Edaphic Factors Related to Shoalgrass (Halodule wrightii Aschers.) Production

Abstract

A field study was conducted at 2 south Texas [USA] sites to determine the relationship of Fe-Mn-S edaphic conditions to colonizing growth by the seagrass, H. wrightii Aschers. Concentrations of soluble Fe and Mn, free H2S and FeS (acid-volatile H2S) and dissolved PO43- and NH4+, were measured in rhizosphere sediments before and after growth of Halodule into barren areas over the course of a single growing season. Plant tissue contents of Fe, Mn, total S, HCl-insoluble S and total N were also measured. This work was based on the hypothesis that, during Halodule colonization of bare sediments, levels of soluble Fe, Mn and S species should change as a result of microbial activity and the concentrations of these chemical species reflect the sediment environment critical to Halodule growth. Evidently, net H2S production was higher in Halodule sediments than bare sediments; thus a larger steady state pool of soluble sulfide occurred in the former sediments. This correlated with undetectable (< 4 .mu.M) soluble Fe, but measurable quantities of soluble Mn, in Halodule sediments. Apparently, Halodule grows best in reduced sediments with free H2S present, very low in soluble Fe, but with significant amounts of soluble Mn. Mechanisms to protect Halodule from H2S toxicity and trace metal toxicity appear operative, similar to other waterlogged plant systems (e.g. rice, sugarcane, Spartina).