Morphological plasticity of Sagittaria lancifolia in response to phosphorus

Abstract

Sagittaria lancifolia leaf morphology varies in the Everglades of southern Florida, USA, from plants with broadly ovate laminae to plants with linear laminae. To understand the morphological response of S. lancifolia to increased nutrients, we (1) grew S. lancifolia plants in solutions with either 1 mM or 10 μM P and measured morphological responses, as well as tissue N:P content and (2) grew field-collected plants that had a range of leaf morphologies in the greenhouse and measured morphological and tissue N:P responses. Plants in high P (HP), as compared to low P (LP), were larger (biomass 48.3 g HP versus 16.9 g LP), produced more leaves (16.9 HP versus 10.7 LP) and inflorescences (2.9 HP versus 0.3 LP), and branched more (shoots 3.8 HP versus1.1 LP). Biomass allocation to leaves and inflorescences was greater in HP as compared to LP plants (leaves 61% HP versus 37% LP; inflorescences 15% HP versus 2% LP), while plants in LP allocated relatively more biomass to roots and rhizomes than plants in HP (roots 8% HP versus 25% LP; rhizomes 15% HP versus 35% LP). Leaf morphology changed with P-addition, so that plants in high P produced leaves with longer leaf bases (352 mm HP versus 219 mm LP), longer and wider blades (290 mm × 49 mm HP versus 176 mm × 9 mm LP), and a larger leaf area (99 cm 2 HP versus 13 cm 2 LP) than plants in LP, whereas plants in LP produced leaves with longer petioles (277 mm HP versus 346 mm LP). Leaf N:P ratios decreased in HP relative to initial ratios (43 initial to 17 final) and increased in LP (45 initial to 86 final). The direction of change in lamina width of field-collected plants grown under greenhouse conditions depended on the original leaf morphology—plants with narrow blades in the field produced wider laminae in the greenhouse, while plants with wide blades in the field produced narrower laminae. These plastic changes in leaf morphology mimic the differences in leaf morphology between S. lancifolia subsp. media and S. lancifolia subsp. lancifolia. Our results show that S. lancifolia responds rapidly to changes in environmental nutrient status, especially in lamina morphology. Blade shape thus provides a field indicator of soil/pore water nutrient status: narrow blades indicate nutrient limitation, whereas broader blades indicate nutrient enrichment.