Five-year nitrogen addition affects fine root exudation and its correlation with root respiration in a dominant species, Quercus crispula, of a cool temperate forest, Japan
Five-year nitrogen addition affects fine root exudation and its correlation with root respiration in a dominant species, Quercus crispula, of a cool temperate forest, Japan
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DOI：
10.1093/treephys/tpz143
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发表时间：
2020-03-01
期刊：
影响因子：
4
通讯作者：
Hiura, Tsutom
中科院分区：
文献类型：
--
作者：
Ataka, Mioko;Sun, Lijuan;Hiura, Tsutom
在森林生态系统中，细根呼吸直接促进地下碳 (C) 循环。细根的渗出物通过增强土壤有机质的微生物分解间接影响碳循环。尽管这些根部产生的碳通量是地下碳循环的重要组成部分，但氮 (N) 添加如何影响这些通量及其相关性仍不清楚。在这项研究中，测量了在北海道大学苫小牧实验森林这一冷温带森林中发现的优势树冠物种卷叶栎的细根分泌物、呼吸和化学/形态特征，该森林已经经历了五年的氮添加。还测量了大块土壤和根际土壤中的土壤溶解有机碳（DOC），以评估细根分泌物对土壤碳循环的影响。与未施氮处理的对照区相比，施氮区的细根表现出更大的直径和更高的氮浓度，但比根长度和面积更低。在根重的基础上，不同地块的呼吸作用没有差异，但在添加氮的情况下渗出量略高。以根部面积为基础，氮添加图中的渗出量明显更高。此外，在氮添加图中，根际和土体土壤之间的 DOC 差异是对照图的两倍。尽管在对照和施氮小区中，细根呼吸与渗出呈正相关，但渗出 C 与呼吸 C 的比率在施氮 5 年后下降。添加氮还影响细根分泌物的绝对碳分配，并改变了渗出物和呼吸通量之间的碳分配策略。这些发现将有助于增强对未来富氮条件下地下碳分配和碳循环的预测。
In forest ecosystems, fine root respiration directly contributes to belowground carbon (C) cycling. Exudation from fine roots indirectly affects C cycling via enhanced microbial decomposition of soil organic matter. Although these root-derived C fluxes are essential components of belowground C cycling, how nitrogen (N) addition affects these fluxes and their correlations remains unclear. In this study, fine root exudation, respiration and chemical/morphological traits were measured in a dominant canopy species, Quercus crispula Blume, found in a cool temperate forest, the Tomakomai Experimental Forest, Hokkaido University, which has undergone 5-year N addition. Soil-dissolved organic carbon (DOC) was also measured in both bulk and rhizosphere soils to evaluate the impact of fine root exudation on soil C cycling. Compared with a control plot with no N treatment, fine roots in the N addition plot exhibited larger diameters and higher N concentrations, but lower specific root lengths and areas. On a root-weight basis, respiration was not different between plots, but exudation was slightly higher under N addition. On a root-area basis, exudation was significantly higher in the N addition plot. Additionally, differences in DOC between rhizosphere and bulk soils were two times higher in the N addition plot than the control plot. Although fine root respiration was positively correlated with exudation in both the control and N addition plots, the ratio of exudation C to respiration C decreased after 5-year N addition. Nitrogen addition also affected absolute C allocation to fine root exudation and changed the C allocation strategy between exudation and respiration fluxes. These findings will help enhance predictions of belowground C allocation and C cycling under N-rich conditions in the future.