Some Field Observations Relating the Growth of Bog Plants to Conditions of Soil Aeration

Abstract

Peat bogs of any size are often dissected by channels of moving water, and it is well known that the plant communities of such channels are usually very different in composition from those where the water is stagnant. One of the plants which seems to favour an environment with moving water is Molinia caerulea. Jefferies (1915), for example, noted that Molinia grew better on sloping than on flat ground, and concluded that Molinia favours soil maintained by an aerated water supply in preference to 'sour' soil produced under stagnation. Rutter (1955) observed improved growth of Molinia in the presence of a fluctuating water table, and suggested that moving ground water not only improved the oxygen supply to the roots, but also brought about a reduction in the concentration of toxic substances by sweeping them away. In addition he remarks on the possible importance of moving ground water in bringing about the continuous renewal of soluble bases or other plant nutrients, a suggestion which is supported by Newbould & Gorham (1956). Until quite recently it has been extremely difficult to take measurements of oxygen in waterlogged soils in situ, and data on the oxygen regimes of flushed and unflushed habitats are consequently lacking. Recently, however, Lemon & Erickson (1952, 1955) and Poel (1960) have described a polarographic method, in which a platinum microelectrode can be used to measure the oxygen regime in soils. This is a particularly useful technique for it gives a true indication of the potential availability of soil oxygen to plant roots, since oxygen diffusion rate, rather than oxygen concentration, is measured at the sampling points. It is also very suitable for recording the small local differences in oxygen status down soil profiles. A particularly striking example of a differential in Molinia growth between flushed and stagnant soil was noticed by the authors near Laxford Bridge in Sutherland, and a smallscale investigation of the soil oxygen and its relation to the Molinia was carried out in the autumn of 1962. This was followed by a further investigation on 'Fen Bogs', a valley bog on the North Yorkshire Moors where distribution of Molinia was patchy. The two bogs together, therefore, give a series from flushed to stagnant conditions, with and without Molinia, and the platinum micro-electrode was used to investigate whether there was a variation in oxygen content of the peat which corresponded with the distribution and vigour of Molinia. In an attempt to define soil aeration as comprehensively as possible, oxidationreduction potentials and measurements of hydrogen sulphide were made in addition to oxygen diffusion at the Fen Bogs site.