【作者】 陈先江；

【导师】 王彦荣； 侯扶江；

【作者基本信息】 兰州大学 ， 草业科学， 2011， 博士

【摘要】 全球变化是当前最受人们关注的科学问题之一,人类活动干扰下陆地生态系统与大气间温室气体交换研究越来越受到关注。草地生态系统己成为人类活动影响较为严重的陆地生态系统之一,也是陆地生态系统中生态环境较脆弱的生态系统之一。本研究选择黄土高原农牧交错带草地农业系统为研究区域,选择天然草地、栽培草地、一年生作物、农林复合系统和林牧复合系统为研究对象,测定了各农业系统土壤呼吸动态特征与土壤有机碳、氮、磷和水分变化,分析了研究区草地农业系统土壤呼吸与环境和生物因子的关系,确定了对研究区草地农业系统土壤呼吸贡献最大的因子,并量化了研究区草地农业系统演替过程中土壤有机碳、土壤全氮、土壤全磷储量变化与土壤CO2年排放量和Q10值变化。主要研究结果如下：1.黄土高原草地农业系统土壤呼吸特征和碳排放量(1)日变化特征。各系统土壤呼吸速率日变化特征与土壤5cm温度变化较一致,土壤呼吸速率和土壤温度的峰值和最低值同步出现或稍有延迟。土壤呼吸峰值一般出现在12：00-16：00之间,最低值出现在凌晨01：00-06：00之间。(2)季节变化。各系统土壤呼吸季节变化均表现为：8月土壤呼吸速率大于5月,12月土壤呼吸速率最低。(3)CO2日排放量。林牧复合系统(2.51 gCm-2)>栽培草地系统(2.34 gCm-2)>农林复合系统(1.84 gCm-2)>天然草地系统(1.69gCm-2)>作物地系统(1.31 gCm-2)。建植时间较早的紫花苜蓿栽培草地CO2口排放量大于建植时间较晚栽培草地；作物地系统中,马铃薯地(CP)土壤CO2日排放量大于荞麦地(CB)和冬小麦地(CW)；农林复合系统中苜蓿种植区土壤CO2日排放量大于杨树种植区；榆树林牧复合系统土壤CO2日排放量小于杨树林牧复合系统。(4)CO2年排放量。一年中,各农业系统夏季土壤CO2排放量最多,冬季土壤CO2排放量最少。各农业系统土壤CO2年排放量排序为：林牧复合系统(582.2gCm-2)>栽培草地系统(485.8 gCm-2)>农林复合系统(379.1 gCm-2)>天然草地系统(332.9gCm-2)>作物地系统(256.8gCm-2)。2.影响黄土高原草地农业系统土壤呼吸的因素(1)土壤呼吸速率与土壤温度都呈正相关关系,指数方程可用于表示土壤呼吸速率和土壤温度的相关关系。由土壤5cm温度解释各农业系统Q10值排序为：作物地系统(1.95)>天然草地(1.77)>栽培草地系统(1.58)>农林复合系统(1.45)>林牧复合系统(1.27)。(2)天然草地系统、栽培草地系统和农林复合系统土壤呼吸速率和土壤水分存在显著的负相关关系。但土壤水分对作物系统和林牧复合系统土壤呼吸的影响在不同测定时期差异较大,有正相关关系也有负相关关系,且相关性也各异。土壤水分与土壤呼吸季节变化的关系均表现为显著的负相关关系。(3)地上生物量和各农业系统土壤呼吸速率有正相关关系,除了1998年种植紫花苜蓿草地(AP3)、马铃薯地(CP)、农林复合系统(AP)以及林牧复合系统(SE和SP)外,其它农业系统的地上生物量和土壤呼吸速率呈显著正相关关系。地下生物量和农业系统土壤呼吸速率也有正相关关系,其中,荞麦地(CB)、农林复合系统(AP)和林牧复合系统(SE和SP)的地下生物量和土壤呼吸相关性不显著。(4)土壤呼吸速率有较强的空间异质性。植物行位点的土壤呼吸速率显著高于植物行间的土壤呼吸速率,且植物行土壤呼吸速率的变异系数大于植物行间土壤呼吸速率的变异系数。(5)对各农业系统土壤呼吸贡献最大的环境和生物因子因草地农业系统而异。对天然草地土壤呼吸的贡献最大的因子为土壤有机碳,贡献最小因子为地上生物量；对栽培草地系统和一年生作物系统土壤呼吸贡献最大的因子均为地下生物量,最小因子均为土壤有机碳；对农林复合系统土壤呼吸速率贡献最大的因子是降水量,贡献最小因子为土壤全磷,且为负效应；对林牧复合系统土壤呼吸直接贡献最大的因子是降水量,贡献最小因子为地上生物量。3.黄土高原草地农业系统土壤C、N、P储量和水分特征及在系统演替中的变化(1)土壤有机碳储量。各农业系统0-100cm土壤有机碳储量随土层深度的增加而减小,大部分土壤有机碳分布在表层。各农业系统土壤有机碳排序为：天然草地(547.5 Mgha-1)>栽培草地(491.7 Mgha-1)>农林复合系统(464.5 Mg ha-1)>林牧复合系统(454.7 Mgha-1)>作物地系统(345.4 Mgha-1)。(2)土壤全氮储量。各农业系统中,0-40cm土层中土壤全氮储量约占0-100cm土壤权氮储量的49%以上。各农业系统土壤全氮储量高低依次为：天然草地(49.1 Mgha-1)>栽培草地(44.8 Mgha-1)>农林复合系统(39.5 Mgha-1)>林牧复合系统(36.4 Mgha-1)>作物地系统(29.1 Mgha-1)。(3)土壤磷储量。各农业系统土壤剖面磷储量分布特征与土壤全氮和有机碳分布特征相反,各农业系统土壤磷储量大部分集中在深层,土壤0-40cm表层磷储量仅占土壤0-100cm剖面磷储量的36.8%。各农业系统土壤磷储量大小排序为：农林复合系统(48.7 Mg ha-1)>天然草地(46.3 Mg ha-1)>栽培草地(42.5Mg ha-1)>林牧复合系统(39.1 Mg ha-1)>作物地系统(31.9 Mg ha-1)(4)土壤水分。各农业系统土壤含水量表现为：12月>5月>8月,土壤表层土壤水分含量较低,深层土壤水分较高。同一年中各农业系统耗水量差距不显著,但2009年各系统耗水量均高于2008年,且差异极显著(P<0.001)。2008年林牧复合系统系统耗水量为202.3 mm,在所有系统中最高；农林复合系统系统耗水量最低,为186.7 mm。2009年研究结果中栽培草地系统(304.1mm)耗水量大于其它系统,作物系统耗水量最低(292.2 mm)。2009年和2008年间系统耗水量的差异主要由于年季间降水量差异和各月份降水量分布不均所致。(5)农业系统演替中土壤C,N和P的变化。天然草地开垦为作物地后：土壤有机碳储量由54.9 Mg ha-1减少到48.9 Mg ha-1,减少了约11.0%；土壤全氮储量减少了0.84 Mg ha-1,减少了27%；土壤全磷储量减少了0.17 Mg ha-1,约损失了3.7%；土壤CO2年排放量减少了22%,降幅为76 g C m-2；Q10值较天然草地增加了约10%,增幅为0.18。天然草地开垦后转变为人工林地后：土壤有机碳储量减少了约4.4 Mg ha-1；土壤全氮储量较天然草地降低了17.6%,降幅为0.87Mg ha-1；土壤全磷储量损失了约0.28 Mg ha-1(6.1％)；土壤CO2排放量增加了75％(249 g C m-2)；Q10值减小了约28%。作物地退耕为栽培草地系统后：土壤有机碳储量增加了11.9%,共增加土壤有机碳储量约5.8 Mg ha-1；土壤全氮储量增加0.95 Mg ha-1(23.3％)；土壤全磷储量增加了4.9%,增幅约为0.22 Mg ha-1土壤CO2排放量将在将较作物系统增加89％(249 g C m-2)；Q10值降低0.37(19%)。作物地退耕为农林复合系统后：土壤有机碳增加约2.8 Mg ha-1；土壤全氮储量增加约0.29 Mg ha-1；土壤磷储量增加了12.1%；土壤CO2排放量将增加48%；Q10值降低了26%(0.51)。更多还原

【Abstract】 Greenhouse gas emissions from grassland ecosystems have severely impacted on the global climate changes and have become one of the key issues of science. Grassland ecosystems are important terrestrial ecosystems and are intensively affected by human activities. In this study, the Loess Plateau was choosing as the study site and five agrosystems were selected as objects of study. We determined the soil respiration dynamics, soil organic carbon, soil total nitrogen, soil total phosphorus and soil water content and ananysed environmental and biological factors which affect soil respiration and its relationships. The main factor which influenced the soil respiration was confirmed and quantized changes of soil organic carbon, soil total nitrogen, soil total phosphorus, annual soil CO2 emission and Q10 value. The main results are as following:1. Soil respiration characteristics and carbon emission of agrosystems on the Loess Plateau(1) Daily variations of soil respiration. Soil respiration was higher associated with chages of soil temperature at 5 cm depth. The peak and minmum values of soil respiration and soil temperature were observed synchronous. The peak value of soil respiration appeared at between 12:00-16:00 and the minmum values were observed at between 01:00-06:00.(2) Seasonal variations of soil respiration. The series of soil respiration of agrosystems were ranged:August> May> December.(3) Daily soil CO2 emission. The series of daily soil respiration were ranged: silvo-pastoral (2.51 g C m-2)> alfalfa pasute (2.34 g C m-2)> agroforestry (1.84 g C m-2)> rangeland (1.69 g C m-2)> cropping land (1.31 g C m-2).(4) Annual soil CO2 emission. The highest and lowest soil C emission period were summer and spring, respectively, in the year. The series of annual soil CO2 emission among the agrosystems were ranged:silvo-pastoral (582.2 g C m-2)> alfalfa pasture (485.8 g C m-2)> agroforestry (379.1 g C m-2)> rangeland (332.9 g C m-2) > cropping land (256.8 g C m-2)2. The main factors influence soil respiration of agrosystems on the Loess Plateau(1) Positive correlation effects were found between soil respiration and soil temperature. The series of Q10 values were ranged:cropping land (1.95)> rangeland (1.77)> alfalfa pasture (1.58)> agroforestry (1.45)> silvo-pastoral (1.27).(2) Negative correlation effects were found between soil respiration and soil temperature in rangland, alfalfa pasture and agroforestry.(3) Aboveground biomass has positive correlation effects on soil respiration in all agrosystems besides AP3, CP, AP, SE and SP. All belowground biomass of the agrosystems has positie correlation effects on soil respiration.(4) Soil respiration showed strong spatial heterogeneity. The soil respiration in plant site was higher than that in between plant site significantly.(5) The main factors influencing soil respiration were different and that was SOC, belowground biomass, rainfall for rangeland, alfalfa pasture, agroforestry and silvo-pastoral.3. Storae changes of soil carbon, nitrogen, phosporus and water content during the succession of agrosystems(1) Soil organic carbon. The storage of SOC was decreased with the increases of soil depth and most of SOC was stored in top soil. The series of SOC were ranged: rangeland (547.5 Mg ha-1)> alfalfa pasture (491.7 Mg ha-1)> agroforestry (464.5 Mg ha-1)> silvo-pastoral (454.7 Mg ha-1)> cropping land (345.4 Mg ha-1)(2) Soil total nitrogen. The soil profile of 0-40 cm accounted for 49% of the soil total nitrogen in all the agrosystems and the series were ranged:rangeland (49.1 Mg ha-1)> alfalfa pasture (44.8 Mg ha-1)> agroforestry (39.5 Mg ha-1)> silvo-pastoral (36.4 Mg ha-1)> cropping land (29.1 Mg ha-1)(3) Soil total phosphorus. Most of soil phosphorus was sored in deep soil and the series were ranged:agroforestry (48.7 Mg ha-1)> rangeland (46.3 Mg ha-1)> alfalfa pasture(42.5 Mg ha-1)> silvo-pastoral(39.1 Mg ha-1)> cropping land(31.9 Mg ha-1).(4) Soil water content. The water content was decreased with the increases of soil depth and most of water was stored in top soil. Water consumption among the agrosystems was not significant but it was significant between different years for the same agrosystem.(5) Changes of soil C, N and P during the sucession of agrosystems. When rangeland was reclained as cropping land, SOC decreased 11%, TN decreased 27%, TP decreased 3.7%, annual soil CO2 emission decreased 22% and Q10 value increased 10%. When rangeland was reclained as forestry, SOC decreased 4.4 Mg ha-1, TN decreased 0.87 Mg ha-1, TP decreased 0.28 Mg ha-1, annual soil CO2 emission increased 249 g C m-2, Q10 decreased 28%. When cropping land was converted as alfalfa pasture, SOC increased 11.9% about 5.8 Mg ha-1, TN increased 0.95 Mg ha-1, TP increased 4.9%, annual soil CO2 emission increased 89%, Q10 decreased 19%. When cropping land were converted as silvo-pastoral, SOC increased 2.8 Mg ha-1. TN increased 0.29 Mg ha-1, TP increased 12.1%, annual soil CO2 emission increased 48% and Q10 value decreased 26%。更多还原