Effects of soil moisture content on stem respiration rate, stem growth and sapwood nitrogen content in Dalbergia odorifera

Objective  To provide basic data for following study of heartwood formation of Dalbergia odorifera.

Method  Four soil moisture content gradients including heavy drought (HD), light drought (LD), dry-season irrigation (DI) and control (CK) were artificially simulated to investigate the effects of soil moisture content on predawn shoot water potential (Ψ_pd), stem respiration rate (R_s), stem growth, and sapwood nitrogen content and their change characteristics in dry season.

Result  Soil moisture content and Ψ_pd declined continuously in dry season, and significant differences were observed among different treatments since the end of November. R_s increased exponentially with stem temperature (θ) and the coefficients of determination were all greater than 0.65 in every treatment. Temperature sensitivity coefficients (Q₁₀) differed significantly among all water treatments, following the order of DI> CK>LD>HD.θ and R_s declined continuously during dry season and reached their minimum values in January. Significant differences among the θ values of all treatments were only found in winter. DI increased R_s while HD and LD decreased R_s. Stem growth remained stable until the middle of December, and decreased significantly since late December. Stem growth of DI and CK was significantly higher than those of HD and LD. The sapwood nitrogen content remained constant before December and started to decrease since December. Significant differences of the sapwood nitrogen contents among all treatments were found only in winter. R_s explained 56% seasonal variation of stem growth. Sapwood nitrogen content explained 68% seasonal variation of R_s. Ψ_pd explained 49%, 48% and 63% respectively seasonal variation of R_s, stem growth and sapwood nitrogen content.

Conclusion  Soil moisture content likely promotes the interaction of R_s, stem growth and sapwood nitrogen content by affecting Ψ_pd. DI increases R_s while drought decreases R_s. The θ value and sapwood nitrogen content are affected by soil moisture content only in winter. In addition R_s may partially indicate the changes of heartwood formation.