The ability to obtain sufficient field hydrologic data at reasonable cost can be an important limiting factor in applying transport models. A procedure is described for using ponded‐flow‐ and tension‐infiltration measurements to calculate transport parameters in a forest watershed. Thirty infiltration measurements were taken under ponded‐flow conditions and at 3, 6, and 15 cm (H2O) tension. It was assumed from capillarity theory that pores >0.1‐, 0.05‐, and 0.02‐cm diam, respectively, were excluded from the transport process during the tension infiltration measurements. Under ponded flow, 73% of the flux was conducted through macropores (i.e., pores >0.1‐cm diam.). An estimated 96% of the water flux was transmitted through only 0.32% of the soil volume. In general the larger the total water flux the larger the macropore contribution to total water flux. The Shapiro‐Wilk normality test indicated that water flux through both matrix pore space and macropores was log‐normally distributed in space.

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One-year-old dormant white oak (Quercus alba L.) seedlings were planted in a nutrient-deficient forest soil and grown for 40 weeks in growth chambers at ambient (362 microliters per liter) or elevated (690 microliters per liter) levels of CO2. Although all of the seedlings became severely N deficient, CO2 enrichment enhanced growth by 85%, with the greatest enhancement in root systems. The growth enhancement did not increase the total water use per plant, so water-use efficiency was significantly greater in elevated CO2. Total uptake of N, S, and B was not affected by C02, therefore, tissue concentrations of these nutrients were significantly lower in elevated CO2. An increase in nutrient-use efficiency with respect to N was apparent in that a greater proportion of the limited N pool in the C02-enriched plants was in fine roots and leaves. The uptake of other nutrients increased with CO2 concentration, and P and K uptake increased in proportion to growth. Increased uptake of P by plants in elevated CO2 may have been a result of greater proliferation of fine roots and associated mycorrhizae and rhizosphere bacteria stimulating P mineralization. The results demonstrate that a growth response to CO2 enrichment is possible in nutrient-limited systems, and that the mechanisms of response may include either increased nutrient supply or decreased physiological demand.The 'law of the minimum' evolved in physiological ecology both before and after 1840, when Justus von Liebig is credited with its formulation (4). The doctrine that the environmental resource present in least amount determines the amount of plant growth was initially applied to fertilizers; however, the concept was quickly extended to other resources, including light and water. The importance of the amount of nutrients assimilated by the plant, rather than the amount in the soil, was eventually recognized (4). It is now apparent that the concept of limiting factors is simplistic, and interactions between resources can be expected; that is, more than one resource can limit plant growth simultaneously, or the supply of one resource can increase the supply or decrease the demand for another. Temporal and spatial variation in resource limitations within a plant need also be considered.Interactions between environmental resources are critical to the analysis of the response of forest vegetation to rising levels of atmospheric CO2. Increased plant growth is a widely documented

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