Low-phosphate Soil Research Articles

Effect of phosphate status on the sorption and desorption properties of some soils of northern India

Enormous quantities of phosphate have been applied to world soils, yet we know little about effects of phosphate status on sorption properties. We measured sorption and desorption of phosphate on soils from fertilized tea plantations from northern India and compared them with unfertilized soils. We also incubated phosphate at high temperature with a previously unfertilized soil and measured the effects. Sorption of phosphate was less marked on soils of high phosphate status whether derived from inherent fertility or fertilizer application. This occurred because high phosphate status made the surface charge on the reacting surfaces more negative. Phosphate status also affected desorption. The higher the phosphate status, the smaller the difference between sorption and desorption curves. This occurred because on soils of high phosphate status the pathways by which adsorbed anions diffuse were saturated and the slow reaction that follows adsorption was stopped. When low-phosphate soils are first fertilized, it is necessary to supply more phosphate than is removed in produce. However, after long-term phosphate fertilization, it is sufficient to only replace phosphate lost in produce. We need to find how much phosphorus it takes to reach this state and how many of the world’s soils have already reached it.

Overexpression of Thellungiella halophila H+-pyrophosphatase gene improves low phosphate tolerance in maize.

Low phosphate availability is a major constraint on plant growth and agricultural productivity. Engineering a crop with enhanced low phosphate tolerance by transgenic technique could be one way of alleviating agricultural losses due to phosphate deficiency. In this study, we reported that transgenic maize plants that overexpressed the Thellungiella halophila vacuolar H+-pyrophosphatase gene (TsVP) were more tolerant to phosphate deficit stress than the wild type. Under phosphate sufficient conditions, transgenic plants showed more vigorous root growth than the wild type. When phosphate deficit stress was imposed, they also developed more robust root systems than the wild type, this advantage facilitated phosphate uptake, which meant that transgenic plants accumulated more phosphorus. So the growth and development in the transgenic maize plants were not damaged as much as in the wild type plants under phosphate limitation. Overexpression of TsVP increased the expression of genes involved in auxin transport, which indicated that the development of larger root systems in transgenic plants might be due in part to enhanced auxin transport which controls developmental events in plants. Moreover, transgenic plants showed less reproductive development retardation and a higher grain yield per plant than the wild type plants when grown in a low phosphate soil. The phenotypes of transgenic maize plants suggested that the overexpression of TsVP led to larger root systems that allowed transgenic maize plants to take up more phosphate, which led to less injury and better performance than the wild type under phosphate deficiency conditions. This study describes a feasible strategy for improving low phosphate tolerance in maize and reducing agricultural losses caused by phosphate deficit stress.

Overexpression of transcription factor ZmPTF1 improves low phosphate tolerance of maize by regulating carbon metabolism and root growth

A bHLH (basic helix-loop-helix domain) transcription factor involved in tolerance to Pi starvation was cloned from Zea mays with an RT-PCR coupled RACE approach and named ZmPTF1. ZmPTF1 encoded a putative protein of 481 amino acids that had identity with OsPTF1 in basic region. Real-time RT-PCR revealed that ZmPTF1 was quickly and significantly up-regulated in the root under phosphate starvation conditions. Overexpression of ZmPTF1 in maize improved root development, enhanced biomass both in hydroponic cultures and sand pots, and the plants developed more tassel branches and larger kernels when they were grown in low phosphate soil. Compared with wild type, overexpressing ZmPTF1 altered the concentrations of soluble sugars in transgenic plants, in which soluble sugars levels were lower in the leaves and higher in the roots. Overexpression of ZmPTF1 enhanced the expression of fructose-1,6-bisphosphatase and sucrose phosphate synthase1 participated in sucrose synthesis in the leaves but decreased them in the root, and reduced the expression of genes involved in sucrose catabolism in the roots. The modifications on the physiology and root morphology of the plants enhanced low phosphate tolerance and increased the yield under low phosphate conditions. This research provides a useful gene for transgenic breeding of maize that is tolerant to phosphate deficiency and is helpful for exploring the relationship between sugar signaling and phosphate concentrations in cells.

PHOSPHORUS UPTAKE BY DIFFERENT TREE SPECIES ON LOW PHOSPHORUS SOILS

SUMMARY Phosphorus uptake by four tree species commonly used in agroforestry systems was investigated under different treatments using low phosphate soils in the greenhouse. Phosphorus uptake was evaluated by determining the amount of phosphorus in plant tissue. Results indicated that Prosopis juliflora had a greater uptake than Calliandra calothyrsus, Gliricidia sepium and Leucaena leucocephala under these conditions. Intercropping the tree species with millet had no significant effect on phosphorus uptake by millet compared with a millet monoculture.

Influence of plant genotype on mycorrhizal infection: Response of three pea cultivars

Three leafless pea cultivars (JI 1198, BS 142 and BS 4) with the same phenotype and similar patterns of development, were tested in a sterilized low-phosphate soil for their response to phosphate fertilizer and to vesicular-arbuscular mycorrhizal (VAM) infection by threeGlomus species. Cultivar JI 1198 was very responsive to phosphate but not to inoculation withGlomus mosseae, Glomus caledonium orGlomus epigaeum. Phosphate and VAM treatments increased growth of cultivar BS 142 but were ineffective with cultivar BS 4. Fungal infectivity could not be related with endophyte effectiveness at stimulating plant growth, although the percentage of root length infected by each one of the threeGlomus species did not vary between cultivars. Genetic differences among plant cultivars can thus markedly affect the symbiosis between the host root and VAM fungi; this suggests that potential host-endophyte combinations need to be evaluated before being tested in the field.

Effectiveness of single and multiple mycorrhizal inocula on growth of clover and strawberry plants at two soil pHs

Mycorrhizal inocula containing one to four species of Glomus were tested on clover and strawberry plants in a low-phosphate soil at pH 4.8 and pH 6.8. Inoculum containing four species was equally or more effective than inoculum with only a single species in promoting plant growth at both pHs. Spore production following multiple inoculation indicated that Glomus sp. “E3” was the most competitive species at pH 4.8 and Glomus mosseae at pH 6.8. It was concluded that mixed (multi-species) inocula should be used for field inoculation to ensure wider adaptation to different environmental conditions and greater consistency in benefits to the host plant.

ADSORPTION CURVES AND PHOSPHORUS REQUIREMENTS OF ACID SOILS

Four acid, low-phosphate soils from the southeastern United States were limed at four levels and amended with phosphorus (P) at five levels. Barley was grown for 60 days on these amended soils in the greenhouse. Plant yields and P uptake were measured. With these same amended soils, 24-hour equilibration P adsorption curves and equilibrium phosphate concentrations (the P concentration supported in solution by a soil at near field moisture capacity) were determined. The greenhouse and laboratory data were used to develop a two-point adsorption-curve method for estimating soil P additions to correct P deficiencies. The method is simple and includes the use of a correction factor that relates the amount of fertilizer P a soil adsorbs during the first 24 hours of addition to the amount the soil adsorbs during a growing season. Correction factors were estimated for the four soils, each at four different pH levels, on the basis of the lowest equilibrium phosphate concentration that supported 0.25 percent P in barley tissue.

Comparative role of phosphate in soil or inside the host on the formation and effects of endomycorrhiza

Non-mycorrhizal plants grown 5 weeks in a low-phosphate soil with different amounts of soluble P were transplanted to soil also with different levels of phosphate and inoculated with VA mycorrhiza. The intensity of mycorrhizal infection as affected by the interaction of differents levels of phosphate in soil and in the host was examined after a further 8 weeks. In the soil with no added phosphate mycorrhizal infection was not affected by the initial P content of the plants. When 0.8 or 1.5 g K2PO4 was given per kg soil both the external and the internal P negatively influenced the infection. In some conditions a P content that was supraoptimal for infection was not for plant growth. The critical P concentration in plants depends on the age of the host. An interaction between P and N as a factor contributing to phosphate ‘toxicity’ is discussed.

Effects of interactions between different culture fractions of 'phosphobacteria' and Rhizobium on mycorrhizal infection, growth, and nodulation of Medicago sativa.

Interactions between cell-free culture supernatants, cells, and the whole cultures of Rhizobium and phosphobacteria with endomycorrhizal fungi and their effects on growth and nutrition of Medicago sativa grown in a low-phosphate soil were studied. A satisfactory nodulation was greatly dependent on the mycorrhizal symbiosis. Cell-free supernatants of Rhizobium and phosphobacteria improved plant growth, nodulation and mycorrhiza formation. The activity of phosphobacterial culture seemed to be due mainly to the supernatant and the possibility of plant hormones contained in this culture fraction being involved in such interactions is discussed. An increase of the overall pool of soluble P in soil by the inoculated phosphobacteria cells was not found in the conditions of this experiment. It was noteworthy that the best positive effect was achieved by the treatment which consisted of the whole cultures of Rhizobium, phosphobacteria, and the mycorrhizal fungi applied all together.

The epidemiology of common root rot in Manitou wheat. III. Development of lesions on subcrown internodes and the effect of added phosphate

The development of common root rot lesions on subcrown internodes of Manitou wheat was followed in growth-chamber tests. Visible lesions caused by Cochliobolus sativus appeared 3 to 5 days after inoculation. The vertical spread of subcrown internode lesions was much faster than the lateral spread; normally, lateral spread did not start until maximum vertical extension had occurred. Considerable variation in rate of development of lesions was evident between individual plants. The overall mean daily rate of vertical extension of subcrown internode lesions was in the range of 0.3 to 0.5 mm. The rate was faster immediately after infection and declined with time. Lesion development on plants generally was more rapid in low-phosphate soil than in high-phosphate soil. This finding was exemplified by higher percentages of severely diseased plants at the end of the experiments; higher probabilities of transfer of plants from less to more severe categories in the intervals between observations; higher disease ratings; and higher mean daily rates of linear extension of lesions in low- than high-phosphate soil. The possible application of some techniques in developing a model for forecasting severity of disease is discussed.

PLANT GROWTH RESPONSES TO VESICULAR‐ARBUSCULAR MYCORRHIZA

SummaryThe benefits of mycorrhizal infection were compared in four irradiated and unsterilized soils containing little soluble phosphorus. Mycorrhizal infection was produced in onion seedlings by pre‐planting in a heavily infected soil and transplanting into the test soil, or by sowing in situ on a cushion of Endogone inoculum. In all soils, irradiated or not, mycorrhizal seedlings grew very much better than non‐mycorrhizal ones. In two of the soils natural infectivity was very low and most uninoculated seedlings remained non‐mycorrhizal even after 16 weeks. In the other two soils most plants became mycorrhizal in the unsterilized soils. In one of them the indigenous mycorrhizal fungi aided phosphorus uptake of the host plant, in the other they did not. Infections produced by the indigenous fungi in the two soils were anatomically different, though both were typical VA mycorrhiza.It is concluded that inoculation may have practical significance in some low phosphate soils containing either few indigenous mycorrhizal fungi or ineffective strains.