Cybernetic model predictive control of a continuous bioreactor with cell recycle

The control of poly-beta-hydroxybutyrate (PHB) productivity in a continuous bioreactor with cell recycle is studied by simulation. A cybernetic model of PHB synthesis in Alcaligenes eutrophus is developed. Model parameters are identified using experimental data, and simulation results are presented. The model is interfaced to a multirate model predictive control (MPC) algorithm. PHB productivity and concentration are controlled by manipulating dilution rate and recycle ratio. Unmeasured time varying disturbances are imposed to study regulatory control performance, including unreachable setpoints. With proper controller tuning, the nonlinear MPC algorithm can track productivity and concentration setpoints despite a change in the sign of PHB productivity gain with respect to dilution rate. It is shown that the nonlinear MPC algorithm is able to track the maximum achievable productivity for unreachable setpoints under significant process/model mismatch. The impact of model uncertainty upon controller performance is explored. The multirate MPC algorithm is tested using three controllers employing models that vary in complexity of regulation. It is shown that controller performance deteriorates as a function of decreasing biological complexity.     

Water regulated effects of photosynthetic substrate supply on soil respiration in a semiarid steppe

Soil respiration is an important part of the global carbon (C) cycle and the largest component of C flux from terrestrial ecosystems to the atmosphere. Here, we investigated possible effects of photosynthetic substrate supply on soil respiration in a semiarid ecosystem. A field experiment combining water addition and shading (low and high shading) treatments was conducted to manipulate photosynthetic substrate supply in a temperate semiarid steppe in two growing seasons. Our result showed that water addition and/or low shading significantly increased net primary productivity (ecosystem‐level photosynthetic substrate supply) and soil respiration in both two growing seasons. However, the effects of high shading on net primary productivity and soil respiration depended on soil water condition, which were negative in wet year (2008) but positive in dry year (2009). On the diel timescale, soil respiration was out of phase with soil temperature and leaf net photosynthesis, but in phase with leaf sugar and starch contents (leaf‐level photosynthetic substrate production). The results indicated that photosynthetic substrate supply was an important factor in regulating soil respiration on both daily and seasonal timescales. Moreover, its effect on soil respiration increased with increasing water availability in this region. The predominant role of C assimilate supply on soil respiration indicates that the predicted positive influence of rising temperature on soil respiration will be simultaneously mediated by substrate supply and water availability in semiarid steppe ecosystems.     

Temperature‐mediated responses of carbon fluxes to precipitation variabilities in an alpine meadow ecosystem on the Tibetan Plateau

Effects of climate warming and changing precipitation on ecosystem carbon fluxes have been intensively studied. However, how they co‐regulate carbon fluxes is still elusive for some understudied ecosystems. To fill the gap, we examined net ecosystem productivity (NEP), gross ecosystem productivity (GEP,) and ecosystem respiration (ER) responses to multilevel of temperature increments (control, warming 1, warming 2, warming 3, warming 4) in three contrasting hydrological growing seasons in a typical semiarid alpine meadow. We found that carbon fluxes responded to precipitation variations more strongly in low‐level warming treatments than in high‐level ones. The distinct responses were attributable to different soil water conditions and community composition under low‐level and high‐level warming during the three growing seasons. In addition, carbon fluxes were much more sensitive to decreased than to increased precipitation in low‐level warming treatments, but not in high‐level ones. At a regional scale, this negative asymmetry was further corroborated. This study reveals that future precipitation changes, particularly decreased precipitation would induce significant change in carbon fluxes, and the effect magnitude is regulated by climate warming size.     

Coralline algal maerl frameworks-Islands within the phaeophytic kelp belt

Summary In the subtropical belt highly productive ecosystems are formed by coral reefs in oligotrophic seas. Towards more eutrophic conditions, coral reefs diminish and are subsequently replaced by highly productive kelp forests. In high latitudes framework constructing carbonate production is enhanced by the growth of branching coralline algae which predominantly generate maerl-type deposits. On a global view, these coralline algal ecosystems show an island-like distribution pattern within the phaeophytic kelp belt. Compared to kelp ecosystems, coralline-algaldominated ecosystems have low rates of productivity. Therefore, it is reasonable to seek the pronounced competitive value of the extremely slow-growing corallines. Due to their low annual growth increment, the coralline algae studied are very endangered by abiotic physical disturbances and by overgrowth of rapidly growing filamentous algae or sessile invertebrates. To overcome fouling pressure and storm-triggered physical disturbances, coralline algae thrive well in wave-sheltered headlands or skerry areas and generate characteristic ‘denuded areas’ by intense herbivory. This general distributional pattern is also true for high-boreal to subarctic coralline algal bioherms in northern Norway. Such a complex biological feedback maintains a high potential of self-regulation or self-organization in the algal reef bioherms. The different proponents involved in feedback processes include bacterial colonization, diatom microfouling and selective induction of larval metamorphosis. The negative impact of diatom microfouling and the important role of herbivores are relevant activities in the feedback system on a microscopic scale. Macroscopically, intense herbivory on coralline algae create denuded conditions, which are a widespread phenomenon in coralline algal ecosystems.     

植物-土壤反馈理论及其在自然和农田生态系统中的应用研究进展

植物-土壤反馈理论最早源于农业生产,近年来已成为生态学上研究植被动态变化、群落组成和功能,以及生态系统响应人为干扰、气候变化等众多热点问题的重要理论和方法支撑。总结了植物-土壤反馈定义和类型,分析了反馈机制,在此基础上综述了该理论在自然生态系统中的应用,包括物种入侵、群落演替、植物共存及多样性形成、植物多样性-生产力关系、多营养级交互作用以及响应气候变化等关键生态学命题。探讨了植物-土壤反馈理论在农田生态系统中的应用,介绍了该理论在提高多样化种植体系生产力、土壤污染修复、种植体系设计等方面的进展和潜在应用价值。提出了植物-土壤反馈理论在未来发展中进一步研究的方向,对应用该理论提高生态系统服务功能,促进可持续发展等方面进行了展望。     

The need for a canopy perspective to understand the importance of phenotypic plasticity for promoting species coexistence and light-use complementarity in forest ecosystems

Because of their overwhelming size over other organisms, trees define the structural and energetic properties of forest ecosystems. From grasslands to forests, leaf area index, which determines the amount of light energy intercepted for photosynthesis, increases with increasing canopy height across the various terrestrial ecosystems of the world. In vertically well-developed forests, niche differentiation along the vertical gradient of light availability may promote species coexistence. In addition, spatial and temporal differentiation of photosynthetic traits among the coexisting tree species (functional diversity) may promote complementary use of light energy, resulting in higher biomass and productivity in multi-species forests. Trees have evolved retaining high phenotypic plasticity because the spatial/temporal distribution of resources in forest ecosystems is highly heterogeneous and trees modify their own environment as they increase nearly 1,000 times in size through ontogeny. High phenotypic plasticity may enable coexistence of tree species through divergence in resource-rich environments, as well as through convergence in resource-limited environments. We propose that the breadth of individual-level phenotypic plasticity, expressed at the metamer level (leaves and shoots), is an important factor that promotes species coexistence and resource-use complementarity in forest ecosystems. A cross-biome comparison of the link between plasticity of photosynthesis-related traits and stand productivity will provide a functional explanation for the relationship between species assemblages and productivity of forest ecosystems.     

Analysis of the productivity of a continuous algal culture system

We describe a first-principles analysis of a system for the continuous culture of the green alga Scenedesmus obliquus under light-limiting conditions. According to this analysis, the productivity of the algal culture is given by the relation Y = E(m)I(0)AK(1 - e(-alphacl)) - GRcV, where Y = yield (g cells/h), E(m) = 0.20 (the maximum attainable photosynthetic conversion on an energy basis), A = illuminated area (m(2)), K = 0.156[(g cells/h/W), the energy equivalent of the algae], I(0) = light intensity (W/m(2)), alpha = extinction coefficient (L/cm/g),c = cell concentration (g/L), I = light path (cm), R = respiration rate (g carbon/g cells/h), V = culture volume (L), and G = ratio of g cells to g carbon (2.04). This formula is completely determined and has no free adjustable parameters. Using parameter values determined independently, the model accurately predicted the relationship of productivity to cell density in the culture system.     

A twofold role for global energy gradients in marine biodiversity trends

Explanations for major biodiversity patterns have not achieved a consensus, even for the latitudinal diversity gradient (LDG), but most relate to patterns of solar energy influx into Earth systems, and its effects on temperature (as biochemical activity rates are temperature sensitive) and photosynthesis (which drives nearly all of the productivity that fuels ecosystems). Marine systems break some of the confounding correlations among temperature, latitude and biodiversity that typify the terrestrial systems that have dominated theoretical discussions and large‐scale analyses. High marine diversities occur not only in warm shallow seas where productivity may be either low or high, depending on regional features, but also in very cold deep‐sea regions, indicating that diversity is promoted by stability in temperature and in trophic resources (nutrients and food items), and more specifically by their interaction, rather than by high mean values of either variable. The common association of high diversity with stable but low to moderate annual productivity suggests that ecological specialization underlies the similarly high diversities in the shallow tropics and deep sea. Recent work on shallow‐marine bivalves is consistent with this view of decreasing specialization in less stable habitats. Lower diversities in shallow seas are associated with either high thermal seasonality (chiefly in temperate latitudes) or highly seasonal trophic supplies (at any latitude), which exclude species that are adapted to narrow ranges of those variables.     

生物结皮-土壤呼吸对冬季低温及模拟增温的响应

以腾格里沙漠东南缘天然植被区藓类结皮和藻-地衣结皮-土壤为研究对象,利用开顶式生长室(OTC),采用Li-8150系统连续测定了冬季(2015年11月—2016年1月)低温环境下两类结皮-土壤呼吸的变化,分析了低温及模拟增温对两类结皮-土壤呼吸的影响.结果表明: 观测期内,藓类结皮、藻-地衣结皮-土壤呼吸速率分别为-0.052～0.418、-0.032～0.493 μmol·m^-2·s^-1,且藓类结皮显著高于藻-地衣结皮-土壤系统.不同类型结皮-土壤呼吸速率与5 cm土壤温度和土壤体积含水量均呈显著线性正相关,增温主要是通过加速土壤水分蒸散而抑制生物结皮-土壤呼吸速率.在整个观测期,藓类结皮-土壤系统累计排放9.90 g C·m^-2,显著高于藻-地衣结皮-土壤系统的7.00 g C·m^-2.研究区生物结皮-土壤系统冬季累计排放7.40 g C·m^-2,是该荒漠生态系统全年碳收支的重要组成部分.     

全球变暖对太行山植被生产力及土壤水分的影响

将相同的自然植被用Lysimeter从高海拔下移至低海拔,温度升高2℃,同时设置平均降水,增加10％降水,增加20％降水,减少10％降水和减少20％降水5个降水处理,模拟全球变暖带来的温度升高和降水变化对植被生产力和土壤水分的影响,两年的野外实验表明,温度升高造成生态适应性差的野古草（Arundinelia hirta)生产力显著下降,致使整个测试群落生产力降低,低海拔实验点生产力显著低于高海拔实验点,温度升高对铁杆（Artemisia sacrorum)和黄背草（Themeda japonica)的影响较小,太行山区的植被对降水的变化反映,降水增加使植被的生产力水平显著提高,其中降水增加20％的处理生产力比平均降水处理的生产力增加22％,增加降水处理的土壤含水量显著高于平均降水和降水减少的实验处理,由于植被的减少,温度升高的实验点从第二年开始土壤水分较高。     

Some effects of light on the energetics of Daphnia pulex and implications for the significance of vertical migration

Energy budgets were computed from data obtained for Daphnia pulex cultured under nine light intensities, polarized light and four wavelength ranges. The percent assimilation of preadult animals is highest at intensities above 7 ft-c. Net efficiency of growth was highest (> 50%) and the net efficiency of respiration was lowest ( < 49%) at intensities less than 28 ft-c. The percent assimilation of adult animals was highest ( > 10%) at 110, 55 and 14 ft-c. Under the nine intensities the gross efficiencies of growth were less than 1 % and net efficiencies of growth varied from 3.9 to 7.3%. Gross efficiencies of respiration were highest above 7 ft-c. The net efficiency of respiration usually varied between 20 and 30% and the lowest was 9.8% at 1.7 ft-c. and the highest was 50.1% at 110 ft-c. Gross efficiency of reproduction varied from 2.6% at 3.5 ft-c to 12.6% at 14 ft-c and generally varied between 4 and 7.5%. Net efficiency of reproduction varied from 45.9% at 110 ft-c to 84.3% at 1.7 ft-c and usually varied from 62 to 75% at other light intensities. The ratio of energy of respiration to energy of growth and reproduction ranged from 12% to 1.7 ft-c to 105.3% at 110 ft-c. This ratio usually varied from 25 to 34% at 14 ft-c or less and exceeded 37% at intensities above 14 ft-c. The percent assimilation (3.5%), gross (2.0%), and net (56.3%) efficiencies of respiration of preadult animals raised under polarized light were higher than for those at a similar, nonpolarized, intensity. The net efficiency of growth (43.7%) was lower under polarized light. The percent assimilation, gross efficiencies of growth, reproduction and respiration, net efficiencies of growth and reproduction of adult animals under polarized light (6.6 ft-c) were lower than for those under 7 ft-c. For preadult animals assimilation efficiencies were lower in wavelength treatments than in white light or darkness. The gross efficiencies of growth and respiration were lowest under red wavelengths and the net efficiencies of growth were lowest and respiration highest under green wavelengths. For adult animals, the assimilation efficiencies were lower in the wavelength treatments than those obtained in other light treatments. While the gross efficiencies of growth, reproduction and respiration were generally lower, the net efficiencies of growth and reproduction were generally within the range of values for other light conditions. The net efficiencies of respiration, except for red wavelengths, were lower than those for other light conditions except at 1.7 ft-c. The ratio of energy of respiration to energy of growth and reproduction showed similar trends. The effects of wavelength are generally separable from the effects of light intensity.     

冬小麦旺盛生长期间CO2浓度升高对根际呼吸的影响

依托FACE（free air carbon dioxide enrichment）技术平台,利用阻断根法,采用H6400红外气体分析仪（IRGA）-田间原位测定的方法,研究了大气CO2浓度升高和不同氮肥水平对水稻／小麦轮作制中冬小麦旺盛生长期间根际呼吸的影响。结果表明,在整个测定期间,大气CO2浓度升高增强了根际呼吸速率,提高了根际呼吸排放量。在高N和低N处理中,高CO2浓度下的根际呼吸总排放量分别比Ambient极显著增加117．0％和90．8％。根际呼吸速率在孕穗初期达到最大值;使根际呼吸在土壤呼吸中的比重由24．5％（LN）～26．7（HN）提高到39．8％（LN）～47．1％（HN）。CO2浓度升高与氮肥用量对根际呼吸产生交互效应。表明大气CO2浓度升高将加快土壤向大气的CO2排放,结果将有助于评价未来高CO2浓度背景下农田生态系统土壤碳的固定潜力。     

Distinct responses of soil respiration to experimental litter manipulation in temperate woodland and tropical forest

Global change is affecting primary productivity in forests worldwide, and this, in turn, will alter long‐term carbon (C) sequestration in wooded ecosystems. On one hand, increased primary productivity, for example, in response to elevated atmospheric carbon dioxide (CO₂), can result in greater inputs of organic matter to the soil, which could increase C sequestration belowground. On other hand, many of the interactions between plants and microorganisms that determine soil C dynamics are poorly characterized, and additional inputs of plant material, such as leaf litter, can result in the mineralization of soil organic matter, and the release of soil C as CO₂ during so‐called “priming effects”. Until now, very few studies made direct comparison of changes in soil C dynamics in response to altered plant inputs in different wooded ecosystems. We addressed this with a cross‐continental study with litter removal and addition treatments in a temperate woodland (Wytham Woods) and lowland tropical forest (Gigante forest) to compare the consequences of increased litterfall on soil respiration in two distinct wooded ecosystems. Mean soil respiration was almost twice as high at Gigante (5.0 μmol CO₂ m^?2 s^?1) than at Wytham (2.7 μmol CO₂ m^?2 s^?1) but surprisingly, litter manipulation treatments had a greater and more immediate effect on soil respiration at Wytham. We measured a 30% increase in soil respiration in response to litter addition treatments at Wytham, compared to a 10% increase at Gigante. Importantly, despite higher soil respiration rates at Gigante, priming effects were stronger and more consistent at Wytham. Our results suggest that in situ priming effects in wooded ecosystems track seasonality in litterfall and soil respiration but the amount of soil C released by priming is not proportional to rates of soil respiration. Instead, priming effects may be promoted by larger inputs of organic matter combined with slower turnover rates.     

黄土旱塬区免耕玉米田土壤呼吸对降雨的响应

在多年定位试验的基础上,采用LI-8150-16多通道土壤碳通量测量系统对传统耕作和免耕处理下玉米田的土壤呼吸进行了连续观测,以探讨不同耕作措施处理下土壤呼吸对降雨的响应。结果表明:降雨发生瞬间,土壤呼吸受应激反应影响迅速降低,传统耕作和免耕处理下分别较降雨前降低62.9%—92.9%和35.8%—56.9%;降雨后,传统耕作和免耕处理土壤呼吸的降幅范围分别为31.5%—89.2%和15.7%—59.9%;土壤体积含水量接近于18%时,传统耕作下土壤呼吸比免耕下高51.8%,当土壤体积含水量高于30%时,传统耕作下土壤呼吸比免耕处理下低43.0%,表明传统耕作土壤呼吸更易受土壤水分的影响,波动幅度大;传统耕作处理下土壤呼吸随土壤温度的升高而增大,免耕处理下土壤呼吸随土壤温度的升高变化不明显;土壤体积含水量较小(20%)时,不同耕作处理下土壤呼吸均随土壤含水量增加而增加,含水量较高(30%)时则均随土壤含水量的升高而减小,两种情况下均为免耕处理的变化速率更大;双因子线性模型可较好地描述玉米田土壤呼吸对温度和水分变化的响应。     

干旱对陆地生态系统生产力的影响

该文综述了干旱对陆地生态系统生产力的影响,分析了其影响机制,并总结了植被对干旱的响应与适应及其机理机制。干旱通过抑制光合作用来降低陆地生态系统总初级生产力,干旱还可以降低生态系统的自养呼吸和异养呼吸。同时干旱还可以通过影响其它干扰形式来间接影响陆地生态系统生产力,如增加火干扰的发生频率和强度,增加植物的死亡率,增加病虫害的发生等。在生态系统水平上干旱可以降低碳固定,减弱碳汇功能,甚至把生态系统从碳汇改变成碳源。目前生态系统水平上的干旱影响研究主要通过两种方法实现,一种是模型模拟,另一种就是大型模拟实验。作为陆地生态系统生产力的实现者,在干旱胁迫条件下,植物也会采取积极的适应策略以减弱干旱对生态系统生产力的影响,其适应策略主要分以下3种:在一些周期性发生干旱的地区,植物会调整生长期以避开干旱或通过休眠来减弱干旱所造成的伤害;还有一些植物会通过调节体内的代谢过程,改变一些生理特性来抵御干旱;而长期生活在干旱条件下的植物则通过进化来改变了自身的生理生化代谢过程,形成耐旱机制。目前,植物对干旱响应的分子学机制,以及生态系统水平上对干旱的响应和适应仍然是薄弱的领域,也必然成为未来研究的重点。     

森林生态系统碳氮循环功能耦合研究综述

在大气CO2浓度升高和氮沉降增加等全球变化背景下,森林生态系统减缓CO2浓度升高的作用及其对全球变化的响应和反馈存在诸多不确定性.森林生态系统碳氮循环相互作用及功能耦合规律的研究是揭示这些不确定性的基础,也是反映森林生态系统生物产量与养分之间作用规律,涉及林地持久生产力（sustainability of long-term site productivity）的生态学机理问题.森林生态系统碳氮循环的耦合作用表现在林冠层光合作用的碳固定过程,森林植物组织呼吸、土壤凋落物与土壤有机质分解、地下部分根系周转与呼吸等碳释放过程,这些过程存在反馈机理和非线性作用,最终决定森林生态系统的碳平衡.着重在生态系统尺度上,综述了碳氮循环耦合作用研究的一些进展与存在的问题,对今后研究方向进行了展望.     

Perturbation and abrupt shift in trophic control of biodiversity and productivity

Ecology is founded on the view that ecosystem properties like biodiversity and productivity change smoothly with changing environmental conditions. However, emerging theory predicts that environmental change may cause abrupt shifts to alternate states. In many ecosystems, top predators play a pivotal role in controlling plant productivity and diversity. Yet it remains uncertain if altering this control shifts systems to alternate states. I report on a test of the hypothesis that loss of predator control of ecosystem function causes abrupt state changes in diversity and productivity. In this meadow ecosystem, predators enhance plant diversity by causing a highly productive, competitively dominant plant species to be suppressed by herbivores. Experimental predator removal caused rapid proliferation of the competitively dominant plant. Moreover, temporally staggered predator reintroductions failed to restore the ecosystem. This loss of resilience confirmed that the ecosystem crossed a critical threshold and entrained into an alternate state.     

Photoperiod and light quality effects on rate of dark respiration and on photosynthetic capacity in developing seedlings of Chenopodium rubrum

Development and acclimation of energy transduction were studied in seedlings of Chenopodium rubrum L. ecotype selection 184 (50° 10' N; 105° 35' W) in response to photomorphogenic and photoperiodic treatments. Dark respiration and photosynthetic capacity [nmol O₂ (pair of cotyledons)⁻¹ h⁻¹] were measured with an oxygen electrode. Changes in chloroplast ultrastructure were analyzed concomitantly. After germination, seedlings were grown at constant temperature either in darkness or in continuous light (white, red, far-red and blue) or were subjected to diurnal cycles of light/dark or changes in light quality. Dark respiration was low in far-red light treated seedlings. In red light treated seedlings dark respiration was high and the mean value did not depend on fluence rate or photoperiod. Blue light stimulated transitorily and modulated dark respiration in photoperiodic cycles. Photosynthetic capacity was reduced by far-red light and increased by red light. In response to blue light photosynthetic capacity increased, with indications of a requirement for continuous energy input. Phytochrome and a separate blue light receptor seemed to be involved. In continuous red light a clear cut circadian rhythm of dark respiration was observed. Blue light had a specific effect on chloroplast structure.     

Diatom community response along a productivity gradient of shallow Antarctic lakes

Summary Antarctic lakes are simple ecosystems ranging in productivity from extremely low productive melt-water lakes to highly productive guano lakes. With the aim to assess the importance of environmental variables for species composition and abundance of periphytic diatoms, we quantified light availability and nutrient concentration in the water and in the sediment of 21 Antarctic lakes. Of a total of 66 diatom taxa identified, the distribution of 16 species were investigated in detail. Four of these (25%) showed highest abundance in highly productive lakes (low light/high nutrient availability), whereas three species (19%) increased in abundance as productivity decreased (high light/low nutrient availability). Some ecological theories predict that species richness shows a maximum in medium productive systems and a decreasing trend as productivity increases further due to competition. Other theories suggest that physical factors, including climate, is the major factor determining species richness. The results from our study suggest that none of the theories are completely wrong or right, but that they have to be combined to explain as much as possible of the variation in species richness.     

Seedling light limitation does not increase across a natural productivity gradient

Aims A key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites. This idea, and its implications for plant community structure, has been tested many times in artificial productivity gradients (fertilization studies), but whether it applies to natural productivity gradients is unclear.Methods To test whether seedling light limitation would increase across a natural productivity gradient, I conducted a cross-site field experiment in southwest Michigan, USA. At each of six old fields naturally varying in productivity, I exposed transplanted seedlings of big bluestem (Andropogon gerardii) to a light addition (tie-back) treatment that increased light availability and measured their biomass after one and two growing seasons.Important findings Seedlings responded positively to the tie-back treatment, but positive responses did not increase across the natural productivity gradient. These results suggest that although light does limit seedling establishment, the strength of light limitation does not depend on variation in productivity in natural systems. Instead, light limitation interacted with a variety of site differences to determine establishment. Although the general principle that light limitation increases with productivity is well established, these results indicate that it may not always occur in natural systems.