Negative thermal expansion of water in hydrophobic nanospaces

The density and intermolecular structure of water in carbon micropores (w = 1.36 nm) are investigated by small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) measurements between 20 K and 298 K. The SAXS results suggest that the density of the water in the micropores increased with increasing temperature over a wide temperature range (20-277 K). The density changed by 10%, which is comparable to the density change of 7% between bulk ice (I(c)) at 20 K and water at 277 K. The results of XRD at low temperatures (less than 200 K) show that the water forms the cubic ice (I(c)) structure, although its peak shape and radial distribution functions changed continuously to those of a liquid-like structure with increasing temperature. The SAXS and XRD results both showed that the water in the hydrophobic nanospaces had no phase transition point. The continuous structural change from ice I(c) to liquid with increasing temperature suggests that water shows negative thermal expansion over a wide temperature range in hydrophobic nanospaces. The combination of XRD and SAXS measurements makes it possible to describe confined systems in nanospaces with intermolecular structure and density of adsorbed molecular assemblies.ArticlePHYSICAL CHEMISTRY CHEMICAL PHYSICS. 14(2):981-986 (2012)journal articl

Long-term fertilisation impact on temperature sensitivity of aggregate associated soil organic carbon in a sub-tropical inceptisol

Understanding impact of long-term fertilisation on soil aggregation, carbon (C) stabilisation and temperature sensitivity of soil organic C (SOC) mineralisation are necessary to foresee C dynamics. The present study was conducted in an Inceptisol under wheat (Triticum aestivum) based cropping system, with the objective to quantify the effect of 44 years of integrated nutrient management on soil aggregation, enzymatic activity, and temperature sensitivity (Q(10)) of SOC. Treatments were: unfertilised control (UC), 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), integrated application of NPK and farmyard manure (FYM) (NPKF) and 150% recommended dose of N, P and K (1.5NPK). The observed data were analysed using analysis of variance for randomized block design and Tukey's HSD test (P < 0.05) was used for mean separation. In the 0-15 cm soil layer, plots under NPKF had (similar to)121 and 19% larger macroaggregate-associated C than UC and NPK plots, respectively. Irrespective of soil depth and temperature, higher cumulative C mineralisation was observed for NPKF (by (similar to)67-91%) and NPK (by (similar to)42-56%) treated plots than UC. Activation energies for SOC decomposition in 0-15 cm bulk soil were (similar to)205, and 258% higher in NPKF, and 1.5NPK, respectively, than UC plots. Mean Q(10) of macroaggregate-C was higher than microaggregate-C. Aggregate-C of sub-surface soil was more temperature sensitive than surface soil, possibly due to higher recalcitrant/total SOC in the subsurface than surface layer. Thus, it reveals the need of better C management practices to augment the lability of C in subsurface soil layers. Plots under NPKF had higher beta-glucosidase and fluorescein diacetate activities in bulk soils and aggregates over NPK in the both layers. NPKF application is recommended for improved soil aggregation, SOC protection within macroaggregates, enzyme activities in bulk soils and aggregates and capable for less proportional SOC decomposition than NPK or UC plots at higher temperature. Thus, soil management involving organic manure application and mineral fertilisers would enhance the activation energy of SOC and act as a barrier for SOC decomposition by facilitating soil aggregation and enhance SOC sequestration

Differentiating biological and chemical factors of top and deep soil carbon sequestration in semi-arid tropical Inceptisol: an outcome of structural equation modeling

Though soils sequester large amounts of carbon (C), variations in physical and chemical characteristics of top and deep layers necessitate the study of factors governing topsoil and deep soil C sequestration to predict land-use changes to alleviate climate change. Land-use systems involving pasture, trees, trees  pasture and fallow were considered. The upper soil (0–15 cm) had ∼12, 34 and 59% higher microbial biomass C than the 15–30, 30–45 and 45–60 cm layers, respectively. Fluorescein diacetate (FDA) and dehydrogenase activities had similar trends. Across the land uses, topsoil layers had ∼17% lower silt + clay (s + c) content than deep layers. Amorphous iron content significantly increased with soil depth. In the top two soil layers, s + c accounted for ∼19–30% of total soil organic carbon (SOC); in the next two layers s + c could store >30% of total SOC. Stepwise regression analysis revealed FDA to be the most significant biological driver for SOC sequestration. Structural equation modeling showed that biological factors controlled C sequestration in topsoil layers, while s + c and amorphous iron were the major factors of C sequestration in deep layers. Current land uses are largely deficient of SOC and have the potential to store an additional22 Mg CO2e per ha