Abstract
We studied the effect of nitrogen supply (3.3 and 20.0 g°m — 2 °yr — 1 ) on the nitrogen use efficiency (NUE) of three Carex species that differ in maximum growth rate. The rank order of maximum growth rate of these species is: Carex diandra @< Carex rostrata < Carex acutiformis. We distinguished two components of NUE: the mean residence time of nitrogen (MRT) in the plant and the nitrogen productivity (A). In this concept, NUE equals the product of MRT and A, and thus equals total productivity divided by the total N loss in litter. The N productivity (A) of C. diandra was significantly higher than that of C. rostrata and C. acutiformis. In each species A decreased strongly at enhanced N supply. The MRT of N differed substantially between species, but was not significantly affected by N supply. Contrary to what is generally found, the species with the lowest maximum growth rate (C. diandra) had the highest N turnover rate (lowest MRT), while the species with the highest maximum growth rate (C. acutiformis) had the lowest N turnover rate (highest MRT). In all species, the NUE decreased with increasing N supply. As a result of the observed patterns in N productivity and mean residence time, the species with the lowest maximum growth rate (C. diandra) had the lowest nitrogen use efficiency, while the species with the highest maximum growth rate (C. acutiformis) had the highest NUE. These results are not in agreement with the generally observed patterns in NUE along gradients of primary productivity. Comparisons of the results of this study with those of other studies show that generalizations of patterns of NUE along gradients of primary productivity should explicitly take into account which growth forms are compared (evergreen species vs. deciduous species, or [congeneric] species with the same growth form). Moreover, this study shows that factoring NUE into its components is a useful tool in the analysis of the adaptive significance of the N economy of plants.
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Claims 11
Claim · model-written summary
In all Carex species, nitrogen use efficiency decreased with increasing N supply.
CarexNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In all species, the NUE decreased with increasing N supply”
t0“Carex Species”
Claim · model-written summary
Nitrogen productivity of C. diandra was significantly higher than that of C. rostrata and C. acutiformis.
- Taxon
- C. diandra
Carex diandrae1 - Outcome
- N productivity (A)e1
- Direction
- highere1
- Comparator
- C. rostrata and C. acutiformise1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“The N productivity (A) of C. diandra was significantly higher than that of C. rostrata and C. acutiformis”
Claim · model-written summary
In each Carex species, nitrogen productivity decreased strongly at enhanced N supply.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“In each species A decreased strongly at enhanced N supply”
e4“the nitrogen productivity (A)”
t0“Carex Species”
Claim · model-written summary
Mean residence time of nitrogen differed substantially between Carex species.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“The MRT of N differed substantially between species, but was not significantly affected by N supply”
t0“Carex Species”
Claim · model-written summary
Mean residence time of nitrogen was not significantly affected by N supply.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“The MRT of N differed substantially between species, but was not significantly affected by N supply”
t0“Carex Species”
Claim · model-written summary
C. diandra had the highest nitrogen turnover rate, with the lowest mean residence time of nitrogen.
- Taxon
- C. diandraCarex diandrae5
- Outcome
- N turnover ratee5
- Direction
- higheste5
- Qualifier
- lowest MRTe5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e5“the species with the lowest maximum growth rate (C. diandra) had the highest N turnover rate (lowest MRT)”
Claim · model-written summary
C. acutiformis had the lowest nitrogen turnover rate, with the highest mean residence time of nitrogen.
- Taxon
- C. acutiformis
Carex acutiformise6 - Outcome
- N turnover ratee6
- Direction
- loweste6
- Qualifier
- highest MRTe6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e6“the species with the highest maximum growth rate (C. acutiformis) had the lowest N turnover rate (highest MRT)”
Claim · model-written summary
C. diandra had the lowest nitrogen use efficiency among the three Carex species.
- Taxon
- C. diandraCarex diandrae7
- Outcome
- nitrogen use efficiencye7
- Direction
- loweste7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e7“the species with the lowest maximum growth rate (C. diandra) had the lowest nitrogen use efficiency”
Claim · model-written summary
C. acutiformis had the highest nitrogen use efficiency among the three Carex species.
- Taxon
- C. acutiformisCarex acutiformise0
- Outcome
- NUEe0
- Direction
- higheste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the species with the highest maximum growth rate (C. acutiformis) had the highest NUE”
Claim · model-written summary
Generalizations of NUE patterns along productivity gradients should consider which growth forms are compared.
- Outcome
- generalizations of patterns of NUE along gradients of primary productivitye0
- Qualifier
- growth forms are comparede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“generalizations of patterns of NUE along gradients of primary productivity should explicitly take into account which growth forms are compared”
t0“Carex Species”
Claim · model-written summary
Factoring NUE into its components is a useful tool for analysing the adaptive significance of the N economy of plants.
- Outcome
- analysis of the adaptive significance of the N economy of plantse0
- Qualifier
- factoring NUE into its componentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“factoring NUE into its components is a useful tool in the analysis of the adaptive significance of the N economy of plants”
t0“Carex Species”