Sun Lijuan, Ataka Mioko, Kominami Yuji, Yoshimura Kenichi
Lab of Forest Ecology, Graduate School of Agriculture, Kyoto University, Kitashirakawa OiwakeCho, Kyoto 606-8502, Japan.
Graduate School of Agriculture, Kyoto University, Main Building of Agriculture School, Kitashirakawa OiwakeCho, Kyoto 606-8502, Japan.
Tree Physiol. 2017 Aug 1;37(8):1011-1020. doi: 10.1093/treephys/tpx026.
Plants allocate a considerable amount of carbon (C) to fine roots as respiration and exudation. Fine-root exudation could stimulate microbial activity, which further contributes to soil heterotrophic respiration. Although both root respiration and exudation are important components of belowground C cycling, how they relate to each other is less well known. In this study, we aimed to explore this relationship on mature trees growing in the field. The measurements were performed on two canopy species, Quercus serrata Thunb. and Quercus glauca, in a warm temperate forest. The respiration and exudation rates of the same fine-root segment were measured in parallel with a syringe-basis incubation and a closed static chamber, respectively. We also measured root traits and ectomycorrhizal colonization ratio because these indexes commonly relate to root respiration and reflect root physiology. The microbial activity enhanced by root exudation was investigated by comparing the dissolved organic carbon (DOC) and microbial biomass carbon (MBC) between rhizosphere soils and bulk soils. Mean DOC concentration and MBC were ca two times higher in the rhizosphere soils and positively related to exudation rates, indicating that exudation further relates to the C dynamics in the soils. Flux rates of exudation and respiration were positively correlated with each other. Both root exudation and respiration rates positively related to ectomycorrhizal colonization and root tissue nitrogen, and therefore the relationship between the two fluxes may be attributed to fine-root activity. The flux rates of root respiration were 8.7 and 10.5 times as much as those of exudation on a root-length basis and a root-weight basis, respectively. In spite of the fact that flux rates of respiration and exudation varied enormously among the fine-root segments of the two Quercus species, exudation was in proportion to respiration. This result gives new insight into the fine-root C-allocation strategy and the belowground C dynamics.
植物会将大量的碳（C）以呼吸作用和分泌物的形式分配到细根中。细根分泌物能够刺激微生物活动，进而促进土壤异养呼吸。尽管根系呼吸作用和分泌物都是地下碳循环的重要组成部分，但它们之间的相互关系却鲜为人知。在本研究中，我们旨在探究野外成熟树木中这两者的关系。测量工作是在一个暖温带森林中对两种冠层树种——锯齿栎（Quercus serrata Thunb.）和青冈栎（Quercus glauca）进行的。分别使用基于注射器的培养法和封闭静态箱法，平行测量了同一细根段的呼吸速率和分泌速率。我们还测量了根系性状和外生菌根定殖率，因为这些指标通常与根系呼吸作用相关且能反映根系生理状况。通过比较根际土壤和非根际土壤之间的溶解有机碳（DOC）和微生物生物量碳（MBC），研究了根系分泌物增强的微生物活动。根际土壤中的平均DOC浓度和MBC大约高出两倍，且与分泌速率呈正相关，这表明分泌物进一步与土壤中的碳动态相关。分泌速率和呼吸速率彼此呈正相关。根系分泌物和呼吸速率均与外生菌根定殖和根组织氮呈正相关，因此这两种通量之间的关系可能归因于细根活动。基于根长和根重，根系呼吸通量速率分别是分泌通量速率的8.7倍和10.5倍。尽管两种栎树细根段之间的呼吸通量速率和分泌通量速率差异极大，但分泌作用与呼吸作用成比例。这一结果为细根碳分配策略和地下碳动态提供了新的见解。
