Effects of Rising Temperature on the Growth, Stoichiometry, and Palatability of Aquatic Plants

Abstract

Global warming is expected to strengthen herbivore-plant interactions leading to enhanced top-down control of plants. However, latitudinal gradients in plant quality as food for herbivores suggest lower palatability at higher temperatures, but the underlying mechanisms are still unclear. If plant palatability would decline with temperature rise, then this may question the expectation that warming leads to enhanced top-down control. Therefore, experiments that directly test plant palatability and the traits underlying palatability along a temperature gradient are needed. Here we experimentally tested the impact of temperature on aquatic plant growth, plant chemical traits (including stoichiometry) and plant palatability. We cultured three aquatic plant species at three temperatures (15, 20, and 25°C), measured growth parameters, determined chemical traits and performed feeding trial assays using the generalist consumer Lymnaea stagnalis (pond snail). We found that rising temperature significantly increased the growth of all three aquatic plants. Plant nitrogen (N) and phosphorus (P) content significantly decreased, and carbon (C):N and C:P stoichiometry increased as temperature increased, for both Potamogeton lucens and Vallisneria spiralis, but not for Elodea nuttallii. By performing the palatability test, we found that rising temperatures significantly decreased plant palatability in P. lucens, which could be explained by changes in the underlying chemical plant traits. In contrast, the palatability of E. nuttallii and V. spiralis was not affected by temperature. Overall, P. lucens and V. spiralis were always more palatable than E. nuttallii. We conclude that warming generally stimulates aquatic plant growth, whereas the effects on chemical plant traits and plant palatability are species-specific. These results suggest that the outcome of the impact of temperature rise on macrophyte stoichiometry and palatability from single-species studies may not be broadly applicable. In contrast, the plant species tested consistently differed in palatability, regardless of temperature, suggesting that palatability may be more strongly linked to species identity than to intraspecific variation in plant stoichiometry.

Effects of temperature of plant cultivation on plant palatability modify species response to novel climate

“…The effects of temperature on plant palatability are often studied along altitudinal or latitudinal gradients 21,22 . More palatable plants at higher altitudes/latitudes suggest lower palatability at higher temperatures 7 . The plants at lower altitudes/latitudes might be better defended 10,23 , produce leaves morphologically harder to consume (with low specific leaf area or with trichomes 24 ) or have lower nitrogen and phosphorus leaf content 25 .…”

“…Warming is thus expected to strengthen various herbivore-plant interactions 5,6 . However, these predictions do not take into account that increased temperature might also affect the plant traits that determine their palatability to the herbivores 7 .…”

“…Plants tend to suffer higher herbivore damage in wetter, nutrient richer and more shaded habitats 12–14 , i.e., in habitats in which they often grow more vigorously as suggested by Plant vigor hypothesis 15 . Increased leaf quality also contributes to greater levels of herbivory in nutrient richer habitats 7,16 . Leaves of plants growing in benign conditions habitats often also have higher specific leaf area, lower tissue density, thinner leaf lamina and weaker veins 17 and are less tough 18 , which makes them more palatable to the herbivores.…”

“…This might be the reason why not all studies find the above described relationship between altitude/latitude and plant palatability 27–30 . Although temperature is one of the factors which is expected to change significantly under global warming, studies on its direct impact on plant palatability are still limited (but see 7,31 ).…”

“…Previous studies often found contrasting results when exploring the effects of environment on plant-herbivore interactions among different plant species indicating that plant species and environmental conditions interact to jointly determine plant palatability 7,32–34 . To understand the effects of temperature on plant palatability, we thus need to perform studies exploring these interactive effects of plant species and temperature.…”