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Total P (total + p)
Kinds of Total P Selected AbstractsAnalysis of genetic influences on the consistency and variability of the Big Five across different stressful situationsEUROPEAN JOURNAL OF PERSONALITY, Issue 5 2001Gerty Lensvelt-Mulders Several studies have demonstrated that individual differences in personality traits, known as the Big Five, have a genetic component. These personality traits are considered important predictors of everyday behaviour. In addition to personality traits there are also factors in the environment that govern behaviour. This dual influence on behaviour is statistically reflected in a P,×,S interaction. This study examines the genetic and environmental influences on the interactions between a person and his daily life environment for the Big Five. Fifty-seven identical twin pairs and 43 fraternal twin pairs participated in this study. Trait related behaviour was measured in 30 different situations with the aid of an SR inventory. The heritability coefficients for the main effect of P were in the normal range, varying between 0.35 for Agreeableness and 0.53 for Conscientiousness. The heritability coefficients for the P,×,S interactions were moderately high, explaining between 26% and 69% of the total P,×,S variance. The consequences of these results for general and behavioural genetic research on the Big Five will be discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Preferential phosphorus leaching from an irrigated grassland soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2005G. S. Toor Summary Intact lysimeters (50 cm diameter, 70 cm deep) of silt loam soil under permanent grassland were used to investigate preferential transport of phosphorus (P) by leaching immediately after application of dairy effluent. Four treatments that received mineral P fertilizer alone (superphosphate at 45 kg P ha,1 year,1) or in combination with effluent (at , 40,80 kg P ha,1 year,1) over 2 years were monitored. Losses of total P from the combined P fertilizer and effluent treatments were 1.6,2.3 kg ha,1 (60% of overall loss) during eight drainage events following effluent application. The rest of the P lost (40% of overall loss) occurred during 43 drainage events following a significant rainfall or irrigation compared with 0.30 kg ha,1 from mineral P fertilizer alone. Reactive forms of P (mainly dissolved reactive P: 38,76%) were the dominant fractions in effluent compared with unreactive P forms (mainly particulate unreactive P: 15,56%). In contrast, in leachate following effluent application, particulate unreactive P was the major fraction (71,79%) compared with dissolved reactive P (1,7%). The results were corroborated by 31P nuclear magnetic resonance analysis, which showed that inorganic orthophosphate was the predominant P fraction present in the effluent (86%), while orthophosphate monoesters and diesters together comprised up to 88% of P in leachate. This shows that unreactive P forms were selectively transported through soil because of their greater mobility as monoesters (labile monoester P and inositol hexakisphosphate) and diesters. The short-term strategies for reducing loss of P after application of dairy effluent application should involve increasing the residence time of applied effluent in the soil profile. This can be achieved by applying effluent frequently in small amounts. [source] Analysis of phosphorus in two humic acid fractions of intensively cropped lowland rice soils by 31P-NMREUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2000N. Mahieu Summary The organic forms of phosphorus in the soil appear to be changing as rice growing intensifies and the soil is flooded for longer in tropical Asia. To examine these changes, we extracted the labile mobile humic acid (MHA) and more recalcitrant calcium humate (CaHA) fractions from soils supporting long-term field trials in the Philippines and analysed them by solution 31P-nuclear magnetic resonance (NMR) spectroscopy. Diester P and sugar-diester P accumulated moderately with increasing intensity of irrigated rice cropping, reaching a combined 42% of all MHA-P for a triple-cropped irrigated field compared with 28% for fully aerated fields growing dryland crops. The mono- to diester P ratio decreased by 43% for the MHA and CaHA from the aerated fields to the triple-cropped field. Smaller effects on forms of P were noted for the rates and type of N, P and K fertilizer and site effects. The effects of treatment and site were more noticeable in the MHA than in the CaHA. The proportions in the NMR spectra were tightly correlated with visible light absorption, concentrations of organic free radicals and H, and 15N-NMR spectral proportions, which indicate the degree of humification. The MHA and CaHA accounted for only 0.6,8.3% and 0.9,5.7%, respectively, of total P; most of the P is inorganic. [source] The effects of Daphnia on nutrient stoichiometry and filamentous cyanobacteria: a mesocosm experiment in a eutrophic lakeFRESHWATER BIOLOGY, Issue 7 2002M. J. PATERSON 1.,Stoichiometric theory predicts that the nitrogen : phosphorus (N : P) ratio of recycled nutrients should increase when P-rich zooplankton such as Daphnia become dominant. We used an enclosure study to test the hypothesis that an increased biomass of Daphnia will increase the relative availability of N versus P sufficiently to decrease the abundance of filamentous cyanobacteria. The experiment was conducted in artificially enriched Lake 227 (L227) in the Experimental Lakes Area (ELA), north-western Ontario, Canada. Previous studies in L227 have shown that the dominance of filamentous, N-fixing cyanobacteria is strongly affected by changes in the relative loading rates of N and P. 2.,We used a 2 × 2 factorial design with the addition or absence of D. pulicaria and high or low relative loading rates of N and P (+NH4, ,NH4) in small enclosures as treatment variables. If Daphnia can strongly affect filamentous cyanobacteria by altering N and P availability, these impacts should be greatest with low external N : P loading rates. The phytoplankton community of L227 was predominantly composed of filamentous Aphanizomenon spp. at the start of the experiment. 3.,Daphnia strongly reduced filamentous cyanobacterial density in all enclosures to which they were added. The addition of NH4 had only a small impact on algal community composition. Hence, we conclude that Daphnia did not cause reductions in cyanobacteria by altering the N : P ratio of available nutrients. 4.,Despite the lack of evidence that Daphnia affected filamentous cyanobacteria by altering the relative availability of N and P, we found changes in nutrient cycling consistent with other aspects of stoichiometric theory. In the presence of Daphnia, total P in the water column decreased because of an increase in P sedimentation. In contrast to P, a decrease in suspended particulate N was offset by an increase in dissolved N (especially NH4). Hence, dissolved and total N : P ratios in the water column increased with Daphnia as a result of differences in the fate of suspended particulate N versus P. There was minimal accumulation and storage of P in Daphnia biomass in the enclosures. 5.,Our experiment demonstrated that Daphnia can strongly limit filamentous cyanobacterial abundance and affect the biogeochemical cycling of nutrients. In our study, changes in nutrient cycling were apparently insufficient to cause the changes in phytoplankton community composition that we observed. Daphnia therefore limited filamentous cyanobacteria by other mechanisms. [source] Interregional comparisons of sediment microbial respiration in streamsFRESHWATER BIOLOGY, Issue 2 2000B. H. Hill Summary 1The rate of microbial respiration on fine-grained stream sediments was measured at 371 first to fourth-order streams in the Central Appalachian region (Maryland, Pennsylvania, Virginia, and West Virginia), Southern Rocky Mountains (Colorado), and California's Central Valley in 1994 and 1995. 2Study streams were randomly selected from the United States Environmental Protection Agency's (USEPA) River Reach File (RF3) using the sample design developed by USEPA's Environmental Monitoring and Assessment Program (EMAP). 3Respiration rate ranged from 0 to 0.621 g O2 g -1 AFDM h -1 in Central Appalachian streams, 0-0.254 g O2 g -1 AFDM h -1 in Rocky Mountain streams, and 0-0.436 g O2 g -1 AFDM h -1 in Central Valley streams. 4Respiration was significantly lower in Southern Rocky Mountain streams and in cold water streams (< 15 °C) of the Central Appalachians. 5Within a defined index period, respiration was not significantly different between years, and was significantly correlated with stream temperature and chemistry (DOC, total N, total P, K, Cl, and alkalinity). 6The uniformity of respiration estimates among the three study regions suggests that sediment microbial respiration may be collected at any number of scales above the site-level for reliable prediction of respiration patterns at larger spatial scales. [source] Shifts in leaf N : P ratio during resorption reflect soil P in temperate rainforestFUNCTIONAL ECOLOGY, Issue 4 2008Sarah J. Richardson Summary 1Large-scale syntheses of leaf and litter N and P concentrations have demonstrated that leaf and litter N : P ratios both decline with latitude, that litter N : P ratios are generally greater than those of fresh leaves, and that the difference between these two ratios increases towards the tropics. These patterns have been ascribed to either a direct effect of temperature on plant growth rates and leaf-level physiology, or a decline in soil P towards the tropics. We test the hypothesis that global patterns of leaf and litter N : P ratios reflect a soil-P gradient by examining leaf and litter N : P in all species from a temperate rainforest along a soil-P gradient. 2The soil P gradient followed a toposequence of 20 plots. There was > 50-fold variation in soil total P from ridges (23,136 mg kg,1), through faces and terraces (32,744 mg kg,1), to gullies (440,1214 mg kg,1). 3The N : P ratios of leaves and litter both declined as soil total P increased, and the N : P ratio of litter was greater than that of fresh leaves. The difference between litter N : P and fresh leaf N : P declined with increasing soil total P supporting the hypothesis that global patterns of N : P ratios reflect gradients of soil P. 4Compositional turnover with soil P partly contributed to the total plant community leaf and litter nutrient concentration responses. However, consistent within-species responses pointed to a soil-based mechanism for determining responses by the total plant community. 5Comparisons of our litter data to global data sets suggest that the vegetation was well adapted to low soil nutrient concentrations with 37% of litter N and 24% of litter P samples being below published thresholds for highly proficient nutrient resorption. 6The range of leaf N and leaf P concentrations at our site captured a large portion of the range reported in global leaf trait data sets. 7Highly proficient P resorption was responsible for the divergence in leaf and litter N : P ratios on P-poor soils. These results emphasize the significance of proficient nutrient resorption as an advantageous plant trait for nutrient conservation on P-poor soils. [source] Seasonal changes in herbage production and soil phosphorus contents in Japanese lawngrass (Zoysia japonica Steud.) and tall fescue (Festuca arundinacea Schreb.) pasturesGRASSLAND SCIENCE, Issue 1 2008Makoto Kaneko Abstract Seasonal changes in the above-ground phosphorus (P), soil total P (TP), soil Olsen P (OP) and soil microbial biomass P (MBP) were investigated for 2 years in Japanese lawngrass (Zy) and tall fescue (Tf) pastures on Japanese Andosol, with the goal of clarifying P characteristics in the Zy pasture in comparison with the Tf pasture. The soil P attributes were measured in two soil layers (root mat layer, 0,2.5 cm depth; under layer, 5,10 cm depth). The P concentration of the above-ground herbage in the Zy pasture, which was higher than the standard value and similar to those in the Tf pasture, might have contributed to the large amounts of the above-ground P mass. The lack of plowing management and the coverage with Japanese lawngrass might have changed soil TP. The TP, the OP and the OP/TP in the Zy pasture were higher than those in the Tf pasture, and the TP, the OP and the OP/TP at the root mat layer were higher than those at the under layer. A large amount of the TP and high P availability in the soil caused the large amounts of OP. Soil pH, soil microorganisms and MBP might have affected soil P availability in the Zy pasture. Plant litter in the root mat layer of the Zy pasture may have increased soil P accumulation and its availability, which might be reasons for the high P uptake in the present study. Japanese lawngrass pasture may be a system with improved soil P utilization efficiency based on P cycling. [source] THE ROLE OF PERIPHYTON IN PHOSPHORUS RETENTION IN SHALLOW FRESHWATER AQUATIC SYSTEMSJOURNAL OF PHYCOLOGY, Issue 5 2003Article first published online: 26 SEP 200, Walter K. Dodds Eutrophication caused by phosphorus (P) leads to water quality problems in aquatic systems, particularly freshwaters, worldwide. Processing of nutrients in shallow habitats removes P from water naturally and periphyton influences P removal from the water column in flowing waters and wetlands. Periphyton plays several roles in removing P from the water column, including P uptake and deposition, filtering particulate P from the water, and attenuating flow, which decreases advective transport of particulate and dissolved P from sediments. Furthermore, periphyton photosynthesis locally increases pH by up to 1 unit, which can lead to increased precipitation of calcium phosphate, concurrent deposition of carbonate-phosphate complexes, and long-term burial of P. Actively photosynthesizing periphyton can cause super-saturated O2 concentrations near the sediment surface encouraging deposition of metal phosphates. However, anoxia associated with periphyton respiration at night may offset this effect. Linking the small-scale functional role of periphyton to ecosystem-level P retention will require more detailed studies in a variety of ecosystems or large mesocosms. A case study from the Everglades illustrates the importance of considering the role of periphyton in P removal from wetlands. In general, periphyton tends to increase P retention and deposition. In pilot-scale constructed periphyton-dominated wetlands in South Florida, about half of the inflowing total P was removed. [source] Spatial variability of sequentially extracted P fractions in a silty loamJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2005Elena Heilmann Abstract Knowledge of the spatial distribution of soil P forms in agricultural fields is important for evaluating the risk of P transfer to waterways. The objective of this study was to characterize the spatial variation of total P (Pt) and sequentially extracted P forms in the Ap horizon of arable soils at the field scale. Soil samples were taken on a regular grid of 50 m × 50 m with 40 sampling points. Chemical analyses included basic soil properties, Pt, sequentially extracted P forms, and acid phosphomonoesterase activity. The spatial variability was analyzed by geostatistics and descriptive statistics. The concentrations of Pt ranged from 521 to 1020 mg,kg,1 with lower values observed for Gleysols and Stagnic Phaeozems and higher values for Luvisols and Cambisols. For the sequentially extracted P fractions, the largest coefficients of variation (c.v.) were found for NaHCO3 -Po (41%), NaHCO3 -Pi (36%), NaOH-Po (34%), and resin-P (33%). Despite this great spatial variability, no spatial dependence could be proved by geostatistics because the calculated range of P forms (<10 m) was below the smallest sampling distance (50 m). A clear trend of increasing concentrations and proportions of organic NaHCO3 - and NaOH-P fractions and phosphomonoesterase activity towards lower slope positions and the discharging brook indicated that Gleysols were a particular source of P losses to waterways in this catchment. It was concluded that these soils require a specific management with reduced P inputs and, perhaps, chemical treatment to fix leachable P. Räumliche Variabilität sequenziell extrahierter P-Fraktionen in einem Schlufflehm Kenntnisse über die räumliche Verteilung der P-Formen in landwirtschaftlichen Flächen sind notwendig für die Abschätzung des Risikos von P-Austrägen. Gegenstand dieser Untersuchung war die räumliche Verteilung von Gesamt-P (Pt) und P-Formen im Ap-Horizont von landwirtschaftlich genutzten Böden im Feldmaßstab. Dazu wurden Proben auf einem Raster von 50 m × 50 m an 40 Punkten entnommen. Die chemischen Analysen umfassten Grundeigenschaften sowie Pt, sequenziell extrahierte P-Formen und die Aktivität der sauren Phosphomonoesterase. Die räumliche Variabilität wurde mit räumlicher und deskriptiver Statistik untersucht. Die Pt -Gehalte lagen im Bereich von 521 bis 1020 mg,kg,1, wobei Gleye und Pseudogleye die niedrigsten Werte hatten. Bei den sequenziell extrahierten P-Fraktionen wurden die größten Variationskoeffizienten für NaHCO3 -Po (41%), NaHCO3 -Pi (36 %), NaOH-Po (34 %) und Harz-P (33 %) festgestellt. Trotz dieser großen räumlichen Variabilität konnte mit Geostatistik keine räumliche Abhängigkeit nachgewiesen werden, möglicherweise weil die geschätzte Reichweite der P-Formen mit <10 m unterhalb der kleinsten Beprobungsdistanz von 50 m lag. Deutliche gerichtete Trends steigender Gehalte und Anteile organischer NaHCO3 - und NaOH-P-Fraktionen und Phosphomonoesterase-Aktivitäten hin zu niedrigeren Geländepositionen und zur Nachbarschaft zu dem entwässernden Bach deuteten darauf hin, dass insbesondere Gleye eine Quelle der P-Einträge in Oberflächengewässer des Einzugsgebietes sein können. Es ergibt sich daher die Schlussfolgerung, dass diese Böden einer teilschlagspezifischen Bewirtschaftung mit reduzierten P-Zufuhren und eventuell P-fixierenden Behandlungen bedürfen. [source] Effect of phosphate fertilization on crop yield and soil phosphorus status,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2003Anne Gallet Abstract To evaluate the effect of three phosphorus (P) fertilization regimes (no P, P input equivalent to P off-take by crops, P input higher than P off-take) on crop yield, P uptake, and soil P availability, seven field experiments (six in crop rotations, one under permanent grassland) were conducted in Switzerland during nine years (six trials) or 27 years (one trial). Soil total P (Pt), inorganic P (Pi), organic P (Po), and the amount of isotopically exchangeable soil P were measured in the 0,20,cm and 30,50,cm layers of the arable soils and in the 0,10,cm layer of the permanent grassland soil. Omitting P fertilization resulted in significant yield decreases only in one field crop trial as the amount of P isotopically exchangeable within one minute (E1min) reached values lower than 5 mg P (kg soil),1. In the absence of P fertilization Pi decreased on average from 470 to 410 mg P (kg soil),1 in the upper horizon of 6 sites while Po decreased only at two sites (from 510 to 466 mg P (kg soil),1 on average). In all the treatments of the trials started in 1989 the E1min values of the upper horizon decreased on average from 15.6 to 7.4 mg P (kg soil),1 between 1989 and 1998. These decreases were also observed when P inputs were higher than crops needs, showing that in these soils the highest P inputs were not sufficient to maintain the high initial available P levels. Finally for the six arable trials the values of the isotopic exchange kinetics parameters (R/r1, n, CP) and P exchangeable within 1 minute (E1min) at the end of the experiment could be estimated from the values measured at the beginning of trial and the cumulated P balance. Der Einfluss der Phosphordüngung auf den Pflanzenertrag und den Phosphorstatus des Bodens Die Begrenzung der Düngung mit Phosphat (P) bei Böden, die bereits hohe Gehalte an verfügbarem P aufweisen, kann zur Verringerung der P-Verluste in Oberflächen- und Grundwasser beitragen. Sieben Feldversuche (6 Versuche mit Ackerkulturen, 1 Versuch mit Dauerwiese) wurden während 9 Jahren (6 Versuche) resp. 27 Jahren (1 Versuch) durchgeführt mit dem Ziel, den Einfluss von drei Düngungsraten (keine P-Gabe, P-Gabe entsprechend dem P-Entzug durch die Pflanzen und P-Gabe höher als der P-Entzug durch die Pflanzen) auf Pflanzenertrag, P-Aufnahme und P-Verfügbarkeit zu studieren. Die Gehalte an anorganischem P (Pi) und organischem P (Po), sowie deren Summe (Pt) und die Gehalte an isotopisch austauschbarem P wurden in den Bodentiefen von 0,20,cm und 30,50,cm der ackerbaulichen Versuche und in einer Bodentiefe von 0,10,cm in der Dauerwiese gemessen. Der Verzicht auf P-Düngung führte nur in einem der ackerbaulichen Versuche zu einer signifikanten Abnahme des Pflanzenertrags, wobei der Gehalt an isotopisch austauschbarem P (E1min) unter 5 mg P (kg Boden),1 fiel. Pi sank bei Verzicht auf P-Düngung im oberen Horizont von 6 Böden durchschnittlich von 470 auf 410 mg P (kg Boden),1, während Po nur in 2 Böden absank (durchschnittlich von 510 auf 466 mg P (kg Boden),1). Ueber alle Düngungsverfahren jener Versuche, die 1989 begonnen hatten, sank E1min im oberen Horizont von 1989 bis 1998 durchschnittlich von 15.6 auf 7.4 mg P (kg Boden),1. Die Abnahme wurde auch beobachtet, wenn die P-Gabe höher war als der P-Entzug durch die Pflanzen, was zeigt, dass in diesen Böden selbst die höchste P-Gabe nicht genügte, um den ursprünglich hohen Gehalt an verfügbarem P aufrecht zu erhalten. Schließlich wurden in den 6 ackerbaulichen Versuchen die Parameter der Isotopenaustauschkinetik (R/r1, n, CP) und E1min am Ende des Versuches mit den ursprünglichen Werten zu Beginn des Versuchs verglichen. Es ergaben sich signifikante Beziehungen zwischen den Werten am Ende des Versuchs einerseits und den ursprünglichen Werten und der P-Bilanz andererseits. [source] Grass-Shrub Riparian Buffer Removal of Sediment, Phosphorus, and Nitrogen From Simulated Runoff,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2007Kyle R. Mankin Abstract:, Riparian buffer forests and vegetative filter strips are widely recommended for improving surface water quality, but grass-shrub riparian buffer system (RBSs) are less well studied. The objective of this study was to assess the influence of buffer width and vegetation type on the key processes and overall reductions of total suspended solids (TSS), phosphorus (P), and nitrogen (N) from simulated runoff passed through established (7-year old) RBSs. Nine 1-m RBS plots, with three replicates of three vegetation types (all natural selection grasses, two-segment buffer with native grasses and plum shrub, and two-segment buffer with natural selection grasses and plum shrub) and widths ranging from 8.3 to 16.1 m, received simulated runoff having 4,433 mg/l TSS from on-site soil, 1.6 mg/l total P, and 20 mg/l total N. Flow-weighted samples were collected by using Runoff Sampling System (ROSS) units. The buffers were very efficient in removal of sediments, N, and P, with removal efficiencies strongly linked to infiltration. Mass and concentration reductions averaged 99.7% and 97.9% for TSS, 91.8% and 42.9% for total P, and 92.1% and 44.4% for total N. Infiltration alone could account for >75% of TSS removal, >90% of total P removal, and >90% of total N removal. Vegetation type induced significant differences in removal of TSS, total P, and total N. These results demonstrate that adequately designed and implemented grass-shrub buffers with widths of only 8 m provide for water quality improvement, particularly if adequate infiltration is achieved. [source] Effect of land use on some soil properties related to the risk of loss of soil phosphorusLAND DEGRADATION AND DEVELOPMENT, Issue 1 2008F. Troitiño Abstract Although land use clearly modifies soil properties, the intensity of the modifications depends on the management procedures and also on the soil properties themselves. To enable construction of models that describe soil nutrient losses, extensive databases corresponding to soils under different land use must be made available. Analysis of 404 samples of soils (from Galicia, NW Spain), under different types of use revealed that most of the soil properties underwent changes in the following order: forest use (least modified) - grassland - arable (most modified). Decreases in the contents of organic matter, extractable oxides and P-adsorption capacity followed the same order, as did increases in the contents of available P (total, inorganic and organic), P desorbed with distilled water, and degree of P saturation. In general, in all of the soils, independently of their use, the amount of P desorbed (whether total P, molybdate reactive P or particulate P) was more closely related to the degree of P saturation than to the levels of P extracted with bicarbonate. Copyright © 2007 John Wiley & Sons, Ltd. [source] Quantifying the effect of catchment land use and water nutrient concentrations on freshwater river and stream biodiversityAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2009M. J. Weijters 1.A major threat to freshwater taxon diversity is the alteration of natural catchment Land use into agriculture, industry or urban areas and the associated eutrophication of the water. In order to stop freshwater biodiversity loss, it is essential to quantify the relationships between freshwater diversity and catchment Land use and water nutrient concentrations. 2.A literature survey was carried out on biodiversity data from rivers and streams. Fish and macroinvertebrates were selected as focal groups as they are widely used as indicator species of river and stream health. Only published data were selected that (a) compared data found at impaired sites with a pristine reference situation (either in time or space), (b) clearly defined the stressors studied (Land use cover and/or nutrient concentrations), and (c) clearly defined biodiversity (number of native species, species lists or IBI-scores). 3.The number of native taxa found in each study was transferred in an index of relative taxon richness (RTR) ranging from 0 (severely altered) to 100 (pristine reference conditions). Only those taxa were included that were (at least) present in the most pristine situation. This made it possible to combine, compare and analyse results from different studies. Catchment Land use was expressed as the percentage of non-natural Land use (agriculture, industry, housing or mining). As a measure of nutrients, the concentrations of NO3, NH4, PO4, total N and total P in the river and stream water were used. 4.Over 240 published articles have been studied, but only 22 met the criteria described above and could be used for further analysis. 5.This study showed that altered catchment Land use has a major effect on freshwater biodiversity and that the rate of species loss is serious; on average every 10% of lost natural catchment Land use cover leads to a loss of almost 6% (±0.83) of the native freshwater fish and macroinvertebrate species. Copyright © 2008 John Wiley & Sons, Ltd. [source] Labile Phosphorus in Soils of Forest Fallows and Primary Forest in the Bragantina Region, BrazilBIOTROPICA, Issue 1 2003Jacqueline Frizano ABSTRACT We used the Hedley sequential extraction procedure to measure nine different organic inorganic soil phosphorus fractions in forest soil of the Bragantina region of Para, Brazil. We compared the labile fractions (resin-extractable P + HCO3-extractable inorganic and organic P) in Oxisols from three secondary forests (10, 20, and 40 years old) and a primary forest. These stands were located in an area that has supported shifting agriculture for approximately a century. After agricultural use, total P and labile P in soils of young secondary forests are diminished compared to the amounts presents in the primary forest soil. Within each stand, organic carbon content was a good predictor of labile organic and inorganic P, consistent with the large body of research indicating that mineralization of organic matter is important to plant nutrition in tropical ecosystems. During the reorganization of P pools during forest development, the pool of labile organic P (HCO3-extractable) diminishes more than the other labile fractions, suggesting that it is directly or indirectly an important source of P for the regrowing forest vegetation. Across the four age classes of forest, the soil reservoir of labile P was equal to or greater than the total amount of P in the vegetation. If labile P measured by this method adequately represents P available to plants in the short term (as suggested by the current consensus), we would conclude that plant-available P is reasonable abundant, and that the effects of agriculture on available P pools are detectable but not sufficient to compromise forest regrowth in this area. [source] Nitrogen and Phosphorus Release from Decomposing Leaves under Sub-Humid Tropical Conditions,BIOTROPICA, Issue 2 2001A. B. Kwabiah ABSTRACT For many soils of the tropics, inputs of organic materials are essential to sustain soil fertility and crop production. Research in the quality of organic inputs, a key factor controlling rates of decomposition and nutrient release, continues to guide selection and use of organic materials as nutrient sources. The relationship between decomposition patterns and the quality parameters of the fresh leaves of six agroforestry species: Sesbania sesban, Croton megalocarpus, Calliandra calothyrsus, Tithonia diversifolia, Lantana camara, and Senna spectabilis, was investigated in a litterbag study over a period of 77 days in the highlands of western Kenya. The litterbags were buried 1 cm below the soil surface and covered with soil of ca 1 cm thickness. Percent leaf mass and total N and P that remained with time strongly correlated with total P and C/P ratio (R2= 0.60-0.90) during the first 35 days of study; but afterwards, correlation was stronger with the initial soluble polyphenolics (Pp)/P ratio (R2= 0.69-0.92) than with total P and C/P ratio. Loss of leaf mass and release of N and P followed the exponential function, yt= y0* e- kt, from which the specific decay rate constants (k) were calculated for loss of leaf mass (kB) and release of N (kN) and P (Kp). Among the plant species, the k values were lowest in Calliandra with kB= 0.012/d, kN= 0.017/d and kp= 0.044/d. Lantana had the highest K values with kg= 0.067/d and kp= 0.119/d, but the highest kN value of 0.109/d occurred in Tithonia. The kB values for all organic materials were lower than their corresponding kN and kp values, suggesting that leaching of N and P from litters may have augmented the microbial mineralization of N and P. There was a strong correlation between the kB, kN, and kp values and total P (r = 0.82-0.96; P 0.01), but not total N, lignin (LIG), or Pp. Rates of N and P release followed the general trend: Tithonia > Senna > Lantana > Sesbania > Croton > Calliandra. The results indicated that, among the quality parameters studied, total P is the most important factor controlling rate of decomposition and N and P release from organic inputs in the area of study. [source] | |||||||||||||