【作者】 赵娜；

【导师】 孟平；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2014， 博士

【摘要】 为揭示太行山南段森林群落土壤碳组成及其影响因子的变化特征，以加深对森林生态系统碳输入与输出过程的理解。本研究以太行山南段低丘区农田、农田撂荒地、10年刺槐人工林和43年刺槐人工林为研究对象，采用土壤呼吸自动观测系统，结合壕沟法和同位素法区分土壤呼吸组分，进而探讨不同林龄刺槐人工林土壤呼吸及其组分的动态特征及其环境影响机制，主要结论如下：（1）采用土壤质量综合指数对不同土地利用方式土壤质量进行了综合评价，探讨不同土地利用方式对土壤质量的影响。结果表明：随着林龄的增加，刺槐人工林土壤养分的表层富集作用显著，且0-5cm土层土壤改良效果增强；与农田相比，刺槐人工林的土壤物理性状得到改善，养分含量增加，土壤微生物生物量显著提高。不同土地利用方式土壤质量综合指数为43年刺槐林（0.542）>10年刺槐林（0.536）>撂荒地（0.499）>农田（0.498），说明人工造林改善了太行山南段低丘山区的土壤质量。（2）基于LI-8150多通道土壤呼吸自动观测系统的实测数据，对太行山南段刺槐人工林土壤呼吸测定代表性时间进行研究，探讨不同月份土壤呼吸的代表性时刻，并分析土壤呼吸代表性时刻测定值与日均值间偏差大小。结果表明，刺槐人工林的土壤呼吸日变化和季节变化与5cm土壤温度（Ts）的变化格局均趋于一致。各月土壤温度在6-8点达到日最低值，14-16点达到日最高值。除1月土壤体积含水量（W）最低值为18.32%外，其他各月W均在20%以上。刺槐人工林土壤呼吸月均值季节变化呈单峰趋势，在7月最大，1月最低。刺槐人工林在6月-11月8:00-10:00、12月-5月9:00-11:00土壤呼吸测定均值与日均值间的绝对偏差分别为1.27%和4.91%，且土壤呼吸代表时段均值与24h土壤呼吸日均值相对差异均在±10%以内。全年测定期内各月代表性时刻的土壤呼吸测定值与24h日均值呈极显著正相关。因此6月-11月8:00-10:00、12月-5月9:00-11:00土壤呼吸测定均值可作为本研究区刺槐人工林土壤呼吸测定的最佳代表时段。（3）本研究利用13C的自然丰度法来区分土壤呼吸各组分结果发现，土壤CO2气体δ13C随土层梯度减小，植被根系和土壤有机质δ13C则变化不明显。比较埋置管道土壤CO2气体δ13C值与利用GVP（Gas Vapor Probe Kits）50cm土层CO2气体δ13C值，得出本研究区土壤CO2气体50cm土层的δ13C同位素分馏系数为2.03‰。随着土层深度的增加，自养呼吸对土壤总呼吸的贡献率（fRA）逐渐增大。而异养呼吸对土壤总呼吸的贡献率（fRh）随着土层增加逐渐减小。关于壕沟法和同位素法测定自养呼吸贡献率的差异比较可知，壕沟法fRA（23.50%）与埋置管道稳定同位素法fRA（21.03%）差异不显著。（4）基于气体红外分析技术，以农田、撂荒地为对照，分析43年和10年刺槐人工林土壤呼吸速率的季节变化及其环境影响机制，结果表明：人工造林恢复措施的实施显著的提高了土壤固碳能力。43年和10年刺槐人工林0-5cm土层的土壤有机质含量分别是农田的3.9倍和1.6倍。43年、10年刺槐人工林、撂荒地和农田的全年土壤呼吸平均速率分别为2.33、1.21、2.40、2.04μmol·m-2·s-1，其中撂荒地的全年土壤呼吸平均速率最大，43年刺槐林的全年土壤呼吸平均速率大于10年刺槐林。研究区内四种土地利用方式土壤呼吸速率主要受土壤温度（5cm）的影响。43年刺槐林、10年刺槐林、撂荒地及农田的土壤呼吸温度敏感系数Q10分别为2.47、2.53、2.06、1.56，其中刺槐林的Q10均显著高于农田。四种土地利用方式Q10值均存在显著的季节变异，其主要受温度影响。（5）利用壕沟法来区分太行山南段不同林龄刺槐人工林土壤自养呼吸和异养呼吸，结果表明：刺槐人工林土壤呼吸及其组分均呈明显的季节变化，表现为夏季高、冬季低的格局；10年和43年刺槐林土壤总呼吸月均值均显著高于自养呼吸，与异养呼吸无显著差异。土壤呼吸及其组分与5cm土壤温度之间均呈极显著指数相关；与自养呼吸相比，刺槐人工林异养呼吸更易受土壤温度变化的影响，且5cm土壤温度（Ts）分别解释R10和R43的组分RH和RA的77.82%和38.6%，77.87%和43.43%；刺槐人工林土壤呼吸及其组分与土壤体积含水量均呈极显著相关，0-10cm土壤体积含水量（W）分别解释R10和R43的组分RH和RA的25.54%和10.6%，31.72%和11.55%；R10的Rs、RH与ECp、R43的Rs、RA与ECp间呈极显著相关，但0-10cm土壤电导率（ECp）与各呼吸速率的拟合决定系数均较低。与Ts及W相比，ECp不是土壤呼吸的主要控制因子。不同林龄刺槐土壤呼吸及其组分的Q10季节变化与土壤温度变化相反；刺槐林在生长季（5月-7月）内土壤呼吸及其组分的Q10值大小排序均为RH>Rs>RA。10年刺槐在温度较高的生长季内的总呼吸和自养呼吸的温度敏感性变异要大于43年刺槐，而在温度较低的非生长季则出现相反的现象。不同林龄刺槐的自养呼吸对土壤总呼吸的贡献率（RC）呈明显季节变化。刺槐林各月份RC值均无显著差异；在本研究中10年和43年刺槐自养呼吸和异养呼吸的年通量对土壤总呼吸年通量的贡献率分别为25.14%和90.69%、30.84%和70.26%，异养呼吸年通量在不同林龄刺槐林土壤总呼吸的年通量中所占的比重较高。更多还原

【Abstract】 In order to assess the components and influence mechanism of soil carbon flux, andunderstand the carbon input and output of forest communities in southern Taihang Mountains,China, it is necessary to analyse the carbon budget of studied forest communities. In this study,the automatic observation system of soil respiration combined with trenched and stableisotopic method were employed to distinguish the components of soil respiration. Four landuse types, including of cropland (CL), abandoned cropland (AL),10-year-old (R10) and43-year-old Robinia pseudoacacia L. plantations (R43) were measured in southern TaihangMountains, China. The dynamic characteristics of soil respiration rate (Rs) and itssubcomponents, and the effects of environmental factors on the soil respiration wereinvestigated. The main conclusions are as following:(1) In order to obtain influences of different land use types on soil quality, soil qualityindex was employed to compare differences of soil quality among various ages of R.pseudoacacia plantations. The results showed that the nutrient of topsoil increased significantlywith the increase of tree ages. Soil properties were improved with the tree age increasing,especially at the soil layer of0-5cm. In the two R. pseudoacacia plantations (R10and R43), soilphysical and chemical properties were improved and the soil microbial biomass C and N wereincreased significantly compared with the abandoned cropland and the cropland. The soilquality index of43-year-old R. pseudoacacia plantation was0.542, larger than the10-year-oldR. pseudoacacia plantation (0.536), the abandoned cropland (0.499) and the cropland (0.498).The results indicated that the soil quality was improved during the conversion from cropland toforestland.(2) Based on the measured data by LI-8150, the proper measuring times to represent dailyRsof43-year-old R. pseudoacacia plantation were analysed in southern Taihang Mountains.The results showed that the diurnal and seasonal variation of soil respiration was almost consistent with that of soil temperature at5cm depth (Ts) in R. pseudoacacia plantation. Ingeneral, soil temperature reached its lowest value at6:00-8:00and achieved the highest valueat14:00-16:00. Except for the minimum soil volumetric water content (18.32%) at0-10cmdepth (W) in January, the values of W were larger than20%in other months. During themeasurement period, monthly averages of soil respiration reached its peak in July anddecreased to the minimum in January gradually. The relative deviations between daily averagevalues and values measured at8:00-10:00from July to November or at9:00-11:00fromDecember to May were1.27%and4.91%, respectively. Comparing with the daily averagevalues, the relative errors of measured soil respiration rate during representative times werewithin±10%. In this study, the representative times for measuring soil respiration of R.pseudoacacia plantation during the measurement period were8:00-10:00from July toNovember and9:00-11:00from December to May.(3) The measurement of the13C value of soil CO2were used to separate total soilrespiration into subcomponents of RAand RHin R10and R43, and the calculated RC wasemployed to compared to the trenched approach. The results demonstrated that the13C value ofsoil CO2decreased with soil depths, while the δ13C of root and soil organic matter did notchange significantly with soil depths. A preliminary test was performed to compare the δ13C ofsoil CO2extracted from buried steel tubes and from GVP (Gas Vapor Probe Kits) at50cm soildepth. It is concluded that the isotopic fractionation parameter of the δ13C of soil CO2at50cmsoil depth in plantation was about2.03‰. Data analysis indicated that the contribution ofautotrophic respiration on total soil respiration (fRA) increased gradually with soil depths, whilethe contribution of heterotrophic respiration on total soil respiration (fRH) decreasing with soildepths. Analysis on contribution of autotrophic respiration on total soil respiration (fRA) withtrenched method and stable isotopic method showed that the difference between fRAestimatedby trenched-plot method (23.50%) and isotopic method (21.03%) was not significantly.(4) Seasonal variations and influence mechanisms of soil respiration rate (Rs) under43-year-old and10-year-old R. pseudoacacia plantations, abandoned land, and cropland were studied at southern Taihang Mountains. The results showed that sequestration capacity of soilorganic carbon was improved in two plantations significantly. At0-5cm depth, for example,soil organic matter of43-year-old and10-year-old R. pseudoacacia plantations were3.9and1.6times of cropland, respectively. For43-year-old and10-year-old R. pseudoacaciaplantations, abandoned land, and cropland, measured annual soil respiration rates were2.33,1.21,2.40, and2.04μmol·m-2·s-1, respectively. The abandoned land had the largest annual Rs,and the annual Rsof43-year-old R. pseudoacacia plantation was larger than that of10-year-oldR. pseudoacacia plantation. Statistical analysis indicated that soil temperature at5cm depthwas the dominant environmental factor affecting the seasonal variation of Rs. In this study,calculated temperature sensitivity of soil respiration (Q10) was2.47,2.53,2.06, and1.56for43-year-old and10-year-old R. pseudoacacia plantations, abandoned land, and cropland,respectively. In contrast to cropland, two plantations presented a larger temperature sensitivityof soil respiration. Moreover, significant seasonal variations of Q10under four land use typeswere observed, and soil temperature was the key factor affecting the temperature sensitivity ofsoil respiration.(5) The trenched method was used to distinguish the autotrophic respiration (RA) andheterotrophic respiration (RH) of10-year-old and43-year-old R. pseudoacacia plantations.Results showed that soil respiration and its components had obvious seasonal dynamics, andthe maximum rate occurred in the summer whereas the minimum occurring in winter. Monthlymean total soil respiration rate (Rs) of R10and R43was significantly higher than autotrophicrespiration rate. No significant difference was found between total soil respiration andheterotrophic respiration. There were significant exponential relationships between soilrespiration and its components in two R. pseudoacacia plantations and soil temperature at5cmdepth (P<0.01). Compared with autotrophic respiration, heterotrophic respiration was affectedmore with changes of soil temperature at5cm depths, which explained77.82%and77.87%ofRHand38.60%and43.43%of RAin R10and R43, respectively. Soil volumetric water content at0-10cm depth demonstrated a highly significant correlation with soil respiration and its components. The W could explain25.54%and31.72%of RHand10.6%and11.55%of RAinR10and R43. In addition, a significant linear relationship between Rsor RHin R10and soil porewater conductivity at0-10cm (ECp) was found. There were similar correlations between RsorRAand ECpin R43. Due to the lower determination coefficient (R2) between ECpand soilrespiration or its components, ECpwas not the major control factors influencing soil respiration.The seasonal trends of temperature sensitivities of soil respiration (Q10) and its components inR10and R43were opposite with that of soil temperature. Comparing with Rsor RA, RHwas moreaffected by soil temperature change during growing season (from May to July). Thetemperature sensitivity variations of Rsor RAin R10were greater than that in R43in growingseason with higher temperature, while the opposite trend was found at non-growing seasonwith lower temperature. The monthly root respiration contribution to total soil respiration (RC)in R10and R43also presented obvious seasonal variations. There was no significant differenceon monthly RC between R10and R43. The estimated contributions of annual autotrophic andheterotrophic CO2fluxes on annual total soil respiration were25.14%and90.69%on R10, and30.84%and70.26%on R43, respectively. In this study, calculated results showed that annualheterotrophic annual CO2flux generally accounted for a high proportion of total soilrespiration in studied region.更多还原