Drought affects the fate of non-structural carbohydrates in hinoki cypress

Drought responses and carbon allocation strategies of poplar with different leaf maturity

Leaf characteristics can reflect the adaptation of trees to drought stress. However, the effect of leaf maturity on drought stress has been neglected, leading to uncertainty in inferring individual tree responses to drought from leaves. The allocation strategy of photosynthetic carbon between leaf organs (fully expanded young and old leaves) under drought stress remains unclear. Poplar is a diverse and widespread tree species in arid and semi-arid regions. Here, three poplar genotypes (Populus cathayana, P. × euramericana 'Nanlin 895', and P. alba × P. tremula var. glandulosa) were selected and exposed to different watering regimes. The responses and carbon allocation strategies of leaves with different maturity to drought were investigated using a combination of leaf traits and 13 C pulse labelling technique. The results showed that (1) fully expanded young leaves had better osmotic regulation and antioxidant capacity than aged leaves under drought stress. (2) Aged leaves acted as a carbon source during water deficit, where their photosynthetic products were transferred and supplied to upper young leaves to promote stronger photosynthesis in young leaves to acquire resources for tree growth. This study highlights that the effect of leaf maturity should be considered in the future when investigating the effects of drought on woody plants, especially for continuously growing tree species. Therefore, our study not only demonstrates the existence of leaf-age-dependent responses to drought in poplar but also provides new insights into carbon allocation at the leaf level.

Effect of Ectomycorrhizal Fungi on the Drought Resistance of Pinus massoniana Seedlings

Studies on the dynamics of non-structural carbohydrates (NSCs) play an important role in understanding the mechanisms of plant responses to drought stress. The objective of this study was to assess the influence of ectomycorrhizal fungi (ECMF) on the content and distribution of NSCs in Pinus massoniana seedlings under different drought intensities and to further explore the possible mechanism by which ECMF enhances the stress resistance of host plants. We conducted a pot experiment using P. massoniana seedlings that were inoculated (M) or non-inoculated (NM) with Suillus luteus (Sl) under well-watered, moderate, and severe drought stress conditions. The results showed that drought significantly reduced the photosynthetic capacity of P. massoniana seedlings and inhibited their growth rate. P. massoniana could respond to different degrees of drought stress by increasing the accumulation of NSCs and increasing WUE. However, compared with well-watered treatment, NSCs consumption began to appear in the roots of NM due to the decrease in starch content under severe drought, whereas NSCs content in M seedlings was higher than that in the well-watered treatment, showing that the ability to maintain C balance was higher in M seedlings. Compared with NM, inoculation with Sl increased the growth rate and biomass of roots, stems, and leaves under moderate and severe drought. In addition, Sl can also improve the gas exchange parameters (net photosynthetic rate, transpiration rate, intercellular CO₂ concentration and stomatal conductance) of P. massoniana seedlings compared with NM seedlings, which was conducive to the hydraulic regulation of seedlings and improved their C fixation capacity. Meanwhile, the content of NSCs in M seedlings was higher. Moreover, the soluble sugar content and SS/St ratio of leaves, roots, and whole plants were higher under drought stress after Sl inoculation, indicating that Sl could also change the C distribution mode, regulate more soluble sugar to respond to drought stress, which was conducive to improving the osmotic adjustment ability of seedlings, and providing more available C sources for plant growth and defense. Overall, inoculation with Sl could enhance the drought resistance of seedlings and promote their growth under drought stress by improving NSCs storage, increasing soluble sugar distribution, and improving the plant water balance of P. massoniana seedlings.