Forest Ecosystem Function Colloquium 京都大学・森林生態系機能

Forest Ecosystem Function Colloquium (FEFCO) は、地域や地球全体のレベルで森林生態系の機能とその持続的活用法を統合的に理解することを目的とし、研究者間の学術交流を推進します。
第15回森林生態系機能コロキウムは、フィンランド ヘルシンキ大学から来日される Jukka Pumpanen博士に講演していただき
15th FEFCO
2014/12/2 16:00 - 17:30
Faculty of Agriculture Main Building, S128
Dr. Jukka Pumpanen
Feedback mechanisms between below-ground carbon
allocation, soil organic matter turnover and carbon fluxes
The feedback effects resulting from the increasing atmospheric CO2 concentration on the biomass production of terrestrial
ecosystems and soil organic matter (SOM) decomposition are one of the biggest uncertainties in the predictions of future climate.
It has been suggested that root exudates and other easily decomposable carbon could enhance the decomposition of old SOM
and turnover rates of nitrogen in the rhizosphere with possible growth enhancing feedback in vegetation. We are studying the
feedback mechanisms between the assimilation of CO2 and decomposition of SOM and the effects of different environmental
factors (such as precipitation, temperature, drought and fire) on them in multiple scales using detailed laboratory measurements
and long term field experiments. In our recent paper by Lindén et al. (2014), we observed that living rhizosphere and belowground
carbon input of easily decomposable C play an important role in the decomposition of SOM. We also observed that the increased
amount of easily available carbon in the soil was reflected to the photosynthesis, probably through sink limitation. In a fire
chronosequence study by Köster et al. (2014), we studied in a pristine sub-arctic forest, the turnover rate and recovery of soil C
stocks after forest fires, and observed, that the turnover rate of soil carbon was substantially affected by the age of the forest. The
turnover rate was also positively correlated with the amount of ectomycorrhizal biomass in the soil indicating that the
ectomycorrhizal (ECM) fungi are an important driver of the SOM decomposition in boreal forest soil, and that the faster turnover
rate of soil carbon in old forests compared to young forest stands is related to the increasing below ground carbon allocation
which is due to higher nitrogen demand in old vs. young forests. The estimation of below ground carbon allocation without
disturbing the ecosystem is difficult by using conventional girdling and trenching techniques. We have developed a novel
method for separating these two flux components (Pumpanen et al. 2014). The method enables continuous monitoring of soil
CO2 effluxes and separation of the two flux components in an undisturbed manner, unlike the traditional flux partitioning
methods such as girdling and trenching. With the method we were able to estimate the annual contribution of the autotrophic
component in soil respiration and its seasonal variation and connect it to the seasonal variation in gross primary productivity of
the forest. The enhanced decomposition of SOM resulted from the belowground carbon allocation to root exudates and ECM
symbiosis may also significantly affect the transport of terrestrial carbon to the rivers, estuaries and the coastal ocean, a process
with unknown contribution to the global and regional carbon balances. We studied in a recent paper by Pumpanen et al. (2014)
how the short and long-term changes in precipitation, soil temperature, soil water content and net ecosystem exchange (NEE) are
reflected to DOC concentrations and runoff DOC fluxes in two small forested upland catchments in Southern Finland. The DOC
flux was to a large extent determined by the amount of precipitation, but the previous year s NEE and litter production had also a
small but significant effect on runoff DOC fluxes. Another possible explanation for the increasing DOC concentrations in the runoff
could be the increasing soil temperature which could affect the decomposition of SOM, but it may also increase the belowground
carbon sink and thus increase the primary productivity of the forest in the long run (Pumpanen et al. 2012).
Forest Ecosystem Function Colloquium