Abstract: A field experiment with three rainfall reduction levels (natural rainfall, 30% reduction in rainfall, and 50% reduction in rainfall) was conducted in a Pinus sylvestis var. mongolica sand-fixation plantation in Keerqin Sandy Lands to investigate the effects of aridification on the nitrogen (N) and phosphorus (P) cycles. The forest ecosystem was divided into three compartments (tree, soil and aboveground litter layer). The amount and rate of N and P absorption (from soil to tree), return (from tree to litter layer) and decomposition (from litter layer to soil) were measured and calculated. The results showed that, compared with natural rainfall, 30% reduction in rainfall significantly reduced the amount and rate of N return by 27.3% and 37.3%, and did not affect N absorption and decomposition and P cycling. The 50% reduction in rainfall significantly decreased the amount of N absorption, return and decomposition by 59.9%, 36.0% and 50.3%, P return amount by 38.1%, N return and decomposition rate by 39.9% and 32.7%, increased litter P content by 27.4%, and did not affect the amount of P absorption, N and P absorption rates. The decreases in the rates of N and P return and decomposition following rainfall reduction indicated that aridification would bring the risk of nutrient imbalance to pine forest.

Key words: oxygen evolving complex, photosystem Ⅱ, Pseudomonas syringae pv. tabaci,   , reactive oxygen species, D1 protein.