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.

人工智能2.0时代的群体智能理论与技术专题序言

1引言进入21世纪,传感技术、通信技术与人工智能技术的快速发展对工程系统集成与管控方式产生了深刻的影响。从大规模国家基础设施系统到各类军事集成无人系统日益呈现出网络化的结构特征和智能化的单元特性。在迈入人工智能2.0时代,信息化、智能化与网络化融合发展的趋势日益凸显并浮现出引领第四次工业革命的趋势。在此背景下。

Impact of historical pattern of human activities and natural environment on wetland in Heilongjiang River Basin

Mid and high latitude wetlands are becoming fragmented and losing ecosystem functions at a much faster rate than many other ecosystems.This is due in part to increasing human activities and climate change.In this study,we analyzed wetland distribution and spatial pattern changes for the Heilongjiang River Basin over the past 100 yr.We identified the driving factors and quantified the relative importance of each factor based on landscape pattern metrics and machine learning algorithms.Our results show that wetlands have been fragmented into smaller and regular patches with dominant factors that varied at different periods.Geographic features play the most important role in patterns of wetland change for the entire basin(with 50%-60%of relative importance).Human activities are more important than climate change at the century scale,but less important when magnified at the decadal scale.In the early 1900s,human activities were relatively low and localized and remained that way in the subsequent decades.Thus,the effect of human activities on wetland area of the entire basin is weaker when examined at the magnified decadal scale.The results also show that human activities are more important on the Chinese side of the Heilongjiang River Basin,in the ZeyaBureya Plain on the Russian side,and at lower altitudes(0-100 m).Revealing the spatial and temporal processes and driving factors over the past 100 yr helps researchers and policymakers understand and anticipate wetland change and design effective conservation and restoration policies.

Construction of nanofibrous scaffolds with interconnected perfusable microchannel networks for engineering of vascularized bone tissue

Vascularization and bone regeneration are two closely related processes during bone reconstruction.A three-dimensional(3D)scaffold with porous architecture provides a suitable microenvironment for vascular growth and bone formation.Here,we present a simple and general strategy to construct a nanofibrous poly(L-lactide)/poly(ε-caprolactone)(PLLA/PCL)scaffold with interconnected perfusable microchannel networks(IPMs)based on 3D printing technology by combining the phase separation and sacrificial template methods.The regular and customizable microchannel patterns within the scaffolds(spacings:0.4 mm,0.5 mm,and 0.6 mm;diameters:0.8 mm,1 mm,and 1.2 mm)were made to investigate the effect of microchannel structure on angiogenesis and osteogenesis.The results of subcutaneous embedding experiment showed that 0.5/0.8-IPMs(spacing/diameter=0.5/0.8)and 0.5/1-IPMs(spacing/diameter=0.5/1)scaffolds exhibited more vascular network formation as compared with other counterparts.After loading with vascular endothelial growth factor(VEGF),VEGF@IPMs-0.5/0.8 scaffold prompted better human umbilical vein endothelial cells(HUVECs)migration and neo-blood vessel formation,as determined by Transwell migration,scratch wound healing,and chorioallantoic membrane(CAM)assays.Furthermore,the microangiography and rat cranial bone defects experiments demonstrated that VEGF@IPMs-0.5/0.8 scaffold exhibited better performance in vascular network formation and new bone formation compared to VEGF@IPMs-0.5/1 scaffold.In summary,our results suggested that the microchannel structure within the scaffolds could be tailored by an adjustable caramel-based template strategy,and the combination of interconnected perfusion microchannel networks and angiogenic factors could significantly enhance vascularization and bone regeneration.

Global finite-time attitude regulation using bounded feedback for a rigid spacecraft

This paper investigates the problem of global attitude regulation control for a rigid spacecraft under input saturation. Based on the technique of finite-time control and the switching control method, a novel global bounded finite-time attitude regulation controller is proposed. Under the proposed controller, it is shown that the spacecraft attitude can reach the desired attitude in a finite time. In addition, the bound of a proposed attitude controller can be adjusted to any small level to accommodate the actuation bound in practical implementation.