Evaluation of the effect of the 2011 Tsunami on coastal forests by means of multiple isotopic analyses of tree-rings

ABSTRACT The March 2011 Mega-Tsunami in eastern Japan damaged at different degrees the black pine (Pinus thunbergii) forests along the coast. In order to evaluate the recovery of black pine four years later, tree-ring samples from 9 trees for the period 2002–2014 were analyzed for ring growth and stable isotopes (δ13C, δ15N and δ18O). The results showed that annual tree-ring width decreased approximately 70 % from the year 2011 to 2014 compared to the period previous to the tsunami (2002–2010). The multiple isotopic analyses showed that the reduction in growth was caused by soil salinity that prompted stomatal closure and an abrupt increase of tree-ring δ13C. Sea water deposition in the soil did not affect tree-ring δ18O values. Two years after the tsunami, decreasing tree-ring δ13C values caused by apparently photosynthetic recovery did not translate into radial tree-growth, indicating a possible shift in carbon allocation to foliage and mainly roots as a defense mechanism to sodium toxicity. The dual δ13C-δ18O model explains neither the limited growth nor the subsequent recovery in δ13C. Similarly tree-ring δ15N indicated that there was no difference in nitrogen availability before and after the tsunami, suggesting that nutrients were not a limitation but rather soil salinity.

摘要 2011年3月日本东部的大海啸不同程度地破坏了沿海的黑松（黑松属日本黑松）林。为了评估四年后黑松的恢复情况，对9棵树2002 - 2014年期间的树木年轮样本进行了年轮生长和稳定同位素（δ13C、δ15N和δ18O）分析。结果表明，与海啸前（2002 - 2010年）相比，2011年至2014年年轮宽度每年大约减少70%。多种同位素分析表明，生长减少是由土壤盐分导致气孔关闭以及年轮δ13C突然增加所引起的。土壤中的海水沉积没有影响年轮δ18O值。海啸两年后，明显由光合作用恢复引起的年轮δ13C值下降并没有转化为树木的径向生长，这表明碳分配可能转向叶片，主要是根部，作为对钠毒性的一种防御机制。δ13C - δ18O双模型既无法解释有限的生长，也无法解释δ13C随后的恢复。同样，年轮δ15N表明海啸前后氮的可利用性没有差异，这表明养分不是限制因素，而是土壤盐分。