Leticia Soledad Ithurrart

Total soil available nitrogen under perennial grasses after burning and defoliation

Total soil available nitrogen concentrations (NO–3 + NH4+) were determined underneath plants of the more-competitive Poa ligularis, mid-competitive Nassella tenuis and the less-competitive Amelichloa ambigua exposed to various combinations of controlled burning and defoliation treatments. Defoliations were at the vegetative (V), internode elongation (E) or both developmental morphology stages (V + E) during two years after burning in northeastern Patagonia, Argentina. Hypotheses were that (1) concentrations of total soil available nitrogen after burning are greater underneath burned than unburned plants. With time, these differences, however, will gradually disappear; (2) greater total soil available nitrogen concentrations are underneath plants of the more- than less-competitive perennial grasses; and (3) total soil available nitrogen is similar or lower underneath plants defoliated at the various developmental morphology stages in all three study species than on untreated controls at the end of the study. Concentration of total soil available nitrogen increased 35% (p < 0.05) on average after the first six months from burning in comparison to control plants. However, these differences disappeared (p > 0.05) towards the end of the first study year. Total soil available nitrogen concentrations were at least 10% lower underneath the less competitive N. tenuis and A. ambigua than the more competitive P. ligularis on average for all treatments, although differences were not significant (p > 0.05) most of the times. Defoliation had practically no effect on the concentration of total soil available nitrogen. Rather than any treatment effect, total soil nitrogen concentrations were determined by their temporal dynamics in the control and after the experimental fire treatments.

Plant species identity and richness influence microbial respiration of soil microorganisms on various functional groups in northeastern Patagonia, Argentina

Fil: Cardillo, Daniela Solange. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; Argentina

The TTC-technique might not appropriately test the physiological stage of plant tissues

The 2,3,5-triphenyltetrazolium chloride (TTC) technique has been used during decades to distinguish between dead and alive tissues of perennial grasses. This technique did not consider, however, that dormant (i.e., viable) tissues could exist within those erroneously considered dead tissues, thus being unable to report the true physiological stage of those plant tissues. Development of a procedure able to distinguish between metabolically active or dormant or dead tissues is then critical. This study developed a procedure to classify plant tissues of perennial grasses (Poa ligularis (Nees ex Steud.), Nassella longiglumis (Phil.) Barkworth, Amelichloa ambigua (Speg.) Arriaga & Barkworth, and Piptochaetium napostaense (Speg.) Hack.) in a more appropriate physiological stage (i.e., metabolically active, dormant or dead) than the traditional TTC-technique. Perennial grass seeds or meristematic buds were immersed in a TTC solution to obtain metabolically active (red or pink staining) or unstained (either dormant or dead) tissues. TTC-unstained tissues were placed in Evans Blue solution to separate dormant from dead tissues. The combination of TTC and Evans Blue techniques allowed the separation of metabolically active, dormant or dead tissues. Use of Evans Blue on TTC-unstained seeds and buds allowed to determine that some of these tissues were not dead but dormant (i.e., viable). Among the TTC-unstained tissues between 2 to 35% of total grass seeds and from 19.5 to 42% of all evaluated buds were dormant (viable and potentially able to growout) but not dead. Combination of TTC and Evans Blue techniques allowed a better classification of the physiological stages of plant tissues (metabolically active, dormant or dead) than the conventional TTC test.