Effect of molecular weight of condensed tannins from warm-season perennial legumes on ruminal methane production in vitro

The objectives of the present study were to determine if the molecular weight of condensed tannins (CT) from warm-season perennial legumes affects the biological activity of CT relative to suppression of methane (CH₄) production by ruminants, and to identify potential North American native forage plants to use for mitigation of enteric CH₄ emission. Eight North American native warm-season perennial legumes were evaluated: Leucaena retusa Benth. (littleleaf leadtree), Desmanthus illinoensis (Michx.) MacMill. Ex B.L. Rob. & Fernald (Illinois bundleflower), Lespedeza stuevei Nutt. (tall lespedeza), Mimosa strigillosa Torr. & A. Gray (powderpuff), Neptunia lutea (Leavenworth) Benth. (yellow puff), two ecotypes of Acacia angustissima var. hirta (Nutt.) B.L. Rob (prairie acacia), and Desmodium paniculatum (L.) DC. var. paniculatum (panicledleaf ticktrefoil). Two introduced legumes were also included: Arachis glabrata Benth. (rhizoma peanut) and Lespedeza cuneata (Dum. Cours.) G. Don (sericea lespedeza). Forages were fermented with cattle rumen fluid for 48 h anaerobically using an in vitro gas production technique. D. paniculatum, L. stuevei, and M. strigillosa were high in CT, ranging from 11.7 to 12.5%. D. illinoensis, L. cuneata, N. lutea, and two ecotypes of A. angustissima var. hirta had less CT (P < 0.05), ranging from 8.1 to 8.9%, whereas L. retusa and A. glabrata had the least CT (P < 0.05), measuring 3.2 and 0.5%, respectively. Weight-average molecular weight (M_W) of CT ranged from 1483 Da for L. cuneata to 552 Da for L. stuevei. In vitro CH₄ production was greatest for L. retusa and A. glabrata at 40.7 mg/g DM and 38.2 mg/g DM, respectively. The least amount of in vitro CH₄ was produced by fermentation of two ecotypes of A. angustissima var. hirta, which measured 0.8 and 0.6 mg/g DM, respectively. In vitro CH₄ production regressed on CT M_W resulted in a R² of 0.0009 (P = 0.80), strongly suggesting that CT M_W does not explain the biological activity of in vitro CH₄ production by the forage legumes surveyed. Five of the seven North American native warm-season perennial legumes have promise for use in ruminant diets for the purpose of CH₄ emission mitigation.     

Estimates of subtropical forest biomass based on airborne LiDAR and Landsat 8 OLI data

 快速、定量、精确地估算区域森林生物量一直是森林生态功能评价以及碳储量研究的重要问题。该研究基于机载激光雷达(LiDAR)点云与Landsat 8 OLI多光谱数据, 借助江苏省常熟市虞山地区55块调查样地数据, 首先提取并分析了87个特征变量(53个OLI特征变量, 34个LiDAR特征变量)与森林地上、地下生物量的Pearson’s相关系数以进行变量优选, 然后利用多元逐步回归法建立森林生物量估算模型(OLI生物量估算模型和LiDAR生物量估算模型), 并与基于两种数据建立的综合生物量估算模型的结果进行比较, 讨论预测结果及其精确性。结果表明: 3种模型(OLI模型、LiDAR模型和综合模型)在所有样地无区分分析时, 地上和地下生物量的估算精度均达到0.4以上, 基于不同森林类型(针叶林、阔叶林、混交林)分析时地上和地下生物量的估算精度均有明显提高, 达到0.67及以上。利用分森林类型模型估算生物量, 综合生物量估算模型精度(地上生物量: R²为0.88; 地下生物量: R²为0.92)优于OLI生物量估算模型(地上生物量: R²为0.73; 地下生物量: R²为0.81)和LiDAR生物量估算模型(地上生物量: R²为0.86; 地下生物量: R²为0.83)。     

Distribution and diffusion of alamethicin in a lecithin/water model membrane system

Summary Attenuated total reflection infrared spectroscopy has been used to determine the equilibrium distribution of the peptide antibiotic alamethicinR _F30 between dipalmitoyl phosphatidylcholine bilayers and the aqueous environment. The distribution coefficientK=c _eq ^W /c _eq ^M turned out to be concentration dependent, pointing to alamethicin association in the membrane with increasing concentration in the aqueous phase (c _eq ^W ). This concentration was varied within 28 and 310nm, i.e., in a range typical for black film experiments. Furthermore, diffusion coefficients of alamethicin in the hydrophobic phase of the membrane (D _M) and across the membrane/water interface (D _I) have been estimated from the time course of the equilibration process. It was found that the diffusion rate of the uncharged analogueR _F50 is about 10 times higher than that of theR _F30 component, exhibiting one negative charge at theC-terminus. The time constants for transmembrane diffusion of alamethicinR _F30 varied between 2.2 hr at low concentration and 3.2 hr at higher concentration. The corresponding low concentration value of theR _F50 component was found to be 0.25 hr.     

Life history traits of Aphanius ginaonis Holly, 1929 (Cyprinodontidae) and potential risks of extinction in the Geno hot spring (Iran) population

This study presents some traits of the Aphanius ginaonis life history in the Geno hot spring and explains the potential risks of its extinction. Sampling was from March 2009 to February 2010. A total of 61 males and 71 females were measured (total length) and weighed, with data on reproductive biometry also taken. Growth parameters were determined in addition to weight–length relationships: W (t) = 0.012TL^3.42, R² = 0.96 for females and W (t) = 0.0101TL^3.38, R² = 0.94 for males. A. ginaonis females showed an asymptotic total length (TL_∞) of 53.03 mm; the growth coefficient, K (year^?1) 0.15, t₀ (year) 1.01; and natural mortality coefficient M (year^?1) 0.62. In males the value for TL_∞ was 48.83 mm; for K (year^?1) 0.2, t₀ (year) 0.44; and M (year^?1) 0.49. The relationship between absolute fecundity and fish size (total length, body weight or age) showed a strong correlation to body weight. The A. ginaonis population is threatened with extinction – and a co‐management in cooperation with the local population for strong protection measures is urgently needed.     

Moisture adsorption capacity and surface area as deduced from vapour pressure isotherms in relation to hygroscopic water of soils

Six calcareous and alluvial soil profiles differing in their texture, CaCO₃ and salinity were chosen from west and middle Nile Delta for the present study. The 1^st and 2^nd profiles from Borg El-Arab area were sandy loam in texture and > 30% CaCO₃, while the 3^rd and 4^th profiles (from Nubaria area) were sandy clay loam and < 30% CaCO₃. The 2^nd and 4^th profiles were taken from cultivated area with maize. The 5^th profile from Epshan area was non-saline clay alluvial soil and the 6^th from El-Khamsen was saline clay alluvial soil. The relation between soil moisture content (W%) and water vapour pressure (P/P _o) was established for the mentioned soils. Data showed that the specific surface area (S) values were 34–53 and 44–60 m²/g for calcareous soils of Borg El-Arab and Nubaria areas, 206–219 and 206–249 m²/g for non-saline and saline clay alluvial soils of Epshan and El-Khamsen areas, respectively. The corresponding values of the external specific surface area (S _e) were 16–21, 14–22, 72–86 and 92–112 m²/g. Submitting W _m+W _me as an adsorption boundary of moisture films (W _c) (where W _m is mono-adsorbed layer of water vapour on soil particles and W _me is the external mono-adsorbed layer), the maximum water adsorption capacity (W _a) was found to be W _c + W _me or W _m + 2W _me. It was ranged from 1.88 to 2.70%, 1.97 to 2.95%, 9.70–10.70% and 10.80 to 13.12% while the maximum hygroscopic water (M _H) values were 2.43–3.78%, 2.91–4.65%, 16–17% and 18.30–21.9% for the studied soil profiles respectively. The residual moisture content (θ _r) at pF 7 and P/P _o = 0 was ranged from 0.0005–0.0010%, 0.0007–0.0019% and 0.0043–0.0048% in Borg El-Arab, Nubaria and Epshan soil profiles, respectively. The inter-relations between the surface area and the hygroscopic moisture parameters of the soils under investigation were as follows Calcareous soils; W _m = 0.40 M _H, W _c = 0.55 M _H, W _a = 0.70 M _H, S = 14 M _H Non-saline soil; W _m = 0.35 M _H, W _c = 0.49 M _H, W _a = 0.63 M _H, S = 13 M _H Saline soil; W _m = 031 M _H, W _c = 0.45 M _H, W _a = 0.59 M _H, S = 12 M _H These relations give possibility to deduce the soil moisture adsorption capacities and specific surface area via maximum hygroscopic water, which can be obtained through the experimental determination of water vapor adsorption isotherms.     

Functional and physical competition between phospholamban and its mutants provides insight into the molecular mechanism of gene therapy for heart failure

We have used functional co-reconstitution of purified sarcoplasmic reticulum (SR) Ca²⁺-ATPase (SERCA) with phospholamban (PLB), its inhibitor in the heart, to test the hypothesis that loss-of-function (LOF) PLB mutants (PLB_M) can compete with wild-type PLB (PLB_W) to relieve SERCA inhibition. Co-reconstitution at varying PLB-to-SERCA ratios was conducted using synthetic PLB_W, gain-of-function mutant I40A, or LOF mutants S16E (phosphorylation mimic) or L31A. Inhibitory potency was defined as the fractional increase in K_Ca, measured from the Ca²⁺-dependence of ATPase activity. At saturating PLB, the inhibitory potency of I40A was about three times that of PLB_W, while the potency of each of the LOF PLB_M was about one third that of PLB_W. However, there was no significant variation in the apparent SERCA affinity for these four PLB variants. When SERCA was co-reconstituted with mixtures of PLB_W and LOF PLB_M, inhibitory potency was reduced relative to that of PLB_W alone. Furthermore, FRET between donor-labeled SERCA and acceptor-labeled PLB_W was decreased by both (unlabeled) LOF PLB_M. These results show that LOF PLB_M can compete both physically and functionally with PLB_W, provide a rational explanation for the partial success of S16E-based gene therapy in animal models of heart failure, and establish a powerful platform for designing and testing more effective PLB_M targeted for gene therapy of heart failure in humans.     

Effect of carbon source and concentration on the molecular mass of poly(3-hydroxybutyrate) produced by Methylobacterium extorquens and Alcaligenes eutrophus

In shake-flask culture, Methylobacterium extorquens accumulated poly(3-hydroxybutyrate) (PHB) possessing a substantially higher weight-average molecular mass (M_W) than previously reported for this organism. The M_W of PHB produced by M. extorquens was dependent on the initial concentration of methanol or sodium succinate, used as sole carbon sources. The highest M_W values (0.6 and 1.7 × 10⁶) were obtained with low initial concentrations of methanol or sodium succinate (4.0 and 3.0 g l^–1, respectively) and the latter substrate always yielded PHB of higher M_W than that produced from methanol. Thus PHB with an M_W in the range 0.2–1.7 × 10⁶ could be produced by selection of the carbon source and its concentration. In contrast to the findings with M. extorquens, the M_W of PHB produced by Alcaligenes eutrophus was high (1.1–1.6 × 10⁶) and generally unaffected by the choice or concentration of the carbon source. The use of glycerol as sole carbon source did, however, result in the accumulation of PHB with a markedly lower M_W (5.5–8.5 × 10⁵) than that produced from other sole carbon sources by this organism under similar conditions. Correspondence to: A. J. Anderson     

The effects of feeding history and environment on condition,body composition and growth of bluegills Lepomis macrochirus

Initial relative mass (W_R, low v. high) and energetic trajectory in time (starved v. fed) were experimentally manipulated in bluegill Lepomis macrochirus. Fed fish starting at low W_R grew more and gained more W_R than fed fish starting at high W_R. Similarly, starved fish starting at high W_R lost more mass and W_R than did starved fish starting at low W_R. Temporal changes in other variables did not consistently match that of W_R, but, by the end of the experiment, proximate composition showed a high correlation to W_R. Regression slopes of W_R on proximate composition increased with time in the laboratory. Differences between wild and laboratory fish appeared to result from relaxation of environmental stress. When excess resources are available such that L. macrochirus grow, condition indices will increase, but individual response will depend on initial values and thus past environmental experience.     

Response of soil respiration to temperature and soil moisture: Effects of different vegetation types on a small scale in the eastern Loess Plateau of China

Soil respiration is affected by vegetation and environmental conditions. The purpose of this study was to investigate the effect of vegetation type on soil respiration, temperature and water content, and their correlations on a small scale. We measured soil respiration rate (R_s) over a 3-year period at biweekly intervals in three plots in the eastern Loess Plateau of China, with the same soil texture but different vegetation types: pine forest, grassland, and shrub land. Simultaneously, soil temperature (T_s) at 10 cm depth and soil water content (W_s) within 10 cm depth were measured. The seasonal course of R_s and T_s showed a similar temporal variation in the three plots, with higher values in summer and autumn and lower values in winter and spring. No significant differences (P>0.05) were found between plots, except for W_s. The mean cumulative release of CO₂ efflux from March to December was 962.5, 1027.5, and 1166.5 g C m^? 2 a^? 1 for plots 1, 2, and 3, respectively, with no significant difference between plots. The fitted exponential equations of R_s versus T_s from the 3-year data-set were significant (P < 0.05) with an R² of 0.72, 0.64, and 0.72 for plots 1, 2, and 3, respectively. The calculated Q₁₀ from the parameters of the fitted equation was 3.57, 3.52, and 3.61, and the R₁₀ was 2.36, 2.03, and 2.37 μmol CO₂ m^? 2 s^? 1 for plots 1, 2, and 3, respectively. Compared with the T_s, the correlations between R_s and W_s were not significant for the three plots. However, if the T_s was above 10°C, then their correlation was significant, and W_s had an impact on R_s. Four combined regression equations including two variables of T_s and W_s could be well established to model correlations between R_s and both T_s and W_s. Our study demonstrated that the exponential and power model fitted best and no significant different correlations of combined equations existed between the three plots. These results show that vegetation type had little impact on R_s, T_s, W_s, and their correlations, as well as on related parameters such as Q₁₀ and R₁₀. Therefore, while doing R_s research in a horizontal patchy vegetation conditions on a small area, the sampling location of measurements should focus on vertical dominant vegetation and ignore patch vegetation so as to reduce field work load.     

Conformation of mucous glycoproteins in aqueous solvents

Light-scattering techniques have been used to measure the z-average radius of gyration R_g z-average translational diffusion coefficient D_t and weight–average molecular weight M_w of porcine submaxillary mucin (PSM) in solution. PSM isolated at low shear in the presence of protease inhibitors has a M_w about twice as large as a sample prepared without these precautions. The former sample has a M_w of 17 × 10⁶ in 0.1M NaCl, which decreases to 8 × 10⁶ in 6M guanidine hydrochloride (GdnHCl) and then to 2 × 10⁶ on addition of 0.1M mercaptoethanol to the 6M GdnHCl solution. The R_g or D values obtained for PSM in this work superimpose with those of other authors for different mucin glycoproteins, leading to linear log–log relationships to the molecular weight of the protein core. Comparison of these results with those in the literature for denatured proteins suggest that mucins are linear random coils in which the protein core is stiffened by the presence of the oligosaccharide side chains. The length of the oligosaccharides and the nature of the solvent have little effect on the extension of the protein core. This suggests that the stiffness of the protein core is maintained by steric repulsion of the residues at the beginning of the oligosaccharide chains.     

Purification of Pseudomonas sp. proteases through aqueous biphasic systems as an alternative source to obtain bioactive protein hydrolysates

Aqueous biphasic systems (ABSs) are an interesting alternative for separating industrial enzymes due to easy scale-up and low operational cost. The proteases of Pseudomonas sp. M211 were purified through ABS platforms formed by polyethylene glycol (PEG) and citrate buffer salt. Two experimental designs 2³ + 4 were performed to evaluate the following parameters: molar mass of PEG (M_PEG), concentration of PEG (C_PEG), concentration of citrate buffer (C_Cit), and pH. The partition coefficient (K), activity yield (Y), and purification factor (PF) were the responses analyzed. The best purification performance was obtained with the system composed of M_PEG = 10,000 g/mol, C_PEG = 22 wt%, C_Cit = 12 wt%, pH = 8.0; the responses obtained were K = 4.9, Y = 84.5%, PF = 15.1, and tie-line length = 52.74%. The purified proteases of Pseudomonas sp. (PPP) were used to obtain hydrolysates of Lupinus mutabilis (Peruvian lupin cultivar) seed protein in comparison with the commercial protease Alcalase® 2.4L. A strong correlation between hydrolysis degree and radical scavenging activity was observed, and the highest antioxidant activity was obtained with Alcalase® (1.40 and 3.47 μmol Trolox equivalent/mg protein, for 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) and oxygen radical absorbance capacity, respectively) compared with PPP (0.55 and 1.03 μmol Trolox/mg protein). Nevertheless, the IC₅₀ values were lower than those often observed for antioxidant hydrolysates from plant proteins. PEG/citrate buffer system is valuable to purify Pseudomonas proteases from the fermented broth, and the purified protease could be promising to produce antioxidant protein hydrolysates.     

Expression,purification, and characterization of a novel acid phosphatase that displays protein tyrosine phosphatases activity from Metarhizium anisopliae strain CQMa102

The protein tyrosine phosphatase (PTPase) plays an important role in insect immune system. Our group has purified a type of acid phosphatase that could specifically dephosphorylate trans-Golgi p230 in vitro. In order to study this phosphatase further, we have identified and cloned the phosphatase gene from a locust specific Metarhizium anisopliae Strain CQMa102. The CQMa102 phosphatase was expressed in Pichia pastoris to verify its protease activity. The molecular weight (M_W) and the isoelectric point (pI) of the phosphatase were about 85 kDa and 6.15, respectively. Substrate specificity evaluation showed that the purified enzyme exhibited high activity on O-phospho-L-tyrosine. At its optimal pH of 6.5 and optimum temperature of 70 °C, the protein showed the highest activity respectively. It can be activated by Ca²⁺, Mg²⁺, Mn²⁺, Ba²⁺, Co²⁺ and phosphate analogs, but inhibited by Zn²⁺, Cu²⁺, fluoride, dithiothreitol, β-mercaptoethanol and N-ethylmaleimide.     

Differential interactions and structural stability of chitosan oligomers with human serum albumin and α-1-glycoprotein

Chitosan is a naturally occurring deacetylated derivative of chitin with versatile biological activities. Here, we studied the interaction of chitosan oligomers with low degree of polymerization such as chitosan monomer (CM), chitosan dimer (CD), and chitosan trimer (CT) with human serum albumin (HSA) a major blood carrier protein and α-1-glycoprotein (AGP). Since, HSA and AGP are the two important plasma proteins that determine the drug disposition and affect the fate of distribution of drugs. Fluorescence emission spectra indicated that CM, CD, and CT had binding constants of K_CM = 6.2 ± .01 × 10⁵ M^?1, K_CD = 5.0 ± .01 × 10⁴ M^?1, and K_CT = 1.6 ± .01 × 10⁶ M^?1_, respectively, suggesting strong binding with HSA. However, binding of chitooligomers with AGP was insignificant. Thermodynamic and molecular docking analysis indicated that hydrogen bonds and also hydrophobic interaction played an important role in stabilizing the HSA-chitooligomer complexes with free energies of ?7.87, ?6.35, and ?8.4?Kcal/mol for CM, CD, and CT, respectively. Further, circular dichroism studies indicated a minor unfolding of HSA secondary structure, upon interaction with chitooligomers, which are supported with fluctuations of root mean square deviation (RMSD) and radius of gyration (R_g) of HSA. Docking analysis revealed that all three chitooligomers were bound to HSA within subdomain IIA (Site I). In addition, RMSD and R_g analysis depicted that HSA-chitooligomer complexes stabilized at around 4.5 ns. These results suggest that HSA might serve as a carrier in delivering chitooligomers to target tissues than AGP which has pharmacological importance.     

Allometric relationship between body mass and aerobic metabolism in zebrafish Danio rerio

The relationship between body mass (M) and metabolic rate was investigated through the assessment of active (R_A) and standard (R_S) metabolic rate at different life stages in zebrafish Danio rerio (5 day‐old larvae, 2 month‐old juveniles and 6 month‐old adults). Scaling exponents and constants were assessed for standard (R_S = 0·273M^0·965 in mgO₂ g^?1 h^?1) and active metabolic rate (R_A = 0·799M^0·926 in mgO₂ g^?1 h^?1). These data provide the basis for further experiments regarding the effects of environmental factors on aerobic metabolism throughout the life cycle of this species.     

A novel enzymatic dehalogenation of (R)-3-chloro-1,2-propanediol inAlcaligenes sp. DS-S-7G

The mechanism of the novel enzymatic dehalogenating action of (R)-3-chloro-1,2-propanediol [monochlorohydrin (MCH)] was investigated. The (R)-MCH-dechlorinating enzyme system ofAlcaligenes sp. DS-S-7G, which stereoselectively assimilated (R)-MCH from the racemate, was composed of two components (Enzyme 1 and Enzyme 2). Enzyme 1 was a flavoprotein with a relative molecular mass (M _r) of 70,000 and was composed of two kinds of polypeptides (58,000 and 16,000). The enzyme exhibited activity for converting (R)-MCH to hydroxyacetone with the liberation of chloride ions under aerobic conditions. On the other hand, Enzyme 2 with anM _r of 86,000, which was also composed of two kinds of polypeptides (33,000 and 53,000), showed no dechlorinating activity for (R)-MCH. However, in the presence of NAD⁺, when Enzyme 1 was conjugated with Enzyme 2 in the (R)-MCH-dechlorinating reaction, the co-operative dechlorinating activity was four to five times higher than that by Enzyme 1 alone. (R)-MCH was finally degraded to acetic acid and formic acid by the joint action of the two enzymes. These facts indicate that (R)-MCH is oxidatively dechlorinated by the two enzymes in the presence of NAD⁺ inAlcaligenes sp. DS-S-7G.     

Flow properties of high-molecular-weight DNA solutions: viscosity, recoil, and longest retardation time

Viscosity η, recoil Γ, and longest retardation time τ_1R were measured for buffered aqueous solution of T2 DNA (M = 1.3 × 10⁸) and cell lysattes of Bacillus subtiles W23 (DNA M = 2 × 10⁹) as a function of concetration, shear stress σ, and time of shear t, using a cartesian-diver-suspended couette flow system. For the T2 solution, η decreased with increasing σ, Γ(t) going through a maximum with t. For the B. subtiles lysates, the preponderant rheological component of which is chromatin DNA, above a critical σ, the η, Γ(t), and τ_1R increased t over 15 to 45 minutes duration to values up to several times larger, indicating the formation of intermolecular aggregates. The onset of such effects and their significance in th e measurement of molecular properties by hydrodynamic means is disscussed.     

The effect of body size on food consumption, absorption efficiency, respiration, and ammonia excretion by the inland silverside, Menidia beryllina (Cope) (Osteichthyes: Atherinidae)

The inland silverside, Menidia beryllina (Cope), is an annual zooplanktivore that occurs in estuarine and freshwater habitats along the Atlantic and Gulf of Mexico coasts and drainages of the United States. Experiments were conducted at 25 ± 1°C to quantify the relationship between mean dry weight (W_D) and rates of energy gain from food consumption (C), and energy losses as a result of respiration (R) and ammonia excretion (E) during routine activity and feeding by groups of fish. The absorption efficiency of ingested food energy (A) was also quantified. Rates of C, E, and R increased with W_D by factors (b in the equation y = aW_D^b) equal to 0.462, 0.667, and 0.784, respectively. Mean (±SE) rates of energy loss during feeding were 1.6 ± 0.1 (R) and 3.4 ± 0.6 (E) times greater than those for unfed fish. Absorption efficiency was independent of W_D and estimated to be 89% of C. From these measurements, the surplus energy available for growth and activity (G) and growth efficiency (K₁) were estimated. Over the range in sizes of juveniles and adults (5–500 mg W_D), predicted G and K₁ values decreased from 7.42 to 0.20 J mg fish^?1 day^?1 and 63 to 21%, respectively. Measured and predicted bioenergetic parameters are discussed within an ecological context for a northern population of this species.     

红桦幼苗根系对水-氮耦合效应的生理响应

采用两因素随机区组设计,设置了5个水分梯度,即40%(W_1)、50%(W_2)、60%(W_3)、80%(W_4)、100%(W_5)的土壤田间持水量(FC)和3个施氮梯度,即模拟氮沉降施加0(对照,N_0)、20(N_1)、40(N_2)g N m~(-2)a~(-1)的硝酸铵,研究了水-氮耦合效应对川西亚高山主要阔叶树种红桦(Betula albosinensis)幼苗根系生理活性的影响及根系在土壤水、氮胁迫下的生理调控机制。结果表明:1)随土壤含水量降低,根系活力和根系呼吸速率显著降低,膜脂过氧化产物(丙二醛)、渗透调节物质(脯氨酸、可溶性蛋白质和可溶性糖)含量及抗氧化物酶(超氧化物歧化酶、过氧化物酶和过氧化氢酶)活性显著升高。2)水-氮耦合效应对红桦幼苗根系生理特征影响显著:施氮(N_1和N_2)在土壤水分良好(W_4和W_5)时使根系活力和根系呼吸速率显著升高,而在土壤水分不足(W_1和W_2)时显著降低了根系活力和根系呼吸速率;且在水分不足时,施氮浓度越大根系活力、MDA含量、脯氨酸及可溶性蛋白质含量变化越显著;在W_3条件下,只有N_1对根系生理功能促进作用显著。3)根系活力和根系呼吸速率与丙二醛含量呈显著负相关性。因此,一定范围内的氮沉降在土壤水分状况良好时对植物根系生理特征具有显著正效应,而在土壤水分不足时则使根系细胞膜系统受损,抑制根系生理活性,但根系可通过增加渗透调节物质含量和增强抗氧化物酶活性来抵御一定范围的环境胁迫。