Burial of canopy-stored seeds in the annual psammophyte Agriophyllum squarrosum Moq. (Chenopodiaceae) and its ecological significance

Agriophyllum squarrosum Moq. is a dominant annual on sand dunes in the arid regions of central Asia. A high percentage of seeds is retained on dead plants which become covered by moving sand, but little is known about the ecological significance of burial of canopy-stored seeds. We investigated the size and dynamics of the buried canopy-stored seed bank and effects of burial on seed germination. In March (during the windy season), May (beginning of the germination season), and July (middle of the growing season), the number of seeds per square meter in sample plots in the dunes was 623, 223 and 22, respectively, with 54.6, 30.6 and 12.9% of the total seeds retained on buried plant canopies. In a controlled experiment, more seedlings emerged from released (dispersed) than from canopy-stored seeds when burial depth was the same. No viable ungerminated released seeds were found, but 45-80% of the ungerminated canopy-stored seeds were viable. In general, with an increase in applied water germination of released seeds buried at a depth of 1 or 2 cm and of canopy-stored seeds buried at 1 cm increased, but regardless of watering regime few or no released seeds at 4 cm or canopy-stored seeds at 2 or 4 cm germinated. Significantly more seedlings emerged from plants buried in a horizontal than in a vertical position. Seedlings originating from buried canopy-stored seeds on an active dune accounted for only 5.4% of the total seedlings emerging, and most of them emerged later than those from released seeds. Thus, seed release is more effectively postponed in buried than in exposed canopies, and burial of canopy-stored seeds is a mechanism that helps regulate seed germination and seedling emergence of A. squarrosum on active dunes.