Plastic responses of native and exotic herbaceous species to temporal heterogeneity in water conditions

In recent years, many studies have shown that extreme climate events occur more frequently. The extreme climate led to frequent drought and inundation events, which affected the growth of both exotic and native plants. In order to discuss the strategies of exotic and native plants in adapting to temporal heterogeneity in water conditions by investigating their responses to the sequence of drought and inundation events, four native and four exotic perennial herbaceous species in western Montana, USA were used as study objects. All plants were treated with moderate water (CK), initial inundation before drought (I-D) and initial drought before inundation (D-I) conditions, and variations in a series of morphological and biomass traits were measured. The results were as follows: (1) Compared with CK, both D-I and I-D treatments significantly reduced the total biomass of exotic species (P<0.05). (2) D-I treatment significantly reduced the total biomass at the early stage, and late belowground biomass and root/shoot of native species, but significantly improved their later relative growth (P<0.05). (3) D-I treatment significantly reduced the scaling exponent of the allometric relationship between belowground biomass and aboveground biomass for all plants, with a higher allometric exponent for exotic species than native species (P<0.05). In conclusion, the sequence of extreme events (inundation and drought) can alter the allocation of biomass between exotic and native plants. Early drought is more likely to reduce the accumulation of plant biomass than late drought, but it can promote the growth of native species in late period. The total biomass of native species is not reduced under environmental stress, indicating that native species have a strong ability to maintain phenotypic stability. Distribution patterns of aboveground and belowground biomass relationships are different between native and exotic species under D-I treatment.