جستجوی مقالات مرتبط با کلیدواژه "چرخه کربن" در نشریات گروه "آب و خاک"

The qualitative characteristics of forest soils can change under the influence of complex climatic interactions, soil type, management type, and tree species type. The aim of this study was to investigate the variability of soil quality characteristics in two forest plantations of Quercus castaneifolia C. A. Mey and Pinus radiate D. Don in Wood and PaperForests of Mazandaran Province. In both stands, 36 samples were randomly selected for determination of soil physical characteristics, in one season (autumn), and chemical and biological characteristics, in four seasons (autumn, winter, spring and summer). Physical characteristics (clay, silt, sand, moisture, bulk density and lime), chemical characteristics (pH, EC, nitrogen, phosphorus, potassium, carbon to nitrogenratio) and soil biology (soil respiration, microbial biomass carbon, fine root biomass, metabolic rate, and urease enzyme activity) were measured. The results of this study showed that the concentration of nitrogen, phosphorus and enzyme urease activity in oak stands was significantly higher than pine stand (p < /span><0.01), but potassium concentrations were significantly (p < /span><0.01) higher in the pine stand. In all seasons, the rate of soil respiration in the pine stand was higher than in the oak, but this difference was only significant in summer (p <0.05). Characteristics such as carbon to nitrogen ratio, soil carbon, microbial biomass carbon, fine root biomass, and metabolic coefficient were significantly higher in pine stand than in oak in all seasons (p <0.01). The results of this study showed that, in the nitrogen cycle, the oak stand, but in relation to the carbon cycle and global warming, the pine stand had more effects on the soil characteristics. Overall, the practical results of this study suggest that, to improve soil conditions in the degraded forestlands in northern parts of Iran, plantation of oak species is preferred.

Stratification ratio of soil organic matter and aggregate stability are considered as indicators of soil quality under different conditions such as burning rangeland vegetation. The objective of this study was to investigate the impact of fire on stratification ratio of soil organic matter and aggregate stability and distribution of organic matter in two macro and micro fractions in semi-steppe rangeland of Karsanak region in Chaharmahal and Bakhtiari province. Several sites which were affected by fire three، two، and one years before this study (i. e. 2008، 2009، and 2010، respectively) were chosen. Since the soil samples were taken from two depths (0-10 cm and 15-25 cm) of each site with 9 replications، the numbers of soil samples for laboratory analysis were 108. Independent t-test (P= 5%) was used to assess the difference between the measured properties at the burned and control sites. The results showed that the soil organic matter and mean weight diameter of aggregates (MWD) in the surface layer decreased significantly in 1 and 2 years after fire. Particulate organic matter (POM) significantly decreased in surface layer of the burned areas compared with the control areas. The effects of fire on stratification ratio of soil organic matter in 1- and 2-years after fire were significant compared with control areas، and stratification of soil organic matter decreased 26% and 22 percent in 1 and 2 years after fire، respectively. Stratification ratio of aggregate stability was lower in all burned areas compared with control areas، but the differences were not significant. Macro organic matter of both surface and subsurface layers in 1 year after fire was significantly reduced compared with the control، while، micro organic matter of subsurface layer showed significant increase. The study results showed that the effect of fire on physical and chemical soil properties in the surface layer were more than subsurface layer، because of higher-severity fire in surface layer. Furthermore، due to reduction of organic matter and aggregate stability after fire، rangeland soil quality decreased.