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Plant responses to nutrient addition and predictive ability of vegetation N:P ratio in an austral fen
Author(s) -
Burge Olivia Rata,
Clarkson Beverley R.,
Bodmin Kerry A.,
Bartlam Scott,
Robertson Hugh A.,
Sukias James P. S.,
Tanner Chris C.
Publication year - 2020
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.13452
Subject(s) - vegetation (pathology) , wetland , environmental science , biomass (ecology) , plant community , nutrient , agronomy , dominance (genetics) , ecology , biology , species richness , medicine , biochemistry , pathology , gene
Previous studies of the N:P ratio in wetland plants have been carried out in northern hemisphere wetlands where atmospheric nitrogen deposition is higher. There is little research on foliar N:P ratio as a potential indicator of nutrient limitation in vegetation communities in southern hemisphere wetlands. This study aimed to redress this knowledge gap and answer the following questions: how well does the plant tissue nitrogen to phosphorus (N:P) ratio predict wetland plant community nutrient limitation, as indicated by vegetation standing stocks and below‐ground biomass, in southern hemisphere fens? Secondly, what are the impacts of realistic upper levels of farm nutrient run‐off on natural montane fen vegetation? Low (35 kg ha −1 year −1 ) and high (70 kg ha −1 year −1 ) levels of nitrate‐N or ammonium‐N with and without P (20 kg ha −1 year −1 ) were added to 81 vegetation plots over a period of 2.75 years. Species composition, plant nutrient status, and above‐ground live vegetation standing stocks were assessed after 3 years, and below‐ground biomass after 2 years. Plant tissue analysis suggested the community was N limited or N and P co‐limited; we found greater standing stocks of vegetation in plots treated with 70 kg ha −1 year −1 ammonium‐N, indicating N limitation. No difference between other treatments was found in above‐ground standing stocks or below‐ground biomass. Plant species cover increased in both high N treatments, consistent with N limitation. These changes in plant species cover were accompanied by significant decreases in species richness in both high N treatments. Native species dominated the vegetation and this was unaffected by nutrient addition (90% cover). This is one of the first studies to test and find support for the N:P ratio in southern hemisphere wetlands. Observed declines in species richness after N fertilisation in an N‐limited fen suggests increased N may pose risks to austral wetlands. Responses by plant communities (changes in composition, biomass) to lower levels of nutrient addition may require longer periods of fertilisation to be apparent in slow growing ecosystems.