Abstract: Nitrogen (N) deposition and litterfall variation are main pathways by which global change impacts forests, but how they interact to change belowground processes is poorly known. To explore these interactions, we conducted a field manipulative experiment under nitrogen addition (control and N addition as 10 g N·m^-2·a^-1) and litter manipulation (ambient litterfall, litter removal and litter doubling) in a Pinus sylvestris var. mongolica plantation in Keerqin Sandy Land. We measured soil properties such as available N and P concentrations and basal respiration rate in dry and wet seasons (May and August) 3 years after manipulation. The results showed that impacts of litter manipulation on soil variables differed greatly in the control and N addition plots. In the control plots, both litter removal and doubling greatly elevated soil basal respiration, while generally did not change available P and N concentrations. In N addition plots, both litter removal and doubling did not change basal respiration and available P concentration, but greatly decreased available N concentration. Impacts of N addition and litter manipulation were more obvious in wet season than in dry season. Nitrogen addition alone significantly reduced basal respiration and available P concentration in August, while litter doubling effectively lessened the depression of respiration and enhanced P limitation caused by N addition.

Key words: photosynthetic gas exchange, rain-fed semi-arid area, chlorophyll fluorescence parameter, whole field soil-plastic mulching and bunch sowing, spring wheat, water use efficiency.