Algae Volume 20(4): , 2005 구멍갈파래 (Ulva pertusa Kjellman) 의생태생리에대한생육기질의효과 최태섭 * 김광용 ( 전남대학교해양학과 ) The Effect of Substrate on Ecophysiological Ch

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1 Algae Volume 20(4): , 2005 구멍갈파래 (Ulva pertusa Kjellman) 의생태생리에대한생육기질의효과 최태섭 * 김광용 ( 전남대학교해양학과 ) The Effect of Substrate on Ecophysiological Characteristics of Green Macroalga Ulva pertusa Kjellman (Chlorophyta) Tae Seob Choi* and Kwang Young Kim Department of Oceanography, Chonnam National University, Gwangju , Korea Seashore joining with land and sea, which is typical habitat for marine macroalgae, is classified two types of shore as soft- and hard-bottom shore according to topographical (geological) and ecological features. We compared two of Ulva pertusa Kjellman from two contrasting habitats, sandy (soft-bottom, Haenam) and rocky shore (hard-bottom, Hadong) in terms of chlorophyll-a fluorescence and its parameters, and various photosynthetic pigment and nutrient content in the tissue of those. Both of habitats were different in the light environment such as light attenuation coefficient and even in nutrient concentration of ambient seawater. Electron transport rate (ETR) of Ulva from sandy shore was higher than from rocky shore. The range of photosynthetic pigment content in the tissue of U. pertusa was significantly much more in from sandy shore, and also nitrogen and phosphorus content were significantly higher except for carbon content. However, there were no significant differences in the ratio of among photosynthetic pigments, and N:P ratio was similar between each other, even though significantly different. Our result implied on the reason of why most of green tides in the worldwide concentrated and frequently occurred at sites with sandy, muddy and silty bottoms, being classified as soft-bottom shore. Key Words: chlorophyll-a fluorescence, sandy shore, rocky shore, Ulva pertusa, green tides 서론연안은지질특성과생태적관점에서연성기질의해안 (soft-bottom shore) 과경성기질의해안 (hard-bottom shore) 으로구분할수있다. 두가지연안유형의대표적인예로서연성해안의경우는사질해안 (sandy shore) 을, 경성해안의경우는암반해안 (rocky shore) 을들수있으며, 특히연성해안의경우는입자의크기에따라니질 (muddy), 실트질 (silty) 로세분화할수있다 (Little 2000). 기질의종류에관계없이거의모든곳이해조류의생육지가될수있으나, 생육지의기질안정성은형태, 생태, 생리, 생화학적변이의원인이된다 (Lobban and Harisson 1997). 퇴적형사질해안은침식형암반해안에비해해수의탁도 *Corresponding author (ulvapertusa@hanmail.net) (turbidity) 가상대적으로높다 (Dunton 1994). 또해수수괴내에서광의감소는탁도이외에영양염유입이나식물플랑크톤의수도 (abundance) 등과의상호작용에의해영향을받으며 (Abal and Dennison 1996; Koch 2001), 일반적으로해수의소광계수 (light attenuation coefficient) 는사질해안에서더높다 (Cloern 1996). 해조류광합성에필요한빛조건은해안에서생육위치및생육지기질의종류에따라달라진다. 또한해조류조직내에서광합성및비광합성조직의분배는광합성을위해흡수되는총광량및빛스펙트럼에대한적응결과이다 (Hemminga and Duarte 2000). 해조류에도달되는빛의파장은해수내존재하는용존화합물과입자에의한흡수와분산특성에영향을받는데, 이는지역적특성에따라다르게나타난다 (Kenworthy and Fonseca 1996). 암반해안에서온도및염분변화는사질해안에비해변화범위가더크고, 해조류에대한건조스트레스도암반해안이사질해안에비하여더크다 (Davison and Pearson 1996). 이는

2 370 Algae Vol. 20(4), 2005 저조 (low-tide) 시사질해안의퇴적물에존재하는수분이완충작용을함으로서암반해안에비하여극단적인환경변화를보이지않기때문이다 (Little 2000). 또사질해안에서영양염의농도는퇴적물에의한생지화학적순환이나공극수로부터지속적인영양염의공급등으로인하여암반해안에비해상대적으로해수의영양염농도가높게유지된다. 하지만결정적으로기질의불안정성때문에대형해조류를포함한대부분의고착생물들은사질보다는암반해안에서흔하게나타난다. 또한사질은해조류표면을연마 (scouring) 하거나질식 (smothering) 시키는등물리적손상을통해해조군집을교란시킨다 (Kim et al. 1998). 사니질해안 (sand-muddy shore) 에형성된담치밭 (mussel beds) 은불안정한연성기질에서고착생물을위한 2차경성기질 (secondary hard substrate) 의역할을하는데, 여기에해조류생육또한가능하다. 담치밭에서출현하는갈조 Fucus vesiculosus forma mytili (Nienburg) Nienhuis는암반해안에서출현하는같은종에비해모자반류 (Fucoid) 의특징적형태특성인기낭과기부가없으며유성생식을하지않는것으로알려져있다 (Albrecht 1998). 이것은사질해안과암반해안모두에서생육하는동일종의해조류가생육기질의차이로인하여서로다른형태및생태특성을보여주는예이다. 연안의부영양화로인한갈파래류 (Ulva spp.) 나파래류 (Enteromorpha spp.), 대마디말류 (Cladophora spp.) 같은기회성해조류의대발생은전세계적인환경문제로인식되고있다 (Lavery et al. 1991; Schramm and Nienhuis 1996; Choi et al. 2001; Choi 2003), 또한녹조류대발생의발달은암반해안에서보다는사질, 니질또는실트질과같은연성기질의해안에서더일반화된현상이다. 갈파래류에의한녹조류대발생이연성기질의해안에서더자주발생하는원인은기질에부착하지않고서도생육이가능한자체특성과함께유속등의물리적환경요인이복합적으로작용하기때문이다 (Schramm and Nienhuis 1996; Hiraoka et al. 2004). 이러한대발생으로인해연성기질에형성된대형해조류의매트 (mats) 는퇴적물과수괴사이의경계면에서부패로인한무산소환경을만들어 (Wharfe 1977; Bolam et al. 2000), 결국동물군집의종조성및다양성에악영향미치기도한다 (Norkko and Bonsdorff 1996). 유럽이나북미지역에서발생하는녹조류대발생은주로하구나사질해안과같은연성기질의해안에서발생하는반면, 우리나라의경우사질해안에서뿐만아니라암반해안에서도발생하고있다 (Kim et al. 2004). 본연구는서로다른기질특성을갖는사질해안과암반해안에서생육하는녹조구멍갈파래 (Ulva pertusa Kjellman) 의광합성특성과조직내광합성색소및영양염함량을비교하였다. 이때조사지역간의지역적인격리는있으나해황특성이유사하다고판단되는조간대내만지역을조사대상으 로하였다. 생육기질에따른생태생리특성의비교는다양한기질유형에서출현하는본종의분포특성및특정시기에반복해서나타나는대발생기작을이해하는데기여할것이다. 재료및방법갈파래생육환경비교및환경요인측정구멍갈파래 (Ulva partusa, 이후갈파래 ) 를채집한전라남도해남군송지면통호리 (34 19 N, E) 와하동군금남면노량리 (34 53 N, E) 는각각사질해안과암반해안으로해조류생육에있어서뚜렷한기질의차이를가지고있다. 사질해안인해남군통호리에생육하는갈파래는조간대에설치된노후한양식시설이나방치된어구또는굵은자갈등과같은2차경성기질에부착하여생육하고있었다. 이에반해하동군노량리암반해안의갈파래는전형적으로발달한암반조간대에서다양한대형해조류들과혼생하여생육하고있었다. 시료의채집은년중갈파래가가장번무하는시기를선택하여 (Choi et al. 2001; Choi 2003; Kim et al. 2004), 두곳의해안에서건강한갈파래엽상체를대상으로 2002년 2월 27일과 28일에각각 1회채집하였다. 채집된엽상체는직사광선을피하여아이스박스에담은후, 바로실험실로옮겨왔으며, 여과된해수를이용하여부드럽게엽상체표면으로부터퇴적물및부착생물들을제거하였다. 그리고바로해조류의기초적형태특성인엽상체의크기 (cm) 를측정하였다. 이후실험실조건에순응되는것을방지하기위하여계획된실험들을연속해서진행하였다. 특히, 엽록소형광을이용한광합성측정실험은현장온도와비슷한온도를유지시킨 10 항온실에서수행하였다. 시료채집과동시에수온-염분측정기 (Model 3250, JENCO, China) 를이용하여수온및염분을측정하였으며, 당시수온은사질해안 ( 해남 ) 과암반해안 ( 하동 ) 에서각각 7.8 과 10.3 C로암반해안에서약간높았으며, 염분은각각 31.0 과 31.2 psu로유사하였다. 또한시료채집장소인근에서해수를채수하여실험실로옮겨와 Strickland and Parsons (1972) 의방법에따라영양염농도 (µm) 를측정하였다. 암모늄염 (NH + 4 -N) 과아질산염 (NO - 2 -N), 질산염 (NO - 3 -N) 을합한질소계열영양염은사질해안과암반해안에서각각 9.85와 1.51 µm 이었으며, 인산염 (PO 3-4 -P) 은각각 2.4와 0.5 µm로사질해안에서뚜렷이높았다. 해조류생육및분포에중요한환경요인중하나인광환경 (light environment) 을알아보기위해해수수괴내의광소멸정도를측정하였다. 해수의소광계수는수중광센서 (Li- 192 Underwater Quantum Sensor, LI-COR, Inc. USA) 를이용

3 Choi & Kim: Effect of substrate on ecophysiology of Ulva pertusa 371 하여표층에서부터수심별광량을측정하고, Beer s law (I z = I o e kz, I o : 입사광량, I z : 임의수심에서광량, k: 소광계수, z: 수심 ) 를이용하여소광계수 (light extinction coefficient, k, m -1 ) 를계산하였다 (Lobban and Harrison 1997). 그결과사질해안과암반해안에서의소광계수는각각 1.15와 0.79 m -1 값을보였다. 해남통호리에서해수의탁도와밀접한연관을갖는퇴적물의입도분포는사질 (sand) 과실트질을포함한니질 (silt+mud) 로구분하였을때, 사질함량이약 40~80% 였으며, 나머지는니질로구성되어있다 (Kang 2002). 엽록소형광을이용한갈파래의광합성측정및매개변수 (photosynthetic parameters) 의계산갈파래의광합성은엽록소형광측정이가능한 Diving- PAM (Walz, Germany) 를이용하여광화학양자수율 (photochemical quantum yield) 을측정하고, 전자전달율 (electron transport rate, ETR) 을계산하여빠른광반응곡선 (rapid light curve, RLC) 을작성하는것으로측정되었다. 또한다양한광합성매개변수 (photosynthetic parameter) 는빠른광반응곡선을광합성-광도모델을이용하여비선형회귀법으로피팅하여구하였다. 갈파래의빠른광반응곡선은 µmol photons m -2 s -1 까지 9단계광구배를설정하고, 각단계별로 10초간주어진광도 (actinic light) 에노출한후포화광 (saturation pulse) 을조사하여유도된형광변화로부터각광도별양자수율을측정하고, 이양자수율값을이용하여광계2(PS II) 에서의전자전달율 (ETR) 을계산하는것으로측정되었다 (Ralph et al. 2002). 전자전달율값은광량에대해도시하고 Platt et al. (1980) 의함수를이용하여피팅하였다. ETR = ETR s [1-exp(- αe d / ETR s )]exp(- βe d / ETR s ) photons m -2 s -1 ) 는 Talling의정의 (Cullen 1991) 에의하여아래의식으로구하였다. E k = ETR max / α 조직내광합성색소 (photosynthetic pigments) 함량분석갈파래조직내의다양한광합성색소함량분석을위한시료는광합성측정이끝난시료로부터직경 17 mm 코르크보러를이용하여엽체디스크를얻었다. 이시료를 DMF (N,N-dimethyl-formamide; C 3 H 7 NO) 4ml이들어있는알루미늄호일로싼유리vial에넣고, 냉암소에서 20시간이상방치하여모든광합성색소를추출하였다. 색소가추출된시료로부터상등액을취하여 10 mm 큐벳에넣고분광광도계를이용하여각파장별 (664, 647, 480, 725 nm) 흡광도를측정하고, Wellburn(1994) 식을이용하여엽록소 a, 엽록소 b, 카로티노이드의함량 (mg g -1 FW) 을계산하였다. 조직내영양염함량분석갈파래조직내의탄소 (C), 질소 (N), 인 (P) 함량분석을위한시료는광합성및색소함량측정이끝난시료나머지를 60 C에서 48시간이상건조시키고, 잘건조된시료를분쇄기 (Mixer Mill, MM 301, Retsch GmbH & Co. KG, Germany) 에넣어곱게분말화하여얻었다. 탄소와질소함량은자동원소분석기 (EA1110CHNS, Fisons Instrument, Italy) 를이용하여분석하였고, 인함량은분말시료의일정량 ( 약 µg) 을 alkaline persulfate digestion 방법 (D Elia et al. 1977) 으로인을추출한후, GF/F 여과지를이용하여부유물질을제거하고 10ml을취하였다. 그이후의방법은해수중의인산염을측정하는방법과동일하며 (Strickland and Parsons 1972), 최종적인인함량은 Phillips and McRoy(1990) 의식을이용하여계산하였다. 여기서, E d 는조사된광량 (PAR) 이고, ETRs는광저해현상이없을때최대전자전달율 (ETR max ) 로정의되는 scaling 매개변수이며, α(etr [µmol photons m -2 s -1 ] -1 ) 는광에대한전자전달율곡선 (ETR vs I curve) 에서광포화가시작되기전까지곡선의초기경사이며, 광이용에대한효율을의미한다. β는광저해현상이시작된후의빠른광반응곡선의경사를의미한다. 광포화가일어났을때의최대전자전달율은잠재적인광합성능력 (photosynthetic capacity) 을의미하며, 광저해현상이없다면피팅함수로부터바로구할수있지만, 광저해현상이발생하면다음식에의해계산한다. 통계처리사질해안과암반해안에생육하는갈파래의광합성매개변수및생태생리특성들은 paired Student T-test를이용하여기질에따른유의한차이를검증하였다. 통계분석을위한프로그램은 SPSS(Version 10.0, SPSS Inc., Illinois, USA) 를이용하였으며, 광합성-광도모델의피팅을위해서는 Grapher (Version 3.01, Golden Software Inc, Colorado, USA) 를이용하였다. 결과 ETR max = ETR s [α/(α+β)][β/(α+β)] β/α 광합성매개변수중하나인광적응매개변수 (E k, µmol 사질해안 ( 해남 ) 과암반해안 ( 하동 ) 에서생육하는갈파래의다양한생태생리특성들을비교한결과생육기질에따라분명한차이를보였다. 해조류의기초적형태특성인갈파래

4 372 Algae Vol. 20(4), 2005 Fig. 2. Series of rapid light curves (RLCs) of Ulva pertusa from sandy (Haenam, ) and rocky shore (Hadong, ) at February Best-fits to the model of Platt et al. (1980). Units of retr are arbitrary. Error bars represent standard error (n = 5). Fig. 1. Comparison of thallus lengths (cm) of Ulva pertusa between sandy (Haenam) and rocky shore (Hadong) at February Error bars represent the standard error (n = 11 for Haenam and n = 10 for Hadong). Probability value show the result of paired Student T-test; significant difference indicated by asterisk, where p < 엽상체크기는사질해안과암반해안에서각각 18.4±1.96과 11.0±1.11 cm로약1.7배차이를보였다 (Fig. 1, p < 0.05). 광합성갈파래의광합성또한엽상체크기차이만큼이나생육기질에따라뚜렷한차이를보였다. 사질해안에서자란갈파래의광합성이암반해안의것에비해월등하게높았다 (Fig. 2). 전자전달율-광곡선 (retr vs I curve) 의초기기울기값 (α) 은사질해안이 0.44±0.04, 암반해안이 0.13±0.02 retr(µmol photons m -2 s -1 ) -1 로사질해안에서생육한갈파래의광이용에대한효율이유의하게높았다 (Fig 3A, p < 0.01). 광저해현상이나타난전자전달율-광곡선에서추정된최대전자전달율값 (retr max ) 또한사질해안과암반해안에서각각 27.2± 1.5와 9.1±1.2 로사질해안에서유의하게높았다 (Fig. 3C, p < 0.01). 광합성매개변수중하나인광적응매개변수 (E k ) 는사질해안과암반해안에서각각 63.3±5.1 과 76.2±18.6 µmol photons m -2 s -1 이었으며 (Fig 3D), 광저해후전자전달율-광곡선의기울기 (β) 는각각 0.010±0.003과 0.035±0.024로사질해안에서낮게나타났다 (Fig. 3B) Fig. 3. Comparison of photosynthetic parameters obtained from each rapid light curve (RLC) of Ulva pertusa from sandy (Haenam) and rocky shore (Hadong) at February Data indicate mean SE of n = 5. Probability values show the result of paired Student T-test; significant difference indicated by asterisk, where p < 광합성색소함량갈파래조직내의주요광합성색소함량은엽록소 a의경우사질해안과암반해안에서각각 5.51±0.38과 3.66±0.29 mg g -1 FW, 엽록소 b는각각3.26±0.19와 2.37±0.24 mg g -1 FW, 마지막으로카로티노이드는각각 1.54±0.11과 1.02± 0.07 mg g -1 FW이었으며 (Fig 4A, 4B and 4C), 주요광합성색소모두는사질해안에서생육한갈파래가유의하게더많

5 Choi & Kim: Effect of substrate on ecophysiology of Ulva pertusa 373 Fig. 5. Comparison of nutrient contents in the tissue of Ulva pertusa from sandy (Haenam) and rocky shore (Hadong) at February A) tissue carbon (% dry wt), B) tissue nitrogen (% dry wt), C) tissue phosphorus (% dry wt), and D) the ratio of tissue N:P. Error bars represent the standard error (n = 3). Probability values show the result of paired Student T-test; significant difference indicated by asterisk, where p < 0.05, p < 0.01 and p < Fig. 4. Comparison of photosynthetic pigments content in the tissue of Ulva pertusa from sandy (Haenam) and rocky shore (Hadong) at February A) chlorophyll-a (mg g -1 FW), B) chlorophyll-b (mg g -1 FW), C) carotenoids (mg g -1 FW), D) total chlorophyll (mg g -1 FW), E) the ratio of carotenoids to total chlorophyll content, and F) the ratio of chlorophyll-b to chlorophyll-a. Mean SE (n = 10). Probability values show the result of paired Student T-test; significant difference indicated by asterisk, where p < 0.05 and p < 의같은값을보였다 (Fig 5A). 하지만질소 (N) 와인 (P) 함량은사질해안과암반해안에서각각 4.2±0.05와 2.6±0.04 % N, 그리고각각 0.16±0.001과 0.09±0.002 % P로사질해안에서생육하는갈파래가더많은영양염을함유하고있었으며, 통계적으로도유의한차이를보였다 (Fig 5B and 5C, p < and 0.01). 하지만 N:P ratio는사질해안과암반해안에서각각62.3±1.1 과 71.5±2.2 로암반해안에서약 1.2배높았다 (Fig 5D, p < 0.05). 토의 은함량을갖고있었다 (p <0.01, 0.05 and 0.01). 총엽록소함량또한사질해안과암반해안에서각각 8.77±0.54, 6.03± 0.53 mg g -1 FW으로사질해안에서유의하게높았다 (Fig. 4D, p <0.05). 카로티노이드함량에대한총엽록소함량비는암반해안과사질해안에서각각 5.79±0.25와 6.02±0.47이었고, 엽록소 b에대한a의비는각각1.70±0.07과 1.58± 0.05로유의한차이를보이지않았다 (Fig. 4E and 4F). 영양염함량갈파래조직내의영양염함량은탄소 (C) 의경우사질해안과암반해안에서각각 36.5±0.45와 36.4±0.48 % C로거 갈파래를채집한사질해안 ( 해남 ) 과암반해안 ( 하동 ) 의환경차이는수온과염분의경우유사한수준을보였으나, 영양염은암반해안에서보다사질해안에서더높았다. 소광계수또한사질해안이암반해안보다높은값을보였다. 이는사질해안에서생육하는갈파래가암반해안에비해풍부한영양염과낮은광조건하에서생육하고있음을보여주는것이다. 또이러한환경의차이는해조류의외부형태특징중하나인엽상체의크기에서뿐만아니라 (Fig. 1), 광합성및생태생리특성에있어서도유의한차이를보이는결과로나타났다.

6 374 Algae Vol. 20(4), 2005 광합성비교고착성해조류는부유성식물플랑크톤과는달리생육지의주어진광환경에적응해야하기때문에이들의생태특성은광 (light) 을흡수하는능력과흡수된광을효율적으로이용하는능력과관련이깊다. 또한해조류의광조건에대한적응 (photoacclimation) 과이와관련된반응, 즉광합성의광저해정도는해조류의분포와도밀접하게연관되어있다 (Duarte 1991; Dennison et al. 1993; Hanelt 1998; Dring et al. 1996; Bach et al. 1998). 이는유사한형태기능적특성을갖는같은속 (genus) 에속해있는종들이라도서로다른광생물학적반응을보여줄수있음을의미한다. 그예로, 스페인남부, 대서양과지중해가인접한연안의조간대에서생육하는형태적으로유사한홍조우뭇가사리 (Gelidium) 2종에대한형광 kinetics 연구는다양한구배의자연광에노출된후, 광저해정도와저해후회복능력이완전히다르게나타난다는것을밝혔다 (Gómez and Figueroa 1998). 이것은이들우뭇가사리 (Gelidium) 2종의미세한분포패턴 (micro-distribution) 이다르다는것을확인한것이며, 한종은 shade-adapted 종으로서암반의틈새에생육하거나수관 (canopy) 을형성하며, 이에반해다른한종은sun-adapted 타입으로광에직접적으로노출된위치에생육하고있었다. Figueroa et al. (2003) 은같은해안의서로다른위치에서자라는김 (Phorphyra) 에서도같은종류임에도불구하고광적응에따라형태가다른 sun-morphs와 shade-morphs가있음을보고하였다. 이러결과들을바탕으로 Littler and Littler(1980) 은형태적으로유사한해조류는생태적으로도유사한광적응전략을갖는다는가설을제안하기도하였다. 이와같이해조류는서로다른종에서뿐만아니라, 같은종에서도서로다른개체들간에환경구배에따른광적응에따라형태또는생리, 생화학특성들이뚜렷한차이를보이는경우를종종관찰할수있다. 해산식물의광합성양상은광적응유형에따라몇가지로구분할수있다. Jørgensen(1977) 은광적응유형에따라해산식물의광합성양상을 Chlorella-type 과 Cyclotella-type 두가지로구분하였다. 여기에 Miller(2004) 는 Bearnall and Morris(1976) 의결과를바탕으로 Phaeodactylum-type 을추가하여세가지로구분하였다. 또한광적응을통해다양한환경구배에적응하는해조류의능력을이해하는데있어서광합성효율 (photosynthetic efficiency, α) 이나최대광합성율 (P max 또는 ETR max ), 광적응매개변수 (E k ) 와같은다양한광합성매개변수들의이용은매우유용하다 (Pérez-Lloréns et al. 1996). 이를바탕으로, 사질해안과암반해안에서생육하는갈파래가보여준전자전달율-광곡선은서로다른광도에적응하는세가지광적응유형중 Phaeodactylum-type으로분류할수있다 (Fig. 2, Miller 2004). Phaeodactylum-type의특징은 shade-adapted된종의광합성효율 (α) 과최대광합성율 (P max ) 이 sun-adapted된종보다높으며, 하지만광적응매개변수 (E k ) 는 sun-adapted된종에서높은유형을의미한다. 본연구결과에서사질해안에서생육하는갈파래의광합성과매개변수값들중광합성효율 (α) 과최대광합성율 (ETR max ) 이암반해안에서생육하는것에비해높다는것은사질해안의갈파래가낮은광도에적응 (shade-adapted) 한결과로볼수있다 (Fig. 2 and 3). 해조류가높거나낮은광도에적응하는양상 (sun- 또는 shade-adaptation) 은종또는분류군의특징이될수있다 (Littler and Littler 1980). 하지만이것은제한된시간동안낮은광도대한적응의정도나광에대한노출경험에따라달라질수있다 (Miller 2004). 일반적으로, 낮은광도조건에서해조류의광합성색소함량은증가하며 ( 즉, Chlorella-type과 Phaeodactylum-type에서엽록소 a와 P700 반응중심함량의증가 ), 이것은광합성-광곡선 (P vs I curve) 의초기기울기증가로연결된다. 하지만광합성과정의두가지중요한반응중암반응의활성도는높은광도조건에서증가하며 ( 즉, ATP나 NADPH와같은광에너지반응물질의활성증가를유도 ), 이것은 Cyclotellatype에서최대광합성율 (P max ) 의증가를유발한다. 직관적으로, 낮은광도의빛은좀더많은광계구조 (photosystem structure, 광계 1 또는광계 2) 를생산하고, 암반응효소들의양을감소시킬것으로추측되며, 반면에높은광도의빛은광계구조를줄이는대신좀더가치있는암반응에집중할것으로생각된다. 이것은 sun-adapted된것에대해측정한광합성-광곡선이 shade-adapted 것에대해측정한것보다높은최대광합성율 (P max ) 을보여주는데반해낮은광합성효율 (α) 을보여준다는것이다. 그러나이러한직관적인모델에맞는광적응유형은없기때문에일반적으로이것은일어나지않는다. 하지만광합성효율 (α) 의증가는분명히 Phaeodactylum-type과 Chlorella-type에서광합성색소함량의증가에기인한다 (Miller 2004). 광합성색소함량비교사질해안에생육하는갈파래조직내의색소함량이암반해안에생육하는것에서보다종류에관계없이유의하게높았다 (Fig. 4A, 4B and 4C). 갈파래의광합성은조직내색소함량과밀접한연관이있으며, 일반적으로주변해수의영양염이풍부할수록조직내광합성색소함량도증가하는것으로설명할수있다 (Lapointe and Tenore 1981). 하지만광합성색소종류간의함량비 (ratio) 는뚜렷한차이를보이지않았다 (Fig. 4E and 4F). 이것은해조류가생육하는곳의기질특성에따라, 계절또는하루중에도광환경은끊임없이변화하고있으며, 이러한변화는해조류에도달되는광자 (photons) 의양이나파장스펙트럼분포, 특히고착성대형해조류의경우에는광이조사되는각도 (direction of the

7 Choi & Kim: Effect of substrate on ecophysiology of Ulva pertusa 375 radiation) 등의차이때문이다 (Kirk 1994; Mobley 1994). 생육기질의차이에따른갈파래조직내의색소함량차이와는다르게조직내일정한색소함량비는다양한광환경에적응하여광합성을위한모든파장의광을흡수할수있도록적응된결과로볼수있다 (Kenworthy and Fonseca 1996; Falkowski and Raven 1997). 영양염함량비교갈파래조직내주요영양염중질소 (N) 와인 (P) 의함량은생육기질에따라유의한차이를보였다 (Fig 5B, 5C). 하지만탄소 (C) 함량은사질해안과암반해안의갈파래모두에서유사한값을보였다 (Fig. 5A). 조직내질소나인의함량은다양한환경요인및해수내영양염농도에따라민감하게반응한다 (Campbell 2001). 반면, 탄소는해조류의생육환경에서고갈되거나부족해지기쉽지않은영양염으로생육환경의차이를잘반영하지않는것으로추측된다 (Ramus and Venable 1987). Wheeler and Björnsäter(1992) 는생육환경이뚜렷이구분되는두곳에서갈파래를포함한 5종의해조류를채집하여조직내영양염함량의계절변화및생육환경의차이를비교하였다. 그결과파래 (Enteromorpha) 나갈파래 (Ulva), 김 (Porphyra) 과같은엽상체 (leafy) 해조류는생육환경에따라조직내영양염함량변화가심한반면, 청각 (Codium) 이나 Pelvetiopsis와같이엽육이있거나두꺼운분지형 (branched) 해조류의경우계절변동은있지만생육환경의차이는잘반영하지않는것으로나타났다. 이는해조류의외부형태적인차이가조직내영양염함량의차이를유발할수있음을보여주는것이다 (Fong et al. 2001). 해조류조직내의영양염함량은주변해수로부터해조류의영양염흡수에대한직접적인지표로, 질소와인의비율 (N:P ratio) 은영양염의이용능력에대한지시자로활용된다 (Fong et al. 1994; Horrocks et al. 1995; Fong et al. 1998; McCook 1999). 갈파래조직내의 N:P ratio 또한사질해안과암반해안에서유의한차이를보임으로서기회적인해조류의영양염이용능력이생육환경에따라달라지고있음을보여주고있다 (Fig. 5D). 주변육지및하천유역으로부터과도한영양염유입으로인하여해수수괴내영양염농도의증가가녹조류대발생을유발하는가장주요한원인으로인식하고있다 (Rosenberg et al. 1990; Schramm and Nienhuis 1996). 그리고사질해안과암반해안에생육하는갈파래의광합성및생태생리특성을비교한본연구의결과는이러한과도한영양염의유입이어떤종류의연안에집중되는가에따라녹조류대발생의발달은달라질수있음을보여주고있다. Schramm and Nienhuis (1996) 의연구는현재전세계적으로발생하는대부분의녹조류대발생이암반해안에서보다는사질이나니질의해안 에서더자주발생하고집중되고있음을지적하고있다. 이는연성기질의해안에서생육하는녹조류가암반해안에비하여더낮은광도에적응되어있고, 퇴적물로부터지속적인영양염공급과결부되어녹조류대발생을촉발하기때문인것으로사료된다. 사 사 이논문은한국과학재단의해외 Post-doc. 연수지원에의하여연구되었음. 참고문헌 Abal E.G. and Dennison W.C Seagrass depth range and water quality in southern Moreton Bay, Queensland, Australia. Mar. Freshwater Res. 47: Albrecht A.S Soft bottom versus hard rock: community ecology of macroalgae on intertidal mussel beds in the Wadden Sea. J. Exp. Mar. Bio. Ecol. 229: Bach S.S., Borum J., Fortes M.D. and Duarte C.M Species composition and plant performance of mixed seagrass beds along a siltation gradient at Cape Bolinao, The Philippines. Mar. Ecol. Prog. Ser. 174: Bearnall J. and Morris I The concept of light intensity adaptation in marine phytoplankton: some experiments with Phaeodactylum tricornutum. Mar. Biol. 37: Bolam S.G., Fernandes T.F., Read P. and Raffaelli D Effects of macroalgal mats on intertidal sandflats: an experimental study. J. Exp. Mar. Biol. Ecol. 249: Campbell S Ammonium requirements of fast-growing ephemeral macroalgae in a nutrient-enriched marine embayment (Port Phillip Bay, Australia). Mar. Ecol. Prog. Ser. 209: Choi T.S Ecophysiological characteristics of green macroalga Ulva pertusa L. from eelgrass habitats. Ph.D Thesis, Chonnam National University, Kwangju, Korea. Choi T.S., Choi J.K., Park S.M., Kim J.H. and Kim K.Y Winter biomass of Ulva mats in a rocky intertidal zone of the southern coast of Korea. Korean J. Environ. Biol. 19: (in Korean) Cloern J.E Phytoplankton bloom dynamics in coastal ecosystems: a review with some general lessons from sustained investigation of San Francisco Bay, California. Reviews of Geophysics 34: Cullen J.J Hypotheses to explain high-nutrient conditions in the open sea. Limnol. Oceanogr. 36: D Elia C.F., Steudler P.A. and Corwin L Determination of total nitrogen in aqueous samples using persulphate digestion. Limnol. Oceanogr. 22: Davison I.R. and Pearson G.A Stress tolerance in intertidal seaweeds. J. Phycol. 32: Dennison W.C., Orth R.J., Moore K.A., Stevenson J.C., Carter V., Kollar S., Bergstrom P.W. and Batiuk R.A Assessing

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