Ca²⁺ is a crucial second messenger in plant cells that plays a vital role in various physiological and biochemical processes, including plant growth and development, photosynthesis, and enzyme regulation. Exogenous calcium concentrations can have different effects on plant growth. The purpose of this study was to determine the appropriate calcium concentration for the growth of four tree seedlings, namely Pinus tabuliformis, Pinus sylvestris var. mongolica, Populus, and Morus alba seedlings, and whether this optimal calcium concentration varies among different tree species. This study utilized five calcium concentration gradients (0, 100, 200, 400, 800 mg·kg⁻¹) for each species with three repeated treatments. To determine each species’ calcium concentration needs, several growth indices, photosynthetic metrics, chlorophyll fluorescence parameters, water usage efficiency, and antioxidant enzyme activities were analyzed. The results showed that exogenous calcium significantly affected the growth and development of each seedling. The growth, biomass, photosynthetic parameters, photosynthetic products, photosynthetic pigments, water use efficiency, and antioxidant enzyme activity all increased initially and then decreased with the increasing calcium concentration. The exogenous calcium supply increased the concentration of calcium in the leaves. Thus, there was an optimal calcium concentration for plant growth, and a high or low calcium concentration was not conducive to plant growth. Furthermore, this study found that the optimum calcium concentration of different tree species was different. The optimal calcium concentration for Pinus tabuliformis, Pinus sylvestris var. mongolica, Populus, and Morus alba seedlings was 100, 100, 200, and 400 mg·kg⁻¹, respectively, with broadleaf seedlings requiring higher calcium concentrations than coniferous seedlings.

The concentrations of exogenous nitrogen and calcium can significantly regulate plant growth and photosynthesis and mutually affect their absorption and utilization. However, whether there is an optimal nitrogen–calcium ratio (N:Ca ratio) in poplar seedling growth and physiological adaptation and what the mechanism of changes in the transcriptome is remain unclear. In this study, three different N:Ca ratios were used to grow poplar seedlings, and physiological and transcriptomic methods were used to study the molecular mechanisms of poplar growth under nitrogen–calcium synergy and to determine the optimal N:Ca ratio for poplar seedling growth. The results of this study showed that maximum poplar seedling growth occurred in the treatment with an N:Ca ratio of 2, which resulted in significantly greater induction of growth than the two other treatments (p < 0.05). Under the lowest N:Ca ratio, poplar seedlings can ensure normal development by regulating photosynthesis, while under the highest N:Ca ratio, regulating nitrogen metabolism can achieve the same result. These results contribute to a better understanding of the molecular mechanisms by which poplar seedlings respond to different ratios of N:Ca. This study provides a valuable basis for exploring the synergistic effects of nitrogen and calcium on the growth of poplar shelterbelts.

Mongolian pine (Pinus sylvestris var. Mongolia) has been widely utilized as a key species for afforestation projects within the Three-North Shelterbelt of Liaoning Province in China. Its impressive ecological resilience has made it a favorite choice for this endeavor. However, as the stands mature and climate conditions shift, some areas are experiencing premature decline or even mortality. Ecological stoichiometry is capable of uncovering the supply and equilibrium of plant and soil nutrients within ecosystems and is extensively utilized in the identification of limiting elements. Therefore, studying its ecological stoichiometry and internal stability dynamics is of crucial significance for clarifying the nutrient cycling process in the Mongolian pine region and alleviating the decline situation. The eastern and northwestern regions of Liaoning differ significantly in precipitation and soil nutrient availability. This study examines Mongolian pine plantations in both regions, analyzing the carbon (C), nitrogen (N), and phosphorus (P) content in plant tissues, soil, microbial biomass, and stoichiometric ratio under distinct environmental conditions. In order to provide a theoretical basis for alleviating the decline of artificial poplar forests and healthy management. Results indicate that (1) leaf C, N, and P contents in the eastern Liaoning region averaged 496.67, 15.19, and 1.66 g·kg⁻¹, respectively, whereas those in northwestern Liaoning were 514.16, 14.82, and 1.23 g·kg⁻¹, respectively. Soil C, N, and P concentrations exhibited notable regional differences, with eastern Liaoning recording 34.54, 2.62, and 0.48 g·kg⁻¹, compared to significantly lower values in northwestern Liaoning (7.74, 0.77, and 0.21 g·kg⁻¹). Similarly, microbial biomass C, N, and P were higher in eastern Liaoning (18.63, 5.09, and 7.72 mg·kg⁻¹) than in northwestern Liaoning (10.18, 3.46, and 4.38 mg·kg⁻¹). (2) The stoichiometric ratio of soil in the Mongolian pine plantations is higher than that in northwestern Liaoning, but the stoichiometric ratio of plants shows the opposite trend. Specifically, microbial carbon-to-nitrogen (MBC/MBN) ratios are higher in eastern Liaoning, whereas microbial carbon-to-phosphorus (MBC/MBP) and nitrogen-to-phosphorus (MBN/MBP) ratios are greater in northwestern Liaoning. Correlation analysis of plant–soil–microbe stoichiometry indicates that plant growth in both regions is co-limited by nitrogen, with Mongolian pine exhibiting strong internal stability.

Calcium is an essential macronutrient for plant growth and development, and there is an optimal calcium concentration for plant growth. Calcium ion concentration changes create “calcium signals” that regulate plant growth through perception, decoding, transduction, and response processes. However, the mechanisms by which calcium signaling regulates photosynthesis are still not fully understood. In this study, Quercus acutissima seedlings were used to investigate the inhibitory effects of different concentrations of the calcium channel blocker lanthanum chloride (LaCl₃) on photosynthesis and the underlying mechanisms. The results show that increasing LaCl₃ concentration significantly decreased photosynthetic parameters, photosynthetic pigment contents, and photosynthetic product accumulation. Long-term water use efficiency decreased with increasing LaCl₃ concentration, while instantaneous water use efficiency initially increased and then decreased. Structural equation modeling analysis indicated that LaCl₃ concentration was significantly positively correlated with leaf calcium concentration in Quercus acutissima seedlings, while it was significantly negatively correlated with stomatal conductance, carotenoids, and soluble sugar content. The study concludes that LaCl₃ directly inhibits the photosynthetic physiological processes of Quercus acutissima seedlings by blocking calcium signaling, providing insights into the regulatory mechanisms of calcium signaling in plant photosynthesis and a theoretical basis for the cultivation and application of Quercus acutissima under varying environmental conditions.

Nitrogen and calcium are the key elements required for plant growth. Variations in calcium concentration will affect nitrogen absorption in plants, regulate photosynthetic processes, and participate in the absorption and transport of photosynthetic products. The changes of nitrogen and calcium nutrients is conducive to alleviating the decline and mortality of Mongolian pine forests, thus contributing to the preservation of regional ecological security. In this study, an investigation was conducted into the effects of seven nitrogen-to-calcium (N-Ca) ratios (1:8, 1:4, 1:2, 1:1, 2:1, 4:1, and 8:1) on the growth and physiology of Mongolian pine seedlings through pot experiments. The results of the one-way analysis of variance indicated that variations in the N-Ca ratio could significantly affect processes such as plant height, basal diameter, biomass accumulation, and photosynthesis in Mongolian pine seedlings. A low N-Ca ratio caused calcium toxicity, resulting in reduced stomatal conductance (C_i) and a lower net photosynthetic rate (T_r). Conversely, a high N-Ca ratio led to nitrogen toxicity, decreased antioxidant enzyme activity, and adversely affected the accumulation of photosynthetic pigments and photosynthetic products. At an N-Ca ratio of 2:1, Mongolian pine seedlings not only exhibited maximized biomass and photosynthetic capacity but also demonstrated significantly elevated levels of antioxidant enzymes and content of soluble substances. In conclusion, an optimal N-Ca ratio of 2:1 existed for Mongolian pine seedlings, which significantly improved their growth and physiological characteristics.