Abstract
(1) Background: Water transport systems play an important role in maintaining plant growth and development. The plasticity responses of the xylem anatomical traits of different species to the environment are different. Studies have shown that there are annual growth rings in the secondary root xylem of perennial herbaceous species. Studies on xylem anatomical traits, however, have mainly focused on woody species, with little attention given to herbaceous species. (2) Methods: We set 14 sampling sites along a rainfall gradient in arid and semiarid regions, and collected the main roots of native (Potentilla) and non-native (Medicago) perennial forbs. The xylem anatomical traits of the plant roots were obtained by paraffin section, and the relationships between the xylem traits of forbs were analyzed by a Pearson correlation. (3) Results: In the fixed measurement area (850 μm × 850 μm), the vessel number (NV) of Potentilla species was higher than that of Medicago species, while the hydraulic diameter (Dh) and mean vessel area (MVA) of Potentilla species were lower than those of Medicago species. With the increase in precipitation along the rainfall gradient, the Dh (R2 = 0.403, p = 0.03) and MVA (R2 = 0.489, p = 0.01) of Medicago species increased significantly, and NV (R2 = 0.252, p = 0.09) decreased, while the hydraulic traits of Potentilla species showed no significant trend with regard to the rainfall gradient. (4) Conclusions: The hydraulic efficiency of non-native Medicago forbs was higher than that of native Potentilla forbs, and the hydraulic safety of native Potentilla forbs was higher than that of non-native Medicago forbs. With the decrease in precipitation, the hydraulic strategies of non-native Medicago forbs changed from efficiency to safety, while native Potentilla forbs were not sensitive to variations in precipitation.
Highlights
Grasslands are one of the main biological communities on Earth, covering nearly 1/5 of the land surface [1]
The NV of Potentilla is significantly higher than that of Medicago (Figure 4b), and there is no difference in Kh and vessel fraction (VF) between the two genera (Figure 4e), which may suggest that Potentilla forbs compensate for the small vessels with more vessels to ensure the required water transport
Boughalleb et al [73] designed a water control experiment to study the effects of water deficit on Astragalus gombiformis Pomel., and the results showed that the vessel diameter of root xylem decreased and the vessel density increased under water deficit, which was consistent with the results of our study
Summary
Grasslands are one of the main biological communities on Earth, covering nearly 1/5 of the land surface [1]. In China, grassland is the vegetation type with the largest coverage area, and is distributed in arid and alpine areas with the most fragile ecological environment. Climate change will affect water and carbon cycling, mineral cycling and the composition of the plant community, directly and indirectly affecting the primary productivity of grasslands [3,4]. Under the background of global climate change, the warm drought phenomenon in arid and semiarid areas of China has caused soil drought, and the natural water deficit has become an important factor limiting grassland productivity [5]. Studies have shown that the impact of climate change on grassland biomass varies with different grassland types [9]
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