The role of plant traits in shaping community assembly along environmental gradients is a topic of ongoing research. It is well accepted that plant traits of aboveground organs tend to be conservative in stressful conditions. However, there is limited understanding of how belowground traits respond. Plants may have similar strategies above and belowground, but an intriguing possibility is that there is a trade-off between above and belowground traits of communities to both ensure efficient resource-use and limit niche overlap along the gradient. To test this, we asked whether the response of above and belowground traits of communities is coordinated or not along a stress gradient in Mediterranean sand dune communities. We analyzed 80 vegetation plots in Central Italy to test for coordinated vs independent patterns in above vs belowground plant traits using community weighted mean and standardized effect size of functional richness. Our results show that plant communities close to the sea, which experience high stress, were characterized by high convergence towards aboveground resource conservation and conservative water-use strategies but belowground resource acquisition, consistent with a strong effect of habitat filtering and an above-belowground tradeoff favoring adaptation to harsh and dry conditions.  At the opposite end of the gradient with lower stress, plants exhibited higher trait diversity for both above and belowground traits, but overall a dominance of aboveground fast resource acquisition and generally acquisitive water-use strategies, combined with conservative fine-root traits. This suggests that fast growth rate aboveground was compensated by more conservative fine-root strategies, but processes such as competition limited niche overlap overall. Our findings provide new insights into the relationship between functional traits and environmental gradients in plant communities, shedding light on the trade-offs between the above and belowground dimensions.

List of units for all the selected plant traits present in the dataset:
plant height (H) : m
specific leaf area (SLA) : mm2/g
seed mass (SM) : g
specific root lenght (SRL): cm/mg
root tissue density (RTD) : mg/cm3
belowground organ water content (BOWC) : %