Species turnover drives responses of community fine‐root traits to recurrent droughts

Fine roots and their traits are critical for plant drought adaptation, yet predicting their responses to recurrent droughts remains a key challenge under climate change.

We conducted a repeated extreme drought experiment across four semiarid grasslands along an aridity gradient. We compared the effects of single (precipitation reduction in 2021–2023) versus recurrent droughts (precipitation reduction in both 2015–2018 and 2021–2023) on community‐weighted means (CWMs) and functional diversity of fine‐root traits. We also examined the relative contributions of intra‐ and interspecific variation to both CWMs and trait diversity under repeated droughts.

Results showed that the CWMs or functional diversity of key fine‐root traits (diameter, specific length/area, tissue density) varied among grasslands. However, neither single nor recurrent drought altered these traits in any site, indicating community trait conservatism under drought. This resistance was driven by joint contributions of intra‐ and interspecific variation buffering changes in community trait values. Intraspecific variation prevailed under single drought, whereas interspecific variation increased under recurrent drought. Furthermore, recurrent drought altered dominance within the intermediate trait range, favouring different grasses (e.g., Leymus chinensis ) than those favoured by single drought (e.g., Stipa grandis ). However, fine‐root trait CWMs and diversity showed either non‐significant or very weak correlations with grassland primary productivity under drought.

Synthesis . Our study reveals a dual response in grasslands to repeated drought, where community fine‐root traits maintain high resistance through species turnover. This suggests that community functional responses to climate extremes cannot be inferred from species trait shifts alone.