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Microbial activities and biomasses in soils exhibit steep gradients across short distances, forming microhabitats with different qualities. A methodological study was carried out to determine CO 2 production of soil microorganisms in miniature. Soil samples (2-4 g) from 28 different soil types of southern Germany were incubated directly in a small glass ampoule within a 20-mL gas-tight syringe. A high correlation (r = 0.96) between CO 2 production and heat output suggests that this micromethod is useful for the determination of CO 2 respiration and the estimation of microbial biomass of small soil samples.

The uptake of auxin (LAA), abscisic acid (ABA) the synthetic cytokinin benzylaminopurine (BA), gibberellic acid (GA3) and mevalonic acid (lactone) (MVA) into intact chloroplasts and protoplasts from spinach mesophyll cells was measured and the permeability coefficients Ps of the chloroplast envelope and the plasmalemma were calculated. With all solutes tested uptake and P s values were considerably higher in the chloroplast system than in the protoplast system. At an external pH of 7.0, rates of uptake exhibited the order BA > LAA > MVA > ABA > GA3 in both systems. However, the P s values (corrected for the undissociated species of the solutes) exhibited the order LAA > GA3 > (ABA or BA) > MVA. This corrected sequence indicates the theoretical capacity of penetration under the assumption that preferentially the protonated species of phytohormones are capable of readily penetrating membranes. P s values for phytohormones appeared largely to be determined by the distribution coefficient K d and to a lesser extent by the molecular weight (Mr). In the Collander-plot the relation between the logarithm of Ps values for phytohormones and some other solutes such as acetate, glycerol, glucose, sorbitol and sucrose and the logarithm of K J M T 1.5 approached linearity.

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