Root exudation stimulates microbial decomposition and enhances nutrient availability to plants. It remains difficult to measure and predict this carbon flux in natural conditions, especially for mature woody plants. Based on a known conceptual framework of root functional traits coordination, we proposed that root functional traits may predict root exudation. We measured root exudation and other seven root morphological/chemical/physiological traits for 18 coexisting woody species in a deciduous-evergreen mixed forest in subtropical China. Root exudation, respiration, diameter and nitrogen (N) concentration all exhibited significant phylogenetic signals. We found that root exudation positively correlated with competitive traits (root respiration, N concentration) and negatively with a conservative trait (root tissue density). Furthermore, these relationships were independent of phylogenetic signals. A principal component analysis showed that root exudation and morphological traits loaded on two perpendicular axes. Root exudation is a competitive trait in a multidimensional fine-root functional coordination. The metabolic dimension on which root exudation loaded was relatively independent of the morphological dimension, indicating that increasing nutrient availability by root exudation might be a complementary strategy for plant nutrient acquisition. The positive relationship between root exudation and root respiration and N concentration is a promising approach for the future prediction of root exudation.

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The Madison Metropolitan Sewerage District (MMSD) has conducted a five-year (1985)(1986)(1987)(1988)(1989)(1990) field experiment to obtain data that provide a scientific basis for regulating land disposal of sludge con taminated with polychlorinated biphenyls (PCBs). Over 1 400 samples of soil and crop tissue were analyzed. This paper presents all the field data and interpretation. The experimental design included eight different sludge treatments and controls, making it possible to study the effects of sludge concentration, sludge loading rate, and sludge application pat tern on the fate of PCBs in the soil system. Each treatment was replicated three times, giving thirty test plots in all (24 sludge applications and 6 control plots). Seventy-nine PCB congeners were detected during the study and the concentration of each PCB congener was measured in the surface soil, corn stover, and corn grain. Surface runoff runoff studies were conducted in 1988 and 1990 and congener-specific PCB analyses were made on these as well. A first-order disappearance model, C = C 0 exp( -Kt), was appropriate to evaluate the disappearance of PCBs from the surface soil layer. AT is the rate constant for PCB disappearance. Results indicate that the rate constant for disappearance of each individual PCB congener in the soil was independent of the initial PCB sludge concen tration, the sludge loading rate, and sludge application pattern. Most of the 2-, 3-, and 4-chlorinated PCB congeners showed significant decreases in their soil concentration with half-lives in the range of 4 to 58 months. The more highly chlorinated PCBs were more persistent in the sludge amended farmland, but many of them did disappear. The concentration of PCBs in the runoff samples was correlated with surface soil concen tration. The PCBs were associated with the runoff sediments and there was no measurable PCB in the liquid portion of the runoff. It was con cluded that there is no PCB translocation into either corn grain or corn stover samples. The bioconcentration factor for PCBs in the crop tissues is zero. Water Environ. Res., 66, 54 (1994).

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