The response of mesophyll conductance to short- and long-term environmental conditions in chickpea genotypes

Abstract. Mesophyll conductance (g(m)) has been shown to vary between genotypes of a number of species and with growth environments, including nitrogen availability, but understanding of g(m) variability in legumes is limited. We might expect g(m) in legumes to respond differently to limited nitrogen availability, due to their ability to fix atmospheric N(2). Using online stable carbon isotope discrimination method, we quantified genetic variability in g(m) under ideal conditions, investigated g(m) response to N source (N(2)-fixation or inorganic N) and determined the effects of N source and water availability on the rapid response of g(m) to photosynthetic photon flux density (PPFD) and radiation wavelength in three genotypes of chickpea (Cicer arietinum). Genotypes varied 2-fold in g(m) under non-limiting environments. N-fed plants had higher g(m) than N(2)-fixing plants in one genotype, while g(m) in the other two genotypes was unaffected. g(m) response to PPFD was altered by N source in one of three genotypes, in which the g(m) response to PPFD was statistically significant in N-fed plants but not in N(2)-fixing plants. There was no clear effect of moderate water stress on the g(m) response to PPFD and radiation wavelength. Genotypes of a single legume species differ in the sensitivity of g(m) to both long- and short-term environmental conditions, precluding utility in crop breeding programmes.