Diurnal variations in stomatal conductance of Betula ermanii and Pinus pumila at the timberline on Mt. Shogigashira, central Japan

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Diurnal variations in stomatal conductance of Betula ermanii and Pinus pumila at the

timberline on Mt. Shogigashira, central Japan

著者 Takahashi Koichi

journal or

publication title

植物地理・分類研究 = The journal of phytogeography and toxonomy

volume 51

number 2

page range 159‑164

year 2003‑12‑25

URL http://hdl.handle.net/2297/48614

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Introduction

Upper zone of subalpine forests in central Ja- pan is dominated mainly by Betula ermanii Cham., Abies mariesii Mast. and A. veitchii Lindl．（Yoshino 1978）. The upper distribution limit of B. ermanii is higher than that of the two Abies species to some extent. A dwarf pine

（Pinus pumilaRegel）is distributed in the alpine zone above the upper distribution limit ofB.er- manii, and therefore, alpine timberline is an al- titudinal ecotone between the B. ermanii zone and theP.pumila zone（Takahashi 2003）.

Climatic conditions such as low temperature and a short growing season around timberline are generally severe for plant growth and sur- vival. Therefore, many researchers have examined the timberline dynamics in relation to climatic conditions（e.g. Wardle 1968 ; Okitsu 1984 ; Kullman 1993 ; Taylor 1995 ; Gostev et al. 1996）. For example, the growth of several conifer species is positively correlated with summer temperature near or above the timberline in central Japan, while summer rainfall has no or negative influence on the tree growth there

（Sano et al. 1977 ; Okitsu 1988 ; Fujiwara et al.

1999 ; Takahashi 2003）. Thus, it is suggested that water limitation is weak at the timberline in central Japan. However, there are few eco- physiological studies to examine whether or not water limitation is weak for B.ermanii and P.

pumila growing at the timberline. Increased knowledge of water regulation of both species is of great importance for understanding the growth response to climatic conditions at the timberline in central Japan.

Stomatal conductance of leaves decreases in response to water limitation and/or high vapor pressure deficit of air（or low relative humidity）

for the control of water loss from plants（e.g.

Granier and Loustau 1994 ; Kallarackal and Somen 1997 ; Martin et al. 1997）. For example, midday stomatal closure is often observed in clear-sky days because of an increase in vapor pressure deficit（Jones and Muthuri 1984 ; Le Thiec and Dixon 1996）. Therefore, the examination of diurnal variations in stomatal conductance provides useful information to elucidate water regulation ofB.ermanii andP.pumilaat Department of Biology, Faculty of Science, Shinshu University, Matsumoto 390―8621, Japan

!The Society for the Study of Phytogeography and Taxonomy 2003

Koichi Takahashi : Diurnal variations in stomatal conductance of Betula ermanii and Pinus pumila at the timberline on Mt.

Shogigashira, central Japan

Abstract

Diurnal variations in the stomatal conductance ofBetula ermanii andPinus pumila were studied at the timberline（2,630 m a.s.l.）on Mt. Shogigashira in central Japan. Weather conditions at this timberline were usually clear sky in early morning, but foggy or cloudy from late morning or noon during August and mid-September in 2001. Rainfall was also frequently observed in late afternoon during this period. Stomatal conductance ofB.er- manii andP.pumilawas measured on four days during mid-August and mid-September. However, the measurement could not be performed throughout one day of the four because of rainfall from morning. Fog occurred from morning during the other three days that stomatal conductance could be measured. Photosynthetic photon flux density decreased and relative humidity increased in accordance with the occurrence of fog. Diurnal variations in the stomatal conductance of B.ermanii andP.pumila were not large on the three days. Therefore, this study suggests that stomatal closure ofB.ermanii andP.pumilaseems to occur infrequently at the timberline on Mt. Shogigashira, at least, during the examined period because of foggy and rainy climatic conditions.

Key words : Betula ermanii, Mt. Shogigashira,Pinus pumila, stomatal conductance, timberline.

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the timberline. Furthermore, rainfall events strongly influence stomatal conductance by in- creasing soil water content. However, available information is still limited about the diurnal variations in the stomatal conductance ofB.er- manii andP.pumila, coupled with the climatic observation. Therefore, the objective of this study was to examine the diurnal variations in the stomatal conductance of B. ermanii and P.

pumila at the timberline on Mt. Shogigashira in central Japan, with the observation of summer rainfall, air temperature and relative humidity of air.

Materials and methods

This study was carried out near the summit of Mt. Shogigashira（2,699 m above sea level, 35°

48’N, 137°50’E）in the Nishikoma Experimental Forest of Shinshu University, central Japan. The mean monthly air-temperature at Senjojiki

（2,650 m a.s.l., ca. 3.5 km from the study area）

ranged between −12.1℃（January）and 11.9℃

（August）, and the mean annual temperature was 0.8℃during 1990―1992（Fukuyo et al. 1998）. The maximum snow depth around the study area was ca. 3 m（Kajimoto 1989）. The prevail- ing winds come from the west in this region

（Fukuyo et al. 1998）.

Pinus pumila was distributed only near the summit of Mt. Shogigashira. Its altitudinal distribution ranged from the timberline（2,630 m a.

s.l.）to the summit（2,699 m a.s.l.）. On the contrary,B.ermanii was widely distributed from ca.

1,400 m to 2,630 m a.s.l.（timberline）on the east -facing slope of Mt. Shogigashira. This study was conducted at the timberline, which was the altitudinal ecotone between the B. ermanii zone and theP.pumilazone. The canopy height ofB. ermanii and that of P. pumila were ca. 2.8 m and 1.2 m, respectively, at this timberline（Taka- hashi 2003）.

Air temperature and relative humidity were automatically recorded at the front of the Nishikoma hut near the summit of Mt. Shogi- gashira at 1-hour intervals from August 7 to Oc- tober 4 in 2001, by using a thermometer coupled with a humidity sensor（HOBO H 8 Pro, Onset Computer Corp., Pocasset, MA, USA）. The thermometer was set within a radiation shield to

prevent exposure to direct solar radiation. Rain- fall was also measured by using a rain gauge

（Model 7852 M, Davis Corp., USA）with a data logger（HOBO Event, Onset Computer Corp., Pocasset, MA, USA）.

The diurnal variations in the stomatal conductance of B. ermanii and P.pumila were measured on four days in total（August 14, 25 and September 1, 14 in 2001），by using a null bal- ance porometer（Model Li-1600 with a Model 1600―02 square chamber [2―cm×2―cm], Li-Cor, Lincoln, NE, USA）. The porometer measure- ments were performed from approximately 07 : 00 to 17 : 00 hours at about 2-hour intervals, on five replicates for each ofP.pumila and B. er- manii at each measurement time. Leaves were chosen from the top of the canopy for the measurement of each species. Photosynthetic photon flux density（PPFD）was also measured at the porometer measurement.

The current-year shoots ofP.pumila elongate during June and July, and their needle longevity is ca. 4 years（Kajimoto 1993）. The light- saturated photosynthetic rate（Amax）ofP.pumila is higher in the 1-year-old needles than in the other needles by mid-August, but Amax of the current-year needles is higher than Amax of the other older needles thenceforth（Kajimoto 1990）， which suggests that current-year needles have fully developed by mid-August. Thus, the current -year needles of P. pumila were thought to be mature enough for the measurement of this study because the porometer measurement was started from mid-August. It is important to measure not only the stomatal conductance of the current-year needles but also that of the other older needles for the examination of the water use at the individual-tree level. However, for the practical reason, the porometer measure- ments ofP.pumila were conducted only for the current-year needles.

As for the porometer measurement of P.

pumila, five current-year needles from one fasci- cle were placed in the chamber, and their stomatal conductance was measured as one repli- cate. Needle diameter was measured for part of the needles used for the porometer measure- ments by using a digital caliper. The average diameter of needles was 0.61 mm（n = 32）. Total 植物地理・分類研究 第51巻第2号 2003年12月

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surface area of five needles inside the chamber was calculated as the product of the number of needles（i.e. five needles）and the surface area per single needle inside the chamber. The surface area of a single needle inside the chamber was estimated as a cylinder（π×0.061×2 cm²）. The stomatal conductance ofP.pumila was calculated on the basis of the actual leaf area inside the chamber.

Results and discussion

Weather conditions at the timberline on Mt.

Shogigashira were usually clear sky in early morning, but foggy or cloudy from late morning or noon during early August and mid-September in 2001. Rainfall also frequently occurred in late afternoon or evening. Rainfall（＞1 mm/day）was observed in total 20 days from August 7 to Sep- tember 15（total 40 days）, and the total rainfall during this period was 450.4 mm（Fig. 1）. Thus,

entire clear-sky days were infrequent at the timberline on Mt. Shogigashira during the examined period.

Stomatal conductance was measured during the four days（August 14, 25 and September 1, 14）. However, the measurement could not be conducted throughout the daytime on September 14 because of the rainfall from the morning（Fig.

1）. The diurnal changes in PPFD on August 14 were similar to those on September 1（Fig. 2）. PPFD was high in the early morning on both days, but had decreased by 10 : 00 hours due to the occurrence of fog（Fig. 2）. On the contrary, the diurnal changes in PPFD on August 25 were different from those on the other two days（Fig.

2）. PPFD increased from the early morning to the noon on August 25, but abruptly decreased at the noon by the occurrence of fog. However, high PPFD was observed again at around 15 : 00 hours because of the temporal clearance of fog.

The diurnal variations in the stomatal conductance of B. ermanii and P. pumila were not large during the three days（Fig. 3）. The stomatal conductance of P. pumila on August 25 was tended to be more variable than that on the other two days（Fig. 3）, although the reason was unknown. Thus, this study showed that stomatal closure of B. ermanii and P. pumila seems to occur infrequently at the timberline on Mt.

Shogigashira, at least, during the examined period because of foggy and rainy climatic conditions. However, intra- and interannual fluctua- tion of climatic conditions may be large. For example, the total rainfall between August 7 and September 15 in 2002 was only one-thirds of the rainfall observed during the same period in 2001 at this timberline（Takahashi unpublished）. In addition, midday stomatal closure was observed in P. pumila on an entirely clear-sky day in summer of 2002（Takahashi unpublished）. Ishida et al．（2001）also reported the importance of stomatal control forP.pumiladuring snow-melting period. Solar radiation is high, but soil temperature is still low（ca. 0℃）at this period（Maruta et al. 1996）.Pinus pumilaneeds to avoid needle desiccation during the snow-melting season because P. pumila hardly absorbs soil water.

Therefore, the results of this study do not mean that stomatal control is less important forB.er- Fig. 1. Seasonal changes in air temperature（upper

figure）and daily rainfall（lower figure）recorded near the summit of Mt. Shogigashira in central Japan. The upper figure shows the daily range between the maximum and minimum air- temperatures（vertical bar）with the daily mean temperature（solid circle）. Arrows in the lower figure indicate the days that porometer measurement was performed.

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Fig. 2. Diurnal changes in air temperature（open circle）and relative humidity（RH, solid circle）on August 14, 25 and September 1 near the summit of Mt. Shogigashira in central Japan（upper figures）, and diurnal changes in photosynthetic photon flux density（PPFD）at the porometer measurement forBetula ermanii（open circle）andPinus pumila（solid circle）（lower figures）. The lower figure shows the observed range between the maximum and minimum PPFD（vertical bar）with the mean PPFD（circle）at each measurement time.

Fig. 3. Diurnal changes in stomatal conductance inBetula ermanii（upper）andPinus pumila（lower）on August 14, 25 and September 1 at the timberline on Mt. Shogigashira in central Japan. The mean value（solid circle）

with the observed range between the maximum and minimum values（vertical bar）was shown. Note that or- dinate scales are different between the upper and lower figures.

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maniiandP.pumila at this timberline. Further studies are necessary to reveal how these two species respond to climatic conditions in terms of the stomatal control for water regulation by the examination of the stomatal conductance in vari- ous climatic conditions.

Acknowledgements

This study was partially supported by a grant from the Ministry of Education, Science, Sports and Culture of Japan（No. 13780418）.

References

Fujiwara, T., Okada, N. and Yamashita, K. 1999.

Comparison of growth response of Abies and Picea species to climate in Mt. Norikura, central Japan. J. Wood Sci.45: 92―97.

Fukuyo, S., Kurihara, M., Nakashinden, I., Kimura, K., Iijima, Y., Kobayashi, Y., Masuzawa, T., Yamamoto, S., Morimoto, M., Kouyama, T., Kobayashi, S., Yamamoto, T., Mizuno, K. and Machida, H. 1998. Short-term effects of wind shield on phenology and growth of alpine plants in Mount Kiso-Komagatake, central Ja- pan. Proc. NIPR Symp. Polar Biol. 11: 147―

158.

Gostev, M., Wiles, G., D’Arrigo, R., Jacoby, G.

and Khomentovsky, P. 1996. Early summer temperatures since 1670 A.D. for Central Kamchatka reconstructed based on a Siberian larch tree-ring width chronology. Can. J. For.

Res.26: 2048―2052.

Granier, A. and Loustau, D. 1994. Measuring and modelling the transpiration of a maritime pine canopy from sap-flow data. Agr. For. Me- teorol.71: 61―81.

Ishida, A., Nakano, T., Sekikawa, S., Maruta, E.

and Masuzawa, T. 2001. Diurnal changes in needle gas exchange in alpine Pinus pumila during snow-melting and summer seasons.

Ecol. Res.16: 107―116.

Jones, M. B. and Muthuri, F. M. 1984. The diurnal course of plant water potential, stomatal conductance and transpiration in a papyrus

（Cyperus papyrus L．）canopy. Oecologia 63: 252―255.

Kajimoto, T. 1989. Aboveground biomass and lit- terfall ofPinus pumila scrubs growing on the Kiso mountain range in central Japan. Ecol.

Res.4: 55―69.

Kajimoto, T. 1990. Photosynthesis and respira- tion of Pinus pumila needles in relation to needle age and season. Ecol. Res.5: 333―340.

Kajimoto, T. 1993. Shoot dynamics of Pinus pumila in relation to altitudinal and wind exposure gradients on the Kiso mountain range, central Japan. Tree Physiol.13: 41―53.

Kallarackal, J. and Somen, C.K. 1997. Water use by Eucalyptus tereticornis stands of differing density in southern India. Tree Physiol. 17: 195―203.

Kullman, L. 1993. Pine（Pinus sylvestrisL．）tree -limit surveillance during recent decades, central Sweden. Arc. Alp. Res.25: 24―31.

Le Thiec, D. and Dixon, M. 1996. Acclimation of photosynthesis in Norway spruce and red oak grown in open-top chambers and subjected to natural drought and to elevated CO2. Can. J.

For. Res.26: 87―94.

Martin, T. A., Brown, K. J., Cermák, J., Ceule- mans, R., Kucera, J., Meinzer, F. C., Rombold, J. S., Sprugel, D. G. and Hinckley, T. M. 1997.

Crown conductance and tree and stand transpiration in a second-growth Abies amabilis forest. Can. J. For. Res.27: 797―808.

Maruta, E., Nakano, T., Ishida, A., Iida, H. and Masuzawa, T. 1996. Water relations of Pinus pumila in the snow melting season at the alpine region of Mt. Tateyama. Proc. NIPR Symp. Polar Biol.9: 335―342.

Okitsu, S. 1984. Control factors of the forest limit in Mt. Taisetsu, central Hokkaido, Japan.

Jpn. J. Ecol.34: 439―444．（in Japanese）

Okitsu, S. 1988. Geographical variations of annual fluctuations in stem elongation of Pinus pumila Regel on high mountains of Japan.

Jpn. J. Ecol.38: 177―183．（in Japanese）

Sano, Y., Matano, T. and Ujihara, A. 1977.

Growth of Pinus pumila and climate fluctua- tion in Japan. Nature266: 159―161.

Takahashi, K. 2003. Effects of climatic conditions on shoot elongation of alpine dwarf pine

（Pinus pumila）at its upper and lower altitu- dinal limits in central Japan. Arc. Antarc. Alp.

Res.35: 1―7.

Taylor, A.H. 1995. Forest expansion and climate change in the mountain Hemlock（Tsuga mer- tensiana）zone, Lassen Volcanic National Park, 163

(7)

U.S.A. Arc. Alp. Res.27: 207―216.

Wardle, P. 1968. Engelmann spruce（Picea engel- mannii Engel．）at its upper limits on the Front Range, Colorado. Ecology49: 483―495.

Yoshino, M. M. 1978. Altitudinal vegetation belts of Japan with special reference to climatic conditions. Arc. Alp. Res.10: 449―456.

（Received January 21, 2003 ; accepted May 18, 2003）

高橋耕一：中央アルプス将棊頭山の森林限界におけ るダケカンバとハイマツの気孔コンダクタンスの日 変化

中央アルプスに位置する将棊頭山の森林限界（標

高2,630 m）において，ダケカンバとハイマツの気

孔コンダクタンスの日変化を調べた。調査した2001

年8月中旬から9月中旬までの期間において，こ の森林限界では早朝は快晴でも昼前からは霧がよく 発生し，また夕方には降雨もよく観測された。気孔 コンダクタンスの日変化の測定は1〜2週間間隔で計4日間行ったが，そのうちの一日は降雨のため，

測定ができなかった。測定可能だった他の日でも，

昼前から霧が発生し，霧の発生とともに日射量は減 少し，そして大気湿度は増加した。気孔コンダクタ ンスの測定を行った3日間とも，ダケカンバとハ イマツの気孔コンダクタンスの日変化は概して小さ かった。2001年の調査期間中，この森林限界では 霧と降雨が発生しやすい気象状況だったため，気孔 コンダクタンスの低下は頻繁には生じていないと考 えられた。

（〒390―8621 松本市旭3―1―1 信州大学理学部生 物科学科）

植物地理・分類研究 第51巻第2号 2003年12月

164