The Influence Of Drought On Water Parameters Of Larix Gmelinii

Larix gmelinii is the dominant tree species with important position of ecological function in northeast forest region of China. The area that Larix gmelinii distributed had higher average warming rate, drought intensity and drought frequency in summer. In this study, L. gmelinii was taken as study materials to simulate the effects of drought to water parameters and to investigate the response characteristic of drought-tolerant and drought ecological adaptation strategy by a rainfall exclusion experiment on field. The rainfall exclusion experiment conducted from May to September in 2012, whereas re-watering experiment conducted from May to September in 2013. Both of the two experiments included three treatments:100% rainfall exclusion (100%RE),50% rainfall exclusion (50%RE) and control. The main results are as followed:In the natural environment that decreasing precipitation led to a substantial reduction of soil moisture in the two rainfall exclusion treatments. The effects of drought on P-V curve water parameters mainly presented on osmotic potential compared with control, for 100%RE and 50%RE, average decreasing amplitude of Ψπ100,ΨtlP was 24.7%,14.0%,16.1%, and 7.3%, respectively. Moreover, short-term drought impacting on P-V water parameters had obvious seasonal characteristic, major significant variations all focused on June and July, which L.gmelinii showed vigorous physiological activity, Ψπ100,ΨtlP ,RWCtlp and AWC decreased, whereas ε increased. Smaller number of significant variations appeared in May and Auguest, and did not found in September. Compared with control, for 100%RE and 50%RE, average decreasing amplitude of Ψpd was respectively 87.3% and 46.9%, average decreasing amplitude of Ψmid was respectively 31.5% and 15.2%, and average increasing amplitude of wood density was 5.7% and 3.7%, respectively. The above results indicated that L. gmelinii both in 100% and 50% rainfall exclusion maintained the relatively constant RWC and water potential gradient measured as the difference between predawn and midday water potential via decreased stomatal conductance and osmotic adjustment to a certain extent. Regulation of water status for L. gmelinii is the near isohydric behavior along the isohydry/anisohydry continuum.During re-watering process, there were differences among variations of different parameters of L. gmelinii. P-V parameters did not show significant differences among treatments in the same month. For 100%RE, Ψpd was significantly lower than control from May to September; Ψmid was significantly lower than control in June to September; wood density was significantly higher than control in Auguest. For 50%RE, Ψpd was significantly lower than control from May to September; Ψmid was significantly lower than control in September; there was no significant differences between 50%RE and control.Overall,100% rainfall exclusion played a greater influence than 50% to water parameters. The restoration degree of parameters of L. gmelinii declined with the increasing of drought degree. Meanwhile, the compensation index of parameters declined with the increasing of drought degree.