Tomato responses to ammonium and nitrate nutrition under controlled root‐zone pH

Tomato (Lycopersicon esculentum L. Mill. ‘Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO₃ ^‐ or 1.0 mM NH₄ ⁺. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO₃ ^‐ or NH₄ ⁺ can be used efficiently by tomato. Uptake of K⁺ and Ca²⁺ were not altered by N source, but uptake of Mg²⁺ was reduced in NH₄ ⁺‐fed plants. This indicates that uptake of Mg²⁺ was regulated at least partially by ionic balance within the plant.     

Changes in Chemical,Physical and Biological Properties Of Passively-Aerated Cocomposted Poultry Litter And Municipal Solid Waste Compost

Cocomposting of poultry litter with municipal solid waste compost (MSW) was evaluated as a means to stabilize nitrogen and phosphorus in poultry litter and to produce a stable organic soil amendment. Four passively aerated compost piles were established by mixing fixed weight ratios of MSW and composted poultry litter (21:1, 6:1, 3:1, 1:1); moisture was adjusted to 50 percent by weight at pile establishment. These ratios represented a range of initial C:N (26-12) and C:P (150-50) ratios. Composting process parameters monitored over eight months included temperature, oxygen and moisture contents, pH, electrical conductivity, C:N:P ratios, microbial respiration and diversity. Initial feedstock ratios had no significant effect on temperature in the thermophilic phase of composting. After one year of composting, microbial respiration in 21:1 and 6:1 mixtures was high relative to 3:1 and 1:1 mixtures suggesting slow maturation in piles with high MSW content. Salmonella sp. and coliform organisms were detectable for up to 47 days. Results suggest that MSW has potential as a carbon feedstock for poultry litter composting when used in moderate amounts.     

The effect of age and cold hardening on resistance to pink snow mould (Microdochium nivale) in perennial ryegrass (Lolium perenne L)

Abstract

The effect of plant age and cold hardening on resistance to pink snow mould caused by Microdochium nivale was studied in perennial ryegrass. Resistance to M. nivale was estimated as relative regrowth after inoculation and incubation under artificial snow cover at 2°C. Resistance increased with increasing plant age. Cold hardened and unhardened plants of the same age displayed identical resistance. Preliminary studies indicate that expression of genes coding for the PR proteins chitinase and PR-1a increased during incubation of inoculated perennial ryegrass, but no clear difference in expression of these genes was found between plants of different ages, or in hardened versus unhardened plants.     

Effects of alternative water distribution rules on irrigation system performance: a simulation analysis

Based on a simulation model reflecting physical and economic conditions typically found in rice irrigation systems in Asia, the irrigation performance implications of alternative water distribution rules for dry season irrigation are evaluated under varying degrees of water shortage. The rules examined reflect differing water distribution strategies designed either to maximize conveyance efficiency, economic efficiency, or equity; or to achieve a balance between efficiency and equity objectives. Irrigation performance is evaluated using several efficiency measures reflecting the physical, agronomic and economic productivity of water, and one measure of equity. Economic efficiency and equity among farmers within the portion of the irrigation system that is on in any given season are shown to be complementary, and not competing objectives. Economic efficiency and equity among all farmers within the command area of the irrigation system are largely complementary strategies at the lower levels of water shortage, but with increasing shortage, significant tradeoffs develop between these objectives. An operational rule for water distribution under a goal of maximizing economic efficiency is developed, and the data requirements for its implementation are shown to be modest. Under the model's assumed conditions of dry season rice production dependent solely on surface irrigation for water, the distribution strategy designed to maximize conveyance efficiency results in only modestly lower levels of economic efficiency and equity than could be achieved by the strategy designed to maximize economic efficiency.     

Variable-density thinning promotes differential recruitment and development of shade tolerant conifer species after 17 years

Promoting patchy recruitment of shade tolerant tree species into the midstory is an important step in developing structural diversity in second-growth stands. Variable-density thinning (VDT) has been proposed as a strategy for accelerating structural diversity, as its combination of within-stand treatments (harvest gaps, thinning, and non-harvested skips) should create variable overstory and understory conditions. Here we report on western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedling and sapling densities in five mixed-conifer stands and Sitka spruce (Picea sitchensis (Bong.) Carr.) seedling and sapling densities in two stands in western Washington at 3,7, 10, and 16–17 years after VDT. Additionally, we report on western hemlock advance regeneration growth and survival in two stands over 14 years. Western hemlock seedling density was highest in the thinned treatment but only significantly so in Year 10. In contrast, the gaps contained significantly more western hemlock saplings in Years 7 and 10 and significantly greater growth of western hemlock advance regeneration through Year 10. Skips embedded within the VDT did not differ significantly from unharvested reserves in terms of seedling or sapling densities of either species. Sitka spruce seedling density was highest in the gap and thinned treatments, but saplings were uncommon in all treatments. Collectively, these results indicate that our variant of VDT promoted patchy, midstory recruitment of western hemlock but failed to recruit Sitka spruce saplings in either stand where it established. Consequently, more intensive variants of VDT may be required to promote midstory recruitment of species less tolerant of shade than western hemlock.

     

Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants grown in different N regimes and sprayed with urea in autumn

Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants fertigated with different nitrogen (N) treatments and sprayed with urea in autumn were studied. Stock plants propagated from poplar cuttings were trained to a single shoot and fertigated with 0, 5, 10, 15 or 20 mmol l(-1) N during the first growing season. In October, a subset of stock plants from each N fertigation treatment was sprayed twice with either 3% urea or water, and overwintered outside. In March, total tree biomass and total N concentration and content of stems were estimated for stock plants in each treatment, and cuttings were taken from the middle of each stock plant and stored in plastic bags at 2 degrees C. In mid-April, cuttings were planted in 7.5-l pots containing N-free medium and grown outdoors with a weekly fertigation with nutrient solution containing 0 or 10 mmol l(-1) 15NH4 15NO3. In mid-July, cuttings were harvested, and new shoot (new stems and leaves), shank (old cutting stem) and roots were analyzed for new biomass growth and total N and 15N content. Growth of stock plants was positively related to N supply in the previous growing season. Foliar urea application in autumn had no effect on subsequent stock plant growth even though urea sprays increased both N concentration and content in stem tissues. Biomass growth of cuttings obtained from stock plants was closely related to their N content when the cuttings were grown in an N-free medium regardless of previous treatments applied to the stock plants. When N was supplied in the growth medium, the strength of the relationship between regrowth and N content of cuttings was significantly reduced. Cuttings from stock plants treated with foliar urea and grown in a N-free medium remobilized between 75 and 82% of their total N for new growth, whereas cuttings from plants receiving no urea spray remobilized only between 60 and 69% of their total N for new growth. Current N fertilization of the cuttings reduced the percentage of N remobilized. We conclude that new growth of poplar cuttings in spring was more dependent on currently applied N than on reserve N, and urea N applied as a spray in autumn was more easily remobilized than N taken up by roots during the previous season.     

Differential Growth Response to Salt Stress Among Selected Ornamentals

Evaluation of salt tolerance in herbaceous perennials was performed with mature potted plants under greenhouse conditions. Six herbaceous perennial species were evaluated for their tolerance to aqueous solutions of various sodium chloride (NaCl) concentrations over a 21 day period by measuring growth, water transpiration, and leaf nutrient content. Potential exists for utilization of these species in somewhat challenging saline environments along roadsides and in urban landscapes. Species evaluated in a mature growth stage included Achemilla mollis, Nepeta x faassenii, Sedum acre, Thymus praecox, Phlox subulata and Solidago cutleri. On the basis of relative growth rate and water transpiration responses to NaCl (0–400 mM) treatments, groundcovers were grouped into three tolerance categories: highly sensitive to salt treatment (S. acre), those with intermediate sensitivity (A. mollis, N. x faassenii, T. praecox, and P. subulata), and those exhibiting tolerance (S. cutleri). Sodium content in leaf foliage of S. cutleri was about ten-fold lower than other groundcover species in the 200 mM NaCl treatment, consistent with greater tolerance to NaCl treatments in terms of transpiration, biomass accumulation, and retention of green foliage. Comparison of foliar nutrient levels among groundcover species and treatments suggested strong differential response to NaCl treatment, indicating that changes in nutrient levels over time may be a reasonable way to predict NaCl tolerance in groundcovers.     

Dynamic relationships between soil properties and foliar disease as affected by annual additions of organic amendment to a sandy-soil vegetable production system

Additions of organic amendments to agricultural soils can lead to improved soil quality and reduced severity of crop diseases. However, the relationship between disease severity and soil properties as affected by repeated additions of these amendments is poorly understood. The primary objectives of this study were to (i) resolve multivariate relationships between soil properties and foliar disease severity and (ii) identify soil properties that contribute to disease severity in an intensive irrigated vegetable production system receiving annual additions of fresh and composted paper mill residuals (PMR). Foliar diseases caused by Pseudomonas syringae pv. syringae on snap bean (bacterial brown spot) and P. s. pv. lachrymans on cucumber (angular leaf spot) are the focus of this report. The experiment consisted of a 3-year crop rotation of potato (1998 and 2001), snap bean (1999 and 2002), and cucumber (2000). Treatments included a non-amended fertilizer control and two rates of fresh PMR, PMR composted alone (PMRC), and PMR composted with bark (PMRB). Soil measures included total soil carbon (TC) and nitrogen (TN), particulate organic matter carbon (POMC) and nitrogen (POMN), volumetric soil moisture (VM) and in situ NO₃-N. Multiple regression (MR) and principal component analyses (PCA) were conducted to identify key soil properties that influenced the amount of disease. On average, the amount of TC in plots amended with PMR composts increased 77-178% from 1999 to 2002 compared to the non-amended soils. In 1999, a year in which compost additions reduced the amount of bacterial brown spot of bean, TC explained 42% of the total variation in disease severity in the best MR model. Midseason TN alone was inversely related to angular leaf spot incidence in 2000, while POMN explained 51% of the variation in the best MR model for that year. In 2002, a year in which PMRC-amended soils exacerbated brown spot symptoms, midseason quantities of TN explained 80% of the variation in disease severity. Unique to 2002, NO₃-N alone positively correlated with disease severity. Overall, the influence of soil carbon on disease severity was displaced by the increasing importance of TN and NO₃-N, indicating a transition from a C-dependent to an N-dependent system.     

High-speed imaging reveals neurophysiological links to behavior in an animal model of depression

The hippocampus is one of several brain areas thought to play a central role in affective behaviors, but the underlying local network dynamics are not understood. We used quantitative voltage-sensitive dye imaging to probe hippocampal dynamics with millisecond resolution in brain slices after bidirectional modulation of affective state in rat models of depression. We found that a simple measure of real-time activity-stimulus-evoked percolation of activity through the dentate gyrus relative to the hippocampal output subfield-accounted for induced changes in animal behavior independent of the underlying mechanism of action of the treatments. Our results define a circuit-level neurophysiological endophenotype for affective behavior and suggest an approach to understanding circuit-level substrates underlying psychiatric disease symptoms.