The aim of this study was to produce calibration equations between near-infrared reflectance (NIR) spectra and the concentrations of carbon, nitrogen, and phosphorus in heterogeneous material: from living needles to litter in Pinus halepensis stands subjected to prescribed burnings. The aim was to determine whether calibrations should be conducted within each stage in the transformation of needles (local calibrations), giving relationships that were accurate but valid only for each particular stage, or whether it was possible to integrate the various forms of variation in needles (global calibrations) while retaining an acceptable accuracy. A principal component analysis calculated from the sample spectral data was used to distinguish three different sets, each sharing spectral characteristics and corresponding to three categories of needle: needles collected on the pines (N), falling needles (F), and litter (L), and each containing samples collected from the burnt sites and a control site. Samples representative of all the forms of variation in spectral properties were selected from within each category and their carbon, nitrogen, and phosphorus concentrations were measured using standard wet chemistry methods; these constituted the calibration sets n, f, and l. Calibrations were produced between the nutrient concentrations and the NIR spectra of the calibration sets n, f, and l and the grouped sets (n+f, f+l, n+f+l). The results of local calibrations made from each individual category showed that the carbon, nitrogen, and phosphorus concentrations were accurately predictable by NIR spectra. The global calibrations made by lumping together several categories were valid for a wider range of concentrations and for spectrally heterogeneous materials and in most cases were just as accurate as the local calibrations produced from each individual category.

Human-induced changes in land use lead to major changes in plant community composition which have strong effects on ecosystem processes. Here, we tested the hypothesis that changes in traits of living plants induced by such changes resulted in changes in the quality and decay properties of the litter produced by the different communities. This was done in the context of a secondary succession following land abandonment in the Mediterranean region of Southern France.During the course of succession, species with high specific leaf area (the ratio of leaf area to leaf mass), low leaf dry matter content (the ratio of leaf dry mass to leaf fresh mass) and high leaf nitrogen concentration were progressively replaced by species with opposite characteristics. Accordingly, the initial litter concentrations of carbon (C) and nitrogen (N) decreased, while their C:N ratio and their hemicellulose concentration increased with time after abandonment.Early-successional communities had faster rates of litter decay and N release from litter, but these differences damped out with decomposition time. Nitrogen release from litter was related to initial litter chemical composition, particularly to its N concentration. This also held for litter decay rate, but only during the first 18 months of decomposition.Community functional parameters (i.e. trait values weighed according to the relative abundance of species) were tightly linked to initial litter N concentration, and thereby to litter decay and N loss rates. The strongest correlations were found with leaf dry matter content, which therefore appears as a powerful marker of litter properties. This provides further evidence that characteristics of living leaves persist in litter, and that some ecosystem processes can be inferred from plant functional traits.

Remobilization of internal resources is an important mechanism enabling plants to be partly independent of external nutrient availability. We assessed resource remobilization during the growing period in woody and foliar tissues of leafy branches of mature evergreen Mediterranean oak (Quercus ilex L.) at three field sites. We compared nonstructural carbohydrates, lipids, nitrogen and phosphorus pools in leaves and stems before bud burst (March) and at the end of the growing period (July). We also experimentally defoliated leafy branches to determine the storage function of old leaves. Changes in pools of carbon compounds in leaves and stems during spring and in response to defoliation indicated that foliar and woody tissues could provide carbon to support shoot growth. Independently of stem age, soluble sugar and lipid pools decreased significantly during spring. Changes in leaf pools between March and July involved all compounds measured except starch and were accompanied by a 5% decrease in mean leaf biomass. During the same period, 15% of the nitrogen and 25% of the phosphorus were removed from leaves. In contrast, woody tissues did not remobilize nitrogen or phosphorus. Our results support earlier hypotheses that leaves of evergreen species have a primary role in resource remobilization.

Summary — The biochemical nature of leaf litter is a key factor in regulation of its decomposition. Conventional wet chemical analysis of samples is destructive, time-consuming and expensive. The objective of this study was to evaluate the potentiality of near infrared reflectance spectroscopy (NIRS) for determining litter chemistry during the decomposition process using a wide range of species and decomposition stages. The litter of 8 species of evergreen and deciduous broad-leaved trees, conifers and shrubs were used in both laboratory and field experiments. Near-infrared reflectance measurements were made with an NIRS Systems 5000 spectrophotometer over the range 1100-2500 nm. Calibration samples were analysed for ash, carbon and nitrogen. Acid-detergent fiber (ADF) and acid-detergent lignin (ADL) were determined using Van

Twelve leaf litters belonging to 10 Mediterranean species of coniferous and broad-leaved trees and shrubs and grass species were incubated in microcosms in the laboratory at 22 °C and constant humidity for 14 months. Samples were collected at 0.5, 1, 2, 4, 6, 10, and 14 months, the remaining dry weight being measured at each sampling time. At the end of 14 months, the litters had lost between 52 and 74% of their original mass. The comparison of regressions fitted to the various functions showed that for the species studied, the litter mass loss in relation to incubation time best fitted a double-exponential decay function. The mass loss therefore resulted from the simultaneous decomposition of two main compartments, a labile compartment that decreased rapidly (half-life of 20 – 60 days under the experimental conditions) and a resistant compartment that depending on the species, either did not decrease significantly or decreased 10 to 20 times slower than the labile compartment (half-life of 320–630 days). The litters studied could be categorized according to the relative importance of these two compartments. This was related to the initial content of water-soluble substances and of carbon in the litters. It was also strongly correlated with the spectral information of the initial litters obtained by near-infrared reflectance spectroscopy. In contrast, the rate at which the labile and resistant compartments decreased was related to the permeability of the leaves for the former and to their thickness and mass per surface area for the latter. Near-infrared reflectance spectroscopy provides new perspectives for characterizing the capacity of litters to decompose. Key words: litter, decomposition, near infrared reflectance spectroscopy.

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Despite its importance for the understanding of element cycles in ecosystems, organic matter (OM) quality has remained an elusive property that is difficult to measure. In this study, two new approaches, both of which taking into account the complete biochemical composition of the organic material during the decomposition process, have been combined to solve this problem. First, following the continuous‐quality theory where quality is defined as a measure of substrate availability to the decomposers, initial litter OM qualities of a range of plant species from two experiments on litter decomposition were estimated and resulted in highly accurate fits of observed mass loss during decomposition. Applying the same theory, qualities of the litters at all stages of decomposition were then calculated. By comparison, the initial qualities of the same litters were estimated from conventional chemical fractions and resulted in much lower accurate fits. Second, near‐infrared reflectance spectroscopy (NIRS), a highly precise physical method of characterising biochemical composition of OM, was used to obtain a unique spectral signature of each sample. Calibrations were performed between spectral data and calculated qualities on the first half of the sample set and the calibration equations were applied to the second half of the sample set. Results show that theoretical litter OM quality can be calibrated and predicted precisely using NIRS. OM quality, defined according to a theoretical concept of substrate availability to decomposers, then contains and summarises all the relevant biochemical information. We demonstrate how the combination of NIRS and theory allows us to accurately measure OM quality. Measurement of OM quality provides an access to a fundamental property of organic matter and opens up new possibilities for studying element cycles in ecosystems.