Contrasting effects of plant above- and below-ground functional traits on ecosystem services in artificial forestlands and natural grasslands across vegetation zones

Analysing the status of ecosystem services and their driving mechanisms along environmental gradients is highly important for the reconstruction and protection of regional ecosystems. Exploration of the effects of plant functional traits on ecosystem services is important for revealing the formation mechanisms of ecosystem services. However, the complex effects of plant functional traits on ecosystem services, especially below-ground functional traits, which play critical roles in carbon sequestration, water conservation and soil conservation services, have not been explored in depth.

Data on plant functional traits and ecosystem services were collected from different vegetation zones (steppe, forest-steppe and forest) in a loess hilly gully region. Two representative small watersheds were selected for field experiments in each vegetation zone, each watershed contains artificial forestlands (Robinia pseudoacacia and Caragana korshinskii) and natural grasslands (i.e., areas that underwent natural recovery after farmland abandonment), and a total of 162 quadrats were set up throughout the study area.

The leaf area and specific leaf area gradually increased from the steppe zone to the forest zone, and the leaf thickness, leaf tissue density, and leaf carbon content gradually decreased across this gradient. The root functional traits (except for root tissue density and root carbon content) of each vegetation type decreased in all the soil layers in the following order: forest-steppe zone > steppe zone > forest zone. The trends of all ecosystem services were consistent with those of leaf area. In artificial forestlands, plant above-ground functional traits had greater effects on carbon sequestration and soil conservation services than did below-ground functional traits, whereas water conservation services were strongly linked with below-ground functional traits. The above-ground plant functional traits in the natural grasslands had greater effects on all the ecosystem services than did the below-ground functional traits.

Natural grasslands are suitable for vegetation restoration in these three vegetation zones. Moreover, it is necessary to plant artificial forests in forest-steppe and forest zones to improve soil conservation and carbon sequestration services to cope with extreme climate change.