C: N Ratio of the Prairie Ridge Project:
Data Analysis and Nitrogen Distribution Mechanism within Leaves
Yiyi Wong & Zuo Xue, MEAS, NC State University
General C:N Ratios within C3 and C4 Plants
Nitrogen (N) is an important plant nutrient because it is responsible for the growth of
plants. Two forms of photosynthetic pathways (C3 and C4) result in the formation of
energy in terms of Adenosine triphosphate (ATP). The energy is then utilized for growth
depending on the plant’s survival tactics. Generally terrestrial plants have ratios > 20
while aquatic plants have a value between 4 and 10. The C:N ratios in C4 grasses vary
from 20 to 50 while C3 shrubs range from 26 to 49 (Meyers 1990; Muller 1983). C:N
ratios within plants also vary because of different carbon and nitrogen distribution with
respect to growth and photosynthesis.
C%
N%
80
6
70
5
60
4
50
40
3
30
2
C%
C:N
N%
20
1
10
0
0
1
3
5
7
9
11 13 15 17 19 21 23 25 27
Fig.1 Data Distribution among 27 samples
Plants try to efficiently allocate N to photosynthesis because N is a required nutrient for
growth and photosynthesis results in energy for growth. Some plants are more efficient
at using N to create energy than others. Plants using the C4 photosynthetic pathways
have greater photosynthetic nitrogen use efficiency (PUNE) than C3 plants. This means
that C4 plants need less N within its leaves than C3 plants to produce the same amount of
energy for growth (Ehleringer et al. 1993; Sage et al. 1987).
Plants need an N-rich enzyme named Rubisco to carry out photosynthesis. Rubisco
transports carbon dioxide (CO2) within the leaves from one area to another and in some
plants is also a storage unit for extra N. As an enzyme involved in catalytic reactions it
tries to saturate areas where photosynthesis is taking place with CO2. It represents 3060% of soluble protein within C3 plant leaves and 5-20% of soluble protein within C4
plant leaves. Rubisco accounts for 15-30% of total leaf N within C3 plants. The
percentage of Rubisco within C4 plants is not as well documented although maize (corn)
experiments show Rubisco averages approximately 6.5% of leaf N (Sage et al. 1987).
Methods and Results for C:N Sample Analysis
In total 27 plant samples were analyzed on 24th September, 2006. Questionable results
for samples PRP4 Flower, PRP4 Stem & PRP12 Brown blade i.e. abnormally high N
contents, were re-analyzed on 11th Oct, 2006. A summary of %C, %N, and C: N ratio is
listed in the Table.1. For the 27 samples, the mean %C is 43.44% with standard
deviation 3.64. The % N is 1.95% with a standard deviation 1.07 and the mean C: N ratio
is 34.00. As for the data range, the difference among %C data is the least (coefficient
variation 8.40) while the %N results are highly variable with a coefficient variation 61.40
which caused the high difference among C: N ratio (Fig.1).
Table.1 Summery of the Laboratory Data
Sample#
1
2
3
4
5
6
7
12
13
14
8
9
10
11
15
16
17
Common Name
Ambrosic
Ambrosic
Ambrosic
Ambrosic
Ambrosic
Ambrosic
Ambrosic
Horsenettle
Horsenettle
Horsenettle
Bermuda Grass
Bermuda Grass
Bermuda Grass
Bermuda Grass
Bermuda Grass
Bermuda Grass
Bermuda Grass
Plant ID
PRP3
PRP3
PRP3
PRP4
PRP4
PRP4
PRP4
PRP8
PRP8
PRP8
PRP6
PRP6
PRP6
PRP6
PRP11
PRP11
PRP11
Part
Leaf
Stem
Root
Flower
Leaf
Stem
Root
Leaf
Stem
Root
BrownBlade
GreenBlade
Stem
Root
BrownBlade
BrownBlade
GreenBlade
%C
37.49
41.51
42.73
44.25
43.72
38.56
40.98
48.27
42.12
40.19
43.93
43.35
44.36
43.27
45.79
42.83
32.89
%N
2.43
1.46
2.297
4.632
2.701
4.978
2.042
2.589
1.259
1.536
0.9017
1.349
0.666
1.896
0.7419
1.037
2.513
C:N
15.434
28.443
18.61
9.5571
16.193
7.7493
20.077
18.652
33.469
26.176
48.739
32.148
66.634
22.831
61.745
41.319
13.093
18
19
20
21
22
23
24
25
26
27
Bermuda Grass
Fescue
Fescue
Fescue
Fescue
Fescue
Fescue
Fescue
Fescue
Fescue
PRP11
PRP9
PRP9
PRP9
PRP12
PRP12
PRP13
PRP13
PRP14
PRP14
Stem
BrownBlade
GreenBlade
Root
BrownBlade
Root
BrownBlade
Stem
BrownBlade
GreenBlade
44.57
45.17
43.36
53.68
45.37
42.43
44.06
46.88
45.44
45.72
1.07
1.065
0.8702
0.782
0.603
0.8743
1.315
1.401
1.869
2.355
41.671
42.431
49.848
68.673
75.272
48.55
33.52
33.476
24.323
19.422
Results for C:N Variations Within and Between Samples
The %N and C:N ratios in different parts of the plants is shown in Fig.2 (a, leaf; b, stem;
c, root). The leaves of flowering plants Amborsic (mean value 2.55%) and Horsenettle
(2.59%) have a higher %N than that of Bermuda grass (mean value 1.31%) and Fescue
(mean value 1.35%) are these differences significant? What are the standard deviations?
with the exception of two brown blade samples which are PRP11_G (Bermuda grass,
2.51%) and PRG14_G (Fescue, 2.36%). There is no evident difference between the %N
in Horsenettle and Fescue, but within a plant, brown blade samples have lower %N
contents and thus higher C: N ratios than green ones.
C:N in Leaf
N% Contents in Leaf
Ambrosic(PRP3)
Ambrosic(PRP4)
90
80
70
60
50
40
30
20
10
0
Bermuda Grass(PRP6_B)
Bermuda Grass(PRP6_B)
2.5
Bermuda Grass(PRP6_G)
Bermuda Grass(PRP6_G)
Fescue(PRP9_B)
Fescue(PRP9_G)
Fescue(PRP12_B)
Fescue(PRP13_B)
1
Bermuda Grass(PRP11_B)
N%
Bermuda Grass(PRP11_G)
Bermuda Grass(PRP11_B)
2
Bermuda Grass(PRP11_B)
Bermuda Grass(PRP11_B)
Ambrosic(PRP4)
Horsenottle(PRP8)
3
Horsenottle(PRP8)
Ambrosic(PRP3)
1.5
Bermuda Grass(PRP11_G)
Fescue(PRP9_B)
1
Fescue(PRP9_G)
0.5
Fescue(PRP12_B)
0
Fescue(PRP13_B)
Fescue(PRP14_B)
Fescue(PRP14_G)
1
Fescue(PRP14_B)
Fescue(PRP14_G)
Fig 2.a N Contents and C: N ration in leaf samples
As for stem samples (Fig.2b), all of the 6 samples have N contents no more than 2
percent, and among the 4 plants, Ambrosic has the highest N contents followed by
Fescue, Horsenettle and Bermuda grass. In roots (Fig.2c), except for Fescue, plants have
more N contents compared to stem samples: Ambrosic %N contents in roots is more than
2% compared to those in stems which are no more than 1.8%; Horsenettle root sample
has 1.5% N contents and stem has 1.2%.
C:N in Stem
N% Contents in Stem
70
60
Ambrosic(PRP4)
40
Horsenottle(PRP8)
30
Bermuda Grass(PRP6)
20
Bermuda Grass(PRP11)
N%
Ambrosic(PRP3)
50
Fescue(PRP13)
10
0
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1
Ambrosic(PRP3)
Ambrosic(PRP4)
Horsenottle(PRP8)
Bermuda Grass(PRP6)
Bermuda Grass(PRP11)
Fescue(PRP13)
1
Fig2.b N Contents and C: N ration in stem samples
N% Contents in Roots
C:N in Roots
2.5
80
70
Ambrosic(PRP3)
2
Ambrosic(PRP3)
60
Ambrosic(PRP4)
50
Horsenottle(PRP8)
40
Bermuda Grass(PRP6)
30
N%
Ambrosic(PRP4)
1.5
Horsenottle(PRP8)
Bermuda Grass(PRP6)
1
Fescue(PRP9)
Fescue(PRP9)
20
Fescue(PRP12)
10
0.5
Fescue(PRP12)
0
0
1
1
Conclusion: The comparison of the N contents in different parts of the 4 plants is listed in
Fig2.c N Contents and C: N ration in root samples
Table.2. Overall, Amborsic and Horsenettle have more %N than the C4 and C3 plants.
Except for that of leaf, the N content within C4 plant (Bermuda grass) is greater than
those of the C3 plant (Fescue). Within a plant, leaves and roots have a N content higher
than those of stems. The C4 plant has the least N content differentiation among leaves,
stem and roots. And within leaf samples, as mentioned above, brown blade samples have
less N contents and thus higher C: N ratio than green ones.
Table 2 N contents difference among different parts of different plants
Plant
Bermuda
Ambrosic
Horsenettle
N Contents
Grass(C4)
Leaf
2.57*
2.59
1.31*/**
Stem
1.64*
1.26
1.87*
Root
2.17*
1.54
1.90
* Averaged data
**For Bermuda grass, the Greenblade value is1.93/ Brownblade value is 0.67;
***For Fescue, the Greenblade value is1.61/ Brownblade value is 1.21;
Fescue(C3)
1.35*/***
0.40
0.83*
Discussion of C:N Leaf Variations
Leaf nitrogen concentration (LNF) varies among plant species. N leaf variations between
species are the result of differences in light-saturated photosynthetic rates, the efficiency
of N use, and the life expectancy of a leaf (Osone and Tateno 2005). Generally leaves
with a lower LNF have longer-lived leaves. Carbon-rich structures that increase the
leaves’ longevity such as thick cuticles and dense cell walls also reduce space for N-rich
cytoplasm and photosynthetic organs. Internal N concentrations are related to biomass
allocation between roots and leaves. Plant leaves with a high concentration of N
generally have a low concentration within the roots (Osone and Tateno 2005).
As plants decompose, soluble proteins and other more easily degradable materials are
first utilized by microbes. Up to 90% of the N within leaves become labile and are
removed. When plants lose their green color it is due to the loss of chlorophyll and other
soluble proteins that are decomposed by microbes and then leached from the leaves. The
remnants at different stages of plant decomposition are the recalcitrant materials which
are decomposed over longer timeframes. (Sage et al.1987)
References
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Fixation Products and Activities of Enzymes Related to Photosynthesis in Bermudagrass
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[2]Ehleringer, James R. and Russell K. Monson. (1993). Evolutionary and Ecological
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Systematics (24): 411-439.
[31]Evans, John R. (1989). Photosynthesis and nitrogen relationships in leaves of C3
plants. Oecologia (78): 9-19.
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