Ecological Observations on Splachnum ampullaceum

Abstract

Field observations on colonies of Splachnum ampullaceum Hedw. in Isle Royale National Park, Michigan, and laboratory cultures maintained for three years without decline in vigor indicate a possible interrelationship between nutrient and pH factors to explain the habitual decline of colonies in nature. The genus Splachnum has a distribution in North America ranging from the northern tier of states into the Canadian provinces and to Alaska. It is also found in scattered localities in the higher meadows of the western mountain ranges in the United States. The colonies of the plant, in various states of vigor, are usually found in association with the dung of herbivorous animals, especially that of cow, moose, and caribou. This investigation was initiated to determine if factors other than nutrition might play a role in the habitual decline of the colonies. Two species of Splachnum have been collected in Isle Royale National Park, Michigan: Splachnum ampullaceum Hedw., with the characteristic top-shaped hypophysis and the splotches of purple pigment, and S. rubrum Hedw., with the umbrella-like hypophysis and the characteristic red color. They are always found in close association with moose dung in the sphagnum bogs. Splachnum rubrum is in full fruit in late June, while the fruiting period for S. ampullaceum is late August and early September. Colonies of S. ampullaceum are more common than those of S. rubrum. On Isle Royale both species appear to be most abundant in Tollman Swamp, a sphagnum bog one-quarter mile northeast of the Rock Harbor Lodge on the north end of the main island. The colonies observed in the bog were in various states of vigor. Some were pure Splachnum while others were in various stages of decline as evidenced by the presence of Polytrichum strictum and Sphagnum spp. Observations have been made of Splachnum ampullaceum under cultural conditions during a period of three years. Cultures of the moss were obtained by two different procedures: 1) from spore germination and 2) from small sections cut from mature gametophytic plants. Two types of 2% agar media were used. One was Knops medium and the other was a medium composed of distilled water with the addition of 200 cc per liter of an extract from moose dung. This extract was obtained by heating a quantity of the dung in distilled water with the temperature of the solution kept below the boiling point. The solution was decanted and added to the agar and distilled water. The cultures were grown in 500-cc, wide-mouth 1 Department of Biology, Wisconsin State University, Stevens Point, Wisconsin. This content downloaded from 157.55.39.246 on Tue, 27 Sep 2016 05:48:22 UTC All use subject to http://about.jstor.org/terms 1965] WHITMIRE: ECOLOGY OF SPLACHNUM 343 Erlemeyer flasks. The culture room was a walk-in refrigerator (500F) with three fluorescent tubes. The moss spores were dispersed over the surface of the growth medium and the flask was plugged with cotton. Germination of the spores took place in seven days. Three cultures were started and all proved successful. The small apical portions of the mature plants were first sterilized in 10% Chlorox solution to remove algal contaminants and then were placed on the surface of the agar medium. Five cultures were started. Growth continued from the apex of the plants and good regeneration of protonema and rhizoids occurred from the cut ends of all cultures except one. This failure was probably due to an excessive exposure to the Chlorox solution. Growth continued in both the spore culture and the plant culture until the entire bottom of the culture chambers was covered with mature gametophytic plants. The cultures were maintained without additional nutrient material for three years with no evident decline in the colonies. Sporophytes were produced in one of the spore cultures growing on the dung medium. These sporophytes were without the characteristic hypophysis. This does not seem to be unusual, however, since colonies in nature often produce a few sporophytes without the hypophysis. Sporophytes were not produced in the remaining cultures. There was no apparent difference in growth on the dung medium and on Knops medium. Colonies of Splachnum ampullaceum growing under natural conditions are pure after one season's growth. The second season finds encroachment upon the colonies by Sphagnum spp. and Polytrichum strictum which thrive under more acidic conditions. Three samples of fresh moose dung were found to have a pH of 6.5. Comparison of the vigor of the natural colony with that of plants in the controlled environment suggests that a lowering of the pH may cause a decline of the colonies in nature. The dung substrate undoubtedly takes on the pH characteristics of the surrounding bog. This acid condition would make it difficult for Splachnum to compete with Sphagnum and Polytrichum.