FLORA                       


CHEMICAL ASPECTS OF THE RAINFOREST


History of erosion and deposition in the basin has caused extensive leaching of nutrients from the soil including  K+, Ca 2+, Mg 2+, and inorganic phosphate; especially in central and northern areas of the Amazon basin. Primarily growth is limited by the absence of phosphorus. Plants are tolerant of high soil concentrations of mobile aluminum. Also limited (to a lesser degree) by calcium and magnesium. Biomass development and regeneration capacity are not always clearly associated with differences in soil fertility, but are definitely related to rates and patterns of nutrient cycling.
Nutrient cycling tightly regulated mainly by biotic processes

Soils in the Amazon region
    - except quartz, minerals have been weathered to low activity
    -  labile aluminum is present
    - soils acidic
    - depletion of cations and low phosphorus availability

Soil drainage plays an important role in species occurrence. When the density of tree species is analyzed in proportion to stem density, there was a higher species density in the relatively richer soils. Biomass differences explained by differences in water and nutrient availability (although cannot rule out some influence from succesional stage).

Distribution of carbon, phosphorus, and nitrogen in biomass follow those of soil C, N, and available P

60% of C, 65% of N, and 50% of P occurred in particular organic matter, with a mean residency of 4 years
27% of C, 29% of N, and 33% of organic P was mineral associated, with a mean residency of 50 years

Stability is dependent on maintenance and cycling of the faster pool of organic matter

Measurement of litterfall and its associated fluxes of nutrients is a practical way to evaluate the production capacity and availability of nutrients in tropical forests
    - Phosphorus /Nitrogen ratios of leaf littterfall are inversely related to matter/P ratios.
    - There is no relation between p/N ratios and efficiency of N use
    - P/N ratios mainly affected by availability of P, not of N
    - N is not limiting

Seasonality can affect nutrient availability
    - seasonality of rainfall causes pulses in decomposition of soil organic matter, and subsequent nutrient release

Ageotropism - lack of growth toward the soil can result from low Ca levals in soil system

Mg difficiency severely limits root growth, reduces drought resistance, and reduces adaptation to nutrient poor sites

Steps for discovery of a lead candidate medicinal agent from a natural source
1. Selection, collection, and identification of an organism
2. preparation and evaluation of an extract in an array of invitro test systems
3. Priortization of the plants to be further studied
4. Bioactivity - directed fractionation (fractionation - separate into components)
5. Structure determination of the active isotopes

Different methods for plant selection in searching for new biological agents
1. random - take any and all plants from a specific area
2. taxonomic - take plants of a predetermined interesting taxa
3. chemotaxonomic - search for plants likely to produce related compounds
4. information managed - plants of proven biological activity with unknown active agents
5. ethomedical - look for clinical, oral, or written information on plant
6. serendipity - looking for one thing you find another

(Further questions - lab in Brazil or states or both? how does the information get patented.

Concentration of deep tree roots to nutrition of a tropical rainforest
•    Range of leave isotopic ratio was narrow compared to that of bulk soils
•    Ratios fairly similar what ever species and close to litter and near surface
•    roots rations - (suggest No or very little Sr. contribution form deep )
•    Correlations between Sr and Ca, but not the leaf ratios
•    Sr and Ca uptake and cycling mostly superficial in tropical rainforests.

Next: Fungi
References:
Chemistry of the Amazon

          

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