黄土丘陵区植被恢复的土壤碳水效应
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摘要
黄土高原大规模植被恢复显著影响了这一区域土壤水分和有机碳(SOC),从而影响其承载的土壤水源涵养和固碳服务。明确深层土壤水分和有机碳对植被恢复的响应特征是当前黄土高原地区生态水文与生态系统服务研究的一个重要科学问题,其中植被类型以及生长年限是这一过程的重要影响因素。然而,目前关于深层土壤有机碳和土壤水分对植被恢复的响应及二者关系的研究较少。通过对陕北典型黄土丘陵区不同植被类型和生长年限下0—5 m土壤水分与有机碳的监测,分析了深层土壤水分和有机碳对植被恢复的响应及其特征。研究发现:(1)植被恢复后0—5 m土层均出现水分亏缺,土壤水分亏缺在表层1 m最低,2—3 m最高;对于不同恢复方式,林地土壤水分亏缺在恢复至21—30a时显著高于前一阶段(11—20a),而在恢复31a后水分开始恢复,而灌木、草地土壤水分亏缺程度则随恢复年限延长不断增加。(2)林地、灌木、草地0—5 m平均土壤有机碳含量为1.97、1.77、1.72 g/kg;林地土壤固碳量随恢复年限的增加而增加,并且在恢复20a时固碳量与对照农田相比出现净增;灌木土壤固碳量随恢复年限先增加后降低;草地土壤固碳量则随退耕年限增加呈下降趋势并且低于对照农田。(3)表层0—1 m土壤水分随恢复年限增加变化不显著,深层土壤水分则随恢复年限增加显著降低;相比而言,随恢复年限增加,土壤有机碳随年限的变化在各层土壤中均不显著。深层土壤水分与土壤有机碳呈现显著的正相关,且土壤有机碳的增加速率低于土壤水分,研究认为,深层土壤固碳与土壤水分关系密切,且深层土壤固碳需要充足水分参与。深层土壤水分亏缺可能限制植被细根的发展,使深层土壤有机碳输入减少。
Large-scale vegetation restoration in the Loess Plateau has had a major impact on the soil moisture content and soil organic carbon(SOC), as well as soil water conservation and carbon sequestration services in this region. The response of deep soil moisture and SOC contents to vegetation restoration raised serious concerns in current studies regarding eco-hydrology and ecosystem services in the Loess Plateau. However, limited studies have examined the responses of deep SOC and soil moisture along with their coupling relationships to vegetation restoration in this critical area. In this study, vertical distribution(0—5 m depth) of SOC and soil moisture contents in different human-introduced vegetation types(grassland, shrubland and forestland) and restoration ages in a typical loess hilly watershed were analyzed, and soil moisture and SOC contents in cropland were measured as controls. Our analyses showed that:(1) Soil moisture deficit was observed in different human-introduced vegetation types. The surface soil layer(0—1 m depth) had the lowest soil moisture deficit, and the 2—3 m depth layer had the highest soil moisture deficit. In forestland, soil moisture deficit was significantly greater in the 21—30 a stage than that in the previous stage(11—20 a), and subsequently decreased after 31 years of growth. However, soil moisture deficit in shrubland and grassland increased subsequent to abandonment of croplands.(2) The mean SOC contents of forestland, shrubland and grassland in the 0—5 m depth profile were 1.97, 1.77, and 1.72 g/kg, respectively. Soil carbon sequestration in forestland increased with increasing restoration ages, and exhibited net gain in the 20 a stage compared with cropland. Carbon sequestration in shrubland increased initially, but then decreased with increasing restoration age. In contrast to forestland and shrubland, carbon sequestration in grassland decreased with increasing restoration age, and was lower than that of control farmland for all restoration stages.(3) Soil moisture content in the surface layer(0—1 m depth) did not exhibit significant changes with increasing restoration age. However, soil moisture content significantly decreased in deep soil layers with increasing restoration age. Nevertheless, no significant correlation was found between levels of SOC and restoration age at any soil layers tested. In deep soil profiles, soil moisture content and SOC exhibited significantly positive correlations. Furthermore, the rate of increase of SOC was lower than that of soil moisture content. These findings indicated that deep soil carbon sequestration was closely related to soil moisture content. The soil carbon sequestration process may require adequate soil moisture at greater soil depth. Deep soil moisture deficit may restrict carbon sequestration in deep soil layers by constraining fine root development.
Large-scale vegetation restoration in the Loess Plateau has had a major impact on the soil moisture content and soil organic carbon(SOC), as well as soil water conservation and carbon sequestration services in this region. The response of deep soil moisture and SOC contents to vegetation restoration raised serious concerns in current studies regarding eco-hydrology and ecosystem services in the Loess Plateau. However, limited studies have examined the responses of deep SOC and soil moisture along with their coupling relationships to vegetation restoration in this critical area. In this study, vertical distribution(0—5 m depth) of SOC and soil moisture contents in different human-introduced vegetation types(grassland, shrubland and forestland) and restoration ages in a typical loess hilly watershed were analyzed, and soil moisture and SOC contents in cropland were measured as controls. Our analyses showed that:(1) Soil moisture deficit was observed in different human-introduced vegetation types. The surface soil layer(0—1 m depth) had the lowest soil moisture deficit, and the 2—3 m depth layer had the highest soil moisture deficit. In forestland, soil moisture deficit was significantly greater in the 21—30 a stage than that in the previous stage(11—20 a), and subsequently decreased after 31 years of growth. However, soil moisture deficit in shrubland and grassland increased subsequent to abandonment of croplands.(2) The mean SOC contents of forestland, shrubland and grassland in the 0—5 m depth profile were 1.97, 1.77, and 1.72 g/kg, respectively. Soil carbon sequestration in forestland increased with increasing restoration ages, and exhibited net gain in the 20 a stage compared with cropland. Carbon sequestration in shrubland increased initially, but then decreased with increasing restoration age. In contrast to forestland and shrubland, carbon sequestration in grassland decreased with increasing restoration age, and was lower than that of control farmland for all restoration stages.(3) Soil moisture content in the surface layer(0—1 m depth) did not exhibit significant changes with increasing restoration age. However, soil moisture content significantly decreased in deep soil layers with increasing restoration age. Nevertheless, no significant correlation was found between levels of SOC and restoration age at any soil layers tested. In deep soil profiles, soil moisture content and SOC exhibited significantly positive correlations. Furthermore, the rate of increase of SOC was lower than that of soil moisture content. These findings indicated that deep soil carbon sequestration was closely related to soil moisture content. The soil carbon sequestration process may require adequate soil moisture at greater soil depth. Deep soil moisture deficit may restrict carbon sequestration in deep soil layers by constraining fine root development.
引文
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[12] Zhao F H,Yu G R,Li S G,Ren C Y,Sun X M,Mi N,Li J,Ouyang Z.Canopy water use efficiency of winter wheat in the North China Plain.Agricultural Water Management,2007,93(3):99- 108.
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[14] Chen L D,Wei W,Fu B J,Lü Y H.Soil and Water Conservation on the Loess Plateau in China:Review and Perspective.Progress in Physical Geography:Earth and Environment,2007,31(4):389- 403.
[15] Chen H S,Shao M A,Li Y Y.The characteristics of soil water cycle and water balance on steep grassland under natural and simulated rainfall conditions in the Loess Plateau of China.Journal of Hydrology,2008,360(1/4):242- 251.
[16] Zhang H C,Liu S G,Yuan W P,Dong W J,Xia J Z,Cao Y J,Jia Y W.Loess Plateau check dams can potentially sequester eroded soil organic carbon.Journal of Geophysical Research:Biogeosciences,2016,121(6):1449- 1455.
[17] Chang R Y,Jin T T,Lü Y H,Liu G H,Fu B J.Soil carbon and nitrogen changes following afforestation of marginal cropland across a precipitation gradient in Loess Plateau of China.PLoS ONE,2014,9(1):e85426.
[18] Li Z W,Liu C,Dong Y T,Chang X F,Nie X D,Liu L,Xiao H B,Lu Y M,Zeng G M.Response of soil organic carbon and nitrogen stocks to soil erosion and land use types in the Loess hilly-gully region of China.Soil and Tillage Research,2017,166:1- 9.
[19] Li D J,Niu S L,Luo Y Q.Global patterns of the dynamics of soil carbon and nitrogen stocks following afforestation:A meta-analysis.New Phytologist,2012,195(1):172- 181.
[20] Sala O E,Lauenroth W K,Parton W J.Long-term soil water dynamics in the shortgrass steppe.Ecology,1992,73(4):1175- 1181.
[21] Wang S,Fu B J,Gao G Y,Liu Y,Zhou J.Responses of soil moisture in different land cover types to rainfall events in a re-vegetation catchment area of the Loess Plateau,China.Catena,2013,101:122- 128.
[22] Fu B J,Wang J,Chen L D,Qiu Y.The effects of land use on soil moisture variation in the Danangou catchment of the Loess Plateau,China.Catena,2003,54(1/2):197- 213.
[23] 张北赢,徐学选,白晓华.黄土丘陵区不同土地利用方式下土壤水分分析.干旱地区农业研究,2006,24(2):96- 99.
[24] Wang S,Fu B J,Gao G Y,Zhou J,Jiao L,Liu J B.Linking the soil moisture distribution pattern to dynamic processes along slope transects in the Loess Plateau,China.Environmental Monitoring and Assessment,2015,187(12):778.
[25] 穆兴民,徐学选,王文龙,温仲明,杜峰.黄土高原人工林对区域深层土壤水环境的影响.土壤学报,2003,40(2):210- 217.
[26] 兰志龙,潘小莲,赵英,司炳成,汪有科,焦瑞,张建国.黄土丘陵区不同土地利用模式对深层土壤含水量的影响.应用生态学报,2017,28(3):847- 855.
[27] Chen L D,Huang Z L,Gong J,Fu B J,Huang Y L.The effect of land cover/vegetation on soil water dynamic in the hilly area of the loess plateau,China.Catena,2007,70(2):200- 208.
[28] 杨磊,卫伟,陈利顶,蔡国军,贾福岩.半干旱黄土丘陵区人工植被深层土壤干化效应.地理研究,2012,31(1):71- 81.
[29] 从心海,梁一民,李代琼.黄土高原半干旱区沙棘根系特性与土壤水分动态研究.水土保持通报,1990,10(6):98- 103.
[30] 马祥华,白文娟,焦菊英,焦峰.黄土丘陵沟壑区退耕地植被恢复中的土壤水分变化研究.水土保持通报,2004,24(5):19- 23.
[31] 李婧,李占斌,李鹏,陈磊.黄土高原丘陵沟壑区退耕生态系统土壤水分动态变化规律研究.水土保持研究,2009,16(5):153- 156.
[32] Vesterdal L,Ritter E,Gundersen P.Change in soil organic carbon following afforestation of former arable land.Forest Ecology and Management,2002,169(1/2):137- 147.
[33] Gregorich E G,Greer K J,Anderson D W,Liang B C.Carbon distribution and losses:erosion and deposition effects.Soil and Tillage Research,1998,47(3/4):291- 302.
[34] Wang Y F,Fu B J,Lü Y H,Chen L D.Effects of vegetation restoration on soil organic carbon sequestration at multiple scales in semi-arid Loess Plateau,China.Catena,2011,85(1):58- 66.
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