Preparative and analytical size-exclusion chromatography of chitosans

Two chitosan samples (fraction of acetylated units (F_A) 0.15 and 0.52) were fractionated by preparative size exclusion chromatography (SEC). The molecular weights and molecular weight distributions of the fractions were analyzed by analytical size exclusion chromatography coupled to an on-line low angle laser light scattering detector and a differential refractive index detector (SEC-LALLS-DRI), and their intrinsic viscosities were determined. The exponent (a) of the Mark-Houwink-Kuhn-Sakurada (MHKS) equation was found to be 0.92 ± 0.07 and 1.1 ± 0.1, respectively, at I = 0.1 and pH 4.5. No variation in F_A related to molecular weight was found. Reversible interaction between chitosans and different column packings strongly influenced the log M-V relationships. This interaction was generally most pronounced for the low-F_A chitosan, suggesting that the protonated amino groups are involved. Ammonium acetate buffer reduced this effect and the use of a new type of SEC-packing seemed to eliminate it. The more highly acetylated chitosan also had a more pronounced tendency towards concentration dependent self-association, which most probably involve intermolecular hydrophobic interactions between the acetyl groups.     

On the stiffness of chitosan hydrochloride in acid-free aqueous solutions

Chitosan hydrochlorides (F_A=0.226, i.e. DA=22.6%) were randomly degraded by ultrasonication and characterized by viscosity measurements in aqueous acid-free solutions. It is shown that acid-free aqueous solutions of chitosan hydrochloride of variable ionic strengths (0.06 M≤μ≤0.3 M) are free of aggregation as evaluated by the values of the Huggins constants (0.31≤k≤0.63). These solutions were employed to study the solution properties of chitosan hydrochloride at different ionic strengths, which allowed the determination of its salt tolerance as well as its characteristic stiffness parameter. Following Smidsrod's approach chitosan hydrochloride gave a stiffness parameter B=0.06, in agreement with the value reported by Rinaudo et al. It is suggested that the higher values of B reported for chitosan in the literature may be attributed to aggregation.     

Degradation of fully water-soluble, partially N-acetylated chitosans with lysozyme

Chitosans, prepared by homogeneous N-deacetylation of chitin, with degrees of N-acetylation ranging from 4 to 60% (F_A = 0·04 to 0·60) exhibiting full water solubility and known random distribution of acetyl groups, were degraded with lysozyme. Initial degradation rates (r) were determined from plots of the viscosity decrease (Δ1/[η]) against time of degradation. The time course of degradation of chitosans with lysozyme were non-linear, while the time course of degradation of chitosans with an oxidative-reductive depolymerization reaction (using H₂O₂) showed the expected linear relationship for a first-order, random depolymerization reaction, independent of the chemical composition of the chitosan.

The effect of lysozyme concentration and substrate concentration on the initial degradation rates were determined, showing that this lysozyme-chitosan system obeys Michaelis-Menten kinetics.

The initial degradation rates of chitosan with lysozyme increased strongly with increasing fraction of acetylated units (F_A). From a Michaelis-Menten analysis of the degradation data that assumes different catalytic activities of lysozyme for the different hexameric substrates in the polysaccharide chain, it is concluded that the hexameric substrates that contain three-four or more acetylated units contribute mostly to the initial degradation rate when lysozyme degrades partially N-acetylated chitosans.

A chitosan with a very low fraction of acetylated units (F_A = 0·010) was studied as an enzyme inhibitor. Initial degradation rates of chitosan (with different F_A values) decreased as the inhibitor concentration increased, while the relative rates stayed constant, indicating that the ratio between initial reaction rates for productive sites (hexamers containing three-four or more N-acetylated units) are unaffected by non-productive sites, as deduced from the theory of competing substrates.     

Effect of ultrasonic treatment on the biochemphysical properties of chitosan

Four chitosans with different molecular weights and degrees of deacetylation degree and 28 chitosans derived from these initial chitosans by ultrasonic degradation have been characterized by gel permeation chromatography (GPC), FT-IR spectroscopy, X-ray diffraction and titrimetric analyses. Antimicrobial activities were investigated against E. coli and S. aureus using an inhibitory rate technique. The results showed that ultrasonic treatment decreased the molecular weight of chitosan, and that chitosan with higher molecular weight and higher DD was more easily degraded. The polydispersity decreased with ultrasonic treatment time, which was in linear relationship with the decrease of molecular weight. Ultrasonic degradation changed the DD of initial chitosan with a lower DD (<90%), but not the DD of the initials chitosan with a higher DD (>90%). The increased crystallinity of ultrasonically treated chitosan indicated that ultrasonic treatment changed the physical structure of chitosan, mainly due to the decrease of molecular weight. Ultrasonic treatment enhanced the antimicrobial activity of chitosan, mainly due to the decrease of molecular weight.     

Preparation and anticoagulant activity of a low-molecular-weight sulfated chitosan

Synthesis of chitosan sulfates with low molecular weight (M_v 9000–35,000 Da) was carried out by sulfation of low molecular weight chitosan (M_v 10,000–50,000 Da). The oleum was used as sulfating agent and dimethylfornamide as medium. The chitosans were prepared by enzymatic and acidic hydrolysis of initial high molecular weight chitosan as well as by extrusion solid-state deacetylation of chitin. As was shown by FT-IR and NMR-methods and elemental analysis, the sulfation occurred at C-6 and C-3 positions and substitution degree is 1.10–1.63. The molecular weight sulfated chitosan was determined by viscometric method and the Mark–Houwink equation [η]=10⁻⁵ 4.97 M^0.77. Study of anticoagulant activity showed that chitosan sulfates with lowered molecular weight demonstrated a regular increase of anti-Xa activity like heparins.     

Precise derivatization of structurally distinct chitosans with rhodamine B isothiocyanate

Work to date shows that structurally distinct chitosans have reacted inefficiently and unpredictably with fluorescein isothiocyanate (FITC) in an acid–methanol solvent that maintains both chitosan and fluorophore solubility. Since isothiocyanate preferentially reacts with neutral amine groups, and chitosan solubility typically depends upon a minimal degree of protonation, we tested the hypothesis that precise derivatization of chitosan with rhodamine isothiocyanate (RITC) can be achieved by controlling the reaction time and the degree of protonation. Addition of 50% v/v methanol reduced the chitosan degree of protonation in acetic acid but not HCl solutions. At various degrees of protonation, chitosan reacted inefficiently with RITC as previously observed with FITC. Nevertheless, precise derivatization was achieved by allowing the reaction to proceed overnight at a given degree of protonation (p < 0.0001, n = 18) and fixed initial fluorophore concentration. A reproducible 2% to 4% fraction of neutral amines reacted with RITC in proportion to the initial fluorophore concentration (p < 0.005). Using our optimized protocol, chitosans with different degree of deacetylation and molecular weight were derivatized to either 1% or 0.5% mol/mol RITC/chitosan-monomer with a precision of 0.1% mol/mol. The average molecular weight of fluorescent RITC-chitosan was similar to the unlabeled parent chitosan. Precise molar derivatization of structurally distinct chitosans with RITC can be achieved by controlling chitosan degree of protonation, initial fluorophore concentration, and reaction time.     

Anisotropy of photosynthetic membranes and the degree of fluorescence polarization

The degree of fluoresence polarization, P, of unoriented and magnetically oriented spinach chloroplasts as a function of excitation (400–680 nm) and emission wavelengths (675–750 nm) is reported. For unoriented chloroplasts P can be divided into two contributions, P_IN and P_AN. The latter arises from the optical anisotropy of the membranes which is due to the orientation with respect to the membrane plane of pigment molecules in vivo. The intrinsic polarization P_IN, which reflects the energy transfer between different pigment molecules and their degree of mutual orientation, can be measured unambiguously only if (1) oriented membranes are used and the fluorescence is viewed along a direction normal to the membrane planes, and (2) the excitation is confined to the Q_y (≈ 660−680 nm) absorption band of chlorophyll in vivo. With 670–680 nm excitation, values of P using unoriented chloroplasts can be as high as +14%, mostly reflecting the orientational anisotropy of the pigments. Using oriented chloroplasts, P_IN is shown to be +5±1%. The excitation wavelength dependence studies of P_IN indicate that the carotenoid and chlorophyll Q_y transition moments tend to be partially oriented with respect to each other on a local level (within a given photosynthetic unit or its immediate neighbors).     

The preparation of low-molecular-weight chitosan using chitinolytic complex from Streptomyces kurssanovii

Streptomyces kurssanovii are Gram-positive mycelial bacteria ubiquitous in soil. They have a saprophytic way of life and produce many extracellular enzymes with polymer-degrading properties, for example, chitinase (EC 3.2.1.14) and N-acetyl-β- -glucosaminidase (EC3.2.1.30). Biochemical aspects of chitosan degradation were presented. Low-molecular-weight (LMW) chitosans with molecular weight 4–8 kDa were prepared from commercial crab chitosan by means of chitinolytic a complex from S. kurssanovii. The optimum conditions of process in solution (temperature, pH, enzyme-substrate ratio) have been determined. Yields of LMW chitosan were 70–80%.     

N-Deacetylation and depolymerization reactions of chitin/chitosan: Influence of the source of chitin

The deacetylation and depolymerization reactions of chitin/chitosan from three crustacean species (Paralomis granulosa, Lithodes antarcticus and Palinurus vulgaris) were evaluated under the same conditions. The average molecular weight and the mole fraction of N-acetylated units were the parameters studied in the resulting chitosans. During the N-deacetylation process P. granulosa, L. antarcticus and P. vulgaris follow a pseudo-first order kinetics and their apparent rate constants are very similar. However, the degradation rate of chitosan in the first 45 min of this process is higher for P. vulgaris. The depolymerization process follows a pseudo-first order kinetics for the three species, but in the first 9 min P. vulgaris shows a slightly lower depolymerization rate. Hence, depending on the ash contents, crystallinity and the physicochemical characteristics of chitin from these sources, the obtained chitosans show different qualities.     

Binding of ions to chitosan—selectivity studies

Selectivity coefficients for binding of negative and positive ions to chitosans of different chemical composition have been determined by equilibrium dialysis. Chitosans with different fraction of acetylated units (F_A of 0.01 and 0.49) generally behaved similarly in their selectivity towards both negative and positive ions. No selectivity was found in the binding of chloride and nitrate ions, while chitosan showed a strong selectivity towards molybdate polyoxyanions, with selectivity coefficients around 100. Chitosan showed a strong selectivity towards copper (Cu²⁺) compared to the metal ions zinc (Zn²⁺), cadmium (Cd²⁺) and nickel (Ni²⁺), with selectivity coefficients from 10 to 1000, while little or no selectivity could be detected with the other metal ions. Ionic strength and pH did not influence the selectivity coefficients of the chitosans towards the metal ions.     

苯酚废水对垂柳叶片光合生理参数的影响

为探讨垂柳(Salix babylonica)对苯酚污染物的耐受程度及其应用于苯酚污染环境修复的可行性,了解苯酚胁迫对垂柳光合作用生理过程的影响与限制机理,采用水培模拟胁迫实验方法,在5种苯酚溶液浓度(50、100、200、400和800mg·L–1)下,测定垂柳植株叶片光合气体交换及叶绿素荧光参数。结果表明,苯酚对垂柳光合作用具有显著的抑制作用,表现为叶片净光合速率(Pn)、最大光合速率(Pnmax)、光合量子效率(Φ)、PSII最大和实际光化学效率(Fv/Fm和ФPSII)等均明显下降。苯酚胁迫浓度越高,对垂柳光合作用的抑制程度越大;苯酚胁迫限制光合作用主要由非气孔因素引起。将垂柳用于苯酚污染的水体环境修复时,苯酚浓度应在200 mg·L–1以下,否则垂柳的光合作用效能会明显降低。垂柳光合作用生理活性耐受苯酚胁迫的极限浓度还需进一步实验研究。     

紫胶林中蚂蚁-紫胶虫互利关系和寄主植物多样性对节肢动物各营养级的影响

【目的】昆虫之间的互利关系和植物多样性在生态系统中具有重要的作用,本研究旨在探讨蚂蚁-紫胶虫互利关系的下行效应以及寄主植物多样性的上行效应对节肢动物群落各营养级的影响。【方法】试验样地位于云南省普洱市墨江县雅邑乡的人工紫胶林中。通过随机裂区试验方法,于2016年8月和9月分两次用手捡法、网扫法和震落法采集了蚂蚁-紫胶虫3种互利关系处理(有互利关系、无互利关系和自然对照)以及3种植物多样性处理(单一种植、2树种混植和3树种混植,分别代表植物多样性1, 2和3)下样地寄主植物上所有的节肢动物,并按照不同营养级将其分类。【结果】蚂蚁-紫胶虫互利关系会显著降低消费者多度［有互利关系(14.2±0.95)<自然对照(18.57±1.13)<无互利关系(23.27±1.38), (F=4.290, P=0.017)］,植物多样性会显著提高消费者多度［植物多样性1(13.49±2.54)<植物多样性2(16.31±2.50)<植物多样性3(25.01±2.47), (F=56.03, P<0.001)］;在两者的交互作用下,无论哪个植物多样性水平上,有互利关系处理的消费者多度都显著低于无互利关系处理的消费者多度 (F=6.850, P<0.001)。互利关系对捕食者多度无显著影响(F=1.277, P=0.284),植物多样性会显著增加捕食者多度［植物多样性1 (1.72±0.49) <植物多样性2 (3.42±0.54) <植物多样性3 (3.59±0.55), (F=10.976, P<0.001)］,两者的交互作用对捕食者多度无显著影响(F=0.428, P=0.788)。互利关系和植物多样性会显著增加蚂蚁多度［自然对照(44.08±8.94) <有互利关系(324.82±65.35), (F=48.9, P<0.001)］, ［植物多样性1(86.31±12.51)<植物多样性3 (131.20±18.80) <植物多样性2(151.27±21.68), (F=137.85, P<0.001)］, 两者的交互作用也会显著增加蚂蚁多度(F=80.31, P<0.001)。【结论】蚂蚁与紫胶虫的互利关系显著降低植物上的植食性害虫,对捕食者不产生显著作用,但显著提高蚂蚁多度;而植物多样性对节肢动物各营养级都有积极作用;两者会产生一定的联合作用,对各营养级产生不同的影响。     

Calculation of vertical ground reaction force estimates during running from positional data

The purpose of this study was to calculate, as a function of time, segmental contributions to the vertical ground reaction force F_z from positional data for the landing phase in running. In order to evaluate the accuracy of the method, time histories of the sum of the segmental contributions were compared to F_z(t) measured directly by a force plate.

The human body was modeled as a system of seven rigid segments. During running the positions of markers defining these segments were monitored using a video analysis system operating at 200 Hz. Special care was taken to minimize marker movement relative to the mass centers of segments, and low-pass cutoff frequencies of 50 Hz (markers defining leg segments) and 15–20 Hz (markers defining upper body) were used in filtering the position time histories so as to ensure that high signal frequencies were preserved. The magnitude of the high-frequency peak in F_z, also known as ‘impact force peak’, was estimated with errors <10%, while the time of occurrence of the peak was estimated with errors <5 ms. It would appear that the positional data were sufficiently accurate to be used for calculation of intersegmental forces and moments during the landing phase in running.

Analysis of the segmental contributions to F_z(t) revealed that the first peak in F_z has its origin in the contribution of support leg segments, while its magnitude is determined primarily by the contribution of the rest of the body. These contributions could be varied independently by changing running style. It follows that if the possible relationship between ‘impact force peaks’ and injuries is to be investigated, or if the effects of running shoe and surface construction on these force peaks are to be evaluated, the calculation of segmental contributions to F_z(t) is a more suitable approach than measuring only F_z(t).     

Endothelial nitric oxide synthase gene haplotypes and circulating nitric oxide levels significantly associate with risk of essential hypertension

Nitric oxide (NO), a potent vasodilator, plays a pivotal role in blood pressure regulation. Endothelial NO synthase gene (NOS3) polymorphisms influence NO levels. Here, we investigated the role of the – 922A/G, – 786T/C, 4b/4a, and 894G/T polymorphisms of the NOS3 and NO_x levels in 800 consecutive unrelated subjects comprising 455 patients of essential hypertension and 345 controls. The polymorphisms were investigated independently and as haplotypes. Plasma NO_x levels (nitrate and nitrite) were estimated by the Griess method. Genotype frequencies for the –786T/C, 4b/4a, and 894G/T polymorphisms differed significantly (P < 0.001) between patients and controls and were associated with an increased risk of hypertension (OR = 2.0, OR = 3.8, OR = 1.6, respectively). The 4-locus haplotypes ATaG (H1), ATaT (H2), and GCaG (H3) were significantly associated with essential hypertension and served as susceptible haplotypes (P ≤ 0.0001). On the other hand, haplotypes ATbG (H4) and GTbG (H5) were negatively associated with hypertension and served as protective haplotypes (P < 0.0001). NO_x levels were significantly lower in patients than controls (P < 0.0001). The individual polymorphisms showed marginal association with NO_x level; however, the susceptible haplotype H2 associated significantly with lower NO_x levels in patients (P < 0.001) and conversely the haplotype H4 with higher NO_x levels in controls (P < 0.001). In conclusion, the 4b/4a and likely – 786T/C polymorphisms were identified as the determinants modifying the risk of hypertension. This study identifies the NOS3 variants and haplotypes as genetic risk factors and as useful markers of increased susceptibility to the risk of essential hypertension.     

苗期干旱及复水条件下不同花生品种的光合特性

为探索不同花生(Arachis hypogaea)品种的旱后恢复能力, 研究花生品种耐旱性与光合特性的关系, 通过盆栽土壤水分控制实验, 测定了12个花生品种苗期对干旱胁迫与复水过程的光合响应特征, 并讨论了所测各性状参数与抗旱性强弱的关系, 包括对水分胁迫伤害的修复能力。结果表明, 根据苗期生物量抗旱系数, ‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’、‘农大818’的抗旱性较强, 且复水后植株产生超补偿生长效应, 补偿生长能力与抗旱性呈极显著正相关。叶片净光合速率(P_n)、气孔导度(G_s)、胞间CO₂浓度(C_i)、最大光化学效率(F_v/F_m)、实际光化学效率(Φ_PSII)、光化学猝灭系数(q_P)随干旱进程逐渐降低, 复水后逐渐增加, 抗旱性强的花生品种变幅较小。干旱7天, 大多数花生品种的光合参数值未有显著性差异。干旱14天, 抗旱性越强的花生品种光合参数值越高, 不同抗旱性花生品种的光合参数值有显著差异。‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’的P_n、G_s、Φ_PSII、F_v/F_m、q_P在复水5天时恢复至对照水平, 复水10天时超过对照, ‘79266’、‘ICG6848’、 ‘白沙1016’、‘花17’在复水10天时仍未达到对照水平, 复水过程中抗旱性强的品种的光合参数显著高于抗旱性弱的品种。相关分析表明, 干旱胁迫14天和复水5天后, 花生的P_n、Φ_PSII、F_v/F_m、q_P与品种抗旱性呈极显著正相关。因此, 可在苗期用40%土壤相对含水量胁迫14天及复水5天时花生的P_n、Φ_PSII、F_v/F_m、q_P鉴定品种的干旱伤害程度及修复能力, ‘山花11号’可作为强干旱适应性鉴定的标准品种。     

超声波对铜绿微囊藻与蛋白核小球藻生理特征及竞争生长的影响

铜绿微囊藻是常见的水华蓝藻,常常在湖泊中与蛋白核小球藻共存或竞争生长。超声波可用于藻华即时治理,能够降低藻类生理活性,影响藻类生长,还可能改变藻类种间竞争关系。为了探究超声胁迫(35 kHz,0.035 W·cm^-3)对铜绿微囊藻与蛋白核小球藻的生理特征及种间竞争的影响,本研究设置纯藻组和1:1混合组(细胞浓度比)进行试验。结果表明: 铜绿微囊藻对超声胁迫更加敏感。超声处理600 s后,铜绿微囊藻的光合活性(F_v/F_m)和酯酶活性存在显著变化,纯藻组和混合组的F_v/F_m分别降低了51.8%和64.7%。而各组中蛋白核小球藻的光合活性变化较小。同时,铜绿微囊藻释放的荧光溶解性有机物(类色氨酸、类酪氨酸、类富里酸物质)含量多于蛋白核小球藻。两种藻的细胞浓度对超声波的响应也不同,蛋白核小球藻变化较小,而铜绿微囊藻的细胞浓度出现不同程度的下降。尤其是600 s超声处理大幅降低了混合组中铜绿微囊藻的细胞浓度(-42.6%),在超声胁迫解除后的8 d内蛋白核小球藻占优势,种间关系由铜绿微囊藻单边抑制蛋白核小球藻转变为两者互相抑制。在超声处理后,铜绿微囊藻的活性能够逐渐恢复,为了提高控藻效果的持久性,建议在一周后再次进行超声处理。     

古田山国家级自然保护区白颈长尾雉的分布格局及其季节变化

为了解浙江省古田山国家级自然保护区内白颈长尾雉(Syrmaticus ellioti)的分布格局和季节变化, 2014年5月至2016年4月, 我们对其进行了为期2年的网格化监测。共有44个公里网格拍摄到白颈长尾雉, 独立探测数量为211次, 雌雄性比为1 : 1.64。白颈长尾雉主要分布在实验区和缓冲区, 其探测率在常绿落叶阔叶混交林、杉木(Cunninghamia lanceolata)林、针阔叶混交林、人工油茶(Camellia oleifera)林和常绿阔叶林中依次递减, 主要分布在海拔600-800 m。冬、春两季, 白颈长尾雉活动强度和区域相对较小, 而夏、秋两季活动强度和区域相对增加, 其分布在海拔段(F_4,12 = 3.76, P < 0.05)和季节间(F_3,12 = 3.34, P < 0.05)都存在显著差异。对海拔和气候因子进行回归分析发现, 日平均气温和海拔对白颈长尾雉是否出现均有极显著影响(P < 0.01); 白颈长尾雉月探测率和探测到白颈长尾雉位点的海拔均与月平均气温呈极显著正相关(P < 0.001), 而与月平均降水量无显著线性关系(P > 0.05)。这表明白颈长尾雉的活动在很大程度上受海拔和气温影响, 随月平均气温的升高有向高海拔迁移的趋势。模型选择和多模型推断显示, 最优模型仅保留“100 m内水源”这一个变量, 次优模型是“100 m内水源 × 海拔”, 最优和次优模型的权重分别为0.18和0.14, “100 m内水源”和“海拔”是影响白颈长尾雉在保护区内分布的重要因子, 重要值分别为0.82和0.51。因此, 白颈长尾雉的分布并非仅由某一个或几个环境变量决定, 而是由多个环境变量共同决定。气温的变化和对不同海拔段的选择是导致白颈长尾雉形成不同季节分布格局的原因。     

Metal complexes of crosslinked chitosans Part II. An investigation of their hydrolysis to chitooligosaccharides using chitosanase

This paper investigates the behavior of crosslinked chitosans and metal-complexed crosslinked chitosans under similar hydrolytic conditions. Crosslinked chitosans with trimellitic anhydride, diisocyanatohexane, and dibromodecane as crosslinking agents under heterogenous reaction conditions were used as metal complexing agents by equilibrating them with metal salts such as ZnCl₂, MnSO₄, CuSO₄, CdSO₄, Pb(NO₃)₂, and HgCl₂. Crosslinked chitosan without metal complexation had the same hydrolytic behavior as uncrosslinked chitosan. However, when the crosslinked chitosans were complexed with metals, their rates of hydrolysis and extent of hydrolysis were significantly reduced. Thus, while for chitosan about 840 μg/ml reducing sugar was produced in 4 h time, and 780 μg/ml was produced for diisocyanatohexane crosslinked chitosan, only 400 μg/ml and 320 μg/ml reducing sugars were produced for cadmium sulfate with crosslinked chitosan and diisocyanatohexane crosslinked chitosan, respectively. Similar results are obtained for other crosslinking agents. Studies on preincubation of the metal with the enzyme show that of the metals studied, Mn has no effect on preincubatioin with the enzyme, Hg, Cd, Pb, and Cu completely deactivates the enzyme, while Zn reduces the enzyme activity by about 43.3%. Preincubation of the metal salts with the chitosan shows that Hg and Cu completely deactivate the molecule from enzyme hydrolysis, Cd and Zn inactivate it to the extent of 56.8% and 43.3%, respectively, while Mn has no effect. Availability of the amino functions seems to be a key feature for the chitosanase to hydrolyze the chitosan polymer. This was also proved by the significant increase in the extent of hydrolysis for chitosan samples with 88% (final value 1120 μg/ml reducing sugar) and 85% deacetylation (final value 840 μg/ml reducing sugar). HPIC studies of the products show that a variety of oligomers are produced in the chitosanase enzyme hydrolytic reaction.     

Variations and interrelationships of foliar hydraulic and photosynthetic traits for Larix gmelinii

Aims Variations and potential trade-offs of leaf hydraulic and photosynthetic traits are essential for assessing and predicting the effect of climate change on tree survival, growth and distribution. Our aims were to examine variations and interrelationships of leaf hydraulic and photosynthetic traits in response to changes in site conditions for Dahurian larch (Larix gmelinii)—a dominant tree species in Chinese boreal forests.Methods This study was conducted at the Maoershan Forest Ecosystem Research Station. A transect of 27 year-old Dahurian larch plantation was established that consisted of five plots extending from the valley to the ridge of a slope. The predawn leaf water potential (Ψ_pre), area- and mass-based leaf hydraulic conductance (K_area and K_mass, respectively), resistance to embolism capacity (P₅₀), leaf mass per area (LMA), net photosynthetic rate (A), and leaf nitrogen content (N) were measured in August 2016.Important findings The Ψ_pre, K_area, K_mass, P₅₀, A, LMA, and N all varied significantly among the plots (p < 0.05), indicating significant intra-specific variations in these traits in response to the changes in site conditions. The P₅₀ was significantly (p < 0.05) correlated with Ψ_pre, K_area or K_mass, suggesting that a trade-off between hydraulic efficiency and safety exist within the species to some degree. There were significant (p < 0.05) pairwise correlations between A, LMA, and N. Nevertheless, there was no significant (p < 0.05) correlation between the measured photosynthetic traits and hydraulic traits. We concluded that the intra-specific variations and multiple interrelationships of the leaf hydraulic and photosynthetic traits for the larch reflect the plasticity of its leaf traits and strategies of its survival and growth as a result of its acclimation to diverse site conditions.     

On the ecological energetics of 0-group Carcinus maenas (L.) from a shallow sandy bottom in gullmar fjord, Sweden

0-group Carcinus maenas (L.) was investigated from June 1975 to September 1976 on a shallow sandy bottom at Kvarnbukten Bay, Gullmar Fjord (58° 15′N: 11°28′E), Sweden, at an average salinity of 25% and a range of monthly mean temperatures of −0.3 to 197. °C.

The new year-class settles from August to early September at a carapace breath of 2 to 3 mm and a calorific content of 32 cal. The distribution is restricted to clusters of the mussel Mytilus edulis L. Depth, type of substratum, and patches of the eel-grass Zostera marina L. are of no importance for their spatial distribution. There is no migration to deeper water in the autumn. The carapace breadth is ≈ 9.5 mm after one year of benthic life. Sexual maturity is reached after two years. Growth occurs at temperatures above 10 °C, i.e., from August to October and from May to July. During the first year of benthic life the animals moult 7 times. The 0-group seems to be micro-carnivores feeding on the sediment meiofauna.

The individual energy budget for the first year of benthic life is: consumption (C_c) 905 cal., production (P_1c) 236 cal., cast carapaces (P_2c) 153 cal., respiration (R_c) 404 cal., and rejectiction (F_c) 112 cal. The assimilation efficiency (U_c⁻¹) is 88%, the gross growth efficiency (K_1c) 43%, and the net growth efficiency (K_2c) 49%.

At Kvarnbukten Bay there are large variations in size between the separate year-classes. The energy content of the food consumed by the 1975/76 cohort was used as follows: 4% was stored in living biomass after one year, 36% was released to other trophic levels as dead animals and cast carapaces, 13% rejected as faeces, and 47% was lost through respiration.