Reduction in plant size and tissue nutrient concentration is widely considered to increase 30 seedling drought resistance in dry and oligotrophic plantation sites. However, much evidence 31 indicates that increase in size and tissue nutrient concentration improves seedling survival in 32 Mediterranean forest plantations. This suggests that the ecophysiological processes and 33 functional attributes relevant for early seedling survival in Mediterranean climate must be 34 reconsidered. We propose a physiological conceptual model for seedling survival in 35 Mediterranean-climate plantations to provide a physiological explanation of the frequent 36 positive relationship between outplanting performance and seedling size and nutrient 37 concentration. The model considers the physiological processes outlined in the plantation 38 establishment model of Burdett (1990), but incorporates other physiological processes that 39 drive seedling survival, such as N remobilization, carbohydrate storage and plant hydraulics.40 The model considers that seedling survival in Mediterranean climates is linked to high growth 41 capacity during the wet season. The model is for container plants and is based on three main 42 principles, 1) Mediterranean climates are not dry the entire year but usually have two 43 seasons of contrasting water availability; 2) summer drought is the main cause of seedling 44 mortality; in this context deep and large roots is a key trait for avoiding lethal water stress; 3) 45 attainment of large root systems in the dry season is promoted when seedlings have high 46 growth during the wet season. High growth is achieved when seedlings can divert large 47 amount of resources to support new root and shoot growth. Functional traits that confer high 48 photosynthesis, nutrient remobilization capacity, and non-structural carbohydrate storage 49 promote high growth. Increases in seedling size and nutrient concentration, strongly affect 50 these physiological processes. Traits that confer high drought resistance are of low value 51 during the wet season because hinder growth capacity. We provide specific evidence to 52 support the model and finally we discuss its implications and the factors that may alter the 53 frequent increase in performance with increase in seedling size and tissue nutrient 54 concentration.

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-One-year-old Pinus halepensis seedlings were subjected to four water stress conditioning treatments (control,

Functional attributes determine the survival and growth of planted seedlings in reforestation projects. Nitrogen (N) and water are important resources in the cultivation of forest species, which have a strong effect on plant functional traits. We analyzed the influence of N nutrition on drought acclimation of Pinus pinea L. seedlings. Specifically, we addressed if high N fertilization reduces drought and frost tolerance of seedlings and whether drought hardening reverses the effect of high N fertilization on stress tolerance. Seedlings were grown under two N fertilization regimes (6 and 100 mg N per plant) and subjected to three drought-hardening levels (well-watered, moderate and strong hardening). Water relations, gas exchange, frost damage, N concentration and growth at the end of the drought-hardening period, and survival and growth of seedlings under controlled xeric and mesic outplanting conditions were measured. Relative to low-N plants, high-N plants were larger, had higher stomatal conductance (27%), residual transpiration (11%) and new root growth capacity and closed stomata at higher water potential. However, high N fertilization also increased frost damage (24%) and decreased plasmalemma stability to dehydration (9%). Drought hardening reversed to a great extent the reduction in stress tolerance caused by high N fertilization as it decreased frost damage, stomatal conductance and residual transpiration by 21, 31 and 24%, respectively, and increased plasmalemma stability to dehydration (8%). Drought hardening increased tissue non-structural carbohydrates and N concentration, especially in high-fertilized plants. Frost damage was positively related to the stability of plasmalemma to dehydration (r = 0.92) and both traits were negatively related to the concentration of reducing soluble sugars. No differences existed between moderate and strong drought-hardening treatments. Neither N nutrition nor drought hardening had any clear effect on seedling performance under xeric outplanting conditions. However, fertilization increased growth under mesic conditions, whereas drought hardening decreased growth. We conclude that drought hardening and N fertilization applied under typical container nursery operational conditions exert opposite effects on the physiological stress tolerance of P. pinea seedlings. While drought hardening increases overall stress tolerance, N nutrition reduces it and yet has no effect on the drought acclimation capacity of seedlings.

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