Ectomycorrhizal fungi respiration quantification and drivers in three differently-aged larch plantations

Abstract

Soil respiration (Rs) is generally partitioned into autotrophic respiration (by roots and mycorrhizae) and heterotrophic respiration (by decomposers). Boreal and temperate forests are widely associated with ectomycorrhizal (EM) fungi, which play a critical role in belowground carbon dynamics. However, the magnitude and factors controlling EM fungal respiration (Rem) have not been well studied in field experiments. In this study, we quantified Rem using the micro-pore mesh method in three Larix principis-rupprechtii plantations of different ages (i.e., 11-, 20-, and 45-year-old, representing sapling, young, and mature stands, respectively) during the growing seasons from 2014 to 2016 in North China. The results showed clear seasonality of Rem, with an initial increase in spring (May and June), peak in summer (July and August), and decrease in autumn (September and October). Rem represented 37, 47 and 39% of rhizosphere respiration in the sapling, young, and mature stands, respectively, with an average of 41% across the three stands, indicating that a significant portion of rhizosphere respiration originated from EM fungi in larch plantations. Rem was positively correlated with soil temperature and the annual fine root increment, but negatively correlated with soil moisture when values exceeded 0.055 cm3 cm–3. Stand age had no significant effects on Rem, but Rem and the contribution of Rem to Rs in summer in the sapling stand was significantly higher than values in the young and mature stands. These results may be due to the higher values of soil temperature and annual fine root increment and lower soil inorganic nitrogen in the sapling stand relative to the other two stands. Overall, our results emphasize the importance of partitioning and quantifying EM fungal respiration to improve our understanding and predictions of belowground carbon dynamics under global climate change.