Evaluating foliar nitrogen compounds as indicators of nitrogen status in Prunus persica trees

Mobile nitrogen (N) forms may be better N indicators of the N status of trees than total nitrogen (TN) due to their higher sensitivity to increasing N supply. A field experiment was carried out over a 3-year period to compare foliar concentrations of total N (TN), soluble N (SN), chlorophyll (Minolta SPAD readings), NH₄–N and NO₃–N as indicators of soil N availability in nectarine, Prunus persica L. Batsch, cv. ‘Fantasia’ (grafted on ‘Nemaguard’ peach, P. persica × P. davidiana) trees. Young trees were exposed to a range of fertilizer-N application rates. Based on correlation analysis, the best association between leaf N compounds with soil N supply and trunk diameter and/or fruit yield was obtained with TN and chlorophyll SPAD readings. Leaf concentrations of mobile N compounds (NH₄–N and NO₃–N) increased more than any other N compound under high N supply; however, their inconsistency among years and low leaf concentration difficult their use as N indicators. The optimum foliar TN for growth decreased with tree age, 4.4%, 3.6% and 3.3% in non-bearing 1-year-old trees, non-bearing 2-year-old trees and 3.3 fruit-bearing 3-year-old trees. The optimum SPAD readings were 40 in 2-year-old trees and 42 in 3-year-old trees. Stable N compounds (TN and chlorophyll SPAD) could be used to N diagnosis in the zone of N deficiency, and soluble N compounds (NH₄–N and NO₃–N) to diagnoses N excess.     

QTL for IHNV resistance and growth identified in a rainbow (Oncorhynchus mykiss) × Yellowstone cutthroat (Oncorhynchus clarki bouvieri) trout cross

Infectious hematopoietic necrosis virus (IHNV) is a major constraint to rainbow trout culture. Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri) have greater resistance to this virus than do rainbow trout (O. mykiss), but the genetic mechanism of this resistance is not understood. We conducted a genome scan using a backcross of cutthroat trout into a rainbow trout background to estimate the number and locations of quantitative trait loci (QTL) associated with IHNV resistance and growth in trout. IHNV resistance was considered in terms of both survival (binary trait) and days to death (quantitative trait). The genetic map was scanned using interval mapping via two different approaches: one model considered survival alone and a second two-part model combined both survival and days to death. Three QTL were significantly (P ≤ 0.05) associated with virus resistance genome-wide, explaining 32.5% of the phenotypic variation. Cutthroat alleles at two of these QTL resulted in increased resistance to the pathogen, as expected. No growth QTL were detected in this cross. We suggest that these traits are genetically independent.     

Landscape dynamics of floral resources affect the supply of a biodiversity-dependent cultural ecosystem service

Context

Cultural ecosystem services, many of which depend on biodiversity, are recognized as important but seldom quantified biophysically across landscapes. Furthermore, many ecosystem service models are static, and the supply of cultural ecosystem services may be misrepresented if seasonal shifts in biotic communities are ignored.

Objectives

We modeled landscape dynamics of wildflower blooms in a temperate montane landscape to determine (1) how floral resources (wildflower species richness, abundance, timing, and presence of charismatic species) changed over the growing season, (2) how projected wildflower viewing hotspots varied over space and time, and (3) how spatial shifts in floral resources affected potential public access to wildflower viewing.

Methods

Data were collected at 63 sites across a rural-to-urban gradient in the Southern Appalachian Mountains (USA). Generalized linear models were used to identify factors affecting floral resources at two temporal scales. Floral resources were projected across the landscape and hotspots of wildflower viewing were quantified using overlay analysis.

Results

Floral resources were affected by topoedaphic conditions, climate, and surrounding building density and changed seasonally. Seasonal models revealed locational shifts in ecosystem service hotspots, which changed the proportion of hotspots accessible to the public and identified wildflower-viewing opportunities unnoticed by static models.

Conclusion

Relationships between landscape gradients, biodiversity, and ecosystem service supply varied seasonally, and our models identified cultural ecosystem service hotspots otherwise obscured by simple proxies. Landscape models of biodiversity-based cultural ecosystem services should include seasonal dynamics of biotic communities to avoid under- or over-emphasizing the importance of particular locations in ecosystem service assessments.

     

Hormetic UV-C seed treatments for the control of tomato diseases

Hormesis is a dose response phenomenon in which low, non-damaging doses of a stressor bring about a positive response in the organism undergoing treatment. Evidence is provided here that hormetic UV-C treatments of tomato seed can control disease caused by Botrytis cinerea, Fusarium oxysporum f. sp. lycopersici (FOL) and f. sp. radicis-lycopersici (FORL) on tomato (Solanum lycopersicum). Treating seeds with a 4 kJ m⁻² dose of UV-C significantly reduced both the disease incidence and progression of B. cinerea, with approximately 10% reductions in both on cv. Shirley. Disease severity assays for FOL and FORL on cv. Moneymaker showed dose-dependent responses: UV-C treatments of 4 and 6 kJ m⁻² significantly reduced the disease severity scores of FOL, whilst only the 6 kJ m⁻² showed significant reductions for FORL. To determine the effects of treatment on germination and seedling growth, UV-C doses of 4, 8 and 12 kJ m⁻² were performed on cv. Shirley. No negative impacts on germination or seedling growth were observed for any of the treatments. However, the 8 kJ m⁻² treatment showed significant biostimulation, with increases in seedling, root and hypocotyl dry weight of 11.4%, 23.1% and 12.0%, respectively, when compared to the control. Furthermore, significant increases in the root-mass fraction (10.6%) and root:shoot ratio (13.1%) along with a decrease in shoot-mass fraction (2.0%) indicates that the 8 kJ m⁻² treatment stimulated root growth to the greatest extent. There was no effect on hypocotyl and primary root length or the number of lateral roots, indicating no adverse effects to basic root architecture or seedling growth.     

The homogenizing influence of agriculture on forest bird communities at landscape scales

Landscape Ecology - Agricultural expansion is a principal driver of biodiversity loss, but the impacts on community assembly in agro-ecosystems are less clear, especially across regional scales at...     

Validating the use of Cs measurements to estimate rates of soil redistribution by wind

Wind erosion has degraded over one-half billion hectares of land worldwide. ¹³⁷Cesium (¹³⁷Cs) has been used as a tracer to study long-term rates of soil redistribution by water and, to a lesser extent, by wind. Early studies assumed that the decline in ¹³⁷Cs activity for a potentially eroded soil relative to that for an uneroded soil was linearly proportional to soil loss. More recently, models have emerged that consider the effects of soil cultivation and the particle surface area-dependent partitioning of ¹³⁷Cs on soils. We investigated the partitioning of ¹³⁷Cs in wind-eroded sediments and with soil surface samples sieved into contiguous ranges of particle sizes. We also compared the ¹³⁷Cs activities and stratification of several adjacent soils with known wind erosion and deposition histories. Finally, we tested ¹³⁷Cs-based soil loss models with measured data from sites with documented histories. ¹³⁷Cs activities and mean particle diameters of aeolian samples agreed well with the ¹³⁷Cs activities and respective mean diameters of the sieved surface soil samples. Good agreement between model estimations and measured data indicated that ¹³⁷Cs models developed to estimate soil redistribution by water were also applicable to soil redistribution by wind provided that the models contained an appropriate particle size correction parameter.     

Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.     

Organic globules in the Tagish Lake meteorite: remnants of the protosolar disk

Coordinated transmission electron microscopy and isotopic measurements of organic globules in the Tagish Lake meteorite shows that they have elevated ratios of nitrogen-15 to nitrogen-14 (1.2 to 2 times terrestrial) and of deuterium to hydrogen (2.5 to 9 times terrestrial). These isotopic anomalies are indicative of mass fractionation during chemical reactions at extremely low temperatures (10 to 20 kelvin), characteristic of cold molecular clouds and the outer protosolar disk. The globules probably originated as organic ice coatings on preexisting grains that were photochemically processed into refractory organic matter. The globules resemble cometary carbon, hydrogen, oxygen, and nitrogen (CHON) particles, suggesting that such grains were important constituents of the solar system starting materials.     

Application of Line Thinnings in Practice

The discussion covers the need to change our present system of harvesting pine timber thinnings in order to increase productivity. It points out that this productivity increase can only be achieved through technical innovation and by the introduction of machinery suited to do the job. The machinery and work methods call for a type of neutral thinning in conjunction with a selective thinning or followed by a selective thinning. The advantages of this type of thinning, as practised in this country, are illustrated.