Department of Biological Sciences, Aarhus University, Ole Worms Allé 1, DK-8000 Arhus C, Denmark.
BMC Plant Biol. 2010 Feb 8;10:23. doi: 10.1186/1471-2229-10-23.
Cattail (Typha domingensis) has been spreading in phosphorus (P) enriched areas of the oligotrophic Florida Everglades at the expense of sawgrass (Cladium mariscus spp. jamaicense). Abundant evidence in the literature explains how the opportunistic features of Typha might lead to a complete dominance in P-enriched areas. Less clear is how Typha can grow and acquire P at extremely low P levels, which prevail in the unimpacted areas of the Everglades.
Apparent P uptake kinetics were measured for intact plants of Cladium and Typha acclimated to low and high P at two levels of oxygen in hydroponic culture. The saturated rate of P uptake was higher in Typha than in Cladium and higher in low-P acclimated plants than in high-P acclimated plants. The affinity for P uptake was two-fold higher in Typha than in Cladium, and two- to three-fold higher for low-P acclimated plants compared to high-P acclimated plants. As Cladium had a greater proportion of its biomass allocated to roots, the overall uptake capacity of the two species at high P did not differ. At low P availability, Typha increased biomass allocation to roots more than Cladium. Both species also adjusted their P uptake kinetics, but Typha more so than Cladium. The adjustment of the P uptake system and increased biomass allocation to roots resulted in a five-fold higher uptake per plant for Cladium and a ten-fold higher uptake for Typha.
Both Cladium and Typha adjust P uptake kinetics in relation to plant demand when P availability is high. When P concentrations are low, however, Typha adjusts P uptake kinetics and also increases allocation to roots more so than Cladium, thereby improving both efficiency and capacity of P uptake. Cladium has less need to adjust P uptake kinetics because it is already efficient at acquiring P from peat soils (e.g., through secretion of phosphatases, symbiosis with arbuscular mycorrhizal fungi, nutrient conservation growth traits). Thus, although Cladium and Typha have qualitatively similar strategies to improve P-uptake efficiency and capacity under low P-conditions, Typha shows a quantitatively greater response, possibly due to a lesser expression of these mechanisms than Cladium. This difference between the two species helps to explain why an opportunistic species such as Typha is able to grow side by side with Cladium in the P-deficient Everglades.
香蒲（Typha domingensis）在富磷的佛罗里达州大沼泽地贫营养区扩散，取代了锯齿草（Cladium mariscus spp. jamaicense）。文献中有大量证据解释了香蒲的机会主义特征如何导致其在富磷区完全占据优势。不太清楚的是，香蒲如何在大沼泽地未受影响地区普遍存在的极低磷水平下生长并获得磷。
在水培培养中，用适应低磷和高磷的完整香蒲和锯齿草植株测量了明显的磷吸收动力学。与高磷适应植株相比，低磷适应植株的磷吸收饱和速率更高，且在香蒲中更高。与锯齿草相比，香蒲对磷吸收的亲和力高两倍，而与高磷适应植株相比，低磷适应植株高两到三倍。由于锯齿草的生物量有更大比例分配到根部，因此两种物种在高磷水平下的总吸收能力没有差异。在低磷供应的情况下，香蒲比锯齿草增加了更多的生物量分配到根部。两种物种还调整了它们的磷吸收动力学，但香蒲比锯齿草更明显。磷吸收系统的调整和更多的生物量分配到根部导致锯齿草每株植物的吸收量增加五倍，而香蒲的吸收量增加十倍。
当磷供应充足时，锯齿草和香蒲都会根据植物的需求调整磷吸收动力学。然而，当磷浓度较低时，香蒲不仅调整磷吸收动力学，而且比锯齿草更多地增加对根部的分配，从而提高磷吸收的效率和能力。锯齿草不需要调整磷吸收动力学，因为它已经能够从泥炭土壤中有效地获取磷（例如，通过分泌磷酸酶、与丛枝菌根真菌共生、营养保存生长特性）。因此，尽管锯齿草和香蒲在低磷条件下具有提高磷吸收效率和能力的定性相似策略，但香蒲表现出更大的定量响应，这可能是由于其表达这些机制的程度低于锯齿草。这两个物种之间的差异有助于解释为什么像香蒲这样的机会主义物种能够与锯齿草一起在磷缺乏的大沼泽地中生长。
