Analysis of hydraulic and isohydraulic characteristics of leaves of four common trees in Gaotang area of North China

  Objective  This paper aims to study the diversity of water adaptation strategies adopted by different tree species in same environment to provide reference for better silviculture of tree species in the suitable sites.

  Method  We selected four typical suitable tree species with great differences in root distribution depth, wood properties and growth speed, they were Acer truncatum, Prunus cerasifera, Populus tomentosa and Robinia pseudoacacia and planted in Gaotang region, Shandong Province of North China. We compared the hydraulic traits and isohydraulic evaluation of the leaves of these four species. The hydraulic traits included embolism vulnerability parameters, pressure-volume (PV) curve parameters, hydraulic structure and functional properties.

  Result  Different species selected varied water adaptation strategies to adjust to the same environment. Among them, P. cerasifera and A. truncatum owned more conservative water adaptation strategies, while R. pseudoacacia and P. tomentosa adopted more adventurous water adaptation strategies; P. cerasifera is a fast-growing tree species with shallow-rooted diffuse-porous wood, it had the strongest leaf embolism resistance (embolism vulnerability P₅₀ was −2.67 MPa). Meanwhile, the water safety of P. cerasifera was very high (hydraulic safety margin HSM was 1.57 MPa), the water adaptation strategy was conservative; A. truncatum is a slow-growing tree species with shallow-rooted diffuse-porous wood, its leaves inclined to isohydraulic regulation (the hydraulic area was 0.049 MPa²). When drought stress was encountered, the stomata can be closed early to keep the leaf water potential and turbulence stable. Its P₅₀ was relatively high and HSM was relatively low, showing low anti-embolism ability and low hydraulic safety. The adjustment range of leaf water potential was narrow. Its high Huber value (Hv) showed that it had high drought resistance. A more conservative water adaptation strategy had been adopted by it. R. pseudoacacia is a kind of fast-growing tree species, its leaves were inclined to aniso-hydraulic regulation, having strong anti-embolism ability, the range of leaf water potential was wide, and the water adaptation strategy was more adventurous. P. tomentosa is a fast-growing tree species with deep-rooted diffuse-porous wood and low sieve resistance. The water safety factor was close to limit (HSM was 0.002 MPa). Its leaves owned the strongest ability to maintain turgor pressure (water potential at turgor pressure loss point ψ_tlp was −3.36 MPa), to ensure that they can get water from the deep soil in case of water shortage, the water adaptation strategy is more risky.

  Conclusion  In summary, trees can adopt different hydraulic characteristics, isohydraulic characteristics, morphological and structural characteristics, and apply different water adaptation strategies to adapt to the same environment. The diversity of water adaptation strategies is conducive to maintaining the stability of the ecosystem.