Enzyme and osmotic adjustment compounds of key species can help explain shrub encroachment in a semiarid sandy grassland

Abstract

RationaleIn arid and semiarid grasslands where shrub encroachment usually occurs, water plays an important role and might control the process of shrub encroachment. Understanding how species adapt to different sandy environments can help explain the shrub encroachment process. Central methodsFour different grades of shrub encroached grasslands were selected as follows: the Agriophyllum squarrosum community in shifting sandy land (SA), the Artemisia ordosica community in semifixed sandy land (SFA), the A. ordosica community in fixed sandy land (FA) and the Stipa bungeana community in fixed sandy land (FS), which are located on the Ordos Plateau (China) and were selected to analyze the dynamics of enzyme and osmotic adjustment compounds of species in different stages of shrub encroachment. Key resultsThe results showed that from the community in shifting sandy land to the community in fixed sandy land, the average enzyme activities of species decreased and then increased; the malondialdehyde content increased, and the osmotic adjustment compounds increased (or increased and then decreased). The enzyme activities of grasses were significantly higher than those of shrubs. However, there were no significant differences in the malondialdehyde contents of grasses and shrubs. The proline and soluble protein contents of shrubs were significantly higher than those of grasses. The soluble sugar content of grasses was significantly higher than those of shrubs. The D values indicated that the drought resistance of the five species decreased as follows: S. bungeana in FS > S. bungeana in FA > Caragana korshinskii in FA > C. korshinskii in FS > A. ordosica in FS > A. squarrosum in SA > Artemisia sphaerocephala in SFA > A. sphaerocephala in SA > A. ordosica in FA > A. ordosica in SFA. Main conclusionsThe results suggest that the five dominant species in different shrub encroachment stages could enhance their drought resistance by upregulating the antioxidant system and osmotic adjustment in response to drought stress. S. bungeana had a higher drought resistance. For different plant functions, grass had a higher drought resistance than shrubs. It is concluded that S. bungeana can adapt to a drier environment; when the surface soil layer becomes dry, S. bungeana communities developed well due to its high drought ability. Compared to A. ordosica, the S. bungeana community can be a dominant community when human disturbance decreased in the Ordos Plateau.