熱帯泥炭林のオイルパームプランテーションへの土地利用変化が二酸化炭素収支に与える影響

Over millennia, tropical peat swamp forest (PSF) has stored a large amount of carbon (C) both in biomass and soil. Currently, however, this C-rich ecosystem is exposed to disturbances related to land-use change. For example, the large distribution of PSF in southeast Asia chiefly in Indonesia and Malaysia has been affected by the rapid expansion of oil palm plantations (OPP). Other than significant changes in vegetation, plantations need drainage for lowering groundwater level (GWL) to keep better palm growth and potentially enhances oxidative peat decomposition. In order to understand the environmental impact of OPP from the view point of global warming, it is crucial to assess the change of carbon dioxide (CO2) balance through the PSF conversion. To date, however, no study has reported the net ecosystem CO2 exchange (NEE) of OPP established on peat. The objectives of this study are: (a) to monitor NEE of a PSF and an OPP in Sarawak, Malaysia by the eddy covariance technique, (b) to investigate the controlling factors of CO2 fluxes, and (c) to quantify the annual CO2 balances of the two sites and compare them to discuss the effect of the land-use change on ecosystem CO2 balance. 1. Carbon dioxide fluxes above a peat swamp forest. NEE has been measured above a relatively drained secondary PSF since 2010. NEE was partitioned into respiration (RE) and photosynthesis (GPP) using an empirical method. RE differ significantly in the dry and wet periods (p < 0.01). However, no significant difference was found in GPP. Thus, the seasonal difference in NEE (0.52 g C m−2 d−1) was mainly attributable to that in RE (0.57 g C m−2 d−1). Lower GWL in the dry period was the main cause for greater RE, because lower GWL enhances peat aeration and potentially increases oxidative peat decomposition. Mean (± 1 standard deviation) of annual NEE, RE and GPP were −136 ± 51, 3546 ± 149, and 3682 ± 149 g C m−2 yr−1 for four years until 2014. The annual NEE was comparable to those of some tropical rain forests on mineral soil. Aboveground biomass (AGB) was estimated at 140 and 146 t ha-1, respectively, in 2016 and 2017. Mean soil C content at 0-25 cm and 25-50 cm depths from 2011 to 2014 were estimated at 52.2 ± 0.7% and 53.9 ± 0.7% respectively. 2. Carbon dioxide fluxes on an oil palm plantation NEE has also measured above an OPP established in 2004. GWL in OPP (-60 cm) was much lower than in PSF (-17.6 cm) on average and was relatively stable, because GWL was controlled by ditches. Similarly, soil moisture was maintained at around 0.56 m3 m-3. RE showed no significant relationship with GWL but was positively correlated with soil moisture (P < 0.001). Mean annual NEE, RE and GPP from 2011 to 2014 were estimated at 1034 ± 229, 3663 ± 182, 2630 ± 106 g C m−2 yr−1, respectively. AGB was estimated at 21.4 and 54.2 t ha-1, respectively, in March 2011 and July 2014. Soil C content measured annually from 2011 to 2014 were 55.3 ± 0.8% and 56.4 ± 1.0%, respectively, at 0-25 and 25-50 cm. 3. Effect of land conversion on ecosystem-scale carbon dioxide balance The annual NEE was negative in PSF (a moderate CO2 sink) but positive in OPP (a large CO2 source). In contrast, annual RE values were similar each other, though it was expected to increase after the land conversion owing to lowered GWL and much woody debris left on the ground. The unchanged RE was probably caused by less autotrophic respiration due to much less AGB in OPP than in PSF. Thus, the large CO2 emissions from OPP was attributable to 26% reduction in annual GPP mainly because of less AGB

熱帯泥炭林のオイルパームプランテーションへの土地利用変化が二酸化炭素収支に与える影響 [全文の要約]

この博士論文全文の閲覧方法については、以下のサイトをご参照ください。https://www.lib.hokudai.ac.jp/dissertations/copy-guides

Soil carbon dioxide emissions due to oxidative peat decomposition in an oil palm plantation on tropical peat

Soil carbon dioxide (CO₂) efflux was measured continuously for two years using an automated chamber system in an oil palm plantation on tropical peat. This study investigated the factors controlling the CO₂ efflux and quantified the annual cumulative CO₂ emissions through soil respiration and heterotrophic respiration, which is equivalent to oxidative peat decomposition. Soil respiration was measured in close-to-tree ( 3 m, FT) plots, and heterotrophic respiration was measured in root-cut (RC) plots by a trenching method. The daily mean CO2 efflux values (mean ±1 standard deviation) were 2.80±2.18, 1.59±1.18, and 1.94±1.581 μmol m⁻² s⁻¹ in the CT, FT, and RC plots, respectively. Daily mean CO₂ efflux increased exponentially as the groundwater level or water-filled pore space decreased, indicating that oxidative peat decomposition and gas diffusion in the soil increased due to enhanced aeration resulting from lower groundwater levels. Mean annual gap-filled CO₂ emissions were 1.03 ± 0.53, 0.59 ± 0.26, and 0.69 ± 0.21 kg C m⁻² yr⁻¹ in the CT, FT, and RC plots, respectively. Soil CO₂ emissions were significantly higher in the CT plots (P < 0.05), but did not differ significantly between the FT and RC plots. This implies that root respiration was negligible in the FT plots. Heterotrophic respiration accounted for 66% of soil respiration. Annual CO₂ emissions through both soil and heterotrophic respiration were smaller than those of other oil palm plantations on tropical peat, possibly due to the higher groundwater levels, land compaction, and continuous measurement of soil CO₂ efflux in this study. Mean annual total subsidence was 1.55 to 1.62 cm yr⁻¹, of which oxidative peat decomposition accounted for 72 to 74%. In conclusion, water management to raise groundwater levels would mitigate soil CO₂ emissions from oil palm plantations on tropical peatland

Carbon loss from aboveground woody debris generated through land conversion from a secondary peat swamp forest to an oil palm plantation

Palm oil accounts for about 40% of the global demand of vegetable oil. To meet the demand, oil palm plantations have expanded in the humid tropics at the expense of tropical forests. Land conversion begins with clear cutting and generates much woody debris, which was stacked in rows. Woody debris decomposes and emits carbon dioxide (CO2), but the time course of the decomposition is not well understood, especially at the early stage. Thus, we measured carbon (C) stock in woody debris in a newly established plantation after clear cutting of a secondary peat swamp forest in Sarawak, Malaysia. A litter bag method was applied to examine the decomposition of woody debris scattered on the ground. Also, we periodically measured apparent cross-sectional area (ACSA) of a stacking row (about 5 m wide and 90 m long) assuming that the cross-sectional form was triangular. The C stock of the stacking row was estimated from ACSA and measured C fractions using a significant sigmoidal relationship. The decomposition rate constants (k) for C content were determined to be 0.231-0.313 yr-1 for ground woody debris and 0.459 yr-1 for stacked woody debris. In addition, the total decomposition of the aboveground woody debris proceeded according to another k of 0.440 yr-1 during the experimental period of 740 days. The total C stock of aboveground woody debris was 48.4 Mg C ha-1 at the beginning of the field experiment, about 16 months after clear cutting. The C stock accounted for 63% of the C of forest aboveground biomass. Despite the uncertainty in the spatial representativeness, we think that simply measurable ACSA is useful to quantify the C stock of stacked woody debris. The technique could be applicable to large-area estimation using drone technology

Synthesis and Pharmacological Evaluation of Dual Acting Ligands Targeting the Adenosine A_2A and Dopamine D₂ Receptors for the Potential Treatment of Parkinson’s Disease

A relatively new strategy in drug discovery is the development of dual acting ligands. These molecules are potentially able to interact at two orthosteric binding sites of a heterodimer simultaneously, possibly resulting in enhanced subtype selectivity, higher affinity, enhanced or modified physiological response, and reduced reliance on multiple drug administration regimens. In this study, we have successfully synthesized a series of classical heterobivalent ligands as well as a series of more integrated and “drug-like” dual acting molecules, incorporating ropinirole as a dopamine D₂ receptor agonist and ZM 241385 as an adenosine A_2A receptor antagonist. The best compounds of our series maintained the potency of the original pharmacophores at both receptors (adenosine A_2A and dopamine D₂). In addition, the integrated dual acting ligands also showed promising results in preliminary blood–brain barrier permeability tests, whereas the classical heterobivalent ligands are potentially more suited as pharmacological tools