Browsing by Subject "phosphorus"

The Baltic Sea is a unique and delicate brackish water ecosystem with high primary productivity driven by oceanic biogeochemical cycles of oxygen, iron, silicon, nitrogen and phosphorus. Elevated anthropogenic nutrient loading into the Baltic ecosystem has resulted in a large-scale increase in destructive cyanobacterial blooms in the open Baltic Sea over the past century. The toxic cyanobacterium Nodularia spumigena is a major component of surface blooms in the open Baltic Sea and continues to bloom even after the depletion of phosphate from the surrounding waters. This phenomenon has been attributed to an ability to scavenge phosphorus from recalcitrant sources. However, the exact phosphorus species that sustain N. spumigena growth in the Baltic Sea remain largely unknown. Here, I employ a comparative genomics approach to determine the evolutionary dynamics of phosphorus scavenging in eight strains of N. spumigena and predict the range of phosphorus sources that may support their growth. Then, I test these predictions by growing six strains of N. spumigena on a number of potentially bioavailable phosphorus sources. Among the phosphorus scavenging genes identified by the genomic analysis, putative pathways for the enzymatic degradation of phytic acid, phosphite, and phosphonates were present and highly conserved in the species. Subsequent growth experiments demonstrated that the organism may grow using phytic acid and phosphite, as well as the phosphonates methylphosphonic acid, ethylphosphonic acid, and nitrilotris(methylenephosphonic acid), as sole phosphorus sources. These results indicate that N. spumigena blooms may be supported by several phosphorus sources previously not known to contribute to eutrophication in the Baltic Sea. While additional growth experiments and further research on the environmental prevalence of these compounds are necessary, the findings presented in this study expand our knowledge of how N. spumigena dominates phytoplankton blooms in a phosphorus-scarce environment and may help to inform future eutrophication mitigation efforts in the Baltic Sea region.

The ambition of the agricultural environmental programme is to reduce nutrient load, because greater part of the diffuse loading of phosphorus is caused by agriculture. A eutrophic influence of the phosphorus in water systems tends to be limited inter alia by constructed wetlands. Their main task is to allow sedimentation of eroded soil into the bottom of the wetlands. There is ambiguity on the findings of the functionality and the importance of the prevention of water loading among scientific research in Finland. The aim of this study is to examine by utilizing soil analyses what happens to the basin water eroded phosphorus in the wetland sediment and wether the sedimentary constituent of the soil be suitable for a substratum of plant production. Comparing the samples of basin soil and wetland sediments revealed that the eroded constituent of the basin soil got assorted on wetlands. The samples collected from the wetlands contained 48 % more clay than the samples collected from the basin soil. The growth of the clay concentration increased the reactive area of the sediment. In consequence, it contained 45 % more hydroxides of aluminium and iron in the samples of the sediment than the samples of the basin soil. Because of the hydroxides, the phosphorus sorption capacity was 52 % higher than in the samples of the basin soil. However, the degree of phosphorus saturation was equal in the sediment and basin soil, because the oxidized sediment contained 50 % more phosphorus extracted from hydroxides of aluminium and iron. At the time of sampling the sediment was in reduced state and the amount of its water extracable phosphorus was significantly higher compared to the oxidized sediment. Correspondingly, when the sediment became oxidized the sorption capacity for phosphorus increased significantly, therefore the phosphorus was desorbed from reduced sediment to the wetlands water. This was also proven in a pot experiment, where rye-grass that grew in the sediment suffered from a severe shortage of phosphorus. In contrast, rye-grass grown in the basin soil didn’t suffer from the deficiency of phosphorus at the same fertilization levels. After threefold extra fertilization of phosphorus, the dry matter yield, concentration of phosphorus and uptake of phosphorus on the second yield grown in sediment were equal to the results of the first yield grown in basin soil. According to the results of the pot experiment, the sediment in reduced state is weakly suitable for the substratum of plant production, because the sorption capacity of phosphorus is high. Instead, sediment suits well to be utilized in the areas wherein the soil includes plenty of easy soluble phosphorus, such as for the material of subgrade for the corral of livestock, because the sediment reduces the load of phosphorus directed to the environment.

In Finland most of the accumulated phosphorus in the agricultural soils is underutilized and at the same time excess phosphorus in soil is susceptible to leaching. Arbuscular mycorrhiza (AM) has the potential to promote plant phosphorus nutrition and growth, and reduce nutrient leaching. The aim of this study was to investigate the effect of mycorrhizal symbiosis on plant growth and phosphorus nutrition with three different fertilization management practices. The influence of fertilization management history on field AMF population was also studied. To relate the impact on AM to impacts on other soil quality aspects, the effect of the fertilization rates on crop growth and indicators of soil functioning was evaluated. Long term field experiments established in 1965-66 on three sites in Northern Sweden were utilized. Six years’ rotation either with five grass years and a barley year or barley monoculture was treated with recommended (NPK) and double the recommended (2NPK) rate of mineral fertilisation or with farmyard manure (FYM) with a nutrient amount corresponding to the NPK –treatment for 32 years. The effect of three long term practices on the potential AM contribution to crop phosphorus nutrition and growth was studied in a bioassay. To study the impact of longterm management practices on functional properties of AMF, the sterilised soil from the field plots of NPK and FYM treatments was re- and cross-inoculated (5 v-%) with untreated field soil from each of the same treatments. Crop yields were measured in the field and field soil quality was assessed. Benefit from AM in terms of crop phosphorus nutrition and growth was greatest when manure was applied while there were no differences among the mineral fertiliser treatments. There were no statistically significant differences in the bioassay with re- and cross-inoculations. Grass and barley yields were highest when mineral NPK fertiliser was applied at double the recommended rate. Crop performed equally well or better in terms of yield with manure compared to a corresponding nutrient amount in mineral fertilizers. Manure applications seemed to increase soil carbon and nitrogen contents relative to the recommended amount of NPK, yet keeping the plant-available phosphorus concentration liable for leaching at a similarly low level. Thus, enhanced recycling of nutrients through use of farmyard manure to replace mineral NPK fertilisation favoured reliance on AM in phosphorus nutrition of crops with no trade-off in yields, simultaneously enhancing soil quality.

In Finland 90% of all farmers and 95% of cultivated land are committed to the environmental support program of agriculture. One of the goals of this program is to reduce phosphorus (P) runoff from fields to the water system by limiting the amount of P used in cultivation process. Experiments on P rates allowed in environmental support program and practices of P fertilization were conducted at two sites on ley during 2003-2011. The research aimed to define the effects of annual fertilization, incorporated fertilization and the use of liquid manures on ley yield and P status of the soil. Earlier studies have shown that more water soluble P runs off from leys than from cereal fields and that reserved P hasn’t been sufficient for the whole ley rotation. The experiment consisted of seven different fertilization treatments in which phosphorus treatments were done as incorporate fertilization or annual fertilization. Low or high-release mineral fertilizer was used for incorporate fertilization and either mineral fertilizer or at first mineral fertilizer and liquid manures in next rotation for annual fertilization on the surface. P given as liquid manure was used by three members of the experiment group. The experiment included cultivating ley for seven years and cereal forage for two years. The control group used no P fertilization. P given in fertilization treatments had no effect on ley yields compared with control treatment. Negative P balance in all treatments caused the P rate in ploughed layer of the soil to decrease, however the P levels of surface layer fluctuated greatly regardless of the way P treatments were done. The study indicated that using liquid manures for fertilizing ley cultivations does not pose any greater threat to the environment than mineral fertilizers. However, balanced fertilization, sufficient nitrogen and reducing nitrogen loss of liquid manures are required in order to achieve high yields. The results also indicate that it should be made possible to raise the amount of P fertilization of highly productive leys closer to the zero level of the nutrient balance so that productivity of the soil measured by acid ammonium acetate (PAC) would be preserved. Depending on the other qualities of the soil, this can be done when PAC has reached the value nearby 10 mg l-1. More information on controlling P of the surface soil by means of cultivation management is needed.