PARENT SESSION
Oral Session #5: Ecosystem processes: Decomposition and litter. Presiding: K. Lajtha.
Monday, August 6, 2001. 8:00 AM to 12:15 PM. Hall of Ideas E.

Plant-microbe competition for phosphorus in three vertical locations.

Kellogg, Laurie¹, Bridgham, Scott¹, ¹

ABSTRACT- Plants are assumed to be poor direct competitors with soil microorganisms for available phosphorus (P), although little experimental evidence supports this assumption. Our objective was to quantify resource partitioning between plants and soil microorganisms using a radioactive tracer (³²P) at three vertical levels of input (atmospheric, 5 and 15-cm soil depths). We hypothesized that (1) vegetation would intercept the majority of aerially applied P, whereas (2) microorganisms would intercept the majority of P injected into the soil profile (simulating soil mineralization inputs). In nine peatlands in the Upper Peninsula of Michigan, we applied 3.7 x 104 Bq per 30-cm diameter plot in the three application treatments. We then examined ³²P and ³¹P concentrations in above- and belowground vegetation and soil microbial biomass at 0-10 and 10-20 cm at different time points in the growing season. In the aerially applied treatment, vegetation intercepted significantly more than the soil microorganisms. The plants were found to take up as much as 80% of the ³²P in some cases. For the 5-cm injection treatment, microbial biomass in the 0-10 cm depth recovered the most P. In the 15-cm injection treatment, the recovery was similar among the three groups (plant, microbial biomass at 0-10 cm and at 10-20 cm). This study demonstrates vertically segregated competition for P between plants and microbes and that plants are efficient competitors for P even in the soil profile.

KEY WORDS: microorganisms, plant, competition, phosphorus