Dynamic Changes Of Soil Greenhouse Gas Emissions After Conversion From Natural Forest To Plantations

Increasing in atmospheric concentrations of greenhouse gases and their contribution to global warming is a hot topic in the field of global change research.As an important part of terrestrial ecosystems,forest ecosystems account for 33% of global land area,forest soil carbon stocks accounted for about 40% of global soil carbon stocks.Forest soil is an important greenhouse gas emission sources or sinks.Land use and land cover changes on soil greenhouse gas emissions,changing the balance of global greenhouse gases.Conversion of forest land using changed in a common way,by changing the type of forest community structure and soil physical and chemical properties,affecting soil emissions of greenhouse gases directly or indirectly.Subtropical region of China accounted for about 25% of the country's land area,Natural broad-leaved forests?BL?is typical of the region,with the development of commercial forests,large areas of BL cutting into plantations,According to the National Afforestation Committee released the "2007 China afforestation Bulletin",Chinese plantation area of 0.62 million hm2,accounting for 1/3 of the world's plantation area,ranking first in the world,Masson pine plantation?MP?and Chinese fir plantation?CF?are subtropical region of China an important commercial forest.Experimental research of natural forest converted to plantations in greenhouse gases?CO₂,CH₄,and N₂O?fluxes and environmental factors?soil temperature,soil moisture,soil water-soluble organic carbon,soil water-soluble organic nitrogen content,soil NO3--N and soil NH4+-N content by locating a year?seasonal dynamic characteristics,reveals the influence of the mechanism of natural subtropical broad-leaved forest conversion to plantation on soil greenhouse gas fluxes variation and environmental factors.The results showed that:?1?Soil CO₂ emission of BL transformed to CB,MP and CF presents a consistent seasonal dynamics,the highest in summer and autumn,the lowest in winter and spring.Soil CO₂ efflux ranged fromwere 73.4-407.9 mg·m-2·h-1?60.9-417.8 mg·m-2·h-1?67.2-550.6 mg·m-2·h-1 and 14.9-434.9 mg·m-2·h-1 respectively,in BL?CB?MPand CF,soil CO₂ cumulative emissions were 16.5 t·hm-2·a-1?17.1 t·hm-2·a-1?21.1 t·hm-2·a-1 and 12.0 t·hm-2·a-1 respectively.BL converted to MP and CF,There was significant effect on the increasing in soil CO₂ emissions?P < 0.05?;translate to CB,there was no significant effect on soil CO₂ emissions.There was a significanteffect on 4 kinds of forests soil CO₂ emissions with soil temperature at 5cm depth?P < 0.05?,there was no correlation of 4 kinds of forests soil CO₂ emissions with soil moisture;Converting BL to CF and MP significantlyimproved the sensitivity of soil respiration to environmental factors,however,when BL transformed to CB,there was not improved the sensitivity of soil respiration to environmental factors.?2?Seasonal dynamics of 4 kinds of forests of soil N₂O emissions presents a consistent regularity,the highest in summer and autumn,the lowest in winter and spring.The annual average of soil N₂O emission of BL?CB?MP and CF were 35.8 ug·m-2·h-1?18.1 ug·m-2·h-1?27.4 ug·m-2·h-1 and 8.1 ug·m-2·h-1 respectively;The cumulative soil N₂O emission were 3.0 kg·hm-2·a-1?1.7 kg·hm-2·a-1?2.2 kg·hm-2·a-1 and 1.1 kg·hm-2·a-1 respectively,When BL convented to CB,MP and CF,The cumulative of soil N₂O emission was reduced by 42.2%?25.4 % and 63.1%,respectively.There was a significant of 4 kinds of forests of soil N₂O emission with soil temperature at 5cm depth and soil NH4+-N content,there was no correlation of 4 kinds of forests soil N₂O emission with soil moisture content?WFPS?and soil NO3--N content.There was a significant of the other three kinds of forest of soil CH₄ uptake with soil temperature at 5cm depth.There was no significant correlation between the soil CH₄ uptake of 4 kinds of forests and soil moisture.?4?BL,CB,MP and CF integrated total greenhouse effect were 17.2t g·CO₂·hm-2·a-1?17.5t g·CO₂·hm-2·a-1?21.6t g·CO₂·hm-2·a-1and 12.2 t g·CO₂·hm-2·a-1;With MP and CB compared to CF,the comprehensive warming potential of soil greenhouse gases was significantly reduced.