| Karst dynamic system is an important part in the earth surface system. Carbon, water and calcium cycle are the characteristics of the material cycle in karst dynamic system, and these three cycles were interdependence, mutual restraint and simultaneously; people have made a lot research on the carbon and water cycle in the previous study, especially on the carbon cycle, but for the calcium cycle, the study was relatively defectiveness. Research on the calcium cycle can not only elaborate the mechanism of carbon and water cycle, and also can further improve and develop the theory of karst dynamic system, provide theoretical support for the carbon sinks and desertification control in karst ecosystem.This paper chose Yaji karst experimental site and Shanwan non-karst experimental site these two typical karst and non-karst area in Guilin, collected soil samples quarterly:(1) the soil pH value, CEC (cation exchange capacity), SOC (soil organic carbon), total calcium and calcium forms were measured, the changing trends of total calcium and calcium forms as the time and vegetation type changes in karst and non-karst area were grasped, in which calcium was measured using the improved BCR sequential extraction method;(2) in order to understand the correlation between the migration of calcium and humus in the different development stages of limestone soil, rendzina, dark terra fusca, light terra fusca and yellow limestone soil were collected based on the limestone soil developmental sequence in Guilin karst experimental site, the soil calcium and humus contents and forms, soil N, P, K and any other indicators were measured to explore the relationship of calcium and carbon cycle in the development stages of limestone soil. The results were as follows:l.The Humus Contents and the Correlation with Calcium Forms in the Different Development Stages of the Limestone Soil(1) In the different development stages of the limestone soil, the total carbon in the humus of rendzina, dark terra fusca, light terra fusca and yellow limestone soil was230.15mg/g,49.33mg/g,37.49mg/g,17.94mg/g respectively, the proportion of humic acid was31.94%,22.87%,9.44%,7.25%respectively, fluvic acid accounted for1.04%,28.91%,36.14%,66.16%and humin was67.02%,48.23%,54.41%,26.59%respectively;(2) The total calcium of the rendzina, dark terra fusca, light terra fusca and yellow limestone soil was21486.66mg/kg,8125.46mg/kg,6913.33mg/kg,5540.17mg/kg respectively, and with the proportion of57.58%,74.98%,74.69%,80.83%, the acid-soluble calcium has the highest proportion followed by the reduced calcium、 oxidized calcium and residual calcium;(3) The correlation analysis showed that:the soil calcium and its different forms were positively related with SOC, humic acid and humin, negatively related with fluvic acid. It means that the forms and contents of the humus can influence the forms and contents of the soil calcium largely.2. The comparison of calcium in limestone soil and red soil:The limestone soil in Yaji karst experimental site:(1)The pH value was highest in west slope, then was the east slope, the changing trends of pH value as the time were different in different landform; the SOC content was highest in the saddle with an average annual content of46.54mg/kg, in east and west slope, the changing trends of SOC as the time from Dec.2010to Sep.2011were first decrease and then increase, and the plain, saddle and depression SOC showed o gradually increasing trend.(2) In spatial scale, the total calcium content was highest in slopes with the average annual content2636.28mg/kg in the west slope, in plain, the average annual total calcium content was2909.14mg/kg which was the lowest; the total calcium content, acid-soluble calcium and reduced calcium contents showed the same trend as the sampling points changed at the same sampling time, and the oxidized calcium and residual calcium in the different site and time was almost no changing.(3) In time scale, the changing trends as time of total calcium and all kinds calcium forms in plain, saddle, depression was the same, in east and west slope, the calcium forms had a same changing trends in addition to the total calcium and acid-soluble calcium appeared that the east slope was increased and west slope decreased from Jun. to Sep.2011;(4) On the composition of calcium forms, the acid-soluble content was the most, accounting for60-80%of the total calcium, and also the proportion of acid-soluble calcium content of the total calcium had no significant changes in the different landforms at the same sampling time, which was followed by reduced calcium, residual calcium and oxidized calcium;(5) The results of correlation analysis to the soil total calcium, calcium forms, pH value, CEC, SOC using the soil samples collected in Sep.2011showed that:there showed a highly significant positive correlation among pH value, total calcium, acid-soluble calcium and reduced calcium, and the same condition was appeared between SOC, CEC, total calcium and calcium forms, total calcium content had a highly significant positive correlation with acid-soluble calcium, a significant positive correlation with oxidized calcium;The red soill in shanwan non-karst area:(1) Soil pH value was highest in Ginkgo-chestnut forest and lowest in shrub, the changing trends of pH value as the time changing in different vegetation was different; SOC content was highest in shrub with an average annual content23.12mg/g, the changing trends as the time changing in fir forest and fir-shrub forest was the same, SOC content first increased and then decreased from Dec.2010to Sep.2011which reached to highest in Jun.2011; the changing trends of SOC content in Ginkgo forest and Ginkgo-chestnut forest was the same, increasing from Dec.2010to Sep.2011and reaching to the highest in Sep.2011.(2) In spatial scale, the total calcium content was highest in Ginkgo-chestnut forest with an average annual concentration864.52mg/kg, the total calcium and acid-soluble, oxidized calcium and reduced calcium had same changing trends as the sampling changed at the same sampling time, the residual had no significant changing in the different sampling points; (3) In time scale, total calcium and residual calcium was decreased as the time changing in fir-shrub forest and shrub, acid-soluble and oxidized calcium were increased from Dec.2010to Mar.2011and decreased to Sep.2011; the total calcium and residual calcium content in Ginkgo-chestnut forest was increased from Dec.2010to Jun.2011and then decreased, the changing trends of calcium forms in the other vegetation was different;(4) On the composition of calcium forms, the residual calcium contents was highest in the total calcium especially in the fir-shrub forest whose residual calcium content occupied95%of the total calcium in Dec.2010; as the changing of the sampling time, the proportion of residual calcium was changed, the calcium forms contents from high to low was acid-soluble calcium, oxidized calcium and reduced calcium;The comparison of the calcium in limestone soil and red soil:Choosing shrub forest as the same vegetation in karst and non-karst area, the total calcium content and calcium forms was contracted, in the soil of Yaji karst experimental site the total calcium content was15more times higher than that in Shanwan non-karst area, and the main calcium form was acid-soluble calcium which was high bioavailability, but in Shanwan non-karst area the main soil calcium form was residual calcium whose bioavailability was low;... |
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