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Abstract: The effects of a nutrient addition experiment on the plant biomass of garigue vegetation on ultramafic (serpentine) soils in Tuscany, Italy, were ...

Original Paper

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Effects of Nutrient Addition on Community Productivity and Structure of Serpentine Vegetation A. Chiarucci, S. Maccherini, I. Bonini, and V. De Dominicis Dipartimento di Biologia Ambientale, Università di Siena, Siena, taly Received: February 17, 1998; Accepted: September 6, 1998

mass increase of the perennial grasses and perennial forbs was

statistically not significant. Soil extractable elements differed for calcium and potassium in the plots where they were added; sodium and nickel extractabilities were reduced by calcium addition due to the increased soil pH. Biomass production was linked more to major nutrient addition than to reduced nickel extractability, confirming that serpentine vegetation of Tuscany is mainly affected by nutritional stress rather than soil heavy metal content. The addition of calcium had a low effect on primary production of these ultramafic soils.

fic rocks and their vegetation deals not only with a biological curiosity but with an important and under-rated world-wide phenomenon". Ultramafic soils are widespread in many parts of Tuscany, Italy and their most typical vegetation is a garigue (Armerio-Alysseturn bertolonii), characterised by low ground cover, low species richness and many endemic species, the best known of which

is the nickel hyperaccumulator, Alyssum bertolonii (Sasse, 19791321; Arrigoni et al., 1983'; Vergnano Gambi, 1992; Chiarucci et al., 1995]131). Some recent papers (Chiarucci and De Dominicis, 1995112]; Chiarucci, 1996111]) have shown how

pine plantation promotes species richness and total ground cover in the understorey natural vegetation and that a higher exchangeable content of metals was found in the soil under the pine canopy (Chiarucci and De Dominicis, 1995112]) as well as under the more evolved natural plant communities (Chiarucci et al., 1998 bE15], 1998 c]16]). These observations sug-

Key words: Fertilization, plant biomass, species abundance, ultramafic soils.

gested that the most important limiting factor for Tuscan ser-

pentine vegetation is soil nutritional deficiency and not its heavy metal content.

Nomenclature: Pignatti (19821261) for most species, Chiarucci et al. (1995113]) for serpentinophytes.

Introduction Because of their chemical and physical properties, serpentine

soils are inimical to plant growth and productivity. They are distinct environments, in which plant growth and productivity are lowered by a number of factors, including soil shallowness and permeability, low levels of nutrients, calcium deficiency, magnesium toxicity and relatively high contents of potentially

phytotoxic elements, such as chromium, nickel and cobalt (Proctor and Woodell, 19751291; Brooks, 1987'; Baker et al., 1992; Roberts and Proctor, 19921°1). However, serpentine soils and the factors controlling plant growth and productivity may differ from site to site (Proctor and Nagy, 19921281). As remarked by Proctor and Nagy (19921281), several recently published papers "[...] have emphasised that the study of ultrama-

Plant biol. 1(1999)121—126 © Georg Thieme Verlag Stuttgart New York ISSN 1435-8603

A nutrient addition experiment was planned to test the importance of soil nutritional deficiency. The effects of nutrient addition on species diversity have been investigated in different serpentine sites. The results included the disappearance of rare species and an increase in species richness and ground cover (Carter et al., 1988191; Slingsby, 1991; Proctor and Nagy, 19921281), a decrease in species richness and invasion by alien species (Huenneke et al., 19901201). The effects of nutrient addi-

tion on productivity have rarely been investigated and only at a very small spatial scale, about 100 cm2 for the California serpentine (1

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