Screening biomass production of C3 and C4 grasses in response to phosphorus fertilization and mycorrhizal inoculation

CAVAGNARO RA; GRIMOLDI AA; OYARZABAL M; OESTERHELD M

Rosario, Prov. Santa Fe, ARGENTINA

Congreso; IX International Rangeland Congress; 2011

INTA y AAMPN

Introduction: Phosphorus is an essential and one of the most limiting plant nutrients in natural and agricultural habitats worldwide (Bucher 2006). The association with arbuscular mycorrhizas usually increase host plant growth by enhancing nutrient uptake, especially of phosphorus. Development of dependence on mycorrhizae and highly branched roots systems are generally regarded as alternative evolutionary strategies for nutrient acquisition by plants (Baylis 1974; Janos 1980). The purpose of this paper is to investigate the plant growth responses of C3 and C4 forage grasses with contrasting roots systems to phosphorus fertilization and inoculation with arbuscular mycorrhizae. Materials and methods: The plant growth responses of C3 and C4 forage grasses to phosphorus fertilization and mycorrhizal fungus inoculation were assessed in a greenhouse study. Based on root morphology were selected four C3 grasses with highly branched root systems (Thinopyron ponticum, Festuca arundinacea, Dactylis glomerata and Bromus catharticus) and three C4 grasses with weakly branched root systems (Brachiaria brizantha, Panicum coloratum and Paspalum dilatatum). Seeds of each species were germinated in germination chambers. After emergence, the seedlings were individually transplanted to pots containing either sterile sand half of which were inoculated with a mixture of three species of mychorrizal fungus (Glomus sp). Plants were watered with two Hoagland modified solutions: low P (0,05nM/L) and high P (0.2nM/L) and maintained in greenhouse under controlled conditions of temperature. After three months, plants were harvested and were oven-dried for 72h at 70ºC. Fresh and dry weight of shoot and root were weighted and recorded as total biomass. Results and Discussion: In most species, the addition of phosphorus and inoculation with AMF increased plant growth, but the relative effect of AMF inoculation was higher under low than under high phosphorus availability. Under low phosphorus conditions, in terms relative effect of inoculation, C4 grasses produced 60% more biomass than C3 grasses. Conclusions: These results suggest that in C4 species (with weakly branched root systems) the mycorrhizal associations are the better strategy for phosphorus acquisition than in C3 species (with highly branched root systems). References: Baylis, G. T. S., 1974. The evolutionary significance of phycomycetous mycorrhizas. In Mechanisms of regulation of plant growth. R. Soc. N.Z. Bull. No. 12. pp. 191-193. Bucher, M., 2007. Functional biology of plant phosphate uptake at root and mycorrhiza interfaces. New Phytol. 173: 11-26. Janos, D. P., 1980. Mycorrhizae influence tropical succession. Biotropica, 12: 56-64.