1991. A method for measuring hyphal nutrient and water uptake in mycorrhizal plants. Can. J.Bot. 69: 87-94.A new system was designed that permits examination of long distance transport of water and nutrients through mycorrhizal hyphae without the architectural, nutritional, and physiological differences associated with comparing mycorrhizal and nonmycorrhizal plants. The "rhizobox" system consists of a rectangular box with a chamber where mycorrhizal plants are grown and an outer chamber where hyphae proliferate. The two chambers are separated by root-excluding screens and an air gap. Two slightly different experiments examined hyphal transport. The first experiment demonstrated the difficulties of comparing water use by mycorrhizal and nonmycorrhizal plants because of dissimilarities in plant architecture. The second experiment avoided the problem by comparing intact mycorrhizal plants with plants where hyphae passing to the outer chamber were severed. In the outer chamber, a 5 rnM solution of RbCl was injected. Intact mycorrhizal plants transpired 35% more water than plants with severed hyphae in 16 h. The source of transpired water was the outer chamber, as suggested by lower soil moisture in the outer chamber and a higher Rb content in intact plants. This demonstrates an active role in water and nutrient transport by mycorrhizal hyphae, since plants were of a similar nature except for hyphal access to the outer chamber. ., et SHACKEL, K. 1991. A method for measuring hyphal nutrient and water uptake in mycorrhizal plants. Can. J. Bot. 69 : 87-94. Un nouveau systkme a Ct C dCveloppC afin d'examiner le transport sur de longues distances de l'eau et des nutriments dans les hyphes mycorhiziens, en excluant les diffkrences architecturales, nutritionnelles et physiologiques inCvitables lorsqu'on compare des plantes mycorhiziennes et non mycorhiziennes.Le ccrhizobox* est constituC d'une boite rectangulaire comportant une chambre oh se dCveloppent les plantes mycorhiziennes, adjacente a une autre chambre ou se dCveloppent les hyphes.Les deux chambres sont stparCes par des tamis qui retiennent les racines et entre lesquels on trouve un espace d'air. Le transport dans les hyphes a Ct C CtudiC dans deux expkriences 1Cgbrement diffkrentes. La premikre dCmontre les difficultks qui existent comparer l'utilisation de l'eau par des plantes mycorhizCes ou non mycorhiztes, a cause des diffkrences dans l'architecture des plantes. La deuxikme expirience contourne le problbme en comparant des plantes mycorhiziennes intactes avec des plantes dont les hyphes passant a la chambre extCrieure ont Ct C coupks. On injecte une solution de RbCl 5 mM dans la chambre extCrieure. Les plantes dont les hyphes restent intacts montrent, sur une pCriode de 16 h, une transpiration 35% suptrieure a celles dont les hyphes ont Ct C coupCs. La source d'eau transpirke se trouve dans la chambre exterieure, tel que suggtrC par une humidit6 plus basse dans la chambre externe et un contenu en Rb plus ClevC dans les plantes intactes. Ceci dCmontre un r6le ac...

Pot-grown mycorrhizal and non-mycorrhizal sweet corn were grown in a low Zn soil. All treatments received a complete nutrient solution with or without Zn. Treatments were harvested sequentially to detemine temporal mycorrhizal effects on: (a) tissue and water soluble Zn and (b) differential uptake of P and Zn. Plants grown with supplemental Zn had greater growth and Zn tissue concentration than those not receiving Zn. With no supplemental Zn, mycorrhizal treatments had greater growth and Zn concentration than non-mycorrhizal treatments. There was no indication of nutrient interaction between Zn and P. Over the range of tissue Zn found, there appeared to be no advantage to water soluble Zn analysis over total Zn in assessing plant Zn status.

Methods for Zn fertilization of `Hass' avocado (Persea americana Mill.) trees were evaluated in a 2-year field experiment on a commercial orchard located on a calcareous soil (pH 7.8) in Ventura County, Calif. The fertilization methods included soil- or irrigation-applied ZnSO4; irrigation-applied Zn chelate (Zn-EDTA); trunk injection of Zn(NO3)2, and foliar applications of ZnSO4, ZnO, or Zn metalosate. Other experiments evaluated the influence of various surfactants on the Zn contents of leaves treated with foliar-applied materials and on the retention and translocation of radiolabeled 65ZnSO4 and 65Zn metalosate after application to the leaf surface. In the field experiment, tree responses to fertilization with soil-applied materials were affected significantly by their initial status, such that only trees having <50 μg·g–1 had significant increases in foliar Zn contents after fertilization. Among the three soil and irrigation treatments, ZnSO4 applied at 3.2 kg ZnSO4 per tree either as a quarterly irrigation or annually as a soil application was the most effective and increased leaf tissue Zn concentrations to 75 and 90 μg·g–1, respectively. Foliar-applied ZnSO4, ZnO, and Zn metalosate with Zn at 5.4, 0.8, and 0.9 g·liter–1, respectively, also resulted in increased leaf Zn concentrations. However, experiments with 65Zn applied to leaves of greenhouse seedlings showed that <1% of Zn applied as ZnSO4 or Zn metalosate was actually taken up by the leaf tissue and that there was little translocation of Zn into leaf parenchyma tissue adjacent to the application spots or into the leaves above or below the treated leaves. Given these problems with foliar Zn, fertilization using soil- or irrigation-applied ZnSO4 may provide the most reliable method for correction of Zn deficiency in avocado on calcareous soils.

Recycling or collection ponds are often used in outdoor container nursery production to capture and recycle runoff water and fertilizers. Waters in recycling ponds generally have high concentrations of nutrients, pesticides, and dissolved organic matter, as well as elevated salinity and turbidity. Little is known about pesticide degradation behavior in the unique environment of nursery recycling ponds. In this study, degradation of four commonly used pesticides diazinon, chlorpyrifos, chlorothalonil, and pendimethalin in waters from two nursery recycling ponds was investigated at an initial pesticide concentration of 50 microg/L. Results showed that the persistence of diazinon and chlorpyrifos appeared to be prolonged in recycling pond waters as compared to surface streamwaters, possibly due to decreased contribution from biotic transformation, while degradation of chlorothalonil and pendimethalin was enhanced. Activation energies of biotic degradation of all four pesticides were lower than abiotic degradation, indicating that microbial transformation was less affected by temperature than chemical transformation. Overall, the pesticide degradation capacity of recycling ponds was better buffered against temperature changes than that of surface streamwaters.

Potential water quality impacts of agricultural production include runoff and leaching losses of nutrients, pesticides, and sediment. Stormwater runoff and soil water samples were collected from citrus (Citrus spp.), avocado (Persea americana), and ornamental nursery sites in Ventura County, CA, across 19 months. Nitrate–nitrite–nitrogen concentrations in runoff ranged from 0.07 to 31.1 mg·L−1, with medians for groves and nurseries of 4.2 and 5.7 mg·L−1, respectively. Constituents in runoff exceeding benchmarks for surface waters included turbidity, chlorpyrifos, and some organochlorine pesticides. When detected, chlorpyrifos concentration was linearly related to sample turbidity (P = 0.0025, r2 = 0.49). This suggests that the retention of waterborne sediments on-site may be an effective method for mitigating runoff of this pesticide. Bifenthrin, permethrin, and diazinon were also detected in runoff, but concentrations did not exceed water quality benchmarks. Nutrient concentrations in soil water were generally similar to nutrient concentrations in stormwater runoff, suggesting that potential groundwater contamination from leaching at citrus, avocado, and nursery sites may be as much of a concern as stormwater from these operations, particularly on sites with sandy or structured soil texture or flat topography. Nitrate–nitrite–nitrogen and orthophosphate concentrations in soil water were linearly related to nitrogen and phosphorus fertilizer application rates across sites, respectively (P < 0.0001, r2 = 0.49 and 0.50, respectively), suggesting that proper nutrient management is important in reducing potential groundwater contamination at these operations.