土壤水分胁迫对拉瑞尔小枝水分参数的影响

Water parameters of the branch of Larrea tridentata under different soil drought stress

采用压力室法在土壤水势为-0.021、-0.121、-0.698、-0.968 MPa 4种情况下对大田种植的1年生Larrea tridentata的小枝水势进行测定,并绘制PV曲线,通过PV曲线求解各水分参数,用以判定土壤水分胁迫对L.tridentata生理特性的影响。研究结果表明:供水良好的情况下,L.tridentata水势日变化呈双峰曲线,随着土壤水分含量的减少,峰值逐渐变得不明显。在土壤水分胁迫条件下,L.tridentata有一定的渗透调节和保持膨压的能力,它一方面通过细胞壁弹性和拥有较高的束缚水含量来保持膨压,另一方面原生质具有较强的忍耐脱水的能力。随着土壤干旱胁迫的逐渐加重,其耐脱水能力提高,保持膨压的能力逐渐减弱。通过对其在不同土壤水分胁迫条件下渗透调节和维持膨压能力的综合评价,得出其在4种土壤水分状况下的综合抗旱指数分别为0.25、0.17、0.933、0.657,说明随着土壤水分含量的逐渐减少,L.tridentata能逐渐提高自身抵御干旱的能力以适应干旱;通过抗旱模型的判定得出L.tridentata属于高水势延迟脱水型耐旱树种。

Larrea tridentata is a xerophytic evergreen shrub, dominant in arid regions of the southwestern United States. The success of this desert shrub （ creosote bush） has been largely attributed to its capacity for maintaining turgor pressure and stomatal control of photosynthesis under drought stress. However, the drought-resistance characteristics of plants are very complex. In addition to hereditary factors, environmental conditions may have strong impacts on the physiological performance of desert shrub seedlings, which may result in different performance of its drought-resistance capability. To study the drought resistance capability of L. tridentata, which was introduced to China from the United States, water parameters of the branches were determined in this study.The water potential of 1-year-old small branches of creosote bush was measured using the pressure chamber method. Four soil water potential levels were considered, namely, -0.021, -0.121, -0.698 and -0.968 MPa. Pressure-volume curves （PV curves） were generated over a wide range of water potentials to determine drought-resistance characteristics of the species. We obtained q~ （the largest osmotic potential under the saturation moisture content）, qP （osmotic potential when the turgor pressure value is zero）, ~max （elasticity module in the largest volume）, V （free water content）, V （bonded water content）, RWC^（ relative water content when turgor is zero）, ROWC^（ relative content of the penetrated water when turgor is zero）, and qtp（ turgor pressure） from the PV curves. The results show that the diurnal transformation curve of water potential had two peaks when soil water content was sufficient, and the character diminished with decreasing soil water content. The relationship model between soil water potential and ~p is y = 1.0541x^5~33 . It is concluded that the branches of L. tridentata can hold high water potential and its dehydration tolerance is strong, similar to that of conifers. Under drought conditions, L. tridentata took on an ability of osmotic adjustment and maintained ~p, mainly by improving cell-wall elasticity and retaining a higher proportion of water bound. Its capacity of sarcode dehydration tolerance is strong. With increasing drought stress, the capacity of the L. tridentata to maintain turgor pressure declined, whereas its capacity to tolerate dehydration increased. Moreover, we used a membership function to operationalize data from the PV curve into quantitative indices, obtaining fuzzy values of 0.25, 0. 17, 0.933 and 0.657 under four soil water potential conditions. Overall, the drought-resistance ability of L. tridentata was maintained and strengthened as soil moisture decreased. The drought model suggests that L. tridentata belongs to high water potential and dehydration-delaying species. Its drought-enduring mechanism operates mainly by restricting moisture loss and adopting available moisture to maintain higher water potential, combined with enduring dehydration with low water potential. That is, the protoplasm and main organs of the L. tridentata are unharmed or only slightly harmed under serious drought conditions, because of its cell-wall elasticity. These conclusions coincide with results obtained in the United States, and confirm that L. tridentata has maintained good drought resistance capacity after cultivation in China.