Abstract. Clouds can significantly affect carbon exchange process between forest ecosystems and the atmosphere by influencing the quantity and quality of solar radiation received by ecosystem's surface and other environmental factors. In this study, we analyzed the effects of cloudiness on net ecosystem exchange of carbon dioxide (NEE) in a temperate broad-leaved Korean pine mixed forest at Changbaishan (CBS) and a subtropical evergreen broad-leaved forest at Dinghushan (DHS), based on the flux data obtained during June-August from 2003 to 2006. The results showed that the response of NEE of forest ecosystems to photosynthetically active radiation (PAR) differed under clear skies and cloudy skies. Compared with clear skies, the light-saturated maximum photosynthetic rate (P ec,max ) at CBS under cloudy skies during mid-growing season (from June to August) increased by 34%, 25%, 4% and 11% in 2003, 2004, 2005 and 2006, respectively. In contrast, P ec,max of the forest ecosystem at DHS was higher under clear skies than under cloudy skies from 2004 to 2006. When the clearness index (k t ) ranged between 0.4 and 0.6, the NEE reached its maximum at both CBS and DHS. However, the NEE decreased more dramatically at CBS than at DHS when k t exceeded 0.6. The results indicate that cloudy sky conditions are beneficial to net carbon uptake in the temperate forest ecosystem and the subtropical forest ecosystem. Under clear skies, vapor pressure deficit (VPD) and air temperature increased due to strong light. These environmental conditions led to greater decrease in gross ecosystem photosynthesis (GEP) and greater increase in ecosystem respiration (R e ) at CBS than at DHS. As a result, clear sky conditions caused more reduction of NEE in the temperate forest ecosystem than in the subtropical forest ecosystem. The response of NEE of Correspondence to: G.-R. Yu (yugr@igsnrr.ac.cn) different forest ecosystems to the changes in cloudiness is an important factor that should be included in evaluating regional carbon budgets under climate change conditions.

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Frequency doubling of mode-locked frequencytunable CO laser emission in high quality 17-mm long ZnGeP2 nonlinear optical crystal was studied. The internal efficiency of frequency doubling exceeded 25%, which was obtained by stabilization of mode-locking regime and increasing peak power of pump radiation in the scheme "master oscillator -power amplifier". A feasibility of difference frequency conversion of both fundamental and first overtone CO laser lines to cover ∼ 4.0 -5.0 μm spectral range and a possibility of getting spectral range of ∼ 1.25 -10 μm by mixing of all CO laser lines were estimated. Internal efficiency of SHG in ZnGeP2 crystal versus pump energy when the nonlinear crystal after focal plate. CO Laser transition 9→8 P(10) (λ ≈ 5.274 μm)