Abstract
Reclamation of cropland from grassland is regarded as a main reason for grassland degradation; understanding succession from abandoned cropland to grassland is thus crucial for vegetation restoration in arid and semiarid areas. Soil becomes dry when cropland is reverted to grassland, and enzyme and osmotic adjustment compounds may help plants to adapt to a drying environment. Croplands that were abandoned in various years on the Ordos Plateau in China, were selected for the analysis of the dynamics of enzymes and osmotic adjustment compounds in plant species during vegetation succession. With increasing number of years since abandonment, levels of superoxide dismutase increased in Stipa bungeana, first decreased and then increased in Lespedeza davurica and Artemisia frigida, and fluctuated in Heteropappus altaicus. Levels of peroxidase and catalase in the four species fluctuated; levels of proline, soluble sugar, and soluble protein either decreased or first increased and then generally decreased. According to a drought resistance index, the drought resistance of the four species was ranked in descending order as follows: S. bungeana > A. frigida > H. altaicus > L. davurica. The drought resistance ability of the different species was closely linked with vegetation succession from communities dominated by annual and biennial species (with main accompanying species of L. davurica and H. altaicus) to communities dominated by perennial species (S. bungeana and A. frigida) when soil became dry owing to increasing evapotranspiration after cropland abandonment. The restoration of S. bungeana steppe after cropland abandonment on the Ordos Plateau is recommended both as high‐quality forage and for environmental sustainability.
Highlights
10%–20% of arid and semiarid areas throughout the world are changing dramatically as a result of desertification and grasslands degradation (Reynolds et al, 2007)
Among CVs of different parameters, the value for superoxide dismutase (SOD) was large for L. davurica and A. frigida, the values for POD and CAT were large for S. bungeana and L. davurica, the value for Pro was large for S. bungeana and L. davurica, the values for SS and MDA were large for S. bungeana and H. altaicus, and the value for SP was small for all four species (Table 6)
The results of this study clearly indicate why the four species differ in drought resistance abilities, mainly because of their long-term adaptation to different soil water environments, and our results were consistent with the two-layer hypothesis (Cipriotti et al, 2014)
Summary
10%–20% of arid and semiarid areas throughout the world are changing dramatically as a result of desertification and grasslands degradation (Reynolds et al, 2007). Field observations have indicated that after abandonment, croplands reclaimed by semishrub dominated grasslands could be restored to native S. bungeana grasslands through long-term vegetation succession from bare land, to annual, biennial, semishrub, and perennial species During this successional process, at the first stage, when annual grasses dominate, the soil water content is relatively high, and at the last stage, when perennial grasses are dominant and community cover is greater, the soil water content is relatively low; in this semiarid environment, the dominant species in different stages will have different abilities to resist drought (Cai et al, 2018), and enzymes and osmotic adjustment compounds may play an important role in the abilities of species to maintain drought resistance. The objectives of this study are as follows: (a) to understand how the levels of enzyme activity, MDA, and osmotic adjustment compounds of main species changed during vegetation succession in abandoned cropland and (b) to understand their roles in vegetation succession in abandoned cropland Answering these questions will improve our understanding of water use strategies of grass and shrub species and help restore degraded grasslands
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