【作者】 郭志彬；

【导师】 李凤民；

【作者基本信息】 兰州大学 ， 生态学， 2010， 博士

【摘要】 退耕还草是半干旱黄土高原地区改善生态环境的重要途径,但如何还草促进植被恢复是一个重要的科学问题。我们对退耕后的撂荒地进行了不同的人工辅助恢复手段以探讨寻求有效途径来促进生态环境的恢复和改善。从2003年4月起对退耕撂荒地进行3个处理：(1)撂荒地自然恢复；(2)在撂荒地中引入两年生豆科植物草木樨(Melilotus officianalis);(3)在撂荒地中引入多年生的豆科植物紫花苜蓿(Medicago sativa)。实验期间(2003-2008),自然恢复的地上生物量不稳定,年际间波动很大,0-500 cm土壤含水量显著增加。到了2008年,土壤pH值和土壤容重(0-20 cm和20-40 cm)显著下降,水稳性团聚体含量和颗粒直径>0.25mm的土壤团聚体含量显著增加。在大(>0.25 mm)、中(0.05mm<<0.25mm)、小(<0.05 mm)团聚体组分中,土壤有机碳(SOC)含量均表现为增加趋势,土壤全氮(TN)和全磷(TP)含量变化不显著,速效磷(AP)含量明显降低。2003-2008年表层0-20cm的土壤SOC、轻组碳(LFOC)和TN的含量成增加趋势,并与自然恢复年限成正相关(R=0.659**,R=0.939***,R=0.709**)。土壤TN与LFOC呈显著正相关(R=0.515*)。土壤碳磷比(C／P)(土壤有机碳与和速效磷的比值)和土壤微生物碳含量(MBC)显著增加。其中,MBC与SOC(R=0.832*)和LFOC (R=0.839*)表现为正相关性,与AP(P=—0.826*)含量呈负相关。引入两年生豆科植物草木樨的撂荒地地上生物量在2005年显著低于实验期间其他年份。实验期间,土壤0-500 cm含水量呈增加趋势。土壤pH值和容重(0-20cm和20-40 cm)与实验初期相比呈下降趋势。水稳性团聚体含量增加显著。除速效磷含量外,不同组分团聚体中土壤有机碳、全氮呈增加趋势。2003-2008期间每年4月份土壤SOC和TN表现出先增长后下降的趋势,且在2005年达到最大值。LFOC呈增长趋势并与草木樨地年限成正相关性(R=0.702**)。土壤C／N比在2005年显著下降,其他年份间差异不显著。在耕地中引入两年生豆科植物之后,MBC含量增加显著并与SOC (R=0.838*)、TN (R=0.831*)呈显著正相关性。在紫花苜蓿人工草地中,地上生物量表现为增加趋势,并且与生长年限呈正相关性(R=0.817*)。试验期间,苜蓿地0-500 cm的土壤含水量下降非常显著,其中100cm以下的土壤含水量与苜蓿生长年限呈负相关(R=—0.79***)并形成土壤干层；苜蓿地的土壤pH值和土壤容重(0-20 cm和20-40 cm)均显著下降。此外,水稳性团聚体百分含量和直径>0.25 mm范围内的土壤团聚体含量均呈显著增长。在不同团聚体组分中,除了AP含量显著下降外,SOC和TN含量都显著增加。实验期间,苜蓿地每年4月0-20cm的土壤SOC和LFOC含量显著增加,且与苜蓿生长年限成正相关性(R=0.654**,R=0.920***)；土壤TN显著增加,并与苜蓿生长年限以及LFOC成显著正相关(R=0.576*,R=0.562*),土壤碳氮比(C／N)无显著变化；AP含量下降非常显著,土壤中C／P显著增加。种植紫花苜蓿后,MBC显著增加且与SOC(R=0.949**,P<0.01)、LFOC(R=0.966***)和TN(R=0.838*)含量呈正相关,与土壤速效磷(R=—0.986**)含量呈显著负相关性。2003-2008年期间,自然恢复下0-500 cm的土壤水分含量显著高于草木樨地和苜蓿草地；同草木樨地不同,自然恢复和苜蓿草地土壤SOC和TN在实验期间表现为稳定增长,且随着实验年限的增加自然恢复和苜蓿草地土壤SOC和TN含量均高于草木樨地。总之,在撂荒地中引入豆科植物,地上植被生物量以及土壤物理性质均能显著改善,但苜蓿在生长过程中对土壤深层水分消耗过大并在100cm以下形成土壤干层不利于草地的可持续性,草木樨对土壤水分、养分的改善效果不显著。因此,同引入豆科植物的撂荒地相比,自然恢复有利于改善土壤深层水分和土壤养分,进而促进黄土高原农业的可持续发展。更多还原

【Abstract】 It was important way to improve the ecosystem after conversion of farmland for forest and grassland Regeneration. However, it is hard for us to select which species and how to restore the plant cover after the farmland was abandoned. To improve the ecosystem and develop sustainable agriculture, this experiment was designed. In April 2003, cropland was enclosed and three treatments were implemented:(1) natural regeneration (NR); (2) the perennial legume species alfalfa (Medicago sativa Linn.) (AF); and (3) the biennial legume species sweetclover (Melilotus officinalis Linn.) (SF).In NR, the aboveground biomass was unstable and significantly differed among years in the experiment. Beside these, the soil water content at depth of 0-500 cm increased significantly. Compared to 2003, the soil pH and soil bulk density in 0-20 cm and 20-40 cm decreased significantly, and the soil water-stable aggregates in >0.25 mm category increased significantly in 2008; Moreover, in the large soil aggregates (with diameter in>0.25 mm class) (LSA), middle soil aggregates (with diameter in 0.25-0.05 mm class) (MSA) and small soil aggregates (with diameter in <0.05 mm class)(SSA), the soil organic carbon (SOC) increased significantly, and the total nitrogen (TN) and total soil phosphorus (TP) were no significant differences; meanwhile, the soil available phosphorus (AP) decreased significantly in all aggregates classes in 2008. During the experiment, the content of SOC, light fraction organic carbon (LFOC) and TN increased, and a positive correlation was existed between SOC, LFOC and TN and the growth years (the values of R was:R=0.659**, R=0.939***, R=0.709**, respectively). During the experiment, the values of SOC to AP (C/AP) and soil microbial biomass carbon (MBC) increased, and the MBC was positively correlated with SOC (R=0.832*) and LFOC(R=0.839*), negatively correlated with AP (R=-0.826*).In SF, the aboveground biomass was stable except 2005 in the experiment. The soil water content in 0-500 cm increased significant in the experiment. During the experiment, the soil pH and bulk density in 0-20 cm and 20-40 cm decreased but the water-stable soil aggregates increased significantly. In all the soil aggregates classes, the SOC and TN increased. In the experiment, the SOC and TN increased and reached the maximum values in 2005 and then declined. The C/N ratios decreased significantly in 2005 then increased; the LFOC increased and was correlated with the growth years (R=0.702**); The values of soil C/AP increased. Meanwhile, the soil MBC increased significantly in the experiment, and a positive correlationship existed between MBC and SOC (R=0.838*, P<0.05), TN (R=0.831*, P<0.05).In AF, the aboveground biomass increased and a positive correlation-ship existed between the aboveground biomass and the growth year(R=0.817*) during the experiment; the soil water content in 0-500 cm decreased significantly, especially below 100 cm, a negative correlation-ship existed between the soil water content and growth year (R=-0.79***) and a permanent dry soil layer formed as the alfalfa lasted more than five years. During the experiment, the soil pH and bulk density in 0-20 cm and 20-40 cm decreased significantly; Additionally, the water-stable aggregates, soil aggregates in>0.25 mm class and SOC in LSA, MSA and SSA all increased significantly; AP in all soil aggregates categories decreased significantly in the experiment. During the experiment, there was a positive correlation between SOC, LFOC and the growth years (The values of R were:R=0.654**, R=0.920***, respectively); TN increased significantly and was positive correlated with the growth years and LFOC (The values of R were:R=0.576*, R=0.562*, respectively); the soil AP decreased significantly. In experiment, the C/AP and MBC increased significantly. Beside these, the MBC was positively correlated with SOC (R=0.949**) and TN (R=0.838*), and negatively correlated with AP (R=-0.986**).Compared to SF and AF, the soil water in NR at depth of 0-500 cm was higher, which was help to improve the deep soil water. The SOC and TN in NR and AF increased steadily and were higher than SF in April 2008. Above all, the aboveground biomass and soil physical properties had been improved after the legume species introduced into the cropland in the experiment. However, the AF extracted amount of soil water during its growth and formed a dry layer below 100 cm; the SF did not help to improve the soil nutrients. Therefore, the NR was the best way to improve the deep soil water and soil qualtiy, helped to develop the sustainable agriculture.更多还原