关键词: 荒漠草原, 灌丛化, 13C脉冲标记, 光合碳, 分配动态

Abstract: Aims To explore the allocation strategies of plant photosynthates under shrub encroachment in desert steppe. Methods An in situ 13CO2 pulse labeling technique was adopted in this study to trace the translocation and distribution of photosynthetic 13C in the plant-soil continuum of desert steppe, and to analyze the effect of shrub encroachment in desert steppe on the dynamics of photosynthetic carbon allocation in desert steppe plants. Important findings Shrub encroachment significantly increased 13C abundance in multiple plant tissues and surface soil. For both Caragana liouana and herbaceous plants, The total fixed 13C content followed the consistent allocation order: aboveground tissues (leaves and stems) > belowground roots > soil. The 13C allocation proportion was the highest in Caragana liouana leaves, while that in the aboveground parts of herbaceous plants was the highest. The 13C contents in leaves and stems of Caragana liouana in Caragana liouana shrubland (SL) were significantly higher than those in the shrub-encroached desert steppe (SG), whereas the opposite trend was observed in roots. Soil 13C content was generally higher in SL than in SG, with a significant difference observed on the 25 d after labeling, except for the 7-day sampling stage. The 13C content in the aboveground parts of herbaceous plants followed the order of desert steppe (DS)>SG, decreasing with labeling time, while root 13C showed a fluctuating downward trend and soil 13C exhibited an upward trend. Vegetation type was a key factor regulating the ¹³C allocation pattern in the desert steppe shrub encroachment process. Specifically, the ¹³C labeling efficiency was the highest in the Caragana liouana shrub-grass system and the lowest in the Caragana liouana shrubland, demonstrating that the Caragana liouana shrub-grass system is more conducive to the accumulation of photosynthetic carbon. Additionally, the ¹³C loss rate is the highest in the Caragana liouana shrub-grass system and the lowest in the desert steppe. The research results can provide a scientific basis for understanding the ecosystem carbon cycle mechanism during the desert steppe shrub encroachment process.

Key words: desert steppe, shrub encroachment, 13C pulse labeling, photosynthetic carbon, allocation dynamics