Carbon-cycling changes during regeneration of a decinduous broadleaf forest after clear-cutting II. Aboveground net production

Growth and death rates of aboveground plant parts were measured in a mature forest and four different-aged deciduous broadleaf forests regeneratede after clear-cutting, with special reference to rates for woody parts (stems and branches) of different diameters (ø) in rerms of the pipe model theory (Shinozaki et al., 1964). The total biomass increment of woody parts of trees higher than 1.3 m varied within a range of 2.1-4.6 ton ha^?1 yr^?1, the increase beingdue largely to the growth of canopy trees exposed to direct sunlight. Biomass increments of small (ø<1 cm) and medium (1≤ø<5 cm) woody parts were negligibly small except in the youngest forest, and changes in aboveground woody biomass with forest age after clear-cutting mainly resulted from accumulation of large (5 cm<ø) woody parts of canopy trees. Biomass loss of trees due to death and grazing increased with forest age from 4.0 to 8.3 ton ha^?1 yr^?1. Recovery of leaf and small wood falls was observed at the early stage of regeneration, while large wood falls increased during regeneration. Flower and fruit fall was markedly higher in the mature forest than in the other four forest types. Mortality of woody parts became higher with forest age and was 20, 5.0 and 0.46% yr^?1 for small, medium and large parts, respectively, at the mature stage. Aboveground net production of the forest was in therange 7.6-13.3 ton ha^?1 yr^?1 with the undergrowth vegetation lower than 1.3 m being 0.4-1.4 ton ha^?1 yr^?1. Production recovered rapidly at an early stage of regeneration and was highest in mature forest.     

Biomass duration in growth models

To gain a better understanding of growth curve, biomass duration in several growth models, such as the exponential, linear, Gompertz, Mitscherlich, logistic, Richards and Bertalanffy, is formulated. Generally, biomass duration in these models can be given in two ways; thet- andw-representations. The latter representation, which can be defined as the summed value of reciprocal of relative growth rate with respect to biomass, gives a new significance to biomass duration. The utility of both representations is exemplified by the observed data of a fir. The idea of biomass duration is extended to get total amounts of anabolism and catabolism in the Bertalanffy model.     

Voltage dependence of theChara proton pump revealed by current-voltage measurement during rapid metabolic blockade with cyanide

Summary It is generally agreed that solute transport across theChara plasma membrane is energized by a proton electrochemical gradient maintained by an H⁺-extruding ATPase. Nonetheless, as deduced from steady-state current-voltage (I-V) measurements, the kinetic and thermodynamic constraints on H⁺-ATPase function remain in dispute. Uncertainties necessarily surround long-term effects of the relatively nonspecific antagonists used in the past; but a second, and potentially more serious problem has sprung from the custom of subtracting, across the voltage spectrum, currents recorded following pump inhibition from currents measured in the control. This practice must fail to yield the trueI-V profile for the pump when treatments alter the thermodynamic pressure on transport.We have reviewed these issues, using rapid metabolic blockade with cyanide and fitting the resultant whole-cellI-V and difference-current-voltage (dI-V) relations to a reaction kinetic model for the pump and parallel, ensemble leak. Measurements were carried out after blocking excitation with LaCl₃, so that steady-state currents could be recorded under voltage clamp between –400 and +100 mV. Exposures to 1mm NaCN (CN) and 0.4mm salicylhydroxamic acid (SHAM) depolarized (positive-going)Chara membrane potentials by 44–112 mV with a mean half time of 5.4±0.8 sec (n=13). ATP contents, which were followed in parallel experiments, decayed coincidently with a mean half time of 5.3±0.9 sec ([ATP] _t=0, 0.74±0.3mm; [ATP] _t=x , 0.23±0.02mm). Current-voltage response to metabolic blockade was described quantitatively in context of these changes in ATP content and the consequent reduction in pump turnover rate accompanied by variable declines in ensemble leak conductance. Analyses ofdI-V curves (±CN+SHAM) as well as of families ofI-V curves taken at times during CN+SHAM exposures indicated a stoichiometry for the pump of one charge (H⁺) transported per ATP hydrolyzed and an equilibrium potential near –420 mV at neutral external pH; under these conditions, the pump accounted for approximately 60–75% of the total membrane conductance nearV _m. Complementary results were obtained also in fitting previously publishedI-V data gathered over the external pH range 4.5–7.5 Kinetic features deduced for the pump were dominated by a slow step preceding H⁺ unloading outside, and by recycling and loading steps on the inside which were in rapid equilibrium. These characteristics predict, in marked contrast to the situation forNeurospora, that cytoplasmic acid loads inChara should shift the pumpI-V curve negative-going along the voltage axis with little change in maximum current output at positive voltages.     

Inhibition of hexose transport in the human erythrocyte by 5, 5′-dithiobis(2-nitrobenzoic acid): Role of an exofacial carrier sulfhydryl group

Summary The sulfhydryl reagent 5, 5-dithiobis (2-nitrobenzoic acid) (DTNB) was used to study the functional role of an exofacial sulfhydryl group on the human erythrocyte hexose carrier. Above 1mm DTNB rapidly inhibited erythrocyte 3-O-methylglucose influx, but only to about half of control rates. Efflux was also inhibited, but to a lesser extent. Uptake inhibition was completely reversed by incubation and washing with 10mm cysteine, whereas it was only partially reduced by washing in buffer alone, suggesting both covalent and noncovalent interactions. The covalent thiol-reversible reaction of DTNB occurred on the exofacial carrier, since (i) penetration of DTNB into cells was minimal, (ii) blockade of potential uptake via the anion transporter did not affect DTNB-induced hexose transport inhibition, and (iii) DTNB protected from transport inhibition by the impermeant sulfhydryl reagent glutathione-maleimide-I. Maltose at 120mm accelerated the covalent transport inhibition induced by DTNB, whereas 6.5 m cytochalasin B had the opposite effect, indicating under the one-site carrier model that the reactive sulfhydryl is on the outward-facing carrier but not in the substrate-binding site. In contrast to glutathione-maleimide-I, however, DTNB did not restrict the ability of the carrier to reorient inwardly, since it did not affect equilibrium cytochalasin B binding. Thus, carrier conformation determines exposure of the exofacial carrier sulfydryl, but reaction of this group may not always lock the carrier in an outward-facing conformation.     

Current-voltage relationships of a sodium-sensitive potassium channel in the tonoplast ofChara corallina

Summary The membrane of mechanically prepared vesicles ofChara corallina has been investigated by patch-clamp techniques. This membrane consists of tonoplast as demonstrated by the measurement of ATP-driven currents directed into the vesicles as well as by the ATP-dependent accumulation of neutral red. Addition of 1mm ATP to the bath medium induced a membrane current of about 3.2 mA·m^–2 creating a voltage across the tonoplast of about –7 mV (cytoplasmic side negative). On excised tonoplast patches, currents through single K⁺-selective channels have been investigated under various ionic conditions. The open-channel currents saturate at large voltage displacements from the equilibrium voltage for K⁺ with limiting currents of about +15 and –30 pA, respectively, as measured in symmetric 250mm KCl solutions. The channel is virtually impermeable to Na⁺ and Cl^–. However, addition of Na⁺ decreases the K⁺ currents. TheI–V relationships of the open channel as measured at various K⁺ concentrations with or without Na⁺ added are described by a 6-state model, the 12 parameters of which are determined to fit the experimental data.     

Plant competition for light analyzed with a multispecies canopy model

Summary Competition for light among species in a mixed canopy can be assessed quantitatively by a simulation model which evaluates the importance of different morphological and photosynthetic characteristics of each species. A model was developed that simulates how the foliage of all species attenuate radiation in the canopy and how much radiation is received by foliage of each species. The model can account for different kinds of foliage (leaf blades, stems, etc.) for each species. The photosynthesis and transpiration for sunlit and shaded foliage of each species is also computed for different layers in the canopy. The model is an extension of previously described single-species canopy photosynthesis simulation models. Model predictions of the fraction of foliage sunlit and interception of light by sunlit and shaded foliage for monoculture and mixed canopies of wheat (Triticum aestivum) and wild oat (Avena fatua) in the field compared very well with measured values. The model was used to calculate light interception and canopy photosynthesis for both species of wheat/wild oat mixtures grown under normal solar and enhanced ultraviolet-B (290–320 nm) radiation (UV-B) in a glasshouse experiment with no root competition. In these experiments, measurements showed that the mixtures receiving enhanced UV-B radiation had a greater proportion of the total foliage area composed of wheat compared to mixtures in the control treatments. The difference in species foliage area and its position in the canopy resulted in a calculated increase in the portion of total canopy radiation interception and photosynthesis by wheat. This, in turn, is consistent with greater canopy biomass of wheat reported in canopies irradiated with supplemental UV-B.     

Evaluation of two unstructured mathematical models for the penicillin G fedbatch fermentation

The mathematical model for the penicillin G fed-batch fermentation proposed by Heijnen et al. (1979) is compared with the model of Bajpai & Reuß (1980). Although the general structure of these models is similar, the difference in metabolic assumptions and specific growth and production kinetics results in a completely different behaviour towards product optimization. A detailed analysis of both models reveals some physical and biochemical shortcomings. It is shown that it is impossible to make a reliable estimation of the model parameters, only using experimental data of simple constant glucose feed rate fermentations with low initial substrate amount. However, it is demonstrated that some model parameters might be key factors in concluding whether or not altering the substrate feeding strategy has an important influence on the final amount of product.It is illustrated that feeding strategy optimization studies can be a tool in designing experiments for parameter estimation purposes.     

叶片叶肉结构对环境光强的适应及对光合作用的影响

本文利用Kubelka-Munk理论描述了平行光在叶片内的吸收和散射,同时利用叶片分层光合作用非直角双曲线光反应模型,给出了整张叶片光合作用计算式。最后利用优化理论阐明了叶片叶肉分化成光合特性具有明显差异的栅栏组织和海绵组织可能是对叶片内光梯度的一种适应;同时证明了叶片叶肉在一定环境光强下存在一个最佳的栅栏组织和海绵组织比例,并且这个比例随环境光强增大而增大,这最佳比例也受叶肉组织光合特性差异的影响。     

应用一元线性模型理论确定立地条件主导因子——朝阳低山丘陵区农田防护林立地条件类型的划分

本文用一元线性模型理论分析了辽宁西部朝阳、建平、喀左和北票(市)4县17个乡范围内的农田防护林主要树种——杨树(Populus spp.)、白榆(Ulumus pumila)的优势高与地形地貌、土壤肥力等立地条件因子的关系,确定地貌类型、坡位和土层厚度是本区农田防护林立地条件的主导因子,然后以地貌类型为单元将本区农田防护林的立地条件划分为3个大类型。在此基础上,再用坡位和土层厚度分级与3个大类型组合细分为6个基本类型。最后确定各立地条件类型的适宜树种,并定量地评价主要树种对各立地条件类型的适宜性。