Yukiko Sakata Bekku

Temporal and spatial variation of forest biomass in relation to stand dynamics in a mature, lowland tropical rainforest, Malaysia

To clarify consistency in the size of carbon pool of a lowland tropical rainforest, we calculated changes in above-ground biomass in the Pasoh Forest Reserve, Peninsular Malaysia. We estimated the total above-ground biomass of a mature stand using tree census data obtained in a 6-ha plot every 2 years from 1994 to 1998. The total above-ground biomass decreased consistently from 1994 (431 Mg ha−1) to 1998 (403 Mg ha−1) (1 Mg = 103 kg). These are much lower than that in 1973 for a 0.2 ha portion of the same area, suggesting that the the total above-ground biomass reduction might have been consistent in recent decades. This trend contrasted with a major trend for neotropical forests. During 1994–1998, the forest gained 23.0 and 0.88 Mg ha−1 of the total above-ground biomass by tree growth and recruitment, respectively, and lost 51.9 Mg ha−1 by mortality. Overall, the biomass decreased by 28.4 Mg ha−1 (i.e. 7.10 Mg ha−1·year−1), which is almost equivalent to losing a 76-cm-diameter living tree per hectare per year. Analysis of positive and negative components of biomass change revealed that deaths of large trees dominated the total above-ground biomass decrease. The forest biomass also varied spatially, with the total above-ground biomass density ranging 212–655 Mg ha−1 on a 0.2-ha basis (n= 30 subplots, 1998) and 365–440 Mg ha−1 on a 1 ha basis. A large decrease of the total above-ground biomass density (> 50 Mg per ha per 2 years) in several 0.2-ha subplots contributed to the overall decrease in the 6-ha total above-ground biomass. In the present study, we discuss the association between forest dynamics and biomass fluctuation, and the implication for carbon cycling in mature forests with emphasis on forest monitoring and assessments of soil and decomposition systems.

Soil Microbial Biomass, Respiration Rate, and Temperature Dependence on a Successional Glacier Foreland in Ny-Alesund, Svalbard

Abstract We examined soil microbial activities, i.e., biomass, respiration rate, and temperature dependence of the respiration on a glacier foreland in Ny-Ålesund, Svalbard, Norway. We collected soil samples from 4 study sites that were set up along a primary succession (Site 1, the youngest, to Site 4, the oldest). Microbial biomass measured with the SIR method increased with successional age (55 to 724μg Cbiomass g−1 soil d.w. from Site 1 to Site 4). The microbial respiration rate of the soil was measured in a laboratory with an open-flow infrared gas-analyzer system, changing the temperature from 2° to 20°C at 3–4° intervals. The microbial respiration rate increased exponentially with the temperature at all sites. The temperature dependence (Q10) of the microbial respiration rate ranged from 2.2 to 4.1. The microbial respiration rates at a given temperature increased with succession as a step change (0.48, 0.43, 1.26, and 1.29μg C g−1soil h−1 at 8°C from Site 1 to Site 4, respectively). However, the substrate-specific respiration rate (respiration rate per gram soil carbon) decreased with successional age (0.034 to 0.006μg C mg−1Csoil h−1 from Site 1 to Site 4). A comparison of these respiratory properties with other ecosystems suggested that soil microorganisms in arctic soils have a high potential for decomposition when compared to those of other temperate ecosystems.

Soil Respiration in Three Soil Types in Agricultural Ecosystems in Finland

Seasonal changes in soil respiration (SR), soil temperature (ST) and soil water content (SWC) were monitored in three different soil types (peat, sand and clay soils) in Finnish agricultural ecosystems. Rates of CO2 emission were measured by the closed chamber method using an infrared gas analyser (IRGA) at intervals of 2-3 weeks from May to October. The seasonal changes in SR were different among the soil types: peat soil, maximum rate (650 mg CO2 m-2 h-1) in summer, positive significant relation between SR and ST and negative relation between SR and SWC; sandy soil, stable SR (300 mg CO2 m-2 h-1) without seasonal changes, positive relation between SR and SWC and no significant relation between SR and ST; clay soil, maximum rate (500 mg CO2 m-2 h-1) in summer, highly positive significant relation between SR and ST and negative relation between SR and SWC. A statistical model was developed to predict the amount of CO2 evolved from the cultivated soils based on the relationships between SR and certain abio...

Ecosystem development and carbon cycle on a glacier foreland in the high Arctic, Ny-Alesund, Svalbard

The Arctic terrestrial ecosystem is thought to be extremely susceptible to climate change. However, because of the diverse responses of ecosystem components to change, an overall response of the ecosystem carbon cycle to climate change is still hard to predict. In this review, we focus on several recent studies conducted to clarify the pattern of the carbon cycle on the deglaciated area of Ny-Ålesund, Svalbard in the high Arctic. Vegetation cover and soil carbon pools tended to increase with the progress of succession. However, even in the latter stages of succession, the size of the soil carbon pool was much smaller than those reported for the low Arctic tundra. Cryptogams contributed the major proportion of phytomass in the later stages. However, because of water limitation, their net primary production was smaller than that of the vascular plants. The compartment model that incorporated major carbon pools and flows suggested that the ecosystem of the later stages is likely to be a net sink of carbon at least for the summer season. Based on the eco-physiological characteristics of the major ecosystem components, we suggest several possible scenarios of future changes in the ecosystem carbon cycle.

Ecological Significance of Different Growth Forms of Purple Saxifrage, Saxifraga oppositifolia L., in the High Arctic, Ny-Ålesund, Svalbard

Saxifraga oppositifolia is morphologically variable, and many scientists recognize two morphs; the Prostrate form (P-form) and Cushion form (C-form). In order to investigate the adaptation of the different growth forms, we analyzed the relationships between growth forms, growth patterns, manner of reproduction, tolerance to disturbance and succession. The distribution of the third internode length of shoots showed bimodality, long-internode shoot, and short-internode shoot, and it was closely related with the growth form-P-form and C-form, respectively. When both C-form and P-form plants were growing in the same moist riverbank, they had similar net photosynthesis per dry weight. The colony expansion rate of P-form was faster than C-form and the shoot fragments of P-form were easy to root and establish. On the other hand, C-form had a larger number of flowers per plant dry weight than P-form, and this caused an increase in seed production. These results showed that growth forms and reproductive characteristics were closely related, and P-form was advantageous in vegetative propagation by shoot fragments while C-form was advantageous in sexual reproduction. Morphological variability within population of S. oppositifolia appeared to be adaptive for this species as a pioneer in the primary succession in High Arctic where the selective forces vary spatially and temporally.

Midday depression in root respiration of Quercus crispula and Chamaecyparis obtusa: its implication for estimating carbon cycling in forest ecosystems

We observed the phenomenon of midday depression in the rate of tree root respiration. Diurnal changes in the root respiration rate of Quercus crispula and Chamaecyparis obtusa were measured under intact conditions using a closed chamber method and a soil respiration measurement system (LI-6400 with a root respiration chamber) in a forest in the foothills of Mt. Fuji. After the measurement of intact root respiration in the field, the root was excised and taken to the laboratory, and the temperature dependence on the respiration rate of the detached root was measured using an open-flow gas exchange system with an infrared gas analyzer (LI-6252). The measurement was conducted in September 2003, August and November 2005, and June 2006. Whereas the root respiration rate of both species under intact conditions increased with increasing soil and root temperatures from dawn to early morning, the respiration rate decreased around midday from 10:00 to 15:00 despite an increment of soil and root temperatures. There was no clear relationship between the intact root respiration rate and root temperature in either species, although the detached root respiration rate of both increased exponentially with the temperature. The amount of the CO2 efflux estimated using the temperature dependence of detached root respiration tended to underestimate the actual measurement value (intact respiration rate) by 20–50% in both species. These results indicate that evaluating midday depression in root respiration would be important for a more accurate estimation of the carbon cycle or net ecosystem production in forests.

Carbon Isotope Discrimination in Diverging Growth Forms of Saxifraga oppositifolia in Different Successional Stages in a High Arctic Glacier Foreland

Abstract We investigated carbon isotope discrimination of two morphs of Saxifraga oppositifolia and other plant species in a glacier foreland in the High Arctic at Ny-Ålesund, Svalbard, Norway. At this site, soil conditions vary considerably along with the progress of primary succession within a small area. We compared growth forms and δ13C values, which reflect long-term leaf gas exchange characteristics, of plants growing in different successional stages with different soil conditions. Even though the soil mass water content (water mass/dry mass) increased from 10% to 140% with the progress of succession, the water and nitrogen content of the soil had negligible effects on the δ13C values of the observed species. The δ13C values were determined mainly by species and growth forms. We compared two morphs of S. oppositifolia, the prostrate form (P-form) and the cushion form (C-form), on the same riverbank in the glacier foreland. Regardless of the successional stage, the δ13C values of the C-form were about 2‰ more negative than those of the P-form. The ground cover area per plant mass (GA) of the C-form was less than 30% that of the P-form, and the product of GA and stomatal conductance appears to be an important factor in the relationship between transpiration and photosynthesis of a whole plant. We suggest that the relationship between GA and the root mass fraction is a crucial factor affecting the water utilization in high arctic environments. We also examined the relationship between life form and water utilization for other phototrophs, including lichens, mosses, narrow-leaved grasses, perennials, and shrubs.

Photosynthetic light responses of a widespread moss, Sanionia uncinata, from contrasting water regimes in the high Arctic tundra, Svalbard, Norway

Abstract Photosynthetic responses to light intensity were investigated under field conditions in Sanionia uncinata growing in contrasting water regimes in the high arctic tundra. Carbon dioxide exchange measurements were made using an infra-red gas analyser under ambient environmental conditions (CO2 concentration, 363–370 p.p.m.; air temperature, 12–15°C) at near optimum hydration on sunny days. The sunlight was reduced using layers of shade cloth. The photosynthetic photon flux density required to saturate net photosynthesis (PPFDsat) of Sanionia growing in a dry and wet site was 484 and 990 μmol m−2 s−1, respectively. The PPFD at which there was zero net exchange of CO2 (PPFDcomp) in dry and wet sites was 34 and 100 μmol m−2 s−1, respectively, and the PPFD at the point of 50% of the light saturated net photosyntheric rate (PPFDhalf) in dry and wet sites was 138 and 306 μmol m−2 s−1, respectively. The findings suggest that Sanionia growing in the wet site appears to require high radiation for photosynthesis. The light-saturated net photosynthetic rate (P max) in dry and wet sites was 0.84 and 1.42 mg CO2 g−1 s−1, respectively, and dark respiration rates (R dark) were 0.21 and 0.57 mg CO2 g−1 s−1, respectively. NPmax and R dark were >1.5-fold lower in the dry site than the wet site. These results suggest that Sanionia found in dry habitats is shade plants (sciophilous) while Sanionia in wet habitats is sun plants heliophilous.

Development of 11 microsatellite markers in Pinus parviflora by the dual-suppression technique and next-generation sequencing

Pinus parviflora Sieb. et Zucc. var. parviflora is a coniferous tree species distributed in mountainous areas of temperate zones from southern Tohoku to the Kyushu area in Japan. Some P. parviflora populations have become small and endangered due to massive death resulting from pine wilt disease, scab canker, and presumably climate change. We developed 11 microsatellite markers for P. parviflora by the dual-suppression technique and next-generation sequencing using 32 individuals of P. parviflora collected from Aokigahara at the foot of Mt. Fuji. The number of alleles for each locus ranged from two to 10. The averages of observed and expected heterozygosities were 0.61 and 0.59, respectively. These markers will become powerful tools for assessing genetic diversity, genetic connectivity, and genetic structure in P. parviflora populations, which will facilitate our understanding and conservation of P. parviflora.