Modern tools to tackle traditional concerns: Evaluation of site productivity and Pinus radiata management via δ13C- and δ18O-analysis of tree-rings

Foresters frequently lack sufficient information about site quality to optimize plantation management and logwood production to local conditions. In the present study we explored the potential of delta C-13- and delta O-18-signatures of tree-rings to provide such information. We studied stem disks collected from two Pinus radiata plantations in south-eastern Australia that had been thinned or treated with fertilizer. Estimated from tree-ring delta C-13, the sites differed markedly in intrinsic water use efficiency of photosynthesis (WOEi = A/g(s)). Stem disks from one site (Lyons) showed pronounced differences in delta C-13 between early- and latewood, depending on stand density. Fertilizer application subsequent to thinning transiently increased foliage-N concentrations, without additional effects on A(max) and delta C-13. Thinning (and fertilization) at the other site (Daylesford) had little effect on delta C-13-variation between early- and late wood. Greater productivity at Lyons is seemingly related to greater flexibility in WUEi such that fluctuating water supply was more efficiently exploited. Current theory suggests delta O-18-signatures in wood at this site acted as a proxy record of Vapor Pressure Deficit (VPD), and the slope of the correlation between delta O-18- and WUEi (as an indicator of stomatal sensitivity to VPD) helped identify growth limiting resources and conditions. In general, delta O-18 and WUEi were positively correlated and WUEi seemed mainly under stomatal control. Employing a General Linear Model, we identified additional influences on WUEi. The slope, and closeness of fit of the correlation between delta O-18 and WUEi depended on stand density, wood type (early- or late wood), and individual trees. These traits were not correlated in early wood immediately after planting, suggesting WUEi was driven by biochemical demand for CO2 in photosynthesis. Conversely, enhanced competition for soil water after canopy closure resulted in positive correlations between delta O-18 and WOE indicating enhanced importance of stomatal resistance to CO2-diffusion. We discuss the limitations to the use of delta C-13- and delta O-18 analysis of bulk wood for determining the balance between demand- and supply-driven control of WUEi. (C) 2012 Elsevier B.V. All rights reserved.