Geographic Linkages of Root Traits to Salt Marsh Productivity

Root traits are fundamental characteristics of belowground ecosystems that regulate plant growth and drive ecosystem functioning. Nevertheless, the way root traits respond to environmental factors and consequently influence productivity remains unexplored on large geographic scales. We examined the root traits of exoticSpartina alternifloraand nativePhragmites australisacross China's coastal salt marshes. Using structural equation models (SEMs), we quantified the direct and indirect effects of mean annual temperature, soil nutrients (e.g., soil dissolved inorganic nitrogen and phosphorus), and root traits on aboveground net primary productivity. Our results showed that root traits ofS. alterniflorawere more sensitive to changing soil nutrient availability than those ofP. australis. The SEMs indicated that soil nutrient availability increasedS. alternifloraproductivity by increasing root nitrogen concentration and root length density. InP. australis, temperature could increase productivity by both increasing root length density and soil nutrient-mediated root nitrogen concentration. The studied root architectural trait (root length density) and nutrient trait (root nitrogen concentration) were effective in predicting productivity, whereas none of the root morphological traits (i.e., specific root length, root tissue density, and root diameter) significantly affected productivity. We provide the first empirical evidence that root trait-based responses modulate the effects of climate and soil nutrients on geographic variation in vegetation productivity, but these effects are species specific.

Automated summary

Root traits play a significant role in regulating plant growth and ecosystem functioning. This study found that the root traits of exotic Spartina alterniflora were more sensitive to changing soil nutrient availability compared to native Phragmites australis. Climate and soil nutrient availability had different effects on the productivity of the two species, with root traits playing a species-specific role in mediating these effects.