利用沉水性葉綠素螢光分析儀實測石蓴類海藻對期間帶海草Thalassia hemprichii於無機碳源使用的影響

[[abstract]]Blooms of ulvoid macroalgae (mainly Enteromorpha and Ulva) have covered 80% of the intertidal seagrass bed at Wanlitung, southern Taiwan, effectively shading the seagrasss species Thalassia hemprichii resulting in a decrease in photosynthetic performance and low inorganic carbon (C(subscript i)) uptake. We looked for evidence of C(subscript i) limitation and investigated the C(subscript i) utilization characteristics of ulvoid-free and ulvoid-covered T. hemprichii. The rapid light curve (RLC) function of the Diving-PAM (Diving-PAM. Walz, Germany) was used to measure in situ photosynthetic performance (based on the effective quantum yield of PSⅡ [Y] values) of intact seagrasses that were placed in small incubating chambers. Significantly, a lower RETR(subscript max) (maximum relative electron transport rate) and E(subscript k) (light intensity at the onset of saturation) were noted in the ulvoid-covered compared to the ulvoid-free T. hemprichii, suggesting that the former has acclimatized to the low light environment becoming a &quot;shade type&quot; plant. The ulvoid-covered T. hemprichii showed some evidence of C(subscript i) limitation since a significant increase in RETR(subscript max) (up to 46%; P<0.05) was noted after an increase in the concentration of NaHCO3 from 2.2 (normal seawater) to 6.2mM. In terms of C(subscript i) utilization characteristics, T. hemprichii could directly absorb HCO3(superscript -) as the major C(subscript i) source but partially depended on the extracellular carbonic anhydrase (CA) to convert HCO3(superscript -) to CO2 prior to uptake in the ulvoid-free, high light-adapted populations. A wastewater stream with a high nutrient load coming from the urbanized area may have caused the frequent blooms of ulvoid macroalgae.[[abstract]]台灣南部萬里桐地區大型石蓴類海藻藻華覆蓋Thalassia hemperichii海草床面積約近80%，覆蓋的遮蔽效應造成了海草光合作用和無機碳源吸收都降低。本研究利用沉水性葉綠素螢光分析儀的快速光曲線(rapis light curve, RLC)功能在野外實測被遮蔽和未遮蔽海草間的無機碳使用情形，探討其相互間是否有無差異。研究結果顯示，相較於未遮蔽海草族群，被遮蔽族群有顯著較低的RETR(下標 max)和E(下標 k)值(P<0.05)，顯示其已馴化成為適應低光的族群。當無機碳濃度從海水的2.2mM增加到6.2mM時，被遮蔽海草的光合作用顯著增加46% (P