Introducing N2-fixing tree species into Eucalyptus plantations increases organic phosphorus transformation but decreases its accumulation within aggregates in subtropical China

Abstract

Abstract 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 15 years of 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) was 19.28% greater (P < 0.05) in MP than PP. Soil organic matter (SOM), total nitrogen (TN), NO3−-N, C:P and N:P ratios were notably increased but Po content decreased significantly in bulk soil and most of the aggregates in MP than those in 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 aggregate soils 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 which might be a suitable strategy through efficient management of P in subtropical Eucalyptus plantations.