Leaf Physiological Traits and their Importance for Species Success in a Mediterranean Grassland

We related leaf physiological traits of four grassland species (Poa pratensis, Lolium perenne, Festuca valida, and Taraxacum officinale), dominant in a Mediterranean grassland, to their origin and success at community level. From early May to mid-June 1999, four leaf samplings were done. Species originating from poor environments (P. pratensis, F. valida) had low carbon isotope discrimination (), specific leaf area (SLA), leaf water and mineral contents, and net photosynthetic rate on mass basis (P _mass) but high chlorophyll content. The reverse traits were evident for the fast-growing species (L. perenne, T. officinale). Under the resource-limiting conditions (soil nitrogen and water) of the Mediterranean grassland, the physiological traits of P. pratensis and F. valida showed to be more adapted to these conditions leading to high species abundance and dominance.     

Leaf economics and hydraulic traits are decoupled in five species‐rich tropical‐subtropical forests

Leaf economics and hydraulic traits are critical to leaf photosynthesis, yet it is debated whether these two sets of traits vary in a fully coordinated manner or there is room for independent variation. Here, we tested the relationship between leaf economics traits, including leaf nitrogen concentration and leaf dry mass per area, and leaf hydraulic traits including stomatal density and vein density in five tropical‐subtropical forests. Surprisingly, these two suites of traits were statistically decoupled. This decoupling suggests that independent trait dimensions exist within a leaf, with leaf economics dimension corresponding to light capture and tissue longevity, and the hydraulic dimension to water‐use and leaf temperature maintenance. Clearly, leaf economics and hydraulic traits can vary independently, thus allowing for more possible plant trait combinations. Compared with a single trait dimension, multiple trait dimensions may better enable species adaptations to multifarious niche dimensions, promote diverse plant strategies and facilitate species coexistence.     

Variation in bulk‐leaf 13C discrimination,leaf traits and water‐use efficiency–trait relationships along a continental‐scale climate gradient in Australia

Large spatial and temporal gradients in rainfall and temperature occur across Australia. This heterogeneity drives ecological differentiation in vegetation structure and ecophysiology. We examined multiple leaf‐scale traits, including foliar ¹³C isotope discrimination (Δ¹³C), rates of photosynthesis and foliar N concentration and their relationships with multiple climate variables. Fifty‐five species across 27 families were examined across eight sites spanning contrasting biomes. Key questions addressed include: (i) Does Δ¹³C and intrinsic water‐use efficiency (WUE_i) vary with climate at a continental scale? (ii) What are the seasonal and spatial patterns in Δ¹³C/WUE_i across biomes and species? (iii) To what extent does Δ¹³C reflect variation in leaf structural, functional and nutrient traits across climate gradients? and (iv) Does the relative importance of assimilation and stomatal conductance in driving variation in Δ¹³C differ across seasons? We found that MAP, temperature seasonality, isothermality and annual temperature range exerted independent effects on foliar Δ¹³C/WUE_i. Temperature‐related variables exerted larger effects than rainfall‐related variables. The relative importance of photosynthesis and stomatal conductance (g_s) in determining Δ¹³C differed across seasons: Δ¹³C was more strongly regulated by g_s during the dry‐season and by photosynthetic capacity during the wet‐season. Δ¹³C was most strongly correlated, inversely, with leaf mass area ratio among all leaf attributes considered. Leaf N_mass was significantly and positively correlated with MAP during dry‐ and wet‐seasons and with moisture index (MI) during the wet‐season but was not correlated with Δ¹³C. Leaf P_mass showed significant positive relationship with MAP and Δ¹³C only during the dry‐season. For all leaf nutrient‐related traits, the relationships obtained for Δ¹³C with MAP or MI indicated that Δ¹³C at the species level reliably reflects the water status at the site level. Temperature and water availability, not foliar nutrient content, are the principal factors influencing Δ¹³C across Australia.     

Leaf traits and photosynthetic parameters of saplings and adult trees of co-existing species in a temperate broad-leaved forest

In Central European forestry the establishment of broad-leaved mixed forests is attaining increasing importance, but little information exists about gas exchange characteristics of some of the tree species involved, which are less abundant today. In an old-growth forest in Central Germany (Hainich, Thuringia), (i) I compared morphological and chemical leaf traits that are indicative of leaf gas exchange characteristics among eight co-existing species, and (ii) analysed photosynthetic parameters of saplings and adult trees (lower and upper canopy level) in four of these species (Acer pseudoplatanus L., Carpinus betulus L., Fraxinus excelsior L. and Tilia platyphyllos Scop.).Leaves from the upper canopy in the eight species studied varied significantly in their specific leaf area (12.9–19.4 m² kg⁻¹), stomatal density (125–313 stomata mm⁻²), leaf nitrogen concentration (95–157 mmol N m⁻²) and δ¹³C content (–27.81 to –25.85‰). F. excelsior and C. betulus were largely contrasting species, which suggests that the species, which were studied in more detail, include the widest difference in leaf gas exchange among the co-existing species. The saplings of the four selected species exhibited shade acclimated leaves with net photosynthesis rates at saturating irradiance (A_max) between 5.0 and 6.4 μmol m⁻² s⁻¹. In adult trees A_max of fully sunlit leaves was more variable and ranged from 10.5 (C. betulus) to 16.3 μmol m⁻² s⁻¹ (F. excelsior). However, less negative δ¹³C values in F. excelsior sun leaves point to a strong limitation in gas exchange. In the lower canopy of adult trees A_max of F. excelsior (12.0 μmol m⁻² s⁻¹) was also greater than that of A. pseudoplatanus, C. betulus and T. platyphyllos (5.0–5.6 μmol m⁻² s⁻¹). This can be explained by the small leaf area and the absence of shade leaves in mature F. excelsior trees. Thus, a considerable variation in leaf traits and gas exchange was found among the co-existing tree species. The results suggest that species-specific characteristics increase the spatial heterogeneity of canopy gas exchange and should be taken into account in the interpretation and prediction of gas flux from mixed stands.In der Forstwirtschaft Mitteleuropas gewinnt die Begründung von Laubmischwäldern zunehmend an Bedeutung, aber über Eigenschaften im Gasaustausch einiger beteiligter Baumarten, die heute nicht so häufig sind, ist wenig bekannt. In einem Altbestand in Mitteldeutschland (Hainich, Thüringen) habe ich (i) morphologische und chemische Eigenschaften von Sonnenblättern, die Hinweise auf Charakteristika im Blattgaswechsel geben, an acht koexistierenden Baumarten untersucht, und (ii) Photosyntheseparameter von juvenilen und adulten Bäumen (unteres und oberes Kronenniveau) von vier dieser Arten (Acer pseudoplatanus L., Carpinus betulus L., Fraxinus excelsior L. and Tilia platyphyllos Scop.) erhoben.Blätter aus dem oberen Kronenraum der acht untersuchten Arten variierten signifikant in der spezifischen Blattfläche (12.9–19.4 m² kg⁻¹), der Stomatadichte (125–313 Stomata mm⁻²), dem Blattstickstoffgehalt (95–157 mmol N m⁻²) und den δ¹³C-Werten (–27.81 bis –25.85‰). In diesem Kollektiv zeigten F. excelsior und C. betulus groβe Unterschiede, was darauf hindeutet, dass die Arten, die genauer untersucht wurden, die Spannweite an Gaswechseleigenschaften unter den koexistierenden Baumarten umfassen. Die Jungpflanzen der vier ausgewählten Arten besaßen Schattenblätter, deren Netto-Photosyntheserate bei hoher Lichtintensität (A_max) zwischen 5.0 and 6.4 μmol m⁻² s⁻¹ variierte. An Sonnenblättern von Altbäumen war A_max variabler und lag zwischen 10.5 (C. betulus) und 16.3 μmol m⁻² s⁻¹ (F. excelsior). Allerdings weisen hohe δ¹³C-Werte in Sonnenblättern von F. excelsior auf eine starke Limitierung des Gasaustauschs hin. Auch in der unteren Krone der Altbäume war A_max von F. excelsior (12.0 μmol m⁻² s⁻¹) höher als A_max von A. pseudoplatanus, C. betulus und T. platyphyllos (5.0–5.6 μmol m⁻² s⁻¹). Dies kann durch die geringe Blattfläche und die Abwesenheit von Schattenblättern in der Krone adulter Bäume von F. excelsior erklärt werden. Zwischen den koexistierenden Baumarten wurde somit in Bezug auf Blatteigenschaften und Photosyntheseparameter eine erhebliche Variation festgestellt. Die Ergebnisse legen nahe, dass artspezifische Eigenschaften die räumliche Heterogenität des Gaswechsels im Kronenraum erhöhen und bei der Interpretation und Vorhersage von Gasflüssen über Mischbeständen berücksichtigt werden sollten.     

Changes in the abundance of C3/C4 species of Inner Mongolia grassland: evidence from isotopic composition of soil and vegetation

Global warming, increasing CO₂ concentration, and environmental disturbances affect grassland communities throughout the world. Here, we report on variations in the C3/C4 pattern of Inner Mongolian grassland derived from soil and vegetation. Soil samples from 149 sites covering an area of approximately 250 000 km² within Inner Mongolia, People's Republic of China were analyzed for the isotopic composition (δ¹³C) of soil organic carbon (SOC). The contrast in δ¹³C between C3 and C4 plants allowed for calculation of the C3/C4 ratio from δ¹³C of SOC with a two‐member mixing model, which accounted for influences of aridity and altitude on δ¹³C of the C3 end‐member and for changes in δ¹³C of atmospheric CO₂. Maps were created geostatistically, and showed a substantially lower C4 abundance in soil than in recent vegetation (?10%). The difference between soil and vegetation varied regionally and was most pronounced within an E–W belt along 44°N and in a mountainous area, suggesting a spread of C4 plants toward northern latitudes (about 1°) and higher altitudes. The areas of high C4 abundance for present vegetation and SOC were well delineated by the isotherms of crossover temperature based on the climatic conditions of the respective time periods. Our study indicates that change in the patterns of C3/C4 composition in the Inner Mongolia grassland was mainly triggered by increasing temperature, which overrode the antagonistic effect of rising CO₂ concentrations.     

Productivity, leaf traits and carbon isotope discrimination in 29 Populus deltoides x P. nigra clones

Here we tested whether some leaf traits could be used as predictors for productivity in a range of Populus deltoides x P. nigra clones. These traits were assessed in 3-yr-old rooted cuttings from 29 clones growing in an open field trial, in a five randomized complete block design, under optimal irrigation. Variables were assigned to four groups describing productivity (above-ground biomass, total leaf area), leaf growth (total number of leaves increment rate), leaf structure (area of the largest leaf, specific leaf area, carbon and nitrogen contents), and carbon isotope discrimination in the leaves (Delta). High-yielding clones displayed larger total leaf area and individual leaf area, while no correlation could be detected between productivity and either leaf structure or Delta. By contrast, Delta was negatively correlated with number of leaves increment rate and leaf N content. Our study shows that there is a potential to improve water-use efficiency in poplar without necessarily reducing the overall productivity.     

Gender specific patterns of carbon uptake and water use in a dominant riparian tree species exposed to a warming climate

Air temperatures in the arid western United States are predicted to increase over the next century. These increases will likely impact the distribution of plant species, particularly dioecious species that show a spatial segregation of the sexes across broad resource gradients. On the basis of spatial segregation patterns, we hypothesized that temperature increases will have a greater negative impact on female plants compared with co‐occurring male plants of dioecious species. This hypothesis was tested by examining the whole‐plant carbon and water relations of 10‐year‐old female (n = 18) and male (n = 13) Acer negundo Sarg. trees grown in a common garden in Salt Lake City, UT. The trees were established from cuttings collected where the growing season temperature averaged about 6.5 °C cooler than at the common garden. During May and June, stem sap flux (J_s) was similar between genders, but averaged 25% higher in males during the warmer months of July and August. Daytime canopy stomatal conductance (g_s) per unit leaf area was 12% higher in females in May : June, but was 11% higher in males in July : August. We combined measurements of sap flux–scaled transpiration with measurements of tree allometry and δ¹³C of leaf soluble sugars to estimate whole‐tree carbon assimilation (A_tree) and water use efficiency (WUE) (A_tree : E_tree). A_tree was similar between genders until late August when A_tree was 32% higher in male trees. A_tree : E_tree was on average 7% higher in females than in males during the growing season. Patterns of J_s, g_s, A_tree and A_tree : E_tree in the present study were in contrast to those previously reported for A. negundo genders under native growing season temperatures. Results suggest that the spatial segregation of the sexes could shift under global warming such that female plants lose their dominance in high‐resource habitats, and males increase their dominance in relatively lower‐resource habitats.     

Nutrient supply enhanced the increase in intrinsic water‐use efficiency of a temperate seminatural grassland in the last century

Under the increase in atmospheric CO₂ during the last century, variable increases in the intrinsic water‐use efficiency (W_i), i.e., the ratio between carbon assimilation rate (A) and stomatal conductance (g_s), of C₃ vegetation have been observed. Here, we ask if long‐term nutrient status and especially nitrogen supply have an effect on the CO₂ response of W_i in a temperate seminatural C₃ grassland. This analysis draws on the long‐term trends (1915–2009) in W_i, derived from carbon isotope analysis, of archived hay and herbage from the Park Grass Experiment at Rothamsted (South‐East England). Plant samples came from five fertilizer treatments, each with different annual nitrogen (N; 0, 48 or 96 kg ha^?1), phosphorus (P; 0 or 35 kg ha^?1) and potassium (K; 0 or 225 kg ha^?1) applications, with lime as required to maintain soil pH near 7. Carbon isotope discrimination (¹³Δ) increased significantly (P < 0.001) on the Control (0.9‰ per 100 ppm CO₂ increase). This trend differed significantly (P < 0.01) from those observed on the fertilized treatments (PK only: 0.4‰ per 100 ppm CO₂ increase, P < 0.001; Low N only, Low N+PK, High N+PK: no significant increase). The ¹³Δ trends on fertilized treatments did not differ significantly from each other. However, N status, assessed as N fertilizer supply plus an estimate of biologically fixed N, was negatively related (r² = 0.88; P < 0.02) to the trend for ¹³Δ against CO₂. Other indices of N status exhibited similar relationships. Accordingly, the increase in W_i at High N+PK was twice that of the Control (+28% resp. +13% relative to 1915). In addition, the CO₂ responsiveness of ¹³Δ was related to the grass content of the plant community. This may have been due to the greater CO₂ responsiveness of g_s in grasses relative to forbs. Thus, the greater CO₂ response of grass‐rich fertilized swards may be related to effects of nutrient supply on botanical composition.     

Water management practices and climate in ancient agriculture: inferences from the stable isotope composition of archaeobotanical remains

Carbon isotope discrimination (Δ¹³C) in charred grains from archaeological sites provides reliable information about water availability of ancient crops. However, as cereals are cultivated plants, they may reflect not only climatic fluctuations, but also the effect on water status of certain agronomic practices, such as sowing in naturally wet soils or irrigation. In this work, we propose a methodological approach to combine Δ¹³C data from different plant species, in order to discriminate between climate-derived and anthropogenic effects on ancient crops. We updated previous models for estimating water inputs from Δ¹³C of cereal grains of Hordeum vulgare and Triticum aestivum/durum, and we applied them to published data from several archaeological sites, including samples from the Neolithic to the present day in northeast and southeast Spain, as well as from the Neolithic site of Tell Halula (northwest Syria). We found an important decrease in water availability from the Neolithic to the present time in the three areas of study, especially clear for the two driest areas (southeast Spain and northwest Syria). Potential differences in water management practices between wheat and barley, as well as between cereal and legume crops (Vicia faba and Lens culinaris), are also discussed on the basis of the comparison of Δ¹³C values across several archaeological sites.     

Changes in vegetation phenology are not reflected in atmospheric CO2 and 13C/12C seasonality

Northern terrestrial ecosystems have shown global warming‐induced advances in start, delays in end, and thus increased lengths of growing season and gross photosynthesis in recent decades. The tradeoffs between seasonal dynamics of two opposing fluxes, CO₂ uptake through photosynthesis and release through respiration, determine the influence of the terrestrial ecosystem on the atmospheric CO₂ and ¹³C/¹²C seasonality. Here, we use four CO₂ observation stations in the Northern Hemisphere, namely Alert, La Jolla, Point Barrow, and Mauna Loa Observatory, to determine how changes in vegetation productivity and phenology, respiration, and air temperature affect both the atmospheric CO₂ and ¹³C/¹²C seasonality. Since the 1960s, the only significant long‐term trend of CO₂ and ¹³C/¹²C seasonality was observed at the northern most station, Alert, where the spring CO₂ drawdown dates advanced by 0.65 ± 0.55 days yr^?1, contributing to a nonsignificant increase in length of the CO₂ uptake period (0.74 ± 0.67 days yr^?1). For Point Barrow station, vegetation phenology changes in well‐watered ecosystems such as the Canadian and western Siberian wetlands contributed the most to ¹³C/¹²C seasonality while the CO₂ seasonality was primarily linked to nontree vegetation. Our results indicate significant increase in the Northern Hemisphere soil respiration. This means, increased respiration of ¹³C depleted plant materials cancels out the ¹²C gain from enhanced vegetation activities during the start and end of growing season. These findings suggest therefore that parallel warming‐induced increases both in photosynthesis and respiration contribute to the long‐term stability of CO₂ and ¹³C/¹²C seasonality under changing climate and vegetation activity. The summer photosynthesis and the soil respiration in the dormant seasons have become more vigorous which lead to increased peak‐to‐through CO₂ amplitude. As the relative magnitude of the increased photosynthesis in summer months is more than the increased respiration in dormant months, we have the increased overall carbon uptake rates in the northern ecosystems.     

Divergent patterns of foliar δ13C and δ15N in Quercus aquifolioides with an altitudinal transect on the Tibetan Plateau: an integrated study based on multiple key leaf functional traits

Aims With a close association with plant water availability, foliar δ 13 C had been investigated extensively in alpine regions; however, foliar δ 15 N has rarely been concurrently used as an indicator of plant nitrogen availability. Due to the positive correlations between leaf nitrogen content and foliar δ 13 C and δ 15 N found in previous studies, we expected that they should show consistent patterns along an altitudinal gradient.Methods To test our hypothesis, we measured foliar δ 13 C and δ 15 N in conjunction with multiple key leaf functional traits of Quercus aquifolioides, a dominant species of alpine forest on the eastern slopes of the Sygera Mountains, southeastern Tibetan Plateau from 2500 to 3800 m.Important findings (i) Contrary to our hypothesis, foliar δ 13 C exhibited a significant positive linear relationship with altitude; in contrast, foliar δ 15 N initially increased and subsequently decreased with altitude, the change in trend occurring around 3300 m. (ii) Our analyses indicated that leaf internal resistance and stomatal conductance, rather than photosynthetic capacity indicated by leaf N concentration, apparently explained the altitudinal variation in foliar δ 13 C, while differences in foliar δ 15 N were likely the result of soil N availability. (iii) Principal component analysis revealed a clear association between δ 13 C and a tradeoff between water loss and carbon gain, indicated by traits related to gas exchange such as leaf thickness, density, stomatal properties. In contrast, the second axis was associated with δ 15 N and nitrogen acquisition strategy in Q. aquifolioides across its altitudinal distribution, represented by traits related to nitrogen concentration and stomata per gram of leaf nitrogen.     

Relationships between early vigour, grain yield, leaf structure and stable isotope composition in field grown barley

Fast growth and early development in barley are used in breeding programmes to improve the water use efficiency and transpiration efficiency of this crop in Mediterranean conditions. Here, we examine the use of several simple traits based on the structure and stable isotope composition of seedling leaves to assess differences in early vigour, phenology and grain yield, and also the interaction with low temperatures in barley. A set of 260 F₈ lines of two-row barley (Hordeum vulgare L.) derived from the cross of Tadmor and WI 2291 were cultivated in two locations in northwest Syria. Total chlorophyll content on an area basis (SPAD) and specific leaf dry weight (SLDW) were measured in recently fully expanded intact leaves of seedlings. Total leaf area and total dry weight per seedling were evaluated in the same seedlings. The stable isotope compositions of carbon and nitrogen (δ¹³C and δ¹⁵N, respectively) were analyzed in the same leaves on a subset of 75 genotypes. Number of days from planting to heading and grain yield were recorded at both sites. The grain yield measured at both locations was positively correlated with the SPAD value of seedlings, but showed no relationship with SLDW. Days to heading was negatively correlated with SPAD values. Regarding early vigour, a negative relationship between the SLDW and the total leaf area of seedlings was observed. However, no relationship between the δ¹³C of seedlings and early vigour was observed, except when only the genotypes most resistant to low temperatures (i.e. showing the highest SPAD values) were considered. This subset of genotypes showed negative relationships between δ¹³C and either total leaf area or total dry weight. In addition, δ¹⁵N was negatively correlated with SPAD only within the high-SPAD genotypes. This suggests that within the genotypes resistant to low temperatures, those with higher chlorophyll content assimilate more nitrogen from nitrate.     

土层厚度对刺槐旱季水分状况和生长的影响

该研究测定了旱季和雨季刺槐(Robinia pseudoacacia)林不同土层厚度的土壤含水量, 刺槐的树高、胸径、小枝凌晨水势、叶片碳稳定同位素组成(δ¹³C)、叶面积、比叶重和气体交换指标; 分析了刺槐旱季和雨季的水分状况和土层厚度之间的关系; 通过刺槐对季节性干旱胁迫的反应, 估计华北石质山区不同土层厚度土壤水分对刺槐的承载能力; 并求证近年来该地区刺槐衰败和水分因素的关系。结果显示: 随着土层厚度减小, 旱季土壤含水量下降、凌晨小枝水势降低; 气孔导度和最大光合速率都减小, 而瞬时水分利用效率增加, 雨季上述指标无显著性差异, 旱季土壤含水量只有雨季的60%左右。随着土层变薄, 刺槐叶片δ¹³C增高, 叶面积减小, 比叶重增加; 刺槐树高和胸径减小。以上结果表明: 刺槐在不同季节下的水分状况综合反映土壤的供水能力, 土层浅薄导致土壤水分承载力不足, 致使刺槐在旱季受到较严重的水分胁迫, 这可能是刺槐出现衰败的重要原因。     

Angiotensin converting enzyme insertion/deletion polymorphism is associated with increased adiposity and blood pressure in obese children and adolescents

Background

The insertion/deletion polymorphism in the gene encoding the angiotensin-converting enzyme (ACE I/D) was associated with arterial hypertension and obesity in adults, but the data in children are scarce and yielded contrasting results. We assessed the impact of the ACE I/D on blood pressure and obesity related traits in a Brazilian cohort of obese children and adolescents.

Methods and results

ACE I/D was genotyped in 320 obese children and adolescents (64% of girls) aged 7–16 years, referred for a weight-loss program. We observed an association of the D-allele with blood pressure and with pre-hypertension/hypertension in boys (odds ratio 2.44, 95% C.I. 1.34–4.68, p = 0.005 for a codominant model). The D-allele, insulin resistance and body fat mass had independent and additive effects and explained 14% of the variance of pre-hypertension/hypertension. The BMI, waist circumference, and body fat mass were significantly higher in DD/ID boys than in II boys (p < 0.005). Allelic associations with obesity related traits were independent of the association with blood pressure. No genotype associations were observed in girls.

Conclusions

The D-allele of the ACE I/D polymorphism was associated with arterial hypertension and with obesity related traits in boys, but not in girls, in a cohort of obese children and adolescents. These associations were independent of each other, as well as of the effects of other confounding traits such as insulin secretion, insulin sensitivity and glucose tolerance. Our results are in agreement with experimental evidences suggesting that the renin–angiotensin system plays a role in the regulation of visceral adipose tissue accumulation.     

Carbon dioxide diffusion across stomata and mesophyll and photo-biochemical processes as affected by growth CO2 and phosphorus nutrition in cotton

Nutrients such as phosphorus may exert a major control over plant response to rising atmospheric carbon dioxide concentration (CO₂), which is projected to double by the end of the 21st century. Elevated CO₂ may overcome the diffusional limitations to photosynthesis posed by stomata and mesophyll and alter the photo-biochemical limitations resulting from phosphorus deficiency. To evaluate these ideas, cotton (Gossypium hirsutum) was grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.2, 0.05 and 0.01 mM) and two levels of CO₂ concentration (ambient 400 and elevated 800 μmol mol⁻¹) under optimum temperature and irrigation. Phosphate deficiency drastically inhibited photosynthetic characteristics and decreased cotton growth for both CO₂ treatments. Under Pi stress, an apparent limitation to the photosynthetic potential was evident by CO₂ diffusion through stomata and mesophyll, impairment of photosystem functioning and inhibition of biochemical process including the carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxyganase and the rate of ribulose-1,5-bisphosphate regeneration. The diffusional limitation posed by mesophyll was up to 58% greater than the limitation due to stomatal conductance (g_s) under Pi stress. As expected, elevated CO₂ reduced these diffusional limitations to photosynthesis across Pi levels; however, it failed to reduce the photo-biochemical limitations to photosynthesis in phosphorus deficient plants. Acclimation/down regulation of photosynthetic capacity was evident under elevated CO₂ across Pi treatments. Despite a decrease in phosphorus, nitrogen and chlorophyll concentrations in leaf tissue and reduced stomatal conductance at elevated CO₂, the rate of photosynthesis per unit leaf area when measured at the growth CO₂ concentration tended to be higher for all except the lowest Pi treatment. Nevertheless, plant biomass increased at elevated CO₂ across Pi nutrition with taller plants, increased leaf number and larger leaf area.     

Lovastatin biosynthesis by Aspergillus terreus with the simultaneous use of lactose and glycerol in a discontinuous fed-batch culture

The influence of various combinations of glycerol and lactose feed on the biosynthesis of two polyketide metabolites, lovastatin and (+)-geodin, by Aspergillus terreus ATCC20542 in a discontinuous fed-batch culture was presented. In these experiments lactose and/or glycerol were also used as the initial carbon substrates in the cultivation media. The application of glycerol feed, when lactose is the initial substrate, leads to the appreciable lovastatin concentration in the broth (122.4 mg l⁻¹), nevertheless the abundant (+)-geodin level is at the same time obtained (255.5 mg l⁻¹). The cultures with glycerol as the initial substrate and fed with lactose produce less lovastatin and (+)-geodin. The application of the various combined glycerol and/or lactose feeds allows for improving lovastatin production up to 161.8 mg l⁻¹ and decreases (+)-geodin concentration to 98.7 mg l⁻¹. The analysis of product formation rates and yield coefficients indicates that lovastatin is more efficiently produced on lactose, especially in the initial stages of the cultivation. Glycerol efficiently sustains fungal activity to form these polyketides in the late idiophase but it mainly favours (+)-geodin formation, if solely used in the feed. The feeds performed both with lactose and glycerol occur to be the most desired to maximise lovastatin and minimise (+)-geodin formation.