Abstract
Photosynthetic-nitrogen use efficiency (PNUE) is a useful trait to characterize leaf physiology and survival strategy. PNUE can also be considered as part of ‘leaf economics spectrum’ interrelated with leaf nutrient concentrations, photosynthesis and respiration, leaf life-span and dry-mass investment. However, few studies have paid attention to PNUE of N-fixing tree seedlings in subtropical China. In this study, we investigated the differences in PNUE, leaf nitrogen (N) allocation, and mesophyll conductance (gm) in Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Betula alnoides and Castanopsis hystrix (non-N-fixing trees). PNUE of D. odorifera and E. fordii were significantly lower than those of B. alnoides and C. hystrix mainly because of their allocation of a lower fraction of leaf N to Rubisco (PR) and bioenergetics (PB). Mesophyll conductance had a significant positive correlation with PNUE in D. odorifera, E. fordii, and B. alnoides, but the effect of gm on PNUE was different between species. The fraction of leaf N to cell wall (PCW) had a significant negative correlation with PR in B. alnoides and C. hystrix seedling leaves, but no correlation in D. odorifera and E. fordii seedling leaves, which may indicate that B. alnoides and C. hystrix seedling leaves did not have enough N to satisfy the demand from both the cell wall and Rubisco. Our results indicate that B. alnoides and C. hystrix may have a higher competitive ability in natural ecosystems with fertile soil, and D. odorifera and E. fordii may grow well in N-poor soil. Mixing these non-N-fixing and N-fixing trees for afforestation is useful for improving soil N utilization efficiency in the tropical forests.
Highlights
Nitrogen (N) is very important for plants leaves, because main function of leaves- photosynthesis need a lot of N [1,2], and there was a positive correlation between photosynthetic capacity and N content in many species
The Photosynthetic-nitrogen use efficiency (PNUE) in B. alnoides and C. hystrix seedling leaves were higher than those in D. odorifera and E. fordii, which was mainly attributed to their lower Narea and Nmass values
This study indicated that PNUE was significantly lower in two N-fixing trees (D. odorifera and E. fordii) than that in two non-N-fixing trees (B. alnoides and C. hystrix)
Summary
Nitrogen (N) is very important for plants leaves, because main function of leaves- photosynthesis need a lot of N [1,2], and there was a positive correlation between photosynthetic capacity and N content in many species. Studies have shown that N-fixing trees had lower Amax’ and higher Narea, which resulted in a lower PNUE [10, 11]. These contradicting results may imply that some N-fixing species use a different strategy to utilize N compared to non-N-fixing species
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