Elevations in cytosolic free calcium concentration constitute a fundamental signal transduction mechanism in plants; however, the particular characteristics of calcium ion (Ca²⁺) signal occurrence in plants is still under debate. Little is known about how stimulus-specific Ca²⁺ signal fluctuations are generated. Therefore, we investigated the identity of the Ca²⁺ signal generation pathways, influencing factors, and the effects of the signaling network under drought stress on Phyllostachys edulis (Carrière) J. Houz. Non-invasive micro testing and laser confocal microscopy technology were used as platforms to detect and record Ca²⁺ signaling in live root tip and leaf cells of P. edulis under drought stress. We found that Ca²⁺ signal intensity (absorption capacity) positively correlated with degree of drought stress in the P. edulis shoots, and that Ca²⁺ signals in different parts of the root tip of P. edulis were different when emitted in response to drought stress. This difference was reflected in the Ca²⁺ flux and in regional distribution of Ca²⁺. Extracellular Ca²⁺ transport requires the involvement of the plasma membrane Ca²⁺ channels, while abscisic acid (ABA) can activate the plasma membrane Ca²⁺ channels. Additionally, Ca²⁺ acted as the upstream signal of H₂O₂ in the signaling network of P. edulis under drought stress. Ca²⁺ was also involved in the signal transduction process of ABA, and ABA can promote the production of Ca²⁺ signals in P. edulis leaves. Our findings revealed the physiological role of Ca²⁺ in drought resistance of P. edulis. This study establishes a theoretical foundation for research on the response to Ca²⁺ signaling in P. edulis.

Water is crucial to plant growth and development. Under heterogeneous environmental water deficiency, physiological integration of the rhizomatous clonal plant triggers a series of physiological cascades, which induces both signaling and physiological responses. It is known that the rhizome of Phyllostachys edulis, which connects associated clonal ramets, has important significance in this physiological integration. This significance is attributed to the sharing of water and nutrients in the vascular bundle of clonal ramets under heterogeneous water conditions. However, the physiological characteristics of physiological integration under heterogeneous water stress remain unclear. To investigate these physiological characteristics, particularly second messenger Ca²⁺ signaling characteristics, long-distance hormone signaling molecules, antioxidant enzyme activity, osmotic adjustment substance, and nitrogen metabolism, ramets with a connected (where integration was allowed to take place) and severed rhizome (with no integration) were compared in this study. The vascular bundle structure of the rhizome was also observed using laser confocal microscopy. Overall, the results suggest that interconnected rhizome of P. edulis can enhance its physiological function in response to drought-induced stress under heterogeneous water deficiency. These measured changes in physiological indices serve to improve the clonal ramets’ drought adaptivity through the interconnected rhizome.

This study aimed to evaluate the dominant factors of physiological responses of Phyllostachys edulis (Carrière) J. Houz to drought stress. The calcium (Ca²⁺) fluxes in root tips of P. edulis treated by polyethylene glycol were monitored via non-invasive micro-test technology. The physiological indexes of P. edulis under different soil moisture contents were determined. The regression model was built by curve fitting with the main physiological factors of P. edulis using PCA analysis. The variance contribution rates of the first three principal components of the physiological indicators were 75.0%, 13.3% and 5.0%. Calcium signal sensing protein kinase (CDPK) contents accounted for a larger contribution to the load of the first principal component. The contents of calcium signal sensor protein calmodulin (CaM) and calcium-dependent protein kinase (CDPK) increased. Meanwhile, drought induced strong Ca²⁺ influxes in root tips. Additionally, as the soil water content decreased, the contents of malondialdehyde (MDA), proline, betaine, jasmonic acid (JA) and abscisic acid (ABA) increased, and auxin (IAA) decreased in P. edulis leaves, strongly correlating with the CaM and CDPK contents. The calcium signal of P. edulis is activated and cascades plant physiological responses to drought stress. This study will provide physiological evidence for research regarding mechanisms of drought resistance of P. edulis.

Impacts of drought events and nitrogen (N) deposition on forests are increasingly concerning in the context of global climate change, but their effects, in particular, their interactive effects on soil respiration and its components remain unclear. A two-factor random block field experiment was conducted at a subtropical Moso bamboo forest in Southwest China to explore the response of soil respiration (R_s), autotrophic respiration (R_a), and heterotrophic respiration (R_h) to throughfall re-duction and N addition. Our results showed that throughfall reduction significantly decreased R_s, which is mainly attributed to the decrease in R_a as a result of the decline in fine roots biomass. The N addition led to microbial carbon limitation hence significantly decreased R_h, and thus R_s. We also observed the negative effect of throughfall reduction on R_s was exacerbated by N addition, which is attributed to the significant reduction in R_a under the interaction between throughfall reduction N addition. Our findings suggest that R_a tended to respond more sensitively to potential drought, while R_h responds more sensitively to N deposition, and consequently, increased soil N availability caused by N deposition might aggravate the negative effect of expected drought on soil carbon cycling.

Nitrogen (N) deposition has been well documented to cause substantial impacts on ecosystem carbon cycling. However, the majority studies of stimulating N deposition by direct N addition to forest floor have neglected some key ecological processes in forest canopy (e.g., N retention and absorption) and might not fully represent realistic atmospheric N deposition and its effects on ecosystem carbon cycling. In this study, we stimulated both canopy and understory N deposition (50 and 100 kg N ha⁻¹ year⁻¹) with a local atmospheric NH_x:NO_y ratio of 2.08:1, aiming to assess whether canopy and understory N deposition had similar effects on soil respiration (RS) and net ecosystem production (NEP) in Moso bamboo forests. Results showed that RS, soil autotrophic (RA), and heterotrophic respiration (RH) were 2971 ± 597, 1472 ± 579, and 1499 ± 56 g CO₂ m⁻² year⁻¹ for sites without N deposition (CN0), respectively. Canopy and understory N deposition did not significantly affect RS, RA, and RH, and the effects of canopy and understory N deposition on these soil fluxes were similar. NEP was 1940 ± 826 g CO₂ m⁻² year⁻¹ for CN0, which was a carbon sink, indicating that Moso bamboo forest the potential to play an important role alleviating global climate change. Meanwhile, the effects of canopy and understory N deposition on NEP were similar. These findings did not support the previous predictions postulating that understory N deposition would overestimate the effects of N deposition on carbon cycling. However, due to the limitation of short duration of N deposition, an increase in the duration of N deposition manipulation is urgent and essential to enhance our understanding of the role of canopy processes in ecosystem carbon fluxes in the future.