黄土丘陵区人工林土壤氮素积累、转化对土壤碳库的影响

发布时间：2018-05-26 09:26

本文选题：人工林 + 退耕年限　；参考：《西北农林科技大学》2017年博士论文

【摘要】：明确退耕还林下土壤氮库的动态变化特征以及与土壤碳库的关系对于认知植被恢复下土壤氮素固存、提升土壤质量以及改良生态环境效应有重要意义。本研究在退耕还林工程背景下,以黄土丘陵区主要人工林和不同退耕年限刺槐、柠条和荒草作为研究对象,采用时空替代法,通过野外试验与室内分析相结合的方法研究了不同人工林土壤氮组分积累、转化特征以及随退耕年限的演变规律,并结合室内培养试验,分析了凋落物种类、水分和温度对土壤氮素转化的影响,通过比较不同人工林以及不同退耕年限下刺槐、柠条和荒草土壤碳库,明确了土壤氮素积累、转化与土壤碳库的关系。取得以下主要结论:(1)退耕植被恢复对于不同人工林0-200 cm土层氮组分含量、储量和积累量有着明显影响。不同人工林土壤全氮、硝态氮和无机氮含量随土层深度的变化规律基本相似,浅层(0-40 cm)变化大于深层(40-200 cm);铵态氮、可溶性全氮和可溶性有机氮含量随土层深度的变化不明显。与耕地相比,侧柏和刺槐+侧柏土壤硝态氮、无机氮、可溶性全氮和可溶性有机氮储量明显下降,但柠条全氮、铵态氮、硝态氮、无机氮、可溶性全氮和可溶性有机氮储量明显提高,0-200 cm土层氮组分储量分别比耕地高2.24 Mg/ha、8.49 kg/ha、15.00 kg/ha、23.54 kg/ha、429.63 kg/ha和406.44 kg/ha,氮组分积累效果显著。说明植被恢复是影响土壤氮素积累的重要因素,不同人工林土壤氮组分积累效应差异较大。(2)不同退耕年限刺槐、柠条和荒草土壤氮组分储量和积累量不同,深层土壤占据重要地位。不同退耕年限刺槐、柠条和荒草土壤全氮、铵态氮、硝态氮、无机氮、可溶性全氮和可溶性有机氮储量随退耕年限的变化规律不一致,且表层与深层土壤随退耕年限的变化也不同。不同土层氮组分储量分布比例差异显著,深层土壤占据很大比例;100-200 cm土层氮组分储量分布比例最大,为34.18%-57.47%;40-100 cm土层分布比例为20.11%-37.03%。大部分情况下,不同退耕年限刺槐、柠条和荒草土壤全氮和硝态氮积累量随土层0-10 cm、10-40 cm、40-100 cm和100-200 cm呈下降趋势,而铵态氮积累量呈升高趋势。(3)凋落物种类和温度是影响土壤氮素转化的主要因素,对土壤氮素转化起重要作用。不同凋落物处理下土壤硝态氮含量、硝化速率、矿化氮含量和矿化速率差异显著,均表现为柠条凋落物处理最高,其次是刺槐、9:1刺槐+山桃凋落物处理和对照,荒草和1:1刺槐+侧柏凋落物处理最低。不同田间持水量处理下土壤铵态氮含量、氨化速率、硝态氮含量、硝化速率、矿化氮含量和矿化速率差异不显著。不同温度处理下土壤铵态氮含量、硝态氮含量和矿化氮含量有显著差异;38℃处理下土壤铵态氮含量均值为5.87 mg/kg,显著高于12℃和25℃处理;38℃处理下土壤硝态氮和矿化氮含量分别比12℃和25℃处理高11.87mg/kg和2.67 mg/kg(硝态氮)、11.35 mg/kg和7.57 mg/kg(矿化氮)。在同一温度和田间持水量条件下不同凋落物处理土壤硝态氮含量和矿化氮含量差异达极显著水平。在培养过程中,不同凋落物处理土壤硝态氮和矿化氮含量最高的处理是在25℃60%田间持水量条件下柠条凋落物处理,其他凋落物处理最高值出现在38℃60%田间持水量条件下。(4)植被类型、退耕年限以及土层深度是影响土壤碳库的主要因素,三者共同调控土壤碳库变化。不同人工林土壤有机碳、可溶性有机碳、可溶性无机碳和可溶性总碳库存在极显著差异。柠条0-10 cm、0-40 cm、0-100 cm和0-200cm土层有机碳库最高,分别比耕地高2.41 Mg/ha、2.64 Mg/ha、3.12Mg/ha和5.99 Mg/ha;荒草土壤可溶性有机碳、可溶性无机碳和可溶性总碳库最高,0-200 cm土层碳库分别比耕地高10.20%、8.34%和8.62%。不同退耕年限刺槐、柠条和荒草土壤碳库随退耕年限的变化趋势各不相同。(5)植被类型、退耕年限和土层深度是影响土壤氮素积累、转化与土壤碳库关系的重要因素,共同调控土壤碳氮关系。不同人工林各土层氮组分积累量对土壤碳库的影响具有相似性,即0-10 cm和0-40 cm土层表现较为一致,0-100cm和0-200 cm土层较为一致,但不同土层氮组分转化速率对土壤碳库的影响差异较大;所有人工林各土层全氮积累、转化对土壤有机碳影响均为最敏感。不同退耕年限刺槐、柠条和荒草各土层氮组分积累量对土壤碳库的影响差异较大。不同退耕年限刺槐土壤可溶性有机氮和可溶性全氮积累量对土壤可溶性有机碳和可溶性总碳库影响较敏感,可溶性有机氮和可溶性全氮转化速率对土壤可溶性总碳库影响较大。不同退耕年限柠条0-200 cm土层氮组分积累量对土壤碳库的影响较其他土层更明显;土壤铵态氮、硝态氮和无机氮转化速率对土壤可溶性无机碳库影响较大。不同退耕年限荒草土壤氮组分积累、转化对土壤碳库的影响随土层不同差异较大。
[Abstract]:The dynamic change characteristics of soil nitrogen pool under returning farmland to forest and the relationship with soil carbon pool are of great significance to soil nitrogen retention, improving soil quality and improving ecological environment effect under cognitive vegetation restoration. Under the background of returning farmland to forest project, the main artificial forests in loess hilly area and different years of cultivated locust, lime, lime, and lime With the method of space-time substitution, the accumulation of nitrogen components, transformation characteristics and the evolution regularity with the years of returning cultivated land in different plantations were studied by the method of space-time substitution. The effects of litter species, water and temperature on soil nitrogen transformation were analyzed. The relationship between soil nitrogen accumulation and soil carbon storage was clarified by comparing different artificial forests and different cultivated years of Caragana korshinskii and wasteland soil. The following main conclusions were obtained: (1) the restoration of cultivated vegetation has a significant influence on the contents, reserves and accumulation of nitrogen components in 0-200 cm soil layers of different plantation. The soil total nitrogen, nitrate and inorganic nitrogen content was similar to the soil depth, and the change of the shallow layer (0-40 cm) was greater than that in the deep layer (40-200 cm), and the content of ammonium nitrogen, soluble total nitrogen and soluble organic nitrogen were not obvious with the depth of the soil. The reserves of soluble organic nitrogen were obviously decreased, but the reserves of Caragana total nitrogen, ammonium nitrogen, nitrate nitrogen, inorganic nitrogen, soluble total nitrogen and soluble organic nitrogen were obviously improved. The reserves of nitrogen components in the 0-200 cm soil layer were 2.24 Mg/ha, 8.49 kg/ha, 15 kg/ha, 23.54 kg/ha, 429.63 kg/ha and 406.44 kg/ha, respectively. The accumulation effect of soil nitrogen accumulation in soil and soil of different artificial forests has great difference. (2) the reserves and accumulation of nitrogen components of Caragana korshinskii and barren grass soil are different, and the deep soil occupies an important position. The reserves of soluble total nitrogen and soluble organic nitrogen are not consistent with the years of tillage, and the change of surface and deep soil varies with the years of returning farmland. The distribution ratio of nitrogen components in different soil layers is significant, and the deep soil occupies a large proportion; the largest distribution ratio of nitrogen component in 100-200 cm soil layer is 34.18%-57.47%; 40-100 cm The soil layer distribution ratio is 20.11%-37.03%., the accumulation of total nitrogen and nitrate nitrogen in soil of Caragana Caragana and barren grass with different years of tillage is decreased with 0-10 cm, 10-40 cm, 40-100 cm and 100-200 cm, while the accumulation of ammonium nitrogen is increasing. (3) the species and temperature of litter are the main factors affecting the soil nitrogen transformation. The content of nitrate nitrogen, nitrification rate, mineralized nitrogen content and mineralization rate of soil under different litter treatments were significantly different, all of which showed the highest treatment for Caragana litter, followed by Robinia pseudoacacia, 9:1 pseudoacacia + peach litter treatment and control, and the least treatment of wild grass and 1:1 Robinia pseudoacacia + Platycladus orientalis. The soil ammonium nitrogen content, ammoniation rate, nitrate nitrogen content, nitrification rate, mineralized nitrogen content and mineralization rate have no significant difference under water treatment. The soil ammonium nitrogen content, nitrate nitrogen content and mineralized nitrogen content under different temperature treatments are significantly different. The mean value of ammonium nitrogen in soil under 38 centigrade is 5.87 mg/kg, significantly higher than that of 12 and 25. The content of nitrate nitrogen and mineralized nitrogen in soil treated at 38 degrees centigrade was higher 11.87mg/kg and 2.67 mg/kg (nitrate nitrogen), 11.35 mg/kg and 7.57 mg/kg (mineralized nitrogen) respectively. The difference of nitrate nitrogen content and mineralized nitrogen content in soil treated with different litter under the same temperature and field water content was very significant. The highest concentration of nitrate and mineralized nitrogen in soil with different litter treatment was treated with Caragana litter under the condition of 60% field water holding at 25 C. The highest value of other litter treatment appeared under the condition of 38 C 60% field water capacity. (4) the vegetation type, the year of returning farmland and the depth of soil layer were the main factors affecting the soil carbon pool, and the three were the main factors. The soil organic carbon, soluble organic carbon, soluble inorganic carbon and total soluble total carbon pool in different plantations have very significant differences. 0-10 cm, 0-40 cm, 0-100 cm and 0-200cm soil organic carbon pools of Caragana Caragana, 2.41 Mg/ha, 2.64 Mg/ha, 3.12Mg/ha and 5.99 Mg/ha higher than that of cultivated land; Soluble inorganic carbon and soluble total carbon pool are the highest, 0-200 cm soil layer carbon storage is 10.20%, 8.34% and 8.62%., respectively, different years of cultivated locust, Caragana Caragana and grass soil carbon pool changes with the years of conversion of cultivated land. (5) vegetation type, soil depth is the influence of soil nitrogen accumulation, transformation and soil carbon storage relationship. The influence of the accumulation of nitrogen components in different soil layers on soil carbon pool is similar, that is, 0-10 cm and 0-40 cm soil layers are more consistent, 0-100cm and 0-200 cm soil layers are more consistent, but the effect of nitrogen component transformation rate on soil carbon pool in different soil layers is more different; all artificial forests are different. The effects of total nitrogen accumulation and transformation on soil organic carbon were the most sensitive. The effects of nitrogen accumulation on soil carbon pool in Robinia pseudoacacia, Caragana korshinskii and barren grass with different years of tillage, soluble organic nitrogen and total soluble total nitrogen accumulation on soil soluble organic carbon and total soluble carbon pool in different years of cultivated land The effect of soluble organic nitrogen and total nitrogen conversion rate on soluble total carbon pool of soil was greater. The accumulation of nitrogen component in 0-200 cm soil layer of Caragana Caragana was more obvious than that of other soil layers, and the soil ammonium nitrogen, nitrate nitrogen and inorganic nitrogen conversion rate had great influence on the soil soluble inorganic carbon pool. The effects of accumulation and transformation of nitrogen components on soil carbon storage in different soil types were different with different soil layers.
【学位授予单位】：西北农林科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S714.2

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