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T.R. Roper, A.R. Krueger, C.J. DeMoranville, N. Vorsa, J. Hart, and A.P. Poole

Nitrogen fertilizer application is a universal practice among cranberry growers. Cranberries only use ammonium nitrogen sources. This study was undertaken to discover how quickly cranberries in the field would take up fertilizer-derived ammonium nitrogen. Ammonium sulfate labeled with 15N was applied in field locations in Oregon, Massachusetts, New Jersey, and Wisconsin. Samples of current season growth were collected daily for 7 days beginning 24 hours after fertilizer application. In all cases 15N was detectable in the plants from treated plots by 24 hours following application. Additional nitrogen was taken up for the next 3 to 5 days depending on the location. With the exception of Oregon, the maximum concentration of 15N was found by day 7. Oregon was the coolest of the sites in this research. To determine a temperature response curve for N uptake in cranberry, cranberry roots were exposed to various temperatures in aeroponics chambers while vines were at ambient greenhouse temperatures. The optimum temperature for N uptake by cranberry vines was 18 to 24 °C. This research suggests that ammonium fertilizers applied by growers and irrigated into the soil (solubilized) are taken up by the plant within 1 day following application. Soil and root temperature is involved in the rate of N uptake.

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Heidi A. Kratsch* and William R. Graves

Alnus maritima (Marsh.) Muhl. ex Nutt. is unique among alders in its degree of preference for low-oxygen soils of wetlands. An actinorhizal species with promise for use in sustainable horticulture, A. maritima develops a root-nodule symbiosis with nitrogen-fixing Frankia. Nodules of other actinorhizal species that are obligate wetland natives are adapted to low oxygen, and expression of hemoglobin is common to these taxa. Our objectives were to determine the range of oxygen tension under which Alnus maritima subsp. maritima fixes nitrogen and to investigate a potential role for hemoglobin in adaptation of nodules to low oxygen. Roots of plants, cultured aeroponically, were subjected to eight oxygen tensions from 0 to 32 kPa. After four weeks, plant dry weight, nodule fresh weight, nitrogenase activity, and photosynthetic rate were measured. In addition, nodules were assayed spectrophotometrically for the presence of hemoglobin. A quadratic function best described the influence of oxygen on plant dry weight, nodule fresh weight, nitrogenase activity, and photosynthetic rate with maximal values above 20 kPa. Alnus serrulata (Ait.) Willd. is sympatric with A. maritima subsp. maritima but is not an obligate inhabitant of wetlands. In a separate experiment, we found higher nitrogenase activity in A. maritima subsp. maritima than in A. serrulata (0.74 vs. 0.26 μmol/h per plant) at hypoxic oxygen tensions. Further, optical absorption spectra of nodule extracts confirmed hemoglobin within nodules of A. maritima subsp. maritima. Our data suggest that hemoglobin contributes to oxygen regulation in nodules of A. maritima subsp. maritima.

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Thomas E. Marler, Ruben dela Cruz, and Andrea L. Blas

Four papaya (Carica papaya L.) cultivars were cultured aeroponically or in perlite to determine the magnitude, timing, and root locality of Fe reductase induced by Fe deficiency. Five soybean [Glycine max (L.) Merrill] lines with a known range of Fe-deficiency chlorosis scores were cultured in perlite for comparison. Speed of inducement of Fe reductase activity was determined in plants cultured without Fe for 0 to 17 days. Location of Fe reductase activity was determined by sectioning roots from the tip to 60 to 70 mm proximal to the root tip from plants cultured without Fe for 16 to 19 days. The Fe reductase system was induced in all papaya cultivars after 7 to 11 days without Fe, and activity increased through 17 days. Iron reductase activity in all papaya cultivars was comparable to the most tolerant soybean line. The zone of highest activity was the apical 10 mm of roots. These results indicate that papaya roots are highly efficient in induced Fe reductase activity. The highest activity in root tips underscores the importance of maintaining a healthy, continually growing root system with numerous growing points when culturing papaya in alkaline substrates.

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J.M. Quintana, H.C. Harrison, J.P. Palta, J. Nienhuis, K. Kmiecik, and E. Miglioranza

Two commercial snap bean (Phaseolus vulgaris L.) cultivars (Hystyle and Labrador) that differ in pod Ca concentration were grown aeroponically to assess physiological factors associated with these differences. Xylem flow rate, Ca absorbed, and Ca concentration in sieve sap and pods (all and commercial size no. 4) were measured. Flow rate, Ca absorption and pod Ca concentration, but not sap Ca concentration, differed between cultivars, and this suggests that genetic variability in pod Ca concentration is caused mainly by differences in flow rate, rather than differences in sap Ca concentration. `Hystyle' showed 1.6 times greater flow rate, 1.5 times greater pod Ca concentration, and 1.7 times greater Ca absorbed than `Labrador'. Flow rate correlated positively with Ca absorbed (R = 0.90), Ca concentration in pods of size no. 4 (R = 0.55), and total pods (R = 0.65). Plant maturity influenced sap Ca concentration and Ca translocated increased as plant matured. These results provide evidence that flow rate differences may cause variability for pod Ca concentration in snap beans.

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Bryan J. Peterson, Stephanie E. Burnett, and Olivia Sanchez

-free environment. A potential alternative to overhead mist is submist aeroponics, which relies on the application of mist from below the cutting, to the base of the stem inserted into an enclosed chamber. Several systems are available on the consumer market for use

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potential to improve irrigation management for growers in southern Georgia. Propagating Nursery Crops with Submist Aeroponics Submist aeroponic systems have been largely unexplored for the propagation of woody nursery crops, which are generally rooted using

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. Half of the plants from each rate received an application of a PGR, paclobutrazol. Fertigation with 3–5 ppm P and no PGR application provided similar height control to that of 20 ppm P and a standard PGR application. Submist Aeroponics: An Alternative

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Kathryn M. Santos, Paul R. Fisher, and William R. Argo

supply during three rooting phases in propagation of Petunia × hybrida ‘Supertunia Royal Velvet’ and ‘Supertunia Priscilla’ cuttings. Materials and Methods Aeroponics design. An aeroponics system was developed with the capability to apply

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Laban K. Rutto, Myong-Sook Ansari, and Michael Brandt

(1971) demonstrated that stinging nettle benefits from high P availability. In the United States, Hayden (2006) developed a system for aeroponic and hydroponic production of stinging nettle herb and root, and Kleitz et al. (2008) report a

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Bielinski M. Santos and Persio R. Rodriguez

multiplication programs, ensuring tuber quality and supply. Potato seed programs rely on open-field, greenhouse, or hydroponic/aeroponic production systems to obtain small tubers or “minitubers,” which are used for further multiplications. Previous research has