【作者】 王景燕；

【导师】 胡庭兴；

【作者基本信息】 四川农业大学 ， 森林培育， 2011， 博士

【摘要】 水土流失是当今世界普遍关注的重大环境间题,退耕还林(草)是修复土壤、控制水土流失、改善生态环境的根本性措施。退耕还林后林间部分土地荒芜,加之林木生长缓慢,经济效益不高,如何兼顾与协调生态效益、经济效益和社会效益三者的关系,选择适宜的退耕模式成为迫切需要解决的问题。论文从土壤抗蚀性和土壤有机质组分着手,系统地研究了川南坡地及其退耕成慈竹林、杂交竹林、桤木+慈竹混交林和弃耕地5年后土壤养分、土壤层及枯落物层水源涵养功能、土壤抗蚀性、土壤分形特征及土壤有机质组分(包括微生物量碳和氮、水溶性有机碳、活性有机碳、轻组有机碳和氮、颗粒有机碳和氮、腐殖质组分碳和氮、有机碳和氮矿化、团聚体中有机碳和氮)的变化,主要研究结果如下：1)退耕有利于土壤养分含量、微生物数量和酶活性的提高,不同退耕模式的土壤有机质、全氮、碱解氮、全磷、细菌、真菌、放线菌及总微生物数量、蔗糖酶、脲酶和磷酸酶活性的大小顺序为：慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地；有效磷、速效钾含量的大小顺序为：农耕地>慈竹林>杂交竹林>桤木+慈竹林>弃耕地；全钾含量的大小顺序为：慈竹林>杂交竹林>桤木+慈竹林=弃耕地>农耕地,且0-15 cm土层各指标含量均高于15-30 cm土层。土壤有机质、全氮、碱解氮、全磷和全钾含量与蔗糖酶、磷酸酶、脲酶、微生物总数、细菌、真菌和放线菌数量之间呈极显著正相关关系。2)不同退耕模式土壤物理性质及其水源涵养功能差异明显。慈竹林土壤总空隙度、最大持水量和毛管持水量大于杂交竹林、桤木+慈竹林和弃耕地；枯落物储量、最大持水量和有效拦蓄量呈现出慈竹林>杂交竹林>桤木+慈竹混交林>弃耕地的变化规律。4种不同退耕模式枯落物持水量与浸泡时间的关系式为Q=alnt+b,在0-2 h内,枯落物持水量迅速增加,此后增加速度逐渐减缓；其吸水速率与浸泡时间关系式为V=ktn,在0-2 h内,枯落物吸水速率迅速下降,4h后下降速度逐渐减缓。综合土壤层和枯落物层的综合蓄水能力,慈竹林持水能力最强,具有良好的生态水文功能。3)与农耕地对照相比,退耕5年后土壤水稳性团聚体平均重量直径、结构性颗粒指数、团聚状况、团聚度、物理稳定性指数和有机质增加,土壤结构体破坏率、不稳定团粒指数、分散率、侵蚀系数和受蚀性指数降低。各模式土壤抗蚀性综合主成分值为-4.466～3.436,呈现出慈竹林>杂交竹林>桤木+慈竹混交林>弃耕地>农耕地的规律。土壤有机质与大多数抗蚀性指标具有显著相关性,且与抗蚀性综合主成分值呈极显著正相关,说明坡地退耕后土壤有机质增加是土壤抗蚀性增强的关键,坡地退耕成慈竹林更有利于增强研究区土壤抗蚀性。4)退耕后>0.25 mm的土壤团聚体和水稳性团聚体含量均显著增加,团粒结构分形维数介于1.377-2.826之间,且慈竹林<杂交竹林<桤木+慈竹林<弃耕地<农耕地,并随>0.25 mm的土壤团聚体及水稳性团聚体含量的增加而降低。退耕后的慈竹林、杂交竹林、桤木+慈竹林和弃耕地的土壤团粒结构分形维数与抗蚀性综合主成分值、土壤理化性质、微生物数量及酶活性相关性较好。农耕地退耕对增加>0.25 mm的土壤团聚体及水稳性团聚体含量和提高土壤结构稳定性具有较好的作用；土壤团粒结构分形维数可以作为坡地退耕后土壤肥力和抗蚀性变化的理想指标,在研究区坡地退耕种植慈竹具有较好的培肥改土效益。5)退耕后土壤有机质、粘粒(<0.001 mm)含量、颗粒分形维数、颗粒组成中物理性粘粒(<0.01 mm)与物理性砂粒(>0.01 mm)含量的比值增加,呈现出慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地的变化规律,各模式土壤颗粒分形维数在2.507-2.598之间。土壤颗粒分形维数与土壤物理性质、抗蚀性综合主成分值、养分含量、微生物数量和酶活性之间相关性较好。说明农耕地退耕对提高土壤粘粒含量、肥力水平及改善颗粒组成比例具有较好的作用；土壤颗粒分形维数可以作为坡地退耕后土壤肥力和抗蚀性变化的评价指标。6)不同退耕模式土壤微生物量碳和氮含量以慈竹林为最高,且慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地,各模式土壤微生物量碳和氮含量均为0-15 cm土层高于15-30 cm土层。退耕模式慈竹林、杂交竹林、桤木+慈竹林和弃耕地0-30 cm土层土壤微生物量比农耕地相比,微生物量碳分别高出111.6～147.0%,78.4～107.4%,59.2～83.9%,28.7～51.3%,微生物量氮分别增加92.1～107.8%,57.6～78.9%,45.7～62.3%,27.2～43.6%。水溶性有机碳含量排序同土壤微生物量碳和氮,各模式依次比农耕地高出128.4～150.6%、79.2～105.9%、59.3～86.0%、35.8～55.5%,且均为上层大于下层土壤。说明退耕有利于土壤微生物量碳和氮及水溶性有机碳含量的增加。土壤微生物量可以较为敏感地反映退耕地植被恢复对土壤性质的影响。7)在不同退耕模式下土壤活性有机碳的含量为0.121-1.238 g·kg-1。同一退耕模式下,上层土壤的活性有机碳(CL333)、中等活性有机碳(CL167)和高活性有机碳(CL33)的含量均高于下层,且CL333>CL167>CL33。各土层土壤活性有机碳(CL333)、中等活性有机碳(CL167)和高活性有机碳(CL33)含量及碳库管理指数大小均为：慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地；各模式土壤活性有机碳(CL333、CL167和CL33)含量均为0-15 cm土层高于15-30 cm土层。全氮、碱解氮、全磷、全钾、细菌、真菌、放线菌、蔗糖酶、脲酶、磷酸酶和抗蚀性综合主成分值与高活性有机碳、中等活性有机碳、活性有机碳及碳库管理指数呈极显著相关,说明全氮、碱解氮、全磷、全钾、细菌、真菌、放线菌、蔗糖酶、脲酶和磷酸酶与土壤不同活度有机碳和碳库管理指数关系密切,通过对土壤活性有机碳和碳库管理指数的研究可以预测坡地退耕后土壤肥力和抗蚀性的变化。8)退耕后土壤轻组及重组有机碳和氮含量、轻组有机碳和氮分配比例、轻组及重组有机质C/N比、轻组有机碳和氮储量均呈现出慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地的变化规律,且轻组及重组有机碳和氮含量、轻组有机碳和氮分配比例和轻组及重组有机质C/N比均为0-15 cm土层土壤高于15-30 cm土层。9)退耕均能在不同程度上增加土壤颗粒有机碳和氮及矿质结合有机碳和氮含量,提高土壤颗粒有机碳和氮分配比例及颗粒有机质C/N,且上层土壤各指标均高于下层。各模式颗粒有机碳和氮及矿质结合有机碳和氮储量均呈现出慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地的趋势,与农耕地相比,各退耕模式颗粒有机碳和氮储量分别增加60.9%-162.4%和54.5%-136.5%,矿质结合有机碳和氮储量分别增加54.6%-119.8%和50.4%-103.4%。说明退耕是增加土壤颗粒有机碳和氮及矿质结合有机碳和氮的关键。10)土壤腐殖质(胡敏酸、富里酸和胡敏素)及活性腐殖质(活性胡敏酸和活性富里酸)组分碳、氮含量和可浸提腐殖质(胡敏酸和富里酸)及活性腐殖质组分碳、氮分配比例大小顺序均为：慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地,说明慈竹林对增加土壤腐殖质及活性腐殖质组分碳、氮效果更为明显。各退耕模式土壤活性腐殖质碳和氮的增加率均分别高于腐殖质碳和氮,说明活性腐殖质组分碳和氮较腐殖质组分碳和氮对不同退耕模式的响应更灵敏。11)不同退耕模式下各土层土壤有机碳矿化量差异显著,其释放C02-C量的大小顺序为：慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地,且上层土壤高于下层。在培养的前5天,各土层土壤C02-C快速释放,之后趋于平缓,整个培养期土壤有机碳累积矿化量呈曲线增加趋势。与弃耕地相比,慈竹林、杂交竹林、桤木+慈竹林和农耕地土壤中铵态氮、硝态氮和总无机氮含量均增加；0-30 cm土层土壤氮净矿化速率由大到小依次为慈竹林>杂交竹林>慈竹+桤木林>弃耕地>农耕地,且差异显著。12)不同退耕模式土壤各粒级团聚体有机碳和氮含量顺序均为慈竹林>杂交竹林>桤木+慈竹林>弃耕地>农耕地,表明退耕后随着植被的恢复土壤团聚体有机碳和氮含量提高。土壤团聚体有机碳和氮的含量随团聚体粒径的减小而增大呈现出“V”变化规律,即大粒级和小粒级团聚体(>5 mm和<0.25mm粒径)土壤有机碳和氮含量高,而中间粒级团聚体土壤有机碳和氮含量低,且各模式均以<0.25mm团聚体土壤有机碳和氮含量最高。退耕增加了大粒径团聚体中有机碳和氮的分配比例,减少了小粒径团聚体有机碳和氮的分配比例。更多还原

【Abstract】 Water loss and soil erosion is a serious environmental problem in the world, returning farmland to forest (grass) is the essential measure to remedy soil, control water loss and soil erosion, and improve the ecological environment. After de-farming, how to consider and harmonize the ecological, economic and social benefits and choosing feasible de-farming patterns become an exigent problem to settle. By analyzing soil anti-erodibility and soil organic matter fractions, this paper systematically studied the changes of soil nutrients, water conservation function of soil and litter layer, soil anti-erodibility, fractal dimension characteristics and organic matter fractions (including microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), water-soluble organic carbon (WSOC), labile organic C, light fraction organic carbon (LFC) and light fraction organic nitrogen (LFN), particle organic carbon (POC) and particle organic nitrogen (PON), humus fraction C and N, soil organic C and N mineralization, aggregate organic C and N in the slope farmland (CK) and its 5-year de-farmed Neosinocalamus affinis plantation (NAP), Bambusa pervariabilis x Dendrocalamopsis oldhami plantation (BDP), Alnus crenastogyne+Neosinocalamus affinis plantation (ANP) and abandoned farmland (AFL) in southern Sichuan Province of China. The main results were found as follows:1) De-farming could increase soil nutrients content, microbe counts and enzyme activities. Contents of soil organic matter (SOM), total N, alkaline hydrolysis N, total P, soil bacteria, fungi, actinomycete and total microbe counts, and invertase, phosphatase and urase activities followed the order of NAP>BDP>ANP>AFL>CK, contents of available P and available K were followed the order of CK>NAP>BDP>ANP>AFL, content of total K followed the order of NAP>BDP>ANP=AFL>CK, and these in 0-15 cm soil layer were higher than in 15-30 cm soil layer. Soil nutrients content were well correlated with enzyme activities and microbe counts, and SOM, total N, alkaline hydrolysis N, total P and total K contents were positively correlated with invertase, phosphatase and urase activities, and bacteria, fungi, actinomycete and total microbe counts. This indicates that the de-farming of slope farmland was beneficial for improvement of soil fertility.2) Soil physical properties and water conversation of soil and litter layer were significantly different under all de-farming patterns. Soil total porosity, maximum water holding capacity and capillary moisture water holding capacity in NAP were better than the others. Litter storage, maximum water-holding capacity, and modified interception of litter layer were NAP>BDP>ANP>AFL. During the process of water holding, the water holding capacity and absorption speed in first 2 h were superior to the rest of time. The equation between the water holding capacity of the litter layer and the immerse time is Q=alnt+b, the equation between the water absorption speed of the litter layer and the immerse time is V=ktn. Overall, NAP had better water conservation function than the others.3) After 5 years’de-farming, the mean weight diameter of soil water-stable aggregates, structural granular index, aggregation state, aggregation rate and physical stability and SOM increased, while the soil structure deterioration ratio, index of unstable aggregate, dispersion ratio, erosion coefficient and index of erodibility decreased, as compared to CK. The synthetic principal component score value of soil anti-erodibility was-4.466～3.436 and followed the order of NAP>BDP>ANP>AFL>CK. SOM was significantly correlated with most of the soil anti-erodibility indices, as well as the synthetic principal component score value of soil anti-erodibility. The results suggested that SOM increasing after slope farmland de-farming could be the key for enhancing the soil anti-erodibility, and NAP was better for enhancing the soil anti-erodibility than other de-farming patterns.4) In the de-farmed plantations and abandoned farmland, the content of>0.25 mm soil aggregates and water-stable aggregates were increased significantly, compared with those in the slope farmland. The fractal dimension of soil aggregate structure was 1.377-2.826 and followed the order of NAP<BDP<ANP<AFL<CK, the fractal dimension of soil aggregate structure decreased with the increase of the contents of>0.25 mm soil aggregate and water-stable aggregate. There were close relationships between fractal dimension of soil aggregate structure, soil physical and chemical properties, microbe counts and enzyme activities under de-farming patterns. This indicated that the de-farming of slope farmland was beneficial for increasing the contents of>0.25 mm soil aggregate and water-stable aggregate, and improving the stability of soil structure. The fractal dimension of soil aggregate structure could be used as an ideal index to evaluate soil fertility, and planting Neosinocalamus affinis in the de-farming slope farmland, which was best for soil improvement in the research area.5) After 5 years’de-farming, SOM, clay contents (<0.001 mm), fractal dimension of soil particles, ratio of soil physical clay (<0.001 mm) and physical sand (>0.01 mm) were increased. Soil fractal dimension of soil particles was 2.507～2.598 and followed the order of NAP>BDP>ANP>AFL>CK. The fractal dimension of soil particles were well correlated with soil physical properties, synthetic principal component score value of soil anti-erodibility, nutrients contents, microbe counts and enzyme activity. This indicated that de-farming of slope farmland was beneficial for soil clay content increase, soil fertility and proportion of particle composition improvement, fractal dimension of soil particle could be used as comprehensive quantitative index to evaluate soil fertility and anti-erodibility for slope farmland de-farming.6) MBC and MBN contents under different de-farming patterns was highest in NAP, and they were followed the order of NAP>BDP>ANP>AFL>CK. In all patterns, MBC and NAP in 0-15 cm soil layer were higher than those in 15～30 cm soil layer. MBC contents in NAP, BDP, ANP and AFL were 111.6～147.0%,78.4-107.4%,59.2～83.9%,28.7-51.3% higher respectively than that in CK, MBN contents were 92.1～107.8%,57.6-78.9%, 45.7-62.3%,27.2～43.6% higher respectively than that in CK, and WSOC contents were 128.4～150.6%,79.2-105.9%,59.3～86.0%,35.8-55.5% higher respectively than that in CK, and MBC, MBN and WSOC contents in upper layer of soil were higher than those in the subsoil. This indicated that de-farming is beneficial for the increase of MBC, MBN and WSOC. Soil microbial biomass can sensitively reflect the effect of re-farming vegetation pattern on soil properties.7) Soil labile organic C contents were 0.121-1.238 g-kg"1 under different de-farming patterns. In the same pattern, the content of labile organic C (CL333), middle labile organic C (CL167) and high labile organic C (CL33) in upper layer of soil were higher than those in the subsoil, and followed the order of CL333>CL167>CL33 The content of labile organic C (CL333), middle labile organic C (CL167) and high labile organic C (CL33) and soil carbon management index in different soil layers followed the order of NAP>BDP>ANP>AFL>CK. Soil labile organic C (CL333, CL167and CL33) in 0-15 cm soil layer were all higher than those in 15～30 cm soil layer. Total N, alkaline hydrolysis N, total P, total K, soil bacteria, fungi, actinomycete, invertase, phosphatase and urase activities and the synthetic principal component score value of soil anti-erodibility were significantly correlated with high labile organic C (CL33), middle labile organic C (CL167) and labile organic C (CL333) and soil carbon management index, this indicated that total N, alkaline hydrolysis N, total P, total K, soil bacteria, fungi, actinomycete, invertase, phosphatase and urase activities had close relationships with different soil labile organic C and soil carbon management index. The study on soil labile organic C and soil carbon management index can predict the change of soil fertility in de-farming land and soil anti-erodibility.8) The contents of soil LFC and LFN, heavy fraction organic (HFC) and nitrogen (HFN), the distribution ratios of LFC and LFN, C/N ratio of light fraction and heavy fraction, and the storage of LFC and LFN all showed a tendency of NAP>BDP>ANP>AFL>CK. At the same time, the contents of LFC, HFC, LFN and HFN, the proportion of LFC and LFN in total organic carbon and nitrogen, respectively, and C/N ratio of light fraction and heavy fraction in 0-15 cm soil layer were all higher than those in 15-30 cm soil layer.9) De-farming can increase contents of soil POC and PON, incorporated organic carbon (IOC) and nitrogen (ION), and improve the distribution ratios of soil POC and PON, and the C/N ratio of particle organic matter. These indexes in upper layer of soil are all higher than those in the subsoil. The storage of POC and PON, IOC and ION showed a tendency of NAP>BDP>ANP>AFL>CK. Compared with CK, the storage of POC and PON increased 60.9%～162.4% and 54.5%～136.5% respectively, and IOC and ION increased 54.6%～119.8% and 50.4%～103.4%, respectively. This indicated that de-farming is the key to increase soil POC and PON, IOC and ION.10) The contents of soil humus and labile humus compositions of C and N, extractable humus, and proportions of labile humus compositions of C and N followed the order of NAP>BDP>ANP>AFL>CK. This indicated that NAP is more efficient to increase the soil humus C and N fractions and soil labile humus C and N fractions. The increased rate of soil labile humus C and N under different de-farming patterns were higher than that of soil humus C and N fractions respectively, indicating that soil labile humus C and N fractions were more sensitive to different de-farming patterns than soil humus C and N fractions.11) Soil organic carbon (SOC) mineralization under different de-farming patterns was significantly different in every soil layer, and the cummualtive CO2-C in upper layer of soil is higher than that in the subsoil and follows the order of NAP>BDP>ANP>AFL>CK. In the first five days of the mineralization, the cummualtive CO2-C increased sharply in the first five days and then changed moderately, in the whole culture, the cumulative amount of mineralized SOC were increased based curve of objective function. Compared with AFL, NH+-N, NO3-N and total inorganic N in NAP, BDP, ANP and CK all increased. Soil net nitrogen mineralization rate followed the order of NAP>BDP>ANP>AFL>CK.12) SOC and SON contents of all different size aggregates under different de-farming patterns followed the order of NAP>BDP>ANP>AFL>CK respectively, indicating that SOC and SON in soil aggregates would increase with the vegetation restoration in de-farming land. The contents of SOC and SON in soil aggregates increased with the aggregate size decreased, showing a change tendency of V, that means the SOC and SON contents in small particles and micro-aggregates (>5 mm and<0.25 mm) were high, while in intermediate size aggregates was low, and<0.25 mm aggregate SOC and SON were the highest. De-farming increased the distribution ratios of SOC and SON in the lager particle-sized aggregates, and decreased the distribution ratios of SOC and SON in the lower particle-sized aggregate.更多还原