Algae Volume 17(4): 249-257, 2002 잘피밭에서생육하는구멍갈파래 (Ulva pertusa Kjellman) 의생장과영양염흡수의시간적변화 최태섭 김광용 * ( 전남대학교해양학과 ) Time-dependent Variation of Growth and Nutrient Uptake of Ulva pertusa Kjellman (Chlorophyta) from Intertidal Eelgrass Beds Tae Seob Choi and Kwang Young Kim* Department of Oceanography, Chonnam National University, Kwangju 500-757, Korea The growth of green macroalgal mats is becoming increasingly common in many marine intertidal habitats. While the ecological consequences of such growth have been experimentally investigated on various tidal flats, such experiments have rarely been performed on intertidal seagrass beds. This study investigated the ecophysiological characteristics of Ulva pertusa Kjellman (hereafter Ulva) originating from an oligo-mesotrophic eelgrass beds, Haenam, southwestern coast of Korea. The nutrient uptake capacity and growth rate of Ulva were examined over time interval of 2, 4, 7 d. At end of experiment, chlorophyll a and tissue nutrient contents of Ulva were estimated to relate with increasing of nutrient in the culture medium. Growth rate of Ulva showed 0.028-0.063 d 1 according to variation of nitrate and phosphate concentrations. Change of growth rate as a function of time course was not significantly different and similar to change of nutrient uptake. Chlorophyll a concentration was positively related to increasing nitrate concentrations (r 2 = 0.999, p < 0.001). It was also related to the tissue nitrogen content of Ulva. In conclusion, we found that growth rate and nutrient uptake of Ulva did not susceptibly change for short term in laboratory experiment. Especially, Ulva should have a very reduced storage capacity of nitrogen so far as relationship between chlorophyll a with substrate concentration of nitrate and tissue nitrogen content. These results suggest that Ulva from eelgrass beds is well adapted to oligotrophic water as adjusting its growth and nutrient uptake. Key Words: carbon, chlorophyll, growth rate, nitrogen, nutrient uptake, phosphorus, Ulva 서 론 갈파래속 (Genus Ulva) 해조류는높은표면적대부피비를갖는단순한막질 (membranous) 의엽체구조를갖고있다 (Rosenberg and Ramus 1984). 이러한해부형태적이유때문에갈파래는광합성능력과영양염흡수율이크고 (Littler et al. 1983; Duke et al. 1987) 빠른생장률을보인다 (Ramus and Venable 1987). 구멍갈파래 (Ulva pertusa) 는우리나라전해안의중 하부조간대에서흔히단종군락 *Corresponding author (kykim@chonnam.ac.kr) 본연구는 2002 년도한국학술진흥재단지원에의하여연구되었음 (KRF-2002-070-C00088) (monospecfic stand) 을형성하는대표적인해조류로서높은생산력과광범위한지리적분포를나타낸다 (Kim et al. 1998). 구멍갈파래와같은녹조류의대발생은해수내의과다한무기영양염을빠른속도로흡수하거나제거함으로써식물플랑크톤의대발생을차단할수있는긍정적인점도있지만 (Merrill and Fletcher 1991; Merrill 1994), 많은경우부정적인영향을미치는것으로알려져있다. 특히, 연안해역의부영양화로인하여갈파래류 (Ulva spp.) 나파래류 (Enteromorpha spp.) 와같은기회성해조류의대발생이심각한환경문제로부각되고있다. 늦겨울에서봄까지짧은기간에급속한증가율을나타내는구멍갈파래는이시기에가입하는다수해조류의생육공간을선점하고 (Dayton 1975; Rivers and Peckol 1995), 두터운매트를형성할경우
250 Algae Vol. 17(4), 2002 그밑에생육하는소형해조류의광합성을저해하거나하중을가하여피해를준다 (Rasmussen 1990). 갈파래매트 (Ulva mats) 는그자체가먹이생물의분포에영향을주어궁극적으로중 대형저서동물군집구조에변화를야기시킬수도있다 (Bolam et al. 2000). 한편갈파래는어패류의서식처및산란처가되는해양현화식물 (seagrass) 의표면에착생 번성하여이들의성장을저해한다고보고된바있다 (Den Hortog 1994). 해조류대발생에따른용존유기물의증가는산소의소비량을증가시키고부영양화수역에서흔히볼수있는저산소또는무산소환경을조성하게되는데, 여기에누적된해조류가분해되면무산소환경은더빨리나타날것이고또장기화될수있다 (Sfriso et al. 1992). 이러한무산소환경은일차생산자구성의변화는물론이고저서동물의종조성과생물량에큰변화를일으킨다 (Norkko and Bonsdorff 1996). 해조류분류군에따라영양염에대한요구또는흡수전략이다르긴하지만, 질소와인에대한이용능력은대부분의온대연안생태계에서해조류의생장을제한하는기본적인요인이다. 계절에따라서인 (Lapointe 1987) 또는질소와인이동시에 (Short et al. 1990; Wheeler and Björnsater 1992) 해조류의성장을제한하기도한다. 특히, 해조류의세포내부영양염수준이낮을경우생장률은수괴의영양염농도에비례하지만세포내의영양염수준이높을경우생장률은포화에도달하게되어수괴의영양염농도와무관해진다 (Fujita et al. 1989; Thybo-Christensen et al. 1993; Peckol et al. 1994). 이처럼해조류의생장과생산을제한하는영양염의종류는계절과퇴적물성분그리고세포내의영양염수준에따라다르고그기작이매우복잡함을알수있다. 기회적인해조류들은외부영양염환경이일시적으로호전되었을때, 많은양의영양염을이용할수있다 (Campbell 2001). 이들의생장은온도와빛은물론영양염이용능력에따라결정된다. 자연에서이들의생장은영양염농도에대한함수로쉽게표현되지는않지만 (Rosenberg and Ramus 1981), 해조류조직내의화학조성과생장률의상관관계가알려져있지않은경우생장률과외부영양염농도의관계식은유용하게사용될수있다 (Fong et al. 1994). 무기영양염류이용에있어갈파래는질산염과인산염흡수율이매우높은것으로알려져있고 (Fong et al. 1996), 때로는고농도의무기인산이엽체의액포속에축적되어있는것을흔히관찰할수있다. 이는무기인산이결핍된환경하에서갈파래가체내축적된인산염을이용함으로써다른종에비하여경쟁적우위를차지할수있게한다. 갈파래의과도한성장으로인한녹조매트형성은전세계연안에서흔히나타나고있다 (Fletcher 1996; Bolam et al. 2000). 따라서관련녹조류에대한생리 생태학적연구는 암반조간대, 라군, 하구등지에서꾸준히수행되어왔다 (Rivers and Peckol 1995; Kim et al. 1998; De Casabianca and Posada 1998). 그러나해양현화식물인잘피밭 (eelgrass beds) 에나타나는녹조대발생원인종에대한연구는거의이루어지지않았다. 안정적인구조와효율적인무기영양염의재순환이특징인잘피밭은일차생산량이높은지역이다. 특히잘피밭의일차생산에기여하는구성원들간에생산기여도는해조류와잘피간의수괴내질소원이용능력에의해서결정된다 (Coffaro and Bocci 1997). 따라서본연구를통하여잘피밭에생육하는구멍갈파래를대상으로생장과영양염흡수가짧은시간동안어떻게변화하는가? 그리고구멍갈파래의생장률과조직내의화학조성간에특별한상관이존재하는지를파악하고자한다. 이와같은연구결과는녹조대발생의원인을파악하고생육지훼손으로갈수록그생육범위가줄어드는잘피밭보전에필요한부분적인정보를제공하는것이다. 재료및방법시료의채집과준비시료는 2001년 9월에전라남도해남군통호리 (34 18 N, 126 33 E) 갯벌조간대의잘피밭에서채집된건강한구멍갈파래 ( 이후갈파래 ) 엽상체를이용하였다. 주변의간섭없이잘보존되어있는이곳의잘피밭에는 3-10% 피도로곳곳에갈파래가패치를이루고있었다. 2001년 5월부터 9월까지갈파래가생육하는잘피밭의주요환경요인을조사하였는데, 이기간에해수중의암모니움 + 질산염의농도는 3.5-4.0 µm, 인산염의농도는 < 0.02-3.2 µm로다소빈영양해역이었고 (Table 1), 사니질 (sandy-mud bottom) 의퇴적층위에서갈파래는잘피와혼생또는분리되어출현하였다. 영양염흡수와생장에대한실험실실험을수행하기 4-5일전에실험시료를채집하였고, 채집된시료는직사광선을피하여아이스박스에담은후실험실로이동하였다. 엽상체는여과된해수를이용하여부드럽게세척하였으며, 엽상체부착생물들을제거하였다. 그리고계획된실험을시작하기전까지 15 C 항온실에보관하였다. 갈파래의무기영양염흡수와생장률을측정하기위해엽상체로부터직경 22 mm의코르크보러를이용하여엽체디스크를얻었다. 이때상처로인한호흡의증가를피하기위해회복될때까지 2일정도암상태로방치하였다. 막질인갈파래는모든방향으로성장하는패턴을갖기때문에실험에필요한엽체디스크는엽상체전체에서무작위로얻었다. 무기영양염흡수와생장률을측정하기전에디스크시료들은현장조건에서실험실조건으로순응시키기위하여 2-3 일전배양하였다. 실험에이용될엽체디스크의초기건강
Choi & Kim: Growth and Nutrient Uptake of Ulva pertusa 251 Table 1. Physico-chemical parameters recorded for five months (May to September 2001) before sample collecting date in eelgrass beds, Haenam, southwestern coast of Korea (Choi and Kim 2002) Environmental parameter Range (mean ± SD) Temperature ( C) Seawater 19.1-26.1 (22.1 ± 3.2) Air 15.2-29.9 (22.7 ± 3.5) Salinity (psu) 28.8-31.2 (30.1 ± 0.9) Nitrate + Ammonium (µm) 3.45-4.01 (3.70 ± 0.32) Phosphate (µm) 0.02-3.22 (1.89 ± 1.16) 상태를확인하기 Diving-PAM(Waltz, Effeltrich, Germany) 을이용하여광합성을측정하였는데, 그결과갈파래의평균양자수율 (quantum yield) 은 0.72-0.81로매우건강함을확인하였다. 조직내의엽록소 a 농도, 탄소 (C), 질소 (N), 그리고인 (P) 함량의초기값을측정한결과, 엽록소 a는 2.6 µg cm 2 이었으며, 탄소, 질소인의경우각각평균 25.8%, 1.7%, 0.3%( 건중량기준 ) 이었다. 무기영양염흡수실험질산염과인산염의흡수패턴이구해지도록계획되었으며, 질산염과인산염은각각 NaNO 3 와 NaH 2 PO 4 의고농도용액을희석하여실험배양액의농도를조절하였다. 각실험의농도구배는 0.2 µm 여과지로여과한해수 300 ml(34 psu) 에질산염의경우 < 1.5, 7, 30, 191 µm, 인산염의경우 < 0.03, 0.8, 4.1, 21.7 μm 로구성하였다. 각실험농도에는 10개의갈파래디스크를넣었고이를세번반복하여실험하였다. 배양액이들어있는모든비이커는공기펌프를이용, 부드럽게포기 (aeration) 하여해수의유동과가스교환의균형을이루게하였다. 모든실험은 15 C 항온실에서이루어졌으며, 영양염흡수실험을하는동안 200 µmol m 2 s 1 의광을조사하였다. 빛은백색광의형광등 (FL40D, 40W, Kumho) 과금속등 (metal halide lamps, HQI 150W, Osram) 을이용하였다. 조사된광량은 LI-190SA flat quantum sensor(li-cor, Lincoln, NE) 를이용하여균일하게관리하였으며, 명암주기는 16h : 8h로조절하였다. 다양한무기영영염농도조건하에서생장률은매 2-3일마다 0.01 mm까지눈금이새겨진자 (ruler) 를이용하여직경을측정한후면적으로계산하였다. 생장률을측정한후에는새로운배양액으로교체하였으며총 7일간의배양이이루어졌고, 배양액을교체하기전에질산염과인산염의농도변화를측정하기위해적당량의배양해수를채수하였다. 생장률 (µ) 은다음과같은식을이용하여계산하였다 ; µ = ln (L t / L o ) / (t 2 t 1 ), t는날짜 (day) 를, L o 는초기면적을, 그리고 L t 는날짜 (day) t에서의엽체디스크면적을나타낸다. 영양염흡수율 (V) 은배양액의농도변화를이용하여결정하였으며, 갈파래에대한영양염흡수를아래의 Michaelis-Menten 식을이용하여계산하였다. V = V max S/(K m + S) V max 는최대흡수속도이며, S 는영양염의농도, 그리고 K m 은반포화상수로 1/2 V max 에서영양염농도를의미한다. 무기영양염과엽록소 a 농도측정배양액의영양염농도변화를측정하기위해, 배양액교체시에채수된 10-20 ml 해수는 Grasshoff et al.(1983) 의방법으로분석하였다. 질산염분석을위하여해수를 column efficiency 95% 이상의 copper-coated cadmium column 에통과시켜아질산염으로환원시킨후 sulfaniamide와 N- (1-naphthyl)-ethyene-diamine-hydrochloride solution 을가해발색시킨후파장 543 nm에서흡광도를구하였다. 측정된흡광도는 copper-coated cadmium column의환원율을구하여보정한후질산염농도를구하였다. 인산염분석을위하여 ammonia molybdate, H 2 SO 4, potassium antimonyl tartrate의혼합시약을배양액해수에가하고 ascobic acid method로환원하여발색시킨후파장 885 nm 에서흡광도를측정하였다. 조직내엽록소 a 함량은갈파래엽체디스크를알루미늄호일로싼유리 vial에넣고dmf(n, N-dimethyl-formamide; C 3 H 7 NO) 4ml을첨가한후, 냉암소에서 20시간이상색소를추출하여구하였다. 추출된시료는분광광도계로흡광도 (663, 645, 630, 725 nm) 를측정하여 Jeffrey and Humphrey(1975) 식으로계산하였다. 조직내탄소 (C), 질소 (N), 인 (P) 함량분석실험이끝난후, 갈파래조직내의탄소와질소의함량분석을위해시료는 60 C에서 48시간이상건조시킨후, 분쇄기 (Wiley Mill, Fritsch, Germany) 를이용하여곱게분말화하였다. 분말시료는자동원소분석기 (FISONS EA1110CHNS, Italy) 를이용하여탄소와질소함량을분석하였다. 조직내의인함량측정은분말시료의일정량 ( 약 500-700 µg) 을 alkaline persulfate digestion(d Elia et al. 1977) 방법으로인을추출한후, 시료는 GF/F 여과지에여과시켜 10 ml을취하였다. 그이후의방법은해수중의인산염을측정하는방법과동일하며, Phillips and McRoy (1990) 의식을이용하여계산하였다. 통계분석시간에따른생장률변화에대한통계분석은일원분산분
252 Algae Vol. 17(4), 2002 Fig. 1. Time-dependent variation of growth rates (d 1 ) of Ulva pertusa from eelgrass beds according to variation of nitrate (A) and phosphate (B) concentrations. Error bars represent the mean (± SD) of four replicates. 석 (one-way ANOVA) 을이용하였다. 갈파래의생장률과엽록소 a 농도등과같은생물적변수간의관계는 Pearson 상관분석을적용하였다. 질산염과인산염의농도변화에따른엽록소 a 농도의관계는직선회귀로도시하였다. 통계처리를위한프로그램은 SPSS(Verson 7.5, SPSS Inc., Illinois, USA) 를이용하였다. 결과생장률과무기영양염흡수율실험기간 (7일 ) 동안갈파래의성장률은질산염과인산염의농도에따라최소평균 0.028에서, 최대평균 0.063 d 1 의범위를보였다 (Fig. 1). 질산염의경우, < 1.5 µm에서 30 µm까지갈파래의생장률은급격하게증가하였으나그이상의질산염농도에서생장률은증가하지않거나감소하는경향을나타내었다. 인산염농도에따른갈파래의생장률은 0.03 µm에서 0.8 µm까지농도증가와함께증가하였으나, 4.1 µm, 21.7 µm의인산염의농도에서는생장률증가를보이지않았다. 질산염농도와갈파래생장률의관계는시간이경과함에따라뚜렷한변화를보이진않았다 (Fig. 1A). 질산염의최고농도 (191 µm) 조건에서생장률은 Day 4에가장높고 Day 7에감소하는뚜렷한경향을보였지만 30 µm 이하의농도에서는큰차이를보이지않았다. 질산염실험에서시간에따른갈파래의생장률차이는통계적으로유의하지않았다 (ANOVA, p = 0.767). 그렇지만인산염의최대농도 (21.7 µm) 에서생장률은 Day 2에낮고Day 4에증가하며 Day 7에다시감소하는경향 (Fig. 1B) 과함께인산염실험농도범위에서시간에따른생장률은유의한차이를나타내 었다 (ANOVA, p = 0.005). 인산염실험농도에서보여준갈파래의생장률은질산염실험농도구간에서보다모든측정시기에서높았는데, 실험기간동안평균생장률은질산염농도범위에서평균 0.047 d 1, 인산염농도범위에서평균 0.055 d 1 을보였다. 갈파래에의한질산염과인산염의흡수율역시생장률의시간적변화와비슷하게나타났다. 질산염과인산염모두배양을시작한후 Day 4에가장높은흡수율을보였고 Day 7 에다시감소하는경향을보였다 (Fig. 2A, B). 갈파래의최대흡수율 (V max ) 과반포화상수 (K m ) 값의변화도시간에따른생장률과무기영양염흡수패턴과유사한경향을나타내었다 (Table 2). 질산염의경우최대흡수율은 Day 4에 15.09 µm g 1 FW h 1 로가장높았고, Day 2에 3.03 µm g 1 FW h 1 으로가장낮았다. 반포화상수 (K m ) 도 Day 4에 153.87 µm로가장높았으며, Day 2에 19.81 µm로가장낮았다. 갈파래의무기영양염에대한친화도 (affinity) 는대체로질산염보다인산염이높았다. 그중 Day 2에서인산염에대한친화도는 0.64로가장높았으며, 가장낮은경우는 Day 7에질산염에대해서 0.07로나타났다. 인산염의경우최대흡수율은 Day 4에 10.38 µm g 1 FW h 1 로가장높았고, Day 2 에 1.36 µm g 1 FW h 1 으로가장낮았다. 반포화상수 (K m ) 도 Day 4에 38.82 µm로가장높았으며, Day 2에 2.13 µm으로가장낮았다. 갈파래의질산염과인산염에대한흡수는최대흡수율을기준으로 1.5-2 배정도의빠른속도로질산염을많이흡수하는것으로나타났다. 엽록소 a, 조직내탄소, 질소, 인의함량갈파래엽체의엽록소 a 함량과배양액의질산염농도와
Choi & Kim: Growth and Nutrient Uptake of Ulva pertusa 253 Fig. 2. Time-dependent variation of uptake rates (µm g 1 FW h 1 ) for Ulva pertusa as a function of nitrate (A) and phosphate (B) concentrations of the culture medium. The curves represent the best fits of the Michaelis-Menten equation and error bars represent the mean (± SD) of four replicates. Table 2. Parameters (V max and K m ) of the Michaelis-Menten model for nitrate and phosphate uptake on Ulvaa pertusa from eelgrass beds, Haenam, southwestern coast of Korea Nutrient uptake V max K m Affinity (μm g 1 FW h 1 ) (µm) (V max /K m ) r 2 Nitrate Day 2 3.03 19.81 0.15 0.8459 Day 4 15.09 153.87 0.10 0.9946 Day 7 5.17 74.58 0.07 0.9867 Phosphate Day 2 1.36 2.13 0.64 0.9724 Day 4 10.38 38.82 0.27 0.9999 Day 7 3.05 11.39 0.27 0.9974 의관계는질산염농도가증가할수록엽록소 a의함량이증가하는일차선형관계를나타내었다 (r 2 = 0.999, p < 0.001)(Fig. 3A). 그러나엽록소 a 함량과인산염농도의관계는무관하였다 (Fig. 3B). 질산염농도의증가에따른갈파래조직내탄소함량은감소하였으며, 반면질소함량은지속적으로증가하였다. 그리고인은고농도의질산염에서포화되는경향을보였다 (Fig. 4A). 인산염의경우갈파래조직내탄소와질소함량은고농도의질산염에서포화되는경향을보였으며, 조직내인함량의경우인산염의증가와함께증가하는경향을보였다 (Fig. 4B). 갈파래의생장률과조직내탄소함량과는유의한양의상관을보였으나, 조직내인함량과는음의상관관계를갖는것으로나타났다. 또한엽록소 a 함량과조직내질소함량과는유의한양의상관관계를갖는것으로나타났다 (Table 3). 고찰생장률과무기영양염흡수율의시간적변화해조류의생장률에대한연구는주로현장에서계절에따른변화를측정하고이의결과를영양염농도, 광량 (PAR), 수온등과같은환경변화와의상관을설명하여왔다 (Lüning and tom Dieck 1989). 그러나실험실에서배양을통한생장실험의경우, 가능한환경조건을부여했음에도불구하고자연조건 ( 현장 ) 에서측정된생장률보다흔히낮게나타난다. 본연구에서얻어진갈파래의생장률은 0.028-0.063 d 1 로비록다른종이기도하지만다른연구에서얻어진생장률 (U. lactuca, 0.13 d 1, Markham et al. 1980; Ulva, 0.54 week 1, Rosenberg and Ramus 1981; U. rigida, 0.3 d 1, Riccardi and Solidoro 1996) 보다낮거나, 비슷한생장
254 Algae Vol. 17(4), 2002 Fig. 3. The relationship between chlorophyll a concentration (µg cm 2 ) of Ulva pertusa according to variation of nitrate (A) and phosphate (B) concentrations of the culture medium. Error bars represent the mean (± SD) of for replicates. Carbon (C) Nitrogan (N) Phosphorus (P) Fig. 4. Carbon, nitrogen and phosphorus content in the tissue of Ulva pertusa according to variation of nitrate (A) and phosphate (B) concentrations of the culture medium. Error bars represent the mean (± SD) of for replicates. Table 3. Correlation matrix and Pearson correlation coefficient (r) among biotic variables measured after nutrient uptake experiment on Ulva pertusa. Variables Growth rate Chlorophyll a Tissue carbon Tissue nitrogen Chlorophyll a 0.279 Tissue carbon 0.572** -0.029 Tissue nitrogen 0.284 0.787** 0.292 Tissue phosphorus -0.740** -0.057-0.756** -0.117 **Significant correlation coefficient at p < 0.01 (n=16)
Choi & Kim: Growth and Nutrient Uptake of Ulva pertusa 255 률 (U. rigida, 0.017-0.080 d 1, De Casabianca and Posada 1998; U. olivascens, 0.03-0.11 d 1, Altamirano et al. 2000) 을나타내었다. 자연조건에서주변환경에충분한무기영양염이존재함에도불구하고낮은광도와높은온도때문에갈파래의성장이제한되는경우가있다 (De Casabianca and Posada 1998). 본실험조건은갈파래의생장에충분한광조건 (200-300 µmol m 2 s 1 ) 이었으며, 인공조명으로인한온도상승은일어나지않았다. 다만, 갈파래를채집한현장이빈영양조건이었고 (Table 1), 채집한시기의갈파래개체군들은활발하게생장하는시기를약간지난성숙한개체들로구성되었다. 따라서광범위한영양염변화에덜민감하여영양염농도변화에따른차이가작았을수도있다. 빈영양조건에서생육했던갈파래를부영양조건으로옮겨왔을때, 시간의경과에따른갈파래의생장률은대단히짧은시간 (Day 4) 에생장이포화되고있음을보였다 (Fig. 1). 이는갈파래조직내영양염함량이 Day 4에포화되어더이상빠른속도의생장으로연결되고있지않음을보여준것이다. 따라서갈파래에의한무기영양염의흡수도 Day 7에는감소하는것으로사료된다. 매우짧은시간에갈파래의생장이포화되는이유가실험재료를채집한현장의영양염환경을반영하는것인지아니면갈파래의특성인지에대해서는앞으로의연구가요구된다. Ramus and Venable(1987) 은기회적인종인 Ulva olivascens의경우질소이용이가능할때빠르게질소를흡수해서새로운생물량으로전환하는것으로보고한바있다. 하지만본연구결과에서갈파래는인산염보다질산염을빠르게흡수하지만이것이생장으로바로나타나지는않았다. 이는짧은실험기간이기도하지만갈파래의생장률과조직내질소함량의상관관계가유의하지않는결과로부터도알수있다. 반면인산염은질산염에비해갈파래에대한친화도가높은것으로나타났다 (Table 2). 이것은질산염의농도변화에서보다는인산염의농도변화에서좀더성장하는결과와일치하고 (Fig. 1), 실험에이용된갈파래를채집한곳이상대적으로질소보다는인이제한되었던환경으로추측된다. 질산염과인산염농도변화에대한갈파래의흡수율이시간이경과하면서낮은농도에서는큰변화가없었던데반해고농도 (191 µm-n, 21.7 µm-p) 에서는시간의경과에따른흡수율의차이가나타났다. 이것이결국최대흡수율 (V max ) 과반포화상수 (K m ) 값에영향을미쳤으나시간이좀더경과하면서갈파래에의한영양염흡수율의차이는점점줄어들것으로사료된다. 엽록소 a와조직의영양염무기질소와인은해양환경에서식물플랑크톤과해조류의생장을제한하는가장기본적인영양염으로알려져있다 (Chapman and Craigie 1977, Birch et al. 1981). 그리고식물조직내의영양염수준은시료를채집하기전일정기간의외부무기영양염환경을반영한다 (Gerard 1988). 특히, 갈파래조직내질소함량의변화는색소형성 (pigmentation) 과밀접한관련이있다 (Rivers and Peckol 1995). 또색소함량의변화는엽록체구조또는광합성률의변화와함께건조에대한내성을갖는많은해조류들의특징으로보고되고있다 (Lobban and Harrison 1994). 일반적으로, 갈파래의광합성효율은조직내엽록소 a의농도와밀접하게연관이있으며, 영양염의공급이원할할수록조직내엽록소 a의농도도증가하는것으로알려져있다 (Lapointe and Tenore 1981). 본연구에서는조직내질소함량과엽록소 a 농도와의사이에는유의한양의상관관계가있는것으로나타났다 (Table 3). 이것은질소가제한된환경하에서는색소형성이원활하게이루어지지못하고, 결국광합성과생장이저해된다고할수있다. 또한엽록소 a 농도와조직내질소함량과의관계가유의한양의상관관계를갖는다는것은갈파래의조직내질소저장능력이작다는것을시사한다 (Duke et al. 1987; Henley et al. 1991). 조직내의질소함량과생장률과의상관관계가유의하지않는이유는조직내의탄소함량과의불균형때문인것으로알려져있다 (Henley et al. 1991). 조하대 (Surif and Raven 1989) 또는조간대조수웅덩이 (Maberly 1990) 에서생육하는해조류의경우드물게탄소의제한이일어난다. 즉, 광합성을통한해조류조직내의충분한탄소함량은생육환경으로부터흡수한영양염과결합하여생장으로연결될것이나, 조직내탄소와질소함량사이의불균형은해조류의생장을제한한다 (Fig. 4). 다른예로, 갈조류다시마에서엽록소의함량과조직내질소함량에는상관관계가없는것으로보고된것도있다 (Henley and Dunton, 1995). 이것은기회적인해조류의빠른생장과관련이있는데생장률이낮은해조류의경우조직내질소저장이많은반면, 생장률높은갈파래의경우조직내질소함량이낮다 (Naldi and Viaroli 2002). 기회적인해조류의특성인빠른생장과높은광합성능력은다른해조류에비해영양염에대한요구가많다는것을의미하는것으로조직내의영양염의불균형은다양한유형으로나타난다. 갈파래의생장률과조직내인함량과의관계가역상관관계로나타난것은생장률이인산염의농도변화에따라서큰차이를보이지않았고, 엽록소 a 함량의경우인산염의농도가증가함에따라감소하는경향을보이는것은갈파래의생장에따른색소의희석으로판단되며, 이는갈파래조직내에질소보다는인의저장을시사하는것이다. 조직내탄소의함량과생장률의관계는일반적으로양의상관관계를갖는것으로알려져있다 (Altamirano et al. 2000). 광합성을통해가장기본적으로흡수되는탄소는
256 Algae Vol. 17(4), 2002 해조류의생장과직결되어있으며, 본연구의결과에서도이와동일한결과를얻었다 (Table 3). 결론적으로, 갈파래의무기영양염흡수는시간이경과함에따라증가하고, 매우짧은시간에포화된후, 다시초기상태로감소하였다. 그리고갈파래의생장은상대적으로시간이경과함에따라큰변화를보이진않았다. 이는갈파래가적은양의영양염흡수와느린생장으로상대적으로빈영양환경인잘피밭의생육환경에잘적응되어있다고할수있다. 또한, 갈파래의엽록소 a 함량과기질의질산염농도나조직내질소함량과의관계에서갈파래의질소저장능력이작다는것을보여주고있다. 그리고질산염과인산염의농도변화에따른다양한생물적요인들사이의상관관계로미루어볼때, 갈파래가최적의생장을유지하기위해서는조직내영양염의균형이중요함을보여주고있다. 참고문헌 Altamirano M., Flores-Moya A., Conde F. and Figueroa F.L. 2000. Growth seasonality, photosynthetic pigments, and carbon and nitrogen content in relation to environmental factors: a field study of Ulva olivascens (Ulvales, Chlorophyta). Phycologia 39: 50-58. Birch P.B., Gordon D.M. and McComb A.J. 1981. Nitrogen and phosphorus nutrition of Cladophora in the Peel-Harvey estuarine system, western Australia. Bot. Mar. 24: 381-387. Bolam S.G., Fernandes T.F., Read P. and Raffaelli D. 2000. Effects of macroalgal mats on intertidal sandflats: an experimental study. J. Exp. Mar. Biol. Ecol. 249: 123137 Campbell S. 2001. 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