Eleven-year nitrogen addition exacerbates phosphorus limitation by reducing plant roots and soil microbial biomass in a temperate forest

Abstract

Plant roots and microorganisms are integral to the phosphorus (P) transformation process in forest soils. However, the specific mechanisms by which they affect soil P availability under long-term nitrogen (N) addition remain elusive. Therefore, a long-term N addition experiment was conducted in a temperate forest in China. After 11-year N addition, measurements focused on P fractions, soil microbial biomass (SMB), microbial community (PLFAs), phosphatase activity, fine root biomass (FRB), and fine root biomass P (FRBP). The results demonstrated that N addition significantly decreased Resin-P and total extractable organic P (Po), while having no significant effect on total extractable inorganic P (Pi). Moreover, a strong positive correlation was observed between Resin-P and total extractable Po, suggesting that under N addition, organic P serves as the primary source of soluble P. This implies that continuous N deposition may exhaust the potential P source stored as organic P in forest soils. N addition also led to a reduction in SMB and FRB. Notably, microbial biomass P and FRBP were positively correlated with Resin-P and total extractable Po, indicating that the decrease in SMB and FRB is the main contributor to the decline in soluble P and organic P. Additionally, N addition significantly reduced phosphatase activity, suggesting an inhibition of the organic P hydrolysis process. In conclusion, N addition decreases P input into the soil by reducing SMB and FRB, and inhibits the transformation of different P forms by lowering enzyme activity. Consequently, soil organic P and soluble P decline, further intensifying P limitation.

Graphical abstract

Keywords

nitrogen addition / soil P availability / phosphatase activity / plant roots / soil microbes

Highlight

	● Eleven years of N addition decreased soil soluble P and organic P, consequently reducing P availability.
	● Eleven years of N addition reduced soil microbial biomass and fine root biomass.
	● Reductions in microbial biomass and fine root biomass mainly drove the declines in soluble P and organic P.

References

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