Plant species composition and key-species abundance drive ecosystem multifunctionality

Global biodiversity loss has generated great interest in the role of plant
communities in driving ecosystem functions. There is limited understanding
of how soil properties, plant richness, and plant community composition
interact to affect ecosystem multifunctionality. We conducted a
constructed-ecosystem experiment by simultaneously manipulating soil
origin (i.e., fertile farmland soil and relatively infertile bare land
soil), plant richness, and community composition (one-species monoculture,
and all possible two-, three-, and four-species combinations of five
plants) to evaluate their influence on ecosystem multifunctionality
related to the accumulation of biomass, carbon (C) and nitrogen (N) in
plants, greenhouse gas emissions, soil nutrients, soil N fixation, and
mineralization of N and phosphorus (P). We found that ecosystem
multifunctionality was significantly affected by soil origin, plant
community composition, and the community-weighted mean (CWM) of plant
biomass, but not by plant richness. We grouped the community composition
into the N-fixing group (including N-fixing plants) and the non-N-fixing
group (excluding N-fixing plants). The N-fixing plant group exhibited
significantly higher multifunctionality than the non-N-fixing species
group in both soil origins. For bare land soil, multifunctionality
increased with the increasing relative abundance and biomass ratio of
Albizia julibrissin (N-fixing species) in communities, but decreased with
the biomass ratio of Platycladus orientalis (non-N-fixing species). For
farmland soil, multifunctionality increased with the abundance of Toona
sinensis (non-N-fixing species) and the biomass ratio of Albizia
julibrissin, but decreased with the abundance and biomass ratio of Morus
alba (non-N-fixing species). These results indicate that the key-species
determining ecosystem multifunctionality vary under different soil
conditions. Synthesis and applications. We propose that plant community
composition and the relative abundance and biomass ratio of key-species
drive ecosystem multifunctionality. We suggest that selecting the
appropriate plant combination under different soil conditions should be
emphasized in ecological restoration projects. Our study highlights the
differentiated roles of key-species on ecosystem functions under different
resource conditions. The N fixation in general plays a crucial role in
driving ecosystem multifunctionality and the N-fixing plants can serve as
restoration tools in nutrient-poor degraded lands.