Growing in Mixed Stands Increased Leaf Photosynthesis and Physiological Stress Resistance in Moso Bamboo and Mature Chinese Fir Plantations

Abstract

Mixed-stand plantations are not always as beneficial for timber production and carbon sequestration as monoculture plantations. Systematic analyses of mixed-stand forests as potential ideal plantations must consider the physiological-ecological performance of these plantations. This study aimed to determine whether mixed moso bamboo (Phyllostachys pubescens (Pradelle) Mazel ex J. Houz.) and Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) stands exhibited better physiological-ecological performance than monoculture plantations of these species. We analyzed leaf photosynthesis, chlorophyll fluorescence, antioxidant enzyme activities, chlorophyll content and leaf chemistry in a moso bamboo stand, a Chinese fir stand and a mixed stand with both species. The results showed that both species in the mixed stand exhibited significantly higher leaf net photosynthesis rate (Amax), instantaneous carboxylation efficiency (CUE), chlorophyll content, maximum quantum yield of photosynthesis (Fv/Fm), photochemical quenching coefficient (qP), PSII quantum yield [Y(II)], leaf nitrogen content, and antioxidant enzyme activities than those in the monoculture plantations. However, the non-photochemical quenching (NPQ) in Chinese fir and 2-year-old moso bamboo was significantly lower in the mixed stand than in the monocultures. In addition, the water use efficiency (WUE) of Chinese fir was significantly higher in the mixed stand. The results suggest that the increase in leaf net photosynthetic capacity and the improved growth in the mixed stand could be attributed primarily to the (i) more competitive strategies for soil water use, (ii) stronger antioxidant systems, and (iii) higher leaf total nitrogen and chlorophyll contents in the plants. These findings suggest that mixed growth has beneficial effects on the leaf photosynthesis capacity and physiological resistance of moso bamboo and Chinese fir.

Keywords: antioxidant enzyme; bamboo-fir mixture; chlorophyll fluorescence; leaf-level gas exchange; stand carbon sequestration; water use efficiency.

FIGURE 1

Location of the sample site and sampling design. The white area indicates a buffer; 20 m refers to the length of the border around the plots. See section “Materials and methods” for details.

FIGURE 2

Raincloud plot of photosynthetic parameters among (A) Amax, (B) Ci, (C) gsw, (D) Tr, (E) WUE, and (F) CUE combined. The “cloud” represents the data distribution, and the “rain” represents the jittered raw data. The black point represents the mean distribution values, and the black line represents the standard deviations of the distributions. Capital letters indicate significant differences between Chinese fir under monoculture and mixed-stand conditions (P < 0.05). Lowercase letters indicate significant differences between 2-year-old moso bamboo under monoculture and mixed-stand conditions (P < 0.05). Greek letters indicate significant differences between 1-year-old moso bamboo under monoculture and mixed-stand conditions (P < 0.05).

FIGURE 3

Radar plot showing various fluorescence parameters of the different stand types. (A) Chinese fir. (B) 2-year-old moso bamboo. (C) 1-year-old moso bamboo. Each line represents the average of 27 measurements per stand type. *P < 0.05, **P < 0.01, and ***P < 0.001.

FIGURE 4

Antioxidant enzyme activities, Rubisco activity, and malondialdehyde (MDA) content in moso bamboo and Chinese fir leaves in different stand types. Capital letters indicate significant differences between Chinese fir under monoculture (PC) and mixed-stand (PM) conditions (P < 0.05). Lowercase letters indicate significant differences between 2-year-old moso bamboo under monoculture (PM-2a) and mixed-stand (MM-2a) conditions (P < 0.05). Greek letters indicate significant differences between 1-year-old (1a) moso bamboo under monoculture (PM-1a) and mixed-stand (MM-1a) conditions (P < 0.05). SOD: superoxide dismutase; POD: peroxidase; CAT: catalase.

FIGURE 5

Chlorophyll content and leaf N content in moso bamboo and Chinese fir leaves in different stand types. Capital letters indicate significant differences between Chinese fir under monoculture and mixed-stand conditions (P < 0.05). Lowercase letters indicate significant differences between 2-year-old moso bamboo under monoculture and mixed-stand conditions (P < 0.05). Greek letters indicate significant differences between 1-year-old moso bamboo under monoculture and mixed-stand conditions (P < 0.05).