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Net primary production and decomposition of salt marshes of the Ebre delta (Catalonia, Spain)

Abstract:

Net primary production was measured in three characteristic salt marshes of the Ebre delta: an Arthrocnemum macrostachyum salt marsh, A. macrostachyum-Sarcocornia fruticosa mixed salt marsh and S. fruticosa salt marsh. Above-ground and belowground biomass were harvested every 3 mo for 1 yr. Surface litter was also collected from each plot. Aboveground biomass was estimated from an indirect non-destructive method based on the relationship between standing biomass and height of the vegetation. Decomposition of aboveground and belowground components was studied by the disappearance of plant material from litter bags in the S. fruticosa plot. Net primary production (aboveground and belowground) was calculated using the Smalley method. Standing biomass, litter, and primary production increased as soil salinity decreased. The annual average total aboveground plus belowground biomass was 872 g m-2 in the A. macrostachyum marsh, 1,198 g m-2 in the A. macrostachyum-S. fruticosa mixed marsh, and 3,766 g m-2in the S. fruticosa marsh. The aboveground to belowground live biomass ratio was 3.8, 2.6, and 2.1, respectively, in the three plots. Litter biomass (aboveground plus belowground) was 226, 445, and 1,094 g m-2, respectively. Total aboveground plus belowground net primary production was 240, 1,172, and 1,531 g m-2 yr-1. There was an exponential loss of weight during decomposition. Woody stems and roots, the most recalcitrant material, had 70% and 83% of the original material remaining after one year. Only 20-22% of leafy stem weight remained after one year. When results from the Mediterranean are compared to other salt marshes dominated by shrubby Chenopodiaceae in Mediterranean-type climates, a number of similarities emerge. There are similar zonation patterns with elevation and maximum aboveground biomass and primary production occurring in the middle marsh. This is probably because of stress produced by waterlogging in the low marsh and by hypersalinity in the upper marsh.