Abstract
Recent studies indicate that rice fields contribute to the conservation of aquatic plants, however, repeated cultivation can reduce the species diversity harbored by rice fields. Repeated tillage, agrochemical application and environmental homogeneity can reduce plant diversity and select for species more tolerant to disturbance. Our hypotheses were: 1) macrophyte richness and biomass decrease with increased rice crop age; and 2) macrophyte species of rice fields are a subsample of natural wetlands and species loss will increase with crop age. We investigated three rice fields of each different ages (old, intermediate and new ones) and three natural intermittent wetlands for this study. Each area was sampled four times throughout the rice cultivation cycle (off-season, initial growth, final growth and post-harvest). Our results showed that the mean macrophyte richness and biomass were similar between rice fields of different ages and lower than that of natural wetlands. Although species composition in the different-aged rice fields was not markedly different, there was nestedness in the rice fields as age increased. In this study, we verified that macrophyte richness and biomass in rice fields was lower than natural wetlands and the species composition was different among wetland types (rice fields and natural wetlands), however our hypothesis that species richness and biomass will decrease with crop age was not confirmed. All rice crops had similar macrophyte assemblage structure (richness, biomass and species composition). However, the another hypothesis tested was confirmed, macrophyte assemblage of rice fields is a subset of natural wetlands and as, the age of a rice field increases, the species that occur in older rice field are subsets of species that occur in younger ones.
Highlights
Most of the world’s biodiversity lies in areas managed by humans (Pimentel et al, 1992), and biodiversity has been conserved outside of protected areas (Chester and Robson, 2013)
A total of 19 species were exclusive to natural wetlands and 26 species were shared by the natural wetlands and rice fields
We verified that rice fields, regardless cultivation age, can act as partial substitutes for natural wetlands, but the conservation of some species still depends on the existence of natural wetlands
Summary
Most of the world’s biodiversity lies in areas managed by humans (Pimentel et al, 1992), and biodiversity has been conserved outside of protected areas (Chester and Robson, 2013). 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). Rice may help conserve wetland diversity, the effects of rice production on biodiversity could vary with production techniques (Linke et al, 2014)
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