Biogenic Isoprene Emission Mechanism from ^(13)CO_2 Exposure Experiments

Biogenic isoprene emissions have been believed to be from only photosynthesis processes in plant. However nocturnal isoprene emission from pine is detected. And by feeding 13CO2 to plants, it is found that both photosynthesis pathway and light independent processes contribute to isoprene emissions.

Pyrolysis mechanism of glucose and mannose: The formation of 5-hydroxymethyl furfural and furfural

Fast pyrolysis of biomass will produce various furan derivatives, among which 5-hydroxymethyl furfural（5-HMF） and furfural（FF） are usually the two most important compounds derived from holocellulose. In this study, density functional theory（DFT） calculations are utilized to reveal the formation mechanisms and pathways of 5-HMF and FF from two hexose units of holocellulose, i.e., glucose and mannose. In addition, fast pyrolysis experiments of glucose and mannose are conducted to substantiate the computational results, and the orientation of 5-HMF and FF is determined by 13C-labeled glucoses. Experimental results indicate that C1 provides the aldehyde group in both 5-HMF and FF, and FF is mainly derived from C1 to C5 segment. According to the computational results, glucose and mannose have similar reaction pathways to form 5-HMF and FF with d-fructose（DF） and 3-deoxy-glucosone（3-DG） as the key intermediates. 5-HMF and FF are formed via competing pathways. The formation of 5-HMF is more competitive than that of FF, leading to higher yield of 5-HMF than FF from both hexoses. In addition, compared with glucose,mannose can form 5-HMF and FF via extra pathways because of the epimerization at C2 position. Therefore, mannose pyrolysis results in higher yields of 5-HMF and FF than glucose pyrolysis.

The differences in carbon dynamics between boreal dwarf shrubs and Scots pine seedlings in a microcosm study

Aims The ground level of boreal pine forests consists of a dense layer of eri-caceous shrubs,herbs,grasses,mosses and lichens.The primary prod-uctivity of this forest floor vegetation is notable but the role the most common ericoid dwarf shrub plant species,Calluna vulgaris,Vaccinium myrtillus and Vaccinium vitis-idaea,play in carbon(C)cycling in these ecosystems is poorly understood.Here,we studied their C dynamics in detail using plants of similar size(age 14-19 months)in a microcosm study.Methods We determined the full C balances of these dwarf shrubs for the first time and compared them to those of Pinus sylvestris by using long-term biomass accumulation,^(13)C pulse labelling and CO_(2) ex-change measurements in a controlled laboratory experiment.Important Findings Pinus sylvestris had significantly higher biomass-based C fluxes than dwarf shrubs,both aboveground and belowground,but the dwarf shrubs did not differ in the biomass-based fluxes.We showed that root respiration of the evergreen ericoid dwarf shrubs was sensitive to the aboveground light conditions as belowground respiration was 50-70%higher under light compared with dark conditions.Such light-related dif-ferences were not observed for Scots pine.The observed differences in C dynamics are important in estimating the origin of belowground CO_(2) fluxes and in evaluating their biological relevance.Our results improve current understanding of CO_(2) sources and sinks in boreal ecosystems.