Affiliation |
Consejo Nacl Invest Cient & Tecn, Museo Argentina Ciencias Nat Bernardino Rivadavia, MACN, CONICET, Av Angel Gallardo 470, Ciudad Buenos Aires, Buenos Aires, DF, ARGENTINA |
Abstracts |
The impact of deficit and excess of soil water on plant growth, morphological
plant features, N and P plant nutrition, soil properties, Rhizobium nodulation and the symbiosis
between arbuscular mycorrhizal (AM) fungi and Lotus tenuis Waldst. & Kit. Were studied in a
saline-sodic soil. Water excess treatment decreased root growth by 36% and increased shoot growth
by 13% whereas water deficit treatment decreased both root and shoot growth (26 and 32%,
respectively). Differences between stress conditions on shoot growth were due to the ability of
L. Tenuis to tolerate low oxygen concentration in the soil and the sufficiency of nutrients in
soil to sustain shoot growth demands. Water excess treatment decreased pH, and increased
available P and labile C in soil. Water deficit treatment decreased available P and also
increased labile C. In general, N and P acquisition were affected more by water excess than water
deficit. The number of nodules per gram of fresh roots only increased in water excess roots
(97%). Under both stress conditions there was a significant proportion of roots colonized by AM
fungi. Compared to control treatment, arbuscule formation decreased by 55 and 14% under water
excess and water deficit, respectively. Vesicle formation increased 256% in water excess
treatment and did not change under water deficit treatment. L. Tenuis plants subjected to water
deficit or excess treatments could grow, nodulated and maintained a symbiotic association with AM
fungi by different strategies. Under water excess, L. Tenuis plants decreased root growth and
increased shoot growth to facilitate water elimination by transpiration. Under water deficit, L.
Tenuis plants decreased root growth but also shoot growth which in turn significant decreased the
shoot/root ratio. In the present study, under water excess conditions AM fungi reduced nutrient
transfer structures (arbuscules), the number of entry points and spore, and hyphal densities in
soil, but increased resistance structures (vesicles). At water deficit, however, AM fungi reduced
external hyphae and arbuscules to some extent, investing more in maintaining a similar proportion
of vesicles in roots and spores in soil compared to control treatment. |