影响C4草本植物C/N比值变化的因素与土壤有机C积累的关系

文章对采自贵州从低海拔的东部到高海拔的西部且大致平行的石灰岩和砂岩两地带均生长的3种C₄草本植物,即巴茅(Miscanthusfloridulus)、白茅(Imperatacylindrica)和类芦(Neyraudiareynaudiana),以及相对应的土壤表层样品,进行了营养元素和C同位素组成分析;研究营养元素含量随着海拔的不同而出现的变化趋势,以及这些元素之间的相互协变作用,尤其是Ca和N之间的相互协变作用对植物的N含量、C/N比值和^δ13C值的影响,以了解植物的C/N比值(指示植物残留物质量的一种标志)与土壤有机C积累的关系。研究结果表明,植物的N含量和^δ13C值具有随海拔的上升而显著增大趋势,而植物的C/N比值在砂岩地区虽有减小的趋势,在石灰岩地带则没有。对所研究的C4草本植物来说,在土壤pH值为5.8的中性条件下显示出Ca的最大吸收,因此,Ca与其他营养元素之间的协变模式在两种土壤类型中表现出相反的倾向,并存在土壤交换性Ca的边界浓度:当土壤可交换性Ca的含量为2.24mg/g,相应土壤的pH值在5.8以下时,随着土壤可交换性Ca浓度的增大,植物的N含量上升,而植物的C/N比值会显著降低;当Ca在边界浓度以上时,随着土壤可交换性Ca浓度的增大,植物的N含量下降,而植物的C/N比值有增加的趋势。由此可见,植物残留物的N含量和C/N比值受Ca元素含量的相

THE CONTROLLING FACTORS OF C4-GRASS C/N RATIOS AND THEIR RELATIONSHIPS WITH SOIL ORGANIC CARBON ACCUMULATION

Three species of C₄ grasses, Miscanthus floridulus , Imperata cylindrica , and Neyraudia reynaudiana were collected from open shrublands in both limestone and sandstone areas of different altitude in Guizhou in November 2001 . Their soil samples were also collected. Soil samples taken from the rooting zone (0-15cm) provide an indication on nutrient . We tested the change of N concentration, C/N ratio, and ^δ13C values in grasses along with the change of altitude, and investigated the interactions of different nutrient elements, particularly that of Ca and N, and their effects on N concentration, C/N ratio, and ^δ13C value in grasses, on the purpose of understanding the relationship between grass C/N ratio and soil organic carbon accumulation. N concentration and δ13C values of C4 grasses increase with altitude in both limestone and sandstone areas. There is a trend of increase in C/N ratio in sandstone areas, but no in limestone areas. The highest uptaken capability of Ca is at the neutral condition with pH5.8. Grasses Ca appears, therefore, different co-variational patterns with N concentration, C/N ratio and ^δ13C values in limestone and sandstone areas, and there is a boundary concentration of soil exchangeable Ca: When soil exchangeable Ca exceeded 2.24mg/g and the corresponding soil pH is 5.8, C/N ratios increase with increasing soil exchangeable Ca; and C/N ratios decrease with increasing soil exchangeable Ca under the boundary concentration of Ca. Our results indicate that a increased C/N ratio of C₄ grasses is related with decreased soil organic accumulation in sandstone soil, but not in limestone soil. Therefore, whether or not the increased plant C/N ratios influence soil organic carbon accumulation will depend on soil properties, especially soil exchangeable Ca concentration.