Abstract: To explore the relationship between litter inputs and soil respiration in different aged forests, we carried out a leaf litterfall manipulation experiment in Pinus tabuliformis forests inLiaohe River, Northern China. We examined the sensitivity of soil CO₂ emissions to alteration in litter inputs. There were nine experimental plots with three stand ages (middle-aged, nearly mature, and mature stands). Treatments included adding (by doubling) of aboveground litter (DL) (including leaf, twig, bark), removing all aboveground litter (NL), removing aboveground litter and root (NI), and control (CK). Soil respiration was measured with a  LI-8100 infrared gas analysis. The results showed that alterations in litter inputs significantly affected soil temperature and moisture in middle-aged stand. Soil temperature was significantly increased in NL treatment in middle-aged and mature stands, whereas soil moisture was significantly-reduced in NL treatment in middle-aged and nearly mature stands. Alterations in litter inputs did not affect soil temperature in nearly mature stand and soil moisture in mature stand.  Soil respiration rate was significantly increased in DL treatment, whereas soil respiration rate was significantly decreased in NL treatment. The magnitude of increment in soil respiration in DL treatment was greater than that of the decline in NL treatments. The relative contributions of different soil respiration components to total soil respiration following the order mineral soil respiration > litter respiration > root respiration in middle aged and nearly mature stands, and following the order of mineral soil respiration > root respiration > litter respiration in mature forest. The contribution of mineral soil respiration decreased with increasing stand age, but an opposite pattern for the contribution of root respiration. Mineral soil respiration and root respiration were significantly differentbetween middleaged stand and mature stand. Litter removal had significant effects on soil microclimate, which affected soil respiration. Soil respiration in DL treatments was mainly affected by soil temperature. The combined effects of soil temperature and moisture explained 60.2%-77.5% of the variation of soil respiration in different aged P.tabuliformis forests. Soil respiration under different treatments had a significant positive correlation with fine root biomass. The responses of soil respiration to the alteration in litter inputs depended on stand age. Our findings indicate that  alterations of litter inputs should be considered in predicting soil respiration under climate changes.

Key words: Pinus tabuliformisforest, litter input, forest age, soil respiration.