Inclusion of ecologically based trait variation in plant functional types reduces the projected land carbon sink in an earth system model

Earth system models demonstrate large uncertainty in projected changes in terrestrial carbon budgets. The lack of inclusion of adaptive responses of vegetation communities to the environment has been suggested to hamper the ability of modeled vegetation to adequately respond to environmental change. In this study, variation in functional responses of vegetation has been added to an earth system model (ESM) based on ecological principles. The restriction of viable mean trait values of vegetation communities by the environment, called ‘habitat filtering’, is an important ecological assembly rule and allows for determination of global scale trait–environment relationships. These relationships were applied to model trait variation for different plant functional types (PFTs). For three leaf traits (specific leaf area, maximum carboxylation rate at 25 °C, and maximum electron transport rate at 25 °C), relationships with multiple environmental drivers, such as precipitation, temperature, radiation, and CO₂, were determined for the PFTs within the Max Planck Institute ESM. With these relationships, spatiotemporal variation in these formerly fixed traits in PFTs was modeled in global change projections (IPCC RCP8.5 scenario). Inclusion of this environment‐driven trait variation resulted in a strong reduction of the global carbon sink by at least 33% (2.1 Pg C yr^?1) from the 2nd quarter of the 21st century onward compared to the default model with fixed traits. In addition, the mid‐ and high latitudes became a stronger carbon sink and the tropics a stronger carbon source, caused by trait‐induced differences in productivity and relative respirational costs. These results point toward a reduction of the global carbon sink when including a more realistic representation of functional vegetation responses, implying more carbon will stay airborne, which could fuel further climate change.     

The Effect of Hole Transport Material Pore Filling on Photovoltaic Performance in Solid‐State Dye‐Sensitized Solar Cells

A detailed investigation of the effect of hole transport material (HTM) pore filling on the photovoltaic performance of solid‐state dye‐sensitized solar cells (ss‐DSCs) and the specific mechanisms involved is reported. It is demonstrated that the efficiency and photovoltaic characteristics of ss‐DSCs improve with the pore filling fraction (PFF) of the HTM, 2,2’,7,7’‐tetrakis‐(N, N ‐di‐ p ‐methoxyphenylamine)9,9’‐spirobifluorene(spiro‐OMeTAD). The mechanisms through which the improvement of photovoltaic characteristics takes place were studied with transient absorption spectroscopy and transient photovoltage/photocurrent measurements. It is shown that as the spiro‐OMeTAD PFF is increased from 26% to 65%, there is a higher hole injection efficiency from dye cations to spiro‐OMeTAD because more dye molecules are covered with spiro‐OMeTAD, an order‐of‐magnitude slower recombination rate because holes can diffuse further away from the dye/HTM interface, and a 50% higher ambipolar diffusion coefficient due to an improved percolation network. Device simulations predict that if 100% PFF could be achieved for thicker devices, the efficiency of ss‐DSCs using a conventional ruthenium‐dye would increase by 25% beyond its current value.     

The carbon costs of mitigating high‐severity wildfire in southwestern ponderosa pine

Forests provide climate change mitigation benefit by sequestering carbon during growth. This benefit can be reversed by both human and natural disturbances. While some disturbances such as hurricanes are beyond the control of humans, extensive research in dry, temperate forests indicates that wildfire severity can be altered as a function of forest fuels and stand structural manipulations. The purpose of this study was to determine if current aboveground forest carbon stocks in fire‐excluded southwestern ponderosa pine forest are higher than prefire exclusion carbon stocks reconstructed from 1876, quantify the carbon costs of thinning treatments to reduce high‐severity wildfire risk, and compare posttreatment (thinning and burning) carbon stocks with reconstructed 1876 carbon stocks. Our findings indicate that prefire exclusion forest carbon stocks ranged from 27.9 to 36.6 Mg C ha^?1 and that the current fire‐excluded forest structure contained on average 2.3 times as much live tree carbon. Posttreatment carbon stocks ranged from 37.9 to 50.6 Mg C ha^?1 as a function of thinning intensity. Previous work found that these thinning and burning treatments substantially increased the 6.1 m wind speed necessary for fire to move from the forest floor to the canopy (torching index) and the wind speed necessary for sustained crown fire (crowning index), thereby reducing potential fire severity. Given the projected drying and increase in fire prevalence in this region as a function of changing climatic conditions, the higher carbon stock in the fire‐excluded forest is unlikely to be sustainable. Treatments to reduce high‐severity wildfire risk require trade‐offs between carbon stock size and carbon stock stability.     

基于森林清查资料的河南省森林植被碳储量动态变化

利用1994—1998年、1999—2003年、2004—2008年、2009—2013年河南省4期森林资源清查数据,运用生物量转换因子连续函数法和平均生物量法,估算了1998—2013年河南省森林植被的碳储量和碳密度变化。研究结果表明,河南省森林植被碳储量由1998年的45.57 Tg增加到2013年的107.98 Tg,年均碳汇量为4.16 Tg/a。乔木林碳储量和碳密度分别由1998年的33.54 Tg和22.39 Mg/hm~2增加到2013年的97.11 Tg和31.80 Mg/hm~2。乔木林碳储量在所有植被类型中占主体,4个森林清查时期乔木林碳储量占森林植被总碳储量的比例分别为73.60%、79.22%、85.63%和89.93%。2013年森林清查时,乔木林中杨树和栎类碳储量最大,分别占总碳储量的37.61%和25.22%,各龄组乔木林碳密度大小顺序依次为成熟林近熟林中龄林过熟林幼龄林。阔叶林面积、碳储量、碳密度均高于针叶林,阔叶林是河南省森林碳汇的主要贡献者。人工林面积、碳储量、碳密度增加幅度都要高于天然林,人工林碳储量由1998年的9.62 Tg增加到2013年的55.67 Tg,占乔木林碳储量总增量的77.15%,人工林碳密度由1998年的17.86 Mg/hm~2提高到2013年的32.01 Mg/hm~2,人工林在河南省森林碳汇中逐步发挥重要的作用,逐渐成为河南省森林碳汇的主体,随着人工林生长为具有较高碳密度的成熟林,河南省乔木林将具有较大的碳汇潜力。     

Feeding behavior,life history,and virus transmission ability of Bemisia tabaci Mediterranean species (Hemiptera: Aleyrodidae) under elevated CO2

The continuous rise of CO₂ concentrations in the atmosphere is reducing plant nutritional quality for herbivores and indirectly affects their performance. The whitefly (Bemisia tabaci, Gennadius) is a major worldwide pest of agricultural crops causing significant yield losses. This study investigated the plant‐mediated indirect effects of elevated CO₂ on the feeding behavior and life history of B. tabaci Mediterranean species. Eggplants were grown under elevated and ambient CO₂ concentrations for 3 weeks after which plants were either used to monitor the feeding behavior of whiteflies using the Electrical Penetration Graph technique or to examine fecundity and fertility of whiteflies. Plant leaf carbon, nitrogen, phenols and protein contents were also analyzed for each treatment. Bemisia tabaci feeding on plants exposed to elevated CO₂ showed a longer phloem ingestion and greater fertility compared to those exposed to ambient CO₂ suggesting that B. tabaci is capable of compensating for the plant nutritional deficit. Additionally, this study looked at the transmission of the virus Tomato yellow leaf curl virus (Begomovirus) by B. tabaci exposing source and receptor tomato plants to ambient or elevated CO₂ levels before or after virus transmission tests. Results indicate that B. tabaci transmitted the virus at the same rate independent of the CO₂ levels and plant treatment. Therefore, we conclude that B. tabaci Mediterranean species prevails over the difficulties that changes in CO₂ concentrations may cause and it is predicted that under future climate change conditions, B. tabaci would continue to be considered a serious threat for agriculture worldwide.     

Thinner bark increases sensitivity of wetter Amazonian tropical forests to fire

Understory fires represent an accelerating threat to Amazonian tropical forests and can, during drought, affect larger areas than deforestation itself. These fires kill trees at rates varying from < 10 to c. 90% depending on fire intensity, forest disturbance history and tree functional traits. Here, we examine variation in bark thickness across the Amazon. Bark can protect trees from fires, but it is often assumed to be consistently thin across tropical forests. Here, we show that investment in bark varies, with thicker bark in dry forests and thinner in wetter forests. We also show that thinner bark translated into higher fire‐driven tree mortality in wetter forests, with between 0.67 and 5.86 gigatonnes CO₂ lost in Amazon understory fires between 2001 and 2010. Trait‐enabled global vegetation models that explicitly include variation in bark thickness are likely to improve the predictions of fire effects on carbon cycling in tropical forests.     

Structure and nonlinear optical properties of copper phthalocyanine thin films

This paper describes a joint study of the structure and nonlinear optical properties of vacuum evaporated thin films of copper phthalocyanine (CuPc for brevity). Film thickness ranges from 50 to 500 nm. The anisotropic paramagnetic resonance of Cu⁺⁺ ions reveals that the Pc rings lie almost parallel to the substrate plane with however a large angular distribution (30° FWHM). Third harmonic optical generation measurements performed at 1.064 m and 1.907 m fundamental wavelengths give respectively an average value of the cubic susceptibility ⁽³⁾(-3,)=(4±0.4)·10^–12 e.s.u. and (2.1+-0.2) · 10^-12 These values, although significantly higher than for a common ionic crystal, are about one order of magnitude lower than in conjugated 1-D systems, which shows that the 2-D -electron delocalization is less profitable than the 1-D one. Besides third harmonic, we have also observed second harmonic generation. Its polarization dependence is characteristic of a quadratic susceptibility enhanced in one direction, almost perpendicular to the substrate, withd _eff comprised between 30 and 60 · 10^-9 e.s.u. The possible origins ofd _eff are discussed.     

The Dual Arrhenius and Michaelis–Menten kinetics model for decomposition of soil organic matter at hourly to seasonal time scales

Decomposition of soil carbon stocks is one of the largest potential biotic feedbacks to climate change. Models of decomposition of soil organic matter and of soil respiration rely on empirical functions that relate variation in temperature and soil water content to rates of microbial metabolism using soil‐C substrates. Here, we describe a unifying modeling framework to combine the effects of temperature, soil water content, and soluble substrate supply on decomposition of soluble soil‐C substrates using simple functions based on process concepts. The model's backbone is the Michaelis–Menten equation, which describes the relationship between reaction velocity and soluble organic‐C and O₂ substrate concentrations at an enzyme's reactive site, which are determined by diffusivity functions based on soil water content. Temperature sensitivity is simulated by allowing the maximum velocity of the reaction (V_max) to vary according to Arrhenius function. The Dual Arrhenius and Michaelis–Menten kinetics (DAMM) model core was able to predict effectively observations from of laboratory enzyme assays of β‐glucosidase and phenol‐oxidase across a range of substrate concentrations and incubation temperatures. The model also functioned as well or better than purely empirical models for simulating hourly and seasonal soil respiration data from a trenched plot in a deciduous forest at the Harvard Forest, in northeastern United States. The DAMM model demonstrates that enzymatic processes can be intrinsically temperature sensitive, but environmental constrains of substrate supply under soil moisture extremes can prevent that response to temperature from being observed. We discuss how DAMM could serve as a core module that is informed by other modules regarding microbial dynamics and supply of soluble‐C substrates from plant inputs and from desorption of physically stabilized soil‐C pools. Most importantly, it presents a way forward from purely empirical representation of temperature and moisture responses and integrates temperature‐sensitive enzymatic processes with constraints of substrate supply.     

The Fate of Organic Sources of Carbon in Moss‐rich Tundra Soil Microbial Communities: A Laboratory Experimental Study

Effects of glucose‐carbon supplementation on soil respiration and bacterial and protist biomass were investigated in laboratory studies of three soil samples from Alaskan tundra: spring tussock sample 1 (thin surface moss), spring tussock sample 2 (thick surface moss), and a summer tundra open field sample. Addition of 1% (w/v) glucose solution produced an immediate, pronounced two to three fold increase in respiration above basal rate, which declined over 4 h to baseline levels. Less than 1% (w/w) of glucose‐C supplement was respired during the respiratory spike, relative to the 89 μg/g added. A more substantial amount of the glucose‐C became incorporated in microbial biomass. The total difference in microbial carbon (μg/g) between the experimental treatments and controls without glucose after 1 wk was as follows: spring sample 1 (8), spring sample 2 (31), and summer sample (70). The percent (w/w) of glucose‐C incorporated was: spring sample 1 (5%), spring sample 2 (17%), and summer sample (39%), most attributed to biomass of bacteria and heterotrophic nanoflagellates. Although respiratory response to pulsed glucose‐C was minimal, the overall mean basal rate after 1 wk ranged between 4 and 6 nmol/min/g soil, indicating a significant assimilation and respiration of constituent soil organic carbon.     

中国北亚热带天然次生林与杉木人工林土壤活性有机碳库的比较

为了了解北亚热带东部地区天然次生林转变成杉木(Cunninghamia lanceolata)人工林对土壤活性有机碳库的影响, 以浙江省富阳市庙山坞森林生态系统定位研究站杉木人工林和天然次生林为研究对象, 对达到成熟林状态的两种林分类型0-60 cm内各土层土壤活性有机碳含量进行了比较研究。结果表明: 1)天然次生林土壤总有机碳、易氧化有机碳、水溶性有机碳和轻组有机质含量均高于杉木人工林, 与人工杉木林相比, 增幅分别为19.0%-32.6%、0.8%-30.3%、3.8%-54.1%和6.3%-38.6%, 且在0-10和10-20 cm土层差异显著(p < 0.05) (水溶性有机碳仅在0-10 cm土层差异显著); 2)杉木人工林土壤水溶性有机碳与易氧化碳占总有机碳的比率均高于天然次生林; 3)两个林分土壤水溶性有机碳、易氧化碳和轻组有机质与总有机碳含量均呈现极显著相关, 且天然次生林土壤易氧化碳、轻组有机质与总有机碳的相关系数均大于杉木人工林; 4)土壤有机碳、水溶性有机碳、易氧化碳和轻组有机质与土壤养分(全氮、水解氮、速效磷、速效钾、速效钙和速效镁)的相关性均达到显著(p < 0.05)或极显著(p < 0.01)水平。