【作者】 王春阳；

【导师】 周建斌；

【作者基本信息】 西北农林科技大学 ， 生态学， 2011， 博士

【摘要】 凋落物是生态系统中生产的绿色植物光合作用产物的一部分,是生态系统中归还养分的一个主要途径,其分解的快慢直接影响到地表凋落物的积累,也制约着N、P等元素及其他物质向土壤的归还和土壤养分的有效性,进而影响土壤中有机质的形成和累积,以及土壤的理化性质。凋落物的分解是陆地生态系统物质循环和能量转换的主要途径,在维持土壤肥力、保证植物再生长养分的可利用等均起着重要作用,同时对生态系统的碳累积具有重要的影响。黄土高原土地退化、侵蚀严重,是我国乃至世界上水土流失最严重的地区之一。为此,国家从上个世纪末开始在这一地区实施了以退耕还林还草、封山育林为主的生态建设工程。近年来,有关黄土高原区植被恢复重建与生态环境之间的关系已经进行了大量的研究工作,主要集中于植被恢复后对减少径流泥沙、养分流失及植被恢复多年后对土壤性质的影响等方面,而对不同植被下凋落物的分解状况以及在分解过程中对土壤的影响等方面研究较少。本文选取黄土高原退耕还林还草、封山育林区分布较为广泛的几种植物凋落物为研究对象,采用室内和田间试验相结合的方法研究了不同凋落物的基本化学组成、分解特性,及其进入土壤后对土壤微生物量碳、氮和矿质态氮含量的影响,旨在揭示凋落物在土壤中分解过程中碳、氮的转化规律。研究获得以下主要结论:1.利用2种浸提剂(水和0.01 mol·L^-1 CaCl₂)提取不同大小（2 mm粉碎样和1 cm长）的植物凋落物,测定可溶性有机碳的含量及其生物降解特性。结果表明,不同植物凋落物可溶性有机碳的含量在4.21～156.82 g·kg^-1之间,其占凋落物全碳的比例为0.99%～32.84%,且平均草本类凋落物最低。经过7 d的培养,不同植物凋落物可溶性有机碳的生物降解率在34.7%～80.6%之间,平均草本类也最低。培养结束时植物凋落物可溶性有机碳的UV280吸收值和腐殖化指数（HIXem值）均极显著高于起始时测定值,且培养起始时UV280吸收值和HIXem值与植物凋落物的可溶性有机碳的生物降解率呈显著负相关。2.采用室内培养法研究了6种不同植物凋落物及其与不同形态氮素（NH₄⁺-N及NO₃^--N）配施对土壤微生物量碳、氮及矿质态氮含量的影响。结果表明,加入不同凋落物均显著提高了土壤微生物量碳、氮含量,其中加入柠条、沙打旺等碳氮比低的凋落物在培养的一段时期内土壤微生物量碳、氮均高于碳氮比高的凋落物（刺槐、沙柳和长芒草）。将凋落物与NH₄⁺或NO₃^-同时添加,也提高了土壤微生物量碳、氮含量,其中添加铵态氮的土壤微生物量碳、氮含量的增加达显著水平,说明微生物更易利用铵态氮。加入C/N高的凋落物后土壤中的矿质氮发生固持,矿质态氮固持量与凋落物的C/N比呈显著的正相关关系。3.采用室内培养法研究了6种不同植物凋落物及等比例混合后对土壤微生物量碳、氮及矿质态氮含量的影响。结果表明,加入不同植物凋落物均显著提高了培养期间土壤微生物量碳、氮含量。总体平均,添加三种等量混合后植物凋落物的土壤微生物量碳、氮含量高于两种凋落物等量混合处理,而两种凋落物混合高于单种凋落物处理;土壤矿质态氮含量的变化则相反,即单种>两种混合>三种混合。单种和两种混合后土壤微生物量碳、氮含量与其碳氮显著相关,而三种凋落物混合后土壤微生物量碳、氮含量与其碳氮比无相关性,说明多种凋落物混合后土壤微生物量碳、氮含量受多种因素共同影响。4.采用网袋法研究了6种凋落物单种及等质量配比混合后在半湿润易旱区（杨凌）的分解及其碳、氮变化动态。结果表明,不同种类凋落物及配比后分解50%所需的时间在0.79～1.43 a之间,分解95%所需的时间在3.43～6.19 a之间。三种凋落物混合后的平均分解速率和平均分解系数大于两种凋落物混合,单种凋落物处理最小。到分解试验结束时,不同处理凋落物的全碳、全氮平均释放率表现为单种>两种混合>三种混合。不同处理凋落物可溶性有机碳含量、可溶性总氮含量、可溶性有机碳占全碳的比例以及可溶性总氮含量占全氮的比例在培养起始的两个月内有升有降,但在随后的4个月内均显著降低,而后缓慢降低。到分解结束时,不同凋落物可溶性有机碳含量、可溶性总氮含量、可溶性有机碳占全碳的比例及可溶性总氮含量占全氮的比例均表现为单种>两种混合>三种混合。5.采用网袋法研究了6种凋落物单种及等质量配比混合后在半干旱区（神木）的分解及其碳、氮变化动态。结果表明:经过近14个月的分解后,三种凋落物混合后的平均质量损失率高于两种混合凋落物,单种凋落物最低。到分解试验结束时,不同处理凋落物的全碳、全氮平均释放率均表现为单种>两种混合>三种混合;而不同处理的可溶性有机碳平均含量表现为两种混合>三种>单种;可溶性总氮含量则为三种混合>两种混合>单种。相关分析表明,凋落物的质量损失率与可溶性有机物,特别是可溶性有机碳具有一定的相关性。因此,在黄土高原丘陵沟壑区植被恢复重建中在选择植物种类时,有必要采用不同种类植物搭配,利用生物多样性以及不同植物凋落物的碳、氮养分含量及转化特性,协调土壤碳、氮转化过程,促进生态系统健康持续发展。更多还原

【Abstract】 As the product of photosynthesis of plants, plant litter is a major way for nutrients returning to an ecosystem. And litter decomposition rate affects directly on the accumulation of litter, and on the nutrient availability in soil, as well as on the formation and accumulation of organic matter and the physical and chemical properties of soil. Litter decomposition is the primary means of both nutrient cycling and energy conversion in terrestrial ecosystems, and plays an important role in maintaining soil fertility, the availability of nutrients to plant.The Loess Plateau is the one of the most serious areas of land degradation and soil erosion not only in China, but also in the world. Therefore, Chinese government has initated a big ecological project in late 1990s to reestablish the ecology in this region by returning of croplands to forests and grasslands. In recent years, there were a lot of researches to study the relationship between ecological environment and vegetation restoration. However, these researches focused on the reduction of runoff and sediment, nutrient loss and soil properties during vegetation restoring. And there were few researches to study the decomposition and their effects on soil properties during litter decomposing.In this research, both incubation and field experiment were used to study the chemical elements and decomposition of different species litters and their effects on soil microbial biomass carbon and nitrogen and mineral nitrogen in order to understand carbon and nitrogen transformation in soil during litter decomposing. The main conclusions were as follows:1. Plant litters were sampled from Shenmu in the Loess Plateau, and the contents of soluble organic carbon （SOC） in two sizes litters （2 mm and 1 cm length） was extracted with two extractants (distilled water and 0.01 mol·L^-1 CaCl₂). And a 7-day incubation experiment was conducted to compare the biodegradability of soluble organic carbon of the different plant litters. The result showed that the contents of SOC in the different plant species ranged from 4.21 g·kg^-1 to 156.82 g·kg^-1, and the ratios of SOC to total carbon （SOC/TC） of the plant litters were in range of 0.99% and 32.84%. And the average of grass litter was the lowest. After 7-day of incubation, biodegradation rates of SOC in different plant litters ranged from 34.7% to 80.6%, and the average of grass litters was the lowest. The UV280 absorbance and humification index （HIXem） at the end of incubation were significantly higher than that that start of incubation, and the UV280 absorbance and HIXem were significantly negatively correlation with the bio-degradation rate of soluble organic carbon in plant litter.2. A laboratory experiment was conducted to determine the content of soil microbial biomass carbon and nitrogen （SMBC, SMBN） and mineral about both different species litters and nitrogen forms (（NH₄⁺-N and NO₃^--N）. In general, the addition of the sole plant litter significantly increased the contents of SMBC and SMBN. The increasing rates of SMBC and SMBN were higher when the plant litters with low C/N ratios （e.g., A. adsurgens, C. Korshinskii,） than those with a higher C/N ratio （R. pseudoacacia, Salix psammophila, Stipa bungeana）. The dual addition of plant litter and N fertilizer, either as NH₄⁺-N or NO₃^--N, also increased the contents of SMBC and SMBN, and the increasing rate was significant higher under the NH₄⁺-N treatment, but not under the NH₄⁺-N treatment, compared to the sole plant litter treatment. Our results thus indicated that microorganisms in this Losses soil may prefer to use NH₄⁺-N rather than NO₃^--N. In addition, the addition of plant litters with higher C/N ratios increased the immobilization of mineral N in the soil, and there was a positively significant relationship between the immobilized N and the C/N ratio in the plant litters.3. An incubation experiment was conducted to study the effects of addition of different mixtures of litters of plant species on contents of SMBC, SMBN and mineral nitrogen in soil. The results showed that the addition of either one single or two or three mixed plant litters to the soil significantly increased the contents of SMBC and SMBN. Overall, both the averaged SMBC and SMBN during incubation were highest in the treatments with three-plant-species litters, next were the treatments with two-plant-species litters, and then the treatments with single plant species litter. In contrast to the SMBC and SMBN, contents of mineral nitrogen in soil showed a reverse pattern among the three litter treatments: three-plant-species litter > two-plant-species litter > single plant species litter addition. Meanwhile, there was a significantly positive relationship between the SMBC and SMBN and the C/N ratio in one-plant-species or the two-species litters, but not in the three-plant-species litter. These results indicate that SMBC and SMBN contents were affected by a range of factors, including incubation conditions （temperature, soil water holding capacity, incubation time period, etc.） and the chemical properties of the litter （C and N content, organic compounds, etc.）, particularly when the mixed three-plant-species litters were added to soil.4. The different mixures of six plant litters were put into litter bags and buried into 15 cm depth of soil in Yangling to study the litter decomposition in soil. The result showed that it took 0.79～1.43 years for 50% decomposition of the different litter treatments, and 3.43～6.19 years for 95% decomposition. The order of average litter decomposition rates were three-plant-species litter > two-plant-species litter > single plant species litter. At the end of field experiment, the average release rate of total carbon and nitrogen of three-plant-species litters was higher than that under two-plant-species litters; and the single plant species litter was the lowest. The content of soluble organic carbon and total soluble nitrogen and the ratio of the soluble organic carbon/total carbon and total soluble nitrogen/total nitrogen were variable in the first two months; and decreased significantly in the following four months, and then decreased slowly. At the end of experiment, the order of the content of soluble organic carbon and total soluble nitrogen and the ratios of the soluble organic carbon/total carbon and total soluble nitrogen/total nitrogen were single plant species litter > two-plant-species litter > three-plant-species litter.5. The different mixures of six plant litters were put into litter bags and buried into 15 cm depth of soil in Shenmu to study the litter decomposition in soil. The results showed that the average mass loss rate of three-plant-species litter was higher than that of two-plant-species litter; and the lowest was single-species litter. At the end of experiment, the order of the release rate of total carbon and nitrogen was single plant species litter > two-plant-species litter > three-plant-species litter. However, the order of soluble organic carbon was two-plant-species litter > three-plant-species litter > single plant species litter; and the order of total soluble nitrogen was three-plant-species litter > two-plant-species litter > single plant species litter. In addition, there was a close relationship between the mass loss rate and soluble organic carbon of litter.Therefore, we suggest increasing the more species of plants during the vegetation restoration in order to maintain the ecological system sustainable and healthy in the gully and valley region in the Loess Plateau.更多还原