Litter leaching

Neither translocation to roots nor root exudates explain the loss. A major part of the losses must be due to the shedding of various plant parts (pollen, flowers, leaves), leaching of nitrogen from aging leaves, and to herbivory these losses (except for windborne pollen) are mostly internal redistributions of the nutrient, as the litter, leaching, and herbivory return the nutrient to soils. But most of the nitrogen lost from tops of plants is due to volatilization of NHs. ... 

Damage to epicuticular waxes Altered photosynthesis Increased water loss Accumulation of acidic anions Leaching of ions, sugars, etc. Mineral imbalances Altered metabolism Increased susceptibility to winter freezing injury Death of fine roots Destabilization of trees Reduced water/mineral uptake Reduced water uptake Cations leached below roots Accumulation of acidic anions Altered structure/texture Altered microflora Reduced litter decomposition Altered N transformations Solubilization of metal ions... 

Adams PL, Daniel TC, Nichols DJ, Pote DH, Scott HD (1994) Poultry Litter and Manure Contributions to Nitrate Leaching through the Vadose Zone. Soil Sci Soc Am J 58 1206-1211... 

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. 

Blaschke, H. 1979. Leaching of water-soluble organic substances from coniferous needle litter. Soil Biology and Biochemistry 11 581—584. 

With the carbon supply in forest litter equal to 421.lt/km2, from which 12.95 t/km2 are annually leached into the soil, with 82.5% of this amount remaining in the upper soil layer (which can be up to 8 cm thick), we get C18 = 0.31. 

Furthermore, a minimum catalytic turnover can be estimated from the above ratio C/Mg 1,000, that is, how long chlorophyll and rubisco molecules must last before there is loss of Mg to the environment besides photodegradation (bleaching, occurs with chlorophyll) or reconstitution of the molecules, both by rainwater leaching of leaves still alive (Franzle and Schimming 2008) and by litter-fall. Supplies and sinks are thus linked to the stoichiometric ratio once again which leads us to estimate it. 

Fig. 7.1 Total nutrient stocks and in plant biomass plus soil in rain forest, newly planted Pinus caribaea (6 months old), P. caribaea, and Gmelina arborea plantations at the end of the first rotation (9.5 and 8.5 years old, respectively), and second rotation P. caribaea (1.5 years old) at Jari (Sanchez et al. 1985). H = harvest loss from trees taken when clearing the rain forest for the plantations L = leaching. Total nutrient stock is defined as the sum of all the nutrients in plant biomass (aboveground, litter, detritus, roots) plus total N, available P (extracted by the Mehlich method), and exchangeable K, Ca, and Mg in the top meter of the soil.

At places in the Amazon the ferrasol is transformed over time to a podzol, a highly weathered, bleached, sandy soil capped by a thick, peat-like accumulation of litter on the top. Everything except quartz is rapidly leached out of the podzol soil including aluminum and iron. The latter are present initially as constituents of organic complexes, but they are not immobilized, because there is a relative lack of clay minerals for adsorption. 

Figure 2 Conceptual model of carbon cycling in the litter-soil system. In each horizon or depth increment, SOM is represented by three pools labile SOM, slow SOM, and passive SOM. Inputs include aboveground litterfall and belowground root turnover and exudates, which will be distributed among the pools based on the biochemical nature of the material. Outputs from each pool include mineralization to CO2 (dashed lines), humification (labile slow passive), and downward transport due to leaching and physical mixing. Communition by soil fauna will accelerate the decomposition process and reveal previously inaeeessible materials. Soil mixing and other disturbances can also make physically protected passive SOM available to microbial attack (passive slow).

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