Effects of experimental nitrogen and/or phosphorus additions on soil nematode communities in a secondary tropical forest Jie Zhao a, b,1 , Faming Wang a, 1 , Jian Li a, c, 1 , Bi Zou a , Xiaoli Wang a, c , Zhian Li a, * , Shenglei Fu a, ** a Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, PR China b Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, PR China c University of Chinese Academy of Sciences, Beijing 100049, PR China article info Article history: Received 3 January 2014 Received in revised form 18 March 2014 Accepted 21 March 2014 Available online 13 April 2014 Keywords: Nitrogen fertilization Phosphorus fertilization Soil nematodes Soil food web Tropical forest Nitrogen-rich and phosphorus-poor soils abstract In tropical forest ecosystems, highly weathered soils are often considered as relatively nitrogen-rich but phosphorus-poor. Nutrient availability greatly regulates ecosystem processes and functions of tropical forests. However, little is known about how nitrogen and/or phosphorus additions affect the conditions of soil food web which is an important component of belowground ecosystems. In the present study, soil nematode communities were monitored and served as indicators of soil food web conditions under experimental nitrogen and phosphorus additions in a secondary forest in tropical China. The principal response curves of soil nematode community structure revealed same tendency of changes under ni- trogen and/or phosphorus additions compared with control, in terms of nematode functional guild compositions: apparent successions from communities dominated by He 3 and Ba 1 to communities dominated by Ba 2 and Fu 2 occurred after nitrogen and/or phosphorus additions. The diversity of soil nematode genera was not sensitive to either nitrogen or phosphorus addition. Phosphorus addition significantly suppressed total nematode density, density of omnivore-predators, and four nematode faunal indices (i.e. MI25, EI, SI, and SFI), but increased two faunal indices (i.e. CI and BaI). However, nitrogen addition did not induce remarkable changes of these variables in the present study. Our results suggest that nitrogen and/or phosphorus additions suppress soil nematodes in tropical secondary forests, which was inconsistent with our expectation that nitrogen addition was detrimental to and phosphorus addition was conducive to soil nematodes in this nitrogen-rich but phosphorus-poor soil. Furthermore, the effects of phosphorus addition are more powerful than the effects of nitrogen addition. Moreover, phosphorus addition degrades the structure and trophic links of the soil food web, reduces the carbon utilization of soil nematodes, and leads to a more fungal dominated decomposition pathway. The al- terations of soil food web conditions might result in altered ecosystem functioning. Our findings could provide a better understanding of the responses of soil food web to nitrogen and phosphorus additions in nitrogen-rich but phosphorus-poor soils. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Tropical forests possess great biodiversity (Myers et al., 2000; Sala et al., 2000), contain up to 40% of global terrestrial biomass carbon (Dixon and Brown, 1994; Cleveland and Townsend, 2006) and 30e50% of terrestrial productivity (Grace et al., 2001). There- fore, they are considered as one of the most important ecosystems on earth. Their highly weathered soils are often considered as relatively nitrogen-rich but phosphorus-poor. Soil phosphorus level plays a key role on ecosystem functions such as net ecosystem production (NEP) and litter decomposition in those ecosystems (Vitousek, 1984; Hobbie and Vitousek, 2000; Wardle et al., 2004; Cleveland et al., 2006; Kaspari et al., 2008). In addition, global at- mospheric nitrogen deposition is accelerating through time due to anthropogenic activities such as fossil fuel burning and agriculture * Corresponding author. Tel.: þ86 20 37252631; fax: þ86 20 37252615. ** Corresponding author. Tel.: þ86 20 37252722; fax: þ86 20 37252831. E-mail addresses: lizan@scbg.ac.cn (Z. Li), sfu@scbg.ac.cn (S. Fu). 1 These authors contributed equally. Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio http://dx.doi.org/10.1016/j.soilbio.2014.03.019 0038-0717/Ó 2014 Elsevier Ltd. All rights reserved. Soil Biology & Biochemistry 75 (2014) 1e10