Effects of different tending measures on leaf functional traits of Ulmus pumila in Bashang area of northern Hebei province

Leaf functional traits are core indicators of plants' adaptation to the environment. Forest tending can significantly affect the morphological construction and physiological metabolism of plant leaves, thereby driving the trade-off and optimization of their functional traits. As an important part of the Three-North Shelterbelt System and a typical ecologically fragile zone, the Jibei Bashang area currently has relatively few studies on the leaf functional traits of shelterbelts in this region, and the understanding of vegetation ecological adjustment strategies under different tending measures is very limited. In order to reveal the response mechanisms of shelterbelt tree species to tending disturbances in ecologically fragile areas, a 13-year-old Ulmus pumila plantations in the Bashang area of northern Hebei Province as the research object, four tending measures were set up: enclosure, pruning, thinning (reserved plant spacing of 2 m) + pruning and thinning (reserved plant spacing of 4 m) + pruning, with the graze treatment as the control for Enclosure, and enclosure as the control for pruning, thinning (reserved plant spacing of 2 m) + pruning and thinning (reserved plant spacing of 4 m) + pruning. This study systematically analyzed the differences in leaf morphological and physiological traits of Ulmus pumila among different tending measures, and clarify their effects on leaf functional traits. The Results showed that: (1) Leaf morphological traits responded significantly to tending measures. Compared with enclosure, leaf area, leaf fresh weight, and leaf dry weight of Ulmus pumila under the thinning (reserved plant spacing of 4 m) + pruning treatment significantly increased by 80.7%, 70.8%, and 72.7%, respectively; under the pruning and thinning (reserved plant spacing of 2 m) treatments, leaf area, leaf fresh weight, and leaf dry weight increased to a certain extent, but the increments were weaker than those under the thinning (reserved plant spacing of 4 m) treatment; the enclosure treatment had a slight effect, with no significant differences in all leaf morphological indicators compared with graze; (2) Leaf physiological traits were relatively stable, and different tending measures had no significant effects on the contents of chlorophyll a, chlorophyll b, total carbon, total nitrogen, and total phosphorus in leaves; (3) the comprehensive score of membership function method showed that, the total scores under enclosure, pruning, thinning (reserved plant spacing of 2 m) + pruning and thinning (reserved plant spacing of 4 m) + pruning were 3.528, 4.354, 5.623, 5.040, and 6.338, respectively, among which thinning (reserved plant spacing of 4 m) + pruning performed best in 11 indicators such as leaf area and leaf dry weight, and had the highest total score.In conclusion, moderate reduction of stand density and optimization of canopy structure can effectively improve the resource utilization capacity and efficiency of individual Ulmus pumila leaves in the Bashang area of northern Hebei Province. The research results can provide a theoretical basis for the tending and management of young and middle-aged Ulmus pumila forests.