『Abstract
Nitrogen-fixing plants alter the chemical properties of the soil
beneath plant canopies, particularly by concentrating nitrogen-rich
organic matter. We hypothesize that the presence of a legume canopy
inside a plot will more greatly influence the spatial structure
of soil nitrogen (N) than phosphorus (P). We also investigated
whether the effects of legume individuals on the soil properties
beneath their canopies might be mediated by soil texture and water
availability. Thus, we expected that the local effect of a legume
canopy would be more conspicuous in nutrient-poor sandy soils
than in nutrient-rich loamy soils. Moreover, the spatial pattern
should differ during the wet (winter) and dry seasons (summer)
because the microbial processes driving nutrient cycling are sensitive
to water availability. To test these hypotheses, square plots
(4 m×4 m or 3 m×3 m) were placed around isolated mature individuals
of Adenocarpus viscosus in two pine forest stands of the
Canary Islands (Spain) with contrasting soil textures (loamy and
sandy soil). The spatial pattern and scale of microbial biomass-N
(MB-N), dissolved organic-N (DON), and inorganic-N and -P fractions
(NH4-N, NO3-N and PO4-P) were analyzed with geostatistical methods
for two sampling dates (summer and winter). Soil variables with
spatial structure demonstrated a greater spatial dependence in
the loamy than sandy soil, with the exception of MB-N during summer.
Except for NH4-N and NO3-N
in winter plots, the spatial pattern of winter NH4-N,
NO3-N, and DON in the sandy soil; no dependence
was observed for PO4-P on the legume canopy in both soil types.
Our results suggest that the presence of A. viscosus individuals
may be an important source of spatial heterogeneity in the N content
of the soil in these forests. However, soil texture and water
content modulated the magnitude of the legume canopy effect on
the spatial distribution of these N forms beneath canopies.
Keywords: Adenocarpus viscosus; Microbial biomass-N; Dissolved
organic-N; Inorganic-N; Extractable-P; Soil texture』
1. Introduction
2. Methods
2.1. Area of study
2.2. Experimental design
2.3. Laboratory analysis
2.4. Statistical analysis
3. Results
4. Discussion
Acknowledgments
References