The dynamic of the annual carbon allocation to wood in European tree species is consistent with a combined source–sink limitation of growth: implications for modelling

摘要

The extent to which wood growth is limited by carbon (C) supply (i.e. sourcecontrol) or by cambial activity (i.e. sink control) will strongly determinethe responses of trees to global changes. Nevertheless, the physiologicalprocesses that are responsible for limiting forest growth are still a matter of debate.The aim of this study was to evaluate the key determinants of the annual Callocation to wood along large soil and climate regional gradients overFrance. The study was conducted for five tree species representative of themain European forest biomes (Fagus sylvatica, Quercuspetraea, Quercus ilex, Quercus robur and Piceaabies).The drivers of stand biomass growth were assessed on both inter-site andinter-annual scales. Our data set comprised field measurements performed at49 sites (931 site-years) that included biometric measurements and a varietyof stand characteristics (e.g. soil water holding capacity, leaf areaindex). It was complemented with process-based simulations when possibleexplanatory variables could not be directly measured (e.g. annual andseasonal tree C balance, bioclimatic water stress indices). Specifically,the relative influences of tree C balance (source control), directenvironmental control (water and temperature controls of sink activity) andallocation adjustments related to age, past climate conditions, competitionintensity and soil nutrient availability on growth were quantified.The inter-site variability in the stand C allocation to wood waspredominantly driven by age-related decline. The direct effects oftemperature and water stress on sink activity (i.e. effects independentfrom their effects on the C supply) exerted a strong influence on the annualstand wood growth in all of the species considered, including deciduoustemperate species. The lagged effect of the past environmental conditions(e.g. the previous year's water stress and low C uptake) significantlyaffected the annual C allocation to wood. The C supply appeared to stronglylimit growth only in temperate deciduous species.We provide an evaluation of the spatio-temporal dynamics of the annual Callocation to wood in French forests. Our study supports the premise thatthe growth of European tree species is subject to complex control processesthat include both source and sink limitations. The relative influences ofthe growth drivers strongly vary with time and across spatial ecologicalgradients. We suggest a straightforward modelling framework with which toimplement these combined forest growth limitations into terrestrialbiosphere models.