红壤稻田弃耕后植被和土壤有机碳对积水与火烧的早期响应

为了探明积水和冬季火烧对弃耕红壤稻田地表植被和土壤有机碳的影响, 该实验设置了对照(无人为干扰)、积水、冬季火烧和积水-冬季火烧4个不同处理, 采用样方法对样地植物的高度、密度、盖度及物种组成进行了调查。地上部分生物量采用收获法进行测定, 根系采用土柱法获取, 弃耕前后土壤有机碳含量的测定采用K₂Cr₂O₇外加热法。结果表明: 1)积水和冬季火烧对红壤稻田弃耕早期物种组成、丰富度、均匀度及多样性具有重要的影响。双穗雀稗(Paspalum paspaloides)和水竹叶(Murdannia triquetra)是积水条件下的优势种, 而柔枝莠竹(Microstegium vimineum)是冬季火烧条件下的优势种, 大狼杷草(Bidens frondosa)是积水和冬季火烧条件下的共优种。2)分布在0-5 cm表层土壤中的根系占0-20 cm深度土壤中根系的66.50%-80.34%。样地在积水条件下, 2011-2013年0-20 cm深度的土壤根系生物量分别高出对照样地的49.84%、73.34%和28.94%。3)冬季火烧可以提高样地的物种多样性和增加地上部分生物量, 2011-2013年冬季火烧样地分别高出对照样地的25.74%、64.30%和50.24%。4)与稻田弃耕前土壤有机碳含量逐渐上升趋势相反, 稻田弃耕6年后, 对照、积水、冬季火烧和积水-冬季火烧样地中土壤有机碳含量分别降低11.16%、18.99%、9.17%和19.12%, 并且在积水条件下土壤有机碳含量降低更明显(p < 0.05)。研究结果表明, 红壤稻田弃耕后地表植被物种组成、地上和地下生物量、土壤有机碳含量与积水和冬季火烧关系密切(p < 0.05)。

Early responses of vegetation and soil organic carbon to waterlogging and winter wildfire on abandoned red paddy soils

Aims Large tracts of land have been abandoned since last century and the trend continues. Our objectives were to seek an effective solution for facilitating plant diversity on abandoned red paddy soils at an early stage, and to investigate the dynamics of soil organic carbon in relation to changes in vegetation.Methods The experiment consisted of four treatments, including control (no disturbance from human activities), waterlogging, winter wildfire, and a combination of waterlogging and winter wildfire. Measurements were made in each treatment within quadrate sampling method. In each quadrate, the maximum plant height, density, coverage, and composition were surveyed and recorded by species. The above and belowground biomass and soil organic carbon content were determined with the methods of harvesting, soil coring, and K₂Cr₂O₇ calefaction, respectively.Important findings The results showed that waterlogging and winter wildfire significantly altered the vegetation richness, evenness, diversity, and species composition on the abandoned red paddy soils at the early stage. Paspalum paspaloides and Murdannia triquetra were the dominant plant species when the abandoned paddies had suffered waterlogging for the first few years, and Microstegium vimineum was the dominant species on sites experienced winter wildfire. Bidens frondosa was a co-dominant species in all the treatments. Compared with the control, the belowground biomass at the depth of 0-20 cm was increased by 49.84%, 73.34%, and 28.94%, respectively, in the waterlogging treatment in the year 2011, 2012 and 2013, and the aboveground biomass was increased by 25.74%, 64.30%, and 50.24%, respectively, in the winter wildfire treatment. The roots collected from the upper 5 cm soil layer accounted for 66.50%-80.34% of the total from the 0-20 cm layer. Winter wildfire resulted in greater values in the Shannon-Wiener diversity index of the vegetation. Different from the uptrend before abandonment, the soil organic carbon in the treatments of control, waterlogging, winter wildfire, and a combination of waterlogging and winter wildfire was reduced by 11.16%, 18.99%, 9.17%, and 19.12%, respectively, after six years of abandonment, and it was significantly lower in the waterlogging treatment (p < 0.05). Plant species richness, evenness, diversity, composition, biomass, and soil organic carbon all had strong relationships with waterlogging and winter wildfire on abandoned red paddy soils (p < 0.05).