Bert M. Cregg

Physiology and morphology of Pinus sylvestris seedlings from diverse sources under cyclic drought stress

Abstract We examined seed source variation in drought tolerance characteristics of Pinus sylvestris seedlings from 12 diverse geographic origins representing a longitudinal transect across the species range. The seedlings were subjected to three dry-down cycles in raised water-use efficiency in a greenhouse experiment. We measured pre-dawn needle water potential ( Ψ n ) and instantaneous water-use efficiency (WUE) ( W ) during the cyclic droughts. Seedling survival, growth, biomass allocation to roots, and carbon isotope ratio ( δ 13 C) were measured at the end of the experiment. The seed sources varied ( P δ 13 C. In general, seedlings from the drier central Asian seed sources survived longer under drought than seedlings from more mesic European and coastal seed sources. Seedlings from the Asian seed sources were smaller, allocated more biomass to roots, and had higher integrative water-use efficiency (as indicated by higher δ 13 C) than the seedlings from the European sources. Seed source variation in Ψ n and W was not significant ( P >0.05). Carbon isotope ratio was correlated with precipitation at the seed origin ( r =−0.75, P

Evaluation of Vegetable Production on Extensive Green Roofs

Rooftop vegetable gardening is a production system in urban agriculture based on green roof technology. To broaden the scope of this practice, the use of relatively shallow substrate depths must be explored, since most existing flat roofs are unable to support much added weight. Three growing systems—a green roof, raised green roof platforms, and in-ground—were evaluated for vegetable and herb production over three growing seasons (2009–2011). Tomatoes (Solanum lycopersicum), green beans (Phaseolus vulgaris), cucumbers (Cucumis sativus), peppers (Capsicum annuum), basil (Ocimum basilicum), and chives (Allium schoenoprasum) were studied because of their common use in home gardens. All plants, except pepper, survived and produced biomass in all growing systems and yielded crops large enough for analysis in 2009 and 2010. Overall, yields and basil biomass were higher and of better quality in-ground during 2009, the only year irrigation was applied, and similar on the roof and platforms. Variability in success was partially due to annual weather variation with the greatest impact on cucumber. Yields of chive, a perennial crop, were not affected by growing system after the first year. Results suggest that, with proper management, vegetable and herb production in an extensive green roof system is possible and productive.

Variation in stable carbon isotope discrimination among and within exotic conifer species grown in eastern Nebraska, USA

Abstract The study involved the measurement of stable-carbon isotope discrimination and specific leaf area on foliage of mature trees of 11 conifer species grown in a common-garden in eastern Nebraska, USA. Each species was represented by three to six trees from at least three populations. Carbon isotope discrimination differed significantly among species ( F = 31.41, P F = 1.65, P Pinaceae family ( Abies, Larix, Picea, Pinus, Pseudotsuga ) had much higher discrimination (Δ = 18.87, SE = 0.08, n = 141) than species in the Cupressaceae family ( Juniperus ) (Δ = 16.26, SE = 0.12, n = 18). A deciduous conifer, Larix (Δ = 19.09, SE = 0.20, n = 16), did not differ significantly from evergreen members of the Pinaceae family. Although specific leaf area differed among species ( F = 152.62, P r = 0.24, P > 0.14). Annual height growth, specific leaf area, and annual precipitation of seed sources were intercorrelated (0.60 ≤ r ≤ 0.67, P

Comparison of stormwater runoff from sedum, native prairie, and vegetable producing green roofs

Stormwater retention is one of the well-studied benefits of green roofs. A roof’s ability to retain stormwater depends on factors such as the intensity and duration of the rain event as well as substrate depth, substrate moisture content at the start of the rain event, and vegetation type, health, density and water use efficiency. Extensive green roofs used for crop production differ from traditional Sedum and prairie-covered extensive green roofs in plant density and water use efficiency, but their impact on stormwater retention has not been well studied. Three vegetation types (unfertilized Sedum and native prairie species mixes, and a fertilized vegetable and herb species mix) were compared for stormwater runoff quantity over three growing seasons and stormwater runoff quality during one growing season. The prairie covered green roofs had the lowest increase in runoff as precipitation increased, almost half that of Sedum or vegetable producing green roof treatments. Vegetation type had no effect on runoff nitrate-nitrogen (NO3−) concentrations, but NO3− concentrations decreased over the course of the growing season. Runoff phosphorus (P) concentrations also decreased over time in the Sedum and prairie treatments, which were lower than P concentrations from the vegetable green roof throughout the growing season. This is likely a result of the difference between amounts of NO3− and P applied to the vegetable green roof and the needs of the crop plants in that treatment. The similarities in water retention and water quality between vegetable producing extensive green roofs and Sedum green roofs suggest that vegetable production with careful nutrient management will not have a negative impact on stormwater retention or runoff water quality.

Spatial and temporal distribution of trunk-injected imidacloprid in apple tree canopies.

BACKGROUND Pesticide use in orchards creates drift-driven pesticide losses which contaminate the environment. Trunk injection of pesticides as a target-precise delivery system could greatly reduce pesticide losses. However, pesticide efficiency after trunk injection is associated with the underinvestigated spatial and temporal distribution of the pesticide within the tree crown. This study quantified the spatial and temporal distribution of trunk-injected imidacloprid within apple crowns after trunk injection using one, two, four or eight injection ports per tree. RESULTS The spatial uniformity of imidacloprid distribution in apple crowns significantly increased with more injection ports. Four ports allowed uniform spatial distribution of imidacloprid in the crown. Uniform and non-uniform spatial distributions were established early and lasted throughout the experiment. The temporal distribution of imidacloprid was significantly non-uniform. Upper and lower crown positions did not significantly differ in compound concentration. Crown concentration patterns indicated that imidacloprid transport in the trunk occurred through radial diffusion and vertical uptake with a spiral pattern. CONCLUSION By showing where and when a trunk-injected compound is distributed in the apple tree canopy, this study addresses a key knowledge gap in terms of explaining the efficiency of the compound in the crown. These findings allow the improvement of target-precise pesticide delivery for more sustainable tree-based agriculture.

Penetrative and Dislodgeable Residue Characteristics of 14C-Insecticides in Apple Fruit

Infinite- and finite-dose laboratory experiments were used to study the penetrative and dislodgeable residue characteristics of (14)C-insecticides in apple fruit. The differences in dislodgeable and penetrated residues of three radiolabeled insecticides ((14)C-thiamethoxam, (14)C-thiacloprid, and (14)C-indoxacarb), applied in aqueous solution with commercial formulations, were determined after water and methanol wash extractions. The rate of sorption and extent of penetration into the fruit cuticles and hypanthium of two apple cultivars were measured after 1, 6, and 24 h of treatment exposure, using radioactivity quantification methods. For all three compounds, 97% or more of the treatment solutions were found on the fruit surface as some form of non-sorbed residues. For indoxacarb, sorption into the epicuticle was rapid but desorption into the fruit hypanthium was delayed, indicative of a lipophilic penetration pathway. For the neonicotinoids, initial cuticular penetration was slower but with no such delay in desorption into the hypanthium.

Gibberellic acid inhibitors control height growth and cone production in Abies fraseri

ABSTRACT Precocious cone production in Fraser fir (Abies fraseri) results in substantial economic losses for Christmas tree growers in the United States. Cone removal often represents the second highest labor expense, after shearing. Gibberellins (GAs) regulate both reproductive development and shoot elongation, and are used to enhance cone production in conifer seed orchards. We identified plant growth regulators (PGRs) that inhibit GA biosynthesis – paclobutrazol, applied by foliar spray (PBZ-foliar) or soil injection (PBZ-soil), and chlormequat. We evaluated the effects of PGR treatments on cone production and vegetative growth in three tree size classes (small, medium, and large) at four locations over a three-year period. PGRs were applied in spring 2013, but did not affect growth until 2014, nor did they affect cone production until 2015. In 2014, PBZ reduced leader length by 21–29% across size classes and sites, while also increasing bud density by 11–20%. In 2015, PBZ-soil reduced average cone density (cones/tree) in small, medium, and large trees by 33%, 54%, and 40%, respectively. PBZ-soil also reduced leader length by 20–29% and increased bud density by 16–25%, making it the most effective PGR at controlling height growth and cone production in Fraser fir.

Using irrigation and mulch to control cone production in Fraser fir (Abies fraseri)

ABSTRACT Fraser fir (Abies fraseri) is economically important as a Christmas tree in the United States, but trees often produce cones at a young age when grown in plantations in the Midwest. Early cone production is undesirable and decreases the economic value of the tree. High temperatures and drought are associated with increased reproductive output in conifers. Therefore, we investigated the effects of irrigation and mulch on cone production in two Fraser fir plantations in Michigan. At one site, we applied mulch to one tree in each row, with paired controls. In 2013, irrigation increased soil moisture by 47% under drought conditions, compared to non-irrigated control plots. However, irrigation had no effect on cone production in any year. Mulch reduced average maximum daily soil temperatures 7.4°C in 2013 and 4.8°C in 2014. Mulch reduced cone production in 2014 by 51%, but had no effect the following year, after a cooler summer. Our findings suggest that soil temperature, rather than soil moisture, regulates cone formation in Fraser fir, but treatments that reduce soil temperatures may only be effective in warmer locations or years.

Morphology and foliar chemistry of containerized Abies fraseri (Pursh) Poir. seedlings as affected by water availability and nutrition

Abstract• We present the results of a two-year (2007–2008) greenhouse study investigating the effect of water availability and nitrogen fertilization on the growth, biomass partitioning, and foliar nutrient content of Abies fraseri (Pursh) Poir.• Fertilizer and moisture content (irrigation) were varied in a factorial experiment combining four levels of irrigation and three levels of fertilization to evaluate growth and foliar nutrient content. In addition, a numerical optimization was used to estimate appropriate levels of each factor necessary to achieve simulated goals for response variables.• Irrigation increased the height growth by 12 to 35% depending on the fertilization treatment (p = 0.0001). Fertilization increased height growth by 10 to 26% (p = 0.02). A similar response was observed for stem diameter growth (SDG). Total biomass accumulation increased as result of positive response of stem and root biomass development, and foliar nitrogen content was positively affected by nitrogen fertilization and negatively affected by irrigation. The numerical optimization for simulated target growth and nitrogen content responses produced levels of input combinations with high desirability factors to achieve the target responses.• These results suggest that nutrient addition is a strong determining factor for early development of this species. The improved growth efficiency in this study is likely attributed to a combination of factors including, improved photosynthetic capacity, decreased stomatal limitations, or increased resource allocation to stems.