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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Twentieth century trends in tree ring stable isotopes (δ ~(13)C and δ~(18)O) of Larix sibirica under dry conditions in the forest steppe in Siberia
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Twentieth century trends in tree ring stable isotopes (δ ~(13)C and δ~(18)O) of Larix sibirica under dry conditions in the forest steppe in Siberia

机译：西伯利亚森林草原干旱条件下西伯利亚落叶松树轮稳定同位素（δ〜（13）C和δ〜（18）O）的二十世纪趋势

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摘要

Tree ring width, density, and ratio of stable isotopes (~(13)C/~(12)C and ~(18)O/~(16)O) in wood and cellulose were determined for larch (Larix sibirica Ledeb.) growing under water deficit conditions in the forest steppe zone in central Siberia (5424N, 8957E) for the period 1850-2005. Dendroclimatic analysis of the chronologies indicated precipitation to be the most important factor determining indicated parameters. Precipitation of June is significantly correlated with tree ring width and maximum density (r = 0.36 and 0.43, p < 0.05, respectively). Relations of δ~(13)C and δ~(18)O to precipitation are similar, but the most important month is July (r = -0.47, p < 0.05 for δ~(13)C; r = -0.29, p < 0.05 for δ~(18)O). Further, δ~(18)O is positively related to the mean temperatures of July (r = 0.30, p < 0.05). Carbon and oxygen isotope ratios in wood and cellulose showed strong negative trends for the last 100 years. The reason for this decrease could be the observed shift of the beginning of the vegetation period to earlier dates (up to 1 week) in spring and the increased use of precipitation water stored in the soil from October of the previous year, although other explanations cannot be excluded (in particular the physiological effect of increasing atmospheric CO_2 also responsible for lower δ~(13)C values). Thus, an earlier start of the vegetation period could lead to tree ring formation during a period with higher water availability, resulting in stronger isotopic fractionation and ~(13)C depletion, also reflected in a higher earlywood to latewood ratio. At the same time, highly ~(18)O depleted water from October precipitation of the previous year is absorbed. The incorporation of this isotopically lighter water during photosynthesis is reflected in the wood and cellulose of tree rings.
机译：确定了落叶松（Larix sibirica Ledeb。）在木材和纤维素中的年轮宽度，密度和稳定同位素的比率（〜（13）C /〜（12）C和〜（18）O /〜（16）O）。西伯利亚中部森林草原区（5424N，8957E）在缺水条件下生长的时间为1850-2005年。年代学的树状气候分析表明，降水是确定指示参数的最重要因素。 6月的降水量与年轮宽度和最大密度显着相关（r分别为0.36和0.43，p <0.05）。 δ〜（13）C和δ〜（18）O与降水的关系相似，但最重要的月份是七月（r = -0.47，p <0.05对于δ〜（13）C; r = -0.29，p δ〜（18）O <0.05。此外，δ〜（18）O与七月的平均温度呈正相关（r = 0.30，p <0.05）。在过去的100年中，木材和纤维素中的碳和氧同位素比显示出强烈的负趋势。这种减少的原因可能是观察到的春季开始的植被期移到了较早的日期（长达1周），以及从去年10月开始增加了土壤中存储的降水用水的使用，尽管其他解释不能排除（特别是增加大气中CO_2的生理效应也导致较低的δ〜（13）C值）。因此，植被期的较早开始可能会在水利用率较高的时期导致树木年轮的形成，从而导致更强的同位素分馏和〜（13）C耗竭，这也反映在较高的早木与晚木比率上。同时，从上一年的十月降水中吸收了〜（18）O的高耗水。光合作用过程中这种同位素较轻的水的混入反映在树木和树木年轮的纤维素中。

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