The Study On Litter Effects During Old-field Succession In Songnen Plain

Aboveground litter is the total organic matter which fallen from plant shoot andturned into soil surface. Not only aboveground litter impacts nutrient cycling processthrough decomposition, but also indirectly acts on plant, animal and soil microbe byregulating the soil microclimate, including temperature, water and light, further toimpact ecosystem process. In agro-pastoral transition zone of north China,abandonment of reclaiming grassland occurred frequently. Abandonment of arableland induces litter amount increase in soil surface. The ecological effects of increasinglitter amount have important significance to old-field succession process. Forclarifying the ecological effects of primary litter during old-field succession, a litteraddition experiment was conducted to study the effects of different litter amount onvegetation, soil and ecological process during early succession stage in reseeded andnon-reseeded old-field ecosystem. The study found:Litter addition and reseeding significantly impacted soil temperature andmoisture, and the regulating function of litter on soil temperature and water dependedon the annual and seasonal climate condition. The increase of initial litter amountdecreased soil temperature, but increased soil moisture. Initial litter amountsignificantly impacted the soil salty and alkalinity, the increasing initial litter amountdecreased soil salty and alkalinity.Increased litter amount delayed seedling emergence time and rate. Litteraddition below600g/m2could promote the seedling emergence and establishment ofspecies due to improved soil temperature, moisture, salty and alkalinity. Litter over600g/m2would be more beneficial to the emergence and establishment of Chlorisvirgata and Puccinellia tenuiflora, it was because that their subuliform seedlingfeature could be more advantage for penetrating litter layer. With respect to seedlingemergence performance and seed feature, it is predicted that C. virgata will dominatefurther in this natural succession old-field ecosystem as litter accumulation increases.An artificial P. tenuiflora seed addition is potential to accelerate the succession towardmature grassland. Under natural restoration, the vegetation cover decreased with initial litteramount increasing. Whether reseeding or natural restoration, plant density decreasedwith initial litter amount increasing. The species number of community increased withsuccession year increasing, and decreased with initial litter amount increasing. Incontrast to forb biomass, aboveground and grass biomass of community increasedwith initial litter amount. Increasing initial litter amount enhanced litter accumulationon soil surface, but decreased aboveground biomass. Initial litter addition significantlyimpacted soil organic carbon content at the depth of0-10cm and10-20cm. Soilorganic carbon and total nitrogen content increased with initial litter amount.Increasing initial litter amount enhanced soil microbe biomass. Initial litteramount significantly impacted soil respiration and its component, and on the yearscale, the effects of litter on soil respiration and its component depended onvegetation restoration ways. Increased initial litter amount decreased mean rootrespiration rate in growth season, but enhanced microbial respiration and total soilrespiration rate. Initial litter amount impacted the temperature sensibility of root andmicrobial respiration, but it did not impact the response of total soil respiration toincreasing temperature. In two growth season, increasing initial litter amountdecreased temperature sensibility of root respiration. In2011, increasing initial litteramount decreased temperature sensibility of soil microbial respiration under naturalsucession. In2012, increasing initial litter amount enhanced temperature sensibility ofsoil microbial respiration. In two growth season, increasing initial litter amountdecreased temperature sensibility of total soil respiration.