【作者】 张赛；

【导师】 王龙昌；

【作者基本信息】 西南大学 ， 生态学， 2014， 博士

【摘要】 随着全球变化的加剧,减缓温室气体的排放势在必行。陆地生态系统碳循环研究是全球变化研究的热点问题,而农田生态系统是陆地生态系统中最活跃的部分,如何采取有效措施实现农田生态系统的固碳减排成为目前亟待解决的问题之一。以垄作和秸秆覆盖为主体的保护性耕作是西南紫色土丘陵区控制水土流失、改善土壤肥力、抗御季节性干旱灾害、实现农田高产稳产的重要途径,开展保护性耕作条件下农田生态系统碳循环规律与碳汇机制研究,对于应对全球气候变化、改善农业生态环境、增进土地可持续生产能力具有十分重要的理论意义和指导价值。本文通过2个生产年度大田试验的实测资料,结合农田生态系统碳源/汇模型,在重庆北碚西南大学试验农场对传统耕作(traditional tillage, T)、垄作(ridge tillage,R)、传统耕作+秸秆覆盖(traditional tillage+straw mulching, TS)、垄作+秸秆覆盖(ridge tillage+straw mulching, RS)、传统耕作+秸秆覆盖+秸秆速腐剂(traditional tillage+straw mulching+decomposing inoculants, TSD)、垄作+秸秆覆盖+秸秆速腐剂(ridge tillage+straw mulching+decomposing inoculants, RSD)6个处理下的西南紫色土丘陵区“小麦/玉米/大豆”三熟农作制度下农田生态系统碳循环规律进行了研究。从作物固碳、土壤排碳以及土壤碳储量角度分析了3种农作物和不同耕作措施对农田碳收支的影响,以土壤-作物系统为边界估算了作物生长季对大气二氧化碳的贡献,同时考虑农田投入造成的碳排放,综合评价以垄作和秸秆覆盖为主的保护性耕作措施下“旱三熟”农田系统的碳固定、碳排放与净碳汇。主要研究结果如下：(1)在西南“旱三熟”套作模式下中各作物固碳总量表现为小麦<玉米<大豆,3种作物固碳量占整个系统年固碳总量的比例分别为20.29%、21.29%和58.42%。每种作物在不同生育期表现了不同的固碳速率,呈现出增加—减少—再增加—再减少的“比双峰型”趋势,峰值位置因作物不同而不同,在到达成熟期以后固碳速率由正值变为负值。不同耕作措施对作物固碳速率的影响不显著,但是显著影响固碳总量。T、R、TS、RS、TSD和RSD6个处理下3种作物的年固碳总量分别为39312.250、4375.201、47948.284。47049.809、46518.365和49512.140kg·hm-2,与对照相比,R、TS、RS、TSD和RSD处理下的年固碳总量分别增加了11.29%、21.97%、19.68%、18.33和25.95%。以垄作和秸秆覆盖为主的保护性耕作有利于作物固定更多的碳。(2)各作物生长季农田土壤呼吸日均值表现为小麦<玉米<大豆,3种作物土壤呼吸量占土壤呼吸总量的比例分别为16.17%～16.34%、30.48%-33.64%和15.28%～16.35%。在不同耕作方式下,小麦-大豆(w-s)条带土壤呼吸特征表现为T<R<TS<TSD<RS<RSD,空地-玉米-空地(k-c-k)条带土壤呼吸特征表现为R<T<RS<TS<RSD<TSD。秸秆还田较传统耕作在一定程度上增强了土壤呼吸,但是垄作处理对土壤呼吸的影响作用因作物不同而不同,在小麦-大豆条带中垄作耕作下的土壤呼吸高于传统耕作,而玉米条带则相反。土壤温度和土壤水分是影响旱地农田土壤呼吸的主要因素,二者分别解释了土壤呼吸季节变化的28.9%～53.7%和13.7%～42.0%。水热因子与土壤呼吸速率的回归分析表明,指数方程较好地模拟了土壤呼吸与10cm土温的关系,土壤呼吸的温度敏感性指标Q10值在2.25～2.69之间；而土壤呼吸与5cm土壤水分的关系以抛物线型函数模拟最优。土壤呼吸对土壤水分的响应阈值为14.94%。土壤动物在土壤呼吸中的作用不容忽视。在小麦农田生态系统中优势类群有弹尾目和螨目,它们与土壤呼吸表现出一定的相关性,其中以对照处理和垄作下相关性高,而有秸秆覆盖的处理土壤呼吸与土壤动物没有明显的相关性。在玉米农田生态系统中优势类群有弹尾目、螨目和双翅目。垄作减少了土壤动物数量,秸秆覆盖有助于土壤动物数量的增加和土壤动物多样性的提高。地表活动的土壤动物越多,土壤呼吸作用就越强,其中处理R的相关系数最高,r=1.000,p=0.017,处理TS的相关系数r=0.915,p=0.029。本研究中,在垄作、秸秆覆盖条件下土壤呼吸仅与活动在地表的土壤动物数量存在一定的关系；而传统耕作下土壤动物数量与土壤呼吸没有明显的关系。在大豆农田生态系统中优势动物类群有弹尾目、螨目和双翅目,干漏斗法、陷阱法捕获的土壤动物与土壤呼吸均无显著相关性,两种方法所得土壤动物数量加总与土壤呼吸进行相关分析,发现处理T相关性达显著水平,r=0.901,p=0.037。(3)土壤总碳和各活性碳组分的相互关系研究结果表明：土壤团聚体对不同作物的响应不同,种植玉米有利于土壤水稳性微团聚体的形成。团聚体质量分数受耕作措施和种植作物的双重影响。在20cm的耕层土壤中,5～10cm土层土壤团聚体易受秸秆覆盖的影响。空地-玉米-空地条带的固碳潜力显著高于小麦-大豆条带,充分说明了土壤固碳潜力受到耕作措施和种植作物的双重影响。考虑到土壤团聚体对耕作和作物的不同响应规律,应该加大秸秆覆盖面积,将玉米纳入到种植模式中将有利于土壤的固碳作用。土壤活性有机碳含量在不同保护性耕作措施下差异较大,颗粒有机碳、水溶性有机碳、易氧化有机碳、可矿化有机碳与微生物量有机碳对垄作和秸秆覆盖措施的响应趋势基本一致,大体表现为对垄作处理不敏感,而受秸秆覆盖的影响较大,且差异主要出现在0～5cm土层中。其中颗粒有机碳占总有机碳的35.74%～49.66%,二者显著正相关,均可以作为反映土壤有机碳变化的敏感指标。水溶性有机碳约占土壤总有机碳的0.2%,不同处理间的差异不显著,不具有敏感性。易氧化有机碳占土壤总有机碳的比例为6.29%～8.20%,虽然垄作和秸秆覆盖有利于提高土壤中的易氧化有机碳含量,但是易氧化有机碳占总有机碳的比例在垄作处理下增加而在秸秆覆盖中减少,表明秸秆覆盖有利于土壤有机碳的稳定,垄作则刚好相反。(4)农田生态系统碳源/汇特征与设定的系统边界和研究的时空尺度紧密相关,不管是土壤-作物系统还是考虑了人类活动的农田生态系统,均表现为碳汇在作物不同生育期根系呼吸所占比例不同,随着作物生长该比例先升后降。小麦、玉米和大豆田土壤-作物系统碳源/汇规律表现一致,除了在作物生长初期和成熟期表现为碳源特征外其余时间均为碳汇,且R、TS、RS、TSD和RSD处理均高于对照,因此以垄作和秸秆覆盖为主的保护性耕作能显著提高农田生态系统土壤-作物系统的碳汇能力,增汇幅度高达9.93%～30.67%。在耕作方式从传统耕作向保护性耕作转变的过程中,秸秆覆盖措施虽然增加了土壤碳的积累,但是也增加了农田投入碳的排放,综合考虑后表现为大气二氧化碳的“源”。垄作处理不仅减少土壤碳的积累也增加了农田投入碳的排放,同样表现为大气二氧化碳的“源”。作物固碳、土壤呼吸和人类活动对农田生态系统碳固定能力的影响最终体现在土壤有机碳含量的变化上。从长远来看,3个处理的净碳释放量均为正值,即三者均为大气二氧化碳的排放“源”,源强度大小依次为垄作>传统耕作>秸秆覆盖。耕作方式的转变导致的碳累积效应被证明只在一段时间内有效,最终都会达到一个碳累积速率为零的稳定状态。在耕作方式改变的初期土壤碳库会发生变化,而农田投入的碳释放量基本稳定,因此依靠改善农业耕作管理措施增强农固碳减排的潜力还很大。更多还原

【Abstract】 With the intensification of global change, mitigation of greenhouse gas emissions is imperative. Terrestrial ecosystem carbon cycle is the hot issue of global change research. Agricultural ecosystems are the most active part of terrestrial ecosystems. How to take effective measures to achieve the reduction in farmland ecosystem carbon sequestration has become one of the issues currently solved. Conservation tillage with straw mulching and ridge planting as a mainstay is an important approach to control soil erosion, to improve soil fertility, to guard against seasonal drought and to increase crop productivity in purple hilly regions in southwest China. The research on rules of carbon cycle and mechanism of carbon sink in farmland ecosystems under conservation tillage is of important theoretical significance and practical values for responding to global climate changes, improving agro-ecological environment and promoting sustainable land productivity. In this paper, data in field experiments during two production year had been measured, and farmland ecosystem carbon source/sink model was combed for study on laws of carbon budget in the triple intercropping system of wheat/corn/soybean in purple hilly regions of southwest China. There were six treatments including T (traditional tillage), R (ridge tillage), TS (traditional tillage+straw mulching), RS (ridge tillage+straw mulching), TSD (traditional tillage+straw mulching+decomposing inoculants), and RSD (ridge tillage+straw mulching+decomposing inoculants), which were replicated for three times. Form carbon sequestration of crop, soil carbon emissions and soil carbon storage point of view on the effects of three different crops and different farming practices to the carbon cycle. The contribution of atmospheric carbon dioxide from the soil-crop system was estimated in crop growing season. Then considering carbon emissions caused by agricultural inputs, carbon sequestration, carbon emission and net carbon sink was comprehensive evaluated in dry-farmland system under conservation tillage. The main results were as follows:1. The total carbon sequestration of crop was wheat<corn<soybeans, that in the entire system’s total annual carbon sequestration rate was20.29%,21.29%and58.42%. The performance of carbon sequestration rate was different at different growth stages of each crop, which showing an increase-decrease-and then increase-a further reduction of the "bimodal" trend. The peak position varies by crop. The rate of carbon sequestration became positive to negative when reaching maturity. Effect of different tillage methods on crop carbon sequestration rate was not significant, but there was a significant amount of influence in carbon sequestration. The total annual carbon sequestration of crop was39312.250,4375.201,47948.284,47049.809,46518.365and49512.140kg· hm-2in T, R, TS, RS, TSD and RSD treatments, respectively. Compared with the control, the total annual carbon sequestration of crop in other treatments was increased by11.29%,21.97%,19.68%,18.33and25.95%, respectively. As a result, ridge tillage and straw mulching treatments were in favor of more carbon fixation.2. The daily average soil respiration rate of each crop was wheat<corn<soybeans, that accounted for the total soil respiration rates was16.17%-16.34%,30.48%-33.64%and15.28%-16.35%. Under different tillage practice, soil respiration rate in wheat-soybean (w-s) belt was characterized by T<R<TS<TSD<RS<RSD, ridge tillage significantly increased soil respiration rate. Soil respiration rate in space-corn-space (k-c-k) belt was characterized by R<T<RS <TS<RSD<TSD. Compared with conventional tillage, in some extent straw mulching treatment enhanced soil respiration rate, but the ridge tillage had different effects because of the impact of the effect of different crops and different manifestations that is in wheat-soybean belt ridge tillage increased soil respiration rate but in corn belt was opposite.The experiment also shows that soil temperature and soil moisture content were the two major factors affecting soil respiration, explaining28.9%-53.7%and13.7%-42%of its seasonal variation. Regression analysis of the relationship between soil respiration and soil hydrothermal factors reveals that exponential equation (Rs=0.3lle0.095T) fits well the relationship between soil respiration and soil temperature at10cm in soil depth and the temperature sensitivity index (Q10) of soil respiration was2.25-2.69. However, the relationship between soil respiration and soil moisture content can be best described with a parabolic function. The threshold of soil moisture soil respiration responds to was14.94%. The dominant groups of soil animals were Collembola and Acarina, which were correlated with soil respiration to some extent. The correlation was high under the treatments of T and R, being ranged within0.669-0.921, whereas there was no remarkable correlation under the other treatments. The dominant groups of soil animals in maize field were Collembola, Acarina and Diptera. Compared to the control, ridge tillage reduced the number of soil animals, but straw mulching increased it and improved the index of soil animal diversity. This indicated that soil tillage patterns had great impact on soil animals. Soil respiration was only related with the animals above soil surface. The more was the amount of animals being active above soil surface, the stronger was the soil respiration. In all the treatments, the correlation coefficient of R was the highest (r=1.000, p=0.017), followed by TS (r=0.915, p=0.029). However there was no remarkable relationship between soil animals and soil respiration under traditional tillage. The dominant groups of soil animals in the soybean farmland were Collembola, Acarina and Diptera. There was no significant relationship between soil respiration and soil animals captured by tullgren apparatus and pitfall traps method. The correlation coefficient under T was significant, being r=0.901, p=0.037, when added together two methods for soil animals.3. Soil aggregates on the response of different crops were different. It told that planting corn was beneficial to the formation of soil water-stable micro-aggregates. Soil aggregates and organic carbon content were influenced by tillage and planting crops. Straw mulching treatment significantly increased soil organic carbon content in local soil and each particle aggregate both in0-5cm and5-10cm soil layers. The annual change of aggregate indicated that traditional tillage increased water-stable micro-aggregates of organic carbon content, while straw mulching treatment significantly increased organic carbon content of local soil and each particle size aggregate in every soil layers. In the5-10cm soil layer the soil organic carbon content increased slightly, indicating that this soil layer greatly influenced by straw mulching treatment. By estimating the carbon sequestration potential discovered that soil carbon sequestration potential was greater in corn belt than that in wheat-soybean belt. Straw mulching could improve soil carbon sequestration potential and reasonable arrangement of crops also helped enhance the carbon sequestration capacity. It played an important role in soil carbon sequestration and emission reduction by selective planting crops in straw mulching treatment. It suggested that changes in response to TC, POC, DOC, ROC and MBC on tillage measures were consistent:there was no significant response to R treatment but greatly influenced by the straw mulching treatment. The proportion of POC in TC was35.74%-49.66%and there was significant positive correlation between the two. So POC can be used as a sensitive index to reflect the change of soil organic carbon. Water-soluble organic carbon in soil organic carbon accounted for about0.2%, the difference between the different treatments was not significant. So it had no sensitivity. Easily oxidized organic carbon in soil organic carbon in the proportion accounted for6.29%-8.20%. Although the proportion of ridge and straw mulching treatment help improve easily oxidized organic carbon in soil organic carbon, but the proportion in TOC was smaller in ridge tillage treatment than in straw mulching treatment. It was indicated that straw mulching treatment help stabilize the soil organic carbon.4. There was a closely relationship between the farmland ecosystem carbon source/sink system characteristics and setting boundaries and spatial and temporal scales. The results showed that the regardless of soil-crop system or the farmland ecosystems of consideration with human activities were expressed as carbon sinks. The proportion of root respiration in total soil respiration was different in different crops at different growth stages. With the crop growing the proportion was first increased and then decreased. The soil-crop system carbon source/sink law consistent performance in wheat, corn and soybean fields. It was carbon source in the initial crop growth and maturity stage but in the rest of the time it was carbon sink. The carbon sequestration in R, TS, RS, TSD and RSD treatments was higher than the control. As a result, the ridge and straw mulch-based conservation tillage can significantly improve farmland ecosystem soil-crop system carbon sink capacity, increasing as much as9.93%-30.67%. In the course of tillage from conventional tillage to conservation tillage of change, despite there was an increased in soil carbon accumulation in straw mulching, but it was also increased carbon emissions from investment in agricultural system. It was also considered the performance of atmospheric carbon dioxide "source." Ridge tillage treatment not only made the accumulation of carbon in the soil reduced but also increased carbon emissions of the investment in agricultural system, so it was performance as the carbon dioxide "source". It was proved that it was valid only for a period of time the cumulative effect of changes in carbon form farming practice changes. It would eventually reach a steady state which there was no carbon accumulation rate. The changes of soil carbon stock would occur in farming practices when it happend initial changes, while carbon emission was stable from agricultural inputs. Therefore it was great to improve farm to enhance carbon sequestration and emission reduction potential relying on farming management practices.更多还原