摘要
三北防护林是京津冀地区重要的生态屏障,但近十年来张北县4/5的杨树防护林出现退化现象,接近1/3的杨树濒临死亡或枯死,导致杨树防护林生态功能下降.本研究用稳定碳同位素方法追溯研究了退化与未退化杨树年轮中δ^(13)C值和内在水分利用效率(WUE_i)的差异,分析导致杨树退化和死亡的原因及其来源.结果表明:相同年龄杨树的直径随着退化程度增加而下降,退化杨树树轮的δ^(13)C值变化范围为-25.26‰^-22.97‰,未退化杨树为-26.15‰^-23.50‰,从1997年开始,退化杨树δ^(13)C值高于未退化杨树.退化与未退化杨树WUE_i值从1997年开始出现差异但不显著,2002年后其差异达到显著水平,退化与未退化WUE_i的差值ΔWUE_i连续正值可能是退化与未退化杨树产生分化的重要原因之一.退化和未退化杨树WUE_i与降雨量、相对湿度和潜在蒸散量(ET_0)的相关关系均不显著,但与气温和地下水埋深呈极显著的线性关系.1997年极端干旱事件是杨树林退化的起点,随后土地利用方式的改变导致地下水的过度使用,加剧了干旱持续时间和强度,进而加速杨树防护林的退化和死亡.
The Three-North Shelter Forest is an important ecological defense of Beijing-Tianjin-He- bei area. About four-fifths of poplar plantations declined and about a third of them were dying or al- ready dead in the last ten years. The mortality of trees resulted in the decline of ecological function of poplar plantation. In this study, we investigated the differences of ~13C and intrinsic water-use efficiency （WUE~） values in the tree-ring between dieback and non-dieback trees with stable car- bon isotope method. The cause of poplar plantation degradation and mortality was retrospectively ana- lyzed. The results showed that the diameter of poplar trees of nearly the same age decreased with the increase of degradation degree. The δ13C value of rings from dieback trees varied between -25.26%0 and -22.97%0, whereas that of non-dieback ones was -26.15%o to -23.50%0. The δ13C values of dieback trees were higher than that of non-dieback ones from 1997. There was a nonsignificant difference of the WUEi between dieback and non-diehack tree-ring from 1997 to 2001. And the difference of WUE： between dieback and non-dieback tree was significant since 2002. The eontinu- ous occurrence of positive AWUEi （ WUEidieback-WUEinon-dienack ） values might be one of important factors for subsequent divergence of the dieback and non-dieback poplar trees. The WUEi of both dieback and non-dieback trees had no significant relationship to precipitation, relative humidity and ET0, while significantly related with air temperature and ground water depth. The retrospective ana- lysis results showed that extreme drought in 1997 was a threshold when poplar trees began to de- cline. The underground water was overused because of land use change, which increased the inten- sity and duration of the drought, thus accelerated the degradation and mortalitv of lpoplar trees.
出处
《应用生态学报》
CAS
CSCD
北大核心
2017年第7期2119-2127,共9页
Chinese Journal of Applied Ecology
基金
林业公益性行业科研专项经费(201404206)
南京林业大学南方现代林业协同创新中心项目资助~~
关键词
小叶杨
树轮
稳定碳同位素
内在水分利用效率
土地利用方式
Populus simonii
tree rings
stable carbon isotope
intrinsic water-use efficiency
landuse type.
