Time to re-define available P; hints from molecular approaches and landscape patterns in boreal forests

Reiner Giesler1
1 Climate Impacts Research Centre, Dep. of Ecology and Environmental Science, Umeå University

Invited Talk 9 in Critical unknowns in the cycling of P in forest, grassland and wetland ecosystems

15.07.2014, 12:10-12:40, H20

Phosphorus (P) is one of the major nutrients needed to sustain life and is critical for food production. In this context, exploration of how soil P is utilized by plants or microorganisms and the mechanisms behind it is becoming increasingly important. A unique property of phosphates compared to most other essential macronutrients is the unusually large reactivity toward solid particles in the environment such as aluminum (Al) and iron (Fe). In the boreal forest and tundra landscape the sorption of P, both as organic and inorganic P, plays a key role in separating P limited from N limited vegetation types; soils in the former being strongly P sorbing. Thus, surface sorption of P greatly influences biomass production in ecosystems. In this respect a key process is the transfer of P from adsorbed into bioavailable forms. Organic P forms dominate in these boreal forest ecosystems and the hydrolysis of the ester bond in almost all organic P compounds is a necessary step for biouptake of P. This might be , however, be hampered by sorption. Molecular techniques allows us today to study mechanisms at the interface that can give us valuable insights on complex interactions between surfaces, extracellular enzymes and sorbed P species. A recent study using such techniques suggest that mineral surfaces with appropriate surface properties can be very effective in concentrating substrates and enzymes thereby creating microchemical environments of high enzymatic activity. Hence, also strongly adsorbed molecules in soils and aquatic environments may be subjected to biodegradation by extracellular enzymes. In P limited but highly productive boreal forests there are very low concentrations of phosphate in the soils solution. This does, however, not seem to prevent the uptake of P into the above ground biomass. Also, experimental evidence suggests that P utilization by microorganisms is affected by P sorption. This seems to increase the C cost allocated for P mobilization for the microorganisms and may be a strategy to liberate sorbed P. The definition of P pools is generally operational i.e. defined by the methods of determination. Most of these operationally defined P forms are most likely available for biological uptake but at different time-scales. However, some P forms, such as sorbed organic P, may in fact be as available as non-sorbed P and at similar time-scales as non-sorbed P forms. There is a need for more experimental studies were molecular level techniques are used in order to get a better mechanistic insight into P utilization of different P forms by plants and microorganisms. This could potentially give us more insight to what extent and at what time-scales they can utilize different P forms. A challenge for the future is to find ways to put these types of studies into a ecologically relevant context.

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last modified 2014-06-19