地上和地下植食者互作对水稻氮分配及土壤活性氮的影响

Effects of Interactions of Above-and Below-ground Herbivores on Nitrogen Distribution in Rice Plant and Labile Nitrogen in Soil

植物茎叶和根系植食者虽然在空间上隔离,但二者的相互作用被认为是联系地上和地下部生态系统的基础。土壤氮素有效性通过植物影响植食者已得到大量研究的证实,但有关地上和地下部植食者互作对土壤氮素影响的研究却鲜有报道。以水稻褐飞虱和潜根线虫分别作为地上和地下的植食者,采用两因素交互试验设计,两个褐飞虱水平(未接种褐飞虱、接种褐飞虱),两个潜根线虫水平(未接种潜根线虫、接种潜根线虫),探讨二者的交互作用对水稻氮吸收和土壤活性氮(微生物生物量氮、可溶性有机氮以及铵态氮和硝态氮)的影响。结果表明,褐飞虱和潜根线虫相互抑制,二者的共存加剧了对水稻茎叶和根系生长的危害。褐飞虱未影响水稻茎叶和根系含氮量,而潜根线虫显著降低了水稻根系含氮量(p<0.05)。褐飞虱和潜根线虫对土壤活性氮的影响表现出强烈的交互作用,在未接潜根线虫的处理中,褐飞虱显著提高了微生物生物量氮含量(p<0.05),显著降低了硝态氮含量(p<0.05);潜根线虫显著影响了微生物生物量氮含量和土壤活性氮总量。总之,褐飞虱和潜根线虫的相互抑制关系对土壤活性氮的影响格局较为复杂,相比褐飞虱,潜根线虫趋向于提高土壤活性氮水平,这可能影响与氮转化有关的土壤生态功能。

【Objective】Interactions between aboveground and belowground herbivores sharing the same host plantare regarded as the basic linkage between aboveground and belowground ecosystems,though they are separated in space.Much work has been done demonstrating that soil nitrogen availability affects the herbivores via plant by regulating chemical composition,such as nitrogen content of the plant.However,little has been reported on effects of the interactions between the two groups of herbivores on soil nitrogen.In this paper,a microcosm experiment was designed to investigate effects of the interactions between the herbivores on nitrogen distribution in the plant and labile nitrogen（microbial biomass nitrogen,dissolved organic nitrogen,ammonium nitrogen and nitrate nitrogen）in the soil.【Method】In this study,Nilaparvata lugens and Hirschmanniella oryzae were selected as representative of the two groups,aboveground and belowground herbivores,respectively,and a pot experiment was designed to have two rates of Nilaparvata lugens,（zero or eight individuals per plant）,and two rates of Hirschmanniella oryzae（zero or 500 individuals per pot）,totaling four treatments and four replicates for each treatment.The soil used in the pot was first sterilized under 121℃ to kill all the native nematodes,and then was inoculated with the soil bacterial suspension prepared out of the original soil that had been deprived of soil nematodes,and put into a dark incubator for 60 days of incubation under indoor temperature to restore and stabilize microbial communities in the soil.Rice seedlings were transplanted into the pots after 30 days of seedling nursing in nutrient solution.Hirschmanniella oryzae and Nilaparvata lugens was inoculated separately on the fifteenth and twenty fifth day after rice seedlings were transplanted.Ten days after the inoculation of Nilaparvata lugens,samples of the plants and soil were collected.Plant samples were separated into shoot and root for measurement of biomass and nitrogen content,separately.Soil samples were analyzed,separately,for microbial biomass nitrogen,dissolved organic nitrogen,ammonium nitrogen and nitrate nitrogen.【Result】Results showed that Nilaparvata lugens and Hirschmanniella oryzae negatively affected each other.Nilaparvata lugenstended to decrease shoot biomass,but did not affect much root biomass,while Hirschmanniella oryzaesignificantly reduced shoot and root biomass（p 〈0.05）.Nilaparvata lugens showed no significant effect on shoot and root nitrogen content,while Hirschmanniella oryzae significantly reduced root nitrogen content（p 〈0.05）,though they did not affect much shoot nitrogen content.Significantly interactive effects of aboveground and belowground herbivores on soil labile nitrogen were observed.In the absence of Hirschmanniella oryzae,Nilaparvata lugens significantly increased the content of microbial biomass nitrogen（p 〈0.05）and decreased nitrate content significantly（p 〈0.05）,but did not have much effect on dissolved organic nitrogen and ammonium nitrogen,whereas in the presence of Hirschmanniella oryzae,they did not affect the content of soil labile nitrogen significantly.On the other hand,Hirschmanniella oryzaesignificantly and positively affected the content of microbial biomass nitrogen and total soil labile nitrogen（p0.05）.【Conclusion】To sum up,the effects of the interactive suppressions between the aboveground and belowground herbivores on nitrogen content in shoot and root of the rice plants and on soil labile nitrogen are rather complicated.Moreover,compared with Nilaparvata lugens,Hirschmanniella oryzae tends to increase total soil labile nitrogen,which may in turn improve N-transformation-related ecological functions of the soil.