Abstract
To provide a theoretical basis for developing intensive cultivation practices for Populus tomentosa plantations, the leaf phenology variation within the canopy and its relationship with transpiration of well-watered P. tomentosa tree in a dense plantation were investigated. The variation in canopy light interception, indicated by the ratio between net radiation under (Rn-u) and above (Rn-a) canopy, with leaf development was also studied. During the growing season, the achievement of maximum leaf number tended to be later in higher parts of the canopy. In the lower and middle canopy, the leaf number maximized earlier in the east-facing side than in the west-facing side, but this difference disappeared in the upper canopy. The Rn-u/Rn-a was stable in May, but declined and then varied steadily until late August. Generally, in May, the crop coefficient (Kcb) of the tree reached its highest level and was not correlated with leaf area (LA) in all layers (p > 0.05). However, it increased linearly (p < 0.001) with LA in the layers above a canopy height of 3 m from June to late August, and most of its variation was explained by LA in the 5–7 m layer. After late August, Kcb decreased linearly with decreasing LA in all layers (p < 0.001). Consequently, a temporal ecological strategy seems to be adopted by P. tomentosa leaves in different layers and azimuthal sides for efficient light acquisition. The contribution of the different canopy layers to tree transpiration can vary, with the leaves in the upper and all layers mainly controlling transpiration in summer and in spring and autumn, respectively.
Highlights
Poplar has been identified as one of the fastest growing trees in temperate zones, and is one of the main tree species for developing fast-growing and high-yielding plantations in North China.Plantations of poplar can produce a large amount of wood and fiber resources, and provide ecosystem and environmental services, such as watershed services, waste management, carbon sink, biodiversity and wildlife habitat, etc
Tree.InInaddition, addition, in layers all layers θ values profile within the averagegrowing growingspace space around around the rθ rvalues in all were relatively high, with thethe seasonal average were relatively high, with seasonal averagevalues valuesvarying varyingfrom from0.73
The data before early May were absent, our results indicated that the net leaf number variation rate of mature P. tomentosa exhibited a unimodal seasonal pattern with the peak occurring between late May and early June
Summary
Poplar has been identified as one of the fastest growing trees in temperate zones, and is one of the main tree species for developing fast-growing and high-yielding plantations in North China.Plantations of poplar can produce a large amount of wood and fiber resources, and provide ecosystem and environmental services, such as watershed services, waste management, carbon sink, biodiversity and wildlife habitat, etc. The productivities and qualities of these poplar plantations are still very low, and they need to be improved urgently by environmentally friendly intensive cultivation practices, such as water-saving irrigation, fertilization, pruning, and weed control [2,3,4]. Understanding of the growth rhythm of the trees is the basis to improve plantation productivities by intensive cultivation practices that can be refined according to the characteristics of tree growth [5,6]. Leaf phenology can alter the interception and allocation of light, microclimate, and the potential carbon-gain strategy within canopy [7,8,9,10,11]. Information on leaf phenology within the canopy will help to gain more profound insights into tree growth characteristics and to predict forest productivity [12]
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