Carbon allocation in Picea jezoensis:Adaptation strategies of a non-treeline species at its upper elevation limit

Understanding the physiological adaptations of non-treeline trees to environmental stress is important to understand future shifts in species composition and distribution of current treeline ecotone.The aim of the present study was to elucidate the mechanisms of the formation of the upper elevation limit of non-treeline tree species,Picea jezoensis,and the carbon allocation strategies of the species on Changbai Mountain.We employed the^(13)C in situ pulse labeling technique to trace the distribution of photosynthetically assimilated carbon in Picea jezoensis at different elevational positions(tree species at its upper elevation limit(TSAUE,1,700 m a.s.l.)under treeline ecotone;tree species at a lower elevation position(TSALE,1,400 m a.s.l.).We analyzed^(13)C and the non-structural carbohydrate(NSC)concentrations in various tissues following labeling.Our findings revealed a significant shift in carbon allocation in TSAUE compared to TSALE.There was a pronounced increase inδ^(13)C allocation to belowground components(roots,soil,soil respiration)in TSAUE compared to TSALE.Furthermore,the C flow rate within the plant-soil-atmosphere system was faster,and the C residence time in the plant was shorter in TSAUE.The trends indicate enhanced C sink activity in belowground tissues in TSAUE,with newly assimilated C being preferentially directed there,suggesting a more conservative C allocation strategy by P.jezoensis at higher elevations under harsher environments.Such a strategy,prioritizing C storage in roots,likely aids in withstanding winter cold stress at the expense of aboveground growth during the growing season,leading to reduced growth of TSAUE compared to TSALE.The results of the present study shed light on the adaptive mechanisms governing the upper elevation limits of non-treeline trees,and enhances our understanding of how non-treeline species might respond to ongoing climate change.

Biochar application significantly increases soil organic carbon under conservation tillage:an 11-year field experiment

Biochar application and conservation tillage are significant for long-term organic carbon(OC)sequestration in soil and enhancing crop yields,however,their effects on native soil organic carbon(native SOC)without biochar carbon sequestration in situ remain largely unknown.Here,an 11-year field experiment was carried out to examine different biochar application rates(0,30,60,and 90 Mg ha^(−1))on native SOC pools(native labile SOC pool I and II,and native recalcitrant SOC)and microbial activities in calcareous soil across an entire winter wheat-maize rotation.The proportions of C_(3) and C_(4)-derived native SOC mineralization were quantified using soil basal respiration(SBR)combined with 13C natural isotope abundance measurements.The results showed that 39-51%of the biochar remained in the top 30 cm after 11 years.Biochar application rates significantly increased native SOC and native recalcitrant SOC contents but decreased the proportion of native labile SOC[native labile SOC pool I and II,dissolved organic carbon(DOC),and microbial biomass carbon(MBC)].Biochar application tended to increase the indicators of microbial activities associated with SOC degradation,such as SBR,fluorescein diacetate hydrolysis activity,and metabolic quotient(qCO_(2)).Meanwhile,higher biochar application rates(B60 and B90)significantly increased the C_(4)-derived CO_(2) proportion of the SBR and enhanced C_(4)-derived native SOC mineralization.The effect of the biochar application rate on the content and proportion of native SOC fractions occurred in the 0-15 cm layer,however,there were no significant differences at 15-30 cm.Soil depth also significantly increased native labile SOC pool Ⅰ and Ⅱ contents and decreased qCO_(2).In conclusion,the biochar application rate significantly increased native SOC accumulation in calcareous soil by enhancing the proportion of native recalcitrant SOC,and biochar application and soil depth collectively influenced the seasonal turnover of native SOC fractions,which has important implications for long-term agricultural soil organic carbon sequestration.

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.

^(13)C代谢通量估计的量子粒子群优化算法

^(13)C标记实验的代谢通量分析(^(13)CMFA)是探索代谢网络的重要途径。^(13)C通量估计是以碳富集度平衡为条件的全局优化问题,带有众多约束条件和存在多个局部极小点等特点,如何高效地求解是^(13)C MFA中的难点,也是实现通量精确估计的关键。量子粒子群优化算法显著特点是控制参数少,设置简单,具有较好的全局搜索能力,适应于通量估计。本文提出量子粒子群优化算法结合最小二乘计算求解噪音环境下的环磷酸戊糖代谢网络的通量,以带约束的最小化问题为目标优化函数,仿真实验验证了量子粒子群优化算法是1种有效的通量估计分析算法。

Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China

The priming effect is well acknowledged in soil systems but the effect of nitrogen(N)fertilization remains elusive.To explore how N modifies the priming effect in soil organic matter(SOM),one in situ experiment with 13C labeled glucose addition(0.4 mg C g^–1 soil,3.4 atom %^13C)was conducted on soil plots fertilized with three gradients of urea(0,4 and 16 g N m^–2 yr^–1).After glucose addition,the soil CO2 concentration and phospholipid fatty acid(PLFA)were measured on day 3,7,21 and 35.The study found that N fertilization decreased soil CO2,PLFA and the fungi to bacteria ratio.Glucose triggered the strongest positive priming in soil at 0 g N m^–2 yr^–2,meanwhile N fertilization decreased SOM-derived CO2.Soil at 4 g N m^–2 yr^–2 released the largest amount of glucose-derived carbon(C),likely due to favorable nutrient stoichiometry between C and N.Stable microbial community biomass and composition during early sampling suggests"apparent priming"in this grassland.This study concludes that N fertilization inhibited soil priming in semi-arid grassland,and shifted microbial utilization of C substrate from SOM to added labile C.Diverse microbial functions might be playing a crucial role in soil priming and requires attention in future N fertilization studies.

The role of soluble sugars during drought in tropical tree seedlings with contrasting tolerances

Aims Non-structural carbohydrates(NSCs)are plant storage compounds used for metabolism,transport,osmoregulation and regrowth following the loss of plant tissue.Even in conditions suitable for optimal growth,plants continue to store NSCs.This storage may be due to passive accumulation from sink-inhibited growth or active reserves that come at the expense of growth.The former pathway implies that NSCs may be a by-product of sink limitation,while the latter suggests a functional role of NSCs for use during poor conditions.Methods Using 13C pulse labelling,we traced the source of soluble sugars in stem and root organs during drought and everwet conditions for seedlings of two tropical tree species that differ in drought tolerance to estimate the relative allocation of NSCs stored prior to drought versus NSCs assimilated during drought.We monitored growth,stomatal conductance,stem water potential and NSC storage to assess a broad carbon response to drought.Important Findings We found that the drought-sensitive species had reduced growth,conserved NSC concentrations in leaf,stem and root organs and had a larger proportion of soluble sugars in stem and root organs that originated from pre-drought storage relative to seedlings in control conditions.In contrast,the drought-tolerant species maintained growth and stem and root NSC concentrations but had reduced leaf NSCs concentrations with a larger proportion of stem and root soluble sugars originated from freshly assimilated photosynthates relative to control seedlings.These results suggest the drought-sensitive species passively accumulated NSCs during water deficit due to growth inhibition,while the drought-tolerant species actively responded to water deficit by allocating NSCs to stem and root organs.These strategies seem correlated with baseline maximum growth rates,which supports previous research suggesting a trade-off between growth and drought tolerance while providing new evidence for the importance of plasticity in NSC allocation during drought.

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.