Photosynthesis in Response to Different Salinities and Immersions of Two Native Rhizophoraceae Mangroves

Exploring the spatio-temporal patterns of global mangrove gross primary production and quantifying the factors affecting its estimation, 1996-2020

Mangrove ecosystems, as an important component of "Blue Carbon", play a curial role on global carbon cycling; however, the lack of the global estimates of mangrove ecosystem gross primary production (GPP) and the underlying environmental controls on its estimation remain a gap in knowledge. In this study, we utilized global mangrove eddy covariance data and applied Gaussian Process Regression (GPR) to estimate GPP for global mangrove ecosystems, aiming to elucidate the factors influencing these estimates. The optimal GPR achieved favorable estimation performance through cross-validation (R2 = 0.90, RMSE = 0.92 gC/m2/day, WI = 0.86). Over the study period, the globally annual averaged GPP was 2054.53 ± 38.51 gC/m2/yr (comparable to that of evergreen broadleaf forests and exceeds the GPP of most other plant function types), amounting to a total of 304.82 ± 7.71TgC/yr, hotspots exceeding 3000 gC/m2/yr observed near the equator. The analysis revealed a decline in global mangrove GPP during 1996-2020 of -0.89 TgC/yr. Human activities (changes in mangrove cover area) played a relatively consistent role in contributing to this decrease. Conversely, variations in external environmental conditions showed distinct inter-annual differences in their impact. The spatio-temporal distribution patterns of mangrove ecosystems GPP (e.g., the bimodal annual pattern, latitudinal gradients, etc.) demonstrated the regulatory influence of external environmental conditions on GPP estimates. The model ensemble attribution analysis indicated that the fraction of absorbed photosynthetically active radiation exerted the dominant control on GPP estimations, while temperature, salinity, and humidity acted as secondary constraints. The findings of this study provide valuable insights for monitoring, modeling, and managing mangrove ecosystems GPP; and underscore the critical role of mangroves in global carbon sequestration. By quantifying the influences of environmental factors, we enhance our understanding of mangrove carbon cycling estimates, thereby helping sustain of these disproportionately productive ecosystems.

Understanding plant responses to saline waterlogging: insights from halophytes and implications for crop tolerance

MAIN CONCLUSION

Saline and wet environments stress most plants, reducing growth and yield. Halophytes adapt with ion regulation, energy maintenance, and antioxidants. Understanding these mechanisms aids in breeding resilient crops for climate change. Waterlogging and salinity are two abiotic stresses that have a major negative impact on crop growth and yield. These conditions cause osmotic, ionic, and oxidative stress, as well as energy deprivation, thus impairing plant growth and development. Although few crop species can tolerate the combination of salinity and waterlogging, halophytes are plant species that exhibit high tolerance to these conditions due to their morphological, anatomical, and metabolic adaptations. In this review, we discuss the main mechanisms employed by plants exposed to saline waterlogging, intending to understand the mechanistic basis of their ion homeostasis. We summarize the knowledge of transporters and channels involved in ion accumulation and exclusion, and how they are modulated to prevent cytosolic toxicity. In addition, we discuss how reactive oxygen species production and cell signaling enhance ion transport and aerenchyma formation, and how plants exposed to saline waterlogging can control oxidative stress. We also address the morphological and anatomical modifications that plants undergo in response to combined stress, including aerenchyma formation, root porosity, and other traits that help to mitigate stress. Furthermore, we discuss the peculiarities of halophyte plants and their features that can be leveraged to improve crop yields in areas prone to saline waterlogging. This review provides valuable insights into the mechanisms of plant adaptation to saline waterlogging thus paving the path for future research on crop breeding and management strategies.

Protective Effects of Sodium Nitroprusside on Photosynthetic Performance of Sorghum bicolor L. under Salt Stress

In this study, the impacts of the foliar application of different sodium nitroprusside (SNP, as a donor of nitric oxide) concentrations (0-300 µM) on two sorghum varieties (Sorghum bicolor L. Albanus and Sorghum bicolor L. Shamal) under salt stress (150 mM NaCl) were investigated. The data revealed that salinity leads to an increase in oxidative stress markers and damage of the membrane integrity, accompanied by a decrease in the chlorophyll content, the open photosystem II (PSII) centers, and the performance indexes (PI _ABS and PI _total), as well as having an influence on the electron flux reducing photosystem I (PSI) end acceptors (REo/RC). Spraying with SNP alleviated the NaCl toxicity on the photosynthetic functions; the protection was concentration-dependent, and greater in Shamal than in Albanus, i.e., variety specific. Furthermore, the experimental results revealed that the degree of SNP protection under salt stress also depends on the endogenous nitric oxide (NO) amount in leaves, the number of active reaction centers per PSII antenna chlorophylls, the enhanced electron flux reducing end acceptors at the acceptor side of PSI, as well as the stimulation of the cyclic electron transport around PSI. The results showed better protection in both varieties of sorghum for SNP concentrations up to 150 µM, which corresponds to about a 50% increase in the endogenous NO leaf content in comparison to the control plants. Our study provides valuable insight into the molecular mechanisms underlying SNP-induced salt tolerance in sorghum varieties and might be a practical approach to correcting salt intolerance.