Duke University Marine Laboratory, 28516-9721, Beaufort, NC, USA.
Planta. 1991 May;184(2):235-43. doi: 10.1007/BF00197952.
Clonal tissue of the marine chlorophyte macroalga, Ulva rotundata Blid., was transferred from 100 to 1700 μmol photons · m(-2) · s(-1) under limiting (1.5 μM NH 4 (+) maximum, N/P=2) and sufficient (15 μM NH 4 (+) maximum, N/P=20) nitrogen supply at 18° C and 11 h light-13 h darkness daily. Photoinhibition was assayed by light-response curves (photosynthetic O2 exchange), and chlorophyll fluorescence at 77 K and room temperature. Daily surface-area growth rate (μSA) in N-sufficient plants increased sixfold over 3 d and was sustained at that level. During this period, respiration (R d) doubled and light-saturated net photosynthesis capacity (P m) increased by nearly 50%, indicating acclimation to high light. Quantum yield (ϕ) decreased by 25% on the first day, but recovered completely within one week. The ratio of variable to maximum fluorescence (F v/F m) also decreased markedly on the first day, because of an increase in initial fluorescence (F o) and a decrease in F m, and partially recovered over several days. Under the added stress of N deficiency, μSA accelerated fivefold over 4 d, despite chronic photoinhibition, then declined along with tissue-N. Respiration doubled, but P m decreased by 50% over one week, indicating inability to acclimate to high light. Both ϕ and F v/F m decreased markedly on the first day and did not significantly recover. Changes in F o, F m and xanthophyll-cycle components indicate concurrent photodamage to photosystem II (PSII) and photoprotection by thermal deexcitation in the antenna pigments. Increasing μSA coincided with photoinhibition of PSII. Insufficient diel-carbon balance because of elevated R d and declining P m and tissue-N, rather than photochemical damage per se, was the apparent proximate cause of decelerating growth rate and subsequent tissue degeneration under N deficiency in U. rotundata.
在 18°C 和每天 11 小时光照 13 小时黑暗的条件下，将海洋绿藻 Ulva rotundata Blid. 的克隆组织从 100 转移到 1700 μmol 光子·m(-2)·s(-1)，在限制（1.5 μM NH 4 (+) 最大，N/P=2）和充足（15 μM NH 4 (+) 最大，N/P=20）氮供应下。通过光响应曲线（光合 O2 交换）和 77 K 和室温下的叶绿素荧光测定光抑制。在充足氮供应下，植物的日表面积生长率（μSA）在 3 天内增加了 6 倍，并保持在该水平。在此期间，呼吸作用（R d）增加了一倍，饱和光下净光合作用能力（P m）增加了近 50%，表明适应了高光。量子产率（ϕ）在第一天下降了 25%，但在一周内完全恢复。由于初始荧光（F o）增加和 F m 减少，第一天可变荧光与最大荧光（F v/F m）的比值也明显下降，并且在几天内部分恢复。在氮缺乏的额外压力下，μSA 在 4 天内加速了五倍，尽管存在慢性光抑制，但随后随着组织氮的减少而下降。呼吸作用增加了一倍，但 P m 在一周内减少了 50%，表明无法适应高光。第一天和第二天的 ϕ 和 F v/F m 均明显下降，且未显著恢复。F o、F m 和叶黄素循环成分的变化表明，同时发生对 PSII 的光破坏和天线色素的热去激发的光保护。μSA 的增加与 PSII 的光抑制同时发生。由于升高的 R d 和下降的 P m 和组织氮导致的昼夜碳平衡不足，而不是光化学损伤本身，是 U. rotundata 在氮缺乏下生长速率减慢和随后组织退化的明显直接原因。
