[Impacts of future climate change on spring phenology stages of rubber tree in Hainan, China]. / æœªæ¥æ°”å€™å˜åŒ–å¯¹æµ·å—æ©¡èƒ¶æ ‘æ˜¥å­£ç‰©å€™æœŸçš„å½±å“.

To explore the impacts of future climate change on spring phenology stages (first leaf storey expansion stage, spring flowering stage) of rubber tree in Hainan Island, we established a rubber tree spring phenology simulation model based on the crop clock model and developed a computer software RubberSP. The model simulation accuracy was examined with experimental observed phenology data. Five global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) were integrated using Bayesian Model averaging method (BMA) to predict the impacts of climate change on the spring phenology of rubber tree in 2020-2099 (relative to 1986-2017) under climate scenarios of RCP2.6, RCP4.5 and RCP8.5, respectively. The results showed that the RubberSP model had good simulation accuracy, with the determination coefficient (R2) values ranging between 0.73-0.87, the root mean square error (RMSE) ranging from 3.26 to 4.15 d, and the normalized root mean square error (NRMSE) of 3.4%-7.4% between measured and simulated phenology stages. The uncertainty of a single GCM could be avoided by BMA method, which could better reflect the change trend of temperature. Temperature of Hainan Island in the end of 21 century, under the scenarios of RCP2.6, RCP4.5 and RCP8.5, would increase by more than 0.3, 1.0 and 2.5 ℃ compared with the baseline, respectively. The spring phenology stages would appear earlier and yield would increase in the future climate scenario. The time isoline of spring phenology stages would move forward to northwest, which indicated that most suitable area for rubber tree plantation in Hainan Island would expand to the northwest. The spatial difference of the first leaf storey expansion stage would be more evident, but not for spring flowering stage. The amplitude of rubber tree spring phenology variations was closely related to the increases of temperature under different RCP scenarios, with the most apparent change under RCP8.5 scenario and most mild change under RCP2.6 scenario.

[Influence of water level gradient on marsh soil microbial activity of Calamagrostis angustifolia].

Plant aboveground biomass, total organic carbon( TOC), microbial biomass carbon( MBC), basal respiration( BR), microbial quotient (Cmic/Corg) and metabolic quotient (qCO2) in 0-15 cm and 15-50 cm marsh soil of Calamagrostis angustifolia under different water levels were investigated with controlled experiment. The result showed that water level exerted significant effect on plant biomass, which was the highest under 10 cm waterlogged level and of higher productivity under 0-20 cm waterlogged level. TOC, MBC, BR, Cmic/Corg and qCO2 differed significantly under different water levels. BR and TOC responded to different waterlogged levels in the same way. BR and TOC of 0-15 cm marsh soil were the highest under 0 cm waterlogged level, however, BR and TOC of 15-50 cm marsh soil decreased respectively with increasing water, which was corresponding with soil MBC and Cmic/Corg and qCO2 increased with increasing water. As a result, microbial community is altered and microbial activity is decreasing by increasing waterlogged level, and microbial activity is the lowest under 30 cm waterlogged level, which affects organic carbon accumulation and decomposition.

[Contribution of litter to soil respiration under different land-use types in Sanjiang Plain].

By the soil respiration system of Li-6400, the characteristics of soil respiration with and without litter were investigated to explore the litter's contributions to soil respiration and its correlations with the input of litter and environmental factors under different land-use types in Sanjiang Plain. Results demonstrated that the average contribution of litter to soil respiration ranged from - 0.21 to 0.64 micromol/(m2 x s) in the growing season under the four land-use types. The contribution rate showed in the following order: wetland (14%) > artificial forest (12%) > soybean field (8%) > abandoned land (- 5%). As to abandoned land, the value was negative, and the litter inhibited soil respiration. The litter' s contributions to soil respiration may depend on the balance between the decomposition of litter and its shielding effects on soil respiration. There were highly significant correlations between litter's contributions to soil respiration and soil temperature at 10cm depth except for soybean field. Moreover, the influence of rainfall associated with the input of litter, which suggested that besides decomposition litter may take part in the ecological effect of climate changes in the future.