The Refilling Of Embolized Xylem Of Drought-tolerant Tree Species

Growing well six drought-tolerant tree species from the campus of Northwest Agriculture and Forestry University, one-year-old twigs of Robinia pseudoacacia, Hippophae rhamnoides, Ulmus pumila, Corylus heterophylla, Acer truncatum, Salix matsudana were studied. The aim of this study was to explore the relationship between hydraulic structure and refilling of embolism in the xylem of six tree species, to elucidate the influence of xylem hydraulic structure on the embolism refilling, and to provide theoretical evidence for screening drought-resistance tree species. Cochard Cavitron centrifuge was used to induce xylem embolism of one-year-old twigs when percentage loss conductivity was higher than 95%. The “vulnerability curves” of six tree species were plotted and obtained mean value of P50. The recovery level of different periods(20min, 40 min, 60 min, 80 min, 100min) was measured by Low Pressure Flow Meter with multi-channels and staining methods. At the same time, the hydraulic diameter, pre-dawn water potential of xylem and natural percentage loss of conductivity(NPLC) were measured. The main conclusions were as follows.1. The order of the average P50 values of the six species was R. pseudoacacia > U. pumila > H. rhamnoides > S. matsudana > C. heterophylla > A. truncatum. Acer truncatum was the most drought-tolerant tree species. As drought-tolerant tree species, Robinia pseudoacacia was the most vulnerable to embolism.2. The sequence of hydraulic diameter of the six tree species was R. pseudoacacia(51.52±1.14μm) > U. pumila(46.67±2.12μm) > C. heterophylla(32.35±0.53μm) > H. rhamnoides(30.85±1.19μm) > S. matsudana(25.25±1.36μm) > A. truncatum(19.56±0.62 μm).3. The recovery degree of the xylem embolism by staining method was consistent with embolism recovery degree by Low Pressure Flow Meter with multi-channels. The regression equation was y = 1.047x- 7.567,R2 = 0.863. The LPFM method can completely reflect the recovery level of the embolism branches in different time periods.4. The xylem embolism recovery capacity of six tree species was as follows: R. pseudoacacia > U. pumila > H. rhamnoides > S. matsudana > C. heterophylla > A. truncatum. That was to say, the tree species with the high recovery ability of xylem embolism can quickly restore function of transporting water when the plants resupplied water.5. The results showed that the ability of xylem embolism refilling of one-year-old twigs was completely consistent with its embolism vulnerability(R. pseudoacacia > U. pumila > H. rhamnoides > S. matsudana > C. heterophylla > A. truncatum). The ability of embolism refilling increased with embolism vulnerability(R2=0.968). Regression analysis indicated that the ability of embolism refilling in six tree species and hydraulic diameter, pre-dawn water potential of xylem, NPLC had a strong correlation. The values of R2 were 0.868、0.779、0.713, reapectively. The hydraulic traits of xylem were closely related to the refilling ability of xylem embolism. In particular, there was a strong positive correlation among P50, hydraulic diameter and the ability to recover from embolism. Therefore, P50 and hydraulic diameter were the main influencing factors for embolism refilling.