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Accueil du site → Doctorat → Chine → 2015 → The Mechanisms of Different Grazing Managements on Leymus Chinensis Grassland Ecosystem Carbon Sequestration

Université de l’agriculture de Chine (2015)

The Mechanisms of Different Grazing Managements on Leymus Chinensis Grassland Ecosystem Carbon Sequestration

陈文青;

Titre : The Mechanisms of Different Grazing Managements on Leymus Chinensis Grassland Ecosystem Carbon Sequestration

Auteur : 陈文青;

Grade : Doctoral Dissertation 2015

Université : Université de l’agriculture de Chine

Résumé
Grasslands comprise approximately40%of the earth’s land area and over a quarter of the global potential for soil C storage may be influenced by grazing, as it is the most geographically expansive grassland use today. Although mammalian herbivores convert consumed plants into CO2and other greenhouse gases such as methane (CH4), appropriate grazing can often lower net ecosystem C emissions and promote soil C storage. The vegetation removal imposes direct impact on plant production, and thereby on potential soil C inputs. Grazers can also indirectly alter plant community composition through their diet selectivity and consequently influence soil C inputs. However, little is known about how animal consumption impacts plant production and composition, and thereby on soil C input under different grazing managements.In this study, we set a series of seasonal grazing practices to address the following three contents :(1) the mechanisms that mediate the diet selection of animals on natural grassland ;(2) effects of different grazing managements on soil C input ;(3) grazing effects on litter decomposition under different grazing managements. The results are as follows :(1) The diet composition of animal varied greatly according to seasonal variations and was influenced by grazing pressure. Diet proportion for each component plant species showed a positive and linear relationship with dry weight proportion of corresponding plant species on offer in the sward ; the seasonal variation of sheep diet composition is related to the vertical and horizontal availability of plant species ; however, the relative importance of these two variables differed. Horizontal availability was continuously dominant in influencing sheep consumption. Grazing impacts on plant species in different treatments also showed seasonal variations, and the species with higher horizontal availability may face higher grazing pressure.(2) Different grazing managements significantly affected plant above-and belowground production and thereby soil C input. The constant moderate grazing (MMM) exhibited the highest root production and turnover accumulating the most soil carbon. While deferred grazing (RHM and RMH) sequestered less soil carbon compared to MMM, they showed higher standing root mass, maintained a more desirable pasture composition, and had better ability to retain soil N. Constant high grazing pressure (HHH) caused diminished above-and belowground plant production, more soil N losses and an unfavorable microbial environment and had reduced carbon input. Reducing grazing pressure in the last grazing stage (HHM) still had a negative impact on soil carbon.(3) Grazing induced changes in micro-environment only affected the above-litter decomposition rates. The aboveground litter decomposed much faster than belowground litter. Vegetation coverage and soil moisture were the main factors controlling the aboveground litter, while the belowground litter decomposition was mainly affected by soil microbial biomass. Compared to the decomposition of belowground litter, the aboveground litter tended to be much more susceptible by grazing managements.In conclusion, vegetation distribution plays important role in influencing the diet selection of animal grazing on the natural grassland. The variation in plant production and composition under different grazing practices, mediated by animal consumption, affected the soil C input. Appropriate grazing managements can be designed to mitigate greenhouse gases and store soil carbon. Only aboveground litter decomposition was affected by grazing managements, and the aboveground litter tended to be much more susceptible to grazing than belowground litter

Mots clés : grazing managements; diet selection; plant production; soil organic carbon; litterdecomposition;

Présentation (CNKI)

Page publiée le 4 octobre 2017