Mineralisation of carbon and plant uptake of phosphorus from microbially-derived organic matter in response to 19 years simulated nitrogen deposition
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Here we test the hypotheses that 19 years of simulated pollutant N deposition increases both losses of carbon (C) and the ability of plants to access P from organic material in upland heathland. The grass, Dactylis glomerata, and the dwarf shrub, Calluna vulgaris, were grown in soil containing microbial-derived organic matter labelled with 14C and 33P. We found that both soil and root-surface phosphatase activity increased significantly in response to N deposition. We also found a significant positive relationship between root-surface phosphatase activity and 33P uptake for Calluna, but a negative relationship for Dactylis. Efflux of 14C from the microbial-derived organic matter was strongly dependent on an interaction among plant presence, plant species and N deposition. Our results show that mineralisation of C and P, and subsequent plant uptake of P from organic sources is decoupled. In our experimental conditions, stimulation of P turnover coupled with subsequent plant uptake through up-regulation of root phosphatases is little affected by N addition. However, our data indicate that root-surface phosphatases are likely to be more important for uptake of P derived from organic sources for Calluna than for Dactylis.
KeywordsPhosphatase Nitrogen deposition Heathland Carbon mineralisation Organic phosphorus 33P 14C
This work was supported by the Natural Environment Research Council. We thank Dr. S. J. M. Caporn for allowing us to sample from his experimental site, Dr C. J. Trinder for supplying Dactylis plants, J. Brodie for technical support, and two anonymous referees for their comments.
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