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. 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. 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.

Using field slope farmland plots, this study planted the typical crop of maize (Zea mays L.) and investigated the effects of varied chemical fertilizer (organic compound fertilizer of potassium nitrate, containing 17% each of nitrogen, phosphorus, and potassium) application levels (0.5 times the common fertilizer amount (CK, 0.75 t·hm⁻² to 2.5 CK) on the soil fertility in the Yuanmou dry-hot River Valley. The results showed that the soil chemical properties, microbial properties, and enzyme activities increased with the increase of fertilizer application levels from CK to 2.0 CK. However, a declining trend showed both under 0.5 CK level and the 2.5 CK level, and higher in fertilizer application level 3 (1.5 CK) and level 4 (2.0 CK) compared to level 1 (1 CK). Soil chemical properties, microbial properties, and enzyme activities in five-degree slope cropland topsoil were higher than these in 10-degree slope cropland topsoil. Five parameters (available N, nitrifying bacteria, inorganic phosphorus bacteria, organic matter, and invertase) in five-degree slope cropland and three parameters (organic matter, ammonifying bacteria, and total P) in 10-degree slope cropland, which had the greatest weight in the principal components analysis, were selected to calculate the soil quality index (SQI). The SQI calculated by integrating all critical parameters indicated that the highest SQI values were found in fertilizer levels 1.5 CK (0.71) and 2.0 CK (0.69), followed by CK (0.64), and the lowest were found in 0.5 CK (0.62) and 2.5 CK (0.61) in five-degree slope cropland soil. The highest SQI values were found in fertilizer levels 1.5 CK (0.26) and 2.0 CK (0.29), followed by CK (0.23), and the lowest were found in 0.5 CK (0.14) and 2.5 CK (0.20) in 10-degree slope cropland soil. The final SQI values implied that the fertilization treatment 2 (CK), fertilization treatment 3 (1.5 CK) and fertilization treatment 4 (2.0 CK) could improve the soil fertility, whereas the fertilization treatment 1 (0.5 CK) and fertilization treatment 5 (2.5 CK) could decrease the soil fertility. In view of the impact of slope, the soil qualities of five-degree slope cropland of five fertilization treatments were higher than in 10-degree slope cropland. The SQI values in five-degree slope cropland soil were found higher than the SQI values in 10-degree slope cropland soil by 68.65%, 64.20%, 62.22%, 57.46%, and 67.01%, respectively. For this study, the range of fertilization tolerance was 0.75–1.50 t·hm⁻² (organic compound fertilizer of potassium nitrate) in 10-degree slope plot scale and 0.75–1.13 t∙hm⁻² in five-degree slope cropland soil.