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

GOLLUSCIO R.A; IRUETA R.

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 (d 15N) betweenfixing and non-fixing reference species, is the most feasible method for nitrogenfixation studies in xeric shrubs. However, it assumes that both species use the same sources of soil N, thed 15N of such source is clearly different from zero, and the difference between the 15N of both species is5?. On the other hand, the analysis of the difference between the d 15N of nodules and leaves (Dd 15Nnl) does not require a reference species. To evaluate the effect of wáter availability on nitrogenfixation, we analyzed the variation ofd 15N andDd 15Nnl in watered and unwatered plants of Adesmia volckmanniPhil. (Fabaceae) andMulinum spinosum(Cav.) Pers. (Apiaceae), formerly proposed as non-fixing reference species. However, we found thatM. spinosumwas not valid as reference species to study Nfixation inAdesmia volckmannbecause itsd 15N was closer to zero than that of the presumablyfixing species, suggesting they use different soil N sources. In addition, water availability did not affect biological fixation after watering because both leaf d15N and Dd15Nn  of A. volckmannidid not change either as soil dried up along the growing season nor in response to watering. However, the presence of nodules itself, thed 15N closer to zero than in a former dry year, and the Dd15Nnl (þ1.23?) suggest that biologicalfixation could have occurred before watering, probably during early spring.