Leaf and root attributes as growth and phosphorus uptake determinants in two grass species from South America’s natural grasslands

Phosphorus uptake by grass species from natural South American grasslands can change depending on root and leaf attributes capable of determining higher, or lower, relative growth rate. The aim of the current study is to investigate whether leaf and root attributes capable of determining leaf and root area production in native C4 grass species Axonopus affinis and Andropogon lateralis are related to higher relative growth rate (RGR), P uptake capacity (maximum P influx; Imax) and concentration. Species grown in 2-litre pots with added nutrition solution were subjected to two treatments, namely 5 μM P l−1 and 30 μM P l−1. Solution aliquots (10 ml) were collected for 30 hours at the end of the study to determine P concentrations. RGR was 3.6 and 2.8 times higher in A. affinis than in A. lateralis in treatments with 5 μM P and 30 μM P. Axonopus affinis recorded the highest P concentration in leaf tissue. This outcome was associated with Imax 85% higher in A. affinis. High RGR was associated with larger leaf and root surface area per dry mass unit, as well as with high P influx capacity and with higher affinity transporters. These species often prevail in areas accounting for greater natural fertility and are more responsive to phosphate fertilization.

Effect of phosphate solubilising bacteria (Enterobacter cloacae) on phosphorus uptake efficiency in sugarcane (Saccharum officinarum L.)

Phosphorus (P) is an essential nutrient in sustainable production of sugarcane. Due to low labile P in soil under sugarcane cultivation, evaluation of the efficiency of P uptake and the application of phosphate solubilising bacteria (PSB) play important roles in management of P fertiliser. To investigate the effect of using PSB on P uptake in sugarcane (variety CP57–614), a pot experiment was conducted with three replications in greenhouse conditions. The treatments were a combination of three P rates (0 (P0), 50 and 100% (~40 mg kg−1) as triple superphosphate, and two PSB strains (Enterobacter cloacae R13 (R13) and R33 (R33)) which were applied independently and simultaneously. Morphological characteristics of sugarcane and some biochemical parameters were evaluated in the rhizosphere at three harvesting times: 60, 95 and 140 days after planting (DAP). Whereas in low available P (P0), bacterial strain R33 improved P uptake along with sugarcane ageing, P uptake was diminished in non-inoculated treatment over time. Activity of PSBs in the rhizosphere (especially strain R33) prevented the sharp fall of P influx after 95 DAP in low available P condition. Indeed, activity of R33 in the rhizosphere decreased the dependence of P uptake on root development via improving P uptake. Therefore, influx was the main mechanism of P uptake in sugarcane. Sugarcane inoculated by PSBs acquired 76 and 81% of total P uptake from non-Olsen-P fraction in P0R13 and P0R33 respectively at 95 DAP. However, this amount was lower (70.4%) in P0R0. Furthermore, strain R33 improved P uptake efficiency in sugarcane by changing root morphology (e.g. specific root length and root length) and reducing soil limitations (e.g. enhancement of P compound solubility and P influx).

Arbuscular mycorrhiza and kinetic parameters of phosphorus absorption by bean plants

The mechanisms that determine greater P absorption by mycorrhizal plants are still not completely clear, and are attributed, in part, to an increase in the number of absorption sites promoted by the hyphae, and/or to a greater affinity of the colonized hypha or root carriers to P. The effect of mycorrhizae formed by Glomus etunicatum on the kinetic parameters of P absorption by the roots and on P influx in bean plants of the IAC-Carioca cultivar was evaluated, in two distinct plant development periods: at the onset of flowering and at the pod-filling stage (35 and 50 days after sowing, respectively). A mixture of sand and silica (9:1) was utilized as substrate and irrigated with nutrient solution. The kinetics assay was performed by the method of 32P depletion from the solution (depletion curve), using intact plants. Mycorrhization promoted greater growth and P absorption by bean plants, which was more conspicuously observed at the pod-filling stage. Mycorrhizal plants showed higher values of maximum ion uptake rate (Vmax) and net P influx at the flowering stage. Lower minimum ion concentration (Cmin) and Michaelis-Menten constant (Km) values were verified in mycorrhizal plants at the pod-filling stage. Mycorrhizal plants also presented higher net P influx per plant, in both stages. Cmin was the kinetic parameter more intimately related to P absorption, and a significant correlation was obtained between this parameter and shoot P content and accumulation in bean plants.

Corrigendum to: Phosphorus efficiencies and their effects on Zn, Cu, and Mn nutrition of different barley (Hordeum vulgare) cultivars grown in sand culture

A sand-culture experiment was carried out in a growth chamber to investigate the phosphorus (P) efficiencies of 8 barley cultivars that are parents of 4 mapping populations, and the effects of P nutrition on plant uptake of zinc (Zn), copper (Cu), and manganese (Mn). Two sources of phosphate were used, rock phosphate (sparingly soluble) and CaHPO4 (readily available). There were significant differences in P uptake and utilisation efficiencies between the 8 cultivars. Among the cultivars, the Sahara–Clipper pair is of the most interest, because these 2 cultivars had large differences in root/shoot ratios, P allocation between root and shoot, and P uptake/utilisation efficiencies. Higher P availability significantly reduced plant Zn uptake and tissue concentrations in all cultivars. Shoot Zn concentrations were found to decrease significantly with P influx to the xylem (P < 0.01), indicating that genotypic variations in P translocation from roots to shoots may interact with Zn accumulation in shoots. Higher P availability reduced Cu concentrations in shoots, probably due to a dilution effect. P availability (rock phosphate v. CaHPO4) seemed to affect plant uptake of Mn in some cultivars, but further study is needed to elucidate the mechanisms involved and the practical implications of this interaction in Mn-deficient soils.

Phosphorus efficiencies and their effects on Zn, Cu, and Mn nutrition of different barley (Hordeum vulgare) cultivars grown in sand culture

A sand-culture experiment was carried out in a growth chamber to investigate the phosphorus (P) efficiencies of 8 barley cultivars that are parents of 4 mapping populations, and the effects of P nutrition on plant uptake of zinc (Zn), copper (Cu), and manganese (Mn). Two sources of phosphate were used, rock phosphate (sparingly soluble) and CaHPO4 (readily available). There were significant differences in P uptake and utilisation efficiencies between the 8 cultivars. Among the cultivars, the Sahara–Clipper pair is of the most interest, because these 2 cultivars had large differences in root/shoot ratios, P allocation between root and shoot, and P uptake/utilisation efficiencies. Higher P availability significantly reduced plant Zn uptake and tissue concentrations in all cultivars. Shoot Zn concentrations were found to decrease significantly with P influx to the xylem (P < 0.01), indicating that genotypic variations in P translocation from roots to shoots may interact with Zn accumulation in shoots. Higher P availability reduced Cu concentrations in shoots, probably due to a dilution effect. P availability (rock phosphate v. CaHPO4) seemed to affect plant uptake of Mn in some cultivars, but further study is needed to elucidate the mechanisms involved and the practical implications of this interaction in Mn-deficient soils.

Early Palaeolithic bone diagenesis in the Arago cave at Tautavel, France

Bones from level G in the Arago cave (Tautavel, Southern France, 450 ky) were analysed using a combination of particle induced X-ray and gamma-ray emission (PIXE and PIGME) and X-ray diffraction (XRD). Human occupation and guano production by bats introduced a large amount of phosphate into the cave and as a result a decarbonated pocket was formed in the sediment, characterized by the dissolution of clay minerals, calcite and bones, and by the precipitation of phosphate secondary minerals. The Al released by clay minerals was reprecipitated as crandallite in the few remaining bones, and as montgomeryite with traces of crandallite in the surrounding sediments. Bones within the pocket have very high levels of Al, Fe, F and Zn and often have ‘diffusive’ type U-shaped concentration profiles. These profiles show that post-mortem uptake of trace elements occurred, and thus that trace element composition has to be used with care in palaeonutritional studies but is indicative of local palaeoenvironment. This uptake is complicated by a large increase in hydroxylapatite crystallinity in Palaeolithic bones compared to modern or more recent ones, as a result of the large P influx which occurred in the Arago cave after the sediment deposition.

Cellular Phosphorus Concentration as a Criterion for Trophic Status in Rapidly Flushed Lakes

By using the steady-state concentration of cellular phosphorus(P) as the indicator of a lake's trophic status, we derived equations that describe the flushing rate at which cellular washout might be expected, and the range of flushing rates in which cellular P concentrations would be reduced significantly below those of total P. Calculated concentrations of cellular P and total P are virtually identical for lakes with flushing rates below about 10 yr−1; at higher rates they may differ substantially. The P mass balances equations we developed consider total P to consist of two components: cellular P and available P. Lakes are treated as completely mixed flow-through reactors with constant P influx. The equations describe conditions in which available P remains in solution until it is removed by algal uptake or lost through sedimentation or outflow. Algae are lost from the system by sedimentation or are discharged through the lake outlet. The transfer of P from available to cellular forms is described by Michaelis–Menten growth kinetics.