The elusive measurement of nitrogen fixation in xeric shrubs: the case of Adesmia volckmanni, a Patagonian leguminous shrub

GOLLUSCIO, R.A.; IRUETA, R.; CIPRIOTTI, P.A.

JOURNAL OF ARID ENVIRONMENTS

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2014 vol. 111 p. 22 - 26

0140-1963

The comparison of 15N natural abundance (δ 154 N) between fixing and non-fixing reference species, is the most feasible method for nitrogen fixation studies in xeric shrubs. However, it assumes that both species use the same sources of soil N, the δ 15 N of such source is clearly different from zero, and the difference between the δ 15 N of both species is ≥5%o. On the other hand, the analysis of the difference between the δ15N of nodules and leaves (Δδ15 Nn-l) does not require a reference species. To evaluate the effect of water availability on nitrogen fixation, we analyzed the variation of δ15N and Δδ15 Nn-l in watered and unwatered plants of Adesmia volckmanni Phil. (Fabaceae) and Mulinum spinosum (Cav.) Pers. (Apiaceae), formerly proposed as non-fixing reference species. However, we found that M. spinosum was not valid as reference species to study N fixation in A. volckmann because its δ15 N was closer to zero than that of the presumably fixing species, suggesting they use different soil N sources. In addition, water availability did not affect biological fixation after watering because both leaf δ15N and Δδ15 Nn-l of A. volckmanni did not change either as soil dried up along the growing season nor in response to watering. However, the presence of nodules itself, the δ15 N closer to zero than in a former dry year, and the Δδ15 Nn-l (+1.23%o) suggest that biological fixation could have occurred before watering, probably during early spring.