Phosphorus Regimes Research Articles

Reduced root cortical burden improves growth and grain yield under low phosphorus availability in maize.

Root phenes and phene states that reduce the metabolic cost of soil exploration may improve plant growth under low phosphorus availability. We tested the hypothesis that under low phosphorus, reduced living cortical area (LCA) would increase soil exploration, phosphorus capture, biomass, and grain yield. Maize genotypes contrasting in LCA were grown in the field and in greenhouse mesocosms under optimal and suboptimal phosphorus regimes. Percent LCA in nodal roots ranged from 25% to 67%. Plants with 0.2mm2 less LCA under low phosphorus had 75% less root segment respiration, 54% less root phosphorus content, rooted 20cm deeper, allocated up to four times more roots between 60 and 120cm depth, had between 20% and 150% more biomass, 35-40% greater leaf phosphorus content, and 60% greater grain yield compared with plants with high LCA. Low-LCA plants had up to 55% less arbuscular mycorrhizal colonization in axial roots, but this decrease was not correlated with biomass or phosphorus content. The LCA components cortical cell file number and cortical cell size were important for biomass and phosphorus content under low phosphorus. These results are consistent with the hypothesis that root phenes that decrease the metabolic cost of soil exploration are adaptive under phosphorus stress.

Grain Yield, Nutrient Accumulation and Fertilizer Efficiency in Bread Wheat under Variable Nitrogen and Phosphorus Regimes

Balanced crop nutrition is one of the important tools necessary for sustaining crop productivity, maintaining soil fertility and ensuring food security worldwide. Nitrogen and phosphorus are essential plant macronutrients, nevertheless, most of the Pakistani soils exhibit moderate to severe deficiency of these nutrients. Furthermore, considerable genetic variations exist among wheat genotypes for nutrient acquisition and utilization which illustrate their differential nutrient requirements to produce higher yields. A field experiment was conducted in order to formulate balanced fertilizer recommendations for newly evolved wheat genotype SD-998 to achieve maximum yield potential. Ten treatments viz., 0-0 (control), 90-23, 90-45, 90-70, 120-30, 120-60, 120-90, 150-40, 150-75 and 150-110 kg N-P2O5 ha-1 were applied according to randomized complete block design with three replications. Analysis of variance revealed that growth, yield and yield related attributes as well as nutrient accumulation were significantly (P ? 0.05) influenced by varying N and P rates. The maximum plant height (100.8 cm), number of tillers per plant (10), spike length (10.3 cm), number of grains per spike (66), 100-grain weight (4.10 g) and grain yield (4990 kg ha-1) was recorded in treatment having 150-110 kg N-P2O5 ha-1. The highest P recovery efficiency (20.8 %), agronomic N efficiency (19.4 kg kg-1) and agronomic P efficiency (36.8 kg kg-1) were attained at 120-30, 90-70 and 150-40 kg N-P2O5 ha-1, respectively. However, the highest total N accumulation (140.8 kg ha-1), P accumulation (21.0 kg ha-1), N recovery efficiency (71.1 %) and profit (Rs. 73625 ha-1) were noticed at 150 kg N plus 110 kg P2O5 ha-1. Thus, 150-110 kg N-P2O5 ha-1 (N:P2O5 in 4:3 ratio) was suggested as the most balanced and economical dose for the tested wheat genotype.

Agromorphological Performance and Character Association of Finger Millet under Varying Phosphorus Regimes

Finger millet production on more than 30% of world arable land is limited by P availability and more than 70% in the semi-arid and marginalized areas which covers most of the Sub-Saharan Africa. Phosphorus is one of the most important elements significantly affecting plant growth and metabolism. Three finger millet varieties (U-15, P-224 and Ikhulule) were evaluated under four P fertilizer levels (0, 12.5, 25 and 37.5 kg ha-1 P2O5) at the International Crops Research Institute for the Semi-Arid Tropics Station, Alupe and the Kenya Agricultural and Livestock Research Organization Station, Kakamega during the long and short rainy seasons of 2015 with the aim of determining their agromorphological response and trait associations. The on-station experiments were laid out in Randomized Complete Block Design in factorial arrangement with three replications. The statistical analysis of phosphorus levels and variety exhibited significant differences (P<0.05) to stand vigor, plant height, leaf blade length, number of leaves and lodging. The results revealed that application of 25 kg ha-1 P2O5 rate led to the tallest plants (65.0 cm), longest leaf blades (58.0 cm) and highest number of leaves per plant (16) at Alupe site while 37.5 kg ha-1 P2O5 rate eliciting the tallest plants (58.79 cm), longest leaf blades (51.44 cm) and highest number of leaves per plant (13) at Kakamega site. The highest rate led to the greatest vigor in both sites for both seasons while the control had the poorest vigor. Variety P-224 showed the highest lodging count with 32 out of 246 plants per experimental unit during the rainy season at Kakamega. The unit increase in grain yield was positively and significantly correlated with increased values of the harvest index (r=0.375), number of leaves (r=0.393) and plant height (r=0.431) but negatively and significantly correlated to the 1000-grain mass (r=-0.578) and lodging (r=-0.233). The best phosphorus treatment for most of the parameters was 25 kg ha-1 P2O5 at Alupe while maximum levels of the study parameters were realized under the 37.5 kg ha-1 P2O5 rate at Kakamega.

Agronomic bio-fortification and quality enhancement in okra–pea cropping system through arbuscular mycorrhizal fungi at varying phosphorus and irrigation regimes in Himalayan acid alfisol

ABSTRACTA field experimentation was conducted during 2009-2011 at CSK Himachal Pradesh Agricultural University, Palampur, India characterized with wet-temperate climate and acid Alfisol soil having medium available phosphorus content. The study aimed at bio-fortification and quality enhancement of okra (Abelmoschus esculentus)–pea (Pisum sativum) cropping system through arbuscular mycorrhizal fungi (AMF) (Glomus mosseae) at varying inorganic phosphorus (50, 75, and 100% soil-test-based recommended P dose) and irrigation regimes (40 and 80% available water capacity) in a Himalayan acid Alfisol. The results revealed that AMF and inorganic P significantly enhanced the concentrations and uptake of various primary [nitrogen (N), phosphorus (P), and potassium (K)]; secondary [calcium (Ca)]; and micronutrients [iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), boron (B), and molybdenum (Mo)] in okra and pea crops. However, effects of varying irrigation regimes were found to be nominal. In okra, AMF inoculation considerably enhanced N, P, K, B, and Mo uptake by 5, 19, 3, 4, and 15%, respectively, over their non-AMF counterparts. Likewise in pea, a higher amount of N (10%), P (26%), K (7%), Fe (7%), Cu (38%), Zn (20%), Mn (4%), B (7%), and Mo (13%) uptake was registered through AMF inoculation over their non-AMF counterparts. Application of soil-test-based P dose from 50% to 100% P also resulted in significant and consistent improvement in N, P, K, B, and Mo uptake both in okra and pea and in Zn, Cu, Mn, and Fe uptake in pea crop. Magnitude of increase in Ca content was to the tune of 13 and 4%, respectively, in okra fruits and pea pods following AMF inoculation, whereas crude protein content enhanced by 4% each in both the crops. Overall, the current study demonstrates the important role of AMF in nutrient enrichment and quality enhancement of okra and pea crops in acid Alfisol, besides considerable reduction in investment on chemical fertilizers. Results of current study suggest that AMF use in Himalayan production systems is of tremendous significance to harvest nutritionally-rich farm produce for Himalayan communities suffering from malnutrition especially anemia and Zn deficiency, and equally to resource-poor Himalayan farmers who ill-afford expensive external inputs.

Response of Microcystis aeruginosa Growth to Arsenate Under Different Phosphorus Regimes

To better understand and then to predict the ecological risk of arsenic influenced by phosphorus regimes in freshwater environment, the growth differences of Microcystis aeruginosa (M. aeruginosa) as well as its responses to the toxic stress of arsenate [As(Ⅴ)]were investigated under orthophosphate (DIP) and dissolved organic phosphorous (DOP) [adenosine triphosphate (ATP-P) and β-sodium glycerophosphate (β-P)] culture conditions. The results showed that M. aeruginosa grew and proliferated without any differences under DOP and DIP conditions during the first 5 days, while slower growth rates were observed in DOP conditions. Herein, the cell optical density (D) of M. aeruginosa in β-P and ATP-P conditions was 78.0% and 75.4% of that under DIP condition respectively on the 7th day. The negative correlations between actual quantum yield (Yield) and Chlorophyll a (Chl-a) and D indicated that Yield should not be used as a stable index to reflect the nutrition conditions of algae. However, Yield was a sensitive index to exactly represent the responses of M. aeruginosa to As(Ⅴ) toxicity, which showed significant differences under different phosphorus regimes. Obtained by D, Yield and Chl-a, the 96h EC50 was in the order of DIP > β-P > ATP-P. The similar toxic tolerant abilities to As(Ⅴ) of M. aeruginosa under β-P and ATP-P conditions were lower than that of EC50 under DIP conditions by one to five orders of magnitude.

Influence of AM fungi, inorganic phosphorus and irrigation regimes on plant water relations and soil physical properties in okra (Abelmoschus esculentus L.) – pea (Pisum sativum L.) cropping system in Himalayan acid alfisol

ABSTRACTPresent investigation studied plant water relations and soil physical properties through AM fungi (Glomus mosseae) to mitigate drought stress in Himalayan acid Alfisol having low water retentivity. Experimentation was carried out at Palampur, India during 2009–2011 in okra–pea cropping system in randomized block design (RBD) replicated thrice with 14 treatments comprising arbuscular mycorrhizal (AM) fungi, varying phosphorus nutrition and irrigation regimes at 40 and 80% available water holding capacity. Integrated use of AM fungi at varying phosphorus (P) levels and irrigation regimes led to significantly higher relative leaf water content (3% each) in okra and pea besides significantly higher xylem water potential (27%) in pea over non-AM fungi counterparts. AM fungi enhanced water-use-efficiency in okra (5–17%) and pea (12–35%) over non–AM fungi counterparts. AM fungi also improved water holding capacity (5–6%) and mean weight diameter of soil particles (4–9%) over non–AM fungi counterparts; but, had nominal or no effect on bulk density. Mycorrhizal plants maintained higher tissue water content imparting greater drought resistance to plants over non–mycorrhizal plants at moisture stress. It is inferred that integrated application of AM fungi and P at varying irrigation regimes improved the plant water relations vis-à-vis drought resistance, crop productivity, WUE, soil aggregation and water holding capacity in okra–pea sequence in Himalayan acid Alfisol.

Growth Behavior, Nutrient Harvest Index, and Soil Fertility in Okra-Pea Cropping System as Influenced by AM Fungi, Applied Phosphorus, and Irrigation Regimes in Himalayan Acidic Alfisol

The impact of arbuscular mycorrhizal fungi (AMF), inorganic phosphorus (P), and irrigation regimes was studied in an okra (Abelmoschus esculentus)–pea (Pisum sativum) cropping system in an acidic Alfisol. Experimentation was carried out at Palampur, India, in a randomized bock design (RBD), replicated three times with fourteen treatments comprising AM fungi (Glomus mosseae), inorganic phosphorus (50, 75, and 100% soil-test-based recommended P dose), irrigation regimes (at 40 and 80% available water capacity), generalized recommended NPK and irrigations (GRD), and farmers’ practice. Effects of AM fungi on plant height, leaf area index (LAI), and dry-matter accumulation (DMA) were nominal at early crop growth stage, i.e., 50 DAS (days after sowing). However, at 100 DAS, AMF imbedded treatments led to higher plant height (4%), LAI (3%), and DMA (6%) in okra, whereas in pea the magnitude of increase in these parameters following AMF inoculation was 6, 5, and 8%, respectively, over non-AMF counterparts. AMF + 75% soil-test-based P dose at either of these irrigation regimes gave statistically similar yields in both okra and pea as that obtained under 100% soil-test-based P dose at either of two irrigation regimes, thus indicating an economy of about 25% in soil-test-based P dose. Regarding nutrient harvest index in okra and pea, statistically similar values were registered with most nutrients under both AMF inoculated and non-AMF counterparts. In the case of okra, P harvest index was registered less by 3% with AMF inoculation; however, its magnitude increased by 3% in pea following AMF inoculation compared to non-AMF counterparts at similar levels of P and irrigation. At completion of two cycles of okra-pea system, AMF imbedded treatments did not alter available soil nutrient status significantly in comparison to non-AMF counterparts. Overall, current study suggests that practice of AMF inoculation has great potential in enhancing growth parameters for better productivity, fertilizer-P economy, and nutrient harvest efficiency in okra-pea production system in Himalayan acidic Alfisol.

The rice CK2 kinase regulates trafficking of phosphate transporters in response to phosphate levels.

Phosphate transporters (PTs) mediate phosphorus uptake and are regulated at the transcriptional and posttranslational levels. In one key mechanism of posttranslational regulation, phosphorylation of PTs affects their trafficking from the endoplasmic reticulum (ER) to the plasma membrane. However, the kinase(s) mediating PT phosphorylation and the mechanism leading to ER retention of phosphorylated PTs remain unclear. In this study, we identified a rice (Oryza sativa) kinase subunit, CK2β3, which interacts with PT2 and PT8 in a yeast two-hybrid screen. Also, the CK2α3/β3 holoenzyme phosphorylates PT8 under phosphate-sufficient conditions. This phosphorylation inhibited the interaction of PT8 with PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1, a key cofactor regulating the exit of PTs from the ER to the plasma membrane. Additionally, phosphorus starvation promoted CK2β3 degradation, relieving the negative regulation of PT phosphorus-insufficient conditions. In accordance, transgenic expression of a nonphosphorylatable version of OsPT8 resulted in elevated levels of that protein at the plasma membrane and enhanced phosphorus accumulation and plant growth under various phosphorus regimes. Taken together, these results indicate that CK2α3/β3 negatively regulates PTs and phosphorus status regulates CK2α3/β3.

Early stage growth responses of Saccharina latissima spores and gametophytes. Part 1: inclusion of different phosphorus regimes

Cultivation of Laminariales is an expanding industry and intensive investigations have been conducted in order to optimize the entire production chain from spore to sporophyte. However, despite intense research within the field, literature on the very early development of kelp microstages is scarce. In that perspective, the aim of the present study was to clarify the role of different phosphorus (P) regimes on the very early development of Saccharina latissima microstages using spores with different seasonal origin and thereby contribute to the optimization of cultivation conditions for the early life stages of the species. Results indicated that spores of S. latissima had to obtain a given size before developing into multicellular filamentous gametophytes, and this size was reached at least 2 weeks earlier in spores originating from April than in spores originating from February. Nutrient enrichment (P1–P5) had a profound positive effect on spore and gametophyte growth and development, when compared to natural nutrients levels (C), whereas increasing P levels within the range 23–69 μM phosphate-P did not induce any effect on growth of neither the spores nor the gametophytes with spores originating from April. Filamentous gametophytes appeared after 3 weeks cultivation of spores originating from April and although female gametophytes were recognizable approximately 1 week prior to male gametophytes, the female and males were found in the relation 1:1 in all nutrient treatments after 5 weeks cultivation.

Влияние удобрений и извести на агрохимические показатели и фосфатный режим дерново-подзолистой среднесуглинистой почвы

Влияние удобрений и извести на агрохимические показатели и фосфатный режим дерново-подзолистой среднесуглинистой почвы

Enhancing Plant Water Relations, Quality, and Productivity of Pea (Pisum sativum L.) through Arbuscular Mycorrhizal Fungi, Inorganic Phosphorus, and Irrigation Regimes in an Himalayan Acid Alfisol

The present investigation was carried out at Palampur, India, during 2009–11 to enhance plant water relations and productivity in pea through arbuscular mycorrhizal fungi (AMF) in a Himalayan acidic Alfisol. The field experiment was replicated three times in a randomized block design comprising 14 treatments involving AMF, inorganic phosphorus (P), irrigation regimes, generalized recommended nitrogen, phosphorus, and potassium (NPK) dose and irrigations, and farmers’ practice in the region. The study revealed that treatments involving AMF inoculation along with inorganic P nutrition at varying irrigation regimes led to significantly greater relative leaf water content (2%), xylem water potential (12%), and water-use efficiency (10%), respectively, in comparison with non-AMF inoculated counterparts. Similarly, maximum increase in quality parameters such as total soluble solids (6%), ascorbic acid (6%), and crude protein content (3%) in pea was registered under AMF inoculation involving treatments. Further, AMF-inoculated treatments indicated an economy of about 25% in soil-test-based P dose without impairing crop productivity.

Organic matter fractions in soil under coffee with split applications of phosphorus and water regimes

Phosphorus fertilization and irrigation management are essential practices to increase coffee yields, though information is scarce about the effect of these practices on organic matter fractions of soils of the ‘Cerrado’ (savanna-like vegetation). The purpose of this study was to evaluate organic matter fractions of a clayey Oxisol under coffee with split applications of phosphorus (P) and water regimes. The experimental design was a randomized block with 3 x 2 factorial arrangement with three split applications of P (P1: 300 kg ha-1 P2O5 applied annually of which 2/3 applied in September and 1/3 in December; P2: 600 kg ha-1 P2O5 applied at planting and every two years, and P3: 1800 kg ha-1 of P2O5 applied only at planting, corresponding to a 6-year requirement), two water regimes (with and without irrigation) and three replications. Soil from the 0-5 and 5-10 cm layers was sampled. The total organic carbon (TOC), labile carbon (LC), microbial carbon (Cmic), and carbon fractions of fulvic acid (FA), humic acid (HA) and humin (HU) were determined. The irrigation regime of coffee increased the TOC, LC and Cmic levels and the humified fractions of soil organic matter. In general, the form of P splitting had little influence on the fractions of soil organic matter.

Plasticity in stomatal size and density of potato leaves under different irrigation and phosphorus regimes

The morphological features of stomata including their size and density could be modulated by environmental cues; however, the underlying mechanisms remain largely elusive. Here, the effect of different irrigation and phosphorus (P) regimes on stomatal size (SS) and stomatal density (SD) of potato leaves was investigated. The plants were grown in split-root pots under two P fertilization rates (viz., 0 and 100mgkg−1 soil, denoted as P0 and P1, respectively) and subjected to full (FI), deficit (DI), and partial root-zone drying (PRD) irrigation regimes. Results showed that SS and SD were unresponsive to P but significantly affected by the irrigation treatment. FI plants had the largest SS, followed by DI, and PRD the smallest; and the reverse was the case for SD. Compared to FI and DI, PRD plants had significantly lower values of specific leaf area (SLA) and leaf carbon isotope discrimination (Δ13C) under P0. Midday leaf water potential (Ψleaf) and stomatal conductance (gs) was similar for DI and PRD, which was significantly lower than that of FI. Leaf contents of C, N, K, Ca and Mg were higher in PRD than in DI plants, particularly under P0. When analyzed across the three irrigation regimes, it was found that the P1 plants had significantly higher leaf contents of P and Mg, but significantly lower leaf K content compared to the P0 plants. Linear correlation analyses revealed that SS was positively correlated with Ψleaf and Δ13C; whereas SD was negatively correlated with Ψleaf, Δ13C and SLA, and positively correlated with leaf C, N and Ca contents. And gs was positively correlated with SS but negatively correlated with SD. Collectively, under low P level, the smaller and denser stomata in PRD plants may bring about a more efficient stomatal control over gas exchange, hereby potentially enhance water-use efficiency as exemplified by the lowered leaf Δ13C under fluctuating soil moisture conditions.

Low soil temperature inhibits the stimulatory effect of elevated [CO2] on height and biomass accumulation of white birch seedlings grown under three non‐limiting phosphorus conditions

White birch (Betula papyrifera Marsh.) seedlings were exposed to ambient or doubled ambient carbon dioxide concentration ([CO2]), three soil temperatures (Tsoil) (low, intermediate, high), and three phosphorus (P) regimes (low, medium, high) in environment‐controlled greenhouses. Height (H), root‐collar diameter (RCD), biomass, and leaf phosphorus concentration (leaf P) were determined four months after initiation of treatments. The low Tsoil reduced H, RCD, shoot biomass, root biomass and total seedling biomass whereas the high‐P level and the [CO2] elevation increased all the growth and biomass parameters. Elevated [CO2] significantly reduced leaf P. There were significant two‐factor interactions suggesting that the effect of elevated [CO2] on (1) H, total biomass, biomass of plant components, and leaf P was dependent on Tsoil, (2) total biomass was contingent on P regime. For instance, the positive response of H and total biomass to elevated [CO2] was limited to seedlings raised under the intermediate and high Tsoil, respectively. In addition, [CO2] elevation increased total biomass only at the high‐P regime but not at the low‐ or medium‐P level where the effect of [CO2] was statistically insignificant. No significant main effect of treatment or interaction was observed for root to shoot biomass ratio.

Fine mapping a major QTL for kernel number per row under different phosphorus regimes in maize (Zea mays L.)

Phosphorus (P) is one of the essential macronutrients for plant growth and development. Grain yield is the primary trait of interest in maize breeding programs. Maize grain yield and yield-related traits are seriously affected by P deficiency. Kernel number per row (KN), as one of the major components of grain yield, has attracted the attention of more and more breeders. In our previous study, one major QTL (named qKN), controlling KN under different P regimes was mapped to the interval between molecular markers bnlg1360 and umc1645 on chromosome 10 using a F 2:3 population derived from the cross between maize inbreds 178 and 5,003 (107). In order to understand its genetic basis, we developed a population of near isogenic lines (NILs) and two P regimes were used to fine map and characterize qKN. The QTL qKN was finally localized in a region of ~480 kb. A single qKN allele of inbred 178 increased KN by 6.08-10.76 % in the 5,003 (107) background; qKN acted in a partially dominant manner. Our results will be instrumental for the future identification and isolation of the candidate gene underlying qKN. The tightly linked molecular markers that we developed for qKN will be useful in maize breeding programs for improving KN applying the marker-assisted selection.

Phosphatase activities of cultured phototrophic biofilms

The responses of cultured phototrophic biofilms to diverse phosphorus (P) regimes were assessed using a semi-continuous flow incubator. Three biofilms were grown over 18 days under three different P regimes: replete inorganic P, organic P-only and limited inorganic P. Assessing the response of the biofilms took into account the rate of phosphomonoesterase and phosphodiesterase activities, biofilm nutrient contents and biomass accrual across the growth period. Phosphorus limitation was indicated by slower biomass accumulation and higher phosphatase activities of the organic P-only and P-limited biofilms compared to the P-replete biofilms. The cyanobacterium Phormidium sp. dominated the later stages in all the treatments forming a dense layer at the biofilm–medium interface. This layer possibly led to a reduction of light and nutrient diffusion to sub-surface cells and may account for the production of phosphatases under P replete conditions. In addition, the Phormidium-layer possibly produced a top-heavy P (and N) distribution and could explain the large reductions in areal nutrient concentrations. End-product repression and de-repression of phosphatase activity was suggested to be a main controlling factor of phosphatase activity. Consequently, it is proposed that for efficient nutrient removal from wastewaters that biofilms should be regularly removed to continually maintain biofilms at the initial stages (3–7 days).

Patterns of activities of root phosphomonoesterase and phosphodiesterase in wetland plants as a function of macrophyte species and ambient phosphorus regime

Phosphorus (P)-limited plants produce higher amounts of root phosphatases, but research has mostly focused on phosphomonoesterases (PMEs). Because phosphate diesters can form a significant proportion of organic P in wetlands, we aimed to determine whether wetland plants produce both root PMEs and root phosphodiesterases (PDEs), and, if so, what factors influence activities of these enzymes. We measured the activities of root PMEs and PDEs colorimetrically in a wide range of macrophytes from natural and P-enriched wetlands. Hydrolyzable P in sediments was analyzed using commercially available PMEs and PDEs. In all species, both root PMEs and PDEs were always present, and their activities were closely correlated. Sedges and broadleaved emergents had the highest activity of both enzymes, while those of floating-leaved plants were the lowest. Redundancy analysis revealed close association between root enzymes and the proportion of monoesterase- and diesterase-hydrolyzable dissolved unreactive P. Both enzymes were positively correlated with root tissue N : P ratio. Both plant and sediment traits were important when explaining differences in enzyme activities. Although the activities are related to ambient P regime, the relationship was not close enough to use root enzymes as reliable predictors of dissolved unreactive P that is hydrolyzed by sediment phosphomono- and diesterases.

Acúmulo de micronutrientes em porta-enxerto cítrico micorrizado em diferentes doses de fósforo

Com o objetivo de se estudar a influência de doses altas de P e fungo micorrízico arbuscular, na partição de nutrientes absorvidos por porta-enxerto de citros, instalou-se experimento com quatro níveis de P (0, 50, 150 e 250 mg kg-1 de solo), sem e com fungo micorrízico arbuscular (Glomus intraradices). Determinaram-se os micronutrientes (Cu, Fe, Mn e Zn) nas raízes, caules e folhas de Tangerineira “Cleópatra”, Citrus reshni (Rutaceae). Os resultados sugerem o acúmulo de Cu, Fe, Mn e Zn nas raízes de plantas micorrizadas nas doses mais altas de P, o que pode afetar processos fisiológicos vitais e impactar a produção de mudas e interferir na resistência a doenças em citros

Long-term variability of oxygen and mineral phosphorus concentrations in Lake Dal’nee (Kamchatka)

Many-year data on the concentrations of O2 and mineral phosphorus in a fattening-spawning water body for the Pacific salmon (red salmon) are presented; the seasonal and year-to-year dynamics of these con-centrations are analyzed. It is found that the lake water mass features a high concentration of O2, the upper 20-m layer being most aerated. It is shown that the year-to-year variability of the concentration of O2 dissolved in the lake water depends on the amount of organic matter coming with groundwater and surface runoff. The oxygen and phosphorus regimes of the lake at low and abundant entries of puberal red salmon for spawning are considered.

Elevated CO2 alleviates the effects of low P on the growth of N2-fixing Acacia auriculiformis and Acacia mangium

Nodulated seedlings of Acacia auriculiformis Cunn. ex Benth and Acacia mangium Willd were grown with different phosphorus (P) regimes for 90 days, and half of them were exposed to elevated CO2 (800 μl l−1) during the last 30 days. Under ambient CO2, plant growth and the amount of N fixed symbiotically in N2-fixing seedlings decreased with the decrease of supplied P; this relationship did not occur under elevated CO2. The increase in plant biomass by elevated CO2 at low P was accompanied by the increase in internal P use efficiency, the amount of N fixed symbiotically and N use efficiency. Elevated CO2 recovered the low P-induced reduction in leaf dry matter per unit area or unit fresh weight, but it had no effect on the low P-induced increase in partitioning dry matter to roots. These results suggest that elevated CO2 alleviates the low P effect mainly by increasing the use efficiency of internal P for plant growth and symbiotic N2 fixation, and the source-sink relationship is possibly an important driving force for this effect of elevated CO2 in A. auriculiformis and A. mangium.