Environmental conditions in the nursery regulate root system development and architecture of forest tree seedlings: a systematic review

Root system growth dynamics and architecture influence the establishment and field performance of planted forest tree seedlings. Roots display extensive phenotypic plasticity in response to changes in environmental conditions, which can be harnessed through management to produce seedlings with desirable root traits for better field performance. This systematic review synthesizes research on the effects of nutrients, light, soil temperature, water availability, and their interactions on seedling root system development and architecture in nursery production and field establishment. Major findings show that nutrient and water availability have the greatest potential for regulating root system development and architecture. High nutrient availability increases overall root growth, branching, and rooting depth until plants reach nutrient sufficiency that may cause root growth inhibition. Drought preconditioning (i.e., exposure to drought stress in the nursery) effects vary widely, but generally reduces seedling size and promotes root vs. shoot growth. Soil temperature and light availability can control seedling growth and influence stress resistance. For example, shading promotes shoot vs. root growth, while photoperiod reduction has the opposite effect. Forest tree species have an optimal temperature for root growth between 15 and 25 degrees C, outside of which, development is increasingly impaired. Furthermore, seedling morphology and physiology is often a result of additive or interactive effects among environmental factors. Interactions between nutrient availability and other environmental factors show the greatest potential to improve seedling root development and field performance. However, ecological differences among species and ecotypes and complex tradeoffs among trait expression can entangle the identification of clear trends among interacting environmental factors.