Altitudinal variation in soil organic carbon stock in coniferous subtropical and broadleaf temperate forests in Garhwal Himalaya

<p>Abstract</p> <p>Background</p> <p>The Himalayan zones, with dense forest vegetation, cover a fifth part of India and store a third part of the country reserves of soil organic carbon (SOC). However, the details of altitudinal distribution of these carbon stocks, which are vulnerable to forest management and climate change impacts, are not well known.</p> <p>Results</p> <p>This article reports the results of measuring the stocks of SOC along altitudinal gradients. The study was carried out in the coniferous subtropical and broadleaf temperate forests of Garhwal Himalaya. The stocks of SOC were found to be decreasing with altitude: from 185.6 to 160.8 t C ha^-1and from 141.6 to 124.8 t C ha^-1in temperature (<it>Quercus leucotrichophora</it>) and subtropical (<it>Pinus roxburghii</it>) forests, respectively.</p> <p>Conclusion</p> <p>The results of this study lead to conclusion that the ability of soil to stabilize soil organic matter depends negatively on altitude and call for comprehensive theoretical explanation</p

Nitrogen and Carbon Isotopic Dynamics of Subarctic Soils and Plants in Southern Yukon Territory and its Implications for Paleoecological and Paleodietary Studies

We examine here the carbon and nitrogen isotopic compositions of bulk soils (8 topsoil and 7 subsoils, including two soil profiles) and five different plant parts of 79 C3 plants from two main functional groups: herbs and shrubs/subshrubs, from 18 different locations in grasslands of southern Yukon Territory, Canada (eastern shoreline of Kluane Lake and Whitehorse area). The Kluane Lake region in particular has been identified previously as an analogue for Late Pleistocene eastern Beringia. All topsoils have higher average total nitrogen δ15N and organic carbon δ13C than plants from the same sites with a positive shift occurring with depth in two soil profiles analyzed. All plants analyzed have an average whole plant δ13C of −27.5 ± 1.2 ‰ and foliar δ13C of ±28.0 ± 1.3 ‰, and average whole plant δ15N of −0.3 ± 2.2 ‰ and foliar δ15N of ±0.6 ± 2.7 ‰. Plants analyzed here showed relatively smaller variability in δ13C than δ15N. Their average δ13C after suitable corrections for the Suess effect should be suitable as baseline for interpreting diets of Late Pleistocene herbivores that lived in eastern Beringia. Water availability, nitrogen availability, spacial differences and intra-plant variability are important controls on δ15N of herbaceous plants in the study area. The wider range of δ15N, the more numerous factors that affect nitrogen isotopic composition and their likely differences in the past, however, limit use of the modern N isotopic baseline for vegetation in paleodietary models for such ecosystems. That said, the positive correlation between foliar δ15N and N content shown for the modern plants could support use of plant δ15N as an index for plant N content and therefore forage quality. The modern N isotopic baseline cannot be applied directly to the past, but it is prerequisite to future efforts to detect shifts in N cycling and forage quality since the Late Pleistocene through comparison with fossil plants from the same region

Soil organic matter processes: Characterization by 13C NMR and 14C measurements

Soil organic matter (SOM) is a central contributor to soil quality as it mediates many of the chemical, physical, and biological processes controlling the capacity of a soil to perform successfully. SOM properties (e.g. C/N ratio, macro-organic matter) have been proposed as diagnostic criteria of overall soil fitness, but their use is hampered by a poor understanding of the basic biochemical principles underlying SOM processes. The objective of this project was to determine the influence of scrub oak (Quercus dumosa Nutt.) and Coulter pine (Pinus coulteri B. Don) vegetation on decomposition and SOM formation processes in a lysimeter installation constructed in 1936 in the San Gabriel mountains of Southern California. Soil samples archived during construction of the installation, and A horizons sampled in 1987, were fractionated according to density and mineral particle size to isolate the water floatable (macro-organic matter), fine silt and clay fractions. Carbon turnover rates were determined on all fractions from AMS 14C measurements. Solid state CPMAS TOSS 13C NMR was used to semiquantitatively characterize the chemical structure of organic matter on fresh litter and soil fractions. For the two soils, there was a progressive decrease in O-alkyl C, and an increase in alkyl and carbonyl C from the litter to the floatable, fine silt and clay fractions. These compositional differences were due to the oxidative degradation of the litter material, with preferential decomposition of the cellulose and hemicellulose entities and selective preservation of recalcitrant waxes and resins. In all soil fractions, turnover rates of carbon were longer for the pine than for the oak lysimeter (up to 10 times longer). Also under pine, there was a gradual increase in turnover rate progressing from the floatable to the clay fraction, and differences in turnover rates among fractions may be explained based on differences in carbon chemistry. In contrast, under oak, rapid carbon turnover for all fractions suggested intense biological activity in this soil. © 2000 Published by Elsevier Science B.V

Vegetation control on soil organic matter dynamics

Soil organic matter (SOM) formation is one of the least understood steps of the global carbon cycle. An example is uncertainty around the role of plant communities in regulating SOM formation and turnover. Here we took advantage of the highly controlled conditions at the San Dimas lysimeter installation to quantify the influence of oak and pine vegetation on SOM dynamics. SOM turnover rates, estimated using total C and 14C content of litter and physically separable soil fractions, were faster under oak than under pine. In contrast to the rapid turnover for the oak litter (&lt; 2 years), the delay in litter incorporation into the mineral soil under pine was a controlling factor of SOM fluxes. © 2001 Published by Elsevier Science Ltd

Reduced complexity of multidimensional and diffusion NMR spectra of soil humic fractions as simplified by Humeomics

Background: Humeomics is a sequential step-wise chemical fractionation that simplifies the complex matrix of a humic acid (HA) and weakens its supramolecular interactions, thereby allowing a detailed characterization of the involved molecules. A recalcitrant residual end product of Humeomics, namely RES4, was successfully solubilized here in alkaline conditions and subjected to a semi-preparative high-performance size exclusion chromatography (HPSEC). Results: The resulting six size fractions separated by HPSEC were analyzed by different NMR techniques. 1D 1H-NMR spectra did not reveal significant molecular differences among size fractions, although all of them differed from the spectrum of the bulk RES4 especially in signal intensity for aliphatic materials, which were assigned by 2D NMR to lipidic structures. Diffusion-ordered spectroscopy (DOSY)-NMR spectra showed that the homogeneity of RES4 was significantly changed by the HPSEC separation. In fact, nominally large size fractions, rich in lipidic signals, had significantly lower and almost constant diffusivity, due to stable supramolecular associations promoted by hydrophobic interactions among alkyl chains. Conversely, diffusivity is gradually increased with the content of aromatic and hydroxyaliphatic signals, which accompanied the reduction of fractions sizes and was related to smaller superstructures. Conclusions: This study not only confirmed the occurrence of supramolecular structures in the recalcitrant humic residue of Humeomics, but also highlighted that more homogeneous size fractions were more easily characterized by NMR spectroscopy