Disentangling seasonal and interannual legacies from inferred patterns of forest water and carbon cycling using tree‐ring stable isotopes
Disentangling seasonal and interannual legacies from inferred patterns of forest water and carbon cycling using tree‐ring stable isotopes
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DOI：
10.1111/gcb.14395
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发表时间：
2018-08
影响因子：
11.6
通讯作者：
P. Szejner;W. Wright;S. Belmecheri;D. Meko;S. Leavitt;J. Ehleringer;R. Monson
中科院分区：
文献类型：
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作者：
P. Szejner;W. Wright;S. Belmecheri;D. Meko;S. Leavitt;J. Ehleringer;R. Monson
树木年轮碳、氧同位素比值已被用来了解森林碳和水循环的过去动态。最近，通过分离单个年轮内的解剖部分，这已经可以在单个生长季的不同部分实现。这种方法中的不确定性与相关的气候遗产有关，这些气候遗产可能以较高的频率发生，如在连续的季节发生，或以较低的频率发生，如跨年份。这项研究的目的是深入了解北美季风气候系统影响的纬度梯度上13个地点的黄松树早材(EW)和晚材(LW)组分的δ13C和δ18O同位素比值的相互关系。我们观察到，来自EW和LW的δ13C在大多数站点上具有显著的正相关，而EW和LW的δ18O值在大约一半的站点上存在交叉相关。结合统计模型和力学模型，我们发现δ13C和δ18O之间的相互关系可以用一种可能与长期气候变化有关的低频(多年)模式来解释。我们分离并在统计上消除了低频相关性，这导致了EW和LW同位素信号的更大地理差异。利用机械同位素分馏-气候模型探讨了EW和LW同位素比值之间剩余的高频(季节)互相关关系。这表明，与季风雨相关的较低的大气水汽压差增加了南部地点的δ13C和δ18O的东西向西向差异，而不是北部地点。我们的结果支持这样的假设，即与南方双峰降水相比，以单峰降水为主的地区，如北冰洋北部边界附近，更有可能促进EW和LW同位素信号的交叉相关，这可能是由于共同碳水化合物和土壤水资源池的更大共享。
Tree‐ring carbon and oxygen isotope ratios have been used to understand past dynamics in forest carbon and water cycling. Recently, this has been possible for different parts of single growing seasons by isolating anatomical sections within individual annual rings. Uncertainties in this approach are associated with correlated climate legacies that can occur at a higher frequency, such as across successive seasons, or a lower frequency, such as across years. The objective of this study was to gain insight into how legacies affect cross‐correlation in the δ13C and δ18O isotope ratios in the earlywood (EW) and latewood (LW) fractions of Pinus ponderosa trees at thirteen sites across a latitudinal gradient influenced by the North American Monsoon (NAM) climate system. We observed that δ13C from EW and LW has significant positive cross‐correlations at most sites, whereas EW and LW δ18O values were cross‐correlated at about half the sites. Using combined statistical and mechanistic models, we show that cross‐correlations in both δ13C and δ18O can be largely explained by a low‐frequency (multiple‐year) mode that may be associated with long‐term climate change. We isolated, and statistically removed, the low‐frequency correlation, which resulted in greater geographical differentiation of the EW and LW isotope signals. The remaining higher‐frequency (seasonal) cross‐correlations between EW and LW isotope ratios were explored using a mechanistic isotope fractionation–climate model. This showed that lower atmospheric vapor pressure deficits associated with monsoon rain increase the EW‐LW differentiation for both δ13C and δ18O at southern sites, compared to northern sites. Our results support the hypothesis that dominantly unimodal precipitation regimes, such as near the northern boundary of the NAM, are more likely to foster cross‐correlations in the isotope signals of EW and LW, potentially due to greater sharing of common carbohydrate and soil water resource pools, compared to southerly sites with bimodal precipitation regimes.