干旱区生态环境知识资源中心

QuestionsAtmospheric and agricultural inputs of nitrogen have increased significantly. Because riparian zones act as buffers for nutrient transfer and treated municipal effluent and untreated agricultural run-off are released into streams, and because desert riparian ecosystems contain a wide range of functional groups with respect to water relations, we asked if wetland and dryland species respond differently to increasing levels of soil nitrate. Specifically, we asked if seed germination rate, total percentage germination and seedling development varied by species and functional group in response to increasing nitrate levels.

LocationSouthwestern US.

MethodsWe subjected seeds of common wetland and dryland species to distilled water (control), 0.025M (low), 0.05M (intermediate) and 0.075M (high) KNO3 treatments for 30days. We determined seed germination rates, total percentage germination and seedling development for each species. Generalized linear mixed models tested for differences between treatments.

ResultsSeeds of wetland species germinated rapidly and in high percentages, and developed into seedlings regardless of nitrate treatments. Dryland species had unique responses to nitrate treatments, with some species exhibiting high germination rates in control treatments and others showing strong germination responses at low to intermediate nitrate levels. A larger number of dryland germinants developed into seedlings under control to low nitrate treatments.

ConclusionsRiparian plant community dynamics arising from germination responses could change under increased nitrogen inputs, as some species are seemingly unaffected and others significantly impacted. Based on our limited species pool and treatment conditions, the functional group wetland species’ produces a consistent germination and early seedling response regardless of nitrate concentration, while dryland species’ responses are variable and species-specific. Species known to be nitrophiles can be inhibited by high nitrogen concentration as germinants, highlighting the importance of investigating plant community response to changing conditions at a variety of life stages.