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Dendrobium officinale, endemic to China, is a rare and endangered medicinal herb. As a result of its high economic value, slow growth, and diminishing wild population, protected cultivation is preferred. However, little information is available on its growing environment and photosynthetic characteristics. In this study, the photosynthetic patterns of D. officinale were investigated under various environmental conditions by measuring the net CO2 exchange rates continuously for several days or weeks. Under non-stressed growth chamber conditions with 12-hour light and 12-hour dark periods, D. officinale had concomitance of C3 and crassulacean acid metabolism (CAM) photosynthesis patterns. Different degrees of CAM in D. officinale, expressed as the percentage of CO2 exchanges in the dark period to the daily amount of CO2 exchanges, were observed depending on environmental conditions. With decreasing substrate water content, a typical CAM pattern was found, and concomitance of C3 and CAM patterns was found again when plants were rewatered. The accumulation of leaf titratable acidity during a dark period increased as substrate dried out but decreased again as plants were rewatered. A shorter light–dark cycle (4-hour light and 4-hour dark periods) led to a C3 pattern alone. The substrate moisture and light–dark cycle were inducible factors for switching between C3 and CAM patterns in D. officinale. These results indicate that D. officinale is a facultative CAM plant and the C3 pathway can be induced by controlling the growing environment. Further studies are needed to identify the optimal environmental conditions to enhance the growth of D. officinale.

Microbial abundance and diversity in river ecosystems are being increasingly investigated, yet a synthesized understanding is still lacking. Here, studies of microbial abundance and diversity along global rivers are systematically reviewed based on 814 investigations performed across 8376 sites. We found that riverine microbial investigations are extremely heterogeneous regarding the spatiotemporal distribution of the sampling sites, the environmental media concerned, the microbial groups and indices targeted, the methods used, and the physicochemical properties examined. More than 72.23% of the studies were performed in the last 8 years, with most studies conducted in Europe, China, and the United States, while other regions were poorly investigated. Most studies have examined microbes in water, but very few studies have systematically investigated microbes in water, sediments, and riparian soils. Bacteria are the most studied microbial taxonomic groups; microbes with resistance genes and nitrogen cycling genes are the most studied microbial functional groups.High-throughput sequencing has greatly expanded our understanding of microbial diversity along rivers. Nevertheless, the ecological implications of microbial diversity are still poorly understood. Regarding physicochemical properties, researchers tend to examine environmental parameters that are critical for shaping microbial communities, such as pH, nitrogen, and phosphorus. Future research should pay more attention to rivers that have not been well studied, especially large rivers. Additionally, microbial studies along rivers should be conducted in a more systematic way, taking the underinvestigated environmental media, microbial groups, microbial indices, and physicochemical properties into consideration. Advanced microbiology techniques, such as multiple omics technologies, should be increasingly applied.