Abstract
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 (Narea), maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), 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, Narea, Vcmax, and Jmax 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.
Highlights
Radiation is a source of energy for plants
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 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
There was a significant decrease in N content per unit area (Narea) and the leaf mass per unit area (LMA) of all four species under the 10% and 40% irradiance treatments when compared with the 100% treatment (Table 1)
Summary
Radiation is a source of energy for plants. Through photosynthesis, green plants use light to synthesize carbohydrates from water and CO2, which are necessary for maintaining growth and development. Low light intensity can lead to a decrease in photosynthetic capacity, forcing plants to change their leaf photosynthesis system and structure to increase their light-harvesting ability [2,3,4,5]. Plants usually adjust their leaf nitrogen (N) allocation strategies, such as increasing the fraction of leaf nitrogen (N) allocated to light-harvesting (PL) [5,6,7,8], and some plants may change the fraction of leaf N allocated to Rubisco (PR) and bioenergetics (PB) to balance the light reaction with carbon assimilation and achieve optimal photosynthetic efficiency [8,9]. Some plants do not adjust their PR and PB [10], which may be because some plants store many compounds containing N, such as free amino acids [11], inorganic N (NO3−, NH4+) [12], and some inactive Rubisco [12,13], and allocate these N sources to light-harvesting systems under low light levels
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