Nitrogen addition promotes soil organic phosphorus accumulation through increasing microbial biomass phosphorus in a temperate forest

Global nitrogen (N) deposition has been proposed to enhance phosphorus (P) limitation in various terrestrial ecosystems. The impact of N addition on soil P transformation, considering both microbial and abiotic properties, is not well understood.

In this study, the experiment with three levels of N addition (0 (N0, no fertilizer), 25 (N25) and 50 kg N ha⁻¹ yr⁻¹ (N50)) was implemented in a temperate broad-leaved forest to assess the long-term (12 years) effects of N addition on soil P fractions associated with soil properties, iron, aluminum, calcium, phospholipid fatty acids (PLFAs), and enzyme activities.

The results indicated a significant decrease in labile P, despite of a significant increase of approximately 54.0% in available P under N addition (N50). In contrast, the moderately labile P significantly increased under N addition treatment because of the increase in organic P in less labile fractions. The redundancy analysis and mantel-test found soil pH and MBP contributed to the variation of soil P fractions. The results of structural equation model confirmed that the microbial biomass P play a key role in the transformation of soil available P into moderately and occluded P fractions.

These results suggested that the long-term addition of N decreased soil labile P and increased moderate and occluded P fractions through increasing microbial P use efficiency with increased MBP, leading to the enhancement of soil P limitation in the broad-leaved temperate forest.