Plant and soil sampling and climate monitoring
In early August 2020, we harvested all the plant aboveground parts at
ground level and sorted them to species at the plot level. We then dried
plants at 65 ℃ for 48 hours to constant mass and weighed them to 0.01 g;
we then summed the dry biomass of each species from each plot to
quantify aboveground biomass (hereafter ‘AGB ’, see Table 1 for
abbreviations). We also collected four soil cores (5 cm in diameter and
10 cm in depth) in the four corners of each plot and pooled them to form
one sample per plot. We flushed all fine roots collected from each
sample with water and then dried them to measure plant belowground
biomass (BGB ). We measured soil moisture content (W; %)
gravimetrically after 5 h of desiccation at 120 ℃ and used a pH analyzer
and a conductivity analyzer to measure the soil pH (pH) and soil
conductivity (C; ms/s), respectively. We extracted 5 g of fresh soil
with 50 ml 0.2 M KCl for 1 h at 60 rev s-1 using a
shaker, then measured
nitrate-nitrogen
(NO3-; mg/kg) and ammonium-nitrogen
(NH4+; mg/kg) using an auto-analyzer
(AA3, Bran-Luebbe, Germany).
We placed a Temperature-Humidity
Recorder Cos-03-0 (Renke Control Technology Co., Ltd., Jinan, Shandong,
China) at each elevation, which continuously monitored ambient
temperature and humidity every 60 seconds for 72 hours in early August
2020. We then calculated the mean daily temperature (MDT ) and
mean daily humidity (MDH ) for each elevation. Given the
relatively short-term temperature and humidity may not represent the
environmental conditions that were present during pathogens development,
we only test the associations between elevation with MDT andMDH (thereby confirming whether the elevational gradient can
serve as a temperature and humidity gradient), but we did not included
these measurements in other analyses.