| As the base of vegetative reproduction, the bud bank is a potential plant community in the natural regeneration of vegetation, playing a critical role in regulating community succession. How the different species and different types of bud banks respond to climatic change and human disturbance is not only closely related to plant adaptation, succession and evolution, but also has an important practical value for the prediction and restoration of steppes in the context of global change. However, relevant research on bud banks is very limited. For that reason, our research is located in the temperate steppe of Inner Mongolia Autonomous Region, using the platform with Duolun Global Change Multifactor Experiment (GCME).We will explore the response of bud banks under different levels to simulated increased precipitation and nitrogen deposition, clarify the impact of the precipitation and nitrogen deposition on vegetative propagation and sexual reproduction, and elucidate the relative contribution of vegetative propagation and sexual reproduction to the vegetation recruitment. Thereby, we aim to provide a more reliable reference for the vegetation prediction, restoration and sustainable management of steppes in the context of global change.The results are showed as follows:(1)In the community, the densities and proportion of different types of bud banks had different responses to simulated precipitation and nitrogen deposition, and had no interaction between water and nitrogen. The density of rhizome bud and ramet bud showed no significant difference among the treatments. The density of both root sucker bud and bulb bud showed a significant difference among the treatments, and addition water (W) and nitrogen (N) significantly increased and decreased their density, respectively. W, N and the combination (WN) did not significantly change the total density of bud banks, which, however, turned out to be significantly lower in N and WN than in W treatment. This showed that for different types of buds, nitrogen and water had a different role on them. For the proportion of different types of bud banks, it showed the plants which had ramet buds and root sucker buds, were rhe main plants in the community. Nitrogen deposition may benefit the formation of ramet buds, but precipitation was possible to benefit the formation of root sucker buds. Different types of bud banks had a relatively fluctuation relationship.(2)Only PB (the number of buds per ramet) of Stipa krylovii in unmown (MO) showed interaction between water and nitrogen. The bud number and PB of each species in MO and M1(mown) showed no interaction between water and nitrogen. Moreover, while the bud number of Stipa krylovii was affected by interaction between mowing and nitrogen, other parameters of Stipa krylovii and other species were not affected by the interaction of mowing, nitrogen and water. For both, M0and M1, W always significantly decreased the bud number of Stipa krylovii. Therefore, with an increase of precipitation, it was possible to inhibit the formation of ramet buds. Mowing had no significant effect on the number of buds. PB showed no significant difference in the treatments of M1. In the M0, there was a significant reduction of PB in N, and had no interaction between water and nitrogen. Only mowing had a significant effect on PB in control (C) treatment. The treatments of M0and M1had no significant effect on the bud number and PB of Agropyron cristatum. Because Agropyron cristatum had two types of buds (rhizome bud and ramet bud), they complemented each other in different environment, and the bud number showed no significant difference in the treatments. Whether in M0or M1, only WN significantly reduced the bud number of Cleistogenes squarrosa, and mowing had no significant effect on it. Nitrogen, precipitation and mowing had no significant effect on PB of Cleistogenes squarrosa. The bud number of Potentilla tanacetifolia and Allium tenuissimum in response to precipitation and nitrogen differently were due to mowing or not.(3Reproductive allocation of main plants was not affected by the interaction of mowing, nitrogen and water, and different species showed differences in significance and variation trends in the treatments. The reproductive allocation of Stipa krylovii showed no significant difference in M0and M1. The reproductive allocation of Agropyron cristatum just had significant difference in W and N of MO. The reproductive allocation of Cleistogenes squarrosa showed no significant difference in M0. In the M1, WN significantly increased its reproductive allocation. The reproductive allocation of Potentilla tanacetifolia and Allium tenuissimum had no significant difference in MO and Ml. Regardless of the treatments, the reproductive allocation of five species was not significantly affected by mowing, but different species showed different patterns.(4)There was no significant difference between the bud number and tuft diameter of Cleistogenes squarrosa in WN of M1. There were extremely significant positive correlations between tuft diameter, the number of parent ramet and the bud number of other species. It showed that bud number depended on the size of plants. Different species have different growth patterns. The bud number of Agropyron cristatum and its tuft diameter in MO and Ml had an extremely significant power function and linear dependence, respectively. Its bud number and the number of parent ramet was the opposite regulation. There was the power function between the bud number of Stipa krylovii and its tuft diameter in MO, and the bud number was increased logarithmically with its tuft diameter in M1. The bud number and the number of parent ramet was the same regulation. Expect for WN in M1, there was the power function between the bud number of Cleistogenes squarrosa and its tuft diameter in M0and M1, so did the bud number and the number of parent ramet.(5)Except for the individual species in the individual treatments, vegetative propagation and sexual reproduction showed species specific responses showing different trends among different treatments. |
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