关键词: 树轮, 敏感度, 海拔, 阳生树种, 阴生树种

Abstract: To investigate the effects of soil moisture on predawn shoot water potential (ψ_pd), stem respiration (R_s) and non-structural carbohydrates (NSCs) during the dry season, four soil moisture levels including heavy drought (HD), light drought (LD), dry-season irrigation (DI) and control (CK) were set up inDalbergia odorifera plantations. All those parameters weremeasured semimonthly. Soil moisture content and ψ_pd declined continuously and had significant differences among treatments after November.R_s increased exponentially with temperature and the coefficients of determination were all greater than 0.65.Q₁₀ differed significantly amongtreatments, following the order of DI>CK>LD>HD. Stem temperature (T) andR_s declinedcontinuously during the dry season and reached their minimum values in January. There was no significant difference of temperature among moisture treatments except in winter. Irrigationincreased theR_s rate, and drought decreased it. The soluble sugars tended to increase during the dry season at the cost of starch, which caused a small but non-significant increase in NSCs. The effect of moisture treatments on the content of total NSCs was limited; however, the droughttreatment increased the soluble sugars content and decreased the starch content. Low soil moisture induced by drought enhanced the transformation of starch to soluble sugars during winter, when heartwood formed.R_s explained 72% and 49% of the seasonal variation in starch and solublesugars, respectively. Theψ_pd explained 49%, 75% and 85% of the variance in theR_s, stem starch and soluble sugars, respectively. Soil moisture likely affectsR_s by modulating the amounts of sapwood starch and soluble sugars. These strong relationships provide evidence for the hypothesis that drought would promote heartwood formation inD. odorifera. In addition, given the significant relationship betweenR_s and NSCs, the variation in theR_s may also indicate changes in heartwood formation.

Key words: sensitivity, altitude, sun-adapted species, shade-adapted species, tree ring