Morphological and physiological responses of Heteropogon contortus to drought stress in a dry-hot valley

Abstract

Background: Heteropogon contortus is a valuable pasture species that is widely used for vegetation restoration in dry-hot valleys of China. However, to date, its morphological and physiological responses to drought, and the underlying mechanisms are not well understood. This study was aimed to investigate the morphological and physiological changes of H. contortus under drought stress during the dry-hot season. Heteropogon contortus was planted in pots and subjected to four levels of soil water treatments: above 85 % (control), 70-75 % (light stress), 55-60 % (moderate stress) or 35-40 % (severe stress) of field capacity.

Results: Within the total stress period (0-29 days), H. contortus grew rapidly in the light stress, whereas severe stress had a negative impact on growth. Aboveground biomass decreased together with increasing drought stress, whereas root biomass increased. Consequently, the root/shoot ratio of the severe stress treatment increased by 80 % compared to that of the control treatment. The ratio of bound water/free water (BW/FW) was the most sensitive parameter to drought and showed a value under severe stress that was 152.83 % more than that in the control treatment. Although leaf water potential (LWP) and leaf relative water content (RWC) decreased with progressive water stress, H. contortus managed to maintain a relatively high RWC (nearly 70 %) in the severe stress condition. We also detected a significant reduction (below 0.6) in the ratio of variable fluorescence/maximum fluorescence (Fv/Fm) in the severe stress treatment.

Conclusions: Our results show that H. contortus adapts to drought mainly by avoidance mechanisms, and its morphological and physiological characteristics are inhibited under severe stress, but can recover at a certain time after re-watering. These findings might help limited water resources to be fully used for vegetation management in the studied region.

Keywords: Biomass allocation; Chlorophyll fluorescence; Drought stress; Heteropogon contortus; Leaf water potential; Relative water content.

Fig. 1

Temperature and relative humidity between 9:00 and 11:00 during the period of soil water stress

Fig. 2

Plant height (a), crown area (b) and leaf area per leaf (c) of Heteropogon contortus at different stages under four water levels. Values represent means (n = 5) with standard error bars. The different letters above the bars indicate significant differences among the treatments at the same stage at P < 0.05

Fig. 3

Aboveground biomass (a) and root biomass (b) of Heteropogon contortus at different stages under four water levels. Values represent the means (n = 5) with standard error bars. The different letters above the bars indicate significant differences among the treatments at the same stage at P < 0.05

Fig. 4

Bound water/free water ratio (a), total water content (b), relative water content (c) and leaf water potential (d) of Heteropogon contortus on different days under four different water levels. Values represent the mean ± standard error (n = 3) and RW represents the day after re-watering

Fig. 5

F₀ (a) and Fv/Fm (b) of Heteropogon contortus on different days under four different water levels. Values represent the mean ± standard error (n = 3) and RW represents the day after re-watering