Changes in forest stand structure may alter the activity of invertase, urease, catalase and phenol oxidase after thinning Pinus tabuliformis (Carriére) plantations in Yanqing County of Beijing, China. We examined changes in these soil enzymes as influenced by time since thinning (24, 32, and 40 years since thinning) for 3 seasons (spring, summer and autumn) following harvesting at two depths in the mineral soil (0-10 cm and 10-20 cm). Invertase and urease increased significantly with time since thinning. Catalase activity was highest in the 24-year-old stand and there were no statistically significant differences between the 32-and 40-year-old stands. In addition, maximum invertase, urease, catalase, and phenol oxidase activities occurred during the summer; minimum activities occurred in autumn. Invertase and urease were positively correlated with each other, as were catalase and phenol oxidase. Most soil enzyme activity was higher in the 0-10 cm layer than at the 10-20 cm depth. As time from thinning increased, differences among soil depth became less significant. These results suggest that seasonal changes of these enzymes have different roles, as the time since thinning and thinning treatments may have both short-and long-term impacts on soil microbial activity.

Green photosynthetic stems are often responsible for photosynthesis due to the reduction of leaves in arid and hot climates. We studied the response of PSII activity to high irradiance in the photosynthetic stems of Hexinia polydichotoma in the Taklimakan Desert by analysis of the fast fluorescence transients (OJIP). Leaf clips of a chlorophyll fluorometer were used in conjunction with a sponge with a 4-mm-width groove to prevent light leakage for precise in vivo measurements. High irradiance reduced performance indices, illustrating the photoinhibition of PSII to some extent. However, the decrease in active reaction centers (RC) per PSII absorption area and maximum quantum yield indicated a partial inactivation of RCs and an increase in excitation energy dissipation, resulting in downregulation of photosynthetic excitation pressure. In addition, the increased efficiency of electron transport to PSI acceptors alleviated overexcitation energy pressure on PSII. These mechanisms protected the PSII apparatus as well as PSI against damages from excessive excitation energy. We suggested that H. polydichotoma exhibited rather photoadaptation than photodamage when exposed to high irradiance during the summer in the Taklimakan Desert. The experiment also demonstrated that the modified leaf clip can be used for studying dark adaptation in a photosynthetic stem.

Populus euphratica is the only tall tree species that adapts to the desert environment. It has strong drought tolerance and is the subject of extreme concern at home and abroad. After 30 years of development, the scope of research on Populus euphratica is very extensive, but the research content has not yet been crystalized into a mature field, and research directions at home and abroad differ. In this study, we retrieved research references on ‘P. euphratica’ published from 1992 to 2022 in both the China National Knowledge Infrastructure core journals database and the Web of Science core collection database, and CiteSpace software was employed to conduct keyword-centered bibliometric analysis in both the spatial and temporal dimensions. The purpose of this study is to clarify the research areas, developmental changes, differences between domestic and international research priorities in the last 30 years, and future trends in the field of P. euphratica research. The results show that there were 1619 domestic papers published in China related to the field of P. euphratica research, while there were only 656 foreign papers in the same field. The development of domestic P. euphratica research went through three stages initiation (1992–2000), growth (2001–2008) and stability (2009–2021), whereas no significant international trend change was observed. The domestic disciplines focus on biology, while international research focuses on crop science. In terms of content, domestic research focuses on sustainable uses of P. euphratica forests and their response to drought, intending to improve P. euphratica ecosystems. International research, on the other hand, focuses on revealing mechanisms of environmental stresses, including genetic and physiological–morphological characteristics, to exploit the excellent characteristics of P. euphratica to serve agriculture and other fields. The development process of P. euphratica research in the past 30 years has generally evolved from an initial focus on its natural conditions towards the study of the relationship between environmental factors and P. euphratica physiological and morphological characteristics and, finally, the study of stress tolerance mechanisms and gene expression of P. euphratica. There is a trend towards ‘applications of P. euphratica tolerance genes’, which may represent a direction for future growth research.