N-P utilization of Acer mono leaves at different life history stages across altitudinal gradients

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.

Environmental drivers of the leaf nitrogen and phosphorus stoichiometry characteristics of critically endangered Acer catalpifolium

Acer catalpifolium is a perennial deciduous broad-leaved woody plant, listed in the second-class protection program in China mainly distributed on the northwest edge of Chengdu plain. However, extensive anthropogenic disturbances and pollutants emissions (such as SO₂, NH₃ and NO_X) in this area have created a heterogeneous habitat for this species and its impacts have not been systematically studied. In this study, we investigated the leaf nitrogen (N) and phosphorus (P) content of A. catalpifolium in the natural distribution areas, and a series of simulation experiments (e.g., various water and light supply regimes, different acid and N deposition levels, reintroduction management) were conducted to analyze responses of N and P stoichiometric characteristics to environmental changes. The results showed that leaf nitrogen content (LNC) was 14.49 ~ 25.44 mg g^-1, leaf phosphorus content (LPC) was 1.29~3.81 mg g^-1 and the N/P ratio of the leaf (L-N/P) was 4.87~13.93. As per the simulation experiments, LNC of A. catalpifolium is found to be relatively high at strong light conditions (80% of full light), high N deposition (100 and 150 kg N ha^-1), low acidity rainwater, reintroduction to understory area or N fertilizer applications. A high level of LPC was found when applied with 80% of full light and moderate N deposition (100 kg N ha^-1). L-N/P was high under severe shade (8% of full light), severe N deposition (200 kg N ha^-1), and reintroduction to gap and undergrowth habitat; however, low L-N/P was observed at low acidity rainwater or P fertilizer application. The nutrient supply facilitates corresponding elements uptake, shade tends to induce P limitation and soil acidification shows N limitation. Our results provide theoretical guidance for field management and nutrient supply regimes for future protection, population rejuvenation of this species and provide guidelines for conservation and nutrient management strategies for the endangered species.