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Soil Patches of Inorganic Nitrogen in Subtropical Brazilian Plant Communities with Araucariaangustifolia

Garbin, M.L., Zandavalli, R.B., Dillenburg, L.R.
Plant and soil 2006 v.286 no.1-2 pp. 323-337
Pinus elliottii, forest soils, grassland soils, Araucaria angustifolia, soil chemical properties, inorganic compounds, nitrogen, ammonia, nitrates, soil water content, nutrient availability, plant communities, geostatistics, seasonal variation, Brazil
The patchy environment to which plants are subjected may impose restrictions to plant growth and performance. In the present study, geostatistical tools were used to describe the spatial variation of inorganic nitrogen in three subtropical Brazilian plant communities, under two contrasting seasons (summer and winter). We postulated that NH ₄ ⁺ is the major N form present in the different sites, the patch size is smaller and the magnitude of the variation (contrast) is greater in the older sites (native forest and grassland) than in the Pinus plantation, and that seasonality has no influence on these patch attributes. Contrary to expected, nitrate was the major nitrogen form in the native araucarian forest (75 % and 62 % of the total inorganic nitrogen, for summer and winter, respectively), in contrast to the native grassland and Pinus plantation sites (61-71 % of total inorganic nitrogen as ammonium). In general, as expected, the contrast of patches was more pronounced in the older sites (proportion of total variance accounted for by structural variance between 0.22 and 0.76 for the older sites vs. an overall lack of structure in the Pinus plantation), but patch size was greater in the grassland (4.7-9.8 m) than in the forest sites (2.3-3.9 m). Contrary to expected, there was an overall loss of the patchy structure in the winter, except for the grassland. The Pinus plantation and the grassland may be more favorable to the performance of newly established seedlings of A. angustifolia than the native forest itself. We suggest that the patchy distribution of soil nitrogen is another environmental factor to be overcome by newly recruited seedlings of A. angustifolia in the native forest.