Relationships among percentage of open stomates, transpiration, and needle moisture content in seedlings of loblolly pine of two Texas provenances were studied under changing soil moisture conditions. Needle moisture content correlated very well with transpiration under favorable moisture conditions, and with percentage of open stomates under soil moisture stress. Transpiration and percentage of open stomates were correlated under a wide range of moisture conditions. Foliage moisture content was still relatively high in both ecotypes when stomates closed and transpiration drastically declined. The  Lost Pines  seed source appeared to have superior ability to conserve moisture under droughty conditions by closure of stomares and reduction of transpiration. FOREST SCI. 23: 457-462

Bilan, M. Victor

Carter, H.B.

Hogan, C.T.

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Stephen F. Austin State UniversitySFA ScholarWorksFaculty Publications Forestry1977Stomatal Opening, Transpiration, and Need/eMoisture in Loblolly Pine Seedlings From TwoTexas Seed SourcesM. Victor BilanArthur Temple College of Forestry and Agriculture, Stephen F. Austin State UniversityC.T. HoganH.B. CarterFollow this and additional works at: http://scholarworks.sfasu.edu/forestryPart of the Forest Sciences CommonsTell us how this article helped you.This Article is brought to you for free and open access by the Forestry at SFA ScholarWorks. It has been accepted for inclusion in Faculty Publicationsby an authorized administrator of SFA ScholarWorks. For more information, please contact cdsscholarworks@sfasu.edu.Recommended CitationBilan, M. Victor; Hogan, C.T.; and Carter, H.B., "Stomatal Opening, Transpiration, and Need/e Moisture in Loblolly Pine SeedlingsFrom Two Texas Seed Sources" (1977). Faculty Publications. Paper 355.http://scholarworks.sfasu.edu/forestry/355Stomatal Opening, Transpiration, and Need/e Moisture in Loblolly Pine Seedlings From Two Texas Seed Sources M. VICTOR BILAN CLIFFORD T. HOGAN H. BROOKS CARTER ABSTRACT. Relationships among percentage of open stomates, transpiration, and needle moisture content in seedlings of loblolly pine of two Texas provenances were studied under changing soil moisture conditions. Needle moisture content correlated very well with transpiration under favorable moisture conditions, and with percentage of open stomates under soil moisture stress. Transpiration and percentage of open stomates were correlated under a wide range of moisture conditions. Foliage moisture content was still relatively high in both ecotypes when stomates closed and transpiration drastically declined. The "Lost Pines" seed source appeared to have superior ability to conserve moisture under droughty conditions by closure of stomares and reduction of transpiration. FOREST SCI. 23: 457-462. ADDITIONAL KEY WORDS. Ecotype, drought resistance, moisture relations, stomates, provenance. IN BASTROP, FAYETTE, AND CALDWELL COUNTIES of central Texas, isolated stands of loblolly pine (Pinus taeda L.) exist more than 100 miles west of the continuous range of that species. Known as the "Lost Pines," they generally receive 10-20 inches less annual and 4-6 inches less July-August rainfall than trees in the pine belt of East Texas. In field experiments, seedlings of Lost Pines provenance survived better than seedlings from East Texas when grown under droughty conditions (Zobel and Goddard 1955, Goddard and Brown 1959). Natural selection in this semiarid environment has apparently produced a more drought resistant strain of loblolly pine. Drought resistance in a plant may result from drought avoidance---ability to maintain moisture in its tissues, or drought tolerance--ability to survive moisture stress within the plant tissues, or from both (Hopkins 1971). Plants may avoid drought by restricting water loss, by developing extensive or deep root systems, or by both. Some drought tolerant plants are able to maintain life activities when absorbing almost no water (Oppenheimer 1960). There is some evidence that Bastrop pines survive somewhat higher moisture stress than pines of East Texas provenance. x They also produce deeper roots which x Brix, H. 1959. Some aspects of drought resistance in loblolly pine seedlings. Ph D Diss, Tex A&M Univ, College Station, Texas. 94 p. The authors are, respectively, Professor of Forestry and former Graduate Research Assis- tants, School of Forestry, Stephen F. Austin State University, Nacogdoches, TX 75962. The research was funded in part by funds allocated under the McIntire-Stennis Act. Manuscript received February 25, 1976, and in revised form July 15, 1977. VOLUME 23, NUMBER 4, 1977 / 457 may afford access to greater water supplies, 2 but their drought resistance is probably due primarily to ability to conserve water by reduced transpiration (van Buijtenen, Bilan, and Zimmerman 1976). Brix x attributed variation in drought resistance of 1oblolly pines to factors affecting their water economy. Other workers have reported that seedlings from the Lost Pines area have a thicker cuticle and fewer stomates per unit of surface area than similar seedlings from East Texas (Thames 1963, Knauf and Bilan 1972 and 1977). In addition, Haugen a found that their stomates began to close at lower levels of moisture stress. Because stomatal movement is the chief regulator of water loss (Slatyer 1967), especially where leaves have a well-cutinized epidermis, this study simultaneously determined transpiration rates and proportion of open stomates on leaves of lob- lolly pines of Bastrop and East Texas provenance, as affected by progressive drought. PROCEDURE Loblolly pine seeds collected in Polk County, East Texas, and Bastrop County, Lost Pines area, were planted in plastic pots uniformly filled with sandy soil and were grown with frequent watering under 50 percent full sunlight in an air-conditioned greenhouse. Groups of seedlings from each source, aged 6, 10, and 12 months, were studied in separate experiments. On the youngest seedlings, primary needles constituted 30 percent of foliage surface; at age 10 and 12 months proportions of primary needles were negligible. The apparatus used for transpiration measurements i similar to one developed by Bierhuizen and Slatyer (1964), and modified by Unterschuetz and others (1974). Cold and warm water baths, each containing a copper tubing coil and an aspirator bottle, regulate temperature and relative humidity within the system. A seedling is enclosed in a plexiglas water-jacketed cuvette equipped with an externally driven fan. When installed in the cuvette, the shoot of the seedling and its potted root system are in separate air- and water-tight compartments. A third constant temperature bath equipped with a water pump helps to regulate temperature within the cuvette. Four 1250 watt self-ballasted mercury vapor lamps light the seedling. Air is driven through the system at a rate measured by two flowmeters which, due to their location, indicate if the cuvette is properly sealed. The relative humidity of the air before and after passing over the seedling is measured by two electric lithium chloride temperature-compensated hygrosensors (Hygrodynamics Type 15-1811 ) and recorded on a hygrosensor recorder. Hygrosensors are sealed in separate plexi- glas chambers and submerged in the water bath which maintains them at a constant temperature. Tygon tubing was used in limited amounts for flexible connections. Seedlings were organized into experimental pairs (one Lost Pines, one East Texas), based on similarity of shape and size. Five pairs of each age class were used in the experiments. Each pair was acclimated with daily irrigations at 8:00 a.m. in a growth chamber for 1 week prior to the beginning of measurements. The environ- mental conditions maintained in the growth chamber and cuvette are listed in Table 1. '• Davies, G. 1973. Response of loblolly pine seedlings from two seed sources to favorable and unfavorable moisture regimes. Unpublished M S thesis, Stephen F. Austin State Univ. 76 p. *Haugen, R.M. 1972. Effect of some environmental factors on the stomatal reaction of loblolly pine seedlings from two seed sources. Unpublished M S thesis, Stephen F. Austin State Univ. 53 p. 458 / FOREST SCIENCE TABLE 1. Environmental conditions within the growth chamber and the cuvette. Growth Chamber Item Cuvette light dark Temperature ................................ *C .... 31 Relative humidity ................... percent ___ 45-50 Light source ................................................. mercury vapor Light intensity ................ foot-candles .... 1000 Caron dioxide ..................... percent .... 0.05 Turbulence ......................... cm/sec .... 9.14 cm/sec Photoperiod (7 a.m.-8 p.m.) ...... hours .... -- Thermoperiod (7 a.m.-8 p.m) _ hours __ -- 29-35 18-21 40-50 90-100 incandescent/fluorescent 1000 0.05 13 13 Each pair was subjected to drought by withholding irrigation for 7 to 8 days. Percentage of open stomates and rate of transpiration were determined at 2-hour intervals for 6- and 12-month-old plants and at 3-hour intervals for 10-month-old plants. Monitoring began at 8:00 a.m., 1 hour after commencement of the light period, on selected days during the dry-down period. For each pair, determinations began 24 hours after the latest watering. Except as noted, needle moisture content was determined at 8:00 a.m., and 6:00 p.m. on the same days as•the other determi- nations. Oppenheimer and Engelbergs' (1965) dye infiltration method was used to ob- serve open stomates. At each observation, before the seedling was placed in the cuvette, one healthy secondary needle from the base of the crown was immersed for 2 minutes in a dye of the following proportions: 9 ml ether, 9 ml chloroform, 0.6 gm methyl violet. After washing in secondary butanol, needles were rinsed in water and the percentage of open stomates was estimated under a binocular microscope to the nearest 1 percent. Transpiration rate was computed from the increase in relative humidity of the air stream after passing the test plant, and expressed on the basis of total foliage sur- face area progressively corrected for the removed samples. Foliage surface was computed as the product of needle perimeter at midpoint, needle length, and the number of needles on the seedling. Air flow through the system was 2000 ml/min for seedlings of all age classes. Readings were taken after each seedling had been in the cuvette for 20 minutes. Since transpiration could be measured on only one seedling at a time, the first plant of each pair was installed in the cuvette on the hour, and the second about 40 minutes later. A minimum of 20 minutes was allowed between seedlings of the pair for equilibration of the apparatus. Needle moisture content (percent) was determined gravimetrically from one needle from each seedling as follows: NMC = fresh weight - dry weight x 100 dry weight Needle samples for moisture content determination were collected from the same position on the crown as the samples for open stomate percentage determination. RESULTS AND DISCUSSION Because separate analyses of data for each of the three experiments produced similar results, data of all 15 pairs of seedlings were combined for one common statistical VOLUME 23, NUMBER 4, 1977 / 459 TABLE 2. Average needle moisture content, percent open stomates, and transpi- ration rate in J-year-old loblolly pines, by days since last watering. Day since watering and seed source Needle moisture content Open stomates Transpiration Percent t value Percent t value i•g/rnin/crn • t value Day 1 East Texas 224 ñ 4 -0.89 22.9 ñ 1.1 -1.32 10.77 ñ 0.73 0.52 Lost Pines 220 ñ 3 20.7 -4- 1.2 11.30 ñ 0.72 Day 3 East Texas Lost Pines Day 5 East Texas Lost Pines Day 7 East Texas Lost Pines 219 ñ 4 -1.10 16.8 ñ 1.0 -2.38* 6.78 ñ 0.35 0.52 213 ñ 4 13.5 ñ 1.0 7.08 ñ 0.47 213 ñ 4 -1.59 9.4 __+ 0.9 -3.80*** 3.12 ñ 0.14 -0.80 201 ñ 4 5.5 ñ 0.6 2.92 ñ 0.21 193 ñ 5 -1.58 4.8 ñ 0.5 -3.33*** 1.77 ñ 0.17 -2.46* 180 ñ 7 2.3 __+ 0.5 1.20 ñ 0.16 Entire dry-down period East Texas '• 211 __+ 2Lost Pines 204 __+ 3 -2.31' 12.9 __+ 0.6 -3.69*** 5.38 ñ 0.27 0.80 9.9 ñ 0.6 5.41 ñ 0.30 * Values differ significantly at the 5 percent level. *** Values differ significantly at the 0.1 percent level. analysis. Thus daily averages in Table 2 are based on 30-90 values depending on the number of monitorings per day. Average needle moisture content for the entire dry-down period was significantly higher (211 percent) in East Texas than in Lost Pines (204 percent) seedlings, but differences for individual days were not significant. General pattern of needle mois- ture decline from about 225 percent on the first day to 180 percent on the seventh day after the last waterings was similar in both seed sources. Average percentage of open stomates for the dry-down period as a whole was very highly significantly greater in the East Texas plants than in the Lost Pines plants. Differences significant at the 5 percent level were detected on the third day; on the fifth and seventh day of the dry-down period they were significant at the 0.1 percent level. Average percentage of open stomates declined from 23 on the first day to 5 percent on the seventh day in the East Texas pines and from 21 to 2 per- cent in Lost Pines pines. Rate of transpiration was measured at about 11 •g/min/cm 2 for plants of both seed sources on the first day, but decreased to 1.77 •g/min/cm 2 in East Texas plants and to 1.20 •g/min/cm 2 in Lost Pines plants on the seventh day, at which time the difference between seed sources was significant at the 5 percent level. Average transpiration rate for the dry-down period as a whole was about the same; 5.38 •g/min/cm 2 for East Texas and 5.41 •g/min/cm 2 for Lost Pines seed sources. For the dry-down period as a whole, the percentage of open stomates was very highly significantly correlated with needle moisture content and with the rate of transpiration in both seed sources (Table 3). Significant correlations between per- centage of open stomates and needle moisture content were observed on days 1 and 7 in East Texas plants and on days 5 and 7 in Lost Pines plants. The highest value of correlation (0.36) existed on the seventh day of the dry-down period. 460 / FOREST SCIENCE TABLE 3. Pearson coefficients of correlation among needle moisture content, percent open stomares, and transpiration rate of loblolly pine seedlings from East Texas and Lost Pines seed source, by days since last watering. Days since last watering Seed Percent open Transpiration and monitored variable source stomates /•g/min/cm" Day 1 Needle moisture content percent Percent open stomates Day 3 Needle moisture content percent Percent open stomates Day 5 Needle moisture content percent Percent open stomates Day 7 Needle moisture content percent Percent open stomates Entire dry-down period Needle moisture content percent Percent open stomates East Texas -0.3590 (.017) • -0.5578 (.001) Lost Pines -0.0497 (.388) -0.5682 (.001) East Texas 0.6523 (.001) Lost Pines 0.4298 (.001) East Texas -0.1792 (.152) -0.4407 (.004) Lost Pines 0.0253 (.443) -0.3167 (.032) East Texas 0.4274 (.001) Lost Pines 0.2398 (.016) East Texas 0.1831 (.129) -0.0208 (.449) Lost Pines 0.2482 (.061) -0.0039 (.490) East Texas 0.1725 (.047) Lost Pines 0.4374 (.001) East Texas 0.3655 (.015) -0.1005 (.289) Lost Pines 0.3630 (.016) 0.0417 (.412) East Texas 0.2156 (.03 I) Lost Pines 0.2574 (.015) East Texas 0.2332 (.002) 0.0094 (.454) Lost Pines 0.3272 (.001) 0.1207 (.070) East Texas 0.7008 (.001) Lost Pines 0.6683 (.001) Level of confidence. Significant correlation between percentage of open stomates and the rate of transpiration was detected for every day in both provenances, with the highest coefficients (0.70 for East Texas; 0.67 for Lost Pines) for the dry-down period as a whole. Needle moisture content and transpiration rate were significantly correlated only on the first and third days in both seed sources. The coefficients were highest on the first day; 0.56 for East Texas and 0.57 for Lost Pines seedlings. It seems that needle moisture content of loblolly pine seedlings correlates very well with the rate of transpiration under favorable moisture conditions, and with percentage of open stomates under moisture stress. Percentage of open stomates is very well correlated with the rate of transpiration under a wide range of moisture conditions. It was of interest to note that the stomates practically closed and tran- spiration was drastically reduced at the needle moisture content of 180-190 per- cent, almost wice that of lethal moisture stress reported by Brix (1960), Stransky (1963), and Davies? VOLUME 23, NUMBER 4, 1977 / 461 Lower percentage of open stomates and more drastic reduction of transpiration at inceptive moisture stress in the foliage of Lost Pines seedlings are two, of prob- ably many, characteristics which enable this ecotype to maintain itself in the Lost Pines area. LITERATURE CITED BmmUmZEN, J. F., and R. O. SLATYER. 1964. An apparatus for the continuous and simul- taneous measurement of photosynthesis and transpiration under controlled environmental conditions. CSIRO Australian Div Land Res Tech Pap 24. BPdx, H. 1960. Determination of viability of loblolly pine seedlings after wilting. Bot Gaz 121:220-223. GOI>D•V.D, R. E., and C. L. BROWN. 1959. Growth of drought resistant loblolly pines. Texas Forest Serv Res Note 23, 7 p. HOPKINS, E.R. 1971. Drought resistance in seedlings of Pinus pinaster AIT. Forest Dep, Perth, Western Australia, Bull 82, 35 p. KNAUF, T. A., and M. V. BILAN. 1974. Needle variation in loblolly pine from mesic and xefic seed sources. Forest Scl 20:88-90. KN•LrF, T. A., and M. V. BIL•N. 1977. Cotyledon and primary needle variation in loblolly pine from mesic and xeric seed sources. Forest Sci 23:33-36. OPPENHEIMER, H.R. 1960. Adaption to drought: xerophytism. In UNESCO Reviews of research in plant-water relationship in arid and semi-arid conditions, p. 105-108. OPPENHEIMER, H. R., and N. ENGLEBERG. 1965. Mesure du degre d'ouverture des stomates de coniferes methodes anciennes et modernes. (Colloque International de methodologie de L'Eco-Physiologie Vegetale, Montpelier, 1962). UNESCO Arid Zones Res 25:317-323. SLATYEP., R.O. 1967. Plant-water relationships. Academic Press, New York. 366 p. STRANSKY, J. J. 1963. Needle moisture content as mortality index for southern pine seed- lings. Bot Gaz 124:176-179. THAMES, J.L. 1963. Needle variation in loblolly pine from four geographic seed sources. Ecology 44:168-169. UNTERSCHUETZ, P. F., W. F. RUETZ, R. GEPPERT, and W. K. FERRELL. 1974. The effect of age, pre-conditioning, and water stress on transpiration rates of Douglas-fir (Pseudotsuga menziesii) seedlings of several different ecotypes. Physiol Plant 32:214-221. VAN BUIJTENEN, J.P., M. V. BILAN, and R. H. ZIMMERMAN. 1976. Morpho-physiological characteristics related to drought resistance in Pinus taeda L. In Tree physiology and yield improvement (M. G. R. Cannell and F. T. Last, eds), p 349-358. Academic Press. London. ZOBEL, B. J., and R. E. GODDARD. 1955. Preliminary results on tests of drought hardy strains of loblolly pine (Pinus taeda L.). Texas Forest Serv Res Note 14, 22 p. 462 / FOREST SCIENCE 

Stomatal Opening, Transpiration, and Need/e Moisture in Loblolly Pine Seedlings From Two Texas Seed Sources

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Stomatal Opening, Transpiration, and Need/e Moisture in Loblolly Pine Seedlings From Two Texas Seed Sources

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