Response of bacterial community to nutrient

External environmental conditions to aquatic ecosystems often change gradually with time. However, we still know little about whether the response of ecosystems to these gradual changing environmental parameters is gradually or steeply. Here, we used lake water microcosms perturbed with nitrogen and phosphorus for 12 days to investigate temporal variability of bacterial community. We found the variation in bacterioplankton community composition was inert, though the nutrient concentration (nitrogen and phosphorus) decreased rapidly and continuously from day 2 to day 6. However, the community composition changed abruptly from day 6 to day 8, but the nutrient concentration decreased slowly. This is mainly because the homogeneous dispersal and low selection pressure at the beginning of experiment, but increased competition at the end of experiment resulted in the collapse of community resistance. Bacterioplankton co-occurrence network showed that the interactions between bacterioplankton were more intensive at the high nutrient concentration period. The Gammaproteobacteria and Actinobacteria increased abruptly, but Alpha- and Betaproteobacteria increased steeply during the experiment. Moreover, the predicted functions showed the similar tendency with this of the 16S rRNA gene. Gradual environmental change is omnipresent. Our findings suggest that disentangling the response of complex communities to environmental gradual change is essential for understanding ecosystem restoration and catastrophe in future.