Mineral accumulation in plants under drought stress is essential for drought tolerance. The distribution, survival, and growth of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.), an evergreen conifer, can be affected by climate change, particularly seasonal precipitation and drought. Hence, we designed a drought pot experiment, using 1-year-old Chinese fir plantlets, to evaluate drought effects under simulated mild drought, moderate drought, and severe drought, which corresponds to 60%, 50%, and 40% of soil field maximum moisture capacity, respectively. A treatment of 80% of soil field maximum moisture capacity was used as control. Effects of drought stress on mineral uptake, accumulation, and distribution in Chinese fir organs were determined under different drought stress regimes for 0–45 days. Severe drought stress significantly increased phosphorous (P) and potassium (K) uptake at 15, 30 and 45 days, respectively, within fine (diameter < 2 mm), moderate (diameter 2–5 mm), and large (diameter 5–10 mm) roots. Drought stress decreased magnesium (Mg) and manganese (Mn) uptake by fine roots and increased iron (Fe) uptake in fine and moderate roots but decreased Fe uptake in large roots. Severe drought stress increased P, K, calcium (Ca), Fe, sodium (Na), and aluminum (Al) accumulation in leaves after 45 days and increased Mg and Mn accumulation after 15 days. In stems, severe drought stress increased P, K, Ca, Fe, and Al in the phloem, and P, K, Mg, Na, and Al in the xylem. In branches, P, K, Ca, Fe, and Al concentrations increased in the phloem, and P, Mg, and Mn concentrations increased in the xylem under severe drought stress. Taken together, plants develop strategies to alleviate the adverse effects of drought stress, such as promoting the accumulation of P and K in most organs, regulating minerals concentration in the phloem and xylem, to prevent the occurrence of xylem embolism. The important roles of minerals in response to drought stress should be further evaluated.

The Chinese fir Cunninghamia lanceolata (Lamb.) Hook. is an important timber conifer species in China. Much has been studied about Chinese fir, but the distribution of non-structural carbohydrates (NSCs) among different organs (needles, branch, stem, and roots) under drought stress remains poorly understood. In this study, we used one-year-old C. lanceolata plantlets to evaluate the effects of simulated drought under four water regimes, i.e., adequate water or control, light drought, moderate drought, and severe drought stress corresponding to 80%, 60%, 50%, and 40%, respectively of soil field maximum capacity on various NSCs in the needles, branch, stem and roots. The degree and duration of drought stress had significant effects on fructose, glucose, sucrose, soluble sugar, starch, and NSC content in various organs (p < 0.05). Fructose content increased in stem xylem, stem phloem, and leaves. Glucose and sucrose content declined in stem and branch xylem under light drought stress and moderate drought stress, and increased under severe drought stress conditions. Soluble sugars content declined, and starch content increased in leaf and branch phloem, but the latter could not compensate for soluble sugar consumption in the whole plant, and therefore, total NSCs decreased. Correlation analysis showed that a significant positive correlation existed in the soluble sugar content between leaves and roots, and between xylem and phloem in the stems and branches. Chinese fir appears to have different NSCs distribution strategies in response to drought stress, viz., allocating more soluble sugars to fine roots and increasing starch content in the needles, as well as ensuring osmosis to prevent xylem embolism. Our study may broaden the understanding of the various mechanisms that Chinese fir and other plants have to enhance their tolerance to drought stress.

Chinese fir (Cunninghamia lanceolata) is the most cultivated timber species in China, with a plantation area of 11 million ha. Due to its extensive geographical distribution, drought stress caused by the spatial and seasonal heterogeneity of precipitation has limited its survival and productivity. To facilitate the breeding of drought-tolerant clones and understand the inter-response mechanisms to drought stress, we screened two drought-tolerant (DT) clones and evaluated their differences in physiological and molecular response to drought. The results showed that the No. 228 clone (high-DT ability) had higher antioxidant enzyme abilities than the No. 026 clone (low-DT ability) under drought stress, e.g., peroxidase (POD), polyphenol oxidase (PPO), superoxide dismutase (SOD), and catalase (CAT). Transcriptome analyses revealed that 6637 genes and 1168 genes were up-regulated in No. 228 and No. 026 under drought stress, respectively, when compared to the control (CK). The genes may participate in response to drought-stimulated signal transduction, water/oxygen-containing compound synthesis, photosynthesis, and transmembrane transport functions. Particularly, under drought stress, 14,213 up-regulated and differentially expressed genes (DEGs) were observed in the No. 228 clone compared with the No. 026 clone, and 4274 up-regulated genes were differentially expressed (15-fold difference). These significant DEGs were involved in plant hormone signal transduction, flavonoid biosynthesis, peroxisomes, and other key pathways related to drought. Interestingly, under drought stress, two Chitinases (ClCHIs) and four POD genes (ClPERs) were induced to express in No. 228, which was consistent with the higher antioxidant enzyme activities in No. 228. A heat map of 49 DEGs revealed that dehydrin family genes, ion binding/transmembrane proteins, auxin receptor proteins, and ethylene-responsive transcription factors were significantly up-regulated under drought stress. The results can enhance our understanding of drought tolerance mechanisms and provide a guideline for screening DT genes and breeding drought-tolerant Chinese fir clones.