Perennial-like adaptation mechanisms of annual legumes to limited irrigation.

The hydrodynamic behavior of two annual legumes (Trifolium angustifolium L. and Onobrychis caput-galli (L.) Lam.) under water shortage was studied in a rain shelter experiment. Seeds were collected from natural grasslands of northern Greece and were sown in pots. Two months after seedlings' emergence, full irrigation (up to field capacity) and limited irrigation (40% of field capacity) were applied. During the vegetative period the leaf water potential and the relative water content were measured at seven day intervals in both treatments. T. angustifolium retained the lowest values of psi both under full (-0.11 to -1.78 MPa) and limited irrigation (-0.16 to -2.90 MPa), while the highest values in both cases were those of O. caput-galli (-0.05 to -0.5 MPa). The results suggested that T. angustifolium was the species mostly affected by limited water supply. T. angustifolium seemed to display adaptation mechanisms to drought similar to those of perennial plants. O. caput-galli displayed a more isohydric behavior by not altering its water potential under limited irrigation.