Transport of carbon and phosphorus compounds about Sphagnum

Abstract

The bog mosses, Sphagnum , lack any obvious anatomical specialization inside the stem but have a well-developed system of water conduction in capillary spaces among pendent branches around the stem. It has hitherto been assumed that this was the main route for solute transfer too. We describe experiments showing that there is rapid and quantitatively important transport within the stems. The tracers 32 P and 14 C were supplied to S. recurvum . When applied below the top of the plant they moved to the apex whether external mass flow was upward or downward. Autoradiographs showed high concentration of tracers in the stem. Steaming the stem above and below the site of application prevented tracer movement. An experiment lasting four weeks on S. papillosum showed that after 14 C labelling almost all that part of the alcohol-soluble fraction that moved did so from older parts to the apex, with very little transfer to the insoluble fraction, to neighbours, or into the gas phase. For the soluble fraction in the capitulum, the conductance for 14 C from below was about the same as that of its loss in respiration. The conductance to the insoluble fraction was about twice as great, and to neighbours about half as much. A longer experiment showed that predominately acropetal transport continued for at least 22 weeks in five species. By that time about 25% of the remaining 14 C label was incorporated in the new tissues. The stem of S. recurvum contains a central mass of parenchyma 20-50 cells across. The end walls of the parenchyma cells have perforations approximately 100 nm across at a density of 7-13 μm -2 . A single cell wall has about 1500 perforations. They probably house plasmodesmata. These results indicate that Sphagnum has an effective mechanism for retaining and relocating solutes within it. This property, coupled with the ability to grow in a very low supply of solutes, and to make the environment acid by cation exchange, may be seen as causes of the widespread success of Sphagnum .