Studies of comparative biogeochemistry of Virola surinamensis (VSU) and successional forest
ecosystems (FSU) in the coastal tableland region of eastern Amazonia were carried out to
studies on i) factors that cause differences in fluxes and stocks of organic matter and chemical
elements, such as potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe),
copper (Cu) and zinc (Zn) within the biogeochemical matrix of litterfall, the forest floor and
pedochemical matrix stocks, and ii) factors that control the variation in soil carbon dioxide
(CO2) flux within the VSU and FSU ecosystems. The major flux of the biogeochemical matrix
(organic matter) from the trees to the forest floor was higher (p < 0,001) in the successional
forest ecosystem (FSU) than in the Virola surinamensis ecosystem (VSU). This was due to
higher floristic diversity in the FSU, as well as the elevatedlevel of ecosystem manipulation in
the VSU, where the burning of phytomass released K, Ca, Mg, Mn, Fe, Cu and Zn oxides,
causing in situ enrichment of the soil bases. The K, Mn and Zn fluxes were significantly higher
(p < 0,001) in the FSU, although Fe flux was higher (p < 0,001) in the VSU. These results
show the effect of high floristic diversity of the biogeochemical matrix in the successional
ecosystem, while in the Virola surinamensis ecosystem, results indicate the possibility of
biogenic Fe accumulation as a genotypic character of Virola tree species. The Mg, Ca and Cu
fluxes were similar (p <.0,05) between ecosystems, as demonstrated by the semivariogram
nugget effect. This indicated the absence of spatial influence on the processes controlled by
the biogeochemical matrix flux. The geochemical matrix flux occurred with similar patterns at
the mesoscale level, or across the biogeochemical provinces. The element use efficiency
(EUE) for Ca, Mg, Mn, Fe, Cu and Zn was greater (p < 0,001) in the FSU than in the VSU.
This indicates a significant biogeochemical matrix flux effect in the successional forest
ecosystem, contrary to the Virola surinamensis ecosystem with relatively low floristic
diversity. Potassium (K) occurred with similar EUE values (p > 0,05) in both biological
systems suggesting that the VSU ecosystem was an efficient K cycler. The forest floor stocks
of K, Ca, Mg, Mn, Fe, Cu and Zn were higher (p < 0,001) in the FSU than in the VSU. This
may be explained by the more diversified biogeochemical matrix control in the forest
successional ecosystem. The overall water holding capacity was similar (p > 0,05) between
ecosystems, although forest floor storage was higher (p < 0,001) in the FSU, indicating that the
VSU ecosystem has recovered its structure and function over time. The biogeochemical matrix
mean residence times for forest floor organic matter and K, Ca, Mg, Mn, Fe, Cu and Zn were
higher (p < 0,001) in the successional ecosystem (FSU) than in the Virola surinamensis
ecosystem (VSU). This suggests that in FSU the influence of forest floor stocks worked as a
proximal factor, associated with the more distal factor of higher floristic diversity, which likely
introduced recalcitrant substances into the system to minimize the decomposition process. The
dispersion models illustrated in semivariograms for Al, Na, Fe and Cu in the Yellow Latosol
dystrophic (LAd), and Ca in the Yellow Latosol dystrophic endocrecionary (LAdc) showed a
nugget effect. In the LAd soil pedochemical system, the semivariograms models demonstrated
spatial dependence, including H+ (spherical, r2 =0.92); Na (gaussian, r2 =0.49); K (gaussian
r2=0.98); Ca (exponential, r2= 0.82); Mg (gaussian, r2 = 0.87); Mn (exponential, r2 = 0.86), Zn (gaussian, r2 =0.79). In the LAdc soil, cations that showed spatial dependence were Al
(gaussian, r2 = 082); H+ (gaussian, r2 = 092); Na (gaussian, r2 = 0.87); K (gaussian, r2 = 0.86),
Mn (gaussian, r2 0.96) and Fe (gaussian, r2 = 0.87); Cu (gaussian, r2 = 0.80) and Zn (gaussian,
r2 = 0.79). Carbon dioxide (CO2) flux from soils in the were similar (p > 0,05) with values of
4,03 μmol C m-2 s-1 and 4,37 μmol C m-2 s-1 in the VSU and FSU, respectively. Based on
the CO2 soil efflux, I conclude that the Virola surinamensis ecosystem attained similar
metabolic processes in relation to the successional forest ecosystem over time.
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