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This article comments on various issues related to biogeography. Several factors likely contribute to the lack of understanding of the biogeography of plant chemistry. Among these important factors are climate, geomorphology, vegetation type and site history. There has been an increase or renewal of interest in the biogeography and the stoichiometry of ecological chemistry. The Rhizosphere 2004 Congress held in Munich, Germany, was organized to mark the centenary of the publication of a paper by Lorenz Hiltner in which he introduced the term rhizosphere that was defined as the soil compartment influenced by the root.

Leaf anatomical parameters such as leaf mass per area (LMA) and biochemical composition can be used as indicators of leaf photosynthetic capacity. The aims of this study are to evaluate the potential of reflectance spectroscopy of fresh leaves for assessing and predicting Various parameters, anatomical (LMA and tissue thickness) and biochemical (nitrogen concentration). This paper describes results obtained with fresh leaves of holm oak (Quercus ilex), an evergreen oak that is widely distributed from mesic to xeric habitats in the Mediterranean. Fresh leaves (560) were collected over 3 yr at six different sites, from the top to the bottom of the canopy. The reflectance of each leaf was obtained within 1 h of sampling with an NIRSystems 6500 spectrophotometer over the range 400-2500 nm. LMA was determined for all samples; biochemical and anatomical measurements were conducted over representative subsample populations of 92 and 87 leaves, respectively. Stepwise regression calibrations and partial least squares (PLS) calibrations were developed and compared with different spectral regions and mathematical treatments. Calibration equations had high coefficients of determination (r2 ranging from 0.94 for nitrogen to 0.98 for LMA and tissue thickness). The PLS regressions gave better results than stepwise regressions for all parameters studied. Compared with regressions calculated on raw spectral data, calculations on second derivatives of spectra improved results in all cases. The use of scatter corrections also improved results. These results show that visible and near-infra red reflectance can he used for accurately predicting anatomical parameters and the nitrogen concentration of fresh holm oak leaves. The results support the suggestion that high spectral resolution imaging spectrometry can be a useful tool for assessing functional processes in forest ecosystems. [ABSTRACT FROM AUTHOR]

This paper reports the conditions for the assay of sucrose-sucrose fructosyltransferase (SST); fructan-fructan fructosyltransferase (FFT), invertase and fructan hydrolase (FH) in extracts of leaves of Lolium rigidum Gaudin. Invertase had a temperature optimum between 30 and 35 °C and a pH optimum between 4.5 and 5.0 whereas the enzymes of fructan metabolism had temperature optima at 25 °C and pH optima at about 5.5. Analysis of the products of enzyme assays showed that crude SST activity produced mainly 1-kestose from 100 mM sucrose and when incubated with 500 mM sucrose, neokestose and possibly 6-kestose were also formed in low concentrations. FFT produced two tetrasaccharides and neokestose after incubation with 100 mM 1-kestose and FH produced fructose exclusively after incubation with high-molecular-weight fructan extracted from Lolium rigidum and Helianthus tuberosus L. and with a commercial preparation of bacterial levan. Enzyme activities were also measured during a phase of fructan accumulation. FH activity declined by 50% but SST and FFT activities increased about 2.5-fold during this period. The data supported the proposed synthetic pathway of fructan accumulation from sucrose via 1-kestose into high-molecular-weight fructan and indicated that fructan synthesis may occur at low substrate concentrations. Extracts from leaves which had not accumulated fructans contained measurable activities of SST and FFT. [ABSTRACT FROM AUTHOR]