Role of fungal endophyte of tall fescue (Epichloë coenophiala) on water availability, wilting point and integral energy in texturally-different soils

• Actual wilting point (hPWP) of tall fescue is considerably drier than 15000 hPa.
• Actual hPWP was greater in E+ plant-associated soils compared to E− ones.
• E+ plants in coarse- and medium-textured soils had greater actual PAW and EI.
• E+ plants needed lower energy to take up water from the nominal PAW range.
• Endophyte symbiosis would increase plant water productivity in drought periods.

Managing soil water and water uptake by plant roots is more crucial in the arid and semi-arid regions comparing to the other places. Beside the well-known plant available water (PAW) concept, integral energy (EI) is recently suggested to quantify the energy required by plants for water uptake. A greenhouse study was conducted to examine the effect of aboveground fungal endophyte infection (Epichloë coenophiala) in tall fescue (Festuca arundinacea Schreb. = Schedonorus arundinaceus and Lolium arundinaceum) on soil water availability indices such as PAW and EI in six texturally-different soils. The PAW was calculated as the difference between field capacity, θFC [at matric suction, h, of 100 or 330 hPa (1 hPa = 0.1 kPa)] and permanent wilting point, θPWP (nominal value at h of 15000 hPa or actual h value determined in the greenhouse experiment). The EI was computed by integration of soil water retention curve (determined using undisturbed soil samples) over the nominal and actual PAW ranges. The results indicated that hPWP, the matric suction at actual permanent wilting point, of tall fescue is considerably greater than the conventional value (i.e., 15000 hPa) and its value was greater in endophyte-infected (E+) plant associated soils compared to endophyte-free (E−) ones (27572 hPa/2757 kPa for E+ vs. 21780 hPa/2178 kPa for E−) and the difference was greater in the coarse- to medium-textured soils. Moreover, E+ treatments, especially in the coarse- and medium-textured soils, had greater values of actual PAW and EI. This shows that E+ plants were able to tolerate higher h values at similar conditions presumably due to induced drought-tolerance mechanisms. The effect of endophyte presence on increment of PAWactual and EI(actual) in comparison with nominal values was much more evident in the coarse- and medium textured soils. This indicates that the error in calculations of the PAW and EI values by considering θPWP at h = 15000 hPa is relatively smaller in fine-textured soils. Nevertheless, nominal EI values were lower for E+ treatments indicating that in similar PAW, the plant needed lower energy to take up water from the PAW range because endophyte presence can affect soil water release path in the PAW range. Greater contribution of structural pores to water retention in E+ plant associated soils compared to E− ones was related to greater sub-critical water repellency and aggregate stability and better physical quality in E+ plant associated soils. It is concluded that the presence of endophyte in tall fescue, especially in coarse- and medium-textured soils, affects soil water release path, increases PAW and thereby might raise water productivity in drought periods.