『Abstract
Variation of vegetation coverage and canopy height may reflect
the complex spatial heterogeneity of nutrient storage and supply
capacity, soil moisture, and surface hydrology in the karst terrains
suffering from severe land degradation. To assess the patterns
of nutrient limitation under different vegetation covers in the
subtropical karst ecosystems from Guizhou province, southwestern
China, topsoil and leaf samples of dominant tree species were
collected in forest stand (FO), shrub stand (SH) and shrub-grass
stand (SG), respectively. Nutrient concentrations of both soil
and leaf were determined, and ratios of N to P and vegetation
nutrient reuse capacity (VNR) calculated as well as vegetation
coverage, vegetation canopy height and tree density measured across
the three stands. Mean leaf N/P ratio was lowest (16.1±1.4) in
FO and highest (33.5±3.2) in SG. Vegetation nutrient reuse increased
with the decline in n and P availability in soils for these three
stands. VNR of N and P ranged from 8.5 to 25.2 mg N g-1
and from 0.4 to 1.1 mg P g-1, respectively, and appeared
lowest in SG (10.4 mg N g-1 and 0.5 P mg g-1
on average, respectively) and highest in FO (22.4 mg N g-1
and 0.9 mg P g-1 on average, respectively). although
there was no substantial difference in phosphorus reuse efficiencies
between plant species and vegetation stands, concentrations of
N and P of senesced leaves (SLs) were, respectively, found in
positive correlation with the concentrations of mature leaves.
The variation of VNR with elements indicated that P is cycled
within vegetation much more efficiently than N across the stands.
This study demonstrated that the karst vegetations were generally
at P-limited or N- and P- co-limited stresses and that N/P ratio
could be an effective indicator for nutrient limitation in the
karst ecosystems at vegetation community level rather than at
tree species level. It is proposed that phosphorus reuse by mature
leaves could be an adaptation strategy by the dominant species
to the low P availability in the karst soil.
Keywords: Karst terrain; N/P ratio; Nitrogen; Nutrient availability;
Nutrient reuse; Plant leaves; Plant species; Phosphorus; Vegetation
stand』
Introduction
Materials and methods
Site description
Sampling
Leaf samples
Soil samples
Chemical analyses
Leaf analysis
Soil analysis
Calculations and statistical analyses
Results
Vegetation characteristics
Foliar nutrient concentration and stoichiometry
Nutrient conservation
Discussion
Nutrient limitation
Plant adaptation to nutrient stress
Conclusion
Acknowledgments
References