Warming effects on plant biomass allocation and correlations with the soil environment in an alpine meadow, China

Alpine meadow ecosystem is fragile and highly sensitive to climate change. An understanding of the allocation of above- and below-ground plant biomass and correlations with environmental factors in alpine meadow ecosystem can result in better protection and effective utilization of alpine meadow vegetation. We chose an alpine meadow in the Qinghai-Tibetan Plateau of China as the study area and designed experimental warming plots using a randomized block experimental design. We used single-tube infrared radiators as warming devices, established the warming treatments, and measured plant above- (AGB) and below-ground biomass (BGB) during the growing seasons (May to September) in 2012 and 2013. We determined the allocation of biomass and the relationship between biomass and soil environment under the warming treatment. Biomass indices including above-ground biomass, below-ground biomass and the ratio of root to shoot (R/S), and soil factors including soil moisture and soil temperature at different depths were measured. The results showed that (1) BGB of the alpine meadow had the most significant allometric correlation with its AGB (y=298.7x ⁰.⁴⁴, P<0.001), but the relationship decreased under warming treatment and the determination coefficient of the functional equation was 0.102 which was less than that of 0.188 of the unwarming treatment (control); (2) BGB increased, especially in the deeper soil layers under warming treatment (P>0.05). At 0–10 cm soil depth, the percentages of BGB under warming treatment were smaller than those of the control treatment with the decreases being 8.52% and 8.23% in 2012 and 2013, respectively. However, the BGB increased 2.13% and 2.06% in 2012 and 2013, respectively, at 10–50 cm soil depths; (3) BGB had significant positive correlations with soil moisture at 100 cm depth and with soil temperature at 20–100 cm depths (P<0.05), but the mean correlation coefficient of soil temperature was 0.354, greater than the 0.245 of soil moisture. R/S ratio had a significant negative correlation with soil temperature at 20 cm depth (P<0.05). The warmer soil temperatures in shallow layers increased the biomass allocation to above-ground plant parts, which leading to the increase in AGB; whereas the enhanced thawing of frozen soil in deep layers causing by warming treatment produced more moisture that affected plant biomass allocation.