A Preliminary Study On The Effect Mechanism Of Tree Species On Soil Carbon Sequestration And Fertility

Tree species are generally considered having significant effects on soil carbon sequestration and fertility. But there is still no unanimous conclusion about these effects in different soil types or different soil fractions. Therefore, studing on the effects of different plants cultivation on soil physical-chemical properties and fine root growth in saline-alkali soil in Songnen Plain, is trying to investigate the improvement of afforestation on saline-alkali land. And discussing the effects of tree species on soil carbon sequestration and fertility in saline-alkali soil at the same time. Studing on plantations with different forest stands in typical soil types in Northeast China, is trying to reveal how the differences between conifer and broadleaved affect soil carbon sequestration and fertility in the progress of afforestation. And trying to determine whether they have the same differences in different soil types. Trying to find the correlativity between chemical composition of litter or root and soil carbon sequestration and fertility. Focus on effects of tree species on carbon sequestration and fertility and characteristics in different soil fractions within the common afforestation tree species such as Fraxinus mandschurica, Larix gmelinii, Pinus sylvestris and Farmland in Northeast China, aiming to discuss the effects of tree species on carbon sequestration and fertility and confirming which soil fraction it occured. Trying to find the molecular mechanism of the influence. Following conclusions:1) Elm, poplar, scotch pine and larch should be promote as the suitable tree species for afforestation rather than amur corktree and ash in heavy soda saline-alkali land in Songnen Plain. And all of the plantations should be watered frequently and largely. No differences were observed in soil carbon sequestration and fertility such as total N, available-P, etc. among farmland, grassland and woodland. But tree species does affect soil carbon, especially that in poplar (12.3g·kg-1) and scotch pine (13.2g·kg-1) significant lower than that in other tree species (p<0.05). For most soil fertility indexes and organic carbon, the interspecific difference was significant as deep as 60cm within soil depths. All the other parameters showed the same interspecific difference within 0-60cm soil depths except root density, soil pH, available-P and root water.2) There was significant difference of soil carbon sequestration and fertility between coniferous and broad-leaved species. Soil organic carbon and fertility in broad-leaved species were both higher than that in coniferous. There was also significant difference of litter and root chemical composition between coniferous and broad-leaved species. Organic carbon of litter and root in coniferous species was much higher than that in broad-leaved species. But the durable parameters such as litter C/P, litter total phenolics, litter cellulose, litter lignin, root total phenolics, root cellulose, root holocellulose, root lignin in coniferous species was also much higher than that in broad-leaved species. There were strong correlations between C, N, P and the ratio of them three in soil and chemical composition in litter and roots. But there were obvious distinctions between litter and root’s correlation with soil. Root chemical composition was mainly related to soil C and soil fertility. Litter chemical composition was mainly related to soil nutrient ratios. The broad-leaved species would be the first choice for future afforestation no matter in dark brown soil, mollisol, saline-alkali soil or sandy soil in Northeast China. Nitrogen fertilizer needs to be applied for today’s forest management. Differences in carbon sequestration function between conifer and broadleaf forests were significant enough to be payed more attention in today’s stand evaluation.3) Tree species significantly affected the mass of small macroaggregates. The mass of small macroaggregates in ash was 83% higher than that in farmland. The effect of tree species on organic carbon mainly showed in the silt and clay fraction. The soil organic C of silt and clay fraction in ash was 49% higher than that in farmland. While no obvious differences were observed in soil N and C/N of intact and soil fractions among ash, larch, scots pine and farmland. It suggested that the effect of tree species on mass mainly occur in much bigger soil fraction, while the effect of tree species on soil organic C mainly occured in much smaller soil fraction. Tree species affected soil N little. No obvious differences were observed in infrared functional groups of intact and soil fractions among ash, larch, scots pine and farmland. In 11 elements, the interspecific differences of the metallic element Ca and nonmetallic element N in intact were significant, but no obvious differences were observed in 11 elements of the soil fractions among different tree species. The effect of tree species on soil X-ray mineral characteristics mainly occured in intact and soil aggregates, while no obvious differences were observed in soil X-ray mineral characteristics of smaller soil fraction such as silt and clay fraction among ash, larch, scots pine and farmland.