Conclusions
The root growth strategies of S. breviflora can be assessed by two kinds of traits, one was related to root biomass, and another was related to root morphological architecture. For S. breviflora , water was the most contributor to the growth of root system, and cluster fragmentation was the second contributor, followed by N and P in order. Under drought condition, high–level N addition induced roots ofS. breviflora developing an acquisition resource use strategy for escaping adverse environments compared to low–level N addition; under sufficient P condition, low–level water addition induced their roots developing an acquisition resource use strategy for acquiring more resource compared to high–level water addition. S. brevifloracan adjust root growth strategies of sub-clusters by cluster fragmentation, producing smaller clusters was beneficial for improving its adaptability in a low-N condition.