Microbial phosphorus cycling in acquiring and recycling ecosystems (Micro P Cycling)

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Phosphorus (P) is cycled on various scales of all magnitudes: ecosystem level, community level, organism level. Here, we seek to distinguish between microbial P cycling modes at the community and organism levels. We assume that maintenance processes sustain organism level cycling. In contrast, community level P cycling is characterized by i) microbial death and P release, following by ii) microbial growth and P uptake. Thus, we face the fundamental challenge of disentangling the two modes of microbial nutrient cycling in systems under steady state. We hypothesize that 1) P cycling in Death/Growth mode is much faster compared to that in Maintenance mode, and 2) Microbial P cycling in high P soil (acquiring ecosystems) is more intensive and dominated by Death/Growth mode compared to low P soil (recycling ecosystems) dominated by Maintenance mode, as P limitations require more efficient internal resource use. We also hypothesize that 3) high C and N availability stimulate microbial P cycling mainly in Death/Growth mode, which is 4) faster in bacteria compared to fungi.The organism level and community level P cycling will be disentangled by five independent approaches: 1) 33P, 14C and 13C incorporation into phospholipids (analyzed and collected by Prep-UHPLC), 2) 33P and 14C incorporation into DNA, 3) ATP content and Adenylate Energy Charge, 4) effect of P fertilization on CO2 release and 5) on heat release (calorimetry) from soil. For the 33P/14C/13C incorporation into phospholipids of individual microbial groups, and consequently identification of microbial key players, a new preparative approach will be further developed and standardized. The main hypotheses on microbial P cycling will be tested by all five approaches in microcosms and field experiments in soils with contrasting total P levels (Luess vs. Bad Brückenau) and P speciation (Mittelfels vs. Achenpass). Dynamics of 33P and 14C incorporation into and release from microbial groups, distinguished by phospholipids, will allow assessment of microbial P cycling under Maintenance and Death/Growth modes in recycling and acquiring ecosystems.Microbial P cycling under the effects of available C, released in beech rhizosphere by roots grown in soil with homogenous vs. heterogeneous P distribution, will be tested in collaborative microcosm and field experiments. In addition the effects of P and N addition on microbial P cycling will be analyzed in a factorial N × P application field experiment. These studies, based on the five approaches outlined above, will provide novel methods of disentangling P and nutrient cycling between community and organism levels to determine the proportional contribution of Maintenance vs. Death/Growth microbial cycling modes in acquiring and recycling ecosystems.