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

Abstract

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 largely between species and within the same species growing in different topographic conditions. When drought stress occurs, plants that grow in these conditions may respond differently as their topography-driven tolerance and adaptability differ. Insights into topographic variability-driven trait variation and drought response can improve our prediction of ecosystem functioning and ecological impacts. Imaging spectroscopy allows accurate detection of plant species, retrieval of functional traits, and characterization of topography-driven and drought impacts on trait variation across space. However, the use of this data in a heterogeneous grassland ecosystem is challenging as species are small, high mixed, spectrally and texturally similar, and highly varied with small-scale variation in topography. In this paper, we introduce the first study that explores the use of high-resolution airborne imaging spectroscopy to characterize the variation of common traits, including 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 reveal that there were significant relationships between functional traits and topographic variability, and the degree of the relationships deferred among species and under different environmental conditions. The results also show that drought-induced trait responses varied significantly within and between species, especially between drought-tolerant invasive species and native species, between lower and upper slope positions. The study contributes greatly to the advancement in understanding biological and ecological processes for a better prediction of ecosystem functioning under stressed environments.