Long-term Intensive Management Effects On Soil Greenhouse Gases Emission In Lei Bamboo (Phyllostachys Praecox) Forests In Subtropical China

Forests are the world’s largest terrestrial ecosystems,and forest soils are the sources or sinks of atmospheric greenhouse gases.Forest managements（fertilization,cutting,burning,understory management）would react on soil properties and soil micro climate,and thus significantly affect the production and emission of soil greenhouse gases.Lei bamboo（Phyllostachys praecox）forest is an important economic forest tree species and widely distributed in southern China.There are 6.7 × 104 ha of Lei bamboo forests in Zhejiang province,accounting for 7.7% of the whole economic forest areas.Since the 80 s of last century,a method centered on heavy fertilization and use of organic mulch have gained popularity as a core technique for producing bamboo shoots early and increasing productivity.Both of those intensive management practices increased the economic return of bamboo forests.However,the long-term use of the above techniques could also result in a series of negative environmental and ecological consequences,such as soil acidification,soil N and P accumulation and degradation of soil carbon pool in the soil.Several studies demonstrated that intensive management would significantly change the SOC storage,soil nutrients and soil CO₂ emissions.However,the effects of long-term intensive management practices（fertilizer application and mulching）on soil greenhouse gas（GHG）remained poorly understood.To improve our understanding of how longterm intensive management influenced soil greenhouse gases,we conducted a one-year field study in Lei bamboo forests which included different intensive management chronosequence with duration under of 1,5,10,20,and 30 years.The result showed:（1）Intensive managements significantly increased total SOC,TN,AN,available P and K,WSOC,WSON,NH₄+-N,NO3--N concentrations（P<0.05）.MBC and MBN significantly increased in the first 20 years and then it significantly decreased.Soil pH and Bulk density decreased with time since intensive management（P<0.05）.（2）Soil CO₂ fluxes exhibited strong seasonal changes,with the maximum observed in July-August and the minimum value in January-February.Soil CO₂ fluxes in Lei bamboo forests with 1,5,10,20,and 30 years of intensive management were 338.89,337.53,374.52,491.10,364.14 mg·CO₂·m-2·h-1.No significant differences were observed in 1,5,10,30 years of soil CO₂ fluxes,but soil CO₂ fluxes in 20 years significantly increased（P<0.05）.Significant relationships between soil CO₂ emission and soil temperature were observed（P<0.05）.Soil CO₂ emission had significant positive relationships with soil WSOC,except 20 years（P<0.05）.The lack of a significant correlation between soil CO₂ emission and soil water content,MBC content was observed.（3）Soil N₂ O fluxes exhibited strong seasonal changes,with the maximum observed in the growing season and the minimum value in the non-growing season.Soil N₂ O fluxes in Lei bamboo forests with 1,5,10,20,and 30 years of intensive management were 54.10,155.19,202.34,246.53,315.17 μg·N₂O·m-2·h-1,respectively.Intensive management significantly increased the soil N₂ O cumulative fluxes（P<0.05）.The soil N₂ O cumulative with 5,and 30 years of intensive management were 3.07,3.48,4.00,5.74 times of that for the 1-year treatment,respectively.Significant relationships between soil N₂ O emission for 10,20 and 30 years plot and soil temperature were observed（P<0.05）.Soil N₂ O emission for 5,10,30 years had significant relationships with soil WSON（P<0.05）.Soil N₂ O emission for 10,30 years showed a positive correlation with NH₄+-N content（P<0.05）but not with 1,5,20 years.The lack of a significant correlation between soil N₂ O emission and soil water content,MBN,soil NO3--N content was observed.（4）Seasonal variation for soil CH₄ fluxes was not obvious.The annual cumulative soil CH₄ fluxes with 1,5,10,20,and 30 years of intensive management were-0.05,2.89,3.28,6.22,0.80 kg·CH₄·hm-2·a-1,respectively,respectively.In the early stage of intensive management,soils act as sinks for CH₄.Intensive management promoted soil CH₄ emissions.Soil CH₄ for 5 years showed a positive correlation with soil temperature（P<0.05）.The lack of a significant correlation between soil CH₄ fluxes and soil water content,MBC,WSOC content was observed.（5）Global warming potential（GWP）with 1,5,10,20,and 30 years of intensive management were 30.15,33.99,37.19,45.52,39.18 Mg·CO₂·hm-2·a-1,respectively.Total GWP increased with different duration under intensive management（P < 0.05）.During the period of intensive management（from 1 to 20 years）,GWP significantly increased and then decreased.