Age-Related Changes in Water and Nitrogen Utilization in Crop Trees and Understory Vegetation in a Hinoki Cypress Plantation Forest in Kochi City, Southern Japan
Age-Related Changes in Water and Nitrogen Utilization in Crop Trees and Understory Vegetation in a Hinoki Cypress Plantation Forest in Kochi City, Southern Japan
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DOI：
10.3390/nitrogen3020017
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发表时间：
2022-05
期刊：
影响因子：
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通讯作者：
Y. Inagaki;K. Miyamoto;A. Sakai
中科院分区：
文献类型：
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作者：
Y. Inagaki;K. Miyamoto;A. Sakai
研究了日本南部高知市21 ~ 46年生扁柏种植园林中作物和林下植被水分和氮素利用率的变化。扁柏凋落叶中氮含量随林龄的增加呈下降趋势。扁柏叶片δ 15 N呈二次函数关系，从21 ~ 26年生叶片δ 15 N呈上升趋势，到46年生叶片δ 15 N呈下降趋势。这些结果表明，年龄较大的扁柏利用δ 15 N值较低的土壤氮源，林下植被对土壤氮的竞争应较强。扁柏的碳同位素鉴别力（Δ 13 C）在21 ~ 30年生时逐渐降低，到46年生时逐渐升高。而扁柏的内在水分利用效率（iWUE）在21 ~ 36年生时呈上升趋势，到46年生时则呈下降趋势。这些结果表明，扁柏树在早期通过减少气孔开度来提高其iWUE。在前期，随着林分密度的降低，林下植被的气孔开度增加，这是由于土壤水分的有效性增加。后期，由于氮素限制，扁柏光合能力降低，iWUE下降。这些结果表明，增加在扁柏的iWUE在响应大气中的二氧化碳浓度升高，应该是较小的，在后来的时间，因为更强的竞争与林下植被的土壤氮资源。
Age-related changes in water and nitrogen utilization of crop and understory vegetation in a hinoki cypress plantation forest were investigated from the age of 21 to 46 years in Kochi City, southern Japan. Nitrogen concentration in the leaf litter of hinoki cypress showed a decreasing trend with forest age. The leaf δ15N of hinoki cypress was related to a quadratic function and increased from the age of 21 to 26 years and then decreased to the age of 46 years. These results suggest that older hinoki cypress trees utilize soil nitrogen sources with lower δ15N values, and the competition for soil nitrogen with understory vegetation should be stronger. Carbon isotope discrimination (Δ13C) of hinoki cypress decreased from the age of 21 to 30 years and then increased to the age of 46 years. In contrast, the intrinsic water-use efficiency (iWUE) of hinoki cypress increased from the age of 21 to 36 years and then decreased to the age of 46 years. These findings suggest that hinoki cypress trees in the earlier time increased their iWUE by reducing stomatal opening. In the earlier time, the stomatal opening of understory vegetation increased due to higher soil water availability with decreasing stand density of crop trees. In the later time, the iWUE of hinoki cypress decreased due to lower photosynthetic capacity with nitrogen limitation. These results suggest that the increase in the iWUE of hinoki cypress in response to elevated atmospheric carbon dioxide levels should be smaller in the later time because of stronger competition with understory vegetation for soil nitrogen resources.