Anatomic characteristics of transverse lateral roots and adventitious buds of Populus euphratica.

Anatomic characteristics of clonal growth of root suckers of Populus euphratica was studied by means of conventional paraffin method. The results show that primary xylems of transverse lateral roots are triarch or tetrarch, with developed phelloderm in periderm, and formed by six to eight layers of parenchymatous cells. The proportion of secondary phloem, located in the secondary vascular tissue of cross-sections of transverse lateral roots, is significantly less than secondary xylem. The early generated secondary xylems are characterized by the majority of nonwoody wood fiber cell in cell wall, and vascular ray well develops. The clonal growth of root suckers of P. euphratica is due to the development and growth of adventitious buds on transverse lateral roots. Adventitious buds originate from cork cambium of transverse lateral roots, and cork cambium cells form primordia of adventitious buds by cell division. The cell division, proliferation and differentiation of adventitious primordium formed visible primordia on the surface of transverse lateral roots, and these primordia directly develop as root suckers. Primordia present temporal characteristics of synchronous and asynchronous generation, and spatial characteristics of simple-point and multi-point gathering generation. The base of adventitious primordia could generate new sub-primordia during its growth process. This is the key reason that clonal growth of root suckers caused root suckers growing in different sizes and the densely fasciculate shape. It also indicated that P. euphratica had strong ability of clonal growth of root suckers.