Data from: Plant and soil microbe responses to light, warming and nitrogen addition in a temperate forest

1. Temperate forests across Europe and eastern North America have become
denser since the 1950s due to less intensive forest management and global
environmental changes such as nitrogen deposition and climate warming.
Denser tree canopies result in lower light availability at the forest
floor. This shade may buffer the effects of nitrogen deposition and
climate warming on understorey plant communities. 2. We conducted an
innovative in-situ field experiment to study the responses of co-occurring
soil microbial and understorey plant communities to nitrogen addition,
enhanced light availability, and experimental warming in a full-factorial
design. 3. We determined the effects of multiple environmental drivers and
their interactions on the soil microbial and understorey plant
communities, and assessed to what extent the soil microbial and
understorey plant communities co-vary. 4. High light led to lower biomass
of the soil microbes (analysed by phospholipid fatty acids), but the soil
microbial structure, i.e., the ratio of fungal biomass to bacterial
biomass, was not affected by light availability. The composition of the
soil bacterial community (analysed by high-throughput sequencing) was
affected by both light availability and warming (and their interaction),
but not by nitrogen addition. Yet, the number of unique operational
taxonomic units was high in plots with nitrogen addition, and there were
significant interactive effects of light and nitrogen addition. Light
availability also determined the composition of the plant community; no
effects of nitrogen addition and warming were observed. The soil bacterial
and plant communities were co-structured, and light availability explained
most variance of this co-structure. 5. We provide robust evidence for the
key role of light in affecting both the soil microbial and plant
communities in forest understoreys. Our results advocate for more
multifactor global-change experiments that investigate the mechanism
underlying the (in)direct effects of light on the plant–soil continuum in
forests.