Kandelia obovata (Rhizophoraceae) is the most cold-tolerant mangrove species and has been widely used in coastal wetland ecological restoration due to its specific viviparous phenomenon, beautiful shape, and unique floral pattern. Due to long-term adaptation to their local environment, the phenotypic characteristics and stress resistance of widely distributed plants of the same species often differentiate across different locations. The capacity for cold resistance is closely linked to the physiological and structural characteristics of plants. Herein, we explored the temporal variations in the leaf structure and physiological status of K. obovata under −5.5 °C from different areas such as Jiulongjiang Estuary (JLJ, 24°25′ N), Fujian Province, and Longgang City (LG, 27°34′ N) and Jiaojiang District (JJ, 28°67′ N), Zhejiang Province. The morphological variations implied that the cold resistance of K. obovata obviously strengthened after the northward migration and acclimatization, in the following order: LG > JJ > JLJ. More specifically, after exposure to a sustained low temperature, the relative conductivity (REC), an index widely used to evaluate the degree of plant damage, remarkably increased from 33.62 ± 2.39 to 63.73 ± 3.81, 31.20 ± 1.63 to 49.48 ± 1.12, and 23.75 ± 0.13 to 54.24 ± 1.45 for JLJ, LG, and JJ, respectively (p < 0.05). Additionally, the palisade-to-spongy tissue ratio (P/I) of JLJ and JJ decreased from 0.78 ± 0.05 and 0.75 ± 0.03 to 0.5 ± 0.04 and 0.64 ± 0.02 (p < 0.05), whereas no significant changes were found in LG (p > 0.05). The SOD activity of LG significantly kept increasing, with values increased from 352.49 ± 10.38 to 477.65 ± 1.78 U·g⁻¹, whereas no apparent changes in JLJ and JJ were observed with the sustained low temperature. The results of this study improved our understanding of the response of K. obovata to freezing stress, which could provide a sound theoretical foundation for cultivating cold-resistant varieties, as well as expanding mangrove plantations in higher latitudes.

Mangrove ecosystems rank among the most productive on Earth. Conducting research on the biomass prediction model of mangroves, as well as achieving simple and efficient estimations of the biomass of mangrove plant organs and the overall biomass, is of utmost significance for evaluating the productivity of the mangrove ecosystem and offering guidance for the future planning, restoration, and management of mangroves. This study examines the biomass distribution characteristics of Kandelia obovata at the northern edge of its range in China and develops models for estimating the biomass of its various components and individual trees. The findings provide valuable references for accurately assessing the biomass of Kandelia obovata plantations in Zhejiang Province. We measured the biomass of different components (branches, leaves, roots) using the harvest method and employed independent variables, including basal diameter (D), tree height (H), diameter squared (D²), the product of diameter squared and height (D²H), and the product of basal diameter and height (DH). Dependent variables included the leaf, branch, root, and total biomass. We developed linear, quadratic, and power function regression equations, selecting the optimal models based on the coefficient of determination (R²), significance of regression, root mean square error (RMSE), and Akaike Information Criterion (AIC). The total biomass ranged from 0.100 to 0.925 Mg ha⁻¹, while the carbon stocks ranged from 0.038 to 0.377 Mg C ha⁻¹. Results indicated that branch biomass accounted for the highest proportion (47.44%~68.35%), while leaf biomass (8.61%~27.83%) and root biomass (23.04%~25.64%) were relatively lower. Similarly, branch carbon storage constituted the highest proportion (52.68%~77.79%), with leaf (8.70%~29.36%) and root carbon storage (13.51%~20.55%) being lower. The optimal model exhibited R² values ranging from 0.594 to 0.921 and significant F-tests (p < 0.001). Single variables D, D², and combined variables D²H and DH provided the best fits. Basal diameter (D) and tree height (H) effectively predict the biomass of Kandelia obovata across different ages, with combined variables DH and D²H enhancing model accuracy. The biomass estimation model for total biomass is: W_Total = 0.0584(DH)^1.3918 (R² = 0.908, F = 2459.87, RMSE = 0.448). This model serves as a reliable tool for estimating the biomass of Kandelia obovata mangroves at the northern edge of its distribution in China.

Valuable trees are frequently taken from their original habitat and introduced to a different location in the pursuit of better economic development. Global climate change imposes a higher probability of warm spells during chilly seasons; these may increase the threat posed by frost to newly introduced, valuable species. In this study, Dalbergia odorifera was cultured as a valuable tree species that was introduced from an original provenance in Sanya (1° N) to the northern mountains in Pingxiang (22° N), Guangzhou (23° N), Zhangpu (24° N), Xianyou (25° N), and up to the northernmost limit in Wenzhou (28° N). Seedlings of these six provenances were tested in a field study conducted in Wenzhou (control) to examine their resistance to local frost stress and to detect the driving forces related to meteorological factors in the winter–spring period of 2015–2016. The leaves sampled over seven days exhibited the typical characteristics of frost impairment. The daily maximum temperature delivered warm spells, increasing by ~7 °C. The daily minimum temperature (−4.3 to −2.0 °C) did not reach freezing point until the early spring of 2016. The controlled seedlings showed lower malondialdehyde content than those from the southern locations, and no mortality occurred. Invisible frost stress was caused by low nitrogen utilization during the earlier stages during warm spells, as well as damage to membrane integrity during the later stage when the minimum temperature suddenly declined. A warm spell was found to impose a negative driving force five days before a sudden chill, which led to frost having an impact on superoxide accumulation and electrical leakage. We conclude that the D. odorifera seedlings that dwell effectively in Wenzhou obtained stronger resistance to local frost stress than those from the southern locations. Low cell membrane integrity and high electrical leakage in leaf cells accounted for the frost damage.