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 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. 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 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.