施肥对山核桃林地土壤N2O排放的影响

摘要

目的 N2 O是重要的温室气体，其增温潜势是CO2的298倍，而且破坏臭氧层。森林生态系统是陆地生态系统的重要组成部分，占全球陆地面积的33％，森林土壤N2 O排放对全球气候变化有重大的影响。山核桃（ Carya cathayensis）是非常重要的经济林，是山核桃主产区农民的主要经济来源。近年来，农民采取施用无机肥和有机肥等措施来提高山核桃产量，但施肥对山核桃林地土壤N2 O排放的影响尚不清楚，本文以不施肥作为对照（ CK），研究单施有机肥（ Organic fertilizer， OF）、单施化肥（ Inorgnaic fertilizer， IF）、有机无机肥配施（ Organic fertilizer and Inorgnaic fertilizer， OIF）对山核桃林地土壤N2 O气体排放的影响。方法利用静态箱－气相色谱法对山核桃林地土壤N2 O排放通量进行了为期1年的测定。采样箱为组合式，即由底座、顶箱组成，均用PVC板做成，面积为30 cm ×30 cm，高度为30 cm。气体样品采集频率基本为每月1次，采集气体时，将采集箱插入底座凹槽（凹槽内径和深度均为5 cm）中，用蒸馏水密封，分别于关箱后0、10、20、30 min采集，用注射器抽样60 mL置于气袋，带回实验室用岛津GC-2014气相色谱仪进行测定，检测器为电子捕获检测器（ ECD），检测器温度为250℃。结果山核桃林地不同施肥土壤N2 O排放通量均呈现明显的季节性变化，以夏季最高、冬季最低。土壤N2 O的排放通量在N －0.0210.161 mg／（ m2· h）之间变化，不同处理土壤N2 O年累积排放量依次为单施有机肥＞单施化肥＞有机无机肥配施＞对照，对应值分别为N 2.17、2.01、1.94和0.94 kg／（ hm2· a）。与对照相比，施肥处理显著增加N2 O的排放（P＜0.05），但是各施肥处理N2O排放量之间的差异不显著。单施有机肥和有机无机肥配施处理土壤N2O排放通量与土壤水溶性有机碳含量和微生物量碳呈显著相关关系（P＜0.05），而单施化肥和对照则无显著相关性。土壤N2O排放通量与地下5 cm处土壤温度均显著相关（P＜0.05），而土壤N2O排放与土壤含水量间没有显著相关性。结论施肥显著促进了山核桃林地土壤N2 O排放，不同施肥处理之间山核桃林地土壤N2 O排放无显著差异。添加有机肥引起土壤水溶性有机碳和微生物碳的增加可能是有机肥增加山核桃林地土壤N2 O排放速率的主要原因之一。%Objectives]N2 O is a potent greenhouse gas with global warming potentials ( GWP) 298 times greater than that of carbon dioxide ( CO2 ) on a 100-year horizon.Moreover, increasing atmospheric N2 O is an important factor in stratospheric ozone depletion.As an important component of terrestrial ecosystems, forest ecosystems constitute about 33% of the global land surface, emitting between N2 O-N 2.4-5.7 Tg/yr into the atmosphere. Carya cathayensis is one of the popular nut food tree species in subtropical China.To achieve maximum yield and economic return, chemical and organic fertilizers have been applied in recent years.However, there is little information on the effects of management practices on soil N2 O emissions.The objective of this study was to evaluate the effects of fertilizer application ( OF, OIF, IF, CK ) on soil N2 O emission from Carya cathayensis orchards in subtropical China.[Methods]A close-chamber method and gas chromatography techniques were used to determine effluxes of N2 O in the four replicate plots of each plot.The static chamber consisted of a permanently installed base box (0.3 m ×0.3 m ×0.1 m) with a U-shaped groove (50 mm wide and 50 mm deep) at the top of edge to hold a removable cover box (0.3 m ×0.3 m ×0.3 m) .Both the base and cover boxes were made of dark polyvinyl chloride ( PVC) panels, as thick as 5 mm.Prior to gas sampling, the cover box was placed on the base and the groove was filled with distilled water to a depth of 20 mm, acting as an air seal.Gas samples were taken with 60 ml plastic syringes attached to a 3-way stopcock at 0, 10, 20, and 30 minutes following chamber closure, then injected into evacuated bags made of inert aluminium-coated plastic.N2 O concentration in the samples was analysed in the laboratory using gas chromatography equipped with a electron capture detector ( ECD) . The temperature of detector was 250℃.[Results]The results showed that N2 O fluxes from soil under different fertilization treatments exhibited a strong seasonal pattern, with the maximum values being observed during the summer while the minimum values were observed during the winter.N2 O emissions were between N -0.021 0.161 mg/( m2 · h) , the calculated annual emissions of N2 O were OF >IF >OIF >CK, N 2.17 kg/( ha· a)>2.01 kg/( ha · a ) >1.94 kg/( ha · a ) >0.94 kg/( ha · a ) .It was interesting to note that fertilization treatments increased significantly the emissions of soil N2 O ( P<0.05 ) compared with the control.However no significant difference was observed between the fertilizer treatments.Additionally, the content of the WSOC and MBC from the OIF and OF treatments had a significant correlation with the emissions of the soil N2 O ( P<0.05) , but there was no significant correlation between the content of the WSOC and MBC from the IF and CK treatments and the emission of the soil N2 O.There was a significant positive relationship between soil N2 O emission and the soil temperature at 5 cm depth.No significant correlation was found between soil N2 O flux and soil moisture.[Conclusions]Fertilizer application enhanced soil N2 O emission.There was no significant difference between OF, OIF and IF.The increase of soil water soluble organic carbon and microbial biomass carbon caused by organic fertilizer applied might be one of the main reasons that enhanced soil N2 O emission.