Knowledge Resource Center for Ecological Environment in Arid Area
| 民勤绿洲弃耕地土壤有机碳和氮的变化特征研究 | |
| 其他题名 | Changes and characteristics in soil organic carbon and total nitrogen in the abandoned arable land in Minqin oasis of northwest China |
| 王军强 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 苏永中 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 位于石羊河流域下游的民勤绿洲，长期以来对土地的过度开发，导致水资源日益紧缺，并引发土地沙漠化与土壤盐渍化等生态问题。一些边缘绿洲区，如湖区的东湖镇，已成为生态危机的重灾区，不得不进行生态移民而导致大面积耕地弃耕。随着弃耕年限的增加，天然植被逐渐恢复，但土壤性状的演变尚不清楚。为此，本文采用时空替代法，以民勤绿洲区不同年限（3a、12a、20a、30a和40a）的弃耕地为研究对象，以传统农耕地（0a）为参照，分0-20、20-40和40-60cm四个土层取样，通过野外调查取样和室内测试分析，并运用统计和相关分析等方法，比较研究了农田弃耕后不同土层土壤有机碳、氮及其组分的演变特征。揭示弃耕对绿洲区土壤有机碳、氮及其组分的影响。主要研究结果如下:1弃耕地土壤有机碳、氮及其组分演变特征（1）弃耕后土壤剖面TOC和TN出现明显的分层现象。0-20cm土层土壤TOC和TN含量在弃耕3a后显著减少，前12a较为剧烈，和传统农耕地差异显著（P<0.05），12a后趋于平稳；20-40cm土层，TOC和TN含量在弃耕前30a增幅不大，和传统农耕地差异不显著，弃耕30a后其含量显著高于传统农耕地；40-60cm土层，弃耕30a前土壤TOC和TN含量缓慢下降，和传统农耕地差异不显著，30a后降幅较大。（2）弃耕后土壤剖面HFC、HFN的变化趋势和TOC、TN的变化趋势基本相似。0-20cm土层土壤LFC、HFC、LFN和HFN含量弃耕初期（3a）显著降低，弃耕12a后趋于平稳，均明显低于传统农耕地，HFC和HFN的分配比例随弃耕年限而增加，而LFC和LFN的分配比例随弃耕年限而减少；20-40cm和40-60cm土层LFC、HFC、LFN和HFN弃耕30a前和传统农耕地差异不显著，30a后差异显著（P<0.05）。20-40cm土层HFC、LFN分配比例随弃耕年限而增加，LFC和LFN分配比例随弃耕年限而减少，40-60cm土层LFC和HFC各弃耕年限之间差异不显著。（3）不同土层土壤MBC、MBN、POC、PON和ROC随弃耕年限的变化趋势和TOC、TN基本相似。短期弃耕（3a）后0-20cm土层土壤MBC、MBN、POC、PON和ROC分配比例高于传统农耕地（0a），并和其它弃耕地构成显著差异（P<0.05）。20-40cm土层，弃耕地土壤POC、PON和ROC分配比例和传统农耕地差异不显著，但是MBC和MBN的分配比例和传统农耕地差异显著（P<0.05）。弃耕40a后，深层（40-60cm）土壤MBC、MBN、POC、PON和ROC的分配比例明显低于传统农耕地和短期弃耕地（3a），但传统农耕地和短期弃耕地（3a）之间差异不显著。整个土壤剖面（0-60cm），深层（40-60cm）土壤Kos值明显高于表层土壤（0-20cm），而且长期弃耕地Kos值显著高于传统农耕地和短期弃耕地（3a），说明弃耕能提高土壤有机质的氧化稳定性，深层土壤表现的尤为突出。(4)弃耕年限对各组分有机碳、氮及其分配比例产生显著或极显著的影响，而且弃耕年限对各组分有机碳、氮及其分配比例的影响与土层深度有关。弃耕对ROC和Kos的影响与土层深度无关。土壤TOC和TN与各组分有机碳、氮都达到显著或极显著相关，其中HFC与TOC相关性最好，相关系数高达0.798，LFN与TN的相关性最好，相关系数达到0.536，说明在整个土壤取样层，TOC和TN的固持受各组分有机碳、氮的影响，其中HFC和LFN对TOC和TN的贡献尤为突出。（5）土壤TN和TOC以及各组分有机碳、氮与根生物量（BG-b）呈极显著正相关（P<0.001）。土壤中Na+含量与TN呈显著的负相关，EC与LFN呈显著的负相关关系（P<0.01），说明TN和LFN对土壤盐碱化较为敏感。TOC、POC、和HFC与土壤粘粉粒含量（CS）呈显著或极显著正相关，与沙粒含量（Sand）呈显著负相关，而与Kos和BD呈极显著正相关（P<0.01）。表明土壤中CS比例高，有助于提高弃耕地土壤中颗粒有机碳和重组有机碳含量，进而提高土壤总有机碳，盐碱化程度影响着土壤中氮的稳定性。2 弃耕地土壤有机碳和氮与水稳性团聚体的关系（1）弃耕后土壤＞0.25mm水稳性大团聚体和MWD显著提高，传统农耕地0-20，20-40和40-60cm土层MWD平均值分别为0.106±0.01，0.152±0.03和0.150±0.06mm，弃耕40a后，分别增至0.435±0.09，0.596±0.02和0.487±0.02mm，相应土层MWD依次增加了75.7%，74.5%和69.3%。OC和N在＞2mm WSA的富集程度显著影响团聚体的稳定性高低，土壤中51.41%-55.59%的OC和42.61%-48.94%的N累积在＜0.053mm的粘粉粒中，但是，随弃耕年限的延长，其含量持续减少。微团聚体（0.053-0.25mm）中OC和N含量的高低决定土壤TOC和TN含量的高低。总体而言，弃耕有助于提升土壤团聚体的稳定性（MWD增加）。（2）土壤中CS和BD与<0.053mm粒级WSA中OC和N含量呈极显著正相关（P<0.001），与MWD和>2mm粒级WSA中OC和N含量显著负相关（P<0.001）。根生物量（BG-b）与0.25-2mm粒级WSA中OC和N含量和MWD呈极显著的指数正相关（P<0.001），和<0.053mm粒级WSA中OC和N含量呈显著的线性负相关（P<0.05)。EC与0.053-2mm粒级WSA中OC和N含量呈极显著负相关（P<0.01）。说明根生物量有助于大团聚体中有机碳、氮的固存和团聚体稳定性的提高，土壤粘粉粒含量不利于土壤团聚体稳定性的提高。3弃耕地土壤有机碳和氮与球囊霉素相关土壤蛋白及水稳性团聚体的关系（1）t-GRSP和e-GRSP在弃耕地不同土层之间差异极显著（P<0.01）。0-20cm土层e-GRSP和t-GRSP含量随弃耕年限增加，弃耕40a其含量分别为73.65ug/g和275.66ug/g，分别为传统农耕地的2.16和2.99倍。弃耕40a后，20-40cm土层e-GRSP和t-GRSP含量分别为122.53ug/g和495.83ug/g，分别为传统农耕地的3.8和4.6倍，3a、12a和20a弃耕地球囊霉素相关土壤蛋白含量差异不显著。3个取样层中，40-60cm土层球囊霉素相关土壤蛋白含量变幅最小，弃耕30a之前差异不显著，弃耕30a后e-GRSP和t-GRSP含量显著提高。弃耕年限和土层的交互对t-GRSP产生极显著影响（P<0.001），对e-GRSP产生显著影响（P<0.05）。（2）e-GRSP和t-GRSP与0.25-1mm、1-2mm和>2mm粒径土壤水稳性大团聚体存在显著或极显著的正相关关系，与MWD达到显著或极显著正相关。e-GRSP和t-GRSP与>2 mm，0.25-1mm粒级WSA中OC和N含量显著线性正相关，与粘粉粒（<0.053 mm）中OC含量显著负相关，说明e-GRSP和t-GRSP能提高弃耕地土壤水稳性大团聚体的含量和WSA稳定性，并且提高水稳性大团聚体中OC和N含量。e-GRSP和t-GRSP与TOC和TN形成二次函数关系，说明GRSP对TOC和TN的贡献存在一定的范围。（3）土壤粘粉粒含量（<0.053mm）和BD抑制了弃耕地土壤中e-GRSP和t-GRSP含量的提高，而Silt、Ca2+、pH和SAR能促进其含量的提高。根据以上结果可以得出结论：弃耕后土壤有机碳、氮及其组分含量呈现明显的分层现象，与传统农耕地相比，0-20和40-60cm土层土壤有机碳、氮及其组分含量随弃耕年限而减少，而20-40cm土层中增碳优势突出，弃耕有利于土壤重组有机碳、氮和活性有机碳、氮在该土层中的形成和累积，而且该土层中活性有机碳、氮和总有机碳以及全氮的比例也明显高于传统农耕地。弃耕后有机碳、氮主要在水稳性大团聚体中富集，粘粉粒中有机碳、氮的含量逐步减少，而大团聚体中有机碳和氮的富集促进了土壤水稳性大团聚体的形成，并提高了其稳定性，说明弃耕后大团聚体对土壤养分的循环、转化和保存起重要作用。弃耕地球囊霉素相关土壤蛋白能提高土壤团聚体的稳定性，但和土壤有机碳、氮稳定性的关系还需要进一步研究。总体而言，弃耕能改善土壤结构，并使土壤有机质的氧化稳定性提高，且20-40cm土层土壤有机碳和氮随着弃耕时间延长而增加，但旱区生态恢复是一个缓慢的过程，土壤有机碳、氮含量很难在短期内整体恢复到较高的水平。 |
| 英文摘要 | Minqin oasis is typical arid oasis landscape and located at downstream of Shiyang River Basin, due to water resources scarcity and long-term human irrational exploitation, making this area is puzzled with desertification, salinization and other ecological problems, especially for DongHu town located at the Lake District, which become the hardest victim of ecological crisis. and large scale of ecological migration resulted in large area of cultivated lands abandoned at this area. With abandoned time increased, natural vegetation gradually recovered, but the evolution of soil properties is unclear untill now. The research was carried out in desert oasis region of semi-arid environment and interchangeablely space-time method was adopted. Dynamic change of soil OC, N and its components in different times (3, 12, 20, 30 and 40 a) and different soil layers (0-20, 20-40 and 40-60 cm) of abandoned cultivated lands were analyzed in the Minqin Oasis, Northwest China, the cultivated land (0a) was selected as control. Sampling survey, indexes laboratory analysis and statistical methods was used to explore effects of abandoned cultivation practices on soil organic carbon and nitrogen evolution characteristics. The results showed that:1 The changes of soil OC, N and its fractions in abandoned cultivated lands1) The total OC (TOC) and total N (TN) contents presented the phenomenon of stratification across soil depths in this arid ecosystem. Top soil (0-20cm) TOC and TN were reduced dramatically 3a abandoned later, decreased sharply before 12a abandonment, and significant differencecompared with cultivated land (P<0.05); 20-40cm layer, soil TOC and TN content increased slowly before 30a abandonment, there was no significant difference compared with the cultuvated land but reached maximum 30 years later; 40-60cm layer, soil TOC and TN decreased slowly at early stage and reached significant level after 30a compared with cultivated land.2) The HFC and HFN presented the similar trends as TOC and TN on the whole soil profile. LFC, HFC, LFN and HFN contents were reduced dramatically 3a abandoned later and stabilized after12a at top soil (0-20cm), all were significantly lower than cultivated land, the distribution ratio of HFC and HFN increases with abandonment times, however, the distribution ratio of LFC and LFN reduced with the abandonment time; Before 30a abandonment, LFC, HFC, LFN and HFN were no difference compared to cultivated land at 20-40cm and 40-60cm depths, and significant difference after 30a abandonment (P<0.05)。The distribution ratio of HFC and LFN increased with abandonment at 20-40cm depth, but the distribution ratio of LFC and LFN decreased at this depth. The distribution ratio of LFC and HFC can not reach the significant level at 40-60cm depth.3) MBC, MBN, POC, PON and ROC presented the similar trends as TOC and TN on the whole soil profile. The distribution ratio of MBC, MBN, POC, PON and ROC were higher than cultivated land (0a) after short-term abandonment (3a) on 0-20cm soil depth, and significant differences with others (P<0.05). There were no significant difference between abandoned lands and cultivated land of soil POC, PON and ROC distribution ratio at 20-40cm depth, but the distribution ratio of MBC and MBN showed the significant difference between abandoned lands and cultivated land at this depth (P<0.05). After 40a abandonment, the distribution ratio of MBC, MBN, POC, PON and ROC were significantly lower than short-term abandoned land (3a) and cultivated land at deeper soil (40-60cm), but the short-term abandoned land (3a) and cultivated land can not reach the significant different level. The Kos in deeper soil was significantly higher than surface and long-term abandonment caused Kos higher than cultivated land and short-term abandoned land (3a), indicated that cultivated land abandonment can improve soil organic matter oxidation stability and deep soil has obvious superiority.4) Land abandonment time, soil depth and the interaction of these two variables have a significant effect on the OC, N and the their distribution ratio, but they was no impact for ROC and Kos. The OC and N components had significant or extremely significant correlation with TOC and TN. Among them, HFC had the best correlation with TOC (correlation coefficientaccount to 0.798), LFN had the best correlation with TN (correlation coefficient account to 0.536), indicated that the OC and N accumulation affected by its components and HFC and LFN act as key role.5) Soil TN and TOC and its components were significant positively correlated with the root biomass (BG-b) (P<0.001). Na+ was significant negatively correlated with TN, and EC was significant negatively correlated with LFN (P<0.01), so the TN and LFN content were sensitive to soil salinization. TOC, POC and HFC were significant positively correlated with soil silt and clay content (CS) and significant negativelycorrelated with sand content were significantly or very significantly positively correlated with Sand was a correlation, while Kos was highly significant positively correlated with BD (P<0.01). Showed that higher proportion of soil CS can improve the POCand HFC content in abandoned cultivated lands, and soil salinity influence the N content and its stability.2 The relationship between OC, N and water-stable aggregates (WSA)1) Results showed a significant increase in MWD and the proportion of ＞0.25 mm macroaggregates as the time of land abandonment. The effect of time on MWD since land abandonment was determined by the changes in OC and N accumulation in WSA＞2 mm.The WSA with size fraction of＜0.054 mm had the greatest OC ( accounting for 51.41%-55.59% of the total OC) and N ( accounting for 42.61%-48.94% for the total N) contents,and this fraction decreased linearly (P<0.05) over 40a after cultivated land abandonment. The OC and N contents in microaggregates (0.053-0.25mm) were the dominant factors that influenced the total OC and N variations in abandoned cultivated land. The results of this study suggested that cultivated land abandonment may result in the recovery of WSA stability (i.e. MWD and WSA proportion) and shift soil organic matter from the clay plus silt and microaggregate fractions to the macroaggregate fractions.2) The CS and BD were linearly positive correlated with OC and N in clay and silt fraction (<0.053mm, P<0.001), while="" negative="" correlated="" with="" oc="" and="" n="" in="" megaggregates="">2 mm, P<0.001). MWD was significant positively correlated with BG-b, OC and N within 0.25-2mm WSA (P<0.001), but significant negatively correlated with OC and N within clay and silt fraction (<0.053mm, P<0.05). EC was significant negatively correlated with OC and N within 0.053-2mm size WSA (P<0.01). Indicated that BG-b seem highly important for the OC and N sequestration in water stable macroaggregates and MWD, and CS can not.3 The relationship between glomalin-related soil protein(GRSP) and OC, N and WSA1) t-GRSP and e-GRSP were significant difference among soil layers at abandoned cultivated lands (P<0.01). Soil e-GRSP and t-GRSP content increased with the abandonment time at 0-20cm depth, after 40a abandonment, they reached 73.65ug/g and 275.66ug/g, respectively, were 2.16 and 2.99 times to those under cultivated land. 40a cultivated land abandonment caused soil e-GRSP and t-GRSP contents reached 122.53ug/g and 495.83ug/g, respectively, were 3.8 and 4.6 times to those under cultivated land, but they had not significant difference after 3a, 12a and 20a abandonment. Among three sampling layers, GRSP content at 40-60cm had the minimum change range, they were no significant difference before 30a abandonment, and improved significantly after 30a abandonment. The interaction of abandonment time and soil depth had highly significant effected for t-GRSP (P<0.001) and significant effected for e-GRSP (P<0.05).2) e-GRSP and t-GRSP were significant positively correlated with 0.25-1mm, 1-2mm and > 2mm water-stable macroaggregates, respectively, they also significant positively correlated with MWD. e-GRSP and t-GRSP were linearly positive correlated with OC and N content in >2 mm and 0.25-1mm macroaggregates and negatively correlated with OC silt and clay fraction (<0.053 mm), indicating that e-GRSP and t -GRSP can improve the water-stable macroaggregates content and WSA stability after cultivated land abandonment, they also promoted OC and N accumulated in macro-aggregates. There was a siginificant quadratic function relationship between GRSP to TOC and TN, indicated that there has a certain range when discussed the GRSP contribution for TOC and TN.3) Soil CS content (<0.053mm) and BD play an inhibition role for e-GRSP and t-GRSP after cultivated land abandonment, but Ca2+, pH, and SAR had promotion effect on them. From the above results it can be concluded: Soil organic carbon and nitrogen and its components showed significant stratification after cultivated land abandoned. Compared to conventional farmland, OC, N and its components reduced with abandonment time at 0-20 and 40-60cm depth, while increased at 20-40cm depth, abandonment in favor of forming and accumulating of TOC, TN and active OC, N at 20-40cm depth, meanwhile, abandoned lands had higher active OC: TOC and active N: TN ratio compared to cultivated lands. After land abandonment, OC and N enriched in water-stable macroaggregates, and the OC, N content within clay and silt particle gradually reduced, OC and N enriched in large aggregates promoted the formation of water-stable macroaggregates and improved its stability, suggesting that it takes an important role in the cycling, transforming and holding capacity of soil OC and N after cultivated lands abandoned. Glomalin related soil protein could improve the stability of soil aggregates on abandoned cultivated lands, but the relationship between soil OC, N and WSA needs further study. Overall, cultivated lands abandoned can improve soil structure and soil organic matter oxidation stability (especially at 20-40cm depth). In the semi-arid environment, soil properties recovery following abandonment is slow and the improvement of soil OC and N is likely to require a considerably long period of time. |
| 中文关键词 | 有机碳 ; 全氮 ; 土壤团聚体 ; 弃耕地 ; 民勤绿洲 |
| 英文关键词 | Organic carbon Nitrogen Soil aggregates Abandoned cultivated land Minqin oasis |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287693 |
| 推荐引用方式 GB/T 7714 | 王军强. 民勤绿洲弃耕地土壤有机碳和氮的变化特征研究[D]. 中国科学院大学,2016. |
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