Harley P C, Tenhunen J D, Murray K J, Beyers J
Systems Ecology Research Group, San Diego State University, 92182, San Diego, CA, USA.
Oecologia. 1989 May;79(2):251-259. doi: 10.1007/BF00388485.
Photosynthetic characteristics of three species of Sphagnum common in the foothills of the Brooks Range on the North Slope of Alaska were investigated. Generally, light-saturated rates of net photosynthesis decreased in the order S. squarrosum, S. angustifolium, and S. warnstorfii when plants were grown under common growth chamber conditions. For field-grown S. angustifolium, average light compensation point at 10°C was 37 μmol ms photosynthetic photon flux density (PPFD), and light saturation occurred between 250 and 500 μmol m s. At 20°C, compensation point increased to 127 μmol ms and the PPFD required for light saturation increased to approximately 500 μmol ms, while maximum rates of CO uptake increased only slightly. Light response curves of chamber-grown plants exhibited substantially lower compensation points and higher light-saturated rates of CO assimilation than field-grown material, due perhaps to a higher percentage of green, photosynthetically competent tissue. All three species exhibited broad responses to temperature, with optima near 20°C, and maintained at least 75% of maximum assimilation between approx. 13° and 30°C. Rates at 5°C were approx. 50% of maximum. Studies of the microclimate of Sphagnum at the field research site suggest that CO uptake should occur at near light-saturated rates during the day in open tussock tundra but that PPFD may often be limiting under Salix and Betula canopies in a water track drainage. Simulations using a simple model provided a seasonal estimate of 0.78 g dry weight (DW) of S. angustifolium produced from each initial g of photosynthetic tissue under willow canopies, assuming no water limitations. Although the simulation model suggests that production would be 66% higher in open tussock tundra, S. angustifolium is rarely found in this potentially more stressful habitat. To explain the relative abundance of Sphagnum in shaded water track areas as compared to open tussock tundra, we postulate that the vascular plant canopies provide protection from adverse effects of high temperatures, excess irradiance and reduced water availability. Under conditions of normal water availability, removal of the vascular plant cover did not affect the tissue water content of S. squarrosum, but resulted in a strong decrease in photosynthetic capacity, accompanied by chlorophyll bleaching. These results suggest that photoinhibition may limit production under certain conditions.
对阿拉斯加北坡布鲁克斯山脉山麓常见的三种泥炭藓的光合特性进行了研究。一般来说，当植物在普通生长室条件下生长时，净光合作用的光饱和速率按粗叶泥炭藓、狭叶泥炭藓和暖地泥炭藓的顺序降低。对于田间生长的狭叶泥炭藓，10°C时的平均光补偿点为37 μmol m⁻² s⁻¹光合光子通量密度（PPFD），光饱和发生在250至500 μmol m⁻² s⁻¹之间。在20°C时，补偿点增加到127 μmol m⁻² s⁻¹，光饱和所需的PPFD增加到约500 μmol m⁻² s⁻¹，而CO₂吸收的最大速率仅略有增加。生长室中生长的植物的光响应曲线显示，与田间生长的材料相比，补偿点显著更低，CO₂同化的光饱和速率更高，这可能是由于绿色光合活性组织的比例更高。所有这三个物种对温度都有广泛的响应，最适温度接近20°C，并且在约13°至30°C之间保持至少75%的最大同化率。5°C时的速率约为最大值的50%。对田间研究地点泥炭藓微气候的研究表明，在开阔的草丘冻原中，白天CO₂吸收应该以接近光饱和的速率发生，但在水道排水中的柳树和桦树树冠下，PPFD可能经常是限制因素。使用一个简单模型进行的模拟提供了一个季节性估计，即在柳树树冠下，每克初始光合组织可产生0.78克干重（DW） 的狭叶泥炭藓，假设没有水分限制。尽管模拟模型表明在开阔的草丘冻原中产量会高出66%，但在这个可能压力更大的栖息地中很少能找到狭叶泥炭藓。为了解释与开阔的草丘冻原相比，泥炭藓在阴凉的水道区域相对丰富的原因，我们推测维管植物树冠提供了免受高温、过量光照和水分供应减少等不利影响的保护。在正常水分供应条件下，去除维管植物覆盖物不会影响粗叶泥炭藓的组织含水量，但会导致光合能力大幅下降，并伴有叶绿素漂白。这些结果表明，在某些条件下光抑制可能会限制产量。
