Abstract: [Objective] Larix gmelinii plays a vital role in economic development and ecological environment construction in China, however it distributes in the region where summer drought intensity and drought frequency are high. Thus, it is necessary to clarify the water management strategy. [Method] A rainfall exclusion experiment including three water regime treatments (100% rainfall exclusion-100%RE, 50% rainfall exclusion-50%RE, and control-CK, i.e., ambient rainfall) was conducted in Dahurian larch plantations from May to September 2012 to monitor the water relations of trees including water potential, stomatal conductance, relative water content, and pressure-volume water parameters in a natural environment at Maoershan Forest Research Station, Northeast Forestry University. [Result] The midday water potential was lowest for the 100%RE treatment, followed by the 50%RE treatment, and the highest for the CK during the experiment period in which the decreasing precipitation directly led to a substantial reduction of soil moisture. The seasonal variation amplitude of midday water potential for 100%RE, 50%RE, and CK was 0.81, 0.68, and 0.54 MPa, respectively. The greatest difference in midday water potential between 100%RE, 50%RE and CK was 0.49, and 0.37 MPa, however the differences between predawn water potential and midday water potential for the three treatments were all similar, averaging about 0.71 MPa. The highest percentages of decrease in stomatal conductance for 100%RE and 50%RE were 84% and 79%, and the highest percentages of increase in water use efficiency (WUE) for 100%RE and 50%RE sample were 140% and 58% compared with the control. Moreover, the relative water content (RWC) of twigs for 100%RE and 50%RE was similar, and was 7% lower than that of the control. In addition, the main water parameters derived from pressure volume curves for the three treatments were similar, suggesting that the parameters were relatively stable in response to the decrease of soil water content.[Conclusion] The above results indicated that stressed L. gmelinii maintained the relatively constant RWC and water potential gradient measured as the difference between predawn and midday water potential by decreasing stomatal conductance, increasing WUE, and probably via osmotic adjustment. Regulation of water status for L. gmelinii is the near isohydric behavior along the isohydry/anisohydry continuum.

Key words: water potential, stomatal conductance, relative water content, water parameters, isohydric behavior, Larix gmelinii