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P Accumulation (p + accumulation)
Selected AbstractsEffects of increased temperature and nutrient enrichment on the stoichiometry of primary producers and consumers in temperate shallow lakesFRESHWATER BIOLOGY, Issue 7 2008M. VENTURA Summary 1. We studied the effects of increased water temperatures (0,4.5 °C) and nutrient enrichment on the stoichiometric composition of different primary producers (macrophytes, epiphytes, seston and sediment biofilm) and invertebrate consumers in 24 mesocosm ecosystems created to mimic shallow pond environments. The nutrient ratios of primary producers were used as indicative of relative nitrogen (N) or phosphorus (P) limitation. We further used carbon stable isotopic composition (,13C) of the different primary producers to elucidate differences in the degree of CO2 limitation. 2. Epiphytes were the only primary producer with significantly higher ,13C in the enriched mesocosms. No temperature effects were observed in ,13C composition of any primary producer. Independently of the treatment effects, the four primary producers had different ,13C signatures indicative of differences in CO2 limitation. Seston had signatures indicating negligible or low CO2 limitation, followed by epiphytes and sediment biofilm, with moderate CO2 limitation, while macrophytes showed the strongest CO2 limitation. CO2 together with biomass of epiphytes were the key variables explaining between 50 and 70% of the variability in ,13C of the different primary producers, suggesting that epiphytes play an important role in carbon flow of temperate shallow lakes. 3. The ratio of carbon to chlorophyll a decreased with increasing temperature and enrichment in both epiphytes and seston. The effects of temperature were mainly attributed to changes in algal Chl a content, while the decrease with enrichment was probably a result of a higher proportion of algae in the seston and epiphytes. 4. Macrophytes, epiphytes and seston decreased their C : N with enrichment, probably as an adaptation to the different N availability levels. The C : N of epiphytes and Elodea canadensis decreased with increasing temperature in the control mesocosms. Sediment biofilm was the only primary producer with lower C : P and N : P with enrichment, probably as a result of higher P accumulation in the sediment. 5. Independently of nutrient level and increased temperature effects the four primary producers had significantly different stoichiometric compositions. Macrophytes had higher C : N and C : P and, together with epiphytes, also the highest N : P. Seston had no N or P limitation, while macrophytes and epiphytes may have been P limited in a few mesocosms. Sediment biofilm indicated strong N deficiency. 6. Consumers had strongly homeostatic stoichiometric compositions in comparison to primary producers, with weak or no significant treatment effects in any of the groups (insects, leeches, molluscs and crustaceans). Among consumers, predators had significantly higher N content and lower C : N than grazers. [source] The response of manured forage maize to starter phosphorus fertilizer on chalkland soils in southern EnglandGRASS & FORAGE SCIENCE, Issue 2 2000Withers The impact of various starter phosphorus (P) fertilizers on the growth, nutrient uptake and dry-matter (DM) yield of forage maize (Zea mais) continuously cropped on the same area and receiving annual, pre-sowing, broadcast dressings of liquid and semi-solid dairy manures was investigated in two replicated plot experiments and in whole-field comparisons in the UK. In Experiment 1 on a shallow calcareous soil (27 mg l,1 Olsen-extractable P) in 1996, placement of starter P fertilizer (17 or 32 kg ha,1) did not benefit crop growth or significantly (P > 0·05) increase DM yield at harvest. However, in Experiment 2 on a deeper non-calcareous soil (41 mg l,1 Olsen-extractable P) in 1997, placement of starter P fertilizer (19 or 41 kg P ha,1), either applied alone or in combination with starter N fertilizer (10 or 25 kg N ha,1), significantly increased early crop growth (P < 0·01) and DM yield at harvest by 1·3 t ha,1 (P < 0·05) compared with a control without starter N or P fertilizer. Placement of starter N fertilizer alone did not benefit early crop growth, but gave similar yields as P, or N and P, fertilizer treatments at harvest. Large treatment differences in N and P uptake by mid-August had disappeared by harvest. In field comparisons over the 4-year period 1994,97, the addition of starter P fertilizer increased field cumulative surplus P by over 70%, but without significantly (P > 0·05) increasing DM yield, or nutrient (N and P) uptake, compared with fields that did not receive starter P fertilizer. The results emphasized the extremely low efficiency with which starter P fertilizers are utilized by forage maize and the need to budget manure and fertilizer P inputs more precisely in order to avoid excessive soil P accumulation and the consequent increased risk of P transfer to water causing eutrophication. [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] Montezuma pine nutrient status as affected by alder densities nitrogen fertilizationJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 6 2006Miguel Abstract Literature reports both positive and negative effects of N-fixing alders on conifer growth in alder-conifer stands. Such divergent effects probably result from poorly understood species interactions. The aim of this work was to examine how varying alder-to-pine ratios (APRs) and N fertilization affect pine nutrient status. A pseudo-experiment was installed in each of two areas of regeneration (AR) with different amounts of radiation reaching alder. The experimental approach consisted of a series of pseudoreplicated plots with five APRs within each AR. Half of each plot received 200,kg N ha,1. Data were interpreted by vector analysis. Alders in the AR 1987 induced needle-biomass reductions, K deficiency, and P accumulation in pine needles. However, nutrient availability increased with the proportion of alders in the AR 1989, where alders received high sunlight due to a less dense pine stand. Nitrogen fertilization increased needle biomass and N in three out of five alder proportions where alders were sunlight-limited. In the other stand, with the exception of the no-alder and A4 plots, positive effects of N fertilization increased with decreasing alder density. We conclude that sunlight-limited alders may not positively affect associated-species growth even in N-limited sites. [source] | ||||||||||