Abstract
Nitrogen (N) cycling ecosystem function is crucial in primary productivity but also carry various ecological implications such as N losses to environment. In mountainous soil ecosystems, this important function beside soil characteristics is dependent on the litter produced through plant decay which may play a critical role in shaping the hosted soil microbial communities such as those involved in N cycling processes. This study aims at investigating the effects of plant litter amendment, believed to reduce the nitrogen leaching and improve soil health, on nitrogen cycling microbial communities and processes using litterbag approach at field station of COMSATS, Abbottabad. Plant litter collected from the stands of Pine (Pinus wallichiana) and understory Indigo shrub commonly known as Indigo Himalayan (Indigofera heterentha (Fabaceae) wall), near Abbottabad, native to the lower Himalaya, were applied to indigenous loamy soil in four treatments (i.e. Control, Pine, Indigo and Pine + Indigo). The N cycling processes (involved in nitrous oxide GHG emissions, potential nitrification activity - PNA and denitrification enzyme activity - DEA), through measuring enzymes activities and the abundances of nitrifying amoA (ammonia oxidizing bacteria AOB, ammonia oxidizing archaea AOA) and denitrifying functional guilds (nirS, nosZ) were determined using quantitative PCRs by targeting their corresponding genes. The results revealed that the plant litter significantly influenced both nitrification and denitrification but also the size of microbial communities involved in these two processes. The number of archaeal and bacterial amoA gene copies increased with the application of Indigofera treatment with AOA size higher than the AOB with correlation matrix revealing that AOB were dominant in mediating the PNA rates. The DEA was found to increase upon Indigofera litterbag treatment where nosZ were less abundant but interestingly in contrast to nirS denitrifiers strongly correlated with DEA. Though the short term litter application enhanced the nitrification and denitrification rates, low abundance but dominant role of nosZ denitrifiers while AOB as main actors in nitrification across lower Himalayan soil are important to be studied in long perspectives since these functional guilds may differentially impact the N cycling function and thus carry strong implications for overall environment.