RESUMEN
Drosera intermedia grows in acidic bogs in parts of valleys that are flooded in winter, and that often dry out in summer. It is also described as the sundew of the most heavily hydrated habitats in peatlands, and it is often found in water and even underwater. This sundew is the only one that can tolerate long periods of submersion, and more importantly produces a typical submerged form that can live in such conditions for many years. Submerged habitats are occupied by D. intermedia relatively frequently. The aim of the study was to determine the environmental conditions and architecture of individuals in the submerged form of D. intermedia. The features of the morphological and anatomical structure and chlorophyll a fluorescence of this form that were measured were compared with analogous ones in individuals that occurred in emerged and peatland habitats. The submerged form occurred to a depth of 20 cm. Compared to the other forms, its habitat had the highest pH (4.71-4.92; Me = 4.71), the highest temperature and substrate hydration, and above all, the lowest photosynthetically active radiation (PAR; 20.4-59.4%). This form differed from the other forms in almost all of the features of the plant's architecture. It is particularly noteworthy that it had the largest main axis height among all of the forms, which exceeded 18 cm. The number of living leaves in a rosette was notable (18.1 ± 8.1), while the number of dead leaves was very low (6.9 ± 3.8). The most significant differences were in the shape of its submerged leaves, in which the length of the leaf blade was the lowest of all of the forms (0.493 ± 0.15 mm; p < 0.001) and usually the widest. The stem cross-sectional area was noticeably smaller in the submerged form than in the other forms, the xylem was less developed and collaterally closed vascular bundles occurred. Our analysis of the parameters of chlorophyll fluorescence in vivo revealed that the maximum quantum yield of the primary photochemistry of photosystem II is the highest for the submerged form (Me = 0.681), the same as the maximum quantum yield of the electron transport (Me φE0 = 0.183). The efficiency of energy use per one active reaction center of photosystem II (RC) was the lowest in the submerged form (Me = 2.978), same as the fraction of energy trapped by one active RC (Me = 1.976) and the non-photochemical energy dissipation (DI0/RC; Me = 0.916). The ET0/RC parameter, associated with the efficiency of the energy utilization for electron transport by one RC, in the submerged plant reached the highest value (Me = 0.489). The submerged form of D. intermedia clearly differed from the emerged and peatland forms in its plant architecture. The submerged plants had a thinner leaf blade and less developed xylem than the other forms, however, their stems were much longer. The relatively high photosynthetic efficiency of the submerged forms suggests that most of the trapped energy is utilized to drive photosynthesis with a minimum energy loss, which may be a mechanism to compensate for the relatively small size of the leaf blade.
Asunto(s)
Clorofila , Fotosíntesis , Fotosíntesis/fisiología , Clorofila/metabolismo , Hojas de la Planta/fisiología , Hojas de la Planta/anatomía & histología , Hojas de la Planta/crecimiento & desarrollo , Ecosistema , Clorofila A/metabolismo , Temperatura , Concentración de Iones de Hidrógeno , Agua/metabolismoRESUMEN
The aim of this study was to determine the environmental conditions, individual architectures, and photosynthetic efficiencies of three sundew species: Drosera rotundifolia, D. anglica, and D. intermedia, found in well-preserved peatlands and sandy lake shores in NW Poland. Morphological traits and chlorophyll a fluorescence (Fv/Fm) were measured in 581 individuals of Drosera. D. anglica occupies the best-lit and warmest habitats, and also those that are the most heavily hydrated and the richest in organic matter; its rosettes are larger under conditions of higher pH, less organic matter, and less well-lit habitats. D. intermedia occupies substrates with the highest pH but the lowest conductivity, the poorest level of organic matter, and the least hydration. It is highly variable in terms of individual architecture. D. rotundifolia occupies habitats that are the most diverse, and that are often poorly lit, with the lowest pH but the highest conductivity. It is the least variable in terms of individual architecture. The value of the Fv/Fm ratio in Drosera is low (0.616 ± 0.137). The highest photosynthetic efficiency is achieved by D. rotundifolia (0.677 ± 0.111). It is significant for all substrates, indicating its high phenotypic plasticity. The other species have lower and similar Fv/Fm values (D. intermedia, 0.571 ± 0.118; D. anglica, 0.543 ± 0.154). Due to its very low photosynthetic efficiency, D. anglica avoids competition by occupying highly hydrated habitats. D. intermedia has adapted to the occupation of highly variable habitats in terms of hydration, while D. rotundifolia is primarily adapted to variable light conditions.