为了探究云南干热河谷不同退化阶段草地光合碳对土壤有机碳的贡献,采用13C脉冲标记对云南干热河谷不同退化阶段(轻度退化LD、中度退化MD、重度退化HD、极度退化ED、对照CK)草地光合碳分配及其向地下输入特征进行了为期1个生长季的研究。结果 表明:(1)土壤有机碳、全氮、全钾、碱解氮和速效磷含量随着退化程度的增加呈先增加后降低趋势,大致表现为MD>LD>CK>HD>ED,其中MD显著高于其他处理(p0.05); 茎叶、根生物量和地上生物量随着退化程度的增加呈现增加后降低趋势,MD达到最大,而根冠比并没有明显的变化趋势。(2)脉冲标记当天不同退化阶段草地δ13C值均表现为茎叶>根>土壤,随着退化程度的增加呈现先增加后降低趋势,由此可知,草地的根部对光合固定新碳的富集程度较大。(3)标记当天,不同退化阶段草地地上13C固定百分比例较高,说明标记的效率较高且分配差异较大; 脉冲标记21 d后,δ13C值下降,固定的光合碳转移到土壤中的含量显著增加。(4)MD对土壤有机碳的贡献量最大,对土壤有机碳的贡献量随退化程度的增加呈先增加后降低趋势; 有机碳的累积量随退化程度的增加呈先降低后增加趋势。(5)相关性分析结果表明,根系和地上部生物量与13C-SOC之间存在显著的正相关关系。进一步分析结果表明,草地退化显著影响了光合同化碳在地上部和土壤中的分布,其中中度退化草地光合同化碳在植株—土壤系统的响应较为显著。
In order to explore the contribution of photosynthetic carbon of grassland to soil organic carbon in different degradation stages(light degradation LD, moderate degradation MD, high degradation HD, extreme degradation ED and CK)in hot and dry valley of Yunnan Province, the in-situ 13C pulse labeling technique was used to trace the distribution and driving factors of assimilated C pulse-labeled with 13C of degraded ecosystem in dry-hot valley of Yunnan Province. The results show that:(1)the contents of soil organic carbon, total nitrogen, total potassium, available nitrogen and available phosphorus increase at first and then decreased with the increase of degradation degrees, which follows the sequence: MD>LD>CK>HD>ED, these parameters are significantly higher in MD than those in treatments (p0.05); the biomass of stem, leaf, root and aboveground increases and then decreases with the increase of degradation degree, it reaches up to the maximum in MD, but there is no obvious change trend of the ratio of root to canopy;(2)all the 13C values of the grassland at different degradation stages on the day of pulse marking are presented as stems, and decrease in the order: leaves>roots>soil, which increases at first and then decreases with the increase of degradation degree, therefore, the enrichment degree of photosynthetic fixed new carbon at the grass roots is great;(3)on the marking day, the percentage of 13C fixed on the grassland in different degradation stages is higher, indicating that the marking efficiency is higher and the distribution difference is greater; 21 days after the pulse labeling, the value of 13C decreases, and the amount of fixed photosynthetic carbon transferred to the soil increases significantly;(4)there is a higher contribution to soil organic carbon, and then the contribution increases at first and then decreases with the increase of years since the abandonment with the largest in MD, while there is an opposite trend to soil organic carbon accumulation;(5)correlation analysis shows that there is a strong relationship between stem, root biomass and aboveground biomass and 13C-SOC, in total, abandonment years significantly affect photosynthetically fixed carbon in plant and soil, especially for 16-year abandonment.
