Different growth rates of grasses from South American natural grasslands are adaptations to soils of low fertility. Grasses with fast growth rate are species with an accumulation of nutrients in soluble forms, with a high metabolic rate. This work aimed to study whether grasses with different growth rates have different phosphorus (P) uptake and efficiency of P use with high and low P availability in soil, as well as whether phosphatase activity is related to the species growth rate and variations in P biochemical forms in the tissues. Three native grasses (Axonopus affinis, Paspalum notatum, and Andropogon lateralis) were grown in pots with soil. Along plant growth, biomass production and its structural components were measured, as well as leaf acid phosphatase activity and leaf P chemical fractions. At 40 days of growth, leaf acid phosphatase activity declined by about 20-30% with an increase of P availability in soil for A. affinis and P. notatum, respectively. Under both soil P levels, P. notatum showed the highest plant total biomass, leaf dry weight and highest P use efficiency. A. affinis presented the higher P uptake efficiency and soluble organic P concentration in the leaf tissues. A. lateralis showed P-Lipid concentration 1.6 and 1.3 times higher than A. affinis and P. notatum, respectively. In conclusion, acid phosphatase activity in grass of higher growth rate is related to higher remobilization of P due to higher demand, as in A. affinis, and higher growth rates are associated with higher P uptake efficiency.
Peach (Prunus persica L.) rootstock cultivars are typically selected for scion compatibility, ease of propagation, vigor, development, flowering season, yield, low need for cold temperatures, resistance to diseases, effects on the physical-chemical characteristics of the fruit, plant longevity and adaptation to adverse edaphoclimatic conditions. However, kinetic parameters related to nutrient uptake efficiency are usually not considered, such as those of nitrate (NO 3 −) and ammonium (NH 4 +). N is the nutrient that most impacts growth and yield. The objective of this study was to show the importance of the kinetic parameters of NO 3 − and NH 4 + uptake as additional criteria for selecting peach rootstocks. The experiment was conducted in a greenhouse. Three rootstock ('Aldrighi', 'Tsukuba1' and 'Clone 15′) were grown for 30 days in a pot containing 0.1 mol L-1 CaSO4 solution to reduce internal reserves of N. Afterwards, the plants were placed in Hoagland nutrient solution, where periodic collections of the nutrient solution were carried out for three days and the concentrations of NO 3 − and NH 4 + were determined. After the third day of collecting the solution, the plants were collected and then separated into leaves, roots and stems. Dry matter and total N content were assessed. The kinetic parameters related to NO 3 − and NH 4 + uptake (maximum uptake rate-V max , affinity constant-K m , Minimum concentration-C min , Influx-I) were calculated using Cinética software. The most efficient rootstock for NO 3 − and NH 4 + uptake was 'Tsukuba1', as it showed the lowest values of C min and K m and the highest values of V max and I max for NO 3 − and NH 4 +. NO 3 − uptake in 'Tsukuba1' and 'Aldrighi' showed a two-phase uptake pattern, suggesting the presence of low and high affinity transport systems. On the other hand, NH 4 + uptake in the three cultivars apparently followed a one-phase uptake pattern, suggesting the presence of a high affinity transport system. The kinetic parameters of NO 3 − and NH 4 + uptake are additional criteria that can be used in selecting peach rootstocks, as they directly influence shoot and root dry matter production and N accumulation in leaves.
Nitrogen (N) is a key nutrient for rice (Oryza sativa L.) and its availability in soil profile can influence the plant root morphology and total nutrient uptake. This study evaluated if N from deeper soil layers would increase rice root growth, N uptake and influence plant nutritional status. Flooded rice was grown in undisturbed soil samples from three locations with 15 N-labeled ammonium sulfate application at different depths (0, 10, 20, 30, and 45 cm). At rice heading, chlorophyll content and photosynthesis rate were measured at flag leaves and rice biomass production, root morphology, and total N and 15 N uptake were evaluated. Higher biomass and N uptake were observed with N application at near soil surface layers. The majority of rice N uptake was derived from soil, which was more evident when N fertilizer was injected at 45 cm deep (on average 74%). The highest root growth was observed at the near surface layers with constant decrease in depth, up to 60 cm. Roots from deeper layers exhibited smaller diameter, as they were mainly highly branched roots. The N application at 30 and 45 cm depths provided N later in the season, resulting in plants with lower total biomass but with higher N content in aboveground biomass, with higher chlorophyll content, photosynthesis rate, and carboxylation efficiency by Rubisco. The N available below 20 cm contributes to plant nutrition and root growth, hence soils with available N in depth likely cause plants to function more optimally in photosynthates supply.
South American natural grasslands are composed of several species with different growth strategies, with variations in specific leaf area (SLA), leaf dry matter content (LDMC), specific root length (SRL) and specific root area (SRA). The objective of this study was characterizing in grasses cultivated with different levels of phosphorus (P) in the soil if species with higher leaf and root area production per unit of dry matter have higher tissue P concentration, P use efficiency and higher dry matter yield. The plant species were grown in a greenhouse in pots with 5 kg of soil in a completely randomized design with four replicates and two conditions of P availability: addition of 60 mg kg-1 soil and without addition of P. The species with the highest SRA had a higher leaf and root P concentration. The higher production of leaf or root surface area per unit of dry matter did not represent higher tissue P use efficiency. The group formed by species of genre Paspalum had a higher leaf and root P use efficiency, therefore, areas composed of this genre are preferred for P fertilization.
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