A comparison of manometric and membrane-electrode procedures for measuring rates of leaf decay

Two instruments were compared for consistency of decay-rate measurements of four leaf types: Lolium perenne, Typha domingenesis, Casuarina cunninghamiana and Eucalyptus polyanthemos, via progressive biological oxygen demand (BOD). The instruments were (a) a dissolved oxygen probe (i.e. an oxygen-selective membrane electrode) used in two different modes: (1) measurements of sacrificial samples that were successively discarded, and (2) repeated measurements of the same sample, and (b) a mercury free manometer. Measurements of D-glucose:glutamic acid standards were similar for both instruments, and corresponded with values expected after five days of decay. During five days decay of the four leaf types, progressive measurements obtained by both applications of the dissolved oxygen probe were similar, and could be related linearly. Progressive leaf-decay measurements obtained by the manometer and dissolved oxygen probe could be related linearly also. Decay measurements obtained by both instruments were nearly identical for C. cunninghamiana and E. polyanthemos, but there were slight differences in the slopes of linear relationships for L. perenne and T. domingenesis. These comparisons indicate the feasibility of using both instruments for obtaining comparable measurements of leaf decay rates. It is also feasible to briefly reopen the same glass bottle to facilitate temporal BOD measurements with the dissolved oxygen probe. However, because slight differences in decay rates were evident in two comparisons, care should be exercised to derive and verify the association of data between instruments.