基于根部年轮与导管特征的黄土高原苜蓿生长衰退分析
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摘要
紫花苜蓿作为黄土高原退耕还林还草工程的重要人工草本物种,对控制水土流失、植被固碳和生态环境改善等方面都发挥着重要生态作用;但是苜蓿草地在黄土高原普遍出现生长不可持续的特征,在第6年左右植被出现明显生长衰退现象。本研究在黄土高原4个降水梯度(280、400、500 mm和550 mm)的地点采集紫花苜蓿和自然对照草本物种:委陵菜的根部年轮样品,并分析了紫花苜蓿与委陵菜的年轮宽度和导管大小随年龄的变化趋势特征及与气候要素的相关关系。研究结果表明:在气候暖干化环境下,紫花苜蓿和委陵菜的年轮宽度随年龄增加都有不断下降的趋势,且在降水量偏低样点下降更为显著,这是由于植株在降水量偏低地点易遭受严重水分胁迫,以致无法满足生长所需的水分而造成根部生长速率明显减缓。紫花苜蓿根部导管大小随年龄增加均有明显下降趋势,在降水量偏低的样点下降趋势更加显著;这表明水分胁迫随年龄增加逐渐加剧,紫花苜蓿导管大小逐年下降以致不能满足自身生长的水分需求,植被生长呈衰退趋势,且在降雨偏低地区,苜蓿生长衰退出现时间较早。自然草本委陵菜根部导管大小随年龄增加均有明显上升趋势且在降水量偏低样点上升趋势更显著,这表明委陵菜通过增大根部导管大小、增加输水能力来满足随年龄增加不断上升的水分需求,这也说明委陵菜导管结构特征较好的适应了黄土高原干旱半干旱环境,生长处于可持续发展状态。
Alfalfa( Medicago sativa L.) is an important artificial herb species planted widely in the Loess Plateau during the ‘Grain to Green'large-scale revegetation program that been in operation since 1999. It plays an important ecological role in controlling soil erosion,increasing plant carbon sequestration,and improving ecological conditions. However,the growth of alfalfa grassland is unsustainable and shows signs of growth degradation after about 6 years in the Loess Plateau because of its high growth rate and deep root systems. The current understanding of the physiological mechanisms of the growth degradation of alfalfa grassland in the Loess Plateau is still limited. In this study,we collected samples of the main roots of alfalfa and a natural control,the herbaceous species Chinese cinquefoil( Potentilla chinensis) along a precipitation gradient( 280 mm,400 mm,500 mm,and 550 mm) in the Loess Plateau,then analyzed the variations in radial incremental growth( growth rings) and xylem size,as well as the climatic factors that correlate with these characteristics,of the main roots of the two perennial forb species. The results indicated that the annual ring widths of alfalfa and Chinese cinquefoil both decreased noticeably with increasing age,and that the growth reduction was more pronounced at sites with lower precipitation. This shows that the perennial forbs in the Loess Plateau were confronted with deteriorating environmental conditions with increasing age,and the recent trend of a warmer and drier climate is further aggravating water deficits for these forb species. The vessel sizes of plants in the alfalfa grasslands along the precipitation gradient all declined monotonically with increasing age,and the vessel reduction was more obvious at sites with lower precipitation. With the gradually intensifying water deficits with increasing age,the vessel diameter of alfalfa decreased significantly and could not satisfy the self-growing water demand,and serious growth degradation had occurred in recent years. If the alfalfa grassland was located at a dry site with lower precipitation,the time of growth degradation occurred earlier. In contrast,the vessel size of the main roots of Chinese cinquefoil kept consistently increasing with increasing age,and the amplitude of the increase in vessel size at the relatively dry site was comparatively large. This indicated that Chinese cinquefoil could enlarge its vessel size to enhance water-use efficiency,then satisfy its increasing water demand with increasing age. The concurrently accelerated water acquisition ability of Chinese cinquefoil with increasing age also indicated that it can adapt to the semiarid climatic conditions of the Loess Plateau,and maintain a state of sustainable growth development.
Alfalfa( Medicago sativa L.) is an important artificial herb species planted widely in the Loess Plateau during the ‘Grain to Green'large-scale revegetation program that been in operation since 1999. It plays an important ecological role in controlling soil erosion,increasing plant carbon sequestration,and improving ecological conditions. However,the growth of alfalfa grassland is unsustainable and shows signs of growth degradation after about 6 years in the Loess Plateau because of its high growth rate and deep root systems. The current understanding of the physiological mechanisms of the growth degradation of alfalfa grassland in the Loess Plateau is still limited. In this study,we collected samples of the main roots of alfalfa and a natural control,the herbaceous species Chinese cinquefoil( Potentilla chinensis) along a precipitation gradient( 280 mm,400 mm,500 mm,and 550 mm) in the Loess Plateau,then analyzed the variations in radial incremental growth( growth rings) and xylem size,as well as the climatic factors that correlate with these characteristics,of the main roots of the two perennial forb species. The results indicated that the annual ring widths of alfalfa and Chinese cinquefoil both decreased noticeably with increasing age,and that the growth reduction was more pronounced at sites with lower precipitation. This shows that the perennial forbs in the Loess Plateau were confronted with deteriorating environmental conditions with increasing age,and the recent trend of a warmer and drier climate is further aggravating water deficits for these forb species. The vessel sizes of plants in the alfalfa grasslands along the precipitation gradient all declined monotonically with increasing age,and the vessel reduction was more obvious at sites with lower precipitation. With the gradually intensifying water deficits with increasing age,the vessel diameter of alfalfa decreased significantly and could not satisfy the self-growing water demand,and serious growth degradation had occurred in recent years. If the alfalfa grassland was located at a dry site with lower precipitation,the time of growth degradation occurred earlier. In contrast,the vessel size of the main roots of Chinese cinquefoil kept consistently increasing with increasing age,and the amplitude of the increase in vessel size at the relatively dry site was comparatively large. This indicated that Chinese cinquefoil could enlarge its vessel size to enhance water-use efficiency,then satisfy its increasing water demand with increasing age. The concurrently accelerated water acquisition ability of Chinese cinquefoil with increasing age also indicated that it can adapt to the semiarid climatic conditions of the Loess Plateau,and maintain a state of sustainable growth development.
引文
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[2]李文静,王振,韩清芳,任曾辉,闫明科,张鹏,贾志宽,杨宝平.黄土高原人工苜蓿草地固碳效应评估.生态学报,2013,33(23):7467-7477.
[3]Wang G H,Zhang X S.Supporting of potential forage production to the herbivore-based pastoral farming industry on the Loess Plateau.Acta Botanica Sinica,2003,45(10):1186-1194.
[4]傅伯杰,陈利顶,马克明.黄土丘陵区小流域土地利用变化对生态环境的影响---以延安市羊圈沟流域为例.地理学报,1999,54(3):241-246.
[5]焦峰,温仲明,李锐.黄土高原退耕还林(草)环境效应分析.水土保持研究,2005,12(1):26-29,78-78.
[6]温晓霞,翁琴,李生烨,杨改河.黄土高原苜蓿草业开发利用探讨.干旱地区农业研究,2003,21(3):160-163.
[7]王铭财.浅析紫花苜蓿的种植技术及经济价值.农业与技术,2015,35(10):149-149.
[8]廖允成,王立祥,温晓霞.黄土高原苜蓿草业基地组建的可行性分析.草业科学,1996,13(6):45-48.
[9]李裕元,邵明安.黄土高原北部紫花苜蓿草地退化过程与植物多样性研究.应用生态学报,2005,16(12):2321-2327.
[10]李裕元,邵明安,上官周平,樊军,王丽梅.黄土高原北部紫花苜蓿草地退化过程与植被演替研究.草业学报,2006,15(2):85-92.
[11]侯军岐,张社梅.黄土高原地区退耕还林还草效果评价.水土保持通报,2002,22(6):29-31.
[12]苏永中,刘文杰,杨荣,范桂萍.河西走廊中段绿洲退化土地退耕种植苜蓿的固碳效应.生态学报,2009,29(12):6385-6391.
[13]郑江坤,魏天兴,朱金兆,赵健,陈致富,朱文德,大林直.黄土丘陵区自然恢复与人工修复流域生态效益对比分析.自然资源学报,2010,25(6):990-1000.
[14]韩仕峰.宁南山区苜蓿草地土壤水分利用特征.草业科学,1990,7(5):47-53.
[15]罗珠珠,牛伊宁,李玲玲,蔡立群,张仁陟,谢军红.陇中黄土高原不同种植年限苜蓿草地土壤水分及产量响应.草业学报,2015,24(1):31-38.
[16]韩瑞宏,卢欣石,高桂娟,杨秀娟.紫花苜蓿(Medicago sativa)对干旱胁迫的光合生理响应.生态学报,2007,27(12):5229-5237.
[17]李玉山.苜蓿生产力动态及其水分生态环境效应.土壤学报,2002,39(3):404-411.
[18]余玲,王彦荣,Garnett T,Auricht G,韩德梁.紫花苜蓿不同品种对干旱胁迫的生理响应.草业学报,2006,15(3):75-85.
[19]刘建新,王鑫,王凤琴.水分胁迫对苜蓿幼苗渗透调节物质积累和保护酶活性的影响.草业科学,2005,22(3):18-21.
[20]Dietz H,Ullmann I.Age-determination of dicotyledonous herbaceous perennials by means of annual rings:Exception or rule?Annals of Botany,1997,80(3):377-379.
[21]Olano J M,Almería I,Eugenio M,von Arx G.Under pressure:how a Mediterranean high-mountain forb coordinates growth and hydraulic xylem anatomy in response to temperature and water constraints.Functional Ecology,2013,27(6):1295-1303.
[22]Dietz H,von Arx G.Climatic fluctuation causes large-scale synchronous variation in radial root increments of perennial forbs.Ecology,2005,86(2):327-333.
[23]Büntgen U,Trnka M,Krusic P J,Kyncl T,Kyncl J,Luterbacher J,Zorita E,Ljungqvist F C,Auer I,Konter O,Schneider L,Tegel W,Stepanek P,Bronnimann S,Hellmann L,Nievergelt D,Esper J.Tree-ring amplification of the early nineteenth-century summer cooling in central Europe.Journal of Climate,2015,28(13):5272-5288.
[24]von Arx G,Carrer M.ROXAS-A new tool to build centuries-long tracheid-lumen chronologies in conifers.Dendrochronologia,2014,32(3):290-293.
[25]易浪,任志远,张翀,刘雯.黄土高原植被覆盖变化与气候和人类活动的关系.资源科学,2014,36(1):166-174.
[26]谢宝妮,秦占飞,王洋,常庆瑞.黄土高原植被净初级生产力时空变化及其影响因素.农业工程学报,2014,30(11):244-253.
[27]王云强.黄土高原地区土壤干层的空间分布与影响因素[D].北京:中国科学院研究生院(教育部水土保持与生态环境研究中心),2010.
[28]张军周,勾晓华,赵志千,刘文火,张芬,曹宗英,周非飞.树轮生态学研究中微树芯石蜡切片制作的方法探讨.植物生态学报,2013,37(10):972-977.
[29]王章勇,杨保,秦春,史锋.树木径向生长机制监测和模拟研究进展.中国沙漠,2013,31(3):780-787.
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