Background Carbon assimilation depends on the allocation of leaf nitrogen (N) within the photosynthetic apparatus, particularly among light harvesting (NL), electron transport (NB), and carboxylation (NR). Autumnal declines in light and temperature impose concurrent demands to maximize photosynthesis for hardening processes, while pre-senescent N remobilization constrains photosynthetic N pools. Under these conditions, dynamic partitioning among NB, NL, and NR may constitute a key acclimatory mechanism, with the optimal balance varying according to species strategy. Aims We compare seasonal shifts in N allocation among NL, NB, and NR and its effects on photosynthesis and how it is modulated by N soil supply using two deciduous tree species with contrasting resource-use strategies: the fast growing Fraxinus chinensis and the slow growing Quercus variabilis. Methods Plants were fertilized at two levels of N from March to November: low N (13.8 mg N seedling−1) and high N (68 mg N seedling−1). Photosynthesis and N allocation pattern were monitored monthly during autumn (September—October). Results Fraxinus chinensis favored rapid growth, delaying the onset of dormancy to support extended growth and resource acquisition. To sustain photosynthetic rates, F. chinensis reallocated N toward photosynthetic components—particularly to NB and NR—thereby enhancing both maximum carboxylation rate of the enzyme Rubisco (Vcmax) and maximum rate of electron transport (Jmax) independently of soil N fertilization. On the contrary, Q. variabilis prioritized nutrient storage to perennial organs over growth. Despite the stable NR, NB and NL, it decreased the total photosynthetic N through time. However, it also maintained photosynthetic rate during the hardening period by maintaining Vcmax. Surprisingly, fertility significantly influenced its growth: promoting growth further in autumn under high N fertilization. Conclusions Fast-growing and slow-growing species showed contrasting autumn strategies: F. chinensis sustained growth and N use without fertilization response, whereas Q. variabilis prioritized storage and exhibited N-driven growth plasticity. These results highlight that fertilization sensitivity depends more on ecological strategy and seasonal N allocation than intrinsic growth rate.

Comparative patterns of photosynthetic nitrogen allocation in Fraxinus chinensis and Quercus variabilis across the autumn hardening period

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发表日期：

2026年7月22日

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Yufan Zhu,
Shuai Fang,
Guolei Li,
Mercedes Uscola Fernández

摘要

Background

Carbon assimilation depends on the allocation of leaf nitrogen (N) within the photosynthetic apparatus, particularly among light harvesting (N_L), electron transport (N_B), and carboxylation (N_R). Autumnal declines in light and temperature impose concurrent demands to maximize photosynthesis for hardening processes, while pre-senescent N remobilization constrains photosynthetic N pools. Under these conditions, dynamic partitioning among N_B, N_L, and N_R may constitute a key acclimatory mechanism, with the optimal balance varying according to species strategy.

Aims

We compare seasonal shifts in N allocation among N_L, N_B, and N_R and its effects on photosynthesis and how it is modulated by N soil supply using two deciduous tree species with contrasting resource-use strategies: the fast growing Fraxinus chinensis and the slow growing Quercus variabilis.

Methods

Plants were fertilized at two levels of N from March to November: low N (13.8 mg N seedling⁻¹) and high N (68 mg N seedling⁻¹). Photosynthesis and N allocation pattern were monitored monthly during autumn (September—October).

Results

Fraxinus chinensis favored rapid growth, delaying the onset of dormancy to support extended growth and resource acquisition. To sustain photosynthetic rates, F. chinensis reallocated N toward photosynthetic components—particularly to N_B and N_R—thereby enhancing both maximum carboxylation rate of the enzyme Rubisco (V_cmax) and maximum rate of electron transport (J_max) independently of soil N fertilization. On the contrary, Q. variabilis prioritized nutrient storage to perennial organs over growth. Despite the stable N_R, N_B and N_L, it decreased the total photosynthetic N through time. However, it also maintained photosynthetic rate during the hardening period by maintaining V_cmax. Surprisingly, fertility significantly influenced its growth: promoting growth further in autumn under high N fertilization.

Conclusions

Fast-growing and slow-growing species showed contrasting autumn strategies: F. chinensis sustained growth and N use without fertilization response, whereas Q. variabilis prioritized storage and exhibited N-driven growth plasticity. These results highlight that fertilization sensitivity depends more on ecological strategy and seasonal N allocation than intrinsic growth rate.