Search Results (2)

(1) Background: Planting density is an important factor affecting the yield of poplar per unit area. Therefore, determining the optimal height of the photosynthetic canopy layer for different planting densities is critical. (2) Methods: This study takes Populus euramericana ‘N3016’ × Populus ussuriensis as the research object. According to on the average tree height, diameter at breast height, and crown width of the stand, one standard tree was selected from each planting density for the experiment. The canopy of the standard tree was divided into five canopy layers from top to bottom, and the first-order lateral branches of each canopy layer were divided into three sites from outside to inside. The photosynthesis and leaf traits at various positions in different canopy layers were measured. (3) Results: The results revealed significant differences in photosynthetic and leaf traits at different positions of different canopy layers under different planting densities. As the canopy layer gradually declined, photosynthetic traits revealed that instantaneous photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) gradually decreased, while intercellular CO₂ concentration (Ci) increased. Moreover, water use efficiency (WUE) initially increased and then decreased under an 825 trees·ha⁻¹ (D3) planting density. Leaf traits revealed that as leaf length (LL) gradually decreased, leaf width (LW), leaf area (LA), and leaf water content (LWC) gradually increased. Under three planting densities, leaf traits were negatively correlated with Pn, Tr, WUE, and Gs, but positively correlated with Ci. (4) Conclusions: As the planting density decreased, the photosynthetic capacity of poplar gradually increased. With a planting density of D3, all canopy layers were able to carry out efficient photosynthesis, and all living branches within the canopy were functional. However, under the planting density of 1650 trees·ha⁻¹ (D1) and 1089 trees·ha⁻¹ (D2), canopy layers 1 to 4 could perform effective photosynthesis, while the photosynthetic capacity of canopy layer 5 was relatively weak. This study reveals the interactive effects of canopy position and stand density on leaf physiological and morphological traits, providing new insights into the photosynthetic efficiency and growth strategies of poplar under different planting densities. It also offers theoretical support for optimizing stand management and enhancing productivity. Full article

Litter decomposition is a highly complex physical and biochemical process that plays a crucial role in promoting energy transformation in forest ecosystems. This study examines the impact of different concentrations of nitrogen and compound fertilizers on the quality of litter in a plantation of Populus euramericana ‘N3016’ × Populus ussuriensis. The major components and elemental contents of litter from different decomposition layers (the undecomposed layer and semidecomposed layer) were analyzed across various months. Overall, the application of nitrogen fertilizer or compound fertilizer did not significantly alter the cellulose, lignin, or potassium (K) contents of the litter in the different decomposition layers. Nitrogen fertilizer increased the average content of undecomposed layer (U-layer) nitrogen (N) and phosphorus (P) by 0.220% and 0.009%, respectively. Compound fertilizer increased the average content of U-layer nitrogen (N) by 0.055%. These findings suggest that while fertilization can increase the initial N and P contents in litter to some extent, it has a minimal overall impact on litter quality. Future research should be focused on the effects of climatic conditions, soil properties, soil fauna, and microbial activity on litter decomposition. Full article