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- Title
Influence of growth stage and seed nitrogen on B values and potential contributions to error in estimating biological N<sub>2</sub> fixation using the <sup>15</sup>N natural abundance method.
- Authors
Rose, Terry J.; Kearney, Lee J.; Erler, Dirk V.; Rose, Michael T.; Van Zwieten, Lukas; Raymond, Carolyn A.
- Abstract
Aims: The 15N natural abundance technique is increasingly being used to biological nitrogen (N2) fixation by legume crops, but requires the determination of a ‘B value’ which describes the isotopic fractionation for a given plant species and strain of rhizobium. Most B values in the literature are derived for shoot tissue harvested at mid pod filling, when plant N content is generally at its maximum. However, if legumes are grown as green manure inter-crops and growth is terminated at earlier stages, to obtain accurate values for total N2 fixed growth-stage specific B values and correction for seed N contributions may be necessary. This study aimed to evaluate the magnitude of the impact of different values of the N content and 15N abundance of seeds and of B values on the estimates of the proportion of legume N derived from N2 fixation.Methods: We investigated whether B values at pod filling differ from those at earlier growth stages by growing chickpea (<italic>Cicer arietinum</italic>), white lupin (<italic>Lupinus albus</italic>), field pea (<italic>Pisum sativum</italic>) and two faba bean (<italic>Vicia faba</italic>) cultivars, in sand-culture in a glasshouse without N, and quantifying the δ15N values of nodules, roots and shoots at five growth stages including mid pod filling as a control. We then used simulations to investigate the degree of error associated with the use of growth stage-inappropriate or B values uncorrected for seed N on estimates of % N derived from atmosphere (%Ndfa).Results: While the differences in B values between flowering and pod filling were only statistically significant at <italic>P</italic> < 0.1 for white lupin, there was a trend of declining B value with plant age for chickpea and faba beans. Simulations using data from large (Aguadulce) and small (Fiesta)-seeded faba bean cultivars indicated that the magnitude of potential errors in estimating %Ndfa using B values derived at inappropriate growth stages or uncorrected for seed N content were around 10% at early flowering in both faba bean cultivars and were negligible by late flowering (69 days after sowing).Conclusions: Where legumes are grown until flowering or beyond, the magnitude of potential error in estimation of %Ndfa from the use of B values derived at inappropriate growth stages or uncorrected for seed N content is relatively low compared to other sources of error encountered when employing the 15N natural abundance technique.
- Subjects
NITROGEN fixation measurement; RHIZOBIUM; LEGUMES; NITROGEN content of plants; CHICKPEA; LUPINUS albus; FAVA bean; PLANT growth
- Publication
Plant & Soil, 2018, Vol 425, Issue 1/2, p389
- ISSN
0032-079X
- Publication type
Article
- DOI
10.1007/s11104-018-3600-2