Study On The Fine Root Distribution And Ecological Characteristic Of Different Sucessional Stage Grassland In Loess Plateau

The vertical distribution of fine root, soil respiration and soil properties were studied in five grasslands that previously were croplands but have been abandoned without planting crops for different years.The results are as followed:1. The number of the plant species was increased with the increasing abandoned years. There are five common species (L.dahuvicus, Lespedeza floribunda, Artemisia capillaries Artemisia giraldii and Potentilla chinensis that distributed in all the five successinal stages. The community species rich index ranged from 3.1946～4.1810, diversity index ranged from 2.5111～2.8740, Simpson index ranged from 0.8853～0.9218 and Pielou index ranged from 0.7619～0.8749, all the inexes were fluctuated in different years grasslands.2. The fine root biomass are mainly distribute in the 0～40 cm soil depth, the percentage rang from 64%～93% for the five different abandoned years grasslands. We have understood the vertical distribution of the fine root biomass, fine root density, fine root surface, fine root diameter and specific root lengh in the soil. The fine root length density and fine root surface area were consistent with each other, both of them increased with the increasing abandoned years.3. The fine root biomass, surface area and fine root density are all positively correlated with the soil moisture, soil organic matter and soil total nitrogen. The specific root lenth and fine root diameter were negatively correlated with the soil moisture, soil organic matter and soil total nitrogen. The fine root parameters are all relatively weak correlated with the soil pH. The results showed that the soil physical and chemical properties are the main factors that influce the fine root distribution of the herbaceous vegetation.4. The soil respiration are significant different among the five grasslands. The results showed that the soil respiration of the 4a and 9a grasslands was different, but there was no difference among the 15a, 20a and 25a grasslands. The correlantion between soil respiration and aboveground biomass was stronger than the correlatin between soil respiration and belowground biomass. The 30%and 17% variation of the soil respiration can be explained by the above and belowground biomass. The soil respiration decreased with the increasing soil moisture in the surface soil (0~10 cm soil layer), and the relationship between soil respiration and soil moisture become weak with the increasing soil depth. Below the 20cm soil depth, the soil moisture nearly has no influence on the soil respiration. The relationship between soil respiration and soil temperature was different from the soil moisture. The correlation between soil respiration and soil temperature are become more correlated with the increasing soil depth.