CAM植物夜间开放气孔固碳,这种安排在哪些环境下是划算的?
CAM plants open their stomata at night to fix carbon — under which conditions does this arrangement pay off?
夜间温度低、湿度高,同样的二氧化碳摄入量伴随的水分流失远小于白天,苹果酸储存的碳白天脱羧供Calvin循环使用。在荒漠和附生植物栖居的树冠等水分极不稳定的环境里,提高单次用水效率比追求最大光合速率更重要。代价是碳同化总量受限,所以CAM植物普遍生长缓慢,这是干旱环境下的合理权衡。
Night air is cool and humid, so each unit of CO2 taken in costs far less water than daytime uptake would; carbon stored as malate is decarboxylated the next day to feed the Calvin cycle. In habitats with highly unreliable water such as deserts or the canopy where epiphytes live, maximizing water-use efficiency matters more than peak photosynthetic rate. The trade-off is a limited total carbon gain, hence generally slow growth — a rational bargain under drought.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Winter, Smith,《Crassulacean Acid Metabolism》,Ecological Studies,1996 (DOI: 10.1007/978-3-642-79060-7)
Winter and Smith, 'Crassulacean Acid Metabolism', Ecological Studies, 1996, DOI: 10.1007/978-3-642-79060-7
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1007/978-3-642-79060-7
#光合作用 #景天酸代谢
为什么C4植物在炎热环境中更高效？
Why are C4 plants more efficient in hot environments?
C4植物先用PEP羧化酶在叶肉细胞捕获CO₂形成四碳化合物，再送到维管束鞘细胞释放，减少光呼吸损失，在高温强光下更节水高产。
C4 plants first fix CO₂ into a four-carbon compound in mesophyll cells, then release it in bundle-sheath cells, minimizing photorespiration—saving water and boosting yield in heat and strong light.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
Raven 等,《Biology of Plants》第8版,W. H. Freeman,2013
P. H. Raven et al., Biology of Plants, 8th ed., W. H. Freeman, 2013
独立核验依据 · Independent verification: 核验依据 2 OPENLIBRARY 标识 /works/OL16626503W：Biology of plants（按标题+
#C4 #光呼吸 #维管束鞘
光合作用的光反应和暗反应分别做什么？
What do the light and dark reactions of photosynthesis do?
光反应在类囊体膜上利用光能把水分解、产生ATP和NADPH并释放氧；暗反应（卡尔文循环）在基质里用这些能量把CO₂固定成糖。
Light reactions split water using light to make ATP and NADPH and release oxygen at the thylakoid membrane; the Calvin cycle then uses that energy in the stroma to fix CO₂ into sugar.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
Raven 等,《Biology of Plants》第8版,W. H. Freeman,2013
P. H. Raven et al., Biology of Plants, 8th ed., W. H. Freeman, 2013
独立核验依据 · Independent verification: 核验依据 2 OPENLIBRARY 标识 /works/OL16626503W：Biology of plants（按标题+
#光反应 #暗反应 #卡尔文循环
为什么C3植物在强光和高温下光合速率反而下降?
Why does the photosynthetic rate of C3 plants drop under intense light and high temperature?
高温提高了Rubisco对氧气的相对亲和活性,光呼吸随之增强,固定的二氧化碳被重新释放。同时气孔为减少蒸腾而部分关闭,叶肉细胞间隙的二氧化碳浓度进一步降低。两个过程叠加,使净光合速率在强光高温条件下不升反降。
High temperature shifts Rubisco's balance toward its oxygenase activity, so photorespiration intensifies and freshly fixed CO2 is released again. Stomata also partly close to curb water loss, lowering the intercellular CO2 concentration further. Together these two effects make net photosynthesis fall instead of rise under strong light and heat.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Taiz等《植物生理学与发育》(Plant Physiology and Development)第6版第9章关于温度与光呼吸的论述
Taiz et al., Plant Physiology and Development, 6th ed., Chapter 9 on temperature effects and photorespiration
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1093/hesc/9780197614204.001.0001：Plant Ph
#光合作用 #光呼吸
固定CO2的Rubisco为什么会误抓氧气？这个失误让植物付出多大代价？
Why does the CO2-fixing enzyme Rubisco also grab oxygen, and what does this mistake cost the plant?
Rubisco诞生于几乎没有氧气的远古大气中，其活性中心从未进化出对CO2和O2的严格分辨能力。当氧气进入活性中心时，底物会被导入光呼吸途径——该途径消耗ATP、释放已固定的CO2，却不生成任何糖类。玉米等C4植物通过在维管束鞘细胞内富集CO2来抑制这一损耗。
Rubisco arose in an ancient atmosphere nearly devoid of oxygen, so its active site never evolved tight discrimination between CO2 and O2. When oxygen occupies the site, substrates are channeled into photorespiration, a pathway that consumes ATP and releases previously fixed CO2 without producing any sugar. Maize and other C4 plants curb this leak by concentrating CO2 around Rubisco inside bundle-sheath cells.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Bauwe, Hagemann & Fernie,《Photorespiration: players, partners and origin》,Trends in Plant Science,2010 (DOI: 10.1016/j.tplants.2010.03.006)
Bauwe, Hagemann & Fernie, 'Photorespiration: players, partners and origin', Trends in Plant Science, 2010, DOI: 10.1016/j.tplants.2010.03.006
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1016/j.tplants.2010.03.006
#Rubisco #光呼吸