distinct response with large changes in Pittosporum Ae (Aston 1976). phylliraeoides DC. Prunusarmeniaca PLANT WATER POTENTIAL L. Triticum aestivum L. Shifts in plant water potential have *Stomatalapertureresponse inferredfromviscous flowporometermeasurements. been observed in plants growing under differentatmosphericmoisture levels as a result of variations in transpirational chamber is assumed to have near satu- to induce stomatal oscillations in plants water loss from the plants (Biscoe et al. ratedvaporpressure.It has been hypoth- (Bravdo 1977, Farquhar and Cowan 1976, Hoffmanand Jobes 1978, Hoffman esized and appears that the guard cells 1974, Hall and Hoffman 1976). The and Rawlins 1971, Hoffman et al. 1971, or accessory cells are capable of sens- stomata open and close with a periodici- Lawlor and Milford 1975).A more nega- ing an increased Ae and cause clo- ty of about 30 minutes. In cotton, when tive plant water potential has been re- sure of the stomata.This response is rap- the Ae exceeded 14 g/m3(see Table 3 for ported for most plants with higher Ae id with aperturechanges occurringwith- comparison units), oscillations usually levels but only when plants are main- in 10-15 minutes after a significant resulted, but if the Ae was less than 13g/ tained for periods of several days under increase in Ae, and it can be rapidly re- m3,fewer thanone-thirdof the plantsex- reduced atmosphericmoisture levels. versed with decreases in Ae (Davies and hibited oscillations. The oscillations This response has not been consistent- Kozlowski 1974). probably result from stomatal response ly produced when plants are maintained The sensitivityof differentspecies var- to changes in carbon dioxide concentra- for only a few hours under a reduced ies greatly. Sheriff (1977) has divided tion within the tissues (Bravdo 1977):As moisture level (Barrs 1973, Lawlor and species into separate categories of stomata close in response to an in- Milford 1975). For example, an increase stomatal response (Table 2): (a) Ten of creased Ae, photosynthesisdepletes car- in Ae for a few hours with tomato and 26 species had sufficientstomatalclosure bon dioxide withinthe tissues, encourag- cotton lowered plant water potentials in with increasingAe so that transpirational ing stomatal opening to satisfy the these plants, but an increase in Ae upon water loss was less at the increased Ae demand for carbon dioxide. As carbon maize and sunflowerplants for the same levels than at the originallevel; (b) 8 spe- cies showed no evidence of stomatalclo- TABLE3. Watervapor in saturated airfor differentunits of measurementat temper- sure, and water loss increased propor- atures of 0 to 500 C. tionately with the increases in Ae; (c) 6 species showed evidence of some inter- Water vapor in saturated air* mediate stomatal closure with increased Pressure Weight Ae, for water loss did not increase pro- Temperature portionallywith the increase in Ae; (d) 2 ?C mm Hg inches Hg mbars Pa (g/m3) species were classifiedas having anoma- 0 4.59 0.207 6.11 6.11 x 102 4.847 lous response, for stomata appeared to 5 6.56 0.295 8.72 8.72 x 102 6.797 open, and transpirationincreasedpropor- 10 9.23 0.415 12.27 12.27 x 102 9.399 tionatelywith increasingAe. Researchers 15 12.81 0.577 17.04 17.04 x 102 12.830 20 17.57 0.791 23.37 23.37 x 102 17.300 documenting the direct response of 25 23.82 1.072 31.67 31.67 x 102 23.050 stomata to Ae changes have noted that 30 31.91 1.437 42.43 42.43 x 102 30.380 the occurrenceof this response is closely 35 42.29 1.904 56.24 56.24 x 102 39.630 linked with the water potential level 40 55.48 2.498 73.78 73.78 x 102 51.190 within plants (as describedin the section 45 72.08 3.245 95.85 95.85 x 102 65.500 50 92.80 4.178 123.40 123.40 x 102 83.060 on plant water potential). A rapidand large increase in Ae tends *760 mm pressure (29.92 in, 1013 mb). June 1979 359 This content downloaded from 62.122.79.81 on Wed, 18 Jun 2014 10:40:32 AM All use subject to JSTOR Terms and Conditions  period of time caused no change in plant Loweringof plantwater potentialis of ing the darkperiodas duringthe light pe- water potential, even though trans- particular concern in plants at certain riod. In unpublishedstudies with lettuce piration was increased markedly in the stages of growth. When plant water po- grown at 20'C, I have found significantly latterplants (Barrs 1973).Althoughplant tentials were lowered by very dry atmo- reduced growth if dark periods were water potentials decrease with increas- spheres duringfertilizationand early em- maintainedat a Ae of 11.5 mb compared ing or prolonged transpiration, plant bryo enlargement, serious reductions in to a darkperiodwith a 3.5 mb (lightperi- stomata have not been found to close in yield of fruit and seed occurred (Fisher ods at either a Aeof 11.5 mb or 3.5 mb). response to decreasing plant water po- and Weaver 1974, Hoffmanand Rawlins In one study, high relative humidity tentials until a severe water stress was 1970, Kolderup 1975). A reduction in minimized or eliminated the need for a produced (Schulze 1975b). plant water potentials from a high to a dark period cycle for certain plants Low atmospheric moisture levels for low level at a critical stage of develop- (Kristoffersen 1963) so that continuous extended periods lowered plant water ment caused greater reduction in yield light could be provided and maximum potentialswhen plantswere being grown than when plant water potentials were growth rates encouraged. One can theo- under either high or low soil moisture maintained continuously at a low level rize (Kristoffersen1963),then, that high levels. Reductions in atmosphericmois- duringgrowthof plants(Kolderup1975). relative humidityduringthe light period ture levels caused a loweringof plantwa- The plant water potential controls the reduces the moisturestress in the plants. ter potentials even though soil water availabilityof waterwithinthe plantand, Therefore, a dark period is not required stress had initiallylowered the plant wa- therefore, regulates many different bio- for the plants to recover from the exces- ter potential significantly(Hoffmanet al. chemical and physiological processes. sive moisture stress that normally ac- 1971). When plant water potentials were Water is requiredboth as a solvent and companies the light period of a daily decreased as a result of increased soil as a reactant for chemical and physical cycle. moisture stress, stomata of plants were processes within the plant. The entire Rapid changes in Ae have induced more responsiveto suddenchanges in at- metabolic balance within plants is al- rhythmic oscillations in photosynthetic mosphericmoisturelevels (Jensen 1975, tered when water potential is changed. rates as a result of stomatal oscillations Lawlor and Milford 1975, Raschke and Comprehensive discussion of these in- (Hall and Hoffman1976).The photosyn- Kuhl 1969).Thus, a smalleratmospheric teractions has been drawn together in thetic oscillations were phased with moisture change caused stomata to volumes edited by Kozlowski (1968, those of the stomata and not with those close. This response provides a mecha- 1972). in water potential, indicatingthat the os- nism for supplying needed protection cillations in photosynthesiswere a result from atmospheric moisture stresses of CO2availabilityratherthan a result of PHOTOSYNTHESIS when plants are under moderate to se- water potential changes in the tissue. vere water stress. Atmosphericmoisturelevels do not in- Rapidchanges in atmospherichumidi- fluence photosynthetic rates unless Ae ty levels produce rhythmicchanges also levels are large and stomatalclosure has in plant water potential (Hall and Hoff- occurred (Hoffman and Rawlins 1970, NUTRIENTTRANSLOCATION man 1976). Rhythmicoscillations with a Jensen 1975, Khaira and Hall 1976, Pa- It is generally assumed that humidity periodicityof 30 minutes were produced reek et al. 1969, Rawson et al. 1977, levels have little influenceupon nutrient in pinto beans. The oscillations had an Schulze et al. 1975a,Tsuno 1975). When translocation.Even thoughtranspiration amplitudeof 3 bars over the rangeof -5 plants have been maintained over a is increasedwith low humidities,there is to -8 bars and were about 1000 out of range of Ae conditions between approxi- little evidence that the nutrient level of phase with the stomatal cycle (Hall and mately 0 and 10 mb, no significantdif- most nutrients in plants is altered by Hoffman 1976). ferences in photosynthetic rates have transpiration rates (Erlandsson 1975, The control that atmosphericmoisture been found. This lack of photosynthetic Gale and Hagan 1966, Tromp and Oele levels have upon plant water potentialis response is in contrast to consistent re- 1972).Gale and Hagan(1966),in their re- apparently one of the principal factors ports of largevariationsin plant size and view, suggested that transpirationcould leading to plant growth changes under dry matteraccumulationwhen plantsare be reducedby halfwithoutaffectingmin- different humidity levels. Water poten- grown for continuous periods under dif- eral uptake (and accumulation in tis- tial changes result in alteredturgorwith- ferent humidity levels within this range sues). Most nutrientscan be translocated in the cells and tissues (Hoffman and of Ae (Ford and Thorne 1974, Hoffman in both xylem and sieve tube elements Rawlins 1971, Hoffmanet al. 1971);they and Rawlins 1971, Hoffmanet al. 1971, (Epstein 1972)so that adequatenutrition may be the cause of small cell size and Khairaand Hall 1976,Krizeket al. 1971, of tissues is assured regardless of the reduced length and width of leaves for Swalls and O'Leary 1975, Tibbitts and transpirationrate. plantsgrown underreducedatmospheric Bottenberg 1976). The variations in dry However, there is strong evidence to moisture (Ford and Thorne 1974, Hoff- matter accumulation of plants at dif- indicate that the accumulationof certain man and Rawlins 1971; Hoffman et al. ferent atmospheric moisture levels ap- nutrientsin tissues, particularlycalcium 1971, Krizek et al. 1971, Tibbitts and parently result from turgor differences (Ca) and boron (B), is controlledto a sig- Bottenberg 1976). Changes in leaf mor- that alter the total photosynthesizingleaf nificant extent by transpiration rates phology for plants grown under different surfacearea of plants. Differencesin leaf (Bowen 1972, Elgawhary et al. 1972). humidity levels altered the number of area of only 10% could have a multi- Therefore, humidity levels do influence stomata per unit area of leaf (Prisco and plying effect upon dry matteraccumula- the concentration of these nutrients in O'Leary 1973, Tibbitts and Bottenberg tion over time so that differencesof 30- tissues. Translocation of calcium and 1976).However, the total of stomataper 50%in total dry weight could result. possibly of boron is limitedto movement leaf was not changed (Tibbitts and Bot- Humidity levels for dry matter accu- in tracheal elements of the xylem. The tenberg 1976). mulationappearto be as importantdur- translocationof Ca has not been directly 360 BioScience Vol. 29 No.6 This content downloaded from 62.122.79.81 on Wed, 18 Jun 2014 10:40:32 AM All use subject to JSTOR Terms and Conditions  proportionalto watertranspiredfromthe veloping belowground(e.g. peanuts and TABLE5. Leaftemperaturesof cucum- leaves, since the quantityof Ca per vol- white potatoes) also are subject to Ca-re- bers at differenthumiditylevels and air ume of water decreases with increases in lated disorders.These tissues may be de- temperatures.(Adaptedfrom Matsuiand transpirationalwater movement. Thus, pendentupon atmosphericmoisturefluc- Eguchi 1972) there are either unequalrates of Ca and tuations for adequate Ca translocation water uptake from the soil or unequal when direct soil absorptionis limited. Relative Air temperature humidity Ca release rates into the xylem. Continuous high vapor pressure defi- of air (%) 20*C 30* C 40* C Humidity levels can control the com- cits can encourage sufficient trans- 40 24.0 32.0 36.4 partmentalizationof Ca in differentplant piration so that translocationof certain 60 24.0 33.0 38.5 tissues. Witha significantAethat will en- nutrients becomes excessive, with re- 80 24.0 34.5 40.5 courage rapid transpiration,Ca will ac- sulting nutrient accumulation and tox- cumulate in the plant tissues that are icity at the marginsof leaves. The atmo- transpiring,while no appreciableCa will sphere of homes in northern latitudes particulartemperaturesince less cooling accumulate in those that are not trans- duringthe winter is commonly very dry of leaves is necessary to decrease leaf piring(Palzkilland Tibbitts 1977).Thus, and apparentlyis the cause of toxicity in- temperaturesto the dew point temper- exposed leaves accumulate Ca, but en- jury on many house plants. The toxicity ature of the air. With humid conditions, closed leaves surroundingthe growing may be due to B, Cl, and/orMn accumu- condensationis initiatedearly in the eve- point (e.g., leaves within heads of cab- lation in the tip areas, althoughno avail- ning and usuallycontinues duringthe en- bage and lettuce) do not accumulate Ca able data yet supportthis. tire nightperioduntiltemperaturesin the (Maynard and Barker 1972, Thibodeau morningrise above the dew point. and Minotti 1969, Walker et al. 1961). Wateruptakeby planttissues is appar- PLANT TEMPERATURES Fruits of plants that are essentially de- ently not limited to uptake of liquid wa- void of stomata accumulate little Ca The moisturecontent of the air can al- ter, for there is good evidence that tropi- (Shear 1975). The limited Ca movement ter the temperatureof the plant by trans- cal orchids, and even tomatoes and corn, to certain tissues has been found to pirational cooling of the leaves. Plants can absorb water vapor from the air cause certain physiological breakdowns placed under large vapor pressure defi- when atmospheric moisture levels are in these tissues (Palzkillet al. 1976). cits have been found to have leaf temper- near saturation (Breazeale et al. 1950, However, the accumulationof Ca in atures 2-4'C lower than those in atmo- Gindel 1973, Went 1955, 1975). Several nontranspiringtissues can be increased spheres with small vapor pressure chaparral plants growing at high soil by diurnalfluctuationsin Ae. In cabbage deficits (Barrs 1973, Drake et al. 1970, moisturestress were found to absorbwa- and cauliflowerplants, reductions in Ae Matsui and Eguchi 1972). The effect of ter vapor from air at 85% RH (Stone et each night have promotedCa movement humidityupon leaf temperaturesis more al. 1950). to nontranspiringtissues. Small amounts significant at higher air temperatures Condensationalso plays a part in pro- of water apparentlymove throughxylem because Ae is commonly greater and tecting plant tissues from frost damage. elements to reestablish a high level of stomataare open wider, so that a greater If the atmosphericmoisturelevel is high, turgor in the tissues (Krug et al. 1972, amountof transpirationalcooling results so that the dew point is reached before Wiebe et al. 1974). A greater trans- (Table 5). temperatures drop to freezing, con- location of Ca to nontranspiringtissues densation of moistureon the leaves will has been fostered by providinga saturat- release latent heat to the leaf and mini- MOISTURE CONDENSATION ed atmosphereso that root pressurescan mize temperaturedecreases that would be developed (Palzkill and Tibbitts An often neglected aspect of atmo- damage the tissue. Agriculturalistsin- 1977). With maintenance of root pres- spheric moistureeffects on plants is that volved in protecting valuable fruit and sures for a period of time, significant of condensation on plants. The impor- vegetablecrops fromfrost damagewatch amounts of Ca can be translocated as tance of condensation is restricted al- the atmospheric moisture level very water moves throughthe leaf tissues and most exclusively to dark periods, when closely to determinethe necessity of ini- is guttated from the margins(Table 4). temperaturesof leaves drop below the tiating frost protection procedures dur- The influenceof humidityon Ca trans- dew point temperatureof the surround- ing the night period. location may not be restricted to above- ing air, and water vapor in the air is con- Condensationalso can be detrimental ground parts, for certain plant parts de- densed on the leaves as liquid. This pro- to the plant because it encourages the vides significant quantities of liquid germination and penetration of infec- water for plants. Went (1955) suggested tious microorganisms.Thus, high atmo- TABLE 4. Accumulation of 450a* in that as much as 25 cm of water per year spheric moisture levels that encourage leaves of cabbage plants with different can be provided in certain areas by this condensation during dark periods may humidityconditions (Adaptedfrom Palz- process. promote diseases on plants, particularly killet al. 1976) if the plant remains moist the following Some arid plants, such as Prosopis Leaves (cpm/mg dry wt) tamarugo, have evolved mechanismsto day. sustaintheir existence throughuptakeof Condition Exposed Covered condensate by leaves and stems. The CONCLUSION Airwithvapor 1093 68 moistureis then translocatedthroughthe pressuredeficit plant roots to moisten the soil, where It has been the thrust of this paper to of 9 mb roots are concentrated (Gindel 1973, document the thesis that atmospheric Airnear 528 586 Went 1975). The occurrence and quanti- moisturelevels do significantlyinfluence saturation ty of condensation increases with in- plant growth and development. The rate fromnutrientsolution. *Absorption creasingatmosphericmoisturelevels at a of growth, the composition,and the form June 1979 361 This content downloaded from 62.122.79.81 on Wed, 18 Jun 2014 10:40:32 AM All use subject to JSTOR Terms and Conditions that a plant attains are controlled by hu- Principles and Perspectives. John Wiley sumption and Response. Academic Press, and Sons, New York. New York. midity. Commercial plant producers and Erlandsson,G. 1975.Rapideffects on ion and , ed. 1972. Water Deficits and Plant greenhouse managers have long been water uptake induced by changes of water Growth, III. Plant Responses and Control aware of this and have developed and are potential in young wheat plants. Physiol. of Water Balance. Academic Press, New continuously improving systems for con- Plant. 35(3): 256-262. York. trol of atmospheric moisture levels in en- Farquhar,G. D., and I. R. Cowan. 1974. Os- Kristoffersen,T. 1963. 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Plant Response to Climatic 881. Raschke. 1964. Leaf temperaturesin con- Factors. Proc. Uppsala Symp. 1970. Hoffman, G. J., and J. A. Jobes. 1978. trolled environments.Planta 61: 56-72. UNESCO, Paris. Growthand water relationsof cereal crops Mitchell,K. J., R. Robotham,and I. Warring- Biscoe, P. V., Y. Cohen, and J. S. Wallace. as influencedby salinityandrelativehumid- toit. 1976. Physics of controlled environ- 1976. Daily and seasonal changes of water ity. Agron. J. 70: 765-769. ment and plant growth. Pages 141-155 in potential in cereals. Proc. R. Soc. Lond. Hoffman,G. J., and S. L. Rawlins. 1970.De- Proceedings of the Symposium on Climate Ser. B 273: 565-580. sign and performance of sunlit climate and Rice. Int. Rice Res. Inst. Manila,Phil- Breazeale, E. L., W. T. McGeorge,and J. F. chambers. Trans. Am. Soc. Agric. Eng. 13: Breazeale. 1950. Moisture absorption by ippines. 656-660. O'Leary, J. W. 1975. Environmental influ- plants from an atmosphereof high humidi-. 1971. Growth and water potential of ence on total water consumptionby whole ty. Plant Physiol. 25: 413-419. root crops as influencedby salinity and rel- plants. Pages 203-212 in D. M. Gates and Bowen, J. E. 1972. Effect of environmental ative humidity.Agron. J. 63(6): 877-881. R. B. Schmul, eds. Ecological Studies factorson waterutilizationand boronaccu- Hoffman,G. J., S. L. Rawlins, M. J. Garber, Analysis and Synthesis, Vol. 12. Per- mulation and translocation in sugarcane. and E. M. Cullen. 1971Waterrelationsand spectives of Biophysical Ecology. Springer- Plant Cell Physiol. 13(4): 703-714. growth of cotton as influencedby salinity Verlag, New York. Bravdo, B. A. 1977. Oscillatorytranspiration Palzkill,D. A., andT. W. Tibbitts. 1977.Evi- and relative humidity.Agron. J. 63(6):822- and carbon dioxide compensation concen- dence that root pressureflow is requiredfor 826. tration. Physiol. Plant. 41(1): 36-41. calcium transport to head leaves of cab- Cowan, I. R. 1977.Stomatalbehaviorand en- Jensen, C. R. 1975. Effects of salinity in the root medium,II. Photosynthesisand trans- bage. Plant Physiol. 60: 854-856. vironment.Pages 117-229in R. D. Preston pirationin relation to superimposedwater Palzkill,D. A., T. W. Tibbitts,and P. H. Wil- and H. W. Woolhouse, eds. Advances in stress from changeof evaporativedemands liams. 1976.Enhancementof calciumtrans- Botanical Research IV. Academic Press, New York. and of root temperaturefor short periods. port to inner leaves of cabbage for pre- Acta Agric. Scand. 25(1): 3-10, 72-80. vention of tipburn. J. Am. Soc. Hort. Sci. Davies, W. J., and T. T. Kozlowski. 1974. 101(6):645-648. Stomatal responses of 5 woody angio- Kaufmann,M. R. 1976. Stomatalresponse of Engelmannspruce to humidity, light, and Pareek, O. P., T. Sivanayagam, and W. spermsto lightintensityand humidity.Can. J. Bot. 52(7): 1525-1534, waterstress. Plant Physiol. 57(6):898-901. Heydecker. 1969.Relative humidity:a ma- Drake, B. J., K. Raschke, and F. B. Salis- Khaira,M. M. A., and A. E. Hall. 1976.Tem- jor factorin plantgrowth.Rept. Sch. Agric. peratureand humidityeffects on net photo- Univ. Nottingham. 1968-69: 92-95. bury. 1970.Temperaturesand transpiration resistances of Xanthiumleaves as affected synthesis and transpiration of citrus. Prisco, J. T., and J. W. O'Leary. 1973. The Physiol. Plant. 36(1): 29-34. effects of humidityand cytokininon growth by air temperature, humidity, and wind and water relations of salt stressed bean speed. Plant Physiol. 46: 324-330. Kolderup,F. 1975.Effect of soil moisture,air humidity, and temperatureon seed setting plants. Plant Soil 39(2): 263-276. Elgawhary, S. M., G. L. Malzer, and S. A. Barber. 1972.Calciumand strontiumtrans- and ear size in wheat. Acta Agric. Scand. Raschke, K. 1975. Stomatal action. Annu. 25(2): 97-102. Rev. Plant Physiol. 26: 309-340. port to plant roots. Soil Sci. Soc. Am. Proc. 36(5): 794-799. Kozlowski, T. T., ed. 1968. Water Deficits Raschke, K., and U. Kuhl. 1969.Stomatalre- Epstein, E. 1972. Mineral Nutrition of Plants: and Plant Growth, II. Plant Water Con- sponses to changes in atmospherichumidi- 362 BioScience Vol. 29 No.6 This content downloaded from 62.122.79.81 on Wed, 18 Jun 2014 10:40:32 AM All use subject to JSTOR Terms and Conditions  ty and water supply. Experimentswith leaf sections of Zea mays in CO,-free air. Planta 87: 36-48. Second Conferenceon Rawson, H. M., J. E. Begg, and R. G. Wood- ward. 1977. The effect of atmospherichu- ScientificResearch in the National Parks midityon photosynthesis,transpirationand Sheraton-Palace Hotel water use efficiency of leaves of several San Francisco, California plant species. Planta 134(1):5-10. Schulze, E.-D., O. L. Lange, M. Evenari, L. 26-30 November 1979 Kappen, and U. Buschbom. 1974.The role of air humidityand leaf temperaturein con- You are cordially invited to participate in the Second Conference on Scientific trollingstomatalresistanceof Prunusarme- Research in the National Parks, which will convene at the Sheraton-Palace Hotel niaca underdesert conditions, I. A stimula- in San Francisco from 26 to 30 November 1979. The program will consist of key- tion of the daily course of stomatal note addresses, plenary sessions, poster sessions, a film theater, and contributed resistance. Oecologia 17(2): 159-170. papers.. 1975a. The role of air humidity and Contributed papers are invited. Please use the listing of topics/sessions below as a temperaturein controlling stomatal resis- tance of Prunus armeniaca under desert guide in selecting the appropriate sessions in which your paper could be presented. To be considered for presentation, titles and abstracts (not to exceed 400 words) conditions, III. The effect on water use effi- must be submitted to the chairperson of the session representing your field of ciency. Oecologia 19(4):303-314. interest by 9 July 1979. Schulze, E.-D., O. L. Lange, L. Kappen, M. Evenari, and U. Buschbom. 1975b. The For instructions on submitting abstracts, or for further information concerning the role of air humidityand leaf temperaturein conference program, registration, and housing, contact Janet Barrett, AIBS Meet- controlling stomatal resistance of Prunus ings Department, 1401 Wilson Blvd., Arlington, VA 22209; 703/527-6776. armeniaca underdesert conditions, II. The significanceof leaf water status and internal CONFERENCE CHAIRMAN: G. Jay Gogue, Regional Chief Sci- carbon dioxide concentration. Oecologia entist, Southeast Region, National Park Service, 1895 Phoenix 18(3):219-234. Blvd., Atlanta, GA 30349; 404/996-2520 or FTS 260-9340 Shear, C. B. 1975. Calcium-relateddisorders of fruits and vegetables. HortScience 10: SESSION CHAIRPERSONS 361-365. Sheriff,D. W. 1977.The effect of humidityon ANTHROPOLOGY & ARCHEOLOGY PHYSICALSCIENCES water uptake by, and viscous flow resis- Douglas H. Scovill Ray Herrmann,Chief tance of, excised leaves of a numberof spe- ChiefAnthropologist Divisionof Air& WaterResources cies: physiologicaland anatomicalobserva- NationalParkService Departmentof Interior tions. J. Exp. Bot. 28(107):1399-1407. MainInteriorBuilding Washington,DC 20240 Washington,DC 20240 202/343-5181 or FTS 343-5181 Stone, E. C., F. W. Went, and C. L. Young. 202/343-6975 or FTS 343-6975 1950. Water absorption from the atmo- SOCIOLOGY sphere by plants growing in dry soil. Sci- AQUATICBIOLOGY Donald R. Field ence 111: 546-548. Leo F. Marnell RegionalChief Scientist Swalls, A. A., and J. W. O'Leary. 1975. The AquaticEcologist College of Forest Resources effect of relativehumidityon growth, water GlacierNationalPark Universityof Washington consumption,andcalciumuptakein tomato NationalParkService Seattle, WA98195 West Glacier,MT59936 206/543-6210 or FTS 392-6210 plants. J. Ariz. Acad. Sci. 10(2): 87-89. 406/888-5441 or FTS 585-5011 Thibodeau, P. 0., and P. L. Minotti. 1969. TECHNOLOGY The influence of calcium on the develop- ENVIRONMENTAL CONCERNSIN RichardB. Bowser ment of lettuce tipburn. J. Am. Soc. Hort. URBAN/IMPACTED PARKS AppropriateTechnology Sci. 94: 372-376. RichardHammerschlag NationalParkService Tibbitts, T. W., and G. Bottenberg. 1976. EcologicalServices Laboratory 1100 L Street, N.W. Growthof lettuce undercontrolledhumidi- NationalCapitalRegion Room No. 3405 ty levels. J. Am. Soc. Hort. Sci. 101(1): 70- 1100 Ohio Drive,S.W. Washington,DC 20240 73. Washington,DC 20242 202/523-5166 or FTS 523-5166 202/426-6796 or FTS 426-6796 Tromp, J., and J. Oele. 1972. Shoot growth TERRESTRIAL BIOLOGY:Botany and mineral composition of leaves and ENVIRONMENTAL EDUCATION Resource Management,Coastal Biology fruitsof appleas affectedby relativeair hu- BarbaraB. Clark,Chief Paul J. Godfrey midity. Physiol. Plant. 27(2): 253-258. EnvironmentalEducationSpecialist Associate Professor Tsuno, Y. 1975.The influenceof transpiration NationalParkService Departmentof Botany upon the photosynthesis in several crop 1100 L Street, N.W. Universityof Massachusetts Room No. 3401 Amherst,MA01003 plants. Proc. Crop Sci. Soc. Jpn. 44(1): 44- 413/545-2235 or 413/549-1140 53. Washington,DC 20240 202/523-5153 or FTS 523-5153 Walker, J. C., L. V. Edgington, and M. V. TERRESTRIAL BIOLOGY:Zoology Nayudu. 1961. Tipburnof cabbage: nature INFORMATION SCIENCES Resource Management and control. Univ. Wis. Res. Bull. 230. Charles H. Douglas MaryMeagher Went, F. W. 1975.Watervapor absorptionin Directorof General Research SupervisoryResearch Biologist Universityof Georgia YellowstoneNationalPark Prosopis. Pages 67-75 in E. J. Vernberg, 616 Grad.Studies Research Center P.O. Box 168 ed. Physiological Adaptation to the Envi- YellowstoneNationalPark,WY82190 Athens, GA 30602 ronment. Intext Educ. Pub., New York. 404/542-3360 or FTS 289-2011 307/344-7381 or FTS 585-0248 Wiebe, H. J., H. P. Schiatzler,and W. Kiihn. 1974. Diurnalfluctuationsof the mass of a cabbage plant. Kerntechnik16: 532-533. June 1979 363 This content downloaded from 62.122.79.81 on Wed, 18 Jun 2014 10:40:32 AM All use subject to JSTOR Terms and Conditions