Effects of drought in biomass production and allocation in three varieties of Trichloris crinita P. (Poaceae) a forage grass from the arid Monte region of Argentina

Trichloris crinita, a perennial forage grass native to the west arid Monte region of Argentina, has shown great variability in forage production among populations originated in different environments. In a previous study under irrigated conditions we concluded that higher productivity of some varieties was associated with larger total plant biomass and higher dry matter partitioning to aboveground organs. The goal of the present study was to investigate the ecophysiological basis of differential productivity in three varieties of T. crinita under water stress conditions. Varieties PICHI, ARROYITO and ENCON of high, medium and low productivity were evaluated under high and low water availability. Two cycles of water stress, maintained until leaves folded, were applied to each variety. Leaf folding occurred at different leaf water potential (Psi(L)) for each variety. At the end of the first stress cycle Psi(L) were: PICHI -4.27 MPa, ARROYITO -3.26 MPa and ENCON -1.82 MPa. Each variety finished the stress cycle at a different time. Shoot/root ratio and DM partitioning to different organs were not modified by the water stress treatment for the three varieties thus, the relative differences among them were maintained. Shoot/root ratio of PICHI (3.2) was more than double of the least productive variety (ENCON). The higher productivity of PICHI is associated to a larger shoot/root ratio, faster production of leaf area and higher leaf, sheath, culm and panicle DM production. Root DM was not different among varieties. ENCON, coming from an area with lower rainfall and higher temperature, was the last to fold their leaves and had a higher leaf water potential at the end of the drought cycle, probably linked to its smaller leaf area and relatively larger root system.