<p>Nitrogen (N) is one of the major nutrient elements that
affects growth, development, and quality of floriculture crops. Both sub-optimal
and supra-optimal levels of N can negatively affect crop growth. In addition,
over- fertilization may cause run-off and leaching of the N fertilizer leading
to environmental pollution. Therefore, it is crucial to maintain optimal N
level in plant tissue to produce good quality crops and increase productivity.
This requires regular monitoring and measurement of plant N status. Laboratory
analysis, the only direct method available to measure tissue N content, is
destructive of plant tissue and expensive. Other available indirect methods are
laborious, expensive, and/ or less reliable. In addition to measuring plant N
status, it is crucial to understand acclimation responses at biochemical, leaf,
and whole-plant levels in floriculture crops to N-deficit conditions. This will
aid in developing a mechanistic model of plant responses to sub-optimal levels
of N, proper fertilizer guidelines during production, and screening tools for
identifying new varieties with tolerance to low-N level in the root zone. Unfortunately,
there is limited research on floriculture crops that is simultaneously focused
on plant responses at different scales to N-deficit conditions. The objectives
of this research were to (i) assess the feasibility of image-based
reflectance ratios for estimating tissue N content in poinsettia (Expt. 1), (ii)
develop an affordable, remote sensor that can
accurately and non-destructively estimate tissue N <a>content</a>
in poinsettia (Expt. 2), (iii) study the physiological acclimation at whole-plant, leaf,
and biochemical scales in poinsettia cultivars to N-deficit conditions (Expt.
3).</p>
<p>In Expt. 1, we compared several spectral ratios
based on the ratio of reflectance of near infrared <i>(R<sub>870</sub>)</i> to reflectance
of blue (<i>R</i><i><sub>870</sub>/R<sub>450</sub></i>),
green (<i>R<sub>870</sub>/R<sub>521</sub></i>),
yellow (<i>R<sub>870</sub>/R<sub>593</sub></i>),
red (<i>R<sub>870</sub>/R<sub>625</sub></i>),
hyper-red (<i>R<sub>870</sub>/R<sub>660</sub></i>),
and far-red(<i>R<sub>870</sub>/R<sub>730</sub></i>)
wavelengths from plants<i><sub> </sub></i>to
measure whole-plant tissue N content in<i><sub>
</sub></i>four cultivars of poinsettia (<i>Euphorbia pulcherrima</i>)
using a multispectral image station. Results indicated the reflectance ratio <i>R<sub>870</sub>/R<sub>625</sub></i> was most suitable for assessing tissue N content
in plants. In Expt. 2, a low-cost remote sensor was developed
based on the findings of Expt. 1 that captured red and near-infrared images of
plants, from which a reflectance ratio (<i>R<sub>ratio</sub></i>) was developed. The
ratio was linearly related to tissue N content
in all poinsettia cultivars. Furthermore, <i>R<sub>ratio</sub></i><sub> </sub>was
found to be more specific to N than to other elements in the tissue and related
to the chlorophyll concentration of the plant. In Expt. 3, poinsettia cultivars ‘Jubilee Red’
(‘JR’) and ‘Peterstar Red’ (‘PSR’) displayed different acclimation strategies
for physiology and growth under N-deficit conditions. Significantly higher
growth was observed in ‘JR’ than in ‘PSR’ in the sub-optimal treatment, which
indicates that ‘JR’ is more tolerant to N stress compared to ‘PSR’. Further
analyses indicated that N uptake was higher in ‘JR’ than in ‘PSR’ under N-deficit
conditions, without any changes in root morphology or growth. This is possible
when higher levels of energy are available to transport nitrate and/or ammonia
from the substrate into the root cells. Supporting this, significantly higher photosynthesis
and carboxylation efficiency were observed in ‘JR’ than ‘PSR’ under N-deficit condition.
These results shows that higher growth of ‘JR’ than ‘PSR’ under N-deficit
conditions was likely due to increased N uptake (likely due to increased
energy-driven transporter activity), which increased tissue N and chlorophyll
levels. Further, these increases resulted in higher carboxylation efficiency
and photosynthesis by ‘JR’ than ‘PSR’. Increased carbohydrate synthesis
supported leaf growth and provided required energy in the fine root cells for N
uptake from the substrate.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14502039 |
| Date | 06 May 2021 |
| Creators | Ranjeeta Adhikari (10710357) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/NITROGEN_N_MANAGEMENT_IN_FLORICULTURE_CROPS_DEVELOPING_A_NOVEL_IMAGE-ANALYSIS-BASED_TECHNIQUE_FOR_MEASURING_TISSUE_N_CONTENT_AND_UNDERSTANDING_PLANT_PHYSIOLOGICAL_RESPONSE_TO_N_SUPPLY/14502039 |
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