Floristic diversity of the soil weed seed bank in a rice-growing area of Brazil: in situ and ex situ evaluation

Abstract

The objective of this study was to compare the ex situ and in situ floristic diversity of the soil weed seed bank of a rice field in northeastern Brazil. In a rice field in the county of Bacabal, located in the state of Maranhão, thirty 25-m 2 plots were laid out. From 15 plots, soil samples (6/plot; n = 90) were taken with a soil probe (25 × 16 × 3 cm) and placed in aluminum trays in the greenhouse. From the remaining 15 plots, weed samples (6/plot; n = 90) were taken with the same soil probe. The number of seeds was estimated by germination. We evaluated the numbers of species and individuals, as well as the density, frequency, abundance and importance value (IV) for each species. Diversity was computed by the Shannon index (H'). We recorded 13,892 individuals (among 20 families, 40 genera and 60 species), of which 11,530 (among 50 species) germinated ex situ and 2,362 (among 34 species) germinated in situ. The family Cyperaceae had the highest number of species (16), followed by Poaceae (10). The dominant species, in situ and ex situ, were Schoenoplectus juncoides (IV=47.4%) and Ludwigia octovalvis (IV=34.8%), respectively. Floristic diversity was higher ex situ (H'=2.66). The information obtained here could help determine the infestation potential of these species, which could lead to improved management strategies.

Floristic and Phytosociology of Weeds in Upland Rice in the Humid Tropics

“…And that the greatest species diversity occurred in Alto Alegre do Pindaré, probably due to two areas subject to flooding, which provided more favorable conditions for weeds, and/or the larger sample area relative to Buriticupu. Similar values for floristic diversity were obtained by Mesquita et al (2013) and Silva et al (2014) in upland rice cultivation in the cutting and burning system in areas located in the humid tropic region of the Brazilian state of Maranhão. …”

“…This result is consistent with that obtained by Silva et al (2014) when studying a weed seed bank in rice crops in the municipality mentioned, where the Cyperaceae family also presented great diversity of species. Mesquita et al (2013), also in a rice bank seed study in the central region of the state of Maranhão, have identified this family with great species richness. Touré et al (2013) have verified the importance of this family in rice cultivation in northern Guinea.…”

“…The Poaceae family was represented by many species of fast initial growth and accumulation of biomass, which produce dense soil cover, which causes competition with the crop mainly by the nutrients of the soil and, consequently, reduces the production of upland rice cultivation. This family was 6 also identified among the most important ones in upland rice cultivation in several surveys (Cobucci et al, 2001;Durigan, 2006, 2009;Touré et al, 2013;Mesquita et al,2013;Silva et al, 2014Silva et al, , 2015.…”

“…It infests in wet or flooded areas, including rice floodplain fields (Kissmann and Groth, 2000). Mesquita et al (2013), evaluating the weeds seed bank in rice crop in a cutting and burning system of the vegetation, have verified the occurrence of this species with great plasticity, that is, capacity to adapt to different locations, as well as tolerance to human activities and stress conditions imposed by environmental factors.…”

“…This indicates that management should also be directed to these plants. A study conducted by Mesquita et al (2013) with weed seed bank in situ and ex situ in an area cultivated with upland rice in the humid tropics has found species of the genus Panicum as important in the study area.…”