黄土区不同退耕方式下土壤碳氮的差异及其影响因素

研究植被恢复对土壤碳氮动态的影响,对了解陆地生态系统碳氮循环,应对全球温室效应具有重要意义.本研究以黄土丘陵区不同人工恢复植被为对象,以农田为参照,分析了不同人工植被恢复方式对0～100 cm剖面土壤有机碳(SOC)和全氮(TN)含量影响的差异及其影响因素.结果表明: 退耕还林还草显著提高了土壤的SOC和TN含量.退耕后,SOC和TN含量均较农田明显提高.0～100 cm土层SOC平均含量人工乔木林为农田的1.43倍,增幅最大;其次是人工灌木,为1.36倍;最后是人工草地,为1.21倍.0～100 cm土层TN平均含量人工乔木林增幅最大,是农田的1.30倍;其次是人工草地,为1.21倍;而人工灌木增幅最小,为1.13倍.与农田相比,人工恢复植被类型间SOC和TN含量及细根密度的差异在土壤剖面深度上表现出不同,人工乔木和灌木最明显,影响深度＞100 cm;草地最小,仅为60 cm.恢复植被的细根密度、C∶N和凋落物量显著高于农作物,细根密度与SOC、TN呈显著线性相关(P<0.01).细根的质和量以及凋落物量是不同人工恢复植被下SOC和TN含量差异的重要影响因素.

Differences in soil organic carbon and total nitrogen and their impact factors under different restoration patterns in the Loess Plateau

Knowledge of the effect of different vegetation restoration measures on soil organic carbon (SOC) and total soil nitrogen (TN) is of importance to better understand carbon and nitrogen cycling in terrestrial ecosystems and deal with the global greenhouse effect. The differences in SOC and TN content in 0-100 cm soil profile between different restoration measures and their impact factors were investigated in the Loess Plateau. The results showed that artificial vegetation restoration led to a significant increase in both SOC and TN content in the 0-100 cm soil profile compared with that of cropland. The highest increase in average SOC content was observed in the artificial woodland(1.43 times that of the cropland), followed by the artificial shrubland (1.36 times) and artificial grassland (1.21 times); whereas the highest increase in average TN content was observed in the artificial woodland (1.30 times that of the cropland), followed by the artificial grassland (1.21 times) and artificial shrubland (1.13 times). Compared with the cropland, there was a significant difference in SOC and TN content and fine root density up to a maximum depth of >100 cm in the artificial woodland and shrubland, but about 60 cm in the artificial grassland. The fine root density, soil C:N ratio and aboveground litter production of artificial woodland, shrubland and grassland were significantly higher than that of cropland, and fine root density was significantly linearly correlated with SOC and TN (P<0.01). The quantity and quality of fine root and litter biomass might be the dominant factors contributing to the observed difference in SOC and TN contents between the different artificial vegetation types in the Loess Plateau.