Responses of two dominant desert plant species to the changes in groundwater depth in hinterland natural oasis, Tarim Basin

Abstract

Groundwater is increasingly becoming a permanent and steady water source for the growth and reproduction of desert plant species due to the frequent channel cutoff events in arid inland river basins. Although it is widely acknowledged that the accessibility of groundwater has a significant impact on plant species maintaining their ecological function, little is known about the water use strategies of desert plant species to the groundwater availability in Daryaboyi Oasis, Central Tarim Basin. This study initially determined the desirable and stressing groundwater depths based on ecological and morphological parameters including UAV-based fractional vegetation cover (FVC) images and plant growth status. Then, leaf δ¹³C values of small- and big-sized plants were analyzed to reveal the water use strategies of two dominant woody species (Populus euphratica and Tamarix ramosissima) in response to the groundwater depth gradient. The changes in FVC and growth status of plants suggested that the actual groundwater depth should be kept at an appropriate range of about 2.1-4.3 m, and the minimum groundwater depth should be less than 7 m. This will ensure the protection of riparian woody plants at a normal growth state and guarantee the coexistence of both plant types. Under a desirable groundwater condition, water alternation (i.e., flooding and rising groundwater depth) was the main factor influencing the variation of plant water use efficiency. The obtained results indicated that big-sized plants are more salt-tolerant than small ones, and T. ramosissima has strong salt palatability than P. euphratica. With increasing groundwater depth, P. euphratica continuously decreases its growth status to maintain hydraulic efficiency in drought condition, while T. ramosissima mainly increases its water use efficiency first and decreases its growth status after then. Besides, in a drought condition, T. ramosissima has strong adaptability than P. euphratica. This study will be informative for ecological restoration and sustainable management of Daryaboyi Oasis and provides reference materials for future research programs.

Keywords: Daryaboyi oasis; Keriya River Basin; health status; leaf carbon isotope; vegetation cover index; water use strategies.

FIGURE 1

Sketch map of the study area and the locations of UAV vegetation surveying and experimental sampling sites

FIGURE 2

Vegetation cover ratios under different groundwater depths in the Daryaboyi Oasis. In UAV fractional vegetation cover images, the green color represents vegetation, and the dark yellow represents bare land

FIGURE 3

Carbon isotope content of P. euphratica leaves of small‐ and big‐sized plants. Different letters indicate significant differences (p < .05) between δ¹³C values of P. euphratica at different groundwater depths and vice versa (capital letters for big‐sized plants and lowercase letters for small‐sized plants)

FIGURE 4

Carbon isotope content of T. ramosissima leaves for small‐ and big‐sized plants. Different letters indicate significant differences (p < .05) between δ¹³C values of T. ramosissima. at different groundwater depths and vice versa (capital letters for big‐sized plants and lowercase letters for small‐sized plants)

FIGURE 5

Difference in δ¹³C value in leaves of small‐ and big‐sized P. euphratica and T. ramosissima plants grown at different groundwater depths. The asterisk (*) indicates a significant difference between δ¹³C values of two plant species at the same groundwater depth (*p ≤ .05, **p ≤ .01, and ***p ≤ .001)

FIGURE 6

Foliar δ¹³C, plant growth degree (V, Table 1), TDS (total dissolved solid), and SWC (subsurface soil water content from 50‐ to 100‐cm soil layer) values of experimental plots under different groundwater table depths