Ecosystem Functioning Of Facilitation Between Co-cultured Species

In natural ecosystem, ecosystem functioning of biodiversity can be partially explained by positive interactions between species (interspecific facilitation). In modern, intensive agricultural system, however, biodiversity is simplified and interactions between species are largely neglected. High and stable crop yields required high input (e. g. chemical fertilizers, pesticides). Whether and how biodiversity can be used to strengthen the stability of intensive agriculture, while not negatively impact environment? It is a critical question that agroecology should be addressed.Traditional rice-fish system is a successful case in utilizing biodiversity in agriculture. Recently, large-scale and intensive rice fish systems are developed in China and in the world (the term’fish’ refers to a wide range of aquatic animals including fish, prawn, shrimp, crabs, soft shell turtles, etc. in this study). These diverse, large-scale and intensive rice-’fish’systems (RFS) provide an interesting case to study the ecosystem functioning of biodiversity in agriculture. Here I use field and farmer surveys, field and mesocosm experiments to evaluate the ecosystem functioning of facilitation between rice and different aquatic animals. I try to address the follow questions:(1) whether RFSs can enhance productivity and reduced inputs of pesticides and fertilizers;(2) how the interactions between rice and’fish’can enhance efficient resource use in RFSs;(3) whether RFSs could minimize negative impacts of intensive agriculture on environment. The main results were as bellows.1Productivity and the inputs of pesticide and fertilizer in RFSThe field and farmer surveys covered13provinces and five major RFS model (rice-carp, rice loach, rice-shrimp, rice-crab and rice-turtle). The average rice yield of the five RFSs was8.34ton ha-1,2.98%higher than that in rice monoculture (FM). Among the five RFSs, the increased rice yields in rice-carp and rice-crab were much higher than in the other three RFSs compared to the corresponding RM. Rice yields in rice-loach and rice-turtle did not changed compare to their RMs. Spatial stability of rice yield was the same in RM and RFS, while chemical fertilizers and pesticides used were significantly reduced in the five RFSs by26.52%and61.08%respectively.2Activity patterns of the’fish’in rice fieldVideo recording showed that the pattern of carp activity in the field with rice (rice-carp) was different from that without rice (carp monoculture). In carp monoculture, carps mainly stayed in the entrance of the irrigation water, while in the rice-carp field, carps swam throughout the field. The distribution diversity and evenness of fish in the field with rice was2.85and2.11times that in monoculture. Rice changed physical environment and biotic community, providing more feeding opportunities for fish. The stay time (positive correlated with feeding time) of fish in the quadrats was increased by41.84%.Pitfall trap study showed crabs tended to stayed with rice, especially at night. Rice plants seem to promote the activity of crab. The frequency of crab activity in rice-crab system was37.95%higher than in crab monoculture system.3Resource use in rice-’fish’systemsResults from the investigation of natural abundance of13Cå'Œ15N showed that’fish’can use natural "food" in the rice field. This natural "food"(including alage, plankton, insects, weed, ect.) contributed3.00%-50.17%to the’fish’in rice-carp, rice-crab and rice-turtle.Results from the mesocosm experiment showed that15N in the unconsumed fish feeds can be used by rice. The efficiency of fish feeds was13.02%-35.13%the three RFSs (rice-carp, rice-crab and rice-turtle). Rice increased efficiency of the feed-N by7.57%-42.00%. The unconsumed feed-N was44.99%-71.96%among the total feed-N in these RFSs.Test of soil15N after the experiment showed that the unconsumed fish feeds can accumulated in soil by5.06%-11.77%(rice-carp, rice-crab and rice-turtle) than in the corresponding’fish’ monoculture.4Decomposition in RFSsCompared to’fish’monoculture, rice plants can promoted organic matter decomposition in RFSs. Results from15N showed that decomposition rates were5.63%-20.47%and3.46%-8.12%respectively higher in the three RFSs than in the corresponding’fish’monoculture in40days and80days after the tests.5The impact of RFS on environmentThe three intensive RFSs (rice-carp, rice-crab and rice-turtle) showed higher productivity under high density of’fish’. Compared’fish’monoculture, the yield of’fish’did not change. Rice yields, however, were significantly increased under rice-carp and rice-crab. Compared with rice monoculture, introducing’fish’into rice field did did not increase total N, total P and COD in water. Compared with’fish’(turtle) monoculture, rice-turtle system significantly reduces the total N and COD in the water.