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P Deficiency (p + deficiency)
Selected AbstractsPhytoplankton production and growth rate in Lake Tanganyika: evidence of a decline in primary productivity in recent decadesFRESHWATER BIOLOGY, Issue 11 2007STEPHANE STENUITE Summary 1. This study focused on phytoplankton production in Lake Tanganyika. We provide new estimates of daily and annual primary production, as well as growth rates of phytoplankton, and we compare them with values published in former studies. 2. Chlorophyll- a (chl- a) in the mixed layer ranged from 5 to 120 mg chl- a m,2 and varied significantly between rainy and dry seasons. Particulate organic carbon concentrations were significantly higher in the south basin (with 196 and 166 mg C m,3 in the dry and the rainy season, respectively) than in the north basin (112 and 109 mg C m,3, respectively). 3. Carbon : phosphorus (C : P) ratios varied according to season. Phosphorus limitation seemed to occur more frequently than nitrogen limitation, especially during the rainy season. Severe P deficiencies were rare. 4. Measured particulate daily primary production ranged from 110 to 1410 mg C m,2 day,1; seasonal contrasts were well marked in the north basin, but less in the south basin, where primary production peaks occurred also in the rainy season. Estimates of annual primary production, based on daily primary production calculated from chl- a and water transparency, gave values lower than those reported in previous studies. Picophytoplankton accounted on average for 56% of total particulate production in the south basin during the wet season of 2003. 5. Phytoplankton growth rates, calculated from primary production, ranged from 0.055 to 0.282 day,1; these are lower than previously published values for Lake Tanganyika. [source] Citrate exudation from white lupin induced by phosphorus deficiency differs from that induced by aluminumNEW PHYTOLOGIST, Issue 3 2007B. L. Wang Summary ,,Both phosphorus (P) deficiency and aluminum (Al) toxicity induce root exudation of carboxylates, but the relationship between these two effects is not fully understood. Here, carboxylate exudation induced by Al in Lupinus albus (white lupin) was characterized and compared with that induced by P deficiency. ,,Aluminum treatments were applied to whole root systems or selected root zones of plants with limited (1 µm) or sufficient (50 µm) P supply. ,,Aluminum stimulated citrate efflux after 1,2 h; this response was not mimicked by a similar trivalent cation, La3+. P deficiency triggered citrate release from mature cluster roots, whereas Al stimulated citrate exudation from the 5- to 10-mm subapical root zones of lateral roots and from mature and senescent cluster roots. Al-induced citrate exudation was inhibited by P limitation at the seedling stage, but was stimulated at later growth stages. Citrate exudation was sensitive to anion-channel blockers. Al treatments did not affect primary root elongation, but inhibited the elongation of lateral roots. ,,The data demonstrate differential patterns of citrate exudation in L. albus, depending on root zone, developmental stage, P nutritional status and Al stress. These findings are discussed in terms of possible functions and underlying mechanisms. [source] Interactions between the effects of atmospheric CO2 content and P nutrition on photosynthesis in white lupin (Lupinus albus L.)PLANT CELL & ENVIRONMENT, Issue 5 2006CATHERINE D. CAMPBELL ABSTRACT Phosphorus (P) is a major factor limiting the response of carbon acquisition of plants and ecosystems to increasing atmospheric CO2 content. An important consideration, however, is the effect of P deficiency at the low atmospheric CO2 content common in recent geological history, because plants adapted to these conditions may also be limited in their ability to respond to further increases in CO2 content. To ascertain the effects of low P on various components of photosynthesis, white lupin (Lupinus albus L.) was grown hydroponically at 200, 400 and 750 µmol mol,1 CO2, under sufficient and deficient P supply (250 and 0.69 µm P, respectively). Increasing growth CO2 content increased photosynthesis only under sufficient growth P. Ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco) content and activation state were not reduced to the same degree as the net CO2 assimilation rate (A), and the in vivo rate of electron transport was sufficient to support photosynthesis in all cases. The rate of triose phosphate use did not appear limiting either, because all the treatments continued to respond positively to a drop in oxygen levels. We conclude that, at ambient and elevated CO2 content, photosynthesis in low-P plants appears limited by the rate of ribulose biphosphate (RuBP) regeneration, probably through inhibition of the Calvin cycle. This failure of P-deficient plants to respond to rising CO2 content above 200 µmol mol,1 indicates that P status already imposes a widespread restriction in plant responses to increases in CO2 content from the pre-industrial level to current values. [source] Interactions between atmospheric CO2 concentration and phosphorus nutrition on the formation of proteoid roots in white lupin (Lupinus albus L.)PLANT CELL & ENVIRONMENT, Issue 8 2002C. D. Campbell Abstract Atmospheric [CO2] affects photosynthesis and therefore should affect the supply of carbon to roots. To evaluate interactions between carbon supply and nutrient acquisition, the [CO2] effects on root growth, proteoid root formation and phosphorus (P) uptake capacity were studied in white lupin (Lupinus albus L.) grown hydroponically at 200, 410 and 750 µmol mol,1 CO2, under sufficient (0·25 mm P) and deficient (0·69 µm P) phosphorus. Plant size increased with increasing [CO2] only at high P. Both P deficiency and increasing [CO2] increased the production of proteoid clusters; the increase in response to increased [CO2] was proportionally greater from low to ambient [CO2] than from ambient to high. The activity of phosphoenol pyruvate carboxylase in the proteoid root, the exudation of organic acids from the roots, and the specific uptake of P increased with P deficiency, but were unaffected by [CO2]. Increasing [CO2] from Pleistocene levels to those predicted for the next century increased plant size and allocation to proteoid roots, but did not change the specific P uptake capacity per unit root mass. Hence, rising [CO2] should promote nutrient uptake by allowing lupins to mine greater volumes of soil. [source] Phosphorus requirement of common carp (Cyprinus carpio L) based on growth and mineralizationAQUACULTURE RESEARCH, Issue 3 2010L C Nwanna Abstract The effect of diets supplemented with varied levels of inorganic phosphorus (P) (NaH2PO4) on the growth, body composition, nutrient digestibility and mineralization in common carp (Cyprinus carpio L) was evaluated to determine the optimum P requirements. The six diets used were DPO, as the basal diet with a total P content of 1.30 g kg,1, and DP1, DP2, DP3, DP4 and DP5, which contained 4.10, 6.70, 11.6, 14.9 and 23.4 g P kg,1 respectively. Weight gain, SGR, apparent digestibility coefficient of organic matter and P, whole body ash, P, Ca and Mg increased significantly with increasing dietary P levels while dry matter (DM), fat and Zn content decreased. Feed conversion ratio was the poorest (P<0.05) in fish fed DPO, suggesting P deficiency. The apparent digestibility coefficient of P was 18% in the DPO-fed group, which increased from 69% in DP1 to 92% in DP5 after P supplementation, revealing lower digestibility of the native P than that in NaH2PO4. Broken-line analyses based on weight gain, P content of fish bones and whole body against total dietary and digestible P (data in brackets) contents showed the optimum P requirement for the growth of common carp to be 6.87 (5.55) g kg,1 DM, and the requirement for optimum mineralization in bones and whole body to be 9.10 (7.62) and 14.7 (13.2) g kg,1. [source] | ||||||||||