Physiological mechanism for the reduction in soil water in poplar (Populus deltoides) plantations in Dongting Lake wetlands

Abstract

The use of large-scale tree plantations has provoked increasing concern regarding the negative effects on local environments in different ecosystems. However, the physiological mechanism underlying the reduction in soil water by tree plantations in wetlands is not clear. The aims of this study were to investigate the effects of poplar (Populus deltoides) plantations on soil water content and to elucidate the underlying physiological mechanisms. To this end, we conducted a 1-year fixed-plot investigation of soil water content (SWC), plant photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and water-use efficiency (WUE) of individual leaves of 11-and 5-year-old poplars and of reed (Triarrherca sacchariflora, a native herbaceous plant) in the Dongting Lake wetlands, China. SWC was highest in reed, intermediate in 11-year-old poplar, and lowest in 5-year-old poplar, suggesting that poplar plantations produce a lower soil water content in wetlands. From May to July, Pn was significantly higher in reed than in the two poplar stands, but did not differ between the different-aged poplars. As a whole, Gs and Tr were higher, but WUE was lower, in the poplar stands than in reed during the growing season, indicating that Gs and Tr are the key physiological mechanisms associated with the lower soil water in poplar stands. Relationships among Pn, Gs, and Tr showed positive correlations (P \ 0.01) for each type of vegetation. These data suggest that poplar plantations may cause the transformation of wetlands into dry land due to a lower WUE leading to a massive water loss from soil. This, in turn, would have an influence on community composition and ecosystem function after establishment of the plantations.

Effects of young poplar plantations on understory plant diversity in the Dongting Lake wetlands, China

“…In wetland ecosystems, studies have shown that elevation had a strong influence on understory vegetation due to the hydrological conditions such as soil moisture and water level fluctuations14. In monitored plots at the same elevation, the mean soil water content was lower in poplar areas (23.5%) versus in the reedy areas (31.3%), presumably due to higher transpiration capacity in the poplars17. Excessive loss of soil water might have changed wetlands to dry lands and resulted in a lower ratio of hygrophytes, but a higher ratio of mesophytes or xerophytes, in the poplar areas compared to that in the reed areas.…”

Effects of terracing on soil water and canopy transpiration of Pinus tabulaeformis in the Loess Plateau of China

“…Previous studies have shown that sap flow characteristics vary with species and growth status, as well as with meteorological, environmental, and edaphic features (Brito et al, 2015;Du et al, 2011). In areas with insufficient water, for example, soil water conditions can restrict many physiological processes (Li et al, 2014b). Plants in these areas tend to deepen and extend their root systems to exploit substantial quantities of soil water for transpiration (Chen et al, 2014c;Limousin et al, 2009).…”

Spatial and temporal characteristics of 2H and 18O in the basin of Dongting Lake: impact of monsoon precipitation

“…The average annual temperature is 16.2-17.8°C. Temperature is highest in July and lowest in January, and the region has a frost-free period of 259-277 days per year [21].…”