Abstract
BackgroundSoil water and nitrogen (N) are considered to be the main environmental factors limiting plant growth and photosynthetic capacity. However, less is known about the interactive effects of soil water and N on tree growth and photosynthetic response in the temperate ecosystem.Methods/Principal FindingsWe applied N and water, alone and in combination, and investigated the combined effect of different water and N regimes on growth and photosynthetic responses of Fraxinus mandshurica seedlings. The seedlings were exposed to three water regimes including natural precipitation (CK), higher precipitation (HW) (CK +30%) and lower precipitation (LW) (CK −30%), and both with and without N addition for two growing seasons. We demonstrated that water and N supply led to a significant increase in the growth and biomass production of the seedlings. LW treatment significantly decreased biomass production and leaf N content, but they showed marked increases in N addition. N addition could enhance the photosynthetic capability under HW and CK conditions. Leaf chlorophyll content and the initial activity of Rubisco were dramatically increased by N addition regardless of soil water condition. The positive relationships were found between photosynthetic capacity, leaf N content, and SLA in response to water and N supply in the seedling. Rubisco expression was up-regulated by N addition with decreasing soil water content. Immunofluorescent staining showed that the labeling for Rubisco was relatively low in leaves of the seedlings under LW condition. The accumulation of Rubisco was increased in leaf tissues of LW by N addition.Conclusions/SignificanceOur study has presented better understanding of the interactions between soil water and N on the growth and photosynthetic response in F. mandschurica seedlings, which may provide novel insights on the potential responses of the forest ecosystem to climate change associated with increasing N deposition.
Highlights
Human activities such as fossil fuel burning, forest disturbance, and land conversion have globally elevated the atmospheric concentration of carbon dioxide (CO2) and atmospheric deposition of nitrogen (N) [1]
We demonstrated significant interactive effects of N addition and soil water on the whole-plant growth and photosynthetic capacity of F. mandschurica seedlings in the temperate forest ecosystem in northeastern China
We showed that N addition increased seedling growth including plant height, total biomass and aboveground biomass under different soil water conditions
Summary
Human activities such as fossil fuel burning, forest disturbance, and land conversion have globally elevated the atmospheric concentration of carbon dioxide (CO2) and atmospheric deposition of nitrogen (N) [1]. Less is known about the relationships between photosynthetic capacity, leaf N content, and the expression and activity of Rubisco in response to N and water in the seedling. We aimed to examine potential impacts of increased soil N and water availability and their interaction on whole-plant growth, biomass allocation, photosynthetic gas exchange, specific leaf area, leaf N content and photosynthetic pigment content in the seedlings. We studied the changes in the expression and activity of Rubisco to clarify how N addition and water treatment affect photosynthetic functions of the seedlings. Better understanding of the interactions between soil water and N on trees may provide critical insights on the potential responses of the forest ecosystem to climate change associated with increasing atmospheric N deposition
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