The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
Daniel Epron - One of the best experts on this subject based on the ideXlab platform.
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Relating coarse root respiration to root diameter in clonal Eucalyptus stands in the Republic of the Congo
Tree physiology, 2008Co-Authors: Claire Marsden, Yann Nouvellon, Daniel EpronAbstract:Root respiration is an important component of the carbon balance of a forest ecosystem. We measured CO2 efflux of excised fine roots and intact coarse roots in 3-, 4- and 13-year-old Eucalyptus stands in the region of Pointe-Noire, Republic of the Congo. A transportable and adaptable closed Chamber Gas exchange system directly measured CO2 efflux of roots from 0.5 to 32 mm in diameter. Fluxes were corrected for measurement system leaks and normalized to a reference temperature of 30 degrees C. Mean fine root respiration rates at the reference temperature varied between 8.5 and 10.8 micromol CO2 kg(-1) s(-1) depending on the stand. Coarse root respiration was strongly negatively correlated to root diameter. We propose a model based on a radial gradient of respiratory activity within the root to simulate the exponential decrease in respiration with diameter. Although many sources of uncertainty in the measurements remain, as discussed in this paper, these results provide a basis for scaling up organ-level root respiration measurements to the tree and stand levels.
Liwei Wang - One of the best experts on this subject based on the ideXlab platform.
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the influence of nitrogen fertiliser rate and crop rotation on soil methane flux in rain fed potato fields in wuchuan county china
Science of The Total Environment, 2015Co-Authors: Liwei Wang, Hui Xu, Cheng Wang, Peiyi Zhao, Zhiqiang Dong, Jingting Zhang, Sen Wang, Hui ZhaoAbstract:As one of the important greenhouse Gases, the characteristics and principles of methane exchange characteristics in cultivated lands have become hot topics in current climate change research. This study examines the influences of nitrogen fertilisation, temperature and soil water content on methane exchange characteristic and methane exchange functional gene-pmoA gene abundance based on experimental observations of methane exchange fluxes using the static Chamber–Gas chromatographic method and measurements of methanotroph gene copy numbers in three growing periods by real-time PCR in rain-fed potato fields. The results indicate that the rain-fed potato fields were a CH4 sink with an average annual methane absorption (negative emission) of 940.8 ± 103.2 g CH4-C/ha/year. The cumulative methane absorption first exhibited flat and subsequently increasing trend with the increase of nitrogen fertilisation from 0 ~ 135 kg N·ha− 1. Methane cumulative absorption significantly increased with the increase of temperature when temperatures were below 19.6 °C. Methane oxidation capacity (methanotroph pmoA gene copy numbers) showed an increasing and subsequently decreasing trend with the increase of soil moisture. Crop rotation was observed to increase the methane absorption in rain-fed potato fields and nearly one time higher than that under continuous cropping. A mechanism concept model of the methane exchange in rain-fed potato fields was advanced in this paper.
Claire Marsden - One of the best experts on this subject based on the ideXlab platform.
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Relating coarse root respiration to root diameter in clonal Eucalyptus stands in the Republic of the Congo
Tree physiology, 2008Co-Authors: Claire Marsden, Yann Nouvellon, Daniel EpronAbstract:Root respiration is an important component of the carbon balance of a forest ecosystem. We measured CO2 efflux of excised fine roots and intact coarse roots in 3-, 4- and 13-year-old Eucalyptus stands in the region of Pointe-Noire, Republic of the Congo. A transportable and adaptable closed Chamber Gas exchange system directly measured CO2 efflux of roots from 0.5 to 32 mm in diameter. Fluxes were corrected for measurement system leaks and normalized to a reference temperature of 30 degrees C. Mean fine root respiration rates at the reference temperature varied between 8.5 and 10.8 micromol CO2 kg(-1) s(-1) depending on the stand. Coarse root respiration was strongly negatively correlated to root diameter. We propose a model based on a radial gradient of respiratory activity within the root to simulate the exponential decrease in respiration with diameter. Although many sources of uncertainty in the measurements remain, as discussed in this paper, these results provide a basis for scaling up organ-level root respiration measurements to the tree and stand levels.
Paul Meredith - One of the best experts on this subject based on the ideXlab platform.
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electron Gas interactions in the environmental scanning electron microscopes Gaseous detector
Scanning, 2006Co-Authors: Paul Meredith, A M Donald, Bradley L ThielAbstract:The construction of high signal-to-noise, artefact free secondary electron images in the elevated pressure conditions of an environmental SEM is a nontrivial process. The interactions of information carrying species, as well as probe beam electrons, with the Chamber Gas are the major reasons for such complications. In this paper, we discuss and review the present understanding of these phenomena. In addition, we outline procedures for assessing the signal-amplifying and charge-neutralising capabilities of an environmental Gas. It is only with a knowledge of such parameters and an appreciation of the Gas-electron collision processes that one can optimise the microscope's operating parameters. Moreover, such information enables the separation of topographic detail from artefactual features in the detected electron images.
Guang-li Yang - One of the best experts on this subject based on the ideXlab platform.
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effects of winter cover crops straws incorporation on ch4 and n2o emission from double cropping paddy fields in southern china
PLOS ONE, 2014Co-Authors: Hai Ming Tang, Xiao Ping Xiao, Weiyan Li, Wen-guang Tang, Ke Wang, Guang-li YangAbstract:Residue management in cropping systems is believed to improve soil quality. However, the effects of residue management on methane (CH4) and nitrous oxide (N2O) emissions from paddy field in Southern China have not been well researched. The emissions of CH4 and N2O were investigated in double cropping rice (Oryza sativa L.) systems with straw returning of different winter cover crops by using the static Chamber-Gas chromatography technique. A randomized block experiment with three replications was established in 2004 in Hunan Province, China, including rice–rice–ryegrass (Lolium multiflorum L.) (Ry-R-R), rice–rice–Chinese milk vetch (Astragalus sinicus L.) (Mv-R-R) and rice–rice with winter fallow (Fa-R-R). The results showed that straw returning of winter crops significantly increased the CH4 emission during both rice growing seasons when compared with Fa-R-R. Ry-R-R plots had the largest CH4 emissions during the early rice growing season with 14.235 and 15.906 g m−2 in 2012 and 2013, respectively, when Ry-R-R plots had the largest CH4 emission during the later rice growing season with 35.673 and 38.606 g m−2 in 2012 and 2013, respectively. The Ry-R-R and Mv-R-R also had larger N2O emissions than Fa-R-R in both rice seasons. When compared to Fa-R-R, total N2O emissions in the early rice growing season were increased by 0.05 g m−2 in Ry-R-R and 0.063 g m−2 in Mv-R-R in 2012, and by 0.058 g m−2 in Ry-R-R and 0.068 g m−2 in Mv-R-R in 2013, respectively. Similar result were obtained in the late rice growing season, and the total N2O emissions were increased by 0.104 g m−2 in Ry-R-R and 0.073 g m−2 in Mv-R-R in 2012, and by 0.108 g m−2 in Ry-R-R and 0.076 g m−2 in Mv-R-R in 2013, respectively. The global warming potentials (GWPs) from paddy fields were ranked as Ry-R-R>Mv-R-R>Fa-R-R. As a result, straw returning of winter cover crops has significant effects on increase of CH4 and N2O emission from paddy field in double cropping rice system.