Abstract
Chlorophyll is the molecular basis for the function of photosystems and is also a promising tool for ecological prediction. However, the large-scale patterns of chlorophyll variation in grasslands remain poorly understood. We performed consistent measurements of chlorophyll a, b, a+b, and the a:b ratio (chlorophyll a/b) for 421 species across northern hemisphere grassland transects, recorded their distributions, variations, and influencing factors, and examined their relationships with leaf nitrogen. The results showed that the distributional ranges were 0.52–28.33 (mean 5.49) mg·g−1 dry weight, 0.15–12.11 (mean 1.83) mg·g−1 dry weight, 0.67–39.29 (mean 7.32) mg·g−1 dry weight, and 1.28–7.84 (mean 3.02) for chlorophyll a, b, a+b, and a/b, respectively. The chlorophyll averages differed among regions (higher in the Loess Plateau and the Mongolian Plateau than in the Tibetan Plateau), grassland types (desert grasslands > meadow > typical grasslands), life forms, life spans, and taxonomies. In the entire northern hemisphere grassland, chlorophyll concentrations and chlorophyll a/b were negatively correlated to photosynthetically active radiation and the soil N:P ratio, and positively correlated to the mean annual temperatures. These results implied that chlorophyll in grasslands was shaped by the layered structure of grasses, distinct plateau environments, and phylogeny. The allocation patterns of leaf nitrogen to chlorophyll differed among regions and grassland types, showing that caution is required if simply relating single leaf N or chlorophyll to productivity separately. These findings enhance our understanding of chlorophyll in natural grasslands on a large scale, as well as providing information for ecological predictive models.
Highlights
Photosynthesis, the initiator of materials and energy cycles on Earth, can be divided into three continuous processes: 1) light harvesting; 2) zigzag electron transport, and 3) carbon fixation
According to a previous study on tropical to temperate forests, the total chl concentration ranged from 1.20–22.58 mg·g−1 fresh weight (FW), showing grater plasticity compared with grasslands when converted to dry weight (Li et al, 2018b)
Excessive radiation in plateau grasslands may be the reason for the lower chl concentration, because acclimation to high light can result in chloroplast reduction activated by photoprotection (Hallik et al, 2009)
Summary
Photosynthesis, the initiator of materials and energy cycles on Earth, can be divided into three continuous processes: 1) light harvesting; 2) zigzag electron transport, and 3) carbon fixation (the Calvin cycle). There are two types of PS: PSI and PSII The two most common types of chl in the PS of terrestrial plants are chla and chlb. Both have strong light absorption and function mainly in the RC and LHC of photosystems in combination with proteins (Atsushi et al, 2018). The relative amounts of chla and chlb (i.e., the chla/b ratio) are an indication of the allocation to the PS core and LHC, as well as of the plant’s functional balance between the efficiency of light capture and electron transport (Leong et al, 1985; Terashima and Hikosaka, 1995)
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