Site and treatments
The study was conducted at the Dinghushan Biosphere Reserve in southern
China (112°10′ E, 23°10′N). The reserve is characterized by a tropical
monsoon humid climate with a mean annual temperature of 21 °C and mean
relative humidity of 80%. The mean annual precipitation of 1900 mm has
a distinct seasonal pattern, with about 80% of it falling from April to
September (warmer wet season) and 20% occurring from October to March
(cooler dry season).
The experimental warming site was constructed by translocating the
microcosm forest ecosystem from the high-elevation site (control: 600 m)
to low-elevation sites (+1.0°C treatment: 300 m; +2.1°C treatment: 30 m)
(Fig. S1). In May 2012, three plots
(open-top chambers; 3 m length × 3 m width × 0.8 m depth) were
established at each of the elevation sites, representing three
replicates of each temperature treatment. Each belowground plot was
surrounded by concrete brick wall bonding with ceramic tile, with one
hole connected with PVC tubing at the bottom and the top of the chamber
wall to collect underground water and surface runoff, respectively. All
plots were separated by a 3 m buffer zone. Before planting, we collected
soil from each of the three horizons (0-20, 20–40, and 40-70 cm) in the
adjacent naturally occurring mountain evergreen broad-leaved forest, and
homogenized each layer separately, and then placed each soil horizon
into each plot. Six one-year old dominant plant species, including
arbuscular mycorrhiza-forming species (Schima superba , Itea
chinensis , Machilus breviflora , Myrsine seguinii , andArdisia lindleyana ) and only one ectomycorrhiza-forming species
(Syzygium rehderianum ) at an elevation of 600 m in the natural
forest, were collected and then randomly planted in each plot (six
individuals per species). Four 0.2 m × 0.2 m
litter
traps were placed randomly in each plot. One tree per species was
randomly harvested in December 2014, December 2015, and June 2018 to
avoid crowding in the chambers.
Soil temperature and soil volumetric water content at 5 cm soil depth
were measured in each plot using Campbell 109 constantan-copper
thermocouples and time-domain reflectometer probes (CS616, Campbell,
USA), respectively. Data were recorded every 30 min using Campbell
Scientific (Logan, UT, USA) CR1000 data loggers. Further detailed
information regarding the experimental site was described in Lie et al.,
(2021).