【作者】 李晓东；

【导师】 傅华；

【作者基本信息】 兰州大学 ， 草业科学， 2009， 硕士

【摘要】 土地利用方式是影响陆地生态系统碳循环最重要的因素之一,土壤是该系统中最大的有机碳库,同时又是土壤肥力重要的物质基础。本研究以甘肃陇中黄土高原区至少已有50年传统耕作历史的两种雨养轮作农耕地(耕作与休闲)和退耕20年的两种草地系统(围封和放牧)为研究对象,通过2年的野外调查和室内试验及数据分析,探讨了不同土地利用方式下土壤有机碳、氮、微生物碳、可浸提碳、团聚体碳和水溶性有机碳等的特征,以及土壤微生物碳和水溶性有机碳的季节变化及影响因素。主要结论如下:1.土地利用方式对土壤有机碳、全氮、速效磷、pH值和容重有显著影响。土壤有机碳含量0-10cm土层草地显著高于农田,全氮含量差异不显著,20-100cm土层有机碳和全氮农田高于草地(P<0.05);土壤全磷含量农田与草地无明显差异。土壤C/N比除0-10cm土层外,农田高于草地。在整个土壤剖面上,草地土壤pH显著高于农田(P<0.05);除10-20cm和底层土壤外,草地土壤容重也高于农田。草地土壤有机碳和全氮随土壤深度增加而降低,而农田土壤在0-30cm土层随土壤深度的增加而增加,在30cm土层以下与草地有相同趋势。草地土壤全磷含量各土层间没有显著差异,农田土壤全磷含量与土壤有机碳和全氮含量变化趋势一致;草地和农田土壤速效磷含量都呈减少趋势。土壤pH值随土壤深度的增加而增加。各样地土壤有机碳、全氮、全磷、速效磷与土壤容重和土壤pH之间呈极显著负相关性,土壤容重与土壤pH值呈极显著正相关,土壤有机碳、全氮、全磷和速效磷之间也呈现极显著正相关关系。2.两年的研究结果表明,各样地土壤微生物量碳主要受土壤水分和生物量的影响,与温度无显著相关性。土壤微生物量碳表现一定的季节变异,0-10cm土壤微生物量碳,在春季(5月)和初冬(11月)生物量较大的围封草地显著高于其他样地(P<0.05),休闲耕地最低;而水热条件较好的7月和9月谷子地>围封草地>放牧草地=休闲耕地;且各样地各土层均表现为9月>7月>5月≥(≤)11月,9月和7月之间且与其他各月间差异显著(P<0.05)。0-10cm土层围封草地、放牧草地、谷子地和休闲耕地土壤微生物量碳含量变幅两年平均分别在183.49-576.72mg/kg、121.13-366.76mg/kg、127.99-725.62mg/kg,44.05-354.58mg/kg之间。各样地在各季节土壤微生物量碳均随土壤深度的增加而降低。3.各样地土壤水溶性有机碳主要受水分的影响,谷子地与生物量也密切相关,但都与温度无相关性。各样地土壤水溶性有机碳在水分含量最高的9月显著高于其他各月(P<0.01),5月、7月和11月间没有显著差异。0-10cm土层围封草地、放牧草地谷子地和休闲耕地土壤水溶性有机碳含量变幅分别在31.88-13.58mg/kg、9.78-22.22mg/kg、8.34-23.72mg/kg,13.00-26.0mg/kg之间。沿土壤剖面,水溶性有机碳各样地0-10cm土层最高,且随土壤深度的增加,随季节变化表现出不同程度的降低,雨季降幅显著减小,降雨导致的水溶性有机碳的淋溶可能是农田系统20-100cm土层有机碳含量高于草地的原因之一。4.土地利用方式改变显著影响土壤团聚体含量,由于耕作引起大团聚体的损失和小团聚体的增多。0-20cm土层土壤团聚体含量,>0.5mm粒级草地显著高于农田(P<0.05);<0.05mm农田均显著高于草地(P<0.05);20-30cm土层,除>1mm粒级草地显著高于农田外,其他各粒级农田均显著高于草地(P<0.05)。各样地不同粒径团聚体的分配主要集中在<0.25mm微团聚体,达87.89%-96.22%,>0.25mm大团聚体含量仅在13%以内。5.团聚体有机碳表现和土壤有机碳一致的规律,0-10cm土层各粒级围封草地均显著高于农田;10-40cm土层,除>1mm土壤团聚体有机碳围封草地和谷子地没有显著差异外,其他粒级农田均显著高于草地。各样地>0.25mm的团聚体有机碳显著高于<0.25mm的微团聚体(P<0.05)。土壤剖面上各粒级土壤团聚体有机碳在草地和农田系统变化规律不一致,>0.5mm各粒级随土壤深度的增加而降低;<0.5mm各粒级草地随土壤深度的增加呈降低趋势,农田在0-30cm土层随深度增加而增加,随后减少。各粒级土壤团聚体有机碳含量,草地与土壤有机碳呈显著正相关,而农田仅<0.25mm微团聚体有机碳含量与土壤有机碳呈显著相关。更多还原

【Abstract】 Land use mode is one of the biggest factors which affect carbon cycle in terrestrial ecosystems.Soil is the largest and the most active organic carbon pool in terrestrial ecosystems,the most important material basis in soil fertility as well.In this study,two types of rain-fed rotated farmland（cultivated and fallowed） which at least have 50 years traditional farming history and two types grassland system that have been returned from farmland to grassland for 20 years（fenced and grazing） were chosed as the research objects in the Loess Plateau in Gansu.Based on 2 years field investigation,laboratory test and data analysis,the characteristics of soil organic carbon（SOC）,nitrogen（TN）,soil microbial biomass carbon（SBMC）,K₂SO₄--extracted carbon（K₂SO₄-C）,soil aggregates organic carbon（SAOC）,seasonal dynamics and influencing factors of water-soluble organic carbon（WSOC） and soil microbial biomass carbon were discussed in this paper.The main conclusions are as follows:1.Different land uses resulted in significant differences in SOC,TN,total phosphorous,available phosphorous,soil bulk density and soil pH.In surface soil（0-10 cm）,SOC contents were significantly higher in grasslands than that in croplands,while TN show no significance.In the soil layers from 20 to 100cm,SOC and total nitrogen contents were significantly higher in croplands than that in grasslands（P<0.05）.The soil total phosphorous was higher in croplands than that in grasslands but the difference was not significant.In the soil profile down to 100cm,the C/N ratios in croplands were much higher than that in grasslands,except in 0-10cm layer.The soil pH in grasslands was significant higher than that in croplands in each layer（P<0.05）.The soil bulk densities in the grasslands were higher than that in croplands,except in 10-20 cm layer.The SOC and TN decreased with the increase of soil depth in grasslands,while this phenomenon was only found in the soil layers below 30cm in croplands;in the upper 30cm soil layers,the SOC increased with depth.Total phosphorous content did not show significant differences in different soil layers in grasslands.In croplands,the changes of total phosphorous showed the same trends with that of SOC and total nitrogen.The available phosphorous contents decreased with soil depth in both grasslands and croplands while the soil pH showed completely converse trend.Results showed that in both of grasslands and croplands,SOC,TN,total phosphorous and available phosphorous showed significant negative correlations with soil BD and soil pH.There were significant positive correlation between soil BD and soil pH.The significant positive correlations were also found among SOC,TN,total phosphorous and available phosphorous.2.Two years study showed that SMBC was mainly influenced by soil water content and plant biomass,not significantly correlated with temperature.In May and November, SMBC content in the 0-10cm layer was significantly higher in the fenced grassland than in other plots,while the lowest value was found in the fallow.The big difference in plant biomass was the main reason（P＜0.05）.In July and September,when the soil temperature and soil water content were relatively higher,the sequence was millet＞fenced grassland＞grazing grassland＝fallow,and there was same trend among all plots: September＞July＞May≥（≤） November,there was significant difference among all months（P＜0.05）.In 0-10 cm layer,the ranges of SMBC content of the four plots（fenced grassland,grazing grassland,millet cropland and fallow） in two years were 183.49-576.72mg/kg,121.13-366.76mg/kg,127.99-725.62mg/kg,44.05-354.58mg/kg, respectively.In each plot,SMBC content decreased with the depth in all seasons.3.In all plots,soil WSOC was mainly influenced by soil water content,and it did not correlate with soil temperature,while in millet cropland,it also tightly correlated with plant biomass.In September,when the soil water content was highest,WSOC was significantly higher than in other months in all plots（P＜0.01）,and there was no significant difference among May,July and November.In 0-10cm soil layer,the ranges of WSOC content in fenced grassland,grazing grassland,millet cropland and fallow were 31.88-13.58mg/kg,9.28-22.22mg/kg,8.34-23.72mg/kg,13.00-26.0mg/kg, respectively.Along the soil profile in each plot,WSOC content was highest in 0-10cm layer,and decreased sharply in May and slightly in rainy season with soil depth. Compared with surface soil,WSOC content in 30-60 cm layer was only 0.8%lower in September（at this time of year,precipitation was much higher） in millet cropland. WSOC content in each layer of millet cropland was higher than that in other plots. WSOC leak resulting from precipitation may be one reason why SOC content in 10-100cm soil layer of cropland system was higher than in grassland.4.The change of land uses affected the content of soil aggregates significantly. Tillage activities could decrease small aggregates and increase large aggregates,resulting in the higher content of soil aggregates of＞0.5mm particle size in upper soil layer （0-20cm） in grasslands than that in croplands,while soil aggregates＜0.05mm in 0-20cm layer in croplands were higher than that in grasslands.The content of soil aggregates of different particle size except that bigger than 1mm were higher in croplands than in grasslands,while that of bigger than lmm were higher in grasslands（P＜0.05）. Distribution of different particle size aggregates mainly concentrated in＜0.25mm micro-aggregates,ranging between 87.89%and 96.22%,while the large aggregates （＞0.25mm） content was less than only 13%.5.The distribution of SAOC along soil profile showed same pattern with that of SOC.In 0-10 cm layer,the content of soil organic carbon in soil aggregates of different particle sizes was higher in fenced grassland than in cropland;while in 10-40 cm layer, the content of soil aggregates of different particle size were higher in croplands than in grasslands except that bigger than lmm which was at the same level in the two plots, especially for that of＜0.25mm which account for 93.61%.The content of SAOC of＞0.25mm were significantly higher than that of＜0.25mm micro-aggregates in all plots （P＜0.05）.The distribution of SAOC of different particle size along soil profile showed different pattern.The content of SAOC of＞0.5mm decreased with soil depth while that of＜0.5mm showed the same pattern with SOC.The content of SAOC of different particle sizes showed significant positive correlation with SOC in grasslands,but the same correlation was only found for the soil aggregates with particle size＜0.25mm in croplands.更多还原