Effects of nutrient level on thinning and non-thinning crowding in even-aged populations of subterranean clover

Populations of subterranean clover were used to examine the effect of lowering nutrient supply on crowding in even-aged monospecific populations. Two hypotheses were being tested. Under one, termed ‘altered-speed’, reducing the nutrient supply to populations merely slows down the crowding process. Under the other, called ‘altered-form’, reducing the nutrient supply intensifies the crowding process (Morris & Myerscough 1984). The populations were grown at eight densities of sowing and three levels of nutrient supply. Non-thinning yield-density curves and self-thinning lines were fitted to the data. For the thinning populations, reducing the nutrient supply led to altered-form crowding, with thinning lines of reduced slope and intercept for total and shoot weight being observed in populations grown at lower levels of nutrient supply. For the non-thinning yield-density curves, lowering the nutrient supply did alter crowding effects, but not to the extent necessary to give full altered-form crowding. Rather, crowding effects intermediate between altered-speed and altered-form were observed. No altered-speed crowding was observed in this experiment. Comparison was made between the altered-speed crowding observed in other data (Hozumi & Ueno 1954: White & Harper 1970) with the altered-form crowding observed here and elsewhere (Hozumi & Ueno 1954). In these data, altered-form crowding was consistently associated with an increase in the proportion of root in the plants' growth as nutrient level was reduced, while in altered-speed crowding there was a complete lack of any such nutrient effect on root-shoot proportion. This was taken as evidence that under altered-speed crowding, variations in the level of nutrient supply did not lead to major change in the way that plants interfered with each other. For altered-form crowding, major change in the way plants interfered with each other's growth did occur as nutrient level fell.     

Yield-density Relationships: the Influence of Resource Availability on Growth and Self-thinning in Populations of Vulpia fasciculata

Monocultures of Vulpia fasciculata were grown over a wide rangeof densities to investigate the influence of crowding and nutrientsupply on growth and self-thinning. For a given time and densityseries the relationship between mean yield per plant (w) andthe density of survivors (N) could be described by the equation w= w_m (1+aN)^–b. where w_m is the yield of an isolated plant, a is the area requiredto achieve a yield of w_m and b describes the effectiveness withwhich resources are taken up from the area. All three parametersincreased with time. Adding nutrients changed not only the rate at which the effectsof crowding occurred but also the intensity of crowding since w_m = C(a^b)^D. where C and D are constants. The addition of nutrients resultedin an increase in the value of C. Such an increase means thata larger weight can be supported by a given area because theresources within that area are greater. During the early phases of growth, populations of V. fasciculataconformed to the –3/2 power law, w = cN^–3/2, butonly at very high densities with a plentiful supply of nutrients.However, once the maximum standing crop had been reached thetrajectory of the thinning line switched to a slope of justless than –1 when weight was ploted against density onlogarithmic scales. The intercept of the –3/2 thinningline was considerably higher (log c = 5.74) than those for mosttrees and forbs but was similar to those of a number of othergrasses. Vulpia fasciculata, dune fescue, yield-density models, self-thinning, density-dependence, nutrient supply     

Unthinned slow-growing ponderosa pine (Pinus ponderosa) trees contain muted isotopic signals in tree rings as compared to thinned trees

Key message

The muted wood isotopic signal in slow-growing trees of unthinned stands indicates lower responsiveness to changing environmental conditions compared to fast-growing trees in thinned stands.

Abstract

To examine the physiological processes associated with higher growth rates after thinning, we analyzed the oxygen isotopic values in wood (δ¹⁸O_w) of 12 ponderosa pine (Pinus ponderosa) trees from control, moderately, and heavily thinned stands and compared them with wood-based estimates of carbon isotope discrimination (?¹³C), basal area increment (BAI), and gas exchange. We found that (heavy) thinning led to shifts and increased inter-annual variability of both stable carbon and oxygen isotope ratios relative to the control throughout the first post-thinning decade. Results of a sensitivity analysis suggested that both an increase in stomatal conductance (g _s) and differences in source water among treatments are equally probable causes of the δ¹⁸O_w shift in heavily thinned stands. We modeled inter-annual changes in δ¹⁸O_w of trees from all treatments using environmental and physiological data and found that the significant increase in δ¹⁸O_w inter-annual variance was related to greater δ¹⁸O_w responsiveness to changing environmental conditions for trees in thinned stands when compared to control stands. Based on model results, the more muted climatic response of wood isotopes in slow-growing control trees is likely to be the consequence of reduced carbon sink strength causing a higher degree of mixing of previously stored and fresh assimilates when compared to faster-growing trees in thinned stands. Alternatively, the muted response of δ¹⁸O_w to climatic variation of trees in the control stand may result from little variation in the control stand in physiological processes (photosynthesis, transpiration) that are known to affect δ¹⁸O_w.     

Canopy structure,photosynthetic capacity and nitrogen distribution in adjacent mixed and monospecific stands of <Emphasis Type="Italic">Phragmites australis</Emphasis> and <Emphasis Type="Italic">Typha latifolia</Emphasis>

Shifts in canopy structure associated with nonnative plant invasions may interact with species-specific patterns of canopy resource allocation to reinforce the invasion process. We documented differences in canopy light availability and canopy resource allocation in adjacent monospecific and mixed stands of Phragmites australis and Typha spp. in a Great Lakes coastal wetland presently undergoing Phragmites invasion to better understand how light availability influences leaf nitrogen content (N_mass) and photosynthetic capacity (A_max) in these species. Due to their horizontally oriented leaves, light attenuates more rapidly in monospecific stands of Phragmites than in monospecific stands of Typha, where leaves are more vertically-oriented. Whereas Typha canopies followed our prediction that patterns of N_mass and A_max should closely parallel patterns of canopy light availability, N_mass and A_max were consistent throughout Phragmites’ canopies. Moreover, we observed overall greater N_mass and lower photosynthetic nitrogen use efficiency in leaves of Phragmites than in leaves of Typha. Improved understanding of the link between N_mass and A_max in these canopies should improve our understanding of carbon and nitrogen cycling consequences of Phragmites invasion in wetland ecosystems.     

Density effects on the growth of self-thinning Eucalyptus urophylla stands

Density effects on the growth of self-thinning Eucalyptus urophylla stands were examined for 7 years. Tree height and stem diameter at breast height were measured during the experimental period. Stems, branches, leaves, bark and roots of 45 E. urophylla trees were sampled in three different density stands in order to establish their biomass equations. Change trends of the biological time τ and density ρ were described used corresponding equations. The stem weight ratio increased and leaf weight ratio decreased, whereas those of branch, bark and root were relatively steady from 2 years after the planting. The competition-density (C-D) effect equation of mean organ weight w _o was derived by combining the allometric power relationship between mean tree weight w and w _o with the C-D effect equation of self-thinning stands. The equations of the C-D effect for w and ρ and for w _o and ρ were used to describe the C-D effects in tree and organs during course of self-thinning, respectively, and showed a good fit to the data. Leaf biomass of different density stands reached a more or less constant level with time elapse. High density produced the greatest biomass and stem biomass, so that it is the best choice in silvicultural practice.     

Zur Bedeutung der wahren maximalen spezifischen Wachstumsrate

In this report the biokinetic parameter μ_max, m and Y_max for the denitrification of a medium containing acetat as C-source and a soft coal gasification water containing volatile fatty acids as main components have been compared. An expression for a true maximum specific growth rate is proposed (μ_maxw = μ_max + mY_max) and it could be shown that despite different values for μ_max the values for μ_maxw correspond fairly well.     

SELF‐THINNING AND SIZE INEQUALITY DYNAMICS IN A CLONAL SEAWEED (SARGASSUM LAPAZEANUM,PHAEOPHYCEAE)1

Fronds of clonal seaweeds with extensive holdfasts relative to frond size are known not to self‐thin during growth, even in crowded stands. We tested whether frond self‐thinning would occur for such a seaweed since these traits are more similar to those of unitary seaweeds, which do self‐thin in crowded conditions. We used Sargassum lapazeanum Setch. et N. L. Gardner (Fucales, Phaeophyceae) from the Pacific coast of Mexico, for which we first confirmed its clonal nature by performing a regeneration experiment in culture tanks. During the growth season (winter to late spring), S. lapazeanum stand biomass increased, while frond density and size inequality (Gini coefficient for frond biomass) decreased. These results indicate that self‐thinning occurred at the frond level. We propose a conceptual model for frond dynamics for clonal seaweeds in general. In stands of clonal species with small fronds and relatively extensive holdfasts (particularly when holdfasts are perennial), frond dynamics would be determined mostly by intraclonal regulation, which seems to prevent excessive crowding from occurring. Such species display a positive biomass–density relationship during the growth season. On the contrary, in stands of clonal species with large fronds relative to holdfast size, frond dynamics would be determined mostly by interactions among genets. For such species, self‐thinning may be detected at the frond level in crowded stands, resulting in a negative biomass–density relationship during growth.     

THE IMPACT OF FROND CROWDING ON FROND BLEACHING IN THE CLONAL INTERTIDAL ALGA MAZZAELLA CORNUCOPIAE (RHODOPHYTA, GIGARTINACEAE) FROM BRITISH COLUMBIA, CANADA

The importance that frond crowding represents for the survival of fronds of the clonal intertidal alga Mazzaella cornucopiae (Postels et Ruprecht) Hommersand (Rhodophyta, Gigartinaceae) was investigated in Barkley Sound, British Columbia, Canada. Frond density is high for this species, up to 20 fronds·cm^?2 in the most crowded stands. Frond crowding imposes a cost in the form of reduced net photosynthetic rates when fronds are fully hydrated as a result of reduced irradiance compared with experimental (not found naturally) low-density stands. However, the interaction between desiccation and irradiance alters this relationship between net photosynthetic rates and frond density. During a typical daytime low tide in spring, irradiance is 10–30 μmol·m^?2·s^?1 below the canopy of fronds, and frond desiccation (relative to total water content) can reach 43% at the end of the low tide. In contrast to natural stands, fronds from experimentally thinned stands are subjected to irradiances up to 2000 μmol·m^?2·s^?1 because of the spatial separation among fronds and can desiccate up to 81% at the end of the same low tide. Laboratory experiments showed that negative net photosynthetic rates occur between 40% and 80% desiccation at an irradiance of 515 μmol·m^?2·s^?1, and the literature suggests that strong bleaching could occur as a result. At 20 μmol·m^?2·s^?1 of irradiance and desiccation levels up to 40%, simulating understory conditions of natural stands, net photosynthetic rates are never negative. Experimental thinning of stands of M. cornucopiae done during spring effectively resulted in a stronger extent of frond bleaching compared with natural stands. Therefore, the cost of reduced net photosynthetic rates at high frond densities when fronds are fully hydrated is counterbalanced by the protective effects of frond crowding against extensive bleaching, essential for survival at the intertidal zone. Future research will have to demonstrate the possible relationship between the frequency and duration of negative net photosynthetic rates and the extent of frond bleaching.     

Influence of water activity on deoxynivalenol accumulation in wheat

The influence of water activity (a_w) on deoxynivalenol accumulation in wheat at 25°C was studied. Gnotobiotic grains were conditioned at different a_w levels, inoculated with a toxigenic Fusarium graminearum strain, and incubated for ten weeks. The highest accumulation of deoxynivalenol (1130 ug/kg) was detected at a_w 0.980. At a_w 0.945 and 0.925 the maximum quantities of toxin accumulated were 113 ug/kg and 93 ug/kg respectively. Deoxynivalenol was not detected in the substrate at a_w 0.900. Results suggest that intermediate a_w levels (0.97 – 0.92) are particularly critical at post harvest time because those are conditions under which deoxynivalenol production is most likely to be initiated naturally.     

PEGylation kinetics of recombinant hirudin and its application for the production of PEGylated HV2 species

A critical challenge of PEGylation is the production of the desired PEGylated protein form at a high yield. In this study, a kinetic model was constructed successfully to describe the PEGylation reaction of recombinant hirudin variant-2 (HV2) with monomethoxy-PEG-succinimidyl carbonate (mPEG-SC) by fitting the experimental data. Moreover, PEGylation reaction conditions were investigated using the established model and the corresponding experiments to determine the optimal condition to achieve the mono-PEG-HV2 at the desired yield. The model predictions agreed well with the experimental data. Several important process parameters (maximum theoretical yield of mono-PEG-HV2 (y_max), critical PEG/HV2 molar ratio (m_crit) and reaction time to achieve y_max (t_max)) and their mathematical equations were obtained to determine the optimum reaction conditions. Among reaction conditions affecting the PEGylation rates, pH and temperature displayed little effect on y_max, but y_max increased as PEG size increased. Optimal reaction condition to produce mono-PEG-HV2 was as follows: pH and temperature could vary in a certain range; whereas PEG/HV2 molar ratio should be slightly greater than m_crit and the reaction should be stopped at t_max. The results of this study indicate that the proposed reaction kinetic model can provide a possible mechanism interpretation for real PEGylation reactions and optimize efficiently the PEGylation step.     

Sapwood hydraulic conductivity and leaf area – sapwood area relationships following thinning of a Eucalyptus nitens plantation

This study tested the hypothesis that the relationship between leaf area (projected, or one‐sided) and sapwood area in Eucalyptus nitens (Deane and Maiden) Maiden is affected by thinning treatment. However, no difference in the relationship between leaf area and sapwood area was found 8 years after thinning. This result suggests that a single regression equation can be used to predict the leaf area of trees in thinned and unthinned stands. The relationship was non‐linear, implying a causal relationship between growth rate and the ratio of leaf area to sapwood area (A_l : A_s). Sapwood hydraulic conductivity increased by approximately 100% from breast height to crown base, whereas sapwood area decreased by 19%. This implies that the efficiency of water transport through the sapwood increased by 60% along this length. This conclusion is supported by the A_l : A_s relationships which showed that the sapwood area at crown base supported, on average, close to 60% more leaf area than a similar amount of sapwood area at breast height. That large trees in this study had greater hydraulic conductivity and higher A_l : A_s lends support to the argument that resource capture, and hence growth rate, influence sapwood hydraulic conductivity.     

Effects of water activity on Vmax and KM of lipase catalyzed transesterification in organic media

Summary The V_max and K_M of various forms of lipase from Pseudomonas cepacia (powder, adsorbed onto Celite or covalently linked to polyethylene glycol) were determined in organic solvents preequilibrated to water activities (a _w) from <0.1 to 0.84. The model reaction was the transesterification between n-octanol and vinyl butyrate. It was found that K_M for the nucleophile increased with increasing a _w for all three lipase forms. V_max increased with increasing a _w for polyethylene glycol-lipase, whereas there was an optimum at intermediate a _w values (0.11 – 0.38) for lipase powder and Celite-immobilized lipase.     

Dynamics of Competition in Populations of Carrot (Daucus carota)

Populations of carrot (Daucus carota) were raised over a widerange of densities (79–5763 plants m^-2) to examine thedynamics of competition in terms of yield–density relationshipsand size variability, and to investigate the effects of nutrientsupply on competition. While the relationship between shootyield and density was asymptotic, the relationship between rootand total yield and density tended to be parabolic. For a giventime and density series the relationship between yield per unitarea and density could best be described by the model: y=w_mD_(1+aD)^b wherey is the yield per unit area,D is density,w_m, a andb arefitted parameters. The parametersw_m anda increased over timebut nutrient availability affected onlyw_m. An extension of thebasic yield-density model is proposed to describe the dynamicsof the yield–density relationship over time: y=kD_{[1+cexp(-rt)]{1+}     

The use of genetic markers in the analysis of competitive interactions in Drosophila melanogaster

A range of long established inbred lines derived from the TEXAS population of Drosophila melanogaster have been used to elucidate the nature of the competitive interactions which occur in genetically heterogeneous mixtures. A prerequisite for this type of investigation is the ability to distinguish the genotypes which compete in mixed culture. Specific marker alleles are generally used to achieve this distinction although in the past little attention has been given to the possibility of competitive bias introduced by the marker alleles themselves. For the experiments reported in this paper two specific marker alleles (y ² and w ^a) have been introduced independently into the TEXAS inbred lines. In this way the original wild type inbred lines could be compared with similar series of genotypes marked with either y ² or w ^a and the effects of the marker alleles determined.The results indicated that the body colour mutation (y ²) was neutral in its effect on the competitive interaction of recipient strains. The introduction of the white apricot eye colour mutation (w ^a) however, had a pronounced and deleterious effect on competitive ability. This effect was to render genotypes less able to compete effectively in mixed culture by depressing inter-genotypic competitive ability. These effects were found to be consistent over a range of genotypes and for each of two characters measuring competitive success.     

Kinetics of formation of fibrin oligomers. I. Theory

The course of formation of fibrin oligomers is treated theoretically for the condition that self-assembly of fibrin monomers is rapid compared with the loss of A peptides by the enzymatic action of thrombin. The rate constant for removal of the second A peptide is taken to be larger than that for the first by an arbitrary factor q; the association of activated A sites with their complementary a sites is assumed to be random and independent of oligomer size. Two types of oligomers are considered: noncovalently bonded protofibrils formed by the staggered overlap of thrombin-activated monomers and covalently bonded linear oligomers formed by factor XIIIa-mediated end-to-end ligation of adjacent monomers within protofibrils. Oligomers of the first type, if ligated, are dissociated to oligomers of the second type by solubilization in SDS–urea. Theoretical curves are presented for x _w and x ′_w (weight-average degree of polymerization of staggered overlap and linear ligated oligomers, respectively) and for the weight fractions of monomer, dimer, and decamer of both ligated and unligated species as functions of y, the fraction of A peptide removed; and also for w_x and w′_x, the weight fractions of x-mer of the respective oligomer types, as a function of x at y = 0.5. With increasing q, the maximum w_x or w′_x that a low oligomer will reach during the reaction decreases and the size distribution is broadened toward larger oligomers. Comparison with experiment is made in a companion paper.     

Self-thinning lines differ with fertility level

The effect of variations in fertility level of the substrate on the self-thinning lines followed by populations of Ocimum basilicum L. was investigated experimentally by establishing populations over a range of densities at two fertility levels. Populations from each fertility level followed different self-thinning lines for shoot biomass. Self-thinning began at a lower biomass in populations grown at the higher fertility level; the subsequent slope of the thinning line was –0.5 for these stands on a log shoot biomass versus log density plot. The slope of the self-thinning line was flatter (–0.29) at the lower fertility level. Fitting the self-thinning line by the Structural Relationship rather than the Major Axis made little difference to line estimates. Biomass packing differed with fertility level, with plants from the higher fertility stands requiring more canopy volume for given shoot biomass than plants from lower fertility levels. Biologically, this would mean shoot competition intensified more rapidly at the higher fertility level as biomass accumulated in stands. The difference in slope between fertility levels was associated with changes above- and belowground. The radial extension of the canopy versus shoot mass relationships of individual plants differed with fertility level. Plants at the lower fertility level allocated more biomass to root growth, and had less leaf area per unit root length. The differences in slope of the self-thinning lines may have been because of differences in the radial extension of the canopy versus shoot mass relationships of individual plants at each fertility level, and/or to an increase in root competition at the lower fertility level.     

Triazine Resistance without Reduced Vigor in Phalaris paradoxa

A triazine-resistant (R) biotype of Phalaris paradoxa L. (hood canarygrass) was superior to a triazine-susceptible (S) biotype in seed-germinability and seedling emergence. It was equal or superior to the S-biotype in growth under noncompetitive conditions. Rates of CO₂ uptake by R-plants were similar to those of S-plants, except at very low photon flux densities, where S-plants exhibited higher rates of CO₂ uptake. Fluorescence induction curves of chloroplasts isolated from R-plants indicated an alteration in photosystem II. Analysis of the light dependence of electron transport shows a reduction in quantum yield (Q_y) in R- compared to S-chloroplasts. The same analysis, however, shows for R-chloroplasts an increase in the light-saturated electron transport rate (V_max). The increase in V_max compensates for the reduction of Q_y over a wide range of photon flux densities, which may explain the similarity between R- and S-biotypes in photosynthetic potential and growth.     

Phototoxic effect of UVR on wild type, ebony and yellow mutants of Drosophila melanogaster: Life Span, fertility, courtship and biochemical aspects

Melanin plays an important role in protecting organisms from ultraviolet radiation (UVR). Therefore, it is possible that differently colored strains can show different sensitivities to UVR. In the present work, life span, fertility and courtship behavior of wild type (w), ebony (e) and yellow (y) strains of Drosophila melanogaster were studied to evaluate their sensitivity to ultraviolet (UV). Because a range of phototoxic effects of UVR are mediated through generation of free radicals, levels of free radicals, lipid peroxide (malondialdehyde, MDA) and superoxide dismutase (SOD) activity of three strains were examined to indicate their antioxidant defending ability and oxidative status. It was shown that w always had the highest lifespan and fertility not only in the control but also in UV-exposed groups. Moreover, lifespan and fertility of e were significantly higher (P<0.0001) than those of y in the UV-exposed groups, but not for the control. On the other hand, UV exposure had an adverse effect on courtship of flies. Stronger electron paramagnetic resonance (EPR) signals could be detected in w, e and y exposed to 5 min UV. And there were more significant changes of EPR signals in y than in w and e. UVR had no significant (P=0.1782) effect on the SOD activities. After pooling data from the control and UV-exposed groups, we found that w had a significantly (P<0.05) higher level of SOD activity, but e and y were nearly at the same levels (P>0.05). MDA levels were increased in the UV dose-dependent manner (P=0.0495). In conclusion, our results suggested that UVR can decrease life span and fertility of flies and do harm to courtship, which may be due to oxidative damage to flies tissues (e.g. central nervous system) induced by free radicals. w had the highest tolerance to UVR, which may be ascribed to its advantage of survival under the natural condition and at high level of SOD activity. Then differences of pigment between e and y in absorbing UV, shielding against UV and scavenging free radicals produced by UVR should be responsible for their different sensitivity to UVR.     

A Mechanistic Analysis of Self-thinning in Terms of the Carbon Balance of Trees

The self-thinning behavior of a monoculture forest is examinedfrom a mechanistic viewpoint, in terms of the carbon balanceof trees at the stand level. Two approaches are described: thefirst is based on simple assumptions concerning the balancebetween growth, photosynthesis and respiration; the second usesthe process-based I.T.E. EDINBURGH FOREST model, extended toinclude tree birth and death, to examined the assumptions ofthe first approach at a more mechanistic level and to interpretthe observed variation in the responses to shading and soilfertility in terms of a single model. The first approach leads to a power law relation m n ^-1/y betweenmean biomass per tree (m) and the number of trees per unit groundarea (n), where y is the exponent characterising the rate atwhich respiration (r) scales with biomass (i.e. r m^y). Forvalues of y less than 1, m and n are predicted to increase anddecrease, respectively, as powers of time (t) such that thebiomass per unit ground area (M) increases linearly with t forany value of y. When y equals 1, m and n vary exponentiallywith t and M remains constant. When r is assumed to be proportional to stem cambium surfacearea, the value of y is shown to lie in the range 0·5to 1 depending on the rate of stem taper. This leads to slopeson a log m vs. log n self-thinning plot in range -1 to -2 andtypically around -1·5 for rates of taper based on mechanicalrequirements. For the second approach, the I.T.E. EDINBURGH FOREST model,a previously published mechanistic model of plantation growthat the stand level (Thornley, 1991), is extended to naturalstands by introducing average stem birth and death rates thatare functions of the carbon and nitrogen substrate status oftrees. Growth of even-aged and mixed-age forest over about 500years is simulated under a variety of environmental and physiologicalconditions. In general, the forest model predicts a curved log m vs. logn thinning line, but has a reasonably well-defined linear sectionunder most conditions. The slope of the linear portion flattensas the rate at which cambium surface area scales with structuralbiomass increases, in qualitative agreement with the analyticalprediction of the first approach. Quantitative differences betweenthe two approaches are interpreted in terms of the process representedin the forest model. In general, the height of the thinningline increases with irradiance, but is relatively insensitiveto soil nitrogen, with no change in slope in either case. However,at very low irradiance or soil nitrogen levels, the slope flattenscontinuously and the entire thinning line becomes markedly non-linear.Even-aged stands and mixed-age stands have different thinningslopes.Copyright 1993, 1999 Academic Press Self-thinning, carbon balance, mechanistic model, forest growth, respiration     

Lipid composition and macromolecular crowding effects on CYP2J2‐mediated drug metabolism in nanodiscs

Lipid composition and macromolecular crowding are key external effectors of protein activity and stability whose role varies between different proteins. Therefore, it is imperative to study their effects on individual protein function. CYP2J2 is a membrane‐bound cytochrome P450 in the heart involved in the metabolism of fatty acids and xenobiotics. In order to facilitate this metabolism, cytochrome P450 reductase (CPR), transfers electrons to CYP2J2 from NADPH. Herein, we use nanodiscs to show that lipid composition of the membrane bilayer affects substrate metabolism of the CYP2J2‐CPR nanodisc (ND) system. Differential effects on both NADPH oxidation and substrate metabolism by CYP2J2‐CPR are dependent on the lipid composition. For instance, sphingomyelin containing nanodiscs produced more secondary substrate metabolites than discs of other lipid compositions, implying a possible conformational change leading to processive metabolism. Furthermore, we demonstrate that macromolecular crowding plays a role in the lipid‐solubilized CYP2J2‐CPR system by increasing the K_m and decreasing the V_max, and effect that is size‐dependent. Crowding also affects the CYP2J2‐CPR‐ND system by decreasing both the K_m and V_max for Dextran‐based macromolecular crowding agents, implying an increase in substrate affinity but a lack of metabolism. Finally, protein denaturation studies show that crowding agents destabilize CYP2J2, while the multidomain protein CPR is stabilized. Overall, these studies are the first report on the role of the surrounding lipid environment and macromolecular crowding in modulating enzymatic function of CYP2J2‐CPR membrane protein system.