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California Native and Invasive Plants as Biological Sensors for Nitrogen Pollution


The Integrated Total Nitrogen Input (ITNI) method is a technique for evaluating nitrogen deposition by utilizing plants as collection interfaces. The ITNI method employs a plant-liquid-sand system (PLS system) in which a plant is hydroponically grown in silica sand and labeled with 15N tracer while growing in a greenhouse. After plants are labeled, they are deployed into the environment where the 15N tracer in the plant tissues is diluted as a result of atmospheric nitrogen deposition input via gaseous, leaf and root uptake. At the end of the sampling period, all components of the plant and system are harvested and analyzed on a mass spectrometer to determine the degree of dilution of the tracer. The 15N values obtained were incorporated into a mass balance equation that accounts for the total deposition occurring on the PLS system surfaces and yields the total nitrogen uptake from the atmosphere. In this study, we will employed coastal sage scrub (CSS), a declining native California plant assemblage, and invasive Mediterranean annual plants to determine total nitrogen deposition occurring in the Inland Empire of Southern California. Traditional nitrogen deposition collection devices such as throughfall and bulk ion exchange resins, inferential method collectors, and a rain collector was co-located with the ITNI PLS systems to compare and assess the accuracy of such traditional collectors. We found that the ITNI method is applicable to non-agricultural systems such as coastal sage scrub habitat, where the method was formerly utilized. Our findings suggest that ITNI methods compare to that of inferential techniques in estimating total nitrogen deposition to Southern California coastal sage scrub habitats. Additionally, it was found that the ITNI method is the most cost effective total nitrogen deposition measurement method when compared to the inferential method. Lastly, it was found that the ITNI system was sensitive enough to delineate between study sites on a nitrogen deposition gradient in the California Inland Empire, ranging from a "high" deposition urban site to a "moderate" deposition rural site.

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