Influence of mycorrhizal associations on foliar δ15N values of legume and non-legume shrubs and trees in the fynbos of South Africa: Implications for estimating N2 fixation using the 15N natural abundance method
Tóm tắt
In this study, we examined the use of the 15N natural abundance method to quantify the percentage N derived from fixation of atmospheric N2 in honeybush (Cyclopia spp.) shrubs and trees in the fynbos, South Africa. Non-fixing shrubs and trees of similar phenology to the Cyclopia species were chosen as reference plants. These reference plants were selected to cover a range of mycorrhizal associations (ericoid mycorrhizal, arbuscular mycorrhizal and non-mycorrhizal). Isotopic analysis revealed a wide range of foliar δ15N values for the reference plants, including many very negative values. The marked differences in δ15N values were defined by the mycorrhizal status of the reference plant species, with the ericoid and arbuscular mycorrhizal plants showing lower foliar δ15N values relative to their non-mycorrhizal counterparts. In contrast, the δ15N values of the N2-fixing Cyclopia species were uniformly clustered around zero, from −0.11‰ to −1.43‰. These findings are consistent with the observation that mycorrhizal fungi discriminate against the heavier 15N isotope during transfer of N from the fungus to the host plant, leaving the latter depleted in 15N (i.e. with a more negative δ15N value). However, a major assumption of the 15N natural abundance method for estimating N2 fixation is that both legume and reference plant should have the same level of fractionation associated with N uptake. But, because mycorrhizal associations may strongly affect the level of fractionation during N uptake and transfer, the test legume should belong to the same mycorrhizal group as the chosen reference plant species. As shown in this study, if the mycorrhizal status of the legume and the reference plant differs, or cannot be assessed, then the 15N natural abundance technique cannot be used to quantitatively estimate N2 fixation.
Tài liệu tham khảo
Agricultural Research Council. Institute for Soil, Climate and Water. Private Bag X5013, Stellenbosch, 7599, South Africa.
Allsopp N and Stock W D 1993 Mycorrhizal status of plants growing in the Cape Floristic Region, South Africa. Bothalia 23 (1), 91–104.
Bajwa R, Abuarghub S M and Read D J 1985 The biology of mycorrhizae in the Ericaceae X The utilisation of protein and the production of proteolytic enzymes by the mycorrhizal endophyte and by mycorrhizal plants. New Phytol. 101, 469–486.
Bergersen F J and Turner G L 1983 An evaluation of 15N methods for estimating nitrogen fixation in a subterranean cloverperennial ryegrass sward. Aust. J. Agric. Res. 34, 391–401.
Bremner E, Gehlen H, Swerhone, G D W and van Kessel C 1993 Assessment of reference crops for the quantification of N2 fixation using natural and enriched levels of 15N abundance. SoilBiol. Biochem. 25 (9), 1197–1202.
Bolger T P, Pate J S, Unkovich M J and Turner N C 1995 Estimates of seasonal nitrogen fixation of annual subterranean clover-based pastures using the 15N natural abundance technique. Plant Soil 175, 57–66.
Chang S X and Handley L L 2000 Site history affects soil and plant 15N natural abundances (?15N) in forests of northern Vancouver Island, British Columbia. Funct. Ecol. 14, 273–280.
Danso S K A 1985 Methods for estimating biological nitrogen fixation. In Biological Nitrogen Fixation in Africa: Proceedings of the First Conference of The African Association for Biological Nitrogen Fixation. Eds. H Ssali and S O Keya. pp. 224–244. MIRCEN, Nairobi, Kenya.
Domenach A M, Kurdali F and Bardin R 1989 Estimation of symbiotic dinitrogen fixation in an alder forest by the method based on natural 15N abundance. Plant Soil 118, 51–59.
Ham G E 1977 The acetylene-ethylene assay and other measures of nitrogen fixation in field experiments In Biological Nitrogen Fixation in Farming Systems of the Tropics. Eds. A Ayanaba and P J Dart. pp. 325–334. Wiley-interscience, Chichester.
Handley L L, Azcon R, Ruiz Lozano J M and Scrimgeour C M 1999 Plant ?15N associated with arbuscular mycorrhiza, drought and nitrogen deficiency. Rapid Commun. Mass Spectrom. 13, 1320–1324.
Hobbie E A, Macko S A and Shugart H H 1999 Interpretation of nitrogen isotope signatures using the NIFTE model. Oecologia 120, 405–415.
Hobbie E A, Macko S A and Williams M 2000 Correlations between foliar ?15N and nitrogen concentrations may indicate plant–mycorrhizal interactions. Oecologia 122, 273–283.
Hogberg P 1990 15N natural abundance as a possible marker of the ectomycorrhizal habit of trees in mixed African woodlands. New Phytol. 115, 483–486.
Hogberg P and Alexander I J 1995 Roles of root symbioses in an African woodland and forest: evidence from 15N abundance and foliar analysis. J. Ecol. 83, 217–224.
Hogberg P 1997 Tansley Review No. 95: 15N natural abundance in soil–plant systems. Oecologia 137, 179–203.
Hogberg P, Hogberg M N, Quist M E, Ekblad A and Nasholm T 1999 Nitrogen isotope fractionation during nitrogen uptake by ectomycorrhizal and non-mycorrhizal Pinus sylvestris. New Phytol. 142, 569–576.
Michelsen A, Schmidt I K, Jonasson S, Quarmby C and Sleep D 1996 Leaf 15N abundance of subarctic plants provides field evidence that ericoid, ectomycorrhizal and non-and arbuscular mycorrhizal species access different sources of soil nitrogen. Oecologia 105, 53–63.
Pate J S, Stewart G R and Unkovich M 1993 15N natural abundance of plant and soil components of a Banksia woodland ecosystem in relation to nitrate utilisation, life form, mycorrhizal status and N2-fixing abilities of component species. Plant Cell Environ. 16, 365–373.
Pate J S, Unkovich M J, Armstrong E L and Sanford P 1994 Selection of reference plants for 15N natural abundance assessment of N2 fixation by crop and pasture legumes in south-west Australia. Aust. J. Agric. Res. 45, 133–147.
Peoples M B, Turner G L, Shah Z, Shah S H, Aslam M, Ali S, Maskey S L, Bhattarai S, Afandi F, Schwenke G D and Herridge D F 1997 Evaluation of the 15N natural abundance technique to measure N2 fixation in experimental plots and farmers fields. In Extending Nitrogen Fixation to Farmers Fields. Eds. O P Rupela, C Johansen and D F Herridge. pp. 57–76. ICRISAT, Patancheru, India.
Rowell D L 1997 Soil Science: Methods and applications. Longman, UK. 294 pp.
Sanginga N, Zapata F and Danso S K A 1988 Nitrogen fixation in tropical trees: Estimations based on 15N techniques. In Maximizing Biological Nitrogen Fixation for Agricultural Production and Forestry in Africa: Proceedings of the Third Conference of The African Association for Biological Nitrogen Fixation. Eds. M Gueye, K Mulongoy and Y Dommergues. pp. 337–350. Institute Senegalais de Recherches Agricoles, Dakar, Senegal.
Sanford P, Pate J S, Unkovich M J and Thomson A N 1995 Nitrogen fixation in grazed and ungrazed subterranean clover pasture in south-west Australia assessed by the 15N natural abundance technique. Aust. J. Agric. Res. 46, 1427–1443.
Schmidt S and Stewart G R 1997 Waterlogging and fire impacts on nitrogen availability and utilization in a subtropical wet heathland (wallum). Plant Cell Environ. 20, 1231–1241.
Shaver G R 1995 Plant functional diversity and resource control of primary production in Alaskan arctic tundras. In Arctic and Alpine Biodiversity. Eds. F S Chapin and C Korner. pp. 199–211. Springer, Berlin.
Shearer G and Kohl D H 1986 N2-fixation in field settings: estimations based on natural 15N abundance. Aust. J. Plant Physiol. 13, 699–756.
Stewart G R, Pate J S and Unkovich M J 1993 Characteristics of inorganic nitrogen assimilation of plants in fire-prone Mediterranean-type vegetation. Plant Cell Environ. 16, 351–363.
Stewart G R, Schmidt S, Handley L L, Turnbull M H, Erskine P D and Joly C A 1995 15N natural abundance of vascular rainforest epiphytes: implications for nitrogen source and acquisition. Plant Cell Environ. 18, 85–90.
Stock W D and Allsopp N 1992 Functional perspective of ecosystems. In The Ecology of Fynbos: Nutrients, Fire and Diversity. Ed. R Cowling. pp. 241–259. Oxford University Press, Cape Town.
Stock W D, Weinand K T and Baker A C 1995 Impacts of invading N2-fixing Acacia species on patterns of nutrient cycling in two Cape ecosystems: Evidence from soil incubation studies and 15N natural abundance values. Oecologia 101, 375–382.
Unkovich M J, Pate J S, Sanford P and Armstrong E L 1994 Potential precision of the ?15N Natural Abundance Method in Field Estimates of Nitrogen Fixation by Crop and Pasture Legumes in South-west Australia. Aust. J. Agric. Res. 45, 119–132.