Methane Dynamics in Northern Peatlands: A Review

Northern peatlands store a large amount of carbon and play a significant role in the global carbon cycle. Owing to the presence of waterlogged and anaerobic conditions, peatlands are typically a source of methane (CH4), a very potent greenhouse gas. This paper reviews the key mechanisms of peatland CH4 production, consumption and transport and the major environmental and biotic controls on peatland CH4 emissions. The advantages and disadvantages of micrometeorological and chamber methods in measuring CH4 fluxes from northern peatlands are also discussed. The magnitude of CH4 flux varies considerably among peatland types (bogs and fens) and microtopographic locations (hummocks and hollows). Some anthropogenic activities including forestry, peat harvesting and industrial emission of sulphur dioxide can cause a reduction in CH4 release from northern peatlands. Further research should be conducted to investigate the in fluence of plant growth forms on CH4 flux from northern peatlands, determine the water table threshold at which plant production in peatlands enhances CH4 release, and quantify peatland CH4 exchange at plant community level with a higher temporal resolution using automatic chambers.

Spatio-temporal Variation of Soil Respiration and Its Driving Factors in Semi-arid Regions of North China

Soil respiration （SR） is the second-largest flux in ecosystem carbon cycling. Due to the large spatio-temporal variability of environmental factors, SR varied among different vegetation types, thereby impeding accurate estimation of CO2 emissions via SR. However, studies on spatio-temporal variation of SR are still scarce for semi-arid regions of North China. In this study, we conducted 12-month SR measurements in six land-use types, including two secondary forests （Populus tomentosa （PT） and Robinia pseudoacacia （RP））, three artificial plantations （Armeniaca sibirica （AS）, Punica granatum （PG） and Ziziphusjujuba （Z J）） and one natural grassland （GR）, to quantify spatio-temporal variation of SR and distinguish its controlling factors. Results indicated that SR exhibited distinct sea- sonal patterns for the six sites. Soil respiration peaked in August 2012 and bottomed in April 2013. The temporal coefficient of variation （CI0 of SR for the six sites ranged from 76.98% to 94.08%, while the spatial CV of SR ranged from 20.28% to 72.97% across the 12-month measurement. Soil temperature and soil moisture were the major controlling factors of temporal variation of SR in the six sites, while spatial variation in SR was mainly caused by the differences in soil total nitrogen （STN）, soil organic carbon （SOC）, net photosynthesis rate, and fine root biomass. Our results show that the annual average SR and Q10 （temperature sensitivity of soil respira- tion） values tended to decrease from secondary forests and grassland to plantations, indicating that the conversion of natural ecosystems to man-made ecosystems may reduce CO2 emissions and SR temperature sensitivity. Due to the high spatio-temporal variation of SR in our study area, care should be taken when converting secondary forests and grassland to plantations from the point view of accurately quantifying C02 emissions via SR at regional scales.

Kinetics of native and added carbon mineralization on incubating at different soil and moisture conditions in Typic Ustochrepts and Typic Halustalf

The carbon dynamics in soils is of great importance due to its links to the global carbon cycle.The prediction of the behavior of native soil organic carbon(SOC)and organic amendments via incubation studies and mathematical modeling may bridge the knowledge gap in understanding complex soil ecosystems.Three alkaline Typic Ustochrepts and one Typic Halustalf with sandy,loamy sand,and clay loam texture,varying in percent SOC of 0.2;S_(1),0.42;S_(2),0.67;S_(3) and 0.82;S_(4) soils,were amended with wheat straw(WS),WS+P,sesbania green manure(GM),and poultry manure(PM)on 0.5%C rate at field capacity(FC)and ponding(P)moisture levels and incubated at 35℃for 1,15,30 and 45 d.Carbon mineralization was determined via the alkali titration method after 1,5,714,21,and 28 d.The SOC and inorganic carbon contents were determined from dried up(50℃)soil samples after 1,15,30,and 45 d of incubation.Carbon from residue mineralization was determined by subtracting the amount ofCO_(2)-C evolved from control soils.The kinetic models;monocomponent first order,two-component first or-der,and modified Gompertz equations were fitted to the carbon mineralization data from native and added carbon.The SOC decomposition was dependent upon soil properties,and moisture,however,added C was relatively independent.The carbon from PM was immobilized in S4.All the models fitted to the data predicted carbon mineralization in a similar range with few exceptions.The residues lead to the OC build-up in fine-textured soils having relatively high OC and cation exchange capacities.Whereas,fast degradation of applied OC in coarse-textured soils leads to faster mineralization and lower build-up from residues.The decline in CaCO_(3) after incubation was higher at FC than in the P moisture regime.

Efflux Estimate of Greenhouse Effect Gases in Three Different Forest Formations and the Influence of Soil

In carbon global cycle, the relationship between the terrestrial ecosystem and the atmosphere where there are, among others, gases that contribute to the greenhouse effect, has become object of relevant scientific interest. The content of organic matter in soil, expressed by its supplies as well as the organic matter degree of stability, are factors that can prevent the soil from acting as a drain and at the same time contribute for it to become a source of those gases. The variations in the way land is used in Brazil are factors responsible for the increase in emission of greenhouse effect gases. Based on these facts, this study was aimed to evaluate the CO2 and CH4 efflux using a gas retention chamber, and to associate these emissions to the organic carbon content in the soil. Two different areas were selected for the study, one in Tijuca Forest National Park, in a forest area, and the other at the Rio de Janeiro Federal Rural University campus. In the latter, the area was stratified in three sub areas according to the vegetation, use and water saturation degree. Samplings were performed during 8 months between 2013 and 2014.

Selective Extraction Methods for Aluminium,Iron and Organic Carbon from Montane Volcanic Ash Soils

Montane volcanic ash soils contain disproportionate amounts of soil organic carbon and thereby play an often underestimated role in the global carbon cycle.Given the central role of Al and Fe in stabilizing organic matter in volcanic ash soils,we assessed various extraction methods of Al,Fe,and C fractions from montane volcanic ash soils in northern Ecuador,aiming at elucidating the role of Al and Fe in stabilizing soil organic matter(SOM).We found extractions with cold sodium hydroxide,ammonium oxalate/oxalic acid,sodium pyrophosphate,and sodium tetraborate to be particularly useful.Combination of these methods yielded information about the role of the mineral phase in stabilizing organic matter and the differences in type and degree of complexation of organic matter with Al and Fe in the various horizons and soil profiles.Sodium tetraborate extraction proved the only soft extraction method that yielded simultaneous information about the Al,Fe,and C fractions extracted.It also appeared to differentiate between SOM fractions of different stability.The fractions of copper chloride-and potassium chloride-extractable Al were useful in assessing the total reactive and toxic Al fractions,respectively.The classical subdivision of organic matter into humic acids,fulvic acids,and humin added little useful information.The use of fulvic acids as a proxy for mobile organic matter as done in several model-based approaches seems invalid in the soils studied.

Recent leveling off of vegetation greenness and primary production reveals the increasing soil water limitations on the greening Earth

Global vegetation photosynthesis and productivity have increased substantially since the 1980s,but this trend is heterogeneous in both time and space.Here,we categorize the secular trend in global vegetation greenness into sustained greening,sustained browning and greening-to-browning.We found that by 2016,increased global vegetation greenness had begun to level off,with the area of browning increasing in the last decade,reaching 39.0 million km^(2)(35.9%of the world’s vegetated area).This area is larger than the area with sustained increasing growth(27.8 million km^(2),26.4%);thus,12.0%±3.1%(0.019±0.004 NDVI a^(-1))of the previous earlier increase has been offset since 2010(2010–2016,P<0.05).Global gross primary production also leveled off,following the trend in vegetation greenness in time and space.This leveling off was caused by increasing soil water limitations due to the spatial expansion of drought,whose impact dominated over the impacts of temperature and solar radiation.This response of global gross primary production to soil water limitation was not identified by land submodels within Earth system models.Our results provide empirical evidence that global vegetation greenness and primary production are offset by water stress and suggest that as global warming continues,land submodels may overestimate the world’s capacity to take up carbon with global vegetation greening.

Distinctive impacts of atmospheric intraseasonal oscillations on the net ecosystem exchange of the southeastern China forest between spring and summer

The southeastern China(SEC)forest is an important terrestrial biospheric carbon sink in the global carbon cycle,with its total net ecosystem exchange(NEE)accounting for about 3.2%of the global forest NEE.The prevailing atmospheric intraseasonal oscillations(ISOs)over East Asia strongly modulate climatic conditions over the SEC during spring and summer,thus leading to significant ISOs in the NEE of the SEC forest.As atmospheric ISOs show strong seasonality,this study examined the distinctive impacts of atmospheric ISOs on the NEE of the SEC forest between spring and summer.During spring,the vertical coupling of 10–30-d atmospheric ISOs in the lower and upper troposphere leads to strong 10‒30-d ISOs of solar radiation and temperature over the SEC.The 10‒30-d ISOs of solar radiation and temperature further result in the 10‒30-d ISOs of gross primary productivity(GPP)and terrestrial ecosystem respiration(TER).With the covariation in GPP and TER,the NEE of the SEC forest exhibits significant 10‒30-d ISOs.In contrast,the intraseasonal variations in climatic conditions over the SEC are associated with the 15‒60-d tropical atmospheric ISO during summer.While the induced 15‒60-d ISO of solar radiation leads to that of GPP,the induced 15‒60-d ISO of temperature is small and less effective;thus,the 15‒60-d ISO of NEE mainly originates from that of GPP.