Abstract
The diversity of plant water use patterns among species and ecosystems is a matter of widespread debate. In this study, Chinese pine (Pinus tabuliformis, CP) and Mongolian Scots pine (Pinus sylvestris var. mongolica, MP), which is co-exist in the shelterbelt plantations in the Horqin Sandyland in northern China, were chosen for comparison of water use traits by monitoring xylem sap flow alongside recordings of the associated environmental factors over four growing seasons. Continuous sap flux density measurements were converted into crown projected area transpiration intensity (Tr) and canopy stomatal conductance (Gs). The results indicated that MP showed a higher canopy transpiration intensity than in CP, with Tr daily means (±standard deviation) of 0.84 ± 0.36 and 0.79 ± 0.43 mm⋅d–1, respectively (p = 0.07). However, the inter-annual variability of daily Tr in MP was not significant, varying only approximately a 1.1-fold (p = 0.29), while inter-annual variation was significant for CP, with 1.24-fold variation (p < 0.01). In particular, the daily mean Tr value for CP was approximately 1.7-times higher than that of MP under favorable soil moisture conditions, with values for relative extractable soil water within the 0–1.0 m soil layer (REW) being above 0.4. However, as the soil dried out, the value of Tr for CP decreased more sharply, falling to only approximately 0.5-times the value for MP when REW fell to < 0.2. The stronger sensitivity of Tr and/or Gs to REW, together with the more sensitive response of Gs to VPD in CP, confirms that CP exhibits less conservation of soil water utilization but features a stronger ability to regulate water use. Compared with MP, CP can better adapt to the dry conditions associated with climate change.
Highlights
The impact of climate change on both natural and plantation forests has been a concern for some time and has been reported on across the world (Allen et al, 2010; Cook et al, 2018)
Our results indicated that the water use intensity of Mongolian Scots pine (MP) and Chinese pine (CP) individuals in semi-arid sandy land was at relatively low levels, with canopy transpiration averaging 0.84 and 0.79 mm·d−1, respectively, during the 4-year period based on sap flow measurements
This shallowrooted feature enhances the ability of trees to use precipitation opportunistically but is not helpful for resisting severe drought because fine roots would die almost immediately when soil turns dry (Vanguelova and Kennedy, 2007), directly leading to a reduction in soil-root water transport (Konôpka et al, 2005). This explains why the shallow-rooted trees can suffer from drought stress when drought occurs in MP forests (Song et al, 2015, 2018) or CP forests. Both MP and CP were found to respond to drought through a fast reduction in canopy transpiration and canopy stomatal conductance, which was attributed to their typical isohydric behavior
Summary
The impact of climate change on both natural and plantation forests has been a concern for some time and has been reported on across the world (Allen et al, 2010; Cook et al, 2018). Plantation forests are much simpler ecosystems, and these forests suffer heightened risk of degradation even under relatively minor changes in the interactions of the ecosystem components in their environment. This is especially true in relation to potentially overwhelming problems associated with changes in water availability (Licata et al, 2008; Payn et al, 2015)
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