Labile and stabile soil organic carbon fractions in surface horizons of mountain soils–relationships with vegetation and altitude

Global and local climate changes could disturb carbon sequestration and carbon stocks in forest soils. Thus, it is important to characterize the stability of soil organic matter and the dynamics of soil organic carbon(SOC) fractions in forest ecosystems. This study had two aims:(1) to evaluate the effects of altitude and vegetation on the content of labile and stabile forms of organic carbon in the mountain soils; and(2) to assess the impact of the properties of soil organic matter on the SOC pools under changing environmental conditions. The studies were conducted in the Karkonosze Mountains(SW Poland, Central Europe). The content of the most labile fraction of carbon(dissolved organic carbon,DOC) decreases with altitude, but the content of fulvic acids(FA), clearly increases in the zone above 1000 m asl, while the stabile fraction(humins, nonhydrolyzing carbon) significantly decreases. A higher contribution of stabile forms was found in soils under coniferous forests(Norway spruce), while a smaller-under deciduous forests(European beech) and on grasslands. The expected climate change and the ongoing land use transformations in the zone above1000 m asl may lead to a substantial increase in the stable humus fraction(mainly of a non-hydrolyzing carbon) and an increase in the SOC pools, even if humus acids are characterized by a lower maturity and greater mobility favorable to soil podzolization.In the lower zone(below 1000 m asl), a decrease in the most stable humus forms can be expected,accompanied by an increase of DOC contribution,which will result in a reduction in SOC pools. Overall,the expected prevailing(spatial) effect is a decreasing contribution of the most stable humus fractions,which will be associated with a reduction in the SOC pools in medium-high mountains of temperate zone of Central Europe.

The variation of sediments organic carbon content in Chongming east tidal flat during Scirpus mariqueter growing stage

The investigations on the organic carbon （OC） of core sediments were carried out in Chongming east tidal fiat （CM） during Scirpus mariqueter growing stage （from April to December 2004） in Yangtze Estuary. The Yangtze River annually transports a runoff discharge of 30,000 m^3/s, carrying about 480 million tons of sediments to the estuarine and coastal area, which formed a great OC pool. In the sampling spots, seven quadrats of 50 cm × 50 cm and five sediments cores of 20 cm deep （40 cm deep in December） were randomly established in order to collect vegetations and core sediments samples during the low tide each month except November. After pretreatment, the core sediments were sieved and their OC contents were measured according to the potassium dichromate method. The results show that the higher surface sediment OC content in summer comes from allochthonous terrigenous particle settlements on the Chongming east middle tidal fiat S. mariqueter zone. In autumn and winter, the decomposing of the defoliated S. mariqueter increases the surface sediments OC content. Settling velocity, sediment temperature and S. mariqueter growth are the main factors that can control the sediment carbon content. Summer is the “carbon losing” period of the tidal fiat sediments, while from September, it changes into the “carbon accumulating” period of sediment OC pool because of the decomposing of dead S. mariqueter community in the sediments. From this alternation of “carbon losing” period and “carbon accumulating” period, we conclude that carbon in the OC pool of the middle tidal fiat S. mariqueter zone sediments mainly comes from the atmospheric carbon rooted by S. mariqueter photosynthesis.

Pool Sizes and Turnover of Soil Organic Carbon of Farmland Soil in Karst Area of Guilin

The three-pool and first-order model separates the mineralizable organic carbon into active,slow,and passive carbon pools.This paper used the model and decomposition curves of the soil organic carbon to fit the active pool and its decomposition rate,slow pool and its decomposition rate.The results showed that the size of the active pool from different profiles accounted for 2.09%-3.08% of the total soil organic carbon and the mean residue time was 3.57-17.21 days.And the size of the slow pool accounted for 3.19%-43.55% and the mean residue time was 1.12-4.94 years.Acid hydrolysis（6M HCl） was used to fractionate the passive organic carbon,which accounted for 50.83%-94.44% of the total soil organic carbon.

Non-climate environmental factors matter to Holocene dynamics of soil organic carbon and nitrogen in an alpine permafrost wetland,Qinghai‒Tibet Plateau

Studies on the responses of soil organic carbon(SOC)and nitrogen dynamics to Holocene climate and environment in permafrost peatlands and/or wetlands might serve as analogues for future scenarios,and they can help predict the fate of the frozen SOC and nitrogen under a warming climate.To date,little is known about these issues on the Qinghai‒Tibet Plateau(QTP).Here,we investigated the accumulations of SOC and nitrogen in a permafrost wetland on the northeastern QTP,and analyzed their links with Holocene climatic and environmental changes.In order to do so,we studied grain size,soil organic matter,SOC,and nitrogen contents,bulk density,geochemical parameters,and the accelerator mass spectrometry(AMS)^(14)C dating of the 216-cm-deep wetland profile.SOC and nitrogen contents revealed a general uptrend over last 7300 years.SOC stocks for depths of 0-100 and 0-200 cm were 50.1 and 79.0 kgC m^(-2),respectively,and nitrogen stocks for the same depths were 4.3 and 6.6 kgN m^(-2),respectively.Overall,a cooling and drying trend for regional climate over last 7300 years was inferred from the declining chemical weathering and humidity index.Meanwhile,SOC and nitrogen accumulated rapidly in 1110e720 BP,while apparent accumulation rates of SOC and nitrogen were much lower during the other periods of the last 7300 years.Consequently,we proposed a probable conceptual framework for the concordant development of syngenetic permafrost and SOC and nitrogen accumulations in alpine permafrost wetlands.This indicates that,apart from controls of climate,non-climate environmental factors,such as dust deposition and site hydrology,matter to SOC and nitrogen accumulations in permafrost wetlands.We emphasized that environmental changes driven by climate change have important impacts on SOC and nitrogen accumulations in alpine permafrost wetlands.This study could provide data support for regional and global estimates of SOC and nitrogen pools and for global models on carbon‒climate interactions that take into account of alpine permafrost wetlands on the northeastern QTP at mid-latitudes.