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Vegetation loss alters soil nitrogen dynamics in an Arctic salt marsh
Author(s) -
BUCKERIDGE KATE M.,
JEFFERIES ROBERT L.
Publication year - 2007
Publication title -
journal of ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.452
H-Index - 181
eISSN - 1365-2745
pISSN - 0022-0477
DOI - 10.1111/j.1365-2745.2007.01214.x
Subject(s) - soil water , abiotic component , environmental science , agronomy , soil carbon , nitrogen cycle , ecosystem , ecology , salt marsh , biology , chemistry , soil science , nitrogen , organic chemistry
Summary1 Plant and microbial nitrogen (N) dynamics were examined in soils of an Arctic salt marsh beneath goose‐grazed swards and in degraded soils. The degraded soils are the outcome of intensive destructive foraging by geese, which results in vegetation loss and near‐irreversible changes in soil properties. The objective of the study was to determine whether vegetation loss led to a decline in microbial activity and a redistribution of N amongst the different soil N pools that potentially could adversely affect plant regrowth. 2 In situ N allocation between plants, microbes and soil was determined based on injection of 15 NH 4 Cl into soil cores; changes in isotopic ratios and N concentrations in the different pools were measured after 24 h. Degraded soils, in contrast to vegetated soils, were characterized by a decline in microbial biomass, reduced microbial 15 N excess, reduced rates of gross N immobilization and an increased microbial residency time of 15 N. In vegetated soils, both microbes and the forage grass, Puccinellia phryganodes , accumulated 15 N such that little remained in the soil abiotic phase after 24 h, unlike in degraded soils. 3 The decline in microbial activity in degraded soils may be linked to a low availability of soil carbon in the absence of plants and to deteriorating abiotic conditions, including the occurrence of hypersalinity in summer. 4 Not all biotic processes respond similarly to the change in ecosystem state. Unlike vascular plant productivity and goose foraging which are absent in degraded soils, soil microbial activity is maintained, albeit at a lower level. In spite of this activity, the greater proportion of 15 N in degraded soils is in the abiotic pool rather than in microbial biomass with an increased potential for soil N loss from leaching and soil erosion. 5 Disturbance linked to herbivory often triggers catastrophic shifts in ecosystem properties resulting in vegetation loss and changes in soil biogeochemical cycling that are irreversible, at least on a decadal time scale, and lead to the loss of N and other nutrients required for plant growth. These results clearly illustrate that microbial activity does not compensate for the effects of plant removal on soil N retention.