Abstract
Prerequisite for selection of appropriate tree species in afforestation programs is to understand their water use strategy. Acacia mangium Willd., Schima wallichii Choisy, and Cunninghamia lanceolata (Lamb.) Hook are the three main vegetation restoration pioneer species in southern China, but no comparative research on the water use strategy of these three tree species have been reported. Our objective was to gain a detailed understanding of how photosynthetically active radiation (PAR), vapor pressure deficit (VPD), and soil water content (SWC) at different soil depths control the sap flux density (Js) in the dry and wet seasons. We measured the Js of these three tree species by using the thermal dissipation method in low subtropical China. We found that both S. wallichii and C. lanceolata differed clearly in their stomatal behavior from one season to another, while A. mangium did not. The canopy conductance per sapwood area of S. wallichii and C. lanceolata was very sensitive to VPD in the dry season, but not in the wet season. The Js of A. mangium was negatively correlated to SWC in all soil layers and during both seasons, while the other two species were not sensitive to SWC in the deeper layers and only positively correlated to SWC in dry season. Our results demonstrate that the three species have distinct water use strategies and may therefore respond differently to changing climate.
Highlights
China, as the second largest plantation country in the world, has implemented large-scale planned afforestation since the 1950s, primarily focused on planting fast-growing and high production timber species during the 1970s and 1980s [1,2]
The difference in mean soil water content (SWC) of all layers between the wet and dry seasons was greater at the A. mangium and S. wallichii sites than at the C. lanceolata site (Figure 2)
At the A. mangium site, average SWC of all layers was lower in the dry season (19%–28%) compared with the wet season
Summary
As the second largest plantation country in the world, has implemented large-scale planned afforestation since the 1950s, primarily focused on planting fast-growing and high production timber species during the 1970s and 1980s [1,2] These programs have altered the coverage of forest in China from 16.0% in the 1980s to 21.66% in 2018 and this increase is expected to continue as China intends. Since the 1980s, exotic pioneer species such as Acacia mangium Willd, an evergreen broad-leaved tree with nitrogen-fixing, drought-tolerant, and fast-growing characteristics, have been introduced in southern China [11,12] They can be effectively used due to the nitrogen fixation of the nodule and rapid growth in the early stage to improve soil conditions at the plantations [13]. Observations show that the growth, photosynthetic rate and water use of A. mangium plantations decreases after approximately
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