沙化草地土壤碳氮磷化学计量特征及其对植被生产力和多样性的影响

Stoichiometry and effects of carbon, nitrogen, and phosphorus in soil of desertified grasslands on community productivity and species diversity

沙化草地土壤碳(C)、氮(N)、磷(P)化学计量特征及其对植被生产力与多样性的影响对于认识草地沙漠化过程中土壤与植被的互馈关系,以及沙漠化发展的生态学机理具有重要的意义。通过对科尔沁沙地75个沙化样地的野外调查,研究了科尔沁沙地不同程度沙化草地的表层土壤C、N、P化学计量特征及其与生产力和多样性的相关关系。结果表明:1)科尔沁沙地沙化草地表层土壤具有较低的有机C、全N、全P含量及C∶N、N∶P和C∶P,平均值分别为1.39mg/g、0.117mg/g、0.079mg/g和7.50、2.22、16.91;草地沙漠化过程中,土壤有机C、全N、全P含量显著降低的同时,C∶N、N∶P和C∶P亦显著降低,表明土壤有机C、全N、全P在沙漠化过程中的损失是不同步的;2)科尔沁沙地沙化草地表层土壤有机C、全N、全P元素间均呈显著正相关,具有一定的耦合关系,且土壤有机C和全P间的耦合关系不随沙漠化的发展而发生改变;3)草地沙化过程中,土壤养分的损失限制着草地生产力,而土壤N∶P较全N、全P含量更能反映土壤养分对生产力的限制作用;4)沙化草地土壤全N含量与物种丰富度间具有显著正相关关系,而土壤全P含量与其无显著相关性;多样性指数与全N、全P含量间均具有显著正相关关系;相对于土壤全N、全P含量,N∶P能更好地反映养分平衡对物种多样性的影响作用。

Information on the stoichiometry of carbon(C), nitrogen,(N) and phosphorus (P) in soils and its effects on community productivity and species richness in desertified grassland is essential to understanding the interactive relationship between soil and vegetation in the process of grassland desertification, and reveals the ecological mechanisms of land desertification. In this study, we measured organic C, total N, total P concentrations, and C ∶N, N ∶P, C ∶P in the topsoil of different desertified grasslands in the Horqin sandy land, and statistically analyzed the correlations among C, N, and P stoichiometry, community productivity, and species diversity. The results showed that the concentrations of organic C (1.39 mg/ g), total N (0.117 mg/ g), and total P (0.079 mg/ g), and the C ∶N (7.50), N ∶P (2.22), and C ∶P (16.91) ratios in the topsoil of desertified grasslands remained at relatively low levels in contrast to the results nationwide or worldwide. It was not surprising that soil C, N, and P significantly decreased during grassland desertification. Their ratios, however, also significantly decreased in the gradient of desertification, suggesting an asynchronous loss of soil C, N, and P in the process of desertification. We found that topsoil organic C, total N, total P, and their ratios were positively correlated, suggesting a coupling relationship among organic C, total N, and total P in topsoil in the study sites. Further, the coupling relationships between organic C and total P did not change with the development of grassland desertification. Expectedly, community productivity was limited by the loss of soil nutrients in desertified grassland in this study. However, soil N ∶P stoichiometry could explain more variations of community productivity than soil N or P concentration could. Similarly, correlation analysis showed that species richness was significantly correlated with soil N, but not P. The diversity index was significantly correlated with soil N and P. Compared with N or P concentration, the soil N ∶P stoichiometry effectively reflected the influence of nutrient balance on species diversity.