A research team led by Prof. LIU Lingli from the Institute of Botany of the Chinese Academy of Sciences (IBCAS), has revealed the vital role of canopy structure in regulating ecosystem carbon use efficiency (CUE) in semi-arid grasslands.

The findings, published in Journal of Ecology, provides compelling evidence that deepened snow cover enhanced the ecosystem CUE by improving the photosynthetic carbon uptake relative to respiratory loss in a temperate grassland. Notably, this response resulted from two main interacting pathways: resource-mediated physiological processes and canopy structure-mediated biophysical processes.

In this study, the researchers conducted a five-year snow manipulated experiment in Inner Mongolia and combined with multi-year high-frequency observations of ecosystem carbon flux, species surveys, and canopy structure analysis during the growing season in temperate grasslands. They found that deepened snow increased soil nitrogen and water availability, synergistically enhancing nutrient uptake and plant nitrogen use efficiency (NUE). Concurrently, C₃ grasses charactered by higher NUE and greater height became dominant in deep-snow plots, further elevating community-level NUE.

The improved NUE allowed plants to accumulate more biomass and larger canopy volumes while spending less carbon on basic metabolic maintenance. As plant canopies became larger and denser, they captured more sunlight and produced more carbon uptake. In addition, the larger canopies also created stronger shading effects, which lowered temperatures beneath the canopy, particularly at night, thereby suppressing heterotrophic respiration. Together, these processes enhanced ecosystem carbon uptake and reduced carbon release, ultimately improving the ecosystem's ability to retain carbon during the growing season.

This research highlights the critical role of canopy structure-mediated biophysical processes in regulating grassland carbon sink dynamics. These findings also underscore the importance of optimizing and managing vegetation structure in grassland conservation and ecological restoration practices.

Biophysical regulation of ecosystem carbon use efficiency through nitrogen use efficiency and canopy structure under deepened snow (Image by LI Ping).

A panoramic view of the experimental field site (Picture by LI Ping).