Background and aims

Soil organic phosphorus (Po) fractions were deemed as potentially significant reservoirs of plant-available phosphorus, profoundly influenced by the physiochemical and biological characteristics of soil. Here we clarify how soil Po fractions and transformation in topsoil aggregates after introducing N₂-fixing tree species into Eucalyptus plantation.

Methods

We measured different Po fractions and used phospholipid fatty acids (PLFAs) and four extracellular enzymes activities as bioindicators of soil microbiota and function, respectively. The research was carried out within a 15-years of monoculture Eucalyptus urophylla plantation (PP) and mixed plantation (MP) of Eucalyptus urophylla × Acacia mangium.

Results

The mean weight diameter (MWD) and geometric mean diameter (GMD were significantly greater in MP than PP. Soil organic carbon (SOC), total nitrogen (TN), NO₃⁻-N, C:P and N:P ratios were notably increased but Po content decreased significantly in bulk soil and all aggregates except Po in the <0.25 mm aggregate in MP than PP. Furthermore, the PLFA contents of total microbes, bacteria, and fungi were more abundant in bulk and aggregate soils in MP than PP. Enzyme activities related to N and P cycles showed significant improvement in bulk and most aggregates in MP than PP.

Conclusions

Our findings extend the evidence that promoting soil Po transformation may be related to the increasing of N availability, SOC, pH, fungi, and AMF colonization. Taken together, our results highlighted the soil Po fractions response to long term N₂-fixing tree species application might be a suitable strategy through efficient management of Po in subtropical Eucalyptus plantations.