Plant P status
During the period of 2013–2019, foliar N:P at ecosystem level in the
control averaged 23.8±0.6. In each treatment, foliar N:P was negatively
correlated with foliar P concentration but was uncorrelated with foliar
N concentration (Fig. S3). In the +2.1°C treatment, foliar N:P was
significantly decreased by 4.7±1.5% without changing foliar P
concentrations throughout the experiment (P < 0.05;
Fig. 1a, b). The +2.1°C treatment significantly increased P
concentrations by 23.4±4.3% in stems, 14.4±5.0% in fine roots and
32.4±6.2% in coarse roots in 2018 (P < 0.05), but it
did not affect tissue P concentrations in 2015 (Fig. S4a). The +2.1°C
treatment significantly increased fine roots and decreased abundance of
arbuscular mycorrhizal fungi in 2015, but it had no effect on these in
2018 (Fig. S4b, c).
Plant P uptake was significantly increased in both 2015 and 2018 under
warming (33.8±7.4% in the +1.0°C treatment and 90.6±11.8% in the
+2.1°C treatment on average; Fig. 1c). During 2014–2015 and 2017–2019,
plant P resorption efficiency was significantly increased by 5.8±2.9%
in the +2.1°C treatment relative to the control (56.8±2.3% on average)
(Fig. 1d). Plant resorption was negatively correlated to foliar P
concentrations, soil NH4Cl-P concentrations, and soil
moisture (Fig. S5). Litter C:P was significantly increased by 26.0±9.7%
in the +2.1°C treatment during 2017–2019 (P < 0.01;
Table S2). Litter P stock and litter phosphatase activity were not
changed under warming during 2017–2019.