To clarify the effects of long‐term warming on ecosystem matter cycling, we conducted an in situ 7‐year experimental warming (2009–2015) using infrared heaters in a cool temperate semi‐natural grassland in Japan. We measured plant aboveground biomass, soil total C and N, soil inorganic N (NH4+‐N and NO3−‐N), and soil microbial biomass for 7 years (2009–2015). We also measured heterotrophic respiration for 2 years (2013–2014) and assessed net N mineralization and nitrification in 2015. We found that warming immediately increased plant aboveground biomass, but this effect ceased in 2013. However, the soil microbial biomass was continuously depressed by warming. Soil inorganic N concentrations in warmed plots substantially increased in the later years of the experiment (2013–2015) and the potential net N mineralization rate was also higher than in the earlier years. In contrast, heterotrophic respiration decreased with warming in 2013–2014. Our observations indicate that long‐term warming has a contrasting effect on plants and soil microbes. In addition, the warming could have different effects on subterranean C and N cycling. To enhance the accuracy of estimation of future climate change, it is essential to continuously observe the warming effects on ecosystems and to focus on the change in subterranean C and N cycling.

To understand the role of forest ecosystems in the global carbon cycle, it is important to clarify the factors affecting the carbon balance of forest ecosystems. However, little is known about the direct effect of forest types, especially dominant species, on their different carbon dynamics. To clarify the effect of difference in forest types, an experiment was conducted in three forests, which were located in the same place and exposed to the same climate conditions. These forests were middle-aged (40-45 years) and dominated by Quercus serrata (Q forest), Larix kaempferi (L forest) and Pinus densiflora (P forest). Net primary production (NPP), heterotrophic respiration (HR) and net ecosystem production (NEP) were estimated in each forest, using a biometric method over one year. For NPP estimated from the annual growth of tree biomass (ΔB) and amount of litter (LF), P forest NPP (5.3 MgC•ha −1 •yr −1) was higher than Q and L forest NPP (4.6 and 3.2 MgC•ha −1 •yr −1). The difference was affected by a significant difference in ΔB (p = 0.032) and LF (p < 0.001) mainly because of leaf biomass. The HR in Q forest (4.1 MgC•ha −1 •yr −1) was higher than L and P forest (2.3 and 2.1 MgC•ha −1 •yr −1). This difference could result from the amount of litter (respiration substrate) and chemical properties of litter (lability of decomposition). The NEP, which was calculated from the difference between NPP and HR, varied widely among the forest types (0.5, 0.9 and 3.2 MgC•ha −1 •yr −1 in Q, L and P forests, respectively). The range of values among the forest types was comparable to those among age sequences and climate zones in previous studies. These results suggest that the difference in forest types (especially dominant species) can potential-How to cite this paper: Tomotsune, M.,

We aimed to clarify the individual and interactive effects of temperature increase during snow‐free seasons and snow depth change (increase/decrease) on litter decomposition and microbial community in cool‐temperate semi‐natural grassland. We conducted a 2‐year in situ composite warming experiment comprising temperature increase (ca. 2°C) using infrared heaters during snow‐free seasons and manual snow depth manipulation (±50% in snow depth) in Japanese grassland. Changes in litter mass remaining and litter carbon‐to‐nitrogen ratio (C/N ratio) were assessed by litter bag methods. Microbial biomass and community structure were determined by phospholipid fatty acid analysis. Litter decomposition constant (k) was low in the plots with temperature increase during snow‐free seasons (0.56) and with less snow cover (0.57), but combining these two treatments resulted in acceleration of decomposition (k = 0.70); probably, decreased decomposition in the cold climate of early spring resulting from advanced snow melting was compensated for by higher temperature. Differences in mass loss among the treatments were well explained by litter C/N, microbial biomass and microbial community structure. The plots with a high mass loss showed lower litter C/N ratio, larger microbial biomass and different microbial community structure comparing to the plots with low mass loss. Our results showed the complex responses of litter decomposition to summer and winter climate change and combination of less snow cover and summer warming seemed to accelerate the decomposition in cool‐temperate semi‐natural grassland.

The chamber method with plant clipping has been widely used for measuring soil respiration (SR) in grassland ecosystems. However, plant clipping may cause overestimation of SR by changing the environmental factors and injuring the plants. To solve these problems, we developed a new non‐destructive method using multiple‐microchambers (3 cm diameter, 8 cm height), which enables measurement of SR without plant clipping by installing chambers into gaps among the grasses. The new method was compared with the conventional method at various flow rates in vitro to assess the accuracy of SR measurement. The new method overestimated the SR rate; however, the ratio of overestimation to the conventional method was constant for each flow rate. These ratios fitted the logarithmic curve, indicating the potential for correction of the SR rate measured by the new method using the logarithmic equation. The corrected SR rate obtained by the new method was equal to the rate by the conventional method. This suggests that accurate measurement of SR in grassland ecosystems is possible using the multiple‐microchambers method. We then compared the non‐destructive method and the destructive method in situ on summer season and found that the destructive method overestimated SR rate in the grassland ecosystem by about 276% on average. There were two possible reasons for this overestimation; first, the clipping treatment may change environmental conditions such as soil temperature and soil water content, and second, it may directly increase plant respiration.