Summary Plants may experience different environmental cues throughout their development which interact in determining their phenotype. This paper tests the hypothesis that environmental conditions experienced early during ontogeny affect the phenotypic response to subsequent environmental cues. This hypothesis was tested by exposing different accessions of Rumex palustris to different light and nutrient conditions, followed by subsequent complete submergence. Final leaf length and submergence‐induced plasticity were affected by the environmental conditions experienced at early developmental stages. In developmentally older leaves, submergence‐induced elongation was lower in plants previously subjected to high‐light conditions. Submergence‐induced elongation of developmentally younger leaves, however, was larger when pregrown in high light. High‐light and low‐nutrient conditions led to an increase of nonstructural carbohydrates in the plants. There was a positive correlation between submergence‐induced leaf elongation and carbohydrate concentration and content in roots and shoots, but not with root and shoot biomass before submergence. These results show that conditions experienced by young plants modulate the responses to subsequent environmental conditions, in both magnitude and direction. Internal resource status interacts with cues perceived at different developmental stages in determining plastic responses to the environment.

The increase in alkalinity and SO 4 2-in softwater lakes can negatively affect pristine isoetid population because the increase in alkalinity and SO 4 2-can stimulate sediment mineralization and consequently cause anoxia. The consequences of increased sediment mineralization depend on the ability of isoetids such as Lobelia dortmanna to oxidize the rhizosphere via radial O 2 loss. To study how alkalinity and SO 4 2-affect the isoetid L. dortmanna, and if negative effects could be alleviated by neighboring plants, three densities of L. dortmanna (''Low'' = 64 plants m -2 , ''Medium'' = 256 plants m -2 and ''High'' = 1,024 plants m -2 ) were exposed to elevated alkalinity in the water column, or a combination of both elevated alkalinity and SO 4 2-, and compared to a control situation. The combination of SO 4 2-and alkalinity significantly increased mortality, lowered areal biomass and reduced actual photosynthetic efficiency. Plant density did not significantly alleviate the negative effects caused by SO 4 2-and alkalinity. However, actual photosynthetic efficiency was significantly positively correlated to redox potential in the sediment, indicating a positive relationship between plant performance and sediment oxidation. The negative effects on L. dortmanna were probably caused by long periods of tissue anoxia by itself or in combination with H 2 S intrusion. Therefore, increase in both SO 4 2-and alkalinity surface water can dramatically affect L. dortmanna populations, causing reduction or even disappearance of this icon species.