Organic acid excretion from roots: a plant mechanism for enhancing phosphorus acquisition,enhancing aluminum tolerance,and recruiting beneficial rhizobacteria

The beneficial effects of organic acids (OAs) excretion from plant roots were first proposed as being associated with the mechanism of superior phosphorus utilization by the cluster roots of white lupin (Lupinus albus L.), and these effects are now widely accepted as pleiotropic effects associated with stress tolerance of plants. Excreted OAs detoxify rhizotoxic aluminum, recruit beneficial bacterium for induced systemic resistance, and modify root architecture to enhance phosphorus starvation. OA excretion is probably optimized in the carbon economy and is coordinately regulated with other traits that additively confer each stress factor. Here we present an overview of the molecular physiology of OA excretion from roots, how plants activate OA excretion, and how this excretion can be managed as a specific response.     

Antioxidative activity in the pericarp and seed of Japanese pepper (Xanthoxylum piperitum DC)

The antioxidative activity of the dried pericarp and seed of Japanese pepper was studied. The ethyl acetate extract from the pericarp and the methanol extract from the seed showed strong antioxidative activity against linoleic acid by the ferric thiocyanate and thiobarbituric acid (TBA) methods. Japanese pepper contained 3.9 and 2.9 mg/100 g of dry weight (dw) of tocopherols in the pericarp and seed, respectively, alpha-Toc in the former constituting 82% of total tocopherol and gamma-Toc in the latter constituting 96%. Arbutin and magnoflorine were isolated as antioxidants and their chemical structures determined by instrumental analyses. The contents of arbutin evaluated as the trifluoroacetate derivative by GC-MS were 35 and 3.0 mg/100 g of dw in the pericarp and seed, respectively. Magnoflorine was present only in the seed, and not in the pericarp. Both arbutin and magnoflorine exhibited antioxidative activity against linoleic acid and radical-scavenging activity against the DPPH radical.     

Hemolytic anemia and red blood cell metabolic disorder attributable to low phosphorus intake in cows

Hypophosphatemia was induced in 2 cows by reducing phosphorus content in their feed after parturition. Serum inorganic phosphorus (Pi) values decreased to 1 mg/dl within 10 days after parturition; and RBC adenosine 5'-triphosphate (ATP) and reduced glutathione values decreased to 50 and 70% of baseline values, respectively. Methemoglobin concentration was moderately higher than normal. These changes preceded the onset of hemolysis, and anemia progressed with decreases in PCV, hemoglobin concentration, and RBC counts. Serum Pi resumed its normal value when anemia was most severe. This RBC disorder was confirmed to be characteristic of hemolytic anemia in cows resulting from hypophosphatemia. The RBC glycolytic intermediates, total triose phosphate (combined glyceraldehyde-3-phosphate and dihydroxyacetone phosphate content) and fructose-1,6-diphosphate, greatly increased in vivo and in vitro with decreases in serum or plasma Pi and RBC ATP. From our results, we concluded that inadequate Pi in the plasma impairs the function and viability of RBC by hindering the production of ATP via disturbance of reactions at the glyceraldehyde-3-phosphate dehydrogenase step.     

The effect of tractor logging on forest soil compaction and growth ofShorea selanica seedlings in Indonesia

The hardness in soil was investigated in four forest areas in Indonesia after a crawler tractor passed over it several times. The hardness in soil, expressed by bulk density, was measured at various depth and various distances from the main track. Recovery of soil hardness was also examined. The bulk density increased markedly by the first and second pass of the tractor, but did not change after the fifth pass. The bulk density was highest just under the main and the log track, and decreased with an increase in distance from the track (0.5 to 1.5 m). The greatest increase in bulk density was observed at the depth of 0–5 cm. The soil hardness tended to show recovery within 9 years after logging, though not completely. Growth and root penetration of seedlingsShorea selanica decreased with the increase of soil hardness. We considered that the 2 tractor passes that caused bulk density of 1.3 g/cm³ is critical for the growth ofS. selanica’s seedling.     

Application of DNDC model to estimate N<Subscript>2</Subscript>O emissions from green tea fields in Japan

Heavy doses of N fertilizers are commonly applied to green tea fields in Japan, and cause large amount of nitrate leaching in ground water and emission of ammonia and nitrous oxide (N₂O) to the atmosphere. The Denitrification and Decomposition (DNDC) model was tested against experimental data on N₂O emissions from the tea field in Nishio, Aichi, Japan. There were reasonable agreements between the simulated and measured values of N₂O emissions for this site. The model was then applied for estimating the environmental impacts as affected by farm management practices, climate change, and soil properties. The model results were assessed with respect to major indicators of agro-ecosystems including crop yield, soil organic carbon sequestration, nitrate leaching loss, and N₂O emission. The results indicated that use of compost significantly reduced nitrate leaching and N₂O emissions in comparison with N fertilizer. When soil pH and texture shifted to non-acidic and coarser soil, N₂O emission increased; and a change in temperature and precipitation affected N₂O emission, nitrate leaching, and SOC sequestration. This study thus revealed the biogeochemistry model as a powerful tool in addressing the complex efficacy of the alternative farm management practices in tea fields across various climate and soil conditions.