Recent achievements and new research opportunities for optimizing macronutrient availability, acquisition, and distribution for perennial fruit crops

CITATION: Kalcsits, Lee et al. 2020. Recent achievements and new research opportunities for optimizing macronutrient availability, acquisition, and distribution for perennial fruit crops. Agronomy, 10(11): 1738, doi.org/10.3390/agronomy10111738.The original publication is available at: https://www.mdpi.comTree responses to fertilizer management are complex and are influenced by the interactions between the environment, other organisms, and the combined genetics of composite trees. Increased consumer awareness of the environmental impact of agriculture has stimulated research toward increasing nutrient-use efficiency, improving environmental sustainability, and maximizing quality. Here, we highlight recent advancements and identify knowledge gaps in nutrient dynamics across the soil–rhizosphere–tree continuum for fruit crops. Beneficial soil management practices can enhance nutrient uptake and there has been significant progress in the understanding of how roots, microorganisms, and soil interact to enhance nutrient acquisition in the rhizosphere. Characterizing root architecture, in situ, still remains one of the greatest research challenges in perennial fruit research. However, the last decade has advanced the characterization of root nutrient uptake and transport in plants but studies in tree fruit crops have been limited. Calcium, and its balance relative to other macronutrients, has been a primary focus for mineral nutrient research because of its important contributions to the development of physiological disorders. However, annual elemental redistribution makes these interactions complex. The development of new approaches for measuring nutrient movement in soil and plant systems will be critical for achieving sustainable production of high-quality fruit in the future.Publisher's versio

An isotope mass balance approach to measure variability in nitrogen fluxes, allocation and assimilation in balsam poplar (Populus balsamifera L.) and other plants

Populus species or their hybrids are being increasingly used as feedstock for the growing bioenergy industry. To optimize carbon uptake efficiencies, fertilizer inputs must be minimized while, at the same time, achieving rapid growth. The complexity of nitrogen uptake and assimilation in plants and environmental heterogeneity force simplifications that limit improvements in nitrogen-use efficiency. In particular, a lack of integration limits the applicability of many traditional nitrogen-use assays to whole plant nitrogen use. Net nitrogen isotope discrimination has potential to act as a time-integrated process indicator of nitrogen-use in plants grown under steady-state conditions. The objective of this thesis was to further develop an isotope discrimination-based integrated measure of nitrogen-use that reflects whole plant and organ level nitrogen use. Observed differences in nitrogen isotope discrimination were proposed to be a function of nitrogen isotope discrimination of the assimilatory enzymes, fluxes across the root plasma membrane and translocation of inorganic nitrogen to the shoot. As a test, nitrogen supply and demand was environmentally varied in black cottonwood (Populus trichocarpa (Torr & Gray)) and genetically manipulated with knockout lines of Arabidopsis (Arabidopsis thaliana L.). Changes in isotopic composition (δ¹⁵N) were interpretable within the context of the proposed model. Furthermore, efflux/influx (E/I) across the root plasma membrane calculated from the isotope mass balance approach was positively correlated with E/I measured using an established ¹⁵N compartmental analysis approach indicating that the isotope mass balance approach produced a reliable measure of E/I. The isotope mass balance approach was then used to determine intraspecific variability in balsam poplar (Populus balsamifera L.), a species used for hybrid poplar breeding. Nitrogen use traits were calculated for 25 genotypes from five climatically dispersed provenances grown hydroponically under steady-state nitrogen conditions with either ammonium or nitrate. Genotypic variation exceeded provenance level variation in most cases and significant variation was observed in growth, nitrogen isotope composition and calculated nitrogen-use traits indicating that there is potential for breeding for nitrogen-use using balsam poplar. The isotope mass balance model presented here provides a new approach for probing integrated nitrogen-use traits in plants, which are often technically difficult to measure.Forestry, Faculty ofGraduat

Exploring how temperature affects dormancy induction and cold acclimation in hybrid poplar

Dormancy, cold hardiness and height growth were examined in four poplar clones exposed to four temperature conditions (13.5ºC/8.5ºC, 18.5ºC/3.5ºC, 18.5ºC/13.5ºC and 23.5ºC/8.5ºC day/night temperatures) under short photoperiod. The selected clones were ‘WP-69’ (‘Okanese’)- early acclimation, ‘Walker’ and ‘Katepwa’ - intermediate acclimation, and ‘Prairie Sky’- late acclimation. Changes in physical water properties and mobility within the vascular tissue region, vascular transition region into the axillary bud and the upper axillary bud were assessed during endodormancy development using Magnetic Resonance Microimaging (MRMI). In summary:a) There were distinct differences between poplar clones during dormancy induction in response to temperature. For example, ‘Katepwa’, ‘Walker’ and ‘WP-69’ clones became endodormant but ‘Prairie Sky’ did not enter endodormancy. Endodormancy development and cold acclimation in ‘WP-69’ were less affected by temperature than ‘Katepwa’ and ‘Walker’ suggesting that genotypic variation exists in response to temperature change.b) Growth cessation, not endodormancy, was a prerequisite for cold acclimation since cold hardiness increased in ‘Prairie Sky’ in the absence of endodormancy. However, increases in endodormancy coincided with increase in cold hardiness in other clones.c) Low night temperatures (18.5ºC/3.5ºC) delayed endodormancy development and cold acclimation in all clones compared to the warm night temperature treatment (18.5ºC /13.5ºC). Night temperature was negatively correlated with time to growth cessation, and cold hardiness and positively correlated with dormancy development. Changes in night temperature may affect time to growth cessation, subsequently altering timing of cold acclimation and endodormancy development since growth cessation appeared to be a prerequisite for both processes. d) ADC (Apparent Diffusion Coefficient), an indicator of water mobility within living tissues, was negatively correlated with endodormancy induction. Specifically, the transition region of vascular tissue between the stem and the lower axillary bud showed the highest correlation with endodormancy development. By contrast, decreases in T1 relaxation times, an indicator of biophysical water properties, were inconsistent with changes in endodormancy levels in axillary buds. Thus, ADC appears to correspond more closely with endodormancy development than changes in T1 relaxation times. It is apparent that temperature impacts dormancy development in hybrid poplar. Underlying changes in water appear to correspond with changes in endodormancy. Under future warming scenarios, genotypes such as WP 69 (‘Okanese’) that are less sensitive to temperature and maintain a consistent, endodormancy induction pattern, may be better fit to changing climates

Water Deficit Timing Affects Physiological Drought Response, Fruit Size, and Bitter Pit Development for ‘Honeycrisp’ Apple

Irrigation is critical to maintain plant growth and productivity in many apple-producing regions. ‘Honeycrisp’ apple characteristically develops large fruit that are also susceptible to bitter pit. Limiting fruit size by restricting irrigation may represent an opportunity to control bitter pit in ‘Honeycrisp’. For three seasons, ‘Honeycrisp’ trees were subject to water limitations in 30-day increments and compared to a fully watered control. Water limitations were imposed from 16–45, 46–75, and 76–105 days after full bloom (DAFB). Soil moisture for the well-watered control was maintained at 80–90% of field capacity for the entire season. For two years, physiological measurements were made every 15 days from 30 to 105 DAFB. Fruit quality, bitter pit incidence, shoot length, and return bloom were also measured to assess impacts on growth and productivity. When water was limited, stomatal conductance and net gas exchange were lower compared to the well-watered control and stem water potential decreased by 30–50% throughout the growing season. Early season water limitations had a lower impact on plant response to abiotic stress compared to late-season limitations. Overall, water deficits during fruit expansion phases contributed to fewer large fruit and decreased overall bitter pit incidence with no negative effects on fruit quality

Microtensiometers Accurately Measure Stem Water Potential in Woody Perennials

Stem water potential (Ψstem) is considered to be the standard measure of plant water status. However, it is measured with the pressure chamber (PC), an equipment that can neither provide continuous information nor be automated, limiting its use. Recent developments of microtensiometers (MT; FloraPulse sensors), which can continuously measure water tension in woody tissue of the trunk of the tree, can potentially highlight the dynamic nature of plant water relations. Thus, this study aimed to validate and assess the usefulness of the MT by comparing the Ψstem provided by MT with those same measurements from the PC. Here, two irrigation treatments (a control and a deficit treatment) were applied in a pear (Pyrus communis L.) orchard in Washington State (USA) to capture the full range of water potentials in this environment. Discrete measurements of leaf gas exchange, canopy temperature and Ψstem measured with PC and MT were made every two hours for four days from dawn to sunset. There were strong linear relationships between the Ψstem-MT and Ψstem-PC (R2 > 0.8) and with vapor pressure deficit (R2 > 0.7). However, Ψstem-MT was more variable and lower than Ψstem-PC when Ψstem-MT was below −1.5 MPa, especially during the evening. Minimum Ψstem-MT occurred later in the afternoon compared to Ψstem-PC. Ψstem showed similar sensitivity and coefficients of variation for both PC and MT acquired data. Overall, the promising results achieved indicated the potential for MT to be used to continuously assess tree water status

Variation in fluxes estimated from nitrogen isotope discrimination corresponds with independent measures of nitrogen flux in Populus balsamifera L

Acquisition of mineral nitrogen by roots from the surrounding environment is often not completely efficient, in which a variable amount of leakage (efflux) relative to gross uptake (influx) occurs. The efflux/influx ratio (E/I) is, therefore, inversely related to the efficiency of nutrient uptake at the root level. Time-integrated estimates of E/I and other nitrogen-use traits may be obtainable from variation in stable isotope ratios or through compartmental analysis of tracer efflux (CATE) using radioactive or stable isotopes. To compare these two methods, Populus balsamifera L. genotypes were selected, a priori, for high or low nitrogen isotope discrimination. Vegetative cuttings were grown hydroponically, and E/I was calculated using an isotope mass balance model (IMB) and compared to E/I calculated using (15) N CATE. Both methods indicated that plants grown with ammonium had greater E/I than nitrate-grown plants. Genotypes with high or low E/I using CATE also had similarly high or low estimates of E/I using IMB, respectively. Genotype-specific means were linearly correlated (r = 0.77; P = 0.0065). Discrepancies in E/I between methods may reflect uncertainties in discrimination factors for the assimilatory enzymes, or temporal differences in uptake patterns. By utilizing genotypes with known variation in nitrogen isotope discrimination, a relationship between nitrogen isotope discrimination and bidirectional nitrogen fluxes at the root level was observed

Using soil moisture sensors in pears

Irrigation sensors are important tools for fine-tuning irrigation. Kicking the dirt or doing a "the-grass-looks-green irrigation check" is not always enough. Old pear orchards have deep roots, and what is happening in the top two inches of soil can be quite different from what is happening two feet underground. Irrigation sensors help you make more informed irrigation decisions based on soil moisture conditions in the root zone

Quantifying remobilization of pre-existing nitrogen from cuttings to new growth of woody plants using 15N at natural abundance

Background: For measurements of nitrogen isotope composition at natural abundance, carry-over of pre-existing nitrogen remobilized to new plant growth can cause deviation of measured isotope composition (δ15N) from the δ15Nof newly acquired nitrogen. To account for this problem, a two-step approach was proposed to quantify and correct for remobilized nitrogen from vegetative cuttings of Populus balsamifera L. grown with either nitrate (δ15N = 58.5‰) or ammonium (δ15N = −0.96‰). First, the fraction of carry-over nitrogen remaining in the cutting was estimated by isotope mass balance. Then measured δ15N values were adjusted for the fraction of pre-existing nitrogen remobilized to the plant. Results: Mean plant δ15N prior to correction was 49‰ and −5.8‰ under nitrate and ammonium, respectively. Plant δ15N was non-linearly correlated to biomass (r2 = 0.331 and 0.249 for nitrate and ammonium, respectively; P < 0.05) where the δ15N of plants with low biomass approached the δ15N of the pre-existing nitrogen. Approximately 50% of cutting nitrogen was not remobilized, irrespective of size. The proportion of carry-over nitrogen in new growth was not different between sources but ranged from less than 1% to 21% and was dependent on plant biomass and, to a lesser degree, the size of the cutting. The δ15N of newly acquired nitrogen averaged 52.7‰ and −6.4‰ for nitrate and ammonium-grown plants, respectively; both lower than their source values, as expected. Since there was a greater difference in δ15N between the carried-over pre-existing and newly assimilated nitrogen where nitrate was the source, the difference between measured δ15N and adjusted δ15N was also greater. There was no significant relationship between biomass and plant δ15N with either ammonium or nitrate after adjusting for carry-over nitrogen. Conclusion: Here, we provide evidence of remobilized pre-existing nitrogen influencing δ15N of new growth of P. balsamifera L. A simple, though approximate, correction is proposed that can account for the remobilized fraction in the plant. With careful sampling to quantify pre-existing nitrogen, this method can more accurately determine changes in nitrogen isotope discrimination in plants.Forest Sciences, Department ofForestry, Faculty ofReviewedFacult

Is calcium deficiency the real cause of bitter pit? A review

Bitter pit is a disorder affecting the appearance of apples. Susceptibility is genetically controlled by both the cultivar and rootstock, with both environmental and horticultural factors affecting its severity and proportional incidence. Symptoms appear more frequently at the calyx end of the fruit and consist of circular necrotic spots, which take on a “corky” appearance visible through the peel. Bitter pit may develop before harvest, or after harvest, reducing the proportions of marketable fruit. In this review, current knowledge of the factors associated with the occurrence of bitter pit in apples is summarized and discussed along with their interactions with Ca uptake and distribution to fruit. This disorder has been previously linked with localized Ca deficiencies in fruit during its development. However, these relationships are not always clear. Even with over a century of research, the precise mechanisms involved in its development are still not fully understood. Additional factors also contribute to bitter pit development, like imbalances of mineral nutrients, low concentration of auxins, high concentration of gibberellins, changes in xylem functionality, or physiological responses to abiotic stress. Bitter pit remains a complex disorder with multiple factors contributing to its development including changes at whole plant and cellular scales. Apple growers must carefully navigate these complex interactions between genetics, environment, and management decisions to minimize bitter pit in susceptible cultivars. Accordingly, management of plant nutrition, fruit crop load, and tree vigor still stands as the most important contribution to reducing bitter pit development. Even so, there will be situations where the occurrence of bitter pit will be inevitable due to cultivar and/or abiotic stress conditions.info:eu-repo/semantics/publishedVersio

Improving irrigation efficiencies in pears case studies

Hot summers and cork spot in d Anjou pear can be a significant challenge in central Washington. Cork spot is responsible for an estimated $7 to$8 million dollars in losses to d Anjou production every year. For example, in 2017 cork spot accounted for approximately one-third of d Anjou culls at three major packinghouses. Irrigation frequency and timing as well as good calcium programs can affect tree growth, productivity, and fruit quality in pears. Fruit size is also critical for high returns. The following case studies illustrate common irrigation system challenges in Washington pear orchards and the results of system upgrades designed to address site specific challenges. These case studies are designed to provide growers with potential solutions to common irrigation challenges in order to improve fruit quality and profitability