Elucidating the response of soil nutrients to long-term drought can better predict the impact of climate change on the ecosystem of moso bamboo (Phyllostachys edulis）forest in the future, and can guide the production and management practice of bamboo forest.

This study measured and analyzed the response of soil organic carbon, total nitrogen, total phosphorus content and storage, as well as their stoichiometric characteristics, to no throughfall exclusion (CK) and long-term throughfall exclusion (DR) in bamboo forests using the “ceiling method” for rain interception.

The results showed that the average value of available phosphorus content, hydrolytic nitrogen and organic carbon content, as well as the average soil C/N and C/P values in the 0-50 cm soil layer of drought soil were significantly lower than those in the control soil (P<0.05). The total phosphorus content and average pH value of drought soil were slightly lower than those in the control, while the total nitrogen content and N/P value of soil were higher than those in the control. There was no significant difference in soil nutrient content between drought and control treatments in each soil layer of 0-10 cm, 10-30 cm, and 30-50 cm. The soil pH values in all drought soil layers were lower than those in the control, with the pH value in the 10-50 cm range being significantly lower than that of the control (P<0.05). The C/P value in the 10-30 cm drought soil layer and the C/N value in the 10-50 cm drought soil layer were significantly lower than those in the control (P<0.05), while the N/P value in the 30-50 cm soil layer was significantly higher than that in the control (P<0.05). Drought has increased the “surface aggregation” phenomenon of soil nutrient content and the chemical stoichiometry. The organic carbon storage and total phosphorus storage in the 0-50 cm soil layer under drought were lower than the control, while the total nitrogen storage in the soil was higher than the control. Relevant analysis shows that the pH value of the control soil is significantly positively correlated with organic carbon, total nitrogen, and total phosphorus storage (P<0.01), while the pH value of soil under drought stress is only significantly negatively correlated with C/N and significantly positively correlated with N/P. The total nitrogen, total phosphorus, and organic carbon content in soil under drought are significantly or extremely significantly positively correlated with N/P (P<0.05 or P<0.01), while the total phosphorus content is significantly negatively correlated with C/N (P<0.05).

The soil pH value, total phosphorus, and available phosphorus content are the main influencing factors of nitrogen and phosphorus balance in soils under drought.

This study aims to clarify the response of the diurnal variation of photosynthesis during bamboo shoot stage to drought for different ages of moso bamboo, and to provide reference for water management for moso bamboo under climate change.

The “ceiling method” was used to simulate throughfall exclusion for the wild bamboo forest. One-year-old, three-year-old, and five-year-old moso bamboo plants served as experimental subjects. The Li-6400 portable photosynthesis meter was used to measure the daily changes of gas exchange parameters and correlation analysis were conducted to explore the influence of environmental factors on the photosynthetic capacity of bamboo under different drought treatments.

1) Significant differences existed in the diurnal variations of gas exchange parameters among control and drought-treated bamboo leaves during the shoot-bearing stage, with these variations influenced by bamboo age. Net photosynthetic rate (P_n) exhibited diverse diurnal patterns: D-3a treatment showed a double-peak pattern, demonstrating the typical photosynthetic ‘midday break’ phenomenon; CK-1a, CK-3a, CK-5a, and D-5a treatments exhibited a single-peak pattern; while D-1a treatment displayed a “U”-shaped curve, peaking at 18:00; Diurnal variations in transpiration rate (T_r) also exhibited treatment specificity: CK-1a showed a single peak (peak at 14:00), D-1a displayed a “W”-shaped pattern (peak at 18:00), while CK-3a, CK-5a, D-3a, and D-5a all exhibited double peaks. Drought delayed the first peak by 4 hours, while the second peak occurred at 16:00 in all cases. Regarding stomatal conductance (G_s), the control bamboo of all ages exhibited a single peak pattern (evening peak at 16:00). The D-5a treatment showed a gradual increase throughout the day (peak delayed to 18:00), while the D-1a and D-3a treatments exhibited a “W”-shaped pattern (peak at 18:00). The diurnal variation of leaf vapor pressure deficit (V_pdL) exhibited a single-peak pattern (peak at 14:00) in CK-1a, CK-3a, D-1a, and D-3a treatments. CK-5a also showed a single peak but delayed to 16:00, while D-5a displayed a double-peak pattern. Water use efficiency (W_UE) exhibited diverse diurnal patterns: D-5a exhibited a single-peak pattern; CK-1a and D-3a showed a double-peak pattern; CK-3a exhibited a gradual decline; CK-5a showed a gradual decrease; and D-1a exhibited a “V”-shaped pattern; 2) Correlation analysis indicated that among the control Phyllostachys edulis parameters, negative correlations were more prevalent, whereas positive correlations were more common under drought conditions. Under drought, P_n and G_s showed positive correlations across all age groups of Phyllostachys edulis, with the correlation being significant (P<0.05) only in 5-year-old bamboo. The CK-3a and CK-5a treatments exhibited weak positive correlations; 3) Path analysis revealed that the primary direct factors influencing P_n in the D-1a, D-3a, and D-5a treatments were C_i, T_r, and V_pdL, respectively. Both D-1a and D-5a exhibited a relatively strong direct influence on P_n through G_s.

The daily peak value of P_n in bamboo of different ages under drought is 4-6 hours earlier than that of different ages of bamboo under the control. After 14:00, P_n, G_s, and W_UE values of all-aged Phyllostachys edulis under drought were higher than those of the control. The second peak of G_s in bamboo of different ages under drought was delayed by 2 hours compared to the control, and drought increased the W_UE of bamboo after 14:00. The correlation between G_s and T_r under drought condition shows a U-shaped regulation with increasing age, first decreasing and then increasing, reflecting the shift in regulatory strategies between G_s and T_r during bamboo shoot stage under drought conditions.