Study On Soil Phosphorus Availability Of Chinese Fir Plantations

Phosphorus(P)is a crucial nutrient element for the growth and development of plants,which the directly available P fractions is small and easily lost.Particularly in subtropical regions with high temperatures,humidity,and highly weathered soil.Chinese fir plantations are the primary fast-growing timber tree species that are extensively planted in subtropical regions of China.Understanding the contents and fraction characteristics of P is crucial for the efficient management of these plantations.We selected Chinese fir plantations located in three different latitude areas of subtropical China based on the mean annual temperature and precipitation as our research subjects.The Biologically-Based Phosphorus(BBP)method was utilized to measure the soil P availability in both the organic(0～5 cm)and mineral layer(5～30 cm).Additionally,an analysis of soil environmental factors and the phoD gene was conducted to investigate the effects factors of soil P availability in Chinese fir plantations within the different areas of subtropical China.The study results mainly include:(1)Chinese fir plantations exhibit significant differences in soil P availability content across different soil layers and areas(P<0.05).The overall variation range is 0.12 mg/kg to 159.33 mg/kg.The contents of HCl-P and Enzyme-P showed a pattern of decreasing and then increasing from high to low latitude in subtropical areas,their contents ranged from 57.9 mg/kg to 159.33 mg/kg and 0.12 mg/kg to 3.92 mg/kg,which was the highest and lowest among all soil P availability fractions respectively.In addition,CaCl2-P showed an increasing trend followed by a decrease,while Citric Acid-P decreased gradually.The contents of CaCl2-P and Citric Acid-P ranged from 0.59 mg/kg to 2.33 mg/kg and 10.09 mg/kg to 17.95 mg/kg,respectively.Soil total phosphorus,microbial biomass phosphorus,and Olsen-P exhibited an upward trend and showed a significant positive correlation with soil P availability fractions(P<0.05).(2)Spatial heterogeneity significantly affects soil environmental factors.From low to high latitude in subtropical areas,there is a gradual increase trend of soil pH,calcium,zinc,and ammonia nitrogen.Conversely,there is a gradual decrease in soil moisture content,bulk density,organic matter,nitrate nitrogen,organic carbon,and iron.Total nitrogen,microbial biomass carbon nitrogen ratio,alkaline hydrolyzed nitrogen,dissolved organic carbon nitrogen,and magnesium first decreased and then increased,while sodium and manganese first increased and then decreased;soil acid phosphatase in the soil organic layer decreased first and then increased,while the mineral layer gradually decreased;soil acetamide glucosidase gradually increased in the organic layer,and then decreased in the mineral layer;the changes of soil β-glucosidase in the organic and mineral layer are consistent with those of acid phosphatase and acetamide glucosidase,respectively.(3)In the Chinese fir plantations ecosystem of different areas,the main phylum of soil phoD gene is Proteobacteria,the main genus are Collimonas,Bradyrhizobium and Cupriavidus.The important value at the top three are Gemmatimonas,Lysobacter and Variibacter in the random forest model analysis.Additionally,the key microbial communities in middle latitude are Cupriavidus and Bradyrhizobium,high and low latitude areas are Bradyrhizobium.There was a significant difference of soil phoD gene Alpha(P<0.05)and Beta(Stress=0.08)diversity.(4)The soil environmental factors and phoD functional bacteria that affect soil P availability have convergence and heterogeneity in Chinese fir plantations ecosystems of different areas.The main influencing factors in middle latitude of subtropical areas are soil organic matter,microbial biomass nitrogen to phosphorus ratio,Cupriavidus,Xanthomonas,Collimonas,ammonia nitrogen,dissolved organic carbon,pH,bulk density,and total potassium.In high latitude of subtropical areas are organic matter,microbial biomass nitrogen phosphorus ratio,ammonia nitrogen,acid phosphatase,pH,bulk density,Pleomorphomonas,Bradyrhizobium,Variibacter and soil moisture content.In addition,in low latitude of subtropical areas are organic matter,dissolved organic carbon,pH,bulk density,Rubrobacter,Streptomyces,Mycobacterium and soil moisture content.In conclusion,the soil pH,bulk density and organic matter are the primary factors that regulate the soil P availability in Chinese fir plantations across the subtropical different latitude areas of China,which helps to understanding of the supply mechanism of soil P availability deficiency under future climate change and provides theoretical guidance for the efficient and high quality management of regional Chinese fir plantations ecosystem.