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Responses of functional traits to seven-year nitrogen addition in two tree species: coordination of hydraulics, gas exchange and carbon reserves
Tree Physiology ( IF 4 ) Pub Date : 2020-09-19 , DOI: 10.1093/treephys/tpaa120
Hongxia Zhang 1, 2 , Fenghui Yuan 1 , Jiabing Wu 1 , Changjie Jin 1 , Alexandria L Pivovaroff 3 , Jinyuan Tian 1, 2 , Weibin Li 4 , Dexin Guan 1 , Anzhi Wang 1 , Nate G McDowell 3, 5
Affiliation  

Abstract
Atmospheric nitrogen (N) deposition has been observed to impact plant structure and functional traits in terrestrial ecosystems. Although the effect of N deposition on plant water use has been well-evaluated in laboratories and in experimental forests, the linkages between water and carbon relations under N deposition are unclear. Here, we report on hydraulics, gas exchange and carbon reserves of two broad-leaved tree species (Quercus mongolica and Fraxinus mandshurica) in mature temperate forests after a seven-year experiment with different levels of N addition (control (CK), low (23 kg N ha−1 yr−1), medium (46 kg N ha−1 yr−1) and high (69 kg N ha−1 yr−1)). We investigated variation in hydraulic traits (xylem-specific hydraulic conductivity (Ks), native percentage loss of conductivity (PLC) and leaf water potential), xylem anatomy (vessel diameter and density), gas exchange (maximum net photosynthesis rate and stomatal conductance) and carbon reserves (soluble sugars, starch and total nonstructural carbohydrates (NSC)) with different N addition levels. We found that medium N addition significantly increased Ks and vessel diameter compared to control, but accompanied increasing PLC and decreasing leaf water potential, suggesting that N addition results in a greater hydraulic efficiency and higher risk of embolism. N addition promoted photosynthetic capacity via increasing foliar N concentration but did not change stomatal conductance. In addition, we found increase in foliar soluble sugar concentration and decrease in starch concentration with N addition, and positive correlations between hydraulic traits (vessel diameter and PLC) and soluble sugars. These coupled responses of tree hydraulics and carbon metabolism are consistent with a regulatory role of carbohydrates in maintaining hydraulic integrity. Our study provides an important insight into the relationship of plant water transport and carbon dynamics under increasing N deposition.


中文翻译:

两个树种功能性状对七年氮素添加的响应:水力学,气体交换和碳储量的协调

摘要
观测到大气中的氮(N)沉积会影响陆地生态系统中的植物结构和功能性状。尽管在实验室和实验森林中已经很好地评估了氮沉降对植物用水的影响,但是在氮沉降下水与碳关系之间的联系尚不清楚。在此,我们对成熟温带森林中两种阔叶树种(蒙古栎水曲柳)的水力,气体交换和碳储量进行了为期七年的试验,试验了不同水平的氮添加(对照(CK),低( 23 kg N ha -1  yr -1),中(46 kg N ha -1  yr -1)和高(69 kg N ha -1  yr)-1))。我们研究了水力性状的变化(木质部特定的水力传导率(K s),电导率的自然损失百分比(PLC)和叶片水势),木质部解剖结构(血管直径和密度),气体交换(最大净光合速率和气孔导度) )和碳含量(可溶性糖,淀粉和总非结构性碳水化合物(NSC))的氮含量不同。我们发现,与对照相比,添加中等量的氮显着增加了K s和血管直径,但同时增加了PLC降低叶片水势,表明氮的添加会导致更高的水力效率和更高的栓塞风险。氮的添加通过增加叶面氮的浓度来促进光合能力,但不改变气孔导度。此外,我们发现随着氮的添加,叶面可溶性糖浓度增加,淀粉浓度降低,水力性状(容器直径和PLC)与可溶性糖之间呈正相关。树木水力学和碳代谢的这些耦合响应与碳水化合物在维持水力学完整性中的调节作用一致。我们的研究为增加氮沉降下植物水分运输与碳动力学之间的关系提供了重要的见识。
更新日期:2020-09-19
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