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SEASONAL SEED BANK PATTERNS OF AN ARTHROCNEMUM MACROSTACHYUM (CHENOPODIACEAE) COMMUNITY ALONG A COASTAL MARSH INUNDATION GRADIENT ON THE ARABIAN SEA NEAR KARACHI, PAKISTAN

BILQUEES GUL AND M. AJMAL KHAN*

Abstract: The seasonal variation of a seed bank was studied along an inundation gradient in a coastal marsh community dominated by Arthrocnemum macrostachyum (Moric.) C. Koch (Syn: Arthrocnemum indicum (Willd.) Moq.; Chenopodiaceae;) near Karachi, Pakistan. The distance from the Avicennia marina edge to mean high tide line (110 m) was divided into five zones. Density and height of the plants were higher in the middle marsh than in other areas. Plant cover and number of branches were lowest in the lower marsh and increased substantially in the next zone and there was no significant difference among other zones. Dry weight accumulation was highest in the lower-middle marsh. The size and composition of the seed bank was determined by monthly counting and identifying the seeds extracted from soil samples. A persistent seed bank flora was dominated by A. macrostachyum. The upper, upper-middle and middle marsh had seeds of five additional species viz., Atriplex stocksii Boiss., Suaeda fruticosa (L.) Forssk., Halopyrum mucronatum (L.) Stapf., Aeluropus lagopoides (L.) Trin. Ex Thwaites, Urochondra setulosa (Trin.) C.E. Hobbard and Cressa cretica L. from adjacent communities. Seed bank size was one of the largest in the samples collected immediately following dispersal ranging from 40,760 ± 123 seeds m^-2 in March to 917,135 ± 567 seeds m^-2 in July. Seed density then declined rapidly over two to three months. Size and diversity of the seed bank progressively increased from the lower to the upper salt marsh.
 

Department of Botany, University of Karachi, Karachi-75270, Pakistan.
Corresponding Author: P.O. Box 8452, University of Karachi, Karachi-75270, Pakistan.
ajmal@botany.ku.edu.pk