David Brauer

Herbage response to spacing of loblolly pine trees in a minimal management silvopasture in southeastern USA

Loblolly pine (Pinus taeda L.) silvopastures often are established and maintained on sites of poor soil fertility and minimal fertilizer input. Our objective was to determine whether row spacing affected yield, quality, and botanical composition of minimally managed herbage in loblolly pine early in the tree rotation. Plots were randomly located equidistant from bordering tree rows in each of eight alley width treatments that were 2.4, 3.6, 4.9, 7.3, 9.7, 12.2, 14.6 m wide, and no trees. Row spacing affected the yield, quality, and botanical composition of pasture five to six years in the rotation especially at densities exceeding 840 trees ha−1. Botanical composition shifted from predominantly cool-season to warm-season grasses between annual first- and second-harvests, respectively, which caused seasonal differences in several yield and quality traits. Tall fescue (Festuca arundinacea Schreb.) production appeared to be unsustainable under minimal management. Herbage yield generally increased, but quality and minerals (crude protein, IVDMD, Ca, and P) tended to decrease with spacing. The 4.9 m row spacing was minimally acceptable for herbage yield and quality. System design should seek to balance tree-crop yield and quality within the context of management constraints and site productivity.

Effects of Bafilomycin A1 and Metabolic Inhibitors on the Maintenance of Vacuolar Acidity in Maize Root Hair Cells.

Proton pumps of tonoplast membranes have been studied extensively in vitro, but data concerning their regulation in vivo are lacking. Effects of either anoxia, or the addition of KCN, 2-deoxy-d-glucose (deoxy-glucose), or bafilomycin-A1 (BAF) on vacuolar pH of maize (Zea mays L.) root hair cells were followed by fluorescence microscopy after loading of 2[prime]7[prime]-bis-(2-carboxyethyl)-5-(and-6) carboxyfluorescein. Root hair cells were able to maintain vacuolar acidity for at least 2 h in the presence of either 10 mM KCN or 50 mM deoxy-glucose or during anoxia. Treatments with either deoxy-glucose or KCN reduced total tissue ATP more than anoxia. ADP accumulated during anoxia and treatment with KCN as detected by in vivo 31P-NMR spectroscopy, but not during deoxy-glucose treatment. With control roots and roots treated with deoxy-glucose, the presence of BAF, a specific inhibitor of the V-type ATPase, caused alkalization of the vacuolar pH. However, either in the presence of KCN or under anoxic conditions, BAF was relatively ineffective in dissipating vacuolar acidity. Therefore, under anoxia or in the presence of KCN, unlike the situation with air or deoxy-glucose, the V-type ATPase apparently is not required for maintenance of vacuolar acidity.

Growth and nut production of black walnut in relation to site, tree type and stand conditions in south-central United States

Black walnut (Juglans nigra) is a prime tree species for agroforestry practices in the United States providing highly prized wood and nuts for human consumption and wildlife. In 54 black walnut stands in south central United States, the site index (i.e., mean dominant height [DH], at age 25 years) ranged between 5.2 and 21.4 m, and was independent of stand density. There were no differences in height and stem diameter (DBH) growth rates between stands with improved varieties and native stock. Most stands were in a “free growth” stage because of either early age or wide spacing. Mean annual increments in DBH and height were positively related both for improved varieties and native stock. Understory competition had a substantial detrimental effect on DH. In a 26 year-old stand, trees growing within Kentucky blue grass (Poa pratensis) had a site index 5 m greater than trees growing within tall fescue (Festuca arundinacea). Predicted nut yields in 2002 varied between 0 and 1370 kg of hulled nuts per ha. Improved varieties had, in general, higher nut yields than predicted from a nut yield-DBH equation developed for individual trees. Nut yields were highly variable both within and among stands, and were related to DBH in native stock but not in improved varieties.

Selective accumulation of the fluorescent pH indicator, BCECF, in vacuoles of maize root-hair cells

Summary The vacuolar-type H+ -ATPase localized on the tonoplast membrane is believed to regulate aciditywithin the vacuolar lumen. However, the ability to monitor vacuolar pH in situ can be difficult because of the use of destructive assays based on cell sap pH or accumulation of weak bases, or elicit ion of wound responses after impaling cells with a pH-sensing microelectrode. The goal of our present study was to identify a fluorescent pH probe that is localized in vacuoles of (Zea mays L.) root cells. When excised corn root segments were exposed to the ester derivative of 2′,7′ -bis-2-(carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) for 30 to 60 min, the root-hair cells preferentially became fluorescent. The distribution of the fluorescence within cells followed closest to that of the vacuole when fluorescent and phase contrast images were compared. The ratio of the fluorescence intensities at 535 nm using excitation wavelengths of 440 and 490 nm varied directly with pH between 4.5 and 7.5. The ratio of fluorescent intensities of BCECF-Iabeled root-hair cells indicated that the majority of the dye was localized in a compartment with an average pH of 5.8. The above data indicated that the BCECF was localized in the vacuoles of root-hair cells from maize seedlings, and the changes in the fluorescence ratio of BCECF may provide a means of monitoring changes of vacuolar pH in situ.

In vivo 133Cs-NMR a probe for studying subcellular compartmentation and ion uptake in maize root tissue.

Three 133Cs-NMR signals were observed in the spectra of CsCl-perfused and CsCl-grown maize seedling root tips. Two relatively broad lower field resonances were assigned to the subcellular, compartmented Cs+ in the cytoplasm and vacuole, respectively. The rate of area increase of the broader cytoplasmic Cs resonance was about 9-times faster than that of the vacuolar signal during the first 300 min of tissue perfusion with CsCl. In addition, the spin lattice relaxation time of the cytoplasmic Cs resonance was approx. 3-times shorter than that of the extracellular resonance, while the Cs+ signal associated with the metabolically less active vacuolar compartment exhibited a relaxation time comparable to that of the extracellular signal. 133Cs spectra of excised, maize root tips and excised top sections of the root adjacent to the kernel, each grown in 10 mM CsCl showed a difference in the relative areas of the Cs resonance corresponding to the distinct cytoplasm/vacuole volume ratio of these well differentiated sections of the root. The high correlation of counterion concentration with 133Cs chemical shifts suggested that the larger downfield shift exhibited by the cytoplasmic confined Cs+ was due principally to the higher ionic strength and protein content in this compartment. Such observations indicate that 133Cs-NMR might be employed for studying ionic strength, and osmotic pressure associated chemical shifts and the transport properties of Cs+ (perhaps as an analogue for K+) in subcellular compartments of plant tissues.

Temperature dependence and mercury inhibition of tonoplast-type H+-ATPase

The effects of changing temperature on ATP hydrolysis and proton pumping associated with the H+-ATPase of tonoplast membrane vesicles isolated from the maize root microsomal fraction were determined. In the range 5 to 45 degrees C, the maximal initial rate of ATP hydrolysis obeyed a simple Arrhenius model and the activation energy determined was approximately 14 kcal/mol. On the other hand, the initial proton pumping rate showed a bell-shaped temperature dependence, with maximum activity around 25 degrees C. Lineweaver-Burke analysis of the activities showed that the Km of ATP hydrolysis, unlike that of proton pumping, was relatively insensitive to temperature changes. Detailed kinetic analysis of the proton pumping process showed that the increase in membrane leakage to protons during the pumping stage constituted a major reason for the decreased transport. Nitrate-sensitive ATPase activities of the tonoplast vesicles were found to be inhibited by the presence of micromolar concentrations of Hg2+. The proton pumping process was more sensitive to the presence of Hg2+. Double-reciprocal analysis of kinetic data indicated that Hg2+ was a noncompetitive inhibitor of proton pumping but was an uncompetitive inhibitor of ATP hydrolysis. Further kinetic analysis of Hg2+ effects revealed that the lower proton transport did not result from enhanced membrane leakage but rather from reduced coupling between H+ pumping and ATP hydrolysis.

The nature of proton‐translocating ATPases in maize roots

Abstract The mechanisms of the coupling between ATP hydrolysis and proton transport catalyzed by the ATPases of the tonoplast and plasma membrane of maize (Lea mays L.) roots were investigated. Proton transport by the tonoplast ATPase was found to be much more sensitive to nitrate than ATP hydrolysis, being inhibited by 80% with almost no effect on hydrolysis at 5 mM NO3. Mercury was also found to be a potent inhibitor of this enzyme, inhibiting transport and hydrolysis by 50% at 60 and 100 μM, respectively. The same type of pattern was seen with other divalent cations. Millimolar concentrations of Cd2+, Co2+, Cu2+, and Zn2+ in the presence of Mg2+ inhibited proton transport significantly more than hydrolysis whereas Ba2+ and Ca2+ had little effect. Both free and ATP‐complexed species of these inhibitory cations appeared to be effective. When the influence of temperature was investigated, both the tonoplast and plasma membrane enzymes showed a similar pattern. ATP hydrolysis by both enzymes generally obey...

Estimating Evapotranspiration for Dryland Cropping Systems in the Semiarid Texas High Plains Using SWAT

The Soil and Water Assessment Tool (SWAT) is one of the most widely used watershed models for simulating hydrology in response to agricultural management practices. However, limited studies have been performed to evaluate the SWAT models ability to estimate daily and monthly evapotranspiration (ET) in semiarid regions. ET values were simulated using ArcSWAT 2012 for a lysimeter field managed under dryland conditions at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, and compared with measured lysimeter values from 2000 to 2010. Two scenarios were performed to compare SWATs performance: (1) use of default plant leaf area index (LAI) values in the embedded plant database and (2) adjusted LAI values. Scenario 1 resulted in an “unsatisfactory” Nash-Sutcliffe efficiency (NSE) of 0.42 and 0.38 for the calibration and validation periods, respectively. Scenario 2 resulted in a “satisfactory” NSE value for the calibration period while achieving a “good” NSE of 0.70 for the validation period. SWAT generally underestimated ET at both the daily and monthly levels. Overestimation during fallow years may be due to the limitations of the pothole function used to simulate furrow diking. Users should be aware of potential errors associated with using default LAI parameters. Inaccuracies in ET estimation may also stem from errors in the plant stress functions, particularly when evaluating water management practices for dryland watersheds.

Trends in tree growth and understory yield in silvopastoral practices with southern pines

Farm-level simulators such as the Agroforestry Estate Model use as inputs either yield tables or outputs from forest modeling tools. Forest models rely upon assumptions on site index, stem diameter (DBH) distribution, wood production and tree mortality, which may or may not apply to agroforestry practices. Differences may arise because of the effects on tree growth of unusual spacings and configurations, fertilizer, pruning and grazing regimes, and tree-understory relationships as well. We examined data from published or existing field trials to determine mid- and long-term trends in tree growth and understory yields in silvopastoral practices with southern pines (Pinus spp.) in the United States. Tree DBH and height were greater in practices with improved pastures than in those with spontaneous grasses. Understory affected DBH more than height and, therefore, DBH-height relationships differed among practices. Sigmoidal models predicted that tree height will peak at different age depending on tree spacing and understory type. These changes may affect the accuracy of site indices and wood yield predictions. Livestock gains decrease linearly with increasing stand basal area and stand age, although forage yields sometimes decay exponentially. In one of the experiments, livestock gains decreased to almost zero at age 19 but with stand basal areas at that age markedly differing (14 and 25 m2 ha–1) for two different spacings. Additional data would allow to generate empirical algorithms to obtain farm-level simulations of broad application, improve economic analysis and generate hypotheses to guide future experimental work.

RAPID INHIBITION OF ROOT GROWTH IN WHEAT ASSOCIATED WITH ALUMINUM UPTAKE AS FOLLOWED BY CHANGES IN MORIN FLUORESCENCE

Acidic soils limit the land available for crop production and increase the cost of production in many regions of the United States and the world. The use of Aluminum (Al)-resistant germplasm is one means of reducing the impact of acidic soils and development of such germplasm is limited by our understanding of the processes that confer resistance. This study sought to associate changes in root growth rate with Al entry into the tissue of two cultivars of wheat (Triticum aestivum L.) differing in sensitivity to Al. Changes in the spectral characteristics of morin were characterized to determine if a dual excitation or emission assay for Al could be developed. It was not possible to develop such a protocol. However, an assay based on changes in fluorescence intensity of morin was adopted from the work of Vitorello and Haug. Addition of Al to a total concentration of 5 μM resulted in a 50% decrease in root elongation rate with the Al-sensitive cultivar, Scout, but little change in root elongation with the Al-resistant cultivar, Atlas. Inhibition of root growth occurred without a noticeable lag. The addition of Al to the external solution of bathing Scout roots caused an increase in the fluorescence of intracellular morin, indicative of Al entry into the root cells. No increase in morin fluorescence was observed with Atlas roots exposed to 5 μM Al. Therefore, there was an association between morin fluorescence, thus presumably Al entry, and inhibition of root growth.