Atrotorquata lineata as a proxy for Juncus roemerianus, Part I: Atrotorquata lineata as a proxy for Juncus roemerianus in surface sediments from high-level salt marshes in the southeastern United States

摘要

Juncus roemerianus is a plant that occurs at the upper reaches of salt water influence in marshes from Delaware to Texas. In 2006 a palynomorphic fingerprint to identify surface sediment from J. roemerianus marshes was discovered in a South Carolina study (Marsh 2006, Marsh & Cohen 2008). This fingerprint had four components: (1) high palynomorphic abundance, (2) high palynomorphic diversity, (3) high concentration of Fungal Type A (greater than 10% of the palynomorphs in a given sample) and (4) the presence of the spores of the fungus Atrotorquata lineata, which occurred in the sediments of J. roemerianus marshes but not in the sediments collected from any other marsh type, even in sediments collected less than a meter away from J. roemerianus. The present study was designed to determine whether (1) Atrotorquata lineata occurs in all present-day Juncus roemerianus marshes regardless of geographic location within the range of the plant, and whether (2) A. lineata is ubiquitous in all surface sediments beneath J. roemerianus regardless of the location of the sample in the marsh. As a result of these two findings, A. lineata can be considered a proxy for the presence of J. roemerianus throughout its range. To test the first hypothesis, 93 surface samples were obtained from Juncus roemerianus marshes throughout the range of the plant (Delaware to Texas). Atrotorquata lineata was found in all samples from this range except for those from the northeasternmost end of the range (Virginia and Delaware). A new hypothesis is proposed that temperature may be the factor that explains the loss of the fungal proxy at this northeastern boundary. Furthermore, evidence is presented that geomorphologic and sedimentological factors, such as type of substrate, distance from the ocean, position relative to the shoreline, distance from tidal streams, amount of urbanization, tidal range, or wave fetch, were found to have no impact on the presence or absence of A. lineata. To test the second hypothesis, concerning whether Atrotorquata lineata was present in all parts of a Juncus stand, surface sediments from a 183 m transect across a monospecific Juncus roemerianus marsh were sampled at 15 m intervals. A. lineata was found in all samples regardless of position in the stand. The results of this study show that Atrotorquata lineata is omnipresent in sediment from Juncus roemerianus marshes throughout all but the most northern edge of the range of J. roemerianus and that it was present across the entire extent of a stand of Juncus roemerianus. Therefore, A. lineata by itself can in fact be considered a proxy for J. roemerianus.