Using Microdialysis to Assess Soil Diffusive P and Translocated Sap Flow P Concentrations in Southern Pinus taeda Plantations

Abstract Aims: To improve soil phosphorus (P) testing in silvicultural systems, we aim to assess microdialysis to study concentrations of soil diffusive P and in-vivo translocated sap flow P under variable rates of P carryover from a previous rotation. Methods: The experiment was a randomized block design, blocked by site, with four treatments and two replications per treatment per block. Soils were collected from each treatment in the field and analyzed in laboratory conditions. Soils were analyzed for diffusive soil P using microdialysis and Mehlich III for comparison. Sap flow P measurements were collected in the field from 16 trees, one tree per treatment and replication over four hours. Results: Spodosol soils had higher diffusive P levels than Alfisol soils. On average, diffusive P increased by 137% in Spodosol and 166% in Alfisol from pre to post-harvest. In the Alfisol, diffusive P showed a strong relationship with tree height, while no significant association was observed in the Spodosol. The Mehlich III soil extraction method did not correlate strongly with diffusive P for either site. Microdialysis samples collected from the trees responded to changes in fertilization rates. Atmospheric conditions substantially impacted sap flow P, with samples collected in full sunlight showing an average increase of 100% compared to overcast conditions. Conclusions: These findings demonstrate the potential of microdialysis as a valuable tool for soil P testing and its application in addressing complex questions related to P translocation and tree physiology in silvicultural settings.