Search

Despite their relatively small numbers, large old trees play disproportionately important roles in global biodiversity and ecosystem functions. There is a lack of systematic reviews and quantitative analyses of the accumulated literature. Understanding the research context and evolution could pump prime research and conservation endeavors. Using the comprehensive Web of Science, we applied VOSviewer (1.6.19) and CiteSpace (6.1R2) bibliometric software to examine the large old tree research field in 2000–2022. The queries of the bibliographic database generated quantitative–visual depictions in the form of knowledge maps. The nodes denote research intensity, and inter-node linkages denote the pathways and frequencies of collaborative activities. The research outputs differed significantly in terms of regions, countries, institutions, high-citation articles, productive researchers, hot topics, and research frontiers. Conspicuous spatial disparities were displayed, with the U.S.A., China, and Australia leading in publication counts and a cluster of European countries making considerable collective contributions. The research collaboration demonstrated a dichotomy: European countries networked more by geographical propinquity, and the top three countries connected by long-distance leap-frog jumps. The entrenched discrepancies between the endowed developed domains vis-à-vis the deprived developing domains were clearly expressed. The research productivity progressed through three stages: initial, growth, and flourishing. The leading institutions, researchers, and highly cited papers were recognized. The keyword analysis pinpointed diverse research hotspots: growth dynamics, conservation and management, ecological functions, and environmental response. This study informs recommendations for future research directions and cooperation on longevity mechanisms, evolutionary adaptation, dynamic monitoring, and temporal–spatial patterns. The integrated application of GIS, machine learning, and big data technologies could strengthen research capability. [ABSTRACT FROM AUTHOR]

Drought is one of the main environmental factors affecting crop growth, and breeding drought-tolerant cultivars is one of the most economic and effective ways of increasing yields and ensuring sustainable agricultural production under drought stress. To facilitate the breeding of drought-tolerant wheat, this study was conducted to evaluate genotypic differences in the drought tolerance of 334 wheat genotypes collected from China and Australia with the aim of screening for drought-tolerant and -sensitive genotypes and to elucidate the corresponding physiological mechanisms. A hydroponic-air experiment (roots exposed to air for 7 h/d and continued for 6 d) showed significant genotypic differences in shoot and root dry weights among the genotypes. The relative shoot and root dry weights, expressed as the percentage of the control, showed a normal distribution, with variation ranges of 20.2–79.7% and 32.8–135.2%, respectively. The coefficients of variation were in the range of 18.2–22.7%, and the diversity index was between 5.71 and 5.73, indicating a rich genetic diversity among the wheat genotypes for drought tolerance. Using phenotypic differences in relative dry weights in responses to drought stress, 20 of each of the most drought-tolerant and drought-sensitive genotypes were selected; these were further evaluated in pot experiments (watering withheld until the soil moisture content reached four percent). The results showed that the trends in drought tolerance were consistent with the hydroponic-air experiment, with genotypes W147 and W235 being the most drought-tolerant and W201 and W282 the most sensitive. Significant genotypic differences in water use efficiency in response to drought were observed in the pot experiment, with the drought-tolerant genotypes being markedly higher and the two sensitive genotypes being no different from the control. A marked increase in bound water content in the drought stress plants was observed in the two drought-tolerant genotypes, while a decrease occurred in the free water. The reductions in photochemical efficiencies of PSII, transpiration rates, net photosynthesis rates, chlorophyll contents and stomatal conduction in the drought-sensitive genotypes W201 and W282 under drought stress were higher than the two tolerant genotypes. This study provides a theoretical guide and germplasm for the further genetic improvement of drought tolerance in wheat. [ABSTRACT FROM AUTHOR]