Effects Of Continuous Cropping On Soil Organic Carbon Storage And Carbon Cycle Process Of Populus × Euramericana Cv. ‘Neva’

Poplar is an important fast growing tree species in China, and it plays an important role in alleviating the contradiction between supply and demand of timber market. However, with the growth of the planting area, the continuous cropping of poplar is also more common.Continuous cropping result in a decrease in soil nutrient availability, the imbalance of microbial community structure, and the self-toxicity effect of the soil, which reduced forest productivity, and seriously restricted the sustainable development of plantations. However, it is not clear whether the continuous cropping of poplar will affect the process of soil carbon storage and carbon cycle. Based on this, this study aims to study soil carbon content and carbon storage, soil enzyme activities, litter decomposition, soil respiration and its components, using I-107 poplar plantation ecosystem with different continuous cropping systems(first, second, and third generation forest) in Dawen River coastal sandy soil. This study explored the effects of continuous cropping of poplar plantation on soil carbon cycle.Research results have significance on carbon sequestration and effects of continuous cropping of poplar plantation, and also provide a basis for maintenance and sustainable management of poplar plantation. The main conclusions are as follows:(1) Three different continuous generation of poplar plantation on soil organic carbon content and microbial biomass carbon content decreased in 0-100 cm soil depth with the deepening of the soil; Continuous cropping of poplar plantation made organic carbon content and microbial biomass carbon content of upper soil(0-40) decreased significantly, but had no significant effect on deep soil(60-100). There is a significant positive linear correlation of three kinds of continuous cropping poplar plantation between organic carbon content and microbial biomass carbon content.Poplar plantation improved the soil urease, catalase and β-Glucosidase activity;Continuous cropping of poplar plantation significantly reduced the soil invertase, urease andβ-Glucosidase activity, and increased catalase activity.(2) Continuous cropping of poplar plantation reduced the decomposition rate of both leaf litter and fine roots. The decomposition rate of leaf litter and fine roots within 1a showed an obvious slow-fast-slow stage characteristics. Soil organic carbon content and soil microbial biomass carbon content and soil β-Glucosidase activity significantly affect the two types of litter decomposition rates.(3) Daily and monthly changes of soil respiration rate(RS), autotrophic respiration rate(RA) and heterotrophic respiration(RH) of three forest types showed a unimodal pattern;Average contribution rate of RA was 40.04%, and showed seasonal differences; Soil respiration rate and its components had a significant exponential relationship with 5cm depth soil temperature, and had no correlation contains soil moisture content, the simulation results showed that the power-exponent model was the best. RA’s Q10 of three forest types was greater than RH; Continuous cropping inhibited the poplar plantation of RS and Rh,continuous cropping soil physical and chemical properties and microbial biomass in the soil respiration rate were the main reasons.(4) TOCR and MBCR of three forest types decreased with the increase of the continuous cropping generation. Three kinds of forest soil ecological system showed a "carbon sink", and continuous cropping of poplar plantation is not conducive to the accumulation of soil organic carbon and carbon storage.Litter decomposition is the main source of soil nutrients in plantation forest, continuous cropping of poplar decreased the soil respiration rate and litter decomposition rate, inhibited the soil carbon turnover, and also retard the nutrient release efficiency and strength. Resulting in the lack of soil nutrient supply, which leaded to the decline of the productivity of forest land. Therefore, the poplar continuous cropping is not conducive to the improvement of the productivity of the forest, in the operation of the poplar plantation, we should try to avoid the continuous cropping management, and increase organic fertilizer and other measures to alleviate the continuous cropping obstacles.