Impacts of Climate Warming on Soil Phosphorus Forms and Transformation in a Tibetan Alpine Meadow

The alpine meadow ecosystem in Tibetan Plateau is highly sensitive and vulnerable to climate change. The impact of climate warming on soil phosphorus (P) forms and transformation remains poorly understood. Here, a 5-year field experiment investigated the influences of warming on soil inorganic P (Pi) and organic P (Po) forms in an alpine meadow of the Tibetan Plateau. The field experiment included three treatments: unwarmed control (CK), winter warming (WW), and year-round warming (YW). Open top chambers were used to impose warming and increased average soil temperature at 5 cm depth by 1.3 °C compared with CK. Chemical fractionation and solution 31P nuclear magnetic resonance (NMR) spectroscopy were used to speciate P forms. Compared with CK, total P concentration decreased by 11.7% (P < 0.05) and 2.46% (P > 0.05) while available P concentration increased by 19.1% and 12.7% (P < 0.05) in WW and YW, respectively. Chemical fractionation showed that water (H2O)- and bicarbonate (NaHCO3)-extractable Pi concentrations were higher, while sodium hydroxide (NaOH)- and hydrochloric acid (HCl)-extractable Pi and H2O-, NaHCO3-, NaOH-, and HCl-extractable Po concentrations were lower in WW and YW than in CK. 31P NMR indicated that orthophosphate concentration was 12.4% and 5.54% (P > 0.05) higher, while pyrophosphate, orthophosphate monoesters, and orthophosphate diester concentrations were lower in WW and YW than in CK. Acid phosphomonoesterase was a significant factor in shaping soil P forms and transformation. Short-term warming can mitigate P limitation by promoting the transformation of moderately labile and stable Pi fractions and various forms of Po to bioavailable P. This study provides novel insights into understanding terrestrial ecosystem P cycling in response to future climate change.