Effects of exogenous glycine betaine on growth and development of tomato seedlings under cold stress.

Low temperature is a type of abiotic stress affecting the tomato (Solanum lycopersicum) growth. Understanding the mechanisms and utilization of exogenous substances underlying plant tolerance to cold stress would lay the foundation for improving temperature resilience in this important crop. Our study is aiming to investigate the effect of exogenous glycine betaine (GB) on tomato seedlings to increase tolerance to low temperatures. By treating tomato seedlings with exogenous GB under low temperature stress, we found that 30 mmol/L exogenous GB can significantly improve the cold tolerance of tomato seedlings. Exogenous GB can influence the enzyme activity of antioxidant defense system and ROS levels in tomato leaves. The seedlings with GB treatment presented higher Fv/Fm value and photochemical activity under cold stress compared with the control. Moreover, analysis of high-throughput plant phenotyping of tomato seedlings also supported that exogenous GB can protect the photosynthetic system of tomato seedlings under cold stress. In addition, we proved that exogenous GB significantly increased the content of endogenous abscisic acid (ABA) and decreased endogenous gibberellin (GA) levels, which protected tomatoes from low temperatures. Meanwhile, transcriptional analysis showed that GB regulated the expression of genes involved in antioxidant capacity, calcium signaling, photosynthesis activity, energy metabolism-related and low temperature pathway-related genes in tomato plants. In conclusion, our findings indicated that exogenous GB, as a cryoprotectant, can enhance plant tolerance to low temperature by improving the antioxidant system, photosynthetic system, hormone signaling, and cold response pathway and so on.

Estimating the frost damage index in lettuce using UAV-based RGB and multispectral images.

Introduction: The cold stress is one of the most important factors for affecting production throughout year, so effectively evaluating frost damage is great significant to the determination of the frost tolerance in lettuce. Methods: We proposed a high-throughput method to estimate lettuce FDI based on remote sensing. Red-Green-Blue (RGB) and multispectral images of open-field lettuce suffered from frost damage were captured by Unmanned Aerial Vehicle platform. Pearson correlation analysis was employed to select FDI-sensitive features from RGB and multispectral images. Then the models were established for different FDI-sensitive features based on sensor types and different groups according to lettuce colors using multiple linear regression, support vector machine and neural network algorithms, respectively. Results and discussion: Digital number of blue and red channels, spectral reflectance at blue, red and near-infrared bands as well as six vegetation indexes (VIs) were found to be significantly related to the FDI of all lettuce groups. The high sensitivity of four modified VIs to frost damage of all lettuce groups was confirmed. The average accuracy of models were improved by 3% to 14% through a combination of multisource features. Color of lettuce had a certain impact on the monitoring of frost damage by FDI prediction models, because the accuracy of models based on green lettuce group were generally higher. The MULTISURCE-GREEN-NN model with R2 of 0.715 and RMSE of 0.014 had the best performance, providing a high-throughput and efficient technical tool for frost damage investigation which will assist the identification of cold-resistant green lettuce germplasm and related breeding.

Stochastic processes drive bacterial and fungal community assembly in sustainable intensive agricultural soils of Shanghai, China.

Sustainable intensive cropping systems have been implemented for three decades in suburban agricultural districts of Shanghai, China. These human-managed soils have been developed from paleosol or alluvial soils across different regions. However, little is known about the geographical distribution patterns of microbes and microbial community assembly in the sustainable intensive soils after decades of anthropogenic disturbances. Here, we investigated the impact of local geochemical properties and geographic distance on stochastic/deterministic microbial community assembly processes using high-throughput sequencing and phylogenetic null modeling analysis. Our results showed that soil pH was the most important environmental factor determining bacterial and fungal community structure. Importantly, only soil organic matter was positively correlated with fungal α-diversity, suggesting the efficient use of carbon substrates in sustainable agricultural systems, compensating for the lack of chemical fertilization and reduced tillage in these systems. Both bacterial and fungal communities had robust distance-decay patterns, but the rate of turnover of bacterial taxa was faster than that of fungi. Variation in bacterial and fungal communities was mostly attributed to the simultaneous effects of environmental variables and spatial factors. We also mapped the spatial distributions of the dominant bacterial and fungal taxa across the sustainable agricultural fields, making it possible to forecast the responses of agricultural ecosystems to anthropogenic disturbance. Based on the patterns of the ß-nearest taxon index, this study demonstrated that stochastic processes shaped substantial bacterial and fungal community variation in sustainable intensive agricultural soils of the Shanghai suburbs. This variation may be attributed to the increasing microbial dispersal caused by hydrological connectivity in the agricultural fields or the release from environmental stress and weakened environmental filtering across the suitable pH range preferable for most soil microbes. These results unveil assembly mechanisms of soil microbial community after several decades of sustainable intensive management, and contribute to understand the role of microbes in ecosystems in establishing a functional equilibrium which may enable sustainability to be preserved.