Effects of climate warming on the production of the pioneer moss Racomitrium japonicum: seasonal and year-to-year variations.

Pioneer mosses are among the dominant vegetation in the early stages of xeric successions. Recent climate warming may have a significant effect on the productivity of these mosses, thereby affecting successional processes. In this study, we investigated the effects of temperature changes on the productivity of Racomitrium japonicum, a pioneer moss species commonly found on open ground in Japan. We examined the microclimate (moss temperature and water content) of a natural R. japonicum stand in Higashi-Hiroshima City, western Japan, and related them to the climate records of the weather station to create a model for estimating microclimate from past climatic data. We also examined the effects of environmental factors (light, temperature, and water) on photosynthesis in the laboratory to construct a production model. Using these models, we estimated the net primary production (NPP) over the last 10 years (2009-2018) based on the climatic data (air temperature and precipitation) recorded at the weather station of Higashi-Hiroshima City. The estimated NPP showed negative values in summer, which indicated that respiratory carbon loss exceeded photosynthetic carbon gain. In contrast, NPP was positive in the spring and winter seasons throughout the 10 years. Autumn NPP varied widely, showing both positive and negative values. The annual NPP also showed considerable year-to-year variations. Additionally, we examined the effects of temperature conditions on NPP assuming annual temperature changes of 0 °C (present temperature), + 1 °C, and + 2 °C. The results indicated that NPP decreased with increasing temperature, except in the winter season. The findings of this study suggest that climate warming has a large impact on the NPP of R. japonicum; however, the impact can be both positive and negative depending on the season. The results also suggest that future climate warming is likely to decrease NPP on an annual basis.

Production of biological soil crusts in the early stage of primary succession on a high Arctic glacier foreland.

*We examined the photosynthetic characteristics and net primary production of biological soil crusts to evaluate their contribution to the carbon cycle in the High Arctic glacier foreland. *Biological soil crust samples were collected from a deglaciated area in Ny-Alesund, Svalbard, Norway. Net photosynthetic rates (Pn) and dark respiration rates (R) of biological soil crusts were determined using CO(2) gas exchange rates. We examined the effects of moisture conditions, temperature and photon flux density on Pn and R, and estimated the net primary production by a model based on the relationships between abiotic factors and Pn and R. *The maximum Pn value occurred at 50% of the maximum water-holding capacity. Pn decreased with increasing temperature and dropped below zero at high temperatures (c. > 13 degrees C). The estimated net primary production of the biological soil crust was greater than the net primary production of other vegetation when based on ground surface area, during the early stage of primary succession. Model simulation showed that the net primary production of the biological soil crust decreased with increasing temperature. *These results suggest that biological soil crust productivity plays an important role in the carbon cycle during the early stage of succession of the High Arctic glacier foreland, and is susceptible to temperature increases from global warming.

Seasonal shift in factors controlling net ecosystem production in a high Arctic terrestrial ecosystem.

We examined factors controlling temporal changes in net ecosystem production (NEP) in a high Arctic polar semi-desert ecosystem in the snow-free season. We examined the relationships between NEP and biotic and abiotic factors in a dominant plant community (Salix polaris-moss) in the Norwegian high Arctic. Just after snowmelt in early July, the ecosystem released CO(2) into the atmosphere. A few days after snowmelt, however, the ecosystem became a CO(2) sink as the leaves of S. polaris developed. Diurnal changes in NEP mirrored changes in light incidence (photosynthetic photon flux density, PPFD) in summer. NEP was significantly correlated with PPFD when S. polaris had fully developed leaves, i.e., high photosynthetic activity. In autumn, NEP values decreased as S. polaris underwent senescence. During this time, CO(2) was sometimes released into the atmosphere. In wet conditions, moss made a larger contribution to NEP. In fact, the water content of the moss regulated NEP during autumn. Our results indicate that the main factors controlling NEP in summer are coverage and growth of S. polaris, PPFD, and precipitation. In autumn, the main factor controlling NEP is moss water content.

Photosynthetic characteristics and biomass distribution of the dominant vascular plant species in a high Arctic tundra ecosystem, Ny-Alesund, Svalbard: implications for their role in ecosystem carbon gain.

Studies on terrestrial ecosystems in the high Arctic region have focused on the response of these ecosystems to global environmental change and their carbon sequestration capacity in relation to ecosystem function. We report here our study of the photosynthetic characteristics and biomass distribution of the dominant vascular plant species, Salix polaris, Dryas octopetala and Saxifraga oppositifolia, in the high Arctic tundra ecosystem at Ny-Alesund, Svalbard (78.5 degrees N, 11.5 degrees E). We also estimated net primary production (NPP) along both the successional gradient created by the proglacial chronosequence and the topographical gradient. The light-saturated photosynthesis rate (A (max)) differed among the species, with approximately 124.1 nmol CO(2) g(-1)leaf s(-1) for Sal. polaris, 57.8 for D. octopetala and 24.4 for Sax. oppositifolia, and was highly correlated with the leaf nitrogen (N) content for all three species. The photosynthetic N use efficiency was the highest in Sal. polaris and lowest in Sax. oppositifolia. Distributions of Sal. polaris and D. octopetala were restricted to the area where soil nutrient availability was high, while Sax. oppositifolia was able to establish at the front of a glacier, where nutrient availability is low, but tended to be dominated by other vascular plants in high nutrient areas. The NPP reflected the photosynthetic capacity and biomass distribution in that it increased with the successional status; the contribution of Sal. polaris reached as high as 12-fold that of Sax. oppositifolia.

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-Alesund, 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.

Predicting the impact of climatic warming on the carbon balance of the moss Sanionia uncinata on a maritime Antarctic island.

The effects of climatic factors, especially those of temperature, on the carbon balance of the moss Sanionia uncinata were examined on King George Island in the maritime Antarctic. Net photosynthesis (P(n)) and dark respiration rates of two colonies (A and B) were measured with a portable infrared gas analyzer. Colony A showed small P(n) compared with its dark respiration rates throughout the growing season. Colony B showed much higher net photosynthetic rates, but the dark respiration rates of the two colonies did not differ significantly. Net photosynthetic rate determined at light saturation was almost constant over a wide temperature range, from 5 degrees to 15 degrees C, while the dark respiration was strongly affected by temperature. To assess the impact of warming on the carbon balance of the moss, cumulative carbon gain of the moss was calculated using a simulation model for the main part of the growing season. The results suggest that climatic warming may cause a reduction of carbon gain in some relatively photosynthetically inactive moss colonies.