Effects Of Different Treatments On Plant Secondary Metabolites Of Dominant Pastures In Inner Mongolia Grassland

Inner Mongolia grassland is the largest animal husbandry production base in China. It plays an important role in our societal economy. However, in recent years, with the development of the productive forces, this grassland has become degraded under unreasonable utilization and overgrazing. The ecological environment of the grassland is deteriorating, rodents are overrun, dust storms and other hazards are increasing. What’s more, the global warming and increased rainfall have also affected the ecological environment of Inner Mongolia grassland to some exte t. So, in this study, some dominant pastures in Inner Mongolia, such as Stipa krylovii Roshev, Leymus chinensis, Cleistogenes squarrosa and Carex tristachya were used to analyse the impact of water addition, food amount and grazing on the content of their total phenols, simple phenol, tannins and CT(Condensed Tannins); Then, the planted Leymus chinensis was used to explore the sequential effect of mechanical damaged, Microtus brandti attack or daubing saliva of Microtus brandti after mechanically damaged on the content of phenolic compounds and6-MBOA (6-methoxyben-zoxazolinone)1h, Id,5d or10d after three treatments. The purpose of this study was to elucidate the influence of environment or wound on the metabolite of second compounds and the role of animal saliva in the plant chemical defense response. The result would provide evidence for co-evolution between animal and plant. The results were as follows.1. Water addition resulted in different variation of content of phenolic compounds in different pastures. There was no significant change of the content of any of phenolic compounds in Cleistogenes squarrosa after all kinds of water addition. Under moderate watering, the simple phenol of Stipa krylovii Roshev decreased (P<0.05), but the tannins in Leymus chinensis and Carex tristachya increased significantly (P<0.05). And the content of total phenols、simple phenol, tannins and CT in Leymus chinensis were significantly higher than control group (P<0.05) under light watering.2. Grazing had no significant effect on the content of phenolic compounds in both of Stipa krylovii Roshev and Cleistogenes squarrosa. However, with the increase of grazing intensity, the content of total phenols and tannins in Leymus chinensis were significantly higher than in control group (P<0.05). In Carex tristachya, the content of CT was significantly increased with light grazing (P<0.05), and the content of simple phenol was significantly increased with moderate grazing (P<0.05).3. Providing fodder for the rodents in the field where the grasses grew didn’t change the content of phenolic compounds in Stipa krylovii Roshev, Cleistogenes squarrosa and Carex tristachya. However, the content of total phenols was significantly reduced (P<0.05) in Leymus chinensis after fodder providing.4. Three kinds of wound treatments had different effects on phenolic compounds in planted Leymus chinensis. The content of total phenols, simple phenol and tannins of cutting group was significantly higher than control (P<0.05), but the simple phenols and CT of grazing group was lower than control (P<0.05)1h after treatments. One day after treatments, all of the total phenols, tannins and CT in daubing and grazing group were significantly lower than control, as well as CT in cutting group (P<0.05). Then,5days later, cutting increased total phenols, simple phenol and tannins in this grass (P<0.05), while daubing reduced its total phenols, tannins and CT (P<0.05), and grazing decreased its phenols and tannins (P<0.05). Finally, it was found that the amount of CT in cut and grazed plant, as well as the total phenols, tannins and CT in daubed plant was much lower than control10days after treatments (P<0.05). The Repeated Measures results have shown that the content of phenolic compounds of cutting group were significantly higher than daubing and grazing group (P<0.05), and there were no significant difference between grazing group and daubing group.5. Wound also induced different change of6-MBOA in planted Leymus chinensis. One hour after treatment, only the plants in daubing group had higher level of6-MBOA immediately. The content of6-MBOA of cutting and daubing group became significantly higher1d,5d and10d after treatments (P<0.05), same as the6-MBOA of grazing group on1st day and in5th day after treatments (P<0.05). But there was no significant change of6-MBOA in grazing group in10th day after treatments. The Repeated Measures results showed that there was no significant difference of6-MBOA between cutting and grazing group, while the content of6-MBOA of daubing group were significantly higher than other two groups (P<0.05).In summary, in field, the content of phenolic compounds in these pastures in Inner Mongolia varied differently to the change of water addition, maybe it was caused by the difference of proportion of phenolic compounds in them. Grazing could increase the content of phenolic compounds of Stipa krylovii Roshev and Carex tristachya significantly, this would be benefit to their resistance to the feeding of herbivorous animals followed. Providing fodder to rodents made the content of total phenols of Leymus chinensis decrease significantly, this meant that the pastures would reduce the syntheses of second metabolite when the grazing pressure they faced was abated.Acutely, all of cutting, daubing and grazing could reduce the phenolic compounds of planted Leymus chinensis. But the response of cutting group was different from that of grazing and daubing group, which proved that, in this plant, the defense reaction induced by mechanical damage was much different from that caused by animal. Maybe the animal saliva was a key reason of this change; the difference of the increase of6-MBOA among three treatments also suggested that animal saliva be the main factor to stimulate the plant to produce more6-MBOA.