Soil Texture Rather Than Water Potential Determines the Root:Shoot Ratio in Ryegrass and Alfalfa

Backgrounds A fixed root:shoot ratio is widely used to estimate the underground biomass in the carbon (C) cycle in grassland ecosystems, although edaphic and climatic factors may influence the root:shoot ratio. Our current understanding of the effects of the soil texture and water potential on the root:shoot ratio is rather poor.Methods Thus, we conducted a pot experiment where we measured the dry weights of the roots and shoots to investigate the responses of ryegrass (Lolium perenne, L.) and alfalfa (Medicago sativa, L.) in terms of C allocation to different soil textures and water potentials.Results The root:shoot ratios in ryegrass and alfalfa were significantly affected by the soil texture, but not by the soil water potential (-400 kPa to -40 kPa). Integrated analysis of previous studies indicated a significant average negative correlation between the root:shoot ratio and clay content according to a linear mixed model (k = -0.0045). This correlation might be related to the hydraulic properties of the root-soil contact zone.Conclusions We assume that the soil water potential in our experiment was insufficient to affect root hydraulic conductivity, but further evidence is required. Our findings could be useful for future estimates of ecosystem C stocks.

Automated summary

The effects of soil texture and water potential on root:shoot ratio were investigated in a pot experiment. The results showed that soil texture significantly influenced the root:shoot ratio in ryegrass and alfalfa, while soil water potential had no effect. These findings are important for future estimations of ecosystem carbon stocks.