Can organic rice crops help conserve aquatic plants in southern Brazil wetlands?

Abstract

Questions: Are organic rice crops better than convention crops for aquatic plant conservation? We tested three hypotheses: (1) richness, diversity and biomass of aquatic macrophytes are higher in organic rice fields than in conventional ones;(2) aquatic macrophyte species composition in organic rice fields is more similar to that of natural wetlands than to conventional rice fields; and (3) aquatic macrophyte richness, diversity, biomass and species composition in natural wetlands will differ from those of organic and conventional rice fields.Location: Coastal plain of southern Brazil. Methods:We sampled macrophytes at four conventional crops, four organic crops and four natural intermittent wetlands. We sampled at six different times at each site throughout the rice cultivation cycle.Results: A total of 55 species was recorded in natural wetlands and 36 species in rice fields, with 23 found in conventional crops and 27 found in organic crops. The richness, biomass and species composition of macrophytes was similar in the two rice production systems and lower than that of natural wetlands over the cultivation cycle studied. Species composition of natural wetlands differed from that of rice crops mainly through the presence of hydrophytes and rushes.Conclusions: Some macrophyte species used rice crops as a complementary habitat, but diversity was lower and composition was different from that of natural wetlands. Both conventional and organic systems negatively impacted macrophyte biodiversity. However, the similar richness and biomass of plants in organic and conventional crops indicated that natural techniques with less impact could be efficient in reducing undesirable plant diversity in agricultural systems.

Comparison of aquatic macrophyte community structure between natural wetlands and rice fields with different cultivation ages

“…The high richness of grasses and sedges observed in this study is similar to the pattern observed in others studies carried out in southern Brazilian rice fields and natural wetlands (Linke et al, 2014;Rolon and Maltchik, 2010;Rolon et al, 2012). However, the high contribution by hydrophytes in these rice fields differed from other studies in which emergent and amphibious species predominated (Linke et al, 2014).…”

“…The plant richness found in the nine different aged crops was 35 species, which is similar to that of other crops in studies developed with similar methodologies in southern Brazil (Linke et al, 2014). Nevertheless, rice field diversity was lower than that of adjacent natural wetlands (45 species) and other natural wetlands of southern Brazil (Rolon et al, 2010).…”

“…Some studies demonstrated that rice fields contribute to maintain a rich biodiversity, especially in areas where natural wetlands have been completely replaced by rice production, such as California's Central Valley (Reid and Heitmeyer, 1995). Rice fields are important habitats for macrophyte development and these agroecosystems could harbor rare and important species (Bambaradeniya et al, 2004;Linke et al, 2014;Rolon and Maltchik, 2010). Rice fields have specific characteristics, such as periodic flooding, that make them similar to temporary wetlands.…”

“…These agroecosystems can help maintain regional biodiversity by acting as supplemental habitats for many species of macrophytes, invertebrates, amphibians, birds and fishes throughout the world (Bambaradeniya and Amerasinghe, 2004;Lawler, 2001;Maltchik et al, 2011;Marambe et al, 2009;Rolon and Maltchik, 2010). Although rice may help conserve wetland diversity, the effects of rice production on biodiversity could vary with production techniques (Linke et al, 2014).…”

“…Macrophyte diversity in southern Brazil can reach up to 500 species and wetland loss by rice field conversion can compromise several macrophyte species, including endemic ones (Maltchik and Rolon, 2004). Recent studies indicate that rice fields contribute to the conservation of some macrophytes in southern Brazil (Linke et al, 2014;Rolon and Maltchik, 2010), however aquatic macrophyte diversity and composition in rice fields differs significantly from natural wetlands and the cultivation cycles reduces macrophyte richness (Linke et al, 2014). The intensification of rice cultivation, use of fertilizer and pesticides, and mismanagement of soil may decrease the importance of rice fields as biological refuges.…”