Leached from plant leaves

Measurement of total nutrient deposition requires studies integrating rainfall, through-fall, and stemflow in the wet component, as well as aerosol dry deposition. No studies in Amazonia have yet integrated all these components. Throughfall studies indicate a large enrichment of potassium, on the order of 2.7 to 10.2, leached from plant leaves (Holscher et al. 1998). This large variation in potassium enrichment could be caused by different floristic composition and precipitation patterns. 

Miscellaneous Identified Inhibitors. 3-Acetyl-6-methoxy-benzaldehyde is present in the leaves of the desert shrub Encelia farinosa. It is apparently leached from the leaves and washed into the soil by rain. Concentrations of approximately 0.5 mg. per gram of dried leaf material have been measured. In sand culture studies, growth of tomato seedlings was inhibited by 50 p.p.m. while 115 p.p.m. reduced growth by 50% (53). A concentration of 250 p.p.m. killed the test plants within one day. The structure was confirmed by synthesis, and the synthetic material was shown to be as active as the natural product (54). Derivatives were also prepared in which a cyano, nitro, or amino group was substituted for the aldehyde moiety. The amino derivative was reported to be the most highly toxic. 

A variety of chemicals may be leached from the aerial portions of plants by rainwater or by fog-drip (16) including organic acids, sugars, amino acids, pectic substances, gibberellic acids, terpenoids, alkaloids, and phenolic compounds. Colton and Einhellig (17) suggested that leaf leachates of velvetleaf (Abutilon theophrasti) may be inhibitory to soybean (Glycine maxT We have recently discovered specialized hairs on the stems of velvetleaf plants which exude toxic chemicals. 

Allelopathic chemicals from plants may be released from living leaves as volatiles or leachates or from roots through exudation or sloughing off of dead tissues. They also may be leached from leaf litter on the soil surface. 

Aquatic humic substances may be found in groundwater, river water, lakes, marshes, bogs, swamps, and seawater. The source of the humates may be autochthonous or allochthonous that is, the humates may be formed from phytoplankton in the water or they may be leached into the aquatic environment from terrestrial plants, leaf litter, soil, or subsurface deposits. Relatively undisturbed marine environments have humic and fulvic acids formed almost entirely from native phytoplankton inland surface waters contain major contributions from allochthonous sources. Mixing of the two types of materials may occur, as in the estuaries of rivers. 

Although this report emphasizes the potential significance of the nutrient supply of precipitation, it is important to recognize that the loss of nutrients from plants by leaching also has been known for more than 70 years (Le Clerc and Breazeale, 1908). Leaching of soluble nutrients from the interior of leaves and removal by rain of materials deposited from the atmosphere or secreted onto leaf surfaces are affected by the chemical composition of the cuticle, morphology of the leaf, age and stage of... 

The removal of substances from plants by the action of aqueous solutions, such as rain, dew, mist and fog" is termed leaching (Tukey, 1970) and represents, on a whole plant level, a component of throughfall (Parker, 1983) and, on a leaf level, a process contributing to the overall balance of ions in the leaf (Pitman, 1988). Besides these ubiquitous processes, leaching may be accelerated by acidic precipitation (Tukey, 1980) and is then classified as an indirect effect of the potential impacts of "acid rain" (Tamm and Cowling, 1977). - On the analogy of the concept of the soil-plant-... 

Leaves from the five plants were combined and divided into two equal weight samples. One sample was leached in distilled water for 2 hours at a ratio of 15 gms leaf fresh weight to 100 ml water. The leaf leachate was decanted and used directly in the bioassay. The second sample was ground in a blendor with distilled water at a ratio of 1 gm leaf fresh weight to 100 ml water. After standing for 15 min, the mixture was filtered and the filtrate was used directly in the bioassay. 

Rain and mist, acid or otherwise, have been shown to leach nutrients from the foliage of woody plants (19). Wood Bormann (13) found that when sugar maple seedlngs were exposed to pH 3.0 (leaf injury), 3.3, and 4.0 of simulated acid rain, there were significant increases in leaching of K, Mg " and Ca " ions. Cronan (21) found that in coniferous throughfall which was exposed to ambient rain of pH 4.0, there was an increase in H, Ca , Mg, K+, Mn, S0 3" and Cl" as compared to bulk precipitation. In contrast, throughfall... 

Depending on the scale of interest (cell-leaf-plant-ecosystem), there are several ways to draw conclusions from the adduced evidence, The following is taken here Leaching of cations as a regular, physiological process may develop to a plant-internal stress with multiple implications if the plant is no longer able to cope with it due to adverse environmental conditions. 

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