Abstract
The response of plant CO2 diffusion conductances (mesophyll and stomatal conductances, gm and gsc) to soil drought has been widely studied, but few studies have investigated the effects of soil nitrogen addition levels on gm and gsc. In this study, we investigated the responses of gm and gsc of Manchurian ash and Mongolian oak to four soil nitrogen addition levels (control, low nitrogen, medium nitrogen and high nitrogen) and the changes in leaf anatomy and associated enzyme activities (aquaporin (AQP) and carbonic anhydrase (CA)). Both gm and gsc increased with the soil nitrogen addition levels for both species, but then decreased under the high nitrogen addition level, which primarily resulted from the enlargements in leaf and mesophyll cell thicknesses, mesophyll surface area exposed to intercellular space per unit leaf area and stomatal opening status with soil nitrogen addition. Additionally, the improvements in leaf N content and AQP and CA activities also significantly promoted gm and gsc increases. The addition of moderate levels of soil nitrogen had notably positive effects on CO2 diffusion conductance in leaf anatomy and physiology in Manchurian ash and Mongolian oak, but these positive effects were weakened with the addition of high levels of soil nitrogen.
Highlights
The response of plant CO2 diffusion conductances to soil drought has been widely studied, but few studies have investigated the effects of soil nitrogen addition levels on gm and gsc
Our results showed that both gm and gsc were enlarged by soil nitrogen addition; these values increased with nitrogen addition from LN to MN and decreased with the addition of HN
We believed that the increases of gm and gsc were largely related to the enlargement of leaf N content in this study because the relationships between leaf N content and gm and gsc strongly supported the promotion of leaf N content to gm and gsc increases, in which gm and gsc both showed a positive correlation with leaf N content, even though they were highly significant in Mongolian oak (P < 0.01) (Fig. 2)
Summary
The response of plant CO2 diffusion conductances (mesophyll and stomatal conductances, gm and gsc) to soil drought has been widely studied, but few studies have investigated the effects of soil nitrogen addition levels on gm and gsc. We investigated the responses of gm and gsc of Manchurian ash and Mongolian oak to four soil nitrogen addition levels (control, low nitrogen, medium nitrogen and high nitrogen) and the changes in leaf anatomy and associated enzyme activities (aquaporin (AQP) and carbonic anhydrase (CA)) Both gm and gsc increased with the soil nitrogen addition levels for both species, but decreased under the high nitrogen addition level, which primarily resulted from the enlargements in leaf and mesophyll cell thicknesses, mesophyll surface area exposed to intercellular space per unit leaf area and stomatal opening status with soil nitrogen addition. Ex Ledeb), two species in Oleaceae and Fagaceae, respectively, are widely distributed in the Changbai Mountains, China Their responses of CO2 diffusion conductance to soil nitrogen additions have rarely been reported; and the mechanisms governing gm and gsc in leaf anatomy and physiology have not been determined. The present study will advance our mechanistic understanding of global nitrogen deposition impacts on carbon cycling in tree species
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