Imaging spectroscopy reveals topographic variability effects on grassland functional traits and drought responses

Functional traits and their variations are essential indicators of plant metabolism, growth, distribution, and survival and determine how a plant and an ecosystem function. Under the same climatic condition, traits can vary significantly between species and within the same species growing in different topographic conditions. When drought stress occurs, plants growing in these conditions may respond in various ways as their tolerance and adaptability are influenced by differences in topography. Insights into topographic variability-driven trait variation and drought response can improve our prediction of ecosystem functioning and ecological impacts. Imaging spectroscopy enables accurate identification of plant species, extraction of functional traits, and characterization of topography-driven and drought-related impacts on trait variation across spatial scales. However, applying these data in a heterogeneous grassland ecosystem is challenging as species are small, highly mixed, spectrally and texturally similar, and highly varied with small-scale variation in topography. This paper presents the first study to explore the use of high-resolution airborne imaging spectroscopy for characterizing the variation of key traits-such as chlorophylls (Chl), carotenoids (Car), Chl/Car ratio, water content (WC), and leaf area index (LAI)-across topographic gradients and under drought stress at the species level in a heterogeneous grassland. The results demonstrate significant relationships between functional traits and topographic variability, with the strength of these relationships varying among species and across different environmental conditions. Additionally, drought-induced trait responses differed notably both within and between species, particularly between drought-tolerant invasive species and drought-sensitive native species, as well as between lower and upper slope positions. The study makes a significant contribution to advancing our understanding of biological and ecological processes, enhancing the ability to predict plant invasion mechanism and ecosystem functioning under stressed environments.