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

Two instruments were compared for consistency of decay-rate measurements of four leaf types: Loliun perenne, Typha domingenesis, Casuarina cunninghami ana and Eucalyptus polyanthemos, via progressive biological oxygen demand ( BOD). The instruments were (a) a dissolved oxygen probe (i.e. an oxygen-sel ective membrane electrode) used in two different modes: (2) measurements of sacrificial samples that were successively discarded, and (2) repeated mea surements of the same sample, and (b) a mercury free manometer. Measurement s of D-glucose:glutamic acid standards were similar for both instruments,an d corresponded with values expected after five days of decay. During five d ays decay of the four leaf types, progressive measurements obtained by both applications of the dissolved oxygen probe were similar, and could be rela ted linearly. Progressive leaf-decay measurements obtained by the manometer and dissolved oxygen probe could be related linearly also. Decay measureme nts obtained by both instruments were nearly identical for C. cunninghamian a and E. polyanthemos, but there were slight differences in the slopes of l inear relationships for L. perenne and T. domingenesis. These comparisons i ndicate 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 dissolv ed oxygen probe. However, because slight differences in decay rates were ev ident in two comparisons, care should be exercised to derive and verify the association of data between instruments.