Effects Of Grassland Degradation On Soil Inorganic Phosphorus And Its Components

Mongolian plateau grasslands has undergone degradation due to global climate change and anthropogenic overuse.Grassland degradation often leads to changes in soil physical and chemical properties,which in turn affects soil quality and normal plant growth.Phosphorus,especially inorganic phosphorus,is an essential nutrient for plant growth and development,and it is important to analyze the changes in soil inorganic phosphorus content and reserves during grassland degradation for the restoration of degraded grasslands and grassland management.In this study,we took a typical steppe on the Mongolian plateau as an example,and classified four degraded community types:undegraded,mildly degraded,moderately degraded and severely degraded,and analyzed the soil pH,capacitance,soil carbon and nitrogen,and cation exchange in each degraded community.The effects of grassland degradation on soil phosphorus elements were determined.The main results and conclusions are as follows:1.Grassland degradation reduced aboveground biomass,resulting in a decrease in the biomass of good forage grasses and an increase in the biomass of degraded indicator species.The aboveground biomass in the typical steppe on the Mongolian plateau at peak growth in July and August ranged from about 34.21 g/m²-176.22 g/m²,and was significantly higher in undegraded（123.17 g/m²）and mildly degraded communities（121.20 g/m²）than in moderately（63.95 g/m²）and severely degraded communities（42.41 g/m²）.Degradation reduced the species richness and diversity indices,but the differences were not significant.2.Grassland degradation reduced soil pH,soil carbon and nitrogen content,increased soil bulk and carbon to nitrogen ratio,and had no significant effect on soil cation exchange.Among them,soil pH varied in the range of 6.32-9.29.The soil pH appeared weakly alkaline when the grassland was degraded to moderate.The bulk density ranged from 1.12-1.72 g/cm³;total soil carbon was 3.04-24.48 g/kg;total soil nitrogen content was 0.31-2.28 g/kg,soil carbon to nitrogen ratio was 5.10-83.91,and cation exchange was 3.23-22.33 cmol/kg.3.The soil inorganic phosphorus content varied among different communities.Leymus chinensis community>S.krylovii community>Agropyron cristatum community>S.grandis community>Artemisia frigida community>Cleistogenes squarrosa community.The grassland types with good forage grasses as the dominant species had higher soil inorganic phosphorus fractions than the community types with degraded indicator plants as the dominant species,indicating that degradation reduced the soil inorganic phosphorus fractions.4.Soil inorganic phosphorus components showed Ca₁₀-P>O-P>Ca₈-P>Fe-P>Ca₂-P>Al-P.Except for Al-P,all other inorganic phosphorus components showed the highest reserves under mild degradation,and the overall reserves of each form of inorganic phosphorus in 0-100 cm are:Ca₂-P reserves are 10.53-223.76 t/hm²,Ca₈-P reserves are 17.24-1923.19 t/hm²,Al-P reserves were 2.61-34.39 t/hm²,Fe-P reserves were 36.72-496.54 t/hm²,Ca₁₀-P reserves were 314.56-9667.34 t/hm²,and O-P reserves were 299.79-1900.35 t/hm²,indicating that moderate disturbance contributes to the maintenance of soil inorganic phosphorus.5.Grassland degradation significantly increased Al-P content,and the degree of grassland degradation and dryness as well as soil depth synergistically affected soil physicochemical properties and aboveground biomass and species richness to indirectly influence other forms of inorganic phosphorus content.