10:45 AM - 11:00 AM
[MIS11-07] Effects of understory vegetation removal on soil nitrogen availability and ectomycorrhizal community composition in a northern forest
Keywords:oak, Sasa dwarf bamboo, ammonium, nitrate, root tip
Trees and understory vegetation compete with resources underground. Productivity of understory vegetation often corresponds to or larger than that of trees. Sasa dwarf bamboo (hereafter Sasa) is one of the major understory vegetation in cool-temperate forests in Japan. It is known that biomass and production of Sasa contribute much to those of ecosystems, but recently understory vegetation including Sasa decreases due to high pressure of deer browsing. On the other hand, most of terrestrial plants live symbiotically with mycorrhiza (e.g., grasses including Sasa with arbuscular mycorrhiza (AM), not all but most trees with ectomycorrhiza (EcM)). However, relationships between EcM colonization or EcM community composition and ecosystem functioning such as nitrogen (N) dynamics are not understood well despite its flexibility depending on stand structure and environmental factors. Decrease of understory vegetation living symbiotically with AM would change EcM dynamics and its relationship with N dynamics in forests. We manipulated removal of above ground understory Sasa and investigated soil N availability, soil physical and chemical properties, EcM colonization rate and EcM community composition before and after the Sasa removal (SR) to clarify the effects of Sasa decline on soil N dynamics and EcM dynamics. We expected that soil N availability increases due to reduced N uptake by Sasa and EcM colonization and composition change in environment without Sasa.
We established twelve plots of 8 m in radius surrounding mature oak (Quecus crispula) trees in cool-temperate forest covered with Sasa (Sasa senanensis) in understory in Nakagawa Experimental Forest in northern Japan. We cut the above ground parts of Sasa and exported them to outside in June 2017 in six SR plots. We collected surface 10 cm soil in May 2017 (before SR) and September 2017 (after SR). We measured gravimetric soil water content, and soil inorganic N content, dissolved organic carbon (DOC) and dissolved organic N (DON) contents after soil extraction (soil:0.5M K2SO4=1:10). We measured microbial biomass C (MBC) and N (MBN) using chloroform fumigation method. We also collected root sample of oak surrounding target oak trees in October 2016 (before SR) and September 2017 (after SR). We observed 300 root tip per sample using stereomicroscope and counted EcM and non-EcM root tips. We further distinguish EcM to the types based on the observation of fungal sheath and recorded number. We calculated EcM colonization rate as the ratio of EcM root tips to the total. We extracted DNA of each EcM type and sequenced, then identified OTU (operational taxonomic unit) by homology analysis in nucleotide search. We tested EcM community structure and effects of SR and soil environments by non-metric multidimensional scaling (NMDS) and PerMANOVA.
There was no significant difference in soil inorganic N, DOC, DON contents, DOC/DON, MBC, MBN, and MBC/MBN between SR treatments. EcM colonization rate did not significantly differ between SR treatments. Regarding EcM composition, eleven and ten OTUs were identified before and after SR, respectively. Dominant OTUs throughout the observation period were Helotiales, Russula, and Lactarius. Community composition was not significantly different between SR treatments. In addition, SR or any soil environmental factors did not significantly affect the EcM community composition. Stable EcM community composition after SR would be attributable to stable soil environment after SR and slow response of root associated EcM community under situation that parent trees remained. Further, Russula and Lactarius, which were dominant even before SR, has been reported to be dominant in N-rich environment, suggesting the possibility that N status before SR in our site was not N limited. This study demonstrated stable root associated EcM community composition and soil N dynamics after understory vegetation removal during relatively short period after the disturbance.
We established twelve plots of 8 m in radius surrounding mature oak (Quecus crispula) trees in cool-temperate forest covered with Sasa (Sasa senanensis) in understory in Nakagawa Experimental Forest in northern Japan. We cut the above ground parts of Sasa and exported them to outside in June 2017 in six SR plots. We collected surface 10 cm soil in May 2017 (before SR) and September 2017 (after SR). We measured gravimetric soil water content, and soil inorganic N content, dissolved organic carbon (DOC) and dissolved organic N (DON) contents after soil extraction (soil:0.5M K2SO4=1:10). We measured microbial biomass C (MBC) and N (MBN) using chloroform fumigation method. We also collected root sample of oak surrounding target oak trees in October 2016 (before SR) and September 2017 (after SR). We observed 300 root tip per sample using stereomicroscope and counted EcM and non-EcM root tips. We further distinguish EcM to the types based on the observation of fungal sheath and recorded number. We calculated EcM colonization rate as the ratio of EcM root tips to the total. We extracted DNA of each EcM type and sequenced, then identified OTU (operational taxonomic unit) by homology analysis in nucleotide search. We tested EcM community structure and effects of SR and soil environments by non-metric multidimensional scaling (NMDS) and PerMANOVA.
There was no significant difference in soil inorganic N, DOC, DON contents, DOC/DON, MBC, MBN, and MBC/MBN between SR treatments. EcM colonization rate did not significantly differ between SR treatments. Regarding EcM composition, eleven and ten OTUs were identified before and after SR, respectively. Dominant OTUs throughout the observation period were Helotiales, Russula, and Lactarius. Community composition was not significantly different between SR treatments. In addition, SR or any soil environmental factors did not significantly affect the EcM community composition. Stable EcM community composition after SR would be attributable to stable soil environment after SR and slow response of root associated EcM community under situation that parent trees remained. Further, Russula and Lactarius, which were dominant even before SR, has been reported to be dominant in N-rich environment, suggesting the possibility that N status before SR in our site was not N limited. This study demonstrated stable root associated EcM community composition and soil N dynamics after understory vegetation removal during relatively short period after the disturbance.