附生兰科植物根被组织研究概述

植物根被组织是指存在于附生兰科植物、地生兰科植物、一些石蒜科、天南星科、薯蓣科以及百合科植物根部的典型适应性结构特征;成熟根被组织是由1～25层左右死细胞构成的白色鞘,其细胞壁多有螺旋式增厚,呈天鹅绒状或网状、羽毛状结构,具有海绵质地.该组织有六种应用于分类学特征的形态,依据这六种形态可将其分为12种类型;根被组织具有...     

On the occurrence of a velamen radicum in Cyperaceae and Velloziaceae

Roots of tree-like Cyperaceae ( Afrotrilepis pilosa, Bulbostylis leucostachya, Coleo-chloa setifera, Microdracoides squamosus ) and Velloziaceae ( Vellozia variegata, Xe-rophyta pinifolia ) were examined by light and scanning electron microscopy. For the first time a velamen is reported for Bromeliiflorae and Commeliniflorae. All species studied possess a velamen radicum that is either one-layered ( Microdracoides, Bulbostylis, Coleochloa ) or multi-layered ( Afrotrilepis, Vellozia, Xerophyta ). Anticlinal walls of the velamen cells of Microdracoides show perforations similar to those found in orchids. A multiple exodermis delimits the velamen towards the cortex. As in epiphytic Orchidaceae, a velamen may be of considerable adaptive value for arborescent Cyperaceae and Velloziaceae. These mainly occur in edaphically and climatologically extreme habitats (e.g. tropical inselbergs) where rapid water uptake is of crucial importance.     

Effects of low water potential on ion uptake and loss for excised roots

Summary In excised roots of barley and tomato plants, lowering the water potential of nutrient solutions to-10.4 and-20.4 atm decreased the uptake of bromide and phosphorus while increasing the loss of these ions to the external solutions.Lowering the water potential greatly increased the rate of loss of potassium and bromide from the cytoplasm, but the increases in loss from the vacuoles were much smaller. The results suggest that the mechanisms of ion uptake are not affected by low water potential and that the decrease in ion accumulation is caused by the increased leakage from the cells.     

First observation of diffusion-limited plant root phosphorus uptake from nutrient solution

Diffusion towards the root surface has recently been shown to control the uptake of metal ions from solutions. The uptake flux of phosphorus (P) from solutions often approaches the maximal diffusion flux at low external concentrations, suggesting diffusion-controlled uptake also for P. Potential diffusion limitation in P uptake from nutrient solutions was investigated by measuring P uptake of Brassica napus from solutions using P-loaded Al(2) O(3) nanoparticles as mobile P buffer. At constant, low free phosphate concentration, plant P uptake increased up to eightfold and that of passive, diffusion-based samplers up to 40-fold. This study represents the first experimental evidence of diffusion-limited P uptake by plant roots from nutrient solution. The Michaelis constant of the free phosphate ion obtained in unbuffered solutions (K(m) = 10.4 μmol L(-1) ) was 20-fold larger than in the buffered system (K(m) ～0.5 μmol L(-1) ), indicating that K(m) s determined in unbuffered solutions do not represent the transporter affinity. Increases in the P uptake efficiency of plants by increasing the carrier affinity are therefore unlikely, while increased root surface area or exudation of P-solubilizing compounds are more likely to enhance P uptake. Furthermore, our results highlight the important role natural nanoparticles may have in plant P nutrition.     

Velamen and exodermis characters of West African epiphytic orchids in relation to taxonomic grouping and habitat tolerance

The velamen and exodermis of roots of 76 species of epiphytic orchids occurring in West Africa were examined and evaluated for the following characters: number of velamen layers; wall striations and hairs of the velamen; wall thickening and lignification of velamen and exodermal cells; size, and uniformity in shape and size, of velamen and exodermal cells. The term epi-velamen is proposed for the distinctive outermost layer of multi-seriate velamen. High correlation is reported between the number of velamen layers and taxonomic as well as habitat-tolerance groupings, together with lower, but still appreciable, correlation between the other characters evaluated and taxonomic and habitat-tolerance groupings.     

STRANGLER FIG ROOTING HABITS AND NUTRIENT RELATIONS IN THE LLANOS OF VENEZUELA

The strangler figs, Ficus pertusa and F. trigonata, are abundant in the seasonally flooded palm savanna (llanos intermedio) near Calabozo, Venezuela. The most common host tree for the hemiepiphytic figs is the palm Copernicia tectorum; nearly half of the palms support either an epiphytic or a ground-rooted fig. During their epiphytic stage the figs are rooted behind the palms' marcescent leaf bases. Material trapped behind the leaf bases is higher in organic matter, nitrogen, magnesium, and potassium than soil from the ground near the palms. The suggestion that nutrient availability to epiphytes is high is supported by the observation that concentrations of several nutrients, including N, P, and K, are significantly higher in epiphytic leaves than in tree leaves. Figs retain access to the epiphytic medium by producing upwardly growing (apogeotropic) roots that remain attached in the host palm's crown long after the fig has become firmly rooted in the ground. Although upward growing roots are expected to be more important in nutrient than water uptake, there are no obvious differences in the xylem anatomy of upward and downward growing fig roots. Terrestrial roots of fig trees are generally infected with vesicular-arbuscular mycorrhizae, but the epiphytic roots of the same individuals are not infected.     

FIELD MEASUREMENTS OF INORGANIC NITROGEN UPTAKE BY EPIFLORA COMPONENTS OF THE SEAGRASS POSIDONIA OCEANICA (MONOCOTYLEDONS,POSIDONIACEAE)1

Crustose corallines, crustose and erect brown algae, and sessile animals are major components of the epiphytic community of the Mediterranean seagrass Posidonia oceanica (L.) Delile. Production, biomass, and specific composition of this epiphyte–seagrass association are impacted by anthropogenic increase of nutrient load in this oligotrophic area. In this context, nitrogen uptake by P. oceanica and its epiflora was measured using the isotope ¹⁵N at a 10 m depth in the Revellata Bay (Corsica, Mediterranean Sea). Epiflora components showed various seasonal patterns of biomass and abundance. The epiphytic brown algae appeared at the end of spring, later than the crustose corallines, and after the nitrate peak in the bay. Because of their later development in the season, epiphytic brown algae mostly rely on ammonium for their N needs. We hypothesize that the temporal succession of epiphytic organisms plays a crucial role in the N dynamics of this community under natural conditions. The epiphytic brown algae, which have a growth rate one order of magnitude greater than that of crustose corallines, showed lower N‐uptake rates. The greater N‐uptake rates of crustose corallines probably reflect the greater N requirements (i.e., lower C/N ratios) of red algae. We determined that the epiflora incorporated ammonium and nitrate more rapidly than their host. Nevertheless, when biomass was taken into account, P. oceanica was the most important contributor to N uptake from the water column by benthic macrophytes in this seagrass bed.     

Ethylene Modulates the Developmental Plasticity and the Growth Balance Between Shoot and Root Systems in the In Vitro Grown Epiphytic Orchid Catasetum fimbriatum

The epiphytic habitat is potentially one of the most stressful environments for plants, making the effective developmental control in response to external cues critical for epiphyte survival. Because ethylene mediates several abiotic stresses in plants, here, we have examined the ethylene influence in both shoot and root systems of the epiphytic orchid Catasetum fimbriatum. Under controlled conditions, ethylene production was quantified during an entire growth cycle of C. fimbriatum development in vitro, while treatments modulating either ethylene concentration or perception were carried out over the early growth phase of these plants. After treatments, growth measurements and histological features were studied in both shoot and root tissues. Ethylene production showed a decreasing trend over the period of organ elongation; however, it increased considerably when leaves were shed, and a new axillary bud was initiating. The early exposure of young plants to higher concentrations of ethylene triggered morphogenic responses that included root hair formation instead of velamen, and a combination of inhibitory effects (decreases in both stem enlargement and cellular/organ elongation) and inductive effects (increases in leaf and root formation, bud initiation and cellular thickening) on plant growth, which favored biomass allocation to roots. Conversely, inhibition of ethylene perception over the plant growth phase generally resulted in the opposite morphogenic responses. Our data indicate that periodic variations in ethylene concentration and/or sensitivity seem to modulate several developmental features in shoot and root systems of C. fimbriatum which could have adaptive significance during the growing phase of this epiphytic orchid.     

Nitrogen uptake

Summary Nitrogen uptake from applied nutrient solutions was evaluated in two old fields, in a pine plantation, and in a hardwood stand, to test the idea that plant communities become more efficient trappers and retainers of plant nutrients during succession. Uptake was estimated as the difference between nutrient concentrations in water collected from beneath soil profiles with and without roots by lysimeters within each successional stage. Results suggest that nitrate uptake decreased while ammonia uptake increased with succession. This apparent shift from a nitrate to an ammonia nitrogen economy during succession has been reported by other workers and is evolutionarily significant as an energy, nitrogen, and cation saving mechanism.     

Physiological diversity of orchids

The Orchidaceae is a diverse and wide spread family of flowering plants that are of great value in ornamental, medical, conservation, and evolutionary research. The broad diversity in morphology, growth form, life history, and habitat mean that the members of Orchidaceae exhibit various physiological properties. Epiphytic orchids are often characterized by succulent leaves with thick cell walls, cuticles, and sunken stomata, whereas terrestrial orchids possess rhizomes, corms, or tubers. Most orchids have a long juvenile period, slow growth rate, and low photosynthetic capacity. This reduced photosynthetic potential can be largely explained by CO₂ diffusional conductance and leaf internal structure. The amount of light required for plant survival depends upon nutritional mode, growth form, and habitat. Most orchids can adapt to their light environments through morphological and physiological adjustments but are sensitive to sudden changes in irradiance. Orchids that originate from warm regions are susceptible to chilling temperatures, whereas alpine members are vulnerable to high temperatures. For epiphytic orchids, rapid water uptake by the velamen radicum, water storage in their pseudobulbs and leaves, slow water loss, and Crassulacean Acid Metabolism contribute to plant-water balance and tolerance to drought stress. The presence of the velamen radicum and mycorrhizal fungi may compensate for the lack of root hairs, helping with quick absorbance of nutrients from the atmosphere. Under cultivation conditions, the form and concentration of nitrogen affect orchid growth and flowering. However, the limitations of nitrogen and phosphorous on epiphytic orchids in the wild, which require these plants to depend on mycorrhizal fungi for nutrients throughout the entire life cycle, are not clearly understood. Because they lack endosperm, seed germination depends upon obtaining nutrients via mycorrhizal fungi. Adult plants of some autotrophic orchids also gain carbon, nitrogen, phosphorus, and other elements from their mycorrhizal partners. Future studies should examine the mechanisms that determine slow growth and flower induction, the physiological causes of variations in flowering behavior and floral lifespan, the effects of nutrients and atmospheric-nitrogen deposition, and practical applications of mycorrhizal fungi in orchid cultivation.     

Functional differences in epiphytic microbial communities in nutrient-rich freshwater ecosystems: an assay of denitrifying capacity

1. The denitrifying capacity of epiphyton was used to evaluate differences in the function of epiphytic microbial communities on submersed macrophytes in nutrient-rich freshwater ecosystems. The denitrifying capacity of epiphyton on Potamogeton perfoliatus shoots of different age and with different epiphytic abundances from a eutrophic lake was investigated in laboratory microcosms in the light and dark. Additionally, differences between epiphyton on shoots of Potamogeton pectinatus grown under different in situ nutrient and hydraulic conditions were investigated by examining their denitrifying capacity.
2. Denitrification was registered in well-developed epiphytic layers on both mature and senescent shoots in the dark, with activities 3- to 10-fold higher in the epiphytic communities of senescent shoots. No activity was detected on young shoots with sparse epiphyton or on shoots from which loosely attached epiphyton had been removed. Denitrification never occurred during illumination.
3. Even though the epiphytic abundance was similar in magnitude, the denitrifying capacity of epiphyton adapted to high nutrient loadings was about a hundred times higher than that of epiphyton adapted to lower nutrient levels. Additionally, epiphytic abundance and denitrifying capacity were higher at sites less exposed to wave turbulence or water currents, than at sites with more water turbulence.
4. The results illustrate how the hydraulic and nutrient conditions of the surrounding water affect both the quantity and function of epiphytic microbial communities in nutrient-rich freshwater ecosystems.     

Functional differences in epiphytic microbial communities in nutrient-rich freshwater ecosystems: an assay of denitrifying capacity

1. The denitrifying capacity of epiphyton was used to evaluate differences in the function of epiphytic microbial communities on submersed macrophytes in nutrient-rich freshwater ecosystems. The denitrifying capacity of epiphyton on Potamogeton perfoliatus shoots of different age and with different epiphytic abundances from a eutrophic lake was investigated in laboratory microcosms in the light and dark. Additionally, differences between epiphyton on shoots of Potamogeton pectinatus grown under different in situ nutrient and hydraulic conditions were investigated by examining their denitrifying capacity.
2. Denitrification was registered in well-developed epiphytic layers on both mature and senescent shoots in the dark, with activities 3- to 10-fold higher in the epiphytic communities of senescent shoots. No activity was detected on young shoots with sparse epiphyton or on shoots from which loosely attached epiphyton had been removed. Denitrification never occurred during illumination.
3. Even though the epiphytic abundance was similar in magnitude, the denitrifying capacity of epiphyton adapted to high nutrient loadings was about a hundred times higher than that of epiphyton adapted to lower nutrient levels. Additionally, epiphytic abundance and denitrifying capacity were higher at sites less exposed to wave turbulence or water currents, than at sites with more water turbulence.
4. The results illustrate how the hydraulic and nutrient conditions of the surrounding water affect both the quantity and function of epiphytic microbial communities in nutrient-rich freshwater ecosystems.     

Ectomycorrhizas and water relations of trees: a review

There is plenty of evidence for improved nutrient acquisition by ectomycorrhizas in trees; however, their role in water uptake is much less clear. In addition to experiments showing improved performance during drought by mycorrhizal plants, there are several studies showing reduced root hydraulic conductivity and reduced water uptake in mycorrhizal roots. The clearest direct mechanism for increased water uptake is the increased extension growth and absorbing surface area, particularly in fungal species with external mycelium of the long-distance exploration type. Some studies have found increased aquaporin function and, consequently, increased root hydraulic conductivity in ectomycorrhizal plants while other studies showed no effect of ectomycorrhizal associations on root water flow properties. The aquaporin function of the fungal hyphae is also likely to be important for the uptake of water by the ectomycorrhizal plant, but more work needs to be done in this area. The best-known indirect mechanism for mycorrhizal effects on water relations is improved nutrient status of the host. Others include altered carbohydrate assimilation via stomatal function, possibly mediated by changes in growth regulator balance; increased sink strength in mycorrhizal roots; antioxidant metabolism; and changes in osmotic adjustment. None of these possibilities has been sufficiently explored. The mycorrhizal structure may also reduce water movement because of different fine root architecture (thickness), cell wall hydrophobicity or the larger number of membranes that water has to cross on the way from the soil to the xylem. In future studies, pot experiments comparing mycorrhizal and nonmycorrhizal plants will still be useful in studying well-defined physiological details. However, the quantitative importance of ectomycorrhizas for tree water uptake and water relations can only be assessed by field studies using innovative approaches. Hydraulic redistribution can support nutrient uptake during prolonged dry periods. In large trees with deep root systems, it may turn out that the most important function of mycorrhizas during drought is to facilitate nutrient acquisition.     

Effects of phosphate and pH stress on the growth and function of apple roots

Summary Effects of phosphate and pH stress on the growth and uptake functions of apple roots were studied over a period of fourteen days using split-root (2-way) seedlings in solution culture. The level of P fed to either or both halves of the root system was varied and a demineralized water control was also included. pH treatments consisted of using acidic nutrient solutions (pH 3 to 4) or nutrient solutions adjusted to pH 5.0 before use.Solution pH proved of paramount importance for the expression of P deficiency effects on root growth and water uptake. Where initial solution pH was favourable for root growth (pH 5), P deficiency stimulated root growth and water uptake per seedling even if the stress was localized. On the other hand, acidic solutions and the water control inhibited root growth and water uptake compared with +P controls. Where solution pH was favourable, P stress also led to an increase in the mean length per root versus the +P control suggesting that the plant adapted to stress by developing an exploratory type of root.Water use per seedling was predominantly a function of root size rather than leaf area since the treatments influenced root size to a much greater extent than leaf area. Uptake was positively related to root size in that adjusted solutions gave a higher water use than nonadjusted solutions. However, efficiency of water use per unit weight of root was consistently higher in the nonadjusted solutions and this appeared to be due to the presence of a larger number of root tips per unit weight of root in such solutions compared with root systems in pH adjusted solutions.Uptake of P per half root was higher from pH adjusted than from nonadjusted solutions and was also increased by increasing the P concentration. Further, for any one treatment P uptake per half root increased throughout the experiment indicating that uptake was influenced by root growth. However, in contrast to water uptake, uptake of P per unit weight or per unit surface area of root was not changed by pH adjustment nor was this parameter of uptake concentration dependent. That is, the above-mentioned pH and concentration effects on P uptake were mediated through effects on root growth.Comparing localized versus uniform placement of P, uptake of P was significantly higher from the uniform application. However, uptake from localized placement at pH 5 was markedly higher than uptake under pH stress and therefore if the pH of the medium remains favourable for root growth then the lower value for localized placement could probably be compensated for by further increasing the concentration of P applied.     

哀牢山山地森林不同附生地衣功能群的水分关系和光合生理特征

附生地衣是热带和亚热带山地森林生态系统中重要的结构性组分, 在生物多样性保护、环境监测、养分循环中发挥着重要作用。附生地衣按共生藻、生活型和繁殖策略的不同可划分为不同的功能群, 不同附生地衣功能群的分布格局存在较大的差异, 然而其生理生态机制仍不清楚。该研究以我国西南地区哀牢山亚热带山地森林中的附生地衣优势类群为研究对象, 对该地区蓝藻地衣、阔叶地衣、狭叶地衣及枝状地衣4种功能群的8种附生地衣的水分关系、光合生理特征等进行了测定分析, 结果显示: 不同功能群附生地衣的持水力和失水速率均存在差异, 其中蓝藻地衣具有较高的最大水分含量, 而枝状地衣的失水速率较快; 过高和过低的水分含量都会抑制附生地衣的光合作用, 但抑制程度有所差异; 蓝藻地衣的光合作用最适水分含量比较高, 表明它们的光合生理活动对水分条件要求较高, 所以它们偏好潮湿的生境, 同时蓝藻地衣的光补偿点比较低但光饱和点却不低, 反映出它们具有较宽的光强适应范围, 所以蓝藻地衣能够同时分布于强光和弱光生境中; 枝状地衣的光合最适水分含量较低, 表明它们的光合生理活动对水分条件要求不是很高, 能够适应较为干旱的环境, 同时枝状地衣的光补偿点和光饱和点都很高, 说明它们的光合生理活动对光照条件要求比较高, 所以它们广泛分布于强光生境中; 阔叶和狭叶地衣的光补偿点比较高, 说明它们更适应有充足光照条件的生境。     

Active and Passive Components of Sulfate Uptake in Sunflower Plants

The aim of the investigation was to identify components of active and passive ion uptake and transport in roots of plants and to assess their quantitative relations under different external and internal conditions. The uptake of radiosulfate and water by young sunflower plants from complete nutrient solutions labelled with ³⁵S was studied. The metabolism-linked nature of the sulfate uptake in the root following the passive migration into the apparent free space (AFS) was demonstrated by the addition of sodium. selenate, 2,4-dinitrophenol, potassium cyanide, and sodium azide to the nutrient solutions. The magnitude of the AFS measured on a root volume basis varied between 14 and 57 per cent depending on the pretreatment of the plants and the sulfate concentration of the nutrient solution. The variations were supposed to be due to different capacity to bind sulfate by exchange-adsorption within the AFS. The amounts of sulfate in different fractions of the total AFS-uptake were computed under certain theoretical assumptions. A quantitative connection was proposed between the magnitude of the adsorbed sulfate fraction in the AFS and the rate of active uptake into the symplasm. The exchange-adsorption probably constitutes the initial stage of active ion uptake. The stimulating effect by water on ion uptake would be an increase of the speed of transporting ions to, from, or along the adsorption sites in the AFS. Experiments conducted at temperatures in the nutrient solution between 5 and 35 C elucidated the multistep nature of ion transport within a root.     

DIAGNOSTIC ANATOMICAL CHARACTERS IN THE PLEUROTHALLIDINAE (ORCHIDACEAE)

An anatomical survey of 200 species in 22 genera of subtribe Pleurothallidinae (Orchidaceae) indicates which vegetative characters are of diagnostic value and at what taxonomic level. Most systematically useful characters are associated with the leaf, and include features of trichomes, cuticle, epidermis, hypodermis, spiral thickenings, and number of vein series. The secondary stem is of limited usefulness at higher levels. Number of velamen layers and protoxylem poles in the root may be reliable taxonomic indicators with certain limitations and precautions. The established subtribal phylogenetic trends of reduction in number of pollinia and specialization of the perianth may be correlated with particular anatomical trends, which are either reductionary also or involve specializations directly related to the water relations of the epiphytic habit.     

Water relations and photosynthetic characteristics in different functional groups of epiphytic lichens in montane forest of Ailaoshan

Aims There are abundant epiphytic lichens in the tropical and subtropical montane forest ecosystems, which are important components of forest canopy and play a vital role in biodiversity conservation, environmental monitoring and nutrient cycling. In accordance with photobiont type, growth form and reproductive strategy, the epiphytic lichens can be divided into different functional groups, with different distribution patterns. In this study we aim to explain this phenomenon from the perspective of physiological ecology. Methods The maximum water content, water loss curves, photosynthetic water and light response curves were determined in four epiphytic lichen functional groups, including cyanolichens, fruticose lichens, broadly lobed foliose lichens and narrowly lobed foliose lichens. Important findings The functional characteristics of epiphytic lichens influence their maximum water-holding capacity and rate of water loss. The cyanolichens have higher maximum water content, while the fruticose lichens have a faster water loss. The cyanolichens that are widely distributed in the moist habitats require particularly high moisture for their photosynthetic activities; their optimal water content for photosynthesis is higher in comparison with other groups. They also have a low light compensation point and a high light saturation point, which explain the wide range of light intensity of the habitat. The fruticose lichens, widely distributed in the relatively arid habitats with high irradiance, have high light compensation point and light saturation point, and low optimum water content for photosynthesis. The broadly lobed foliose lichens and the narrowly lobed foliose lichens have a high light compensation point and light saturation point; they preferably occur in habitats with strong light.     

Nitrogen and phosphorus uptake in seedlings of the seagrass Amphibolis antarctica in Western Australia

The uptake of nitrate, ammonium and phosphate was examined in vitro in seedlings of the seagrass Amphibolis antarctica ((Labill.) Sonder ex Aschers.). Uptake of all three nutrients was significantly correlated with external concentration up to 800 µ g l^–1. The uptake of nitrate (0–200 µ g NO₃-N g dry wt^–1 h^–1) was significantly lower than the uptake of ammonium (0–500 µ g NH₄-N g dry wt^–1 h^–1), suggesting that the seedlings have a higher affinity for this form of nitrogen in the water column.Data were in general agreement with uptake rates recorded for other seagrasses, notably Zostera marina. In comparison to the dominant macroalgae for the same region, seedlings had either similar or higher uptake rates in relation to external concentration, lending support to the hypothesis that seedlings, which do not possess roots, behave like macroalgae in terms of nutrient acquisition from the water column.A comparison with literature data on adult seagrass suggests, however, that seagrasses show lower uptake rates than macroalgae suggesting that the macroalgae, which are totally reliant on the water column for nutrients, are more efficient at uptake than seagrasses which may potentially use the sediment for a nutrient source.     

Measurement of short-term nutrient uptake rates in cranberry by aeroponics

Aeroponics, a soil-less plant culture system in which fresh nutrient solutions are intermittently or continuously misted on to plant roots, is capable of sustaining plant growth for extended periods of time while maintaining a constantly refreshed nutrient solution. Although used relatively extensively in commercial installations and in root physiology research, use of aeroponics in nutrient studies is rare. The object of this study was to examine whether nutrient uptake rates could be calculated for aeroponic systems by difference using measurements of concentrations and volumes of input and efflux solutions. Data were collected from an experiment with cranberry plants (Vaccinium macrocarpon Ait. cv. Stevens) cultured aeroponically with nutrient solutions containing various concentrations of ammonium-N and isotopically labelled nitrate-N. Validation of the calculated uptake rates was sought by: (1) evaluating charge balance of the solutions and total ion uptake (including proton efflux) and (2) comparison with N-isotope measurements. Charge balance and proton efflux calculations required use of chemical modelling of the solutions to determine speciation of dissolved phosphate and acid-neutralizing capacity (ANC). The results show that charge balance requirements were acceptably satisfied for individual solution analyses and for total ion uptake when proton efflux was included. Relative rates of nitrate/ammonium uptake determined by difference were in agreement with those determined by isotopic techniques. Additional information was easily obtained from this experimental technique, including evidence of diurnal variation in nutrient uptake, correlation between ammonium uptake and proton efflux, and the relationship between ion concentration and uptake. Use of aeroponic systems for non-destructive measurement of water and ion uptake rates for numerous other species and nutrients appears promising.