Beyond the visible : The effects of soil moisture and soil nitrogen on leaf characteristics and leaf spectral profiles of the invasive plant Dahurian buckthorn (Rhamnus davurica)

Soils and plants help maintain the balance of nutrients and water in Earth’s ecosystems; however, changes in plant populations due to the arrival of invasive species alter the movement of water and nutrients in the environment. Remote sensing is a developing technology that could monitor these ecosystem changes, but it is still uncertain whether remote sensing can be used to discriminate between different sources of plant stress, such as nitrogen leaching and water loss. This study’s aim is to determine whether changes in soil nitrogen and soil moisture will change plant characteristics that can be observed spectrally in the invasive species Dahurian buckthorn (Rhamnus davurica) and which analyses of spectral profiles are the most representative of those changes. By applying water and nitrogen treatments to buckthorn plants; measuring the changes in nitrogen, carbon and water content in soil and leaves; and taking spectral profiles of the plants, we were able to show that plant characteristics change in response to changes in soil water and nitrogen with a one- to two-week time delay. We were then able to use spectral profiles to represent changes in plant characteristics in response to nitrogen and water availability as well as identify the Canopy Chlorophyll Concentration Index (CCCI) as a reliable indicator of nitrogen stress. Such results are important for developing more accurate ecosystem monitoring methods, which will provide a better understanding of environmental health and stability.