科研之友
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摘要
Phytocoenoses of conventional agroecosystems are subjected, already from several decades, to the reduction of the weed species present in the various crops. Such floristic decreasing is directly proportional to intensity of the agronomic impact. The present work is born from the hypothesis that the agro-ecological oases, managed with the ancient agrotechniques, are linked by an high degree of plant biodiversity. In this perspective it was carried out not only an analysis of the field emerged weeds, but even an evaluation of the seedbank since this one synthesizes the weed flora of a wider period. In the experimental agroecosystems, selected due to the typical Emmer wheat presence, an high degree of weed species diversity was observed, above all of terophytes, in the emerged flora as well in the seedbank. In both cases relative densities of each species were found low and without any weed dominance. Probably it occurs as a function of the high degree of competitive and allelopathic interactions. Almost scarce was the presence of exhumed seeds of graminaceae virtually due to their inability to store in the soil a persistent seedbank. Of particular importance it was the discovery of two rare species such as Agrostemma githago and Centaurea cyanus disappeared from many years by the landscape of ※conventional§ agricultural systems. The seedbank was found uniformly distributed in both sampled soil layers (0-15 and 15-30 cm) confirming that plowing induced an uniform burial of the annually produced seeds. The total examined soil profile (0-30 cm) showed a quantitative seedbank similar to those already found in ※biological§ agricultural systems (from 12.000 to 47.000 seeds m-2). However it was qualitatively formed even from several weed species of negligible agronomic impact as a function of their scarce competitivity like in the case of some caryophyllaceae (Silene noctiflora and S.alba), boraginaceae (Myosotis arvensis and Echium vulgaris) and campanulaceae (Legousia speculum-veneris). Finally both agronomic and ecological involvements of this weed complexity were discussed. This complexity was retained of crucial importance not only regards to the biodiversity conservation but even for their role in the landscape ecology. In synthesis, it has been confirmed the hypothesis that the ancient phytocoenoses are still present but only in these ecological oases in which the agronomic impact was ecologically sustainable. In conclusion, it was stressed the crucial role of these agro-ecological oases not only with the aim of the in situ biodiversity conservation, but
