Abstract:

This research investigated the variation in soil phosphorus content in alpine meadows of different degradation status， using the Hedley sequential fractionation method. Soil phosphorus fractions were measured for undegraded （UD）， lightly degraded （LD）， moderately degraded （MD）， severely degraded （SD）， and extremely degraded （ED） alpine meadow sites in Zoigê， and the environmental factors influencing soil phosphorus fractions were also explored. It was found that： 1） On the whole， the HCl extractable phosphorus （HCl-P） dominated soil phosphorus fractions in the alpine meadow， and the content of the dilute HCl extractable inorganic phosphorus （DHCl-P_i）， concentrated HCl extractable inorganic phosphorus （CHCl-P_i） and concentrated HCl extractable organic phosphorus （CHCl-P_o） together accounted for more than 50% of the total phosphorus （TP）. 2） All categories of soil phosphorus fraction showed a decline trend with increased degradation. Compared with the undegraded meadow， the H₂O extractable phosphorus （H₂O-P）， NaHCO₃ extractable inorganic phosphorus （NaHCO₃-P_i） and NaHCO₃ extractable organic phosphorus （NaHCO₃-P_o） of ED soil were decreased （P<0.05） by 92.51%， 89.57% and 85.10%， respectively， in the 0-10 cm soil horizon. Only NaHCO₃-P_o decreased significantly （by 80.32%） in the 10-20 cm horizon of ED soils. The NaOH extractable inorganic phosphorus （NaOH-P_i）， NaOH extractable organic phosphorus （NaOH-P_o）， CHCl-P_o and residual-P in the 0-20 cm soil horizon decreased with increased degradation and were lowest in ED soil， with values of 12.15， 7.09， 21.14 and 26.48 mg·kg^-1， respectively. 3） There was a significant negative correlation between the H₂O-P and soil bulk density （BD）； The NaHCO₃-P_i， NaHCO₃-P_o， NaOH-P_i， NaOH-P_o， CHCl-P_o and residual-P showed positive correlations with soil total carbon （TC） and total nitrogen （TN） but negative correlations with soil pH and BD. The CHCl-P_i exhibited no significant correlation with any of the environmental factors. Soil BD， pH， soil moisture content （SMC）， TC and TN together explained 78.79% to the variation of soil phosphorus fractions， with soil pH having the largest contribution （52.29%）. In conclusion， the various soil phosphorus fractions presented various patterns of decrease with increased soil degradation. Loss of soil organic phosphorus in degraded soils was relatively high. Those results are expected to provide scientific clues for future soil nutrient conservation initiatives and for planning of ecological restoration management of degraded alpine meadow in Zoigê.

Key words: Zoigê, degraded alpine meadow, soil, phosphorus fractions, Hedley sequential fractionation method