Effect of litter treatment on soil phosphorus components of Betula platyphylla forest in permafrost region of the Greater Khingan Mountains
Phosphorus is essential for plant growth and development,existing in various forms in the soil. These different forms of phosphorus vary in their mobility and biological availability. In forest ecosystems,the return of nutrients through litter is crucial for maintaining the dynamic balance of soil phosphorus. With climate warm-ing,changes in the amount of litter in forests are expected,particularly in cold region of China,where signifi-cant variations are anticipated. To investigate the effects of litter on soil phosphorus components in Betula platy-phylla forests in the permafrost region of the Greater Khingan Mountains,this study employed methods of litter addition and removal to analyze the characteristics of soil phosphorus components following alterations in litter and identify influencing factors. The aim is to provide theoretical references for researching soil phosphorus availability and influencing mechanisms in forest ecosystems in the permafrost region. This study selected Betu-la platyphylla forests of different ages (30 a,45 a,and 66 a) in the permafrost region of the Greater Khingan Mountains as the study site. In October 2021,three sample plots measuring 20 m×30 m were established in typi-cal areas of Betula platyphylla forests of different ages. Within each plot,three sample plots measuring 2 m×2 m were designated for litter removal and litter doubling treatments,alongside three control plots with no interven-tion. In August 2022,soil samples were collected from the 0～5,5～10,and 10～20 cm soil layers. The Sui's modified Hedley phosphorus classification method was used to determine the eight phosphorus components. These components were categorized into three groups based on their ease of absorption and utilization by plants:easily-available phosphorus (H2O-Pi,NaHCO3-Pi,and NaHCO3-Po),moderately-available phosphorus (NaOH-Pi and NaOH-Po),and stable phosphorus (HCl-Pi,HCl-Po,and Residual-P) to explore the effects of litter addi-tion and removal on soil phosphorus components in Betula platyphylla forests of different ages in the permafrost region. The results showed that litter doubling increases the content of H2O-Pi in different soil layers of the three Betula platyphylla forests,although the magnitude of increase diminishes as forest age increases. Additionally,it elevates the NaHCO3-Pi content,with a significant increase observed in the 10～20 cm soil layer of Betula platyphylla forests of all ages (P<0.05). However,its impact on NaHCO3-Po content is relatively small. The NaOH-Pi and NaOH-Po content in different soil layers of Betula platyphylla forests of varying ages also showed increases. Specifically,the soil NaOH-Pi content in the 30 a and 45 a Betula platyphylla forests exhibited a sig-nificant increase (P<0.05). Moreover,the NaOH-Po content in the 0～5 cm soil layer of the 45 a and 66 a Betu-la platyphylla forests showed a significant increase (P<0.05). On the other hand,litter removal reduced the H2O-Pi and NaHCO3-Pi content in different soil layers of the three Betula platyphylla forests,with a greater im-pact observed in the surface layers compared to the deeper layers. Additionally,litter removal significantly af-fected the NaHCO3-Po content only in the 5～10 cm soil layer of the 30 a Betula platyphylla forest,while its im-pact on other ages and soil layers was relatively small. Furthermore,litter removal reduced the NaOH-Pi and NaOH-Po content in different soil layers of birch forests across all three age groups,with significant reductions observed in the NaOH-Pi content of the surface layers of both the 30 a and 45 a Betula platyphylla forests (P<0.05). Moreover,litter removal significantly affected the NaOH-Po content in the 5～10 cm soil layer in all age forests. Litter treatment had a relatively minor effect on the soil stable phosphorus (HCl-Pi,HCl-Po,and Residual-P) in different soil layers of the three Betula platyphylla forests. Apart from a significant difference ob-served in the HCl-Po content of the 0～5 cm soil layer of the 45 a Betula platyphylla forest,no other significant differences were detected (P>0.05). The redundancy analysis showed that the driving factors of soil phosphorus components were different at different ages. The soil phosphorus components were mainly affected by pH and soluble organic carbon in the 30 a Betula platyphylla forest. In the 45 a Betula platyphylla forest,the main influ-encing factors are pH and NO3--N. Meanwhile,in the 66 a Betula platyphylla forest,soil moisture content and soluble organic carbon are the primary influencing factors. These findings demonstrated the litter addition and re-moval exerted a significant impact on the soil easily-available phosphorus and moderately-available phosphorus in three Betula platyphylla forests. However,their influence on stable phosphorus is relatively minor. Increased litter input promotes the activity of phosphorus in the soil of cold-temperate Betula platyphylla forests,enhanc-ing the soil phosphorus availability. Consequently,it is important to safeguard litter in the management of Betu-la platyphylla forests.
permafrost regionsecondary forestlittersoil easily-available phosphorusstand age
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