Natural ecosystem development chronosequences present a unique template to investigate how soil properties and processes influence phosphorus cycling and plant productivity. The Franz Josef chronosequence in New Zealand is a series of land surfaces deposited during glacial retreat over 120,000 years. During the early stages of development phosphorus is abundant and bioavailable, while nitrogen limits plant growth. Nitrogen increases due to biological fixation which facilitates forest establishment and development, while soil phosphorus declines steadily with time due to removal in drainage, which eventually leads to a decline in forest productivity (retrogression). The dynamics and bioavailability of phosphorus in soil during the initial stages of ecosystem development are mainly determined by chemical processes related to the dissolution of calcium phosphate contained in the parent material. However, the quantity and proportion of organic forms of phosphorus increase with time, and the bioavailability of phosphorus is primarily determined by biological and biochemical processes in older soils. This was confirmed by phosphorus-31 nuclear magnetic resonance spectroscopy analysis of soil from across the chronosequence, although these analyses revealed that, contrary to expectations, the relative proportion of “stable” orthophosphate monoester organic phosphorus declined with time while the proportion of “labile” orthophosphate diester organic phosphorus increased. Orthophosphate diesters include phospholipids and nucleic acids of microbial origin, and indicated an increasing role for soil biota in phosphorus dynamics with time. This was corroborated by the collation of a phosphorus mass balance for the Franz Josef chronosequence, which found that microbial biomass phosphorus as a proportion of total soil organic phosphorus increased from 5 to 20% with time, while in the oldest soil microbial biomass phosphorus was equivalent to 80% of plant biomass phosphorus. These findings highlighted the importance of the soil microbial biomass in driving phosphorus dynamics and bioavailability in natural and engineered soil-plant systems.

Role of chemistry in revealing the importance of soil microorganisms in phosphorus biogeochemistry

ACS Fall 2021

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