Responses of Phyllostachys heteroclada f. solida to photosynthesis and physiology under waterlogging stress

To investigate the physiological impacts of different waterlogging depths on Phyllostachys heteroclada f. solida during specific waterlogging periods, and to explore the mechanisms underlying its effects on leaf photosynthesis, chlorophyll fluorescence characteristics, and the antioxidant system, thereby revealing its waterlogging tolerance and response strategies at the physiological and ecological levels.

Two-year-old P. heteroclada f. solida seedlings were subjected to simulated waterlogging treatments, including a control group under normal moisture CK, GY and SY. Measurements of photosynthetic pigment content, gas exchange parameters, chlorophyll fluorescence parameters, osmoregulatory substance levels, and antioxidant enzyme activities were conducted at five time points (Day 0, Day 10, Day 20, Day 30, and Day 40).

1) The content of photosynthetic pigments in P. heteroclada f. solida initially declines and then rises, though remaining lower than that in the CK group. In the GY group, chlorophyll a (Chl a) reaches its nadir on Day 30, decreasing by 48.97% compared to CK. Chlorophyll b (Chl b) in both waterlogging groups shows the lowest levels on Day 30, with reductions of 48.09% (GY) and 62.15% (SY) relative to CK; 2) Waterlogging intensity significantly affects photosynthetic gas exchange parameters (P<0.05). Over time, net photosynthetic rate (P_n), stomatal conductance (G_s), and transpiration rate (T_r) decline in all treatment groups, with SY showing reductions of 86.87%, 78.02% and 60.00%, respectively, compared to CK by the end of the stress period. Intercellular CO₂ concentration (C_i) increases continuously. Chlorophyll fluorescence parameters differ markedly among treatments, though GY and SY exhibit similar trends: initial fluorescence (F_o) and non-photochemical quenching (NPQ) rise, while maximum fluorescence (F_m) and photochemical quenching (qP) decline; 3) Waterlogging duration differentially influences malondialdehyde (MDA) content: GY follows a “rise-decline-rise” pattern, whereas SY peaks on Day 30 (56.92% higher than CK) before declining. Proline (PRO) content increases steadily in both treatment groups; 4) SOD, POD, and CAT activities generally increased rapidly initially and then declined slowly.

P. heteroclada f. solida responds to early waterlogging stress by rapidly elevating SOD, POD, and CAT activities. In the mid-stage, black spots appear on submerged leaves, which subsequently fall off, accompanied by reduced photosynthetic pigment content and photosynthesis. Despite the weakening of photosynthetic parameters over time, antioxidant enzyme activities remain higher than those in CK, and chlorophyll content gradually recovers, indicating that the plant is still in a phase of self-metabolic regulation. In summary, P. heteroclada f. solida demonstrates certain waterlogging tolerance, enabling it to sustain basic growth and metabolism under prolonged waterlogging. Based on this trait, it holds potential as a landscape plant for urban-rural sponge city and waterfront greening projects.