Increasing leaf δ13C values of woody plants in response to water stress induced by tunnel excavation in a karst trough valley: Implication for improving water-use efficiency

Plant species growing in karst shallow-soil areas always experience water deficit especially in seasonally dry. Moreover, such water stress is aggravated by tunnel excavation in karst areas. However, the effects of tunnel excavation on karst ecosystems remain largely unknown. This study aimed at investigating whether there were variations in soil water contents and shifts of water use strategies of plants between rainy and dry seasons in a karst trough valley affected by tunnel excavation, and comparing their differences with those in a tunnel-free karst trough valley in Southwest China. Monthly soil water contents at two soil layers of the upper 0-20 cm and the lower 20-40 cm were measured from January 2017 to December 2018. Foliage of woody plants were sampled in the dry season of December 2017 and March 2018, and in the rainy season of June and September 2018, respectively, and leaf delta C-13 values were analyzed. The soil water contents at both valleys showed significant seasonal variations, and the soil water contents of two soil layers in the tunneling affected valley were significantly lower than that of the tunnel-free valley at both seasons. Plant water use strategy changed from profligate water-use pattern in the rainy season to conservative water-use pattern in the dry season. Moreover, increased leaf delta C-13 values at both seasons in the tunneling affected valley suggests that the water stress resulted from the tunnel excavation has significantly impacted the physiological process of plants in karst areas. These results highlight that improving water use efficiency (WUE) is a common water use strategy to overcome water limitation for native plants in karst areas during unfavorable drought conditions.