Plant Uptake Rates Research Articles

Denitrification in constructed free-water surface wetlands: I. Very high nitrate removal rates in a macrocosm study

Six newly constructed experimental macrocosms (approximately 0.13 ha each) were built to study nitrogen transformation processes in the adjacent Prado Basin constructed wetland, southern California, USA. First year macrocosm data showed that nitrate was the dominant nitrogen species. Nitrate removal rates during September 1992 were measured at 2800 mg N m −2 d −1 while inorganic nitrogen and ammonia transformation rates were an order of magnitude less. Nitrogen trends and transformation rates within the macrocosms were similar to those found within the adjacent wetland. Based on calculated plant uptake rates and the absence of seepage losses, nitrate removal was attributed to denitrification.

Grazing Optimization and Nutrient Cycling: When Do Herbivores Enhance Plant Production?

In a general theoretical ecosystem model, we investigate the conditions under which herbivores increase primary production and lead to grazing optimization through recycling of a limiting nutrient. Analytical and simulation studies of the model lead to several general results. Grazing optimization requires that (1) the proportion of nutrient lost along the herbivore pathway be sufficiently smaller than the proportion of nutrient lost throughout the rest of the ecosystem; and that (2) inputs of nutrient into the system be greater than a threshold value, which depends on the sensitivity of plant uptake rate to an increase in soil mineral nutrient. An increase in nutrient turnover rate is not sufficient to explain grazing optimization in the long term. When a nutrient is the single limiting factor, plant biomass and productivity at equilibrium are determined only by the balance of ecosystem inputs and outputs of nutrient. Processes that do not have an impact on these inputs or outputs have no effect on primary producers. On the other hand, turnover rates are important for the transient dynamics of the system, and the equilibrium analysis is relevant only if it can be reached in a reasonable time scale. The equilibrium is not reached by a compartment with a very slow turnover rate, such as the resistant soil organic matter, before several centuries. On a small time scale, such a compartment can be considered constant, and the trend of the system is predicted with a simplified system. The results at equilibrium are insensitive to the functional form used to describe herbivore consumption: the results obtained for simple, linear, donor-controlled herbivory also apply to most forms of more realistic, recipient-controlled herbivory. We conclude that grazing optimization is most likely to occur in systems with large losses of the limiting nutrient during recycling of plant detritus, or where herbivores bring nutrient from outside the ecosystem considered (which acts to reduce, or even make negative, the fraction of nutrient lost along the herbivore detritus pathway).

GRAZING OPTIMIZATION AND NUTRIENT CYCLING: WHEN DO HERBIVORES ENHANCE PLANT PRODUCTION?

In a general theoretical ecosystem model, we investigate the conditions under which herbivores increase primary production and lead to grazing optimization through recycling of a limiting nutrient. Analytical and simulation studies of the model lead to several general results. Grazing optimization requires that (1) the proportion of nutrient lost along the herbivore pathway be sufficiently smaller than the proportion of nutrient lost throughout the rest of the ecosystem; and that (2) inputs of nutrient into the system be greater than a threshold value, which depends on the sensitivity of plant uptake rate to an increase in soil mineral nutrient. An increase in nutrient turnover rate is not sufficient to explain grazing optimization in the long term. When a nutrient is the single limiting factor, plant biomass and productivity at equilibrium are determined only by the balance of ecosystem inputs and outputs of nutrient. Processes that do not have an impact on these inputs or outputs have no effect on primary producers. On the other hand, turnover rates are important for the transient dynamics of the system, and the equilibrium analysis is relevant only if it can be reached in a reasonable time scale. The equilibrium is not reached by a compartment with a very slow turnover rate, such as the resistant soil organic matter, before several centuries. On a small time scale, such a compartment can be considered constant, and the trend of the system is predicted with a simplified system. The results at equilibrium are insensitive to the functional form used to describe herbivore consumption: the results obtained for simple, linear, donor-controlled herbivory also apply to most forms of more realistic, recipient-controlled herbivory. We conclude that grazing optimization is most likely to occur in systems with large losses of the limiting nutrient during recycling of plant detritus, or where herbivores bring nutrient from outside the ecosystem considered (which acts to reduce, or even make negative, the fraction of nutrient lost along the herbivore detritus pathway).

Effect of ammonium, organic amendments, and plant growth on soil pH stratification

We studied the development of soil layers of different pH (strata) within the surface 10 cm of soil. Substrates which affect nitrogen transformations (ammonium sulfate, sucrose, and lucerne hay) were added to the soil to determine the effect of amendment on the development of pH stratification. A glasshouse experiment used soils of 3 different initial pH(0·01 CaCl2; pHCa) values: 4, 5, and 6. At the end of the experiment, soil was sampled in depth intervals of 0·5 cm between 0 and 2 cm depth and then 1-cm intervals between 2 and 10 cm depth. Soil pHCa decreased over time and pHCa changes could be explained by variations in the concentration of ammonium and nitrate, which were brought about by changes in the rate of mineralisation, nitrification, and plant uptake of nitrogen. Little stratification in soil pHCa was found within the 0–10 cm layer. This minimal stratification was considered to be due to the soil in the pots being a closed system where nitrate was not lost through leaching. A field trial was rotary hoed to a depth of approximately 10 cm to achieve adequate mixing of soil and amendments. Soil pHCa decreased over the 6 months of the growing season, ranging from 0·1 pHCa units in the control to 0·4 pHCa units in the hay amendment. Between the initial and final sampling times there was little change in soil pHCa in the surface 0–2 cm. The pHCa decreased in the layers between 2 and 10 cm, thus producing the stratification of soil pHCa. The growth of oats had little effect on the development of pHCa stratification. Decreases in the soil pHCa from the 0–2 cm to the 8–10 cm layer in the absence of plants were 0·22, 0·27, 0·30, and 0·51 for the control, added sucrose, added ammonium sulfate, and added hay amendments, respectively. The processes of mineralisation and nitrification were considered to be the major causes of change in soil pHCa. Stratification of pHCa in the field trial was attributed to nitrification followed by nitrate leaching in the open system.

Nitrogen cycling in microcosms of yellow birch exposed to elevated CO2: simultaneous positive and negative below‐ground feedbacks

This study investigated simultaneous plant and soil feedbacks on growth enhancement with elevated [CO2] within microcosms of yellow birch (Betula alleghaniensis Britt.) in the second year of growth. Understanding the integrated responses of model ecosystems may provide key insight into the potential net nutrient feedbacks on [CO2] growth enhancements in temperate forests. We measured the net biomass production, C:N ratios, root architecture, and mycorrhizal responses of yellow birch, in situ rates gross nitrogen mineralization and the partitioning of available NH4+ between yellow birch and soil microbes. Elevated atmospheric [CO2] resulted in significant alterations in the cycling of N within the microcosms. Plant C/N ratios were significantly increased, gross mineralization and NH4+ consumption rates were decreased, and relative microbial uptake of NH4+ was increased, representing a suite of N cycling negative feedbacks on N availability. However, increased C/N ratios may also be a mechanism which allows plants to maintain higher growth with a constant or reduced N supply. Total plant N content was increased with elevated [CO2], suggesting that yellow birch had successfully increased their ability to acquire nutrients during the first year of growth. However, plant uptake rates of NH4+ had decreased in the second year. This discrepancy implies that, in this study, nitrogen uptake showed a trend through ontogeny of decreasing enhancement under elevated [CO2]. The reduced N mineralization and relatively increased N immobilization are a potential feedback which may drive this ontogenetic trend. This study has demonstrated the importance of using an integrated approach to exploring potential nutrient‐cycling feedbacks in elevated [CO2].

Sodium Recycling through Plants for Bioregenerative Life Support

As humans explore the solar system, life support will need to be increasingly self-sufficient. Growing higher plants and using recycling technologies can improve self-sufficiency. Sodium is an essential mineral for humans, but not typically for plants. Recycling sodium back to humans through food crops may reduce the need for sodium supplements in the human diet. However, if sodium from waste streams is added to the plant system in greater quantities than it is removed, then plant toxic levels may result. The recommended daily sodium requirement is 3000 mg per person. Based on a 20-m2 growing area per person, 150 mg·m–2 sodium would need to be removed each day. Most crops will not remove enough salt when grown at very low sodium levels; however, when grown in 20 mM sodium, plant uptake may meet the 3000 mg/d human sodium requirement without affecting yields. We grew four different salad crops (lettuce, radish, spinach, and table beet) hydroponically and calculated plant uptake rates and partitioning with 0, 20, 40, or 80 mM sodium supplemented nutrient solutions (corresponding to ≈1.4, 4.0, 8.0, and 13.0 dS·m–1 electrical conductivity). Sodium at 40 and 80 mM reduced edible yields. Sodium replaced tissue potassium in most cases, whereas calcium and magnesium concentrations were much less affected, particularly at 20 mM sodium. This data will be used to model sodium flows within a bioregenerative life support system and determine the feasibility of sodium recycling using food crops.

Comparison of plant uptake and plant toxicity of various ions in wheat

The effects of varying solution concentrations of manganese (Mn), zinc (Zn), copper (Cu), boron (B), iron (Fe), gallium (Ga) and lanthanum (La) on plant chemical concentrations, plant uptake and plant toxicity were determined in wheat (Triticum aestivum L.) grown in a low ionic strength (2.7×10−3M solution culture). Increasing the solution concentration of Mn, Zn, Cu, B, Fe, Ga and La increased plant concentrations of that ion. Asymptotic maximum plant concentrations were reached for Zn (10 mg kg DM−1 in the roots), Ga (2 mg kg DM−1 in the tops and 18 mg kg DM−1 in the roots) and La (0.4 mg kg DM−1 in the tops and 4 mg kg DM−1 in the roots). Plant ion concentrations were, on average, 3 times higher in the roots than the tops for Mn and Zn, 7 times for Cu, 9 times for Fe, 12 times for Ga and 15 times for La. In contrast, B concentrations were higher in the tops than the roots by, on average, 2 times. The estimated toxicity threshold (plant concentration at which a rapid decrease in yield occurred) in the tops was 0.4 mg g DM−1 for B, 2 for Zn, 0.075 for Cu and 0.09 for La and in the roots 0.2 mg g DM−1 for B, 5 for Zn, 0.3 for Cu and 3 for La. Plant uptake rates of the ions (as estimated by the slope of the relationship between solution ion concentrations and plant ion concentrations) was in the order B 250 mg kg DM−1 μM−1). Plant toxicity was estimated as the reciprocal of the plant concentration that reduced yield by 50% (change in relative yield per mg ion kg DM−1). The plant toxicity of the ions tested was in the order Mn<Zn<B<Fe=Ga<La<Cu in the tops and Mn<Ga<Zn<Fe=La<Cu<B in the roots. Copper was unusual in that plant uptake and plant toxicity was high for a plant trace nutrient.

Vapor-phase 2,3,7,8-TCDD sorption to plant foliage — A species comparison

Plant uptake rate constants (k 1) were determined for vapor-phase 2,3,7,8-TCDD using grass, azalea, spruce, kale and pepper foliage, and the fruit from apple, tomato and pepper. Plants were exposed to vapor-phase 3H-2,3,7,8-TCDD for 96 h, and the TCDD sorption rate constant for each plant species was determined from measured air and plant concentrations. Sorption rate constants for the different plant tissues, expressed on a fresh weight basis (k 1FWt with units of g Air g FWt −1 h −1), varied by two orders of magnitude. The rate constants were normalized for the exposed plant surface area (SA) by dividing k 1FWt by the SA/FWt ratio for each plant species. Normalizing the rate constants for exposed surface area resulted in significantly less variation between species (k 1SA = 1.2 g Air cm 2 −1 h −1 ± 0.2 SE). The cuticular wax content of the different plant species did not effect the short-term sorption kinetics of 2,3,7,8-TCDD.

PRODUCTION OF HYALINE HAIRS BY INTERTIDAL SPECIES OF FUCUS (FUCALES) AND THEIR ROLE IN PHOSPHATE UPTAKE1

ABSTRACTA field study to determine the precise times of year at which three intertidal species of Fucus start to produce hyaline hairs and cease producing such hairs was conducted on the Isle of Man, U.K. Hairs were first observed during February, and within 6 days of their initial appearance, all tagged plants of all species at all tidal heights on the shore possessed hairs. Hair production continued until the beginning of October, at which time Fucus plants growing at the lowest stations (+ 3.0 m) had glabrous apical growth. Hair production continued later into the year for plants growing higher on the shore, and it was not until mid‐November that glabrous apical growth was observed in all plants.Phosphate uptake rates of pilose (hairy) and glabrous (hairless) apical sections were measured in November 1988 for F. spiralis L. and in January 1989 for F. spiralis and F. serratus L., at phosphate concentrations ranging from 0.8 μM (ambient seawater) to 9.0 μM. In ambient seawater, pilose plants of F. spiralis removed phosphate 2–3 times faster than glabrous plants, whereas the uptake rates of pilose plants of F. serratus were about 50% greater than those of glabrous plants. The differences between uptake rates of pilose and glabrous plants of both species were smaller or nonsignificant at higher phosphate concentrations. The field and laboratory data are consistent with the hypothesis that hairs are formed in Fucus as a response to increased nutrient demand and that hairs facilitate the uptake of nutrients from seawater at concentrations typical of natural situations.

Nitrate and ammonium uptake by maize: adaptation during relief from nitrogen suppression.

Initial (0-1 h) net rates of nitrate and ammonium uptake from 200 μM NH4 NO3 were progressively increased as 8-d-old maize (Zea mays L.) seedlings, grown on 5 mM nitrate, were exposed to nitrogen-free solutions for up to 48 h. Further nitrogen deprivation to 72 h resulted in a decline in the nitrate uptake rate. Nitrate uptake rates of plants at all stages of nitrogen deprivation increased steadily during an 8 h exposure to 200 μM NH4 NO3 . The pattern of the response of ammonium uptake during the 8 h adaptation period was considerably different. In nitrogen-replete plants the ammonium uptake rate increased steadily, but deprivation of nitrogen for 12 h and longer resulted in complex responses in which the initial rate was followed by a decline, a subsequent increase, and another decline. The responses of the nitrate uptake system are considered to reflect a lifting of the suppressive effects of nitrate and a product of nitrate assimilation during nitrogen deprivation, a concomitant degradation of an induced component of the nitrate uptake system during that time, and reinduction of the uptake system during the adaptation period. The responses of the ammonium uptake system are considered to reflect the interplay of suppression by a product of ammonium assimilation, the accumulation of root ammonium and associated ammonium efflux, and a stimulation by ammonium of its own uptake. As a consequence of the differential responses of the two uptake systems, nitrate and ammonium uptake rates were positively correlated, largely independent, or negatively correlated as the plants progressed through the 8 h adaptation period.

Long-term effects of soil heterogeneity on cadmium behaviour in soil

A deterministic model for long-term behaviour of contaminants in the rootzone is developed that includes sorption, leaching, and plant uptake. The model is applied to cadmium accumulation in a sandy soil and uptake of cadmium by barley. Sensitivity analysis showed that the sensitivity of the leaching rate to changes in soil chemical and soil physical parameters decreases as a function of time, and becomes zero when steady state is reached. In contrast, accumulation of cadmium in soil and the plant uptake rate of barley are increasingly sensitive to soil chemical and soil physical parameters as time preceeds. To analyse cadmium behaviour in a field that is heterogeneous with respect to soil physical properties, the interstitial flow velocity was assumed to be a random, lognormally distributed variate. Using Monte Carlo simulation, the average plant uptake rate appeared to be much higher in the stochastic analysis than in the deterministic approach. Steady state is reached after a very long period of time. For a lognormally distributed proton activity, causing heterogeneity with respect to the sorption capacity of the soil, the model predicted similar deviations from the deterministic approach. It is concluded that reference values for groundwater and crop quality are exceeded earlier in a heterogeneous field than in a homogenous soil profile. Moreover, when average values suggest an acceptable situation, variability of the leaching rate and the plant uptake rate can still cause exceedance of reference values in part of the field. Therefore, it is reasoned that environmental quality standards should take soil heterogeneity into account.

Consequences of rhizosphere acidification on delivery and uptake kinetics of soil phosphorus.

Experiments were undertaken to quantify the mechanisms by which acidity might affect phosphorus movement and uptake by black locust (Robinia pseudoacacia L.). Phosphorus diffusion rates in six forest soils were determined by desorption-isotherm buffer power assays. Changes in diffusion as a function of acidity were measured using pH-adjusted desorption solutions. Depending on soil type and phosphorus source solubility, up to a fivefold increase in phosphorus diffusion rate was observed with an increased acidity of one pH unit. Phosphorus uptake rates of mycorrhizal and non-mycorrhizal black locust at pH 4 and pH 7 were determined from (32)P-labeled nutrient-depletion experiments. In mycorrhizal plants, the rate of phosphorus uptake at pH 4.0 was twice that observed at pH 7.0. Non-mycorrhizal plant uptake rates were similar at both pH 4.0 and pH 7.0. The contribution of soil nutrient supply mechanisms to plant nutrient content increased with rhizosphere acidification. Uptake kinetics were also affected by rhizosphere acidification, but to a lesser extent.

The nitrogen budget of a hybrid poplar plantation in Minnesota

The nitrogen (N) dynamics within short-rotation intensive-culture forest plantations are poorly understood. We developed a N budget for a 3-year-old hybrid poplar plantation under short-rotation intensive-culture management in northwestern Minnesota. Measured pools and fluxes of N included plant content, atmospheric input, litter fall, microbial biomass, mineralization, nitrification, and denitrification. Total aboveground tree biomass represented only 1.6% of the total N capital. Stable soil organic N was the largest pool, 5670 kg N•ha−1, and constituted 93% of all N within the site. Labile soil organic N and microbial N represented 5.6 and 1.6% of stable soil organic N, respectively. Nitrogen mineralization averaged 56 kg N•ha−1•year−1, and 66% of that production was oxidized to NO3−. Losses of N by denitrification and leaching were small compared with the magnitude of the other fluxes. Results suggest that a relatively high rate of plant uptake and production maintained NH4+ and NO3− pools at low levels, minimizing N exports to the atmosphere and groundwater.

Dynamics of soil and plant nitrogen in cultivated and no-till spring wheat systems following old pasture

Abstract When old pasture is cultivated, nitrogen (N) may be released in quantities that exceed crop demand. No-till cropping is an option that may be more conservative of N. This report considers uptake and distribution of N by a wheat crop established by full cultivation or no-till methods, out of 12-year-old clover/grass pasture. N uptake was more rapid in cultivated soil and in both systems was essentially complete after 40 days. The no-till treatment did show some further N accumulation later in the season during grain fill. Mineral N values and plant uptake rates indicate that N mineralisation was rapid in both systems but only just adequate in no-till. Sampling the soil to 1.5 m depth in the winter following the crop showed both systems to have similar and substantial (about 160 kg N/ha) quantities of NO3-N moving through the profile.

A dynamic growth model of vegetative soya bean plants: model structure and behaviour under varying root temperature and nitrogen concentration.

A differential equation model of vegetative growth of the soya bean plant (Glycine max (L.) Merrill cv. Ransom') was developed to account for plant growth in a phytotron system under variation of root temperature and nitrogen concentration in nutrient solution. The model was tested by comparing model outputs with data from four different experiments. Model predictions agreed fairly well with measured plant performance over a wide range of root temperatures and over a range of nitrogen concentrations in nutrient solution between 0.5 and 10.0 mmol NO3- in the phytotron environment. Sensitivity analyses revealed that the model was most sensitive to changes in parameters relating to carbohydrate concentration in the plant and nitrogen uptake rate.

A model for the release of sulfur from elemental S and superphosphate

A mathematical model was developed to predict the release of sulfate from elemental S (S0) and gypsum in single superphosphate. The release algorithm is based on the observation that release is linearly related to particle surface area. Release rates under various conditions could then be described by the change in radius for each time increment, which allows easier comparison of release rates between different particle sizes. A model based on spherical particles was found to be adequate in accounting for the range of particle shapes found in crushed agricultural S0. Release rates calculated from experimental data range from 0.07 to 0.45µm/d depending on environmental conditions. Equations for incorporating the effects of environmental variables and the release of S from S0 and from the gypsum component of single superphosphate (SSP) were developed from the literature, and were incorporated within a larger model of S cycling. The model predicted that after 72 days, 99% of the S in SSP would have been released, compared to a release after one year of 54% of the S in sulfur-fortified superphosphate, and 23% of that in crushed agricultural grade S0. The model provides a means of assessing the effect of the particle size of S0 on release rates and should allow the formulation of fertilizers that supply S at a rate closer to the rate of plant uptake.

Effects of prolonged flooding on soybean at the R2 growth stage II. N and P uptake and translocation

Abstract Knowledge of N and P uptake and translocation is essential for a greater understanding of soybean [Glycine max (L.) Merrill] nutrient relations under flooding conditions. A field experiment was conducted on a Crowley silt loam (Typic Albaqualf) to determine N and P uptake and translocation rates in soybean under flooded and non‐flooded conditions. Forrest soybean were flooded at the R? growth stage for 7 consecutive days at a flood height of 2.5 cm. The soybean were partitioned into stems, branches, leaves, and pods at 0, 7, 14, 21, 36, and 62 days after flooding. Dry matter, N and P concentrations, and total amounts of N and P accumulated for each compartment were determined at each sampling time. Calculations of whole plant uptake and translocation rates of N and P were made of the plant parts and of the nodes during the five intervals. The leaves and then the branches were the first plant parts to respond to the prolonged flooding. Leaves of the flooded plants had a greater decrease in N fluxe...

External phosphorus requirements of five tropical grain legumes grown in flowing-solution culture

Five tropical grain legume species were grown for periods from 4 to 20 days in flowing-solution culture at 7 maintained phosphorus (P) concentrations, ranging from 0.25 μM to 16 μM. Critical external P requirements were 0.8 μM for cowpea cv. Vita 4 and soybean cv. Fitzroy, 1.0 μM for pigeon pea cv. Royes, 2.0 μM for mungbean cv. Regur and 3.0 μM for guar cv. Brooks. Plant responses to P deficiency included reduced growth rate, increased root percentage, and increased P uptake potential. The long-term P uptake rates of guar plants were lower than those of the other species at each external P concentration. Guar plants had a low P uptake potential as indicated by short-term32CP-labelled uptake rate studies from 15 μM P solutions. Cowpea by contrast had high short-term uptake rates indicating a high P uptake potential.

Phosphorus Relationships in Potato Plants1

AbstractMaximum potato (Solanum tuberosum L.) tuber yields occur when an active plant canopy is maintained until normal plant maturation. Plant nutrient concentrations and uptake rates play a major role in maintaining an active plant top. The objectives of this study were to relate the plant P concentrations to the P and dry matter balance between tuber and total plant growth needs. Growth analysis data, plant and leaf total P concentrations and content, and the petiole soluble P concentrations were obtained on a 10‐to 14‐day sampling interval from P fertilization treatments in replicated field studies. The P concentration of the plant tops was significantly related to the petiole soluble P concentration and the P concentration of the active leaves. Total plant P uptake and dry matter production rates were not adequate for the tuber growth rate when the total P concentrations of the tops and active leaves were less than 2.2 g P kg−1. Soluble P concentrations in the fourth petiole down from the growing tip were less than 1000 and 700 mg kg−1 when P uptake and dry matter production rates were not adequate for tuber growth, respectively. Final tuber yields increased from 30 to 70 Mg ha−1 as the number of growing days past tuber set increased from 10 to 60 days for which the P concentration of the tops was above 2.2 g P kg−1. The petiole soluble P concentration decreased during the growing season following a semi‐logarithmic relationship. This relationship enabled the prediction of the petiole soluble P concentration for the rest of the growing season and could be used to predict when to apply supplemental P fertilizer.

Response of source–sink relationship in soybean to temperature

The need for carefully defined conditions to demonstrate sink-source interaction was investigated using 'Biloxi' soybean grown under defined growth conditions. When the source area was reduced in seedlings by removal of the cotyledons and one primary leaf, the CO2 uptake in the remaining leaf was increased at 24 °C but not at 27 °C. The 17% increase in the rate of CO2 uptake at 24 °C was accompanied by an increase of assimilate export of about 5% over 24 h. The effects on CO2 uptake at 21 and 30 °C were smaller than at 24 °C but larger than at 27 °C. The percentage of assimilated 14C that was translocated was also increased at 27 °C, but there was no accompanying stimulation of CO2 uptake. Fruiting plants at 24 °C had close to double the CO2 uptake rates of barren plants; whereas at 27 °C the rates were the same. Removing the pods reduced the CO2 uptake at 24 °C to close to that of barren plants. Sink activity appeared to limit CO2 uptake over a very narrow temperature range below optimum temperatures for growth, whereas at optimum temperatures CO2 uptake appeared to limit growth.