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Soil phosphorus and microbial response to a long-term wildfire chronosequence in northern Sweden
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2009 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 95, no 2/3, 199-213 p.Article in journal (Refereed) Published
Abstract [en]

In the prolonged absence of major disturbances, ecosystems may enter a stage of retrogression, which is characterized by decreased ecosystem process rates both above and belowground, and often reduced availability of phosphorus (P). Disturbance through wildfire can increase soil P losses through leaching or erosion, but in the long-term absence of fire, soil P could potentially become increasingly bound in more stable forms that are less available to microbes. We studied forms of P and microbial respiration kinetics in the humus layer of a group of islands that vary considerably in wildfire frequency (40–5,300 years since last fire), and which are known to enter retrogression in the prolonged absence of fire. We found a decrease in labile P with decreasing fire frequency but no change in total P. Soil microorganisms responded more strongly to N than to P addition, and microbial biomass N:P ratios remained unchanged across the gradient. However, the concentration of labile P was the best predictor of microbial respiration responses across the islands, and this provides some evidence that declining access to P could contribute to the decline in soil microbial activity during retrogression. Our results show that even though N is arguably the main limiting nutrient during retrogression in this chronosequence, long term absence of fire also causes a decline in P availability which negatively affects microbial activity. This in turn could potentially impair microbially driven processes such as decomposition and mineralization and further contribute to the reduced availability of soil nutrients during retrogression.

Place, publisher, year, edition, pages
Springer , 2009. Vol. 95, no 2/3, 199-213 p.
Keyword [en]
Boreal forest, Microbial respiration, Phosphorus, Retrogression, Succession, Wild fire
Identifiers
URN: urn:nbn:se:umu:diva-33734DOI: 10.1007/s10533-009-9331-yOAI: oai:DiVA.org:umu-33734DiVA: diva2:317684
Available from: 2010-05-04 Created: 2010-05-04 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Phosphorus availability and microbial respiration across biomes:  from plantation forest to tundra
Open this publication in new window or tab >>Phosphorus availability and microbial respiration across biomes:  from plantation forest to tundra
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phosphorus is the main limiting nutrient for plant growth in large areas of the world and the availability of phosphorus to plants and microbes can be strongly affected by soil properties. Even though the phosphorus cycle has been studied extensively, much remains unknown about the key processes governing phosphorus availability in different environments.

In this thesis the complex dynamics of soil phosphorus and its availability were studied by relating various phosphorus fractions and soil characteristics to microbial respiration kinetics. The soils used represent a range of aluminium, iron, carbon and total phosphorus content, and were located in four different biomes: subtropical forest, warm temperate forest, boreal forest and tundra.

The results showed that NaOH extractable phosphorus, a fraction previously considered to be available to plants only over long time scales, can be accessed by microbes in days or weeks. Microbial phosphorus availability was not related to aluminium or iron content in any of the studied systems, not even in highly weathered soils with high aluminium and iron content. This is in contrast with other studies of soils with high sorption capacity and shows the variability of factors that govern phosphorus availability in different environments.

In the boreal forest chronosequence, no difference could be seen with age in total phosphorus content or concentrations of occluded phosphorus forms. However, there were lower concentrations of labile phosphorus forms in older systems, which were correlated with a decrease in microbial respiration. This was most likely related to organic matter quality in the system, and not to geochemical factors.

Phosphorus availability was linked to differences in topography (water regime) and vegetation in the tundra ecosystems. The results suggest that the availability of phosphorus, both for microbes and plants, was lower on the meadow vegetation sites compared to the two types of heath vegetation.

Many factors are important for phosphorus availability in soils, but these results suggest that microbes can access less available phosphorus if not restricted by carbon, and this may be important in regard to forest management practices as well as effects of environmental change.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. 32 + 4 papers p.
Keyword
phosphorus availability, microbial bioassay, soil respiration, microbial growth rate, Hedley fractionation, soil sorption, weathered soils, boreal forest, subarctic and tundra
Identifiers
urn:nbn:se:umu:diva-33732 (URN)978-91-7264-989-1 (ISBN)
Public defence
2010-05-27, Institutet för Rymdfysik, Aulan, Rymdcampus 1, Kiruna, 09:00 (English)
Opponent
Supervisors
Available from: 2010-05-06 Created: 2010-05-04 Last updated: 2010-05-06Bibliographically approved

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