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Restoration of endangered fen communities: the ambiguity of iron–phosphorus binding and phosphorus limitation
Author(s) -
Emsens W.J.,
Aggenbach C.J.S.,
Smolders A.J.P.,
Zak D.,
van Diggelen R.
Publication year - 2017
Publication title -
journal of applied ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.503
H-Index - 181
eISSN - 1365-2664
pISSN - 0021-8901
DOI - 10.1111/1365-2664.12915
Subject(s) - phosphorus , mesocosm , vegetation (pathology) , biomass (ecology) , soil water , chemistry , environmental chemistry , nutrient , agronomy , environmental science , ecology , biology , organic chemistry , medicine , pathology
SummaryLow phosphorus (P) availability limits plant biomass production in fens, which is a prerequisite for the persistence of many endangered plant species. We hypothesized that P limitation is linked to soil iron (Fe) content and soil Fe : P ratios as iron compounds provide binding sites for dissolved P, presumably reducing P availability to plants. We sampled 30 fens in a trans‐European field survey to determine how soil Fe pools relate to pools of P and Fe‐bound P, and we measured vegetation P uptake and N : P ratio to assess where P limitation occurs. Next, we determined P uptake by Carex rostrata in experimental fen mesocosms to investigate interactive effects of soil Fe and P pools (and fractions) and water levels (drained or rewetted). The field survey revealed that soil P pools correlate positively with soil Fe pools, regardless of fen degradation level, location or sampling depth. Moreover, soil Fe and P pools correlated positively with P uptake by the vegetation and negatively with vegetation N : P ratios. Generally, N : P ratios dropped below 10 g g −1 whenever thresholds of 15 mmol Fe L −1 soil and 3·3 mmol P L −1 soil were exceeded. Endangered fen species mainly thrived in Fe‐ (and thus P‐) poor fens. The mesocosm experiment further showed that interactions between water levels and P pools determined plant P uptake: although fen rewetting led to an overall increase in P uptake, plants that had grown on drained Fe‐rich soils with large acid‐extractable P pools (>1·6 mmol P acid L −1 ) could still sequester large quantities of P. Soil Fe : P ratio had no effect on P uptake. Synthesis and applications . Our findings have important implications for the management and restoration of endangered fen communities. We demonstrated the existence of an iron–phosphorus (Fe–P) binding ambiguity in fens: large Fe pools ‘trap’ mobile P, thereby enhancing overall P availability to plants rather than diminishing it. For P limitation, we suggest an empirical threshold of <3·3 mmol P L −1 soil, which is mainly found in Fe‐poor fens. Restoring fens by rewetting increases the relative availability of P and may not always result in favourable conditions for endangered fen communities. Rewetting of drained fens is most likely to be successful if soil P and Fe pools are well below 3·3 and 15 mmol L −1 respectively.