Low light intensity can lead to a decrease in photosynthetic capacity. However, could N-fixing species with higher leaf N contents mitigate the effects of low light? Here, we exposed seedlings of Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Castanopsis hystrix and Betula alnoides (non-N-fixing trees) to three irradiance treatments (100%, 40%, and 10% sunlight) to investigate the effects of low irradiance on leaf structure, leaf N allocation strategy, and photosynthetic physiological parameters in the seedlings. Low irradiance decreased the leaf mass per unit area, leaf N content per unit area (N_area), maximum carboxylation rate (V_cmax), maximum electron transport rate (J_max), light compensation point, and light saturation point, and increased the N allocation proportion of light-harvesting components in all species. The studied tree seedlings changed their leaf structures, leaf N allocation strategy, and photosynthetic physiological parameters to adapt to low-light environments. N-fixing plants had a higher photosynthesis rate, N_area, V_cmax, and J_max than non-N-fixing species under low irradiance and had a greater advantage in maintaining their photosynthetic rate under low-radiation conditions, such as under an understory canopy, in a forest gap, or when mixed with other species.

Wetlands are one of the world’s most productive ecosystems, and therefore it is crucial that management decisions regarding wetlands incorporate awareness of accurate assessments of the value of their respective ecosystem services. In this paper, we seek to improve the modelling precision in the scale transform process of ecosystem service evaluation. Firstly, we selected eight services as the criteria to calculate wetland ecosystem values: substance production, flood control, carbon sequestration, gas regulation, climate regulation, wave reduction, adding new lands, recreation and education. Then, six coastal wetlands of Liaoning province were chosen as the case study areas, and their ecosystem values were calculated by empirical method. Next, we simulated ecosystem values of the six cases by two spatial-scales transform methods named meta-analysis and wavelet transform. Finally, we compared the two groups of simulated values with the empirical measured values to examine their evaluation precisions. The results indicated that the total precision of the wavelet transform model (0.968) was higher than that of meta-analysis (0.712). In addition, the simulated values of single services such as substance production, flood control, carbon sequestration, gas regulation, and climate regulation were closer to the measured values using wavelet transform model. This research contributes to identifying an evaluation model with higher precision for evaluating wetland ecosystem services in the process of scale transform.

Photosynthetic-nitrogen use efficiency (PNUE) is a useful trait to characterize leaf economics, physiology, and strategy. In this study, we investigated the differences in PNUE, leaf nitrogen (N) allocation, and mesophyll conductance ( g _m ) in Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Betula alnoides and Castanopsis hystrix (non-N-fixing trees). Seedlings of the four species were cultured in pots and received the same nutrient solution, water volume, and light. LiCor-6400 was used to determine fluorescence yield, photosynthetic response to light, and intercellular CO ₂ concentration ( C _i ). N allocation fractions in the photosynthetic apparatus were calculated according to Niinemets and Tenhunen method; g _m was calculated according to variable J , EDO, and A - C _i curve fitting methods. PNUE of D. odorifera and E. fordii were significantly lower than those of B. alnoides and C. hystrix because of their allocation of a lower fraction of leaf N to Rubisco ( P _R ) and bioenergetics ( P _B ). Mesophyll conductance had a significant positive correlation with PNUE in D. odorifera, E. fordii , and B. alnoides . The fraction of leaf N to cell wall ( P _CW ) had a significant negative correlation with P _R in B. alnoides and C. hystrix . We conclude that B. alnoides and C. hystrix optimized their leaf N allocation toward photosynthesis, with the trade-off being N allocation to the cell wall and Rubisco. Thus, these two species may have a higher competitive ability in natural ecosystems with fertile soil.