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Photosynthesis of Sugarbeets under N and P Stress: Field Measurements and Carbon Balance

Cary, J.W. (1977) Photosynthesis of Sugarbeets under N and P Stress: Field Measurements and Carbon Balance. Agronomy Journal. 69(5):739-744.

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Advances in crop management are limited by our inability
to recognize changes in growth resulting from
short-term fluctuations in plant environment. Simple,
rapid, and nondestructive methods are needed to indicate
daily and hourly rates of growth under field conditions.
Because plant carbon balance is one possible approach
to this problem, CO₂ gas exchange parameters were measured
on Beta vulgaris leaves of field-grown plants to
learn whether or not they might signal the onset of nitrogen
and P stresses. The sugarbeets were grown on
field plots of Portneuf silt loam (Xerollic Calciothid)
soil and allowed to develop severe N and P stresses. Carbon
dioxide exchange and stomatal resistance of intact
plant leaves were measured with small leaf chambers during
1-min periods. Leaf water potentials were also measured
in the field with a hydraulic press. The CO₂ compensation
points, dark respiration, and osmotic pressures
of excised leaf tissue were measured in the laboratory by
standard methods. Photosynthesis per unit leaf area was
reduced in advanced stages of N deficiency; however,
none of the measurements satisfactorily indicated the onset
of N or P stress because of heterogeneity between
leaves. Calculations using the daily carbon balance of
an average plant predicted the relative effects on root
yield of 1) photosynthetic rate per unit leaf area, 2)
photorespiration, 3) stomatal resistance to gas diffusion,
4) mesophyll resistance to carbon dioxide transfer, 5) size
of the seedling tops in the spring, 6) partitioning of
photosynthate between tops and roots near the end of
the season, and 7) date of full plant cover. While all
these factors are important, advances that can be made
by manipulating most of them are limited. Increasing
photosynthesis by reducing mesophyll resistance appears
to offer the greatest potential for large yield increases.

Item Type: Article
NWISRL Publication Number: 0381
Subjects: Irrigated crops > Sugarbeet
Research methodology
Mass Import - autoclassified (may be erroneous)
Depositing User: Dan Stieneke
Date Deposited: 20 Nov 2010 21:51
Last Modified: 06 Feb 2017 22:58
Item ID: 322