Element cycling in a Belgian pine forest

The concentrations of elements (Al, K, Ca, Cl, Mg, Mn) in different compartments in a Pinus Sylvestris stand are analyzed using atomic absorption spectrometry and neutron activation analysis. Together with the biomass distribution several aspects are studied i.e. element relative mass and concentration distributions, inter-compartment ratios and mass and concentration related correlations between the elements. Finally, a simple box model is developed to give approximated inter-compartment transfer rates. The relative mass distribution results show that Ca (94 wt%) and Mn (88 wt%) are mainly present in the wooden compartments, because Ca has a structural role in wooden tissues and Mn participates in the synthesis of lignin. Conversely, Cl (34 wt%) and K (23 wt%) are more present in the needles as these elements are both involved in opening the stomata. Moreover, Cl also participates in the water splitting during the photosynthesis process. Al, toxic in high amounts, is mainly present in the roots and outer bark, where it will be blocked to avoid toxicity. Mass related correlations are found between Ca and Mg (0.90), Mn and Mg (0.98), Mn and Ca (0.89) and K and Cl (0.88). These correlations result from similarities in biological functions (K and Cl are involved in the stomata opening and pressure regulation of the cells) or by a similarity in charge causing a similarity in cell to cell transport (Ca, Mg and Mn, which have a cationic charge of +2). Concentration related correlations are found between Ca and Al (0.90), Mn and Cl (0.91), K and Cl (0.85) and K and Mn (0.84). These correlations can be explained by a similarity in channel transport behaviour (Ca and Al), a biological function similarity (Mn and Cl, involved in water splitting; K and Cl, involved in pressure regulation in the cell and opening of the stomata) or due to different functions in the same compartment (K and Mn, with K involved in opening the stomata, and Mn, involved in water splitting). The inter-compartment ratios confirm the mobility and immobility of elements and give indications of the translocation of elements: a high litter needles/old needles ratio like for immobile Ca (1.31) shows that Ca is not redistributed to other leaves before leaf fall. A high ratio is also obtained for Al (litter needles/old needles ratio of 1.46 and litter twigs/young twigs ratio of 2.44). Al appears to be translocated to compartments to avoid toxicity. The expected translocations for mobile and immobile elements based on inter-compartment ratios are confirmed via the developed box model. A high transfer factor from leaves to floor (0.14 d-1) is found for immobile Ca. Conversely Mg, a mobile element, has a high transfer rate from leaves to wood (0.43 d-1). The similarities between Mn and Mg (both divalent cations, and center of the chlorophyll molecule) can also be deduced from transfer rates that are almost the same for both elements

Concentrations and distributions of Al, Ca, Cl, K, Mg and Mn in a Scotspine forest in Belgium

A Pinus sylvestris stand located in Mol, Belgium was studied for its content of six elements: Ca, K, Mg, Al, Cland Mn. A fractionation of tree components was carried out into 8 classes (heart and sapwood, inner andouter bark, living branches, twigs and young/old needles) and their element contents were measured.Comparisons were made between the different compartments in terms of absolute and relative elementcontents. Quantitatively, Ca and K are the main elements: in young needles, Ca + K reach 83% of theelements’ whole stock. The wood compartments (heartwood + sapwood) have generally low elementcontent, as does the outer bark except for Ca (which is bound to suberin) and Al, possibly from atmosphericclay deposition. The inner bark, twigs and needles have high element contents possibly linked to highsymplasmic content. The Inner bark shows high Ca and K contents as these elements are involved inphloem transport. Positive correlations were found between Ca and Al, Mn and Cl, K and Cl and K andMn, attributed to similarity in chemical and biological function.A simple empirical compartment model was developed to derive numerically the transfer rates thatreproduce the element distribution within tree compartments. The calculated mass flows appear to bewithin range of the limited data available from other pine tree studies.This study highlights the potential for coupling of specific elements (including radionuclides) to Ca, K,Mg, Al, Cl and Mn in context of vegetation modelling, by assuming that these elements follow the samepathways. We found indication that36Cl,90Sr and137Cs (environmentally important from the perspectiveof nuclear power and waste management) can be coupled to Cl, Ca and K fluxes within the tree, increasingthe understanding of the cycling of radionuclides in a forest ecosystem