【作者】 李志鹏；

【导师】 潘根兴；

【作者基本信息】 南京农业大学 ， 土壤学， 2009， 博士

【摘要】 水稻土是我国重要的粮食生产资源和农田土壤碳库,同时产生温室气体排放,对于国家粮食安全和减缓气候变化具有至关重要的地位。我国面临着日益严峻的应对气候变化的严峻挑战,稻田土壤碳汇和温室气体减排已成为稻田可持续发展的重要任务。随着我国经济的快速发展,土地利用变化和环境污染日益加剧,水稻土有机碳碳汇的未来变化成为水稻土碳循环和全球变化研究的重要内容。本文从土壤有机碳的直接变化和土壤呼吸变化的实验测定,研究水稻土转变土地利用和重金属环境污染下水稻土有机碳的损失和温室气体产生和排放的变化,并讨论其土壤和生态系统过程机理,为科学分析土地利用和重金属污染对水稻土碳循环和碳汇的变化提供科学依据。本文以太湖地区典型水稻土-乌泥土为研究对象,就土地利用变化和重金属污染两个因素,选择了一直种植水稻的田块和改种水稻玉米3年的田块,采集其剖面不同深度的土壤样品,进行了土壤团聚体颗粒组分离,分别测定全土和分离的土壤团聚体总有机碳(TOC)、土壤溶解有机碳(DOC)和微生物生物量碳(SMBC),并对选择性样本测定了有机质的δ13C值。选择了重金属严重污染的田块与非污染的田块作为对比,进行了表土有机碳变化和土壤呼吸变化的野外和实验室培养研究,并分析了不同的有机碳组分和微生物生物量、细菌基因多样性变化等,获得的主要结果如下：1,水田改种玉米3年后,耕层土壤TOC明显下降,但DOC和SMBC趋向增加；粗团聚体颗粒组(2～0.2 mm)的TOC含量降低,而其他团聚体颗粒组TOC无显著变化。改种玉米后表层土壤(0～15cm)原土及各粒级团聚体的δ13C值均明显高于原稻田,计算表明玉米新碳绝大部分集中在0～20 cm土层,且主要富集在粗团聚体颗粒组中。水田转变成旱地后,耕层土壤粗团聚体颗粒组中有机碳更新周期明显较短,有机碳分解加速,碳储量快速损失。这说明水稻土中物理保护的有机碳在旱地耕作下团聚体破坏而快速分解,玉米新碳可能刺激了微生物活动而加快水稻土老碳分解。2,重金属污染土壤的基底呼吸速率为81.92 mgCO2-C·m-2·h-1,明显高于无污染农田的土壤呼吸速率71.19 mgCO2-C·m-2·h-1,因而重金属污染显著地提高了水稻土土壤呼吸的强度。与无污染农田的土壤相比,长期重金属污染下土壤呼吸强度提高了15.10%,并且显著降低了土壤的微生物生物量碳、微生物商、土壤有机碳和微生物量碳氮比。相关分析显示,重金属污染还显著提高了土壤呼吸对土壤温度响应的敏感性。因此,重金属污染影响了稻田的土壤有机碳库的积累,降低了土壤有机碳库的稳定性,使其容易受外界的温度变化的影响。3,在整个水稻生长季,稻田生态系统的CO2和CH4排放高峰分别出现在水稻生育前期和中期。重金属污染稻田的CO2和CH4排放量都显著低于未污染的稻田,结合重金属污染显著降低了地上部生物量的结果,可以认为是重金属的污染危害到水稻生长,减弱植株的光合作用从而影响其生物量的生产,导致农田CO2和CH4排放量降低。对比稻田生态系统和土壤的CH4排放差异,可以看出水稻植株对CH4排放具有巨大的贡献。麦田生态系统的CO2排放量显著的低于稻田生态系统的CO2排放量。同时,重金属对小麦生态系统的CO2排放通量的影响显著的低于对稻田生态系统的影响。重金属污染降低土壤-作物系统呼吸排放的同时,显著提高了无植株参与的土壤CO2的排放通量,而对CH4的排放通量没有影响。4,重金属污染下实验室培养的水稻土有机碳的矿化率为0.33 mgC·g-1·OC·d-1,显著高于无污染土壤有机碳矿化率(0.29 mgC·g-1·OC·d-1)。这种差异主要集中于培养前期,这说明重金属污染加快了活性碳库的分解,对土壤惰性碳库的影响不甚强烈；重金属污染下SOC、DOC和土壤微生物生物量碳都降低,土壤有机碳稳定系数(Kos)也低于无污染土壤。重金属污染影响着作物对水稻土有机碳的输入积累并影响了土壤2有机碳的稳定性,从而可能对水稻土长期的固碳潜力产生重要影响。5,重金属污染下水稻土表土细菌数量增加,而放线菌和真菌的数量显著降低,并强烈地降低了土壤真菌/细菌比。PCR-DGGE图谱分析表明,重金属污染降低了土壤细菌的群落结构和多样性,从而影响了土壤微生物群落对有机碳的矿化分解强度。可见,重金属污染通过改变土壤微生物的群落结构而影响了水稻土碳循环与温室气体排放。综上所述,土地利用的变化和重金属污染深刻影响水稻土土壤有机碳的变化。这些变化与土壤团聚体组成和有机碳的性质、土壤微生物的群落结构和多样性,因此,土地利用变化和重金属污染通过有机质性质—土壤微生物结构与功能-土壤生物物理过程的效应和过程的联系而影响水稻土碳循环过程及气候变化效应。这方面的研究还亟待发展,为探讨水稻土的环境治理和环境友好的农田管理对策与途径,实现稻田土壤增产固碳和温室气体减排的综合效益提供理论依据更多还原

【Abstract】 Paddy soils are vital source of rice production and play a fundamental role in food security and socio-economic development of China. These soils are substantial contributor to greenhouse gases and main pool of organic carbon as well. Reduction emission of greenhouse gases from paddy soils has become one of the key isuues in the research on global changes in the background of global warming and national food security. China is facing an increasingly challenges to climate change, paddy soil carbon sinks and greenhouse gas emissions for sustainable development of paddy fields have become an important task. Under China’s rapid economic development, land-use change and increasing environmental pollution, organic carbon changes in the future of paddy soil has been an important research aspect in carbon cycle and global changes. Effects of land usage changes and heavy metal pollutions on soil organic carbon loss and greenhouse gas generation and emissions changes were investigated based on the determination of soil organic carbon and soil respiration, and the mechanisms of soil and land ecosystem processes were also discussed, which provided a scientific basis for the analysis of the effects of land use and heavy metal contamination of paddy soil on carbon cycle and changes in carbon sinks.Therefore, both field and laboratory incubation study were carried to understand the effects of plantation on the carbon dynamics and the mechanism involve in soil respiration under heavy metal polluted paddy soil. Wunitu paddy soil, a typical Southeast Chinese soil, was selected as the object of this research. Two adjacent fields of Wunitu paddy soil (one with rice-wheat rotation and another with double corn for 3 years after rice and wheat) were chosen to study the SOC dynamics. Both topsoil and whole profile was sampled. Soil particle size factions (PSFs) were separated using low energy ultrasonic dispersion. C pools of total organic carbon (TOC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) were determined for bulk soils and PSFs. Selected samples of bulk soil and PSFs from both rice and corn fields were also used for 13C natural abundance measurement. Changes on topsoil organic carbon and soil respiration between the non-polluted and serious polluted soil were studied, compositions of soil organic carbon, microbial biomass and bacterial genetic diversity were also compared. The main results were list as following:1. TOC of topsoil decreased drastically after 3 years of continuous corn cultivation although marked increase of DOC and MBC was observed in the cornfield. This was in coincident with the decrease of SOC in the sand PSF despite no remarkable changes in the other PSFs from the corn filed. Significantly heavier carbon could be detected either in bulk samples or in a single PSF from the cornfield than from rice field. Calculation using the data of 813C%o(PDB) indicated that 80% of young carbon inputted by corn residues was allocated in the topsoil of 0-20cm and mainly found in the coarse PSF as well as in the pools of DOC and MBC. These results indicated that the carbon storage was decreased rapidly as a result of increased decomposition rate after the change of paddy soil into dryland soil. These may contributed to the destruction of the physical protected soil organic carbon due to the tillage, which changed the composition of soil particle fractions.2. Soil basal respiration CO2 flux of heavy metal polluted soil was 81.92 mgCO2-C·m-2·h-1 which was obviously higher than unpolluted soil (71.19 mgCO2-C·m-2·h-1). The paddy soil CO2 emission was significantly increased under heavy metal polluted condition. Compared with unpolluted soil, the soil breath intensity was increased 15% under long term heavy metal polluted condition, and the soil microbial biomass, microbial quotient, soil organic carbon and Cmic/Nmic was significantly decreased. Correlation analysis showed that a more prompt response of CO2 flux to soil temperature was increased under heavy metal polluted condition, and the accumulation and stability of paddy soil organic carbon pool was affected, which was decreased, easily affected by the change of temperature.3. CO2 and CH4 emission of paddy soil under heavy metal polluted condition was significantly lower than unpolluted paddy soil in the whole growing season. The rice growth was affected under heavy metal polluted condition due to inefficient photosynthesis that caused less biomass production ultimately decreasing CO2 and CH4 emission of paddy soil. But soil basal respiration CO2 flux was increased under heavy metal polluted condition. This might be due to the fact that decomposition of soil organic carbon and soil CO2 emission was affected by the change of soil microbial activity under heavy metal polluted condition. Difference of CH4 emissions between rice ecosystem and soil was attributed to the rice plant. CO2 emissions in Wheat field ecosystem were significantly lower than that of the rice ecosystem. At the same time, effects of heavy metals on CO2 emissions in wheat ecosystem were significant lower than rice ecosystem. Heavy metal contamination was found to decrease the soil respiration and increase the CO2 emission in non-plant ecosystem, but no impacts on the flux of CH4 emission.4. The soil organic carbon mineralization rate in heavy metals polluted paddy soil was 0.33 mgC·g-1·OC·d-1, which was significantly higher than non-polluting soil organic carbon mineralization rate 0.29 mgC·g-1·OC·d-1. This difference mainly concentrated on beginning of mineralization, indicated that it’s the activated carbon not the inert carbon in soil which was most effected by heavy metals pollution. Soil carbon pools were also influenced by heavy metals pollution with the decreasing of Cmic, DOC, TOC and Kos. Heavy metal pollution has changed the nature of soil organic carbon, on the other hand is a higher activity in the new accumulated organic carbon. Heavy-metal contamination impacted on the growth and stability of paddy soil organic carbon, thus affecting China’s long-term potential of paddy soil carbon sequestration.5. Heavy metal pollution has increased the number of bacteria in soil, and a significant reduction in the number of actinomycetes and fungi, and a strong reduction of the ratio of fungi to bacteria in paddy soil. Soil bacterial diversity and structure of community were found to be reduced by DGGE, thus affecting the microbial mineralization of organic carbon. Heavy metal pollution can be seen to change the structure of soil microbial community, thus the function of microbial communities.To sum up, organic carbon in paddy soil was deeply affected by land usage changes and the pollutions of heavy metal, which was related to the compositions of soil aggregates, characterizations of soil organic carbon, community structure and diversity of soil microorganisms. That is, soil carbon cycle and climate changes were interrelated by the interactions of organic carbon, structure and functions of microorganisms and soil biogeochemical process. Researches in this area were needed to develop. It provided a theoretical basis to achieve the benefits of carbon sequestration and reducing greenhouse gas emission in paddy soil in particular the current trend of global warming.更多还原