Horton J L, Neufeld H S
Department of Biology, Appalachian State University, Boone, NC 28608, USA, , , , , , US.
Oecologia. 1998 Mar;114(1):11-19. doi: 10.1007/s004420050414.
Microstegium vimineum (Trin.) A. Camus, a shade-tolerant C grass, has spread throughout the eastern United States since its introduction in 1919. This species invades disturbed understory habitats along streambanks and surrounding mesic forests, and has become a major pest in areas such as Great Smoky Mountains National Park. The focus of this study was to characterize the photosynthetic induction responses of M. vimineum, specifically its ability to utilize low light and sunflecks, two factors that may be critical to invasive abilities and survival in the understory. In addition, we were curious about the ability of a grass with the C photosynthetic pathway to respond to sunflecks. Plants were grown under 25% and 50% ambient sunlight, and photosynthetic responses to both steady-state and variable light were determined. Plants grown in both 25% and 50% ambient sun became 90% light saturated between 750-850 μmol m s; however, plants grown in 50% ambient sun had significantly higher maximum steady-state photosynthetic rates (16.09 ± 1.37 μmol m s vs. 12.71 ± 1.18 μmol m s). Both groups of plants induced to 50% of the steady-state rate in 3-5 min, while it took 10-13 min to reach 90% of maximum rates, under both flashing and steady-state light. For both groups of plants, stomatal conductance during induction reached maximum rates in 6-7 min, after which rates decreased slightly. Upon return to low light, rates of induction loss and stomatal closure were very rapid in both groups of plants, but were more rapid in those grown in high light. Rapid induction and the ability to induce under flashing light may enable this species to invade and dominate mesic understory habitats, while rapid induction loss due to stomatal closure may prevent excess water loss when low light constrains photosynthesis. The C pathway itself does not appear to present an insurmountable barrier to the ability of this grass species to respond to sunflecks in an understory environment.
求米草（Microstegium vimineum (Trin.) A. Camus）是一种耐阴的C4草本植物，自1919年引入美国后已扩散至美国东部。该物种侵入溪流沿岸及周边中生林受干扰的林下生境，在大雾山国家公园等地已成为主要害虫。本研究的重点是描述求米草的光合诱导反应，特别是其利用弱光和光斑的能力，这两个因素可能对其入侵能力和林下生存至关重要。此外，我们还对具有C4光合途径的草本植物对光斑的响应能力感到好奇。将植物种植在25%和50%的环境光照下，测定其对稳态光和可变光的光合响应。生长在25%和50%环境光照下的植物在750 - 850 μmol m-2 s-1之间达到90%的光饱和；然而，生长在50%环境光照下的植物具有显著更高的最大稳态光合速率（16.09 ± 1.37 μmol m-2 s-1 对比 12.71 ± 1.18 μmol m-2 s-1）。在闪烁光和稳态光下，两组植物均在3 - 5分钟内诱导至稳态速率的50%，而达到最大速率的90%则需要10 - 13分钟。对于两组植物，诱导过程中的气孔导度在6 - 7分钟达到最大速率，之后速率略有下降。回到弱光后，两组植物的诱导损失速率和气孔关闭都非常迅速，但高光下生长的植物更快。快速诱导以及在闪烁光下诱导的能力可能使该物种能够侵入并占据中生林下生境，而由于气孔关闭导致的快速诱导损失可能在弱光限制光合作用时防止水分过度流失。C4途径本身似乎并未对该草本植物在林下环境中对光斑的响应能力构成不可逾越的障碍。
