(Further) links from rocks to plants

In their recent TREE review, Russ Landeweert et al.1xLinking plants to rocks: ectomycorrhizal fungi mobilize nutrients from minerals. Landeweert, R. et al. Trends Ecol. Evol. 2001; 16: 248–254Abstract | Full Text | Full Text PDF | PubMed | Scopus (295)See all References1 describe how ectomycorrhizal fungi enclose and penetrate mineral grains and mobilize nutrients from alkali feldspar minerals by producing organic acid. This allows plants with mycorrhizal fungi to access nutrients that are inaccessible to roots 1xLinking plants to rocks: ectomycorrhizal fungi mobilize nutrients from minerals. Landeweert, R. et al. Trends Ecol. Evol. 2001; 16: 248–254Abstract | Full Text | Full Text PDF | PubMed | Scopus (295)See all References1. By such means, important macronutrients might be made available from mineral sources, for example phosphate from the mineral apatite, and potassium (K) from biotite.Landeweert et al. identify nitrogen (N) as the most important limiting nutrient in boreal forests, and the only major nutrient that cannot be derived from mineral sources. This is in line with the widely held view, perpetuated in ecology textbooks 2xBegon, M. et al. CrossrefSee all References2, that the atmospheric phase is of over-riding importance in N cycles. However, there is increasing evidence for significant amounts of N in rocks, and the same fungal processes reported by Landeweert et al. might also make rock-based N accessible to plants. Diagenesis of N into rocks can occur when organic matter comes into contact with clays in an anoxic environment. The resulting N compounds can substitute for alkali ions in silicates, such as feldspars, micas and zeolites. Ramseyer et al.3xAuthigenic K–NH4–feldspar in sandstones: a fingerprint of the diagenesis of organic matter. Ramseyer, K. et al. J. Sediment. Petrol. 1993; 63: 1092–1099See all References3 found significant amounts of K–NH4–feldspars in Miocene shales, and large amounts of N have been found in granites 3xAuthigenic K–NH4–feldspar in sandstones: a fingerprint of the diagenesis of organic matter. Ramseyer, K. et al. J. Sediment. Petrol. 1993; 63: 1092–1099See all References3, sandstones 4xThe abundance of ammonium in the granites of central Spain, and the behaviour of the ammonium ion during anatexis and fractional crystallization. Hall, A. et al. Mineral. Petrol. 1996; 56: 105–123CrossrefSee all References, 5xGeologic nitrogen: a potential geochemical hazard in the San Joaquin Valley, California. Strathouse, S.M. et al. J. Environ. Qual. 1980; 9: 54–60CrossrefSee all References, 6xDiagenesis of ammonium during hydrocarbon maturation and migration, Wilcox Group, Louisiana, USA. Williams, L.B. et al. Appl. Geochem. 1992; 7: 123–134Crossref | Scopus (53)See all References, mudstones 5xGeologic nitrogen: a potential geochemical hazard in the San Joaquin Valley, California. Strathouse, S.M. et al. J. Environ. Qual. 1980; 9: 54–60CrossrefSee all References, 6xDiagenesis of ammonium during hydrocarbon maturation and migration, Wilcox Group, Louisiana, USA. Williams, L.B. et al. Appl. Geochem. 1992; 7: 123–134Crossref | Scopus (53)See all References, slates and schists 7xContribution of bedrock nitrogen to high nitrate concentrations in stream water. Holloway, J.M. et al. Nature. 1998; 22: 785–788See all References7. Holloway et al.8xNitrogen release from rock and soil under simulated field conditions. Holloway, J.M. et al. Chem. Geol. 2001; 174: 403–414Crossref | Scopus (26)See all References8 showed that artificial weathering of rocks that contain N yielded both ammonium and nitrate. Biological weathering by ectomycorrhizal fungi could increase the accessibility of this N source.Recent research in New Zealand has shown high concentrations of ammonium (228–1348 μg l−1) in groundwater in locations where the schist bedrock is rich in N (121–809 mg N kg−1 rock: R.M. Thompson, PhD thesis, University of Otago, 2001). Not only is this groundwater source a potential N subsidy for terrestrial plants, but it can also be converted to nitrate by ecosystem processes in streams and other aquatic systems 9xNitrogen transformations in a small mountain stream. Richey, J.S. et al. Hydrobiologia. 1985; 124: 129–139Crossref | Scopus (43)See all References, 10xRegulation of nitrification in aquatic sediments by organic carbon. Strauss, E.A. and Lamberti, G.A. Limnol. Oceanogr. 2000; 45: 1854–1859CrossrefSee all References. Thus, in streams in locations in New Zealand where groundwater ammonium is high, nitrate concentrations are also unusually elevated (400–3000 μg l−1), fuelling algal productivity. Several studies have implicated bedrock N in high concentrations of nitrate in streams 5xGeologic nitrogen: a potential geochemical hazard in the San Joaquin Valley, California. Strathouse, S.M. et al. J. Environ. Qual. 1980; 9: 54–60CrossrefSee all References, 7xContribution of bedrock nitrogen to high nitrate concentrations in stream water. Holloway, J.M. et al. Nature. 1998; 22: 785–788See all References (R.M. Thompson, PhD thesis, University of Otago, 2001). Holloway et al.7xContribution of bedrock nitrogen to high nitrate concentrations in stream water. Holloway, J.M. et al. Nature. 1998; 22: 785–788See all References7 estimate that up to 20% of the global N inventory might be included in bedrock. Landeweert et al. provide a novel mechanism for the utilization of this resource by terrestrial plants with ectomycorrhizal fungi, but geological N might also be a significant resource in aquatic ecosystems.