Vegetation restoration has been widely used in karst rocky desertification (KRD) areas of southwestern China, but the response of microbial community to revegetation has not been well characterized. We investigated the diversity, structure, and co-occurrence patterns of bacterial communities in soils of five vegetation types (grassland, shrubbery, secondary forest, pure plantation and mixed plantation) in KRD area using high-throughput sequencing of the 16S rRNA gene. Bray-Curtis dissimilarity analysis revealed that 15 bacterial community samples were clustered into five groups that corresponded very well to the five vegetation types. Shannon diversity was positively correlated with pH and Ca2+ content but negatively correlated with organic carbon, total nitrogen, and soil moisture. Redundancy analysis indicated that soil pH, Ca2+ content, organic carbon, total nitrogen, and soil moisture jointly influenced bacterial community structure. Co-occurrence network analysis revealed non-random assembly patterns of bacterial composition in the soils. Bryobacter, GR-WP33-30, and Rhizomicrobium were identified as keystone genera in co-occurrence network. These results indicate that diverse soil physicochemical properties and potential interactions among taxa during vegetation restoration may jointly affect the bacterial community structure in KRD regions.
The soils in karst regions, with carbonate rocks as the background material, are characterized by two main factors, drought and high calcium levels. Handeliodendron bodinieri (Levl.) Rehd is an endemic plant species in this area of China. However, few studies have been carried out on the adaptation mechanism of H. bodinieri to drought and high calcium soil. To reveal the physiological responses of H. bodinieri to exogenous calcium under drought stress, 10% PEG-6000 was used to simulate drought stress, and the effects of exogenous calcium at different concentrations on the physiology of H. bodinieri seedlings under drought stress were studied. The results showed that drought stress significantly reduced the relative water content and water potential of H. bodinieri seedlings. Malondialdehyde (MDA) content, O2− and H2O2 production rates significantly increased under drought stress. The addition of exogenous calcium significantly reduced MDA content and O2− and H2O2 production rates. Moreover, peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbic acid peroxidase (APX) and glutathione peroxidase (GPX) activities increased significantly under drought stress. At the same time, the accumulation of osmotic regulators such as soluble sugar, betaine and free proline also increased significantly. The addition of exogenous calcium further increased the activity of antioxidant enzymes and the accumulation of osmotic regulatory substances. Consequently, the oxidative stress and osmotic stress induced by drought decreased. Finally, exogenous calcium enhanced the photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of H. bodinieri under drought stress and significantly improved water use efficiency (WUE). This study confirmed that the application of exogenous calcium can enhance the water condition, photosynthetic capacity, osmotic regulation and antioxidant capacity of H. bodinieri under drought stress. Of the treatments, the 10 mmol·L−1 CaCl2 treatment is more likely to improve survival of H. bodinieri under drought tolerance. This study provides an important reference for describing the adaptation mechanism and appropriate conservation of H. bodinieri under drought and high calcium conditions.
Water deficit and high calcium (Ca 2+ ) content and are two typical soil characteristics in the Karst region. However, the problem of whether high Ca 2+ in Karst calcareous soil could increase drought tolerance in calcicole plants has not been solved. We investigated the ecophysiological responses of Cyclobalanopsis glauca (Thunb.) Oerst. cuttings to short-term drought stress and Ca 2+ application. Drought stress (10% PEG-6000) markedly reduced relative water content (RWC) and water potential (WP), and enhanced the levels of reactive oxygen species (ROS) production (H 2 O 2 and O 2•− ) and malondialdehyde (MDA) content in C. glauca leaves. Under drought treatment, exogenous Ca 2+ application (20 mM CaCl 2 ) markedly increased the RWC and WP, and reduced the H 2 O 2 , O 2 •− , and MDA content. Furthermore, water deficit induced a significant increase in the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and glutathione peroxidase (GPX), and increased the accumulation of osmoregulation substances. External Ca 2+ alleviated drought-induced oxidative stress and osmotic stress with further increased activities of antioxidant enzymes, and enhanced the accumulation of osmoregulation substances. In addition, exogenous Ca 2+ treatment alleviated the reduction of the photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and chlorophyll content (SPAD), and further increased water use efficiency (WUE) under drought stress. This study confirms that exogenouos Ca 2+ application induces improvements in the water status, osmotic adjustment, antioxidant defense, and photosynthesis efficiency of C. glauca under drought stress.Plant ecophysiological characteristics might be changed by soil water deficit. Drought could induce a decrease in the relative water content (RWC) and water potential (WP) of plants [7]. Additionally, it can trigger the overproduction of reactive oxygen species (ROS), resulting in oxidative stress [8,9]. Water deficit can also reduce chlorophyll content, gas exchange parameters, stomatal conductance, and photosystem reaction center activity, resulting in the suppression of photosynthesis [10]. To cope with oxidative stress, plants have established antioxidant defense systems to eliminate ROS, including numerous antioxidant enzymes and non-enzymatic antioxidants [11]. Moreover, plants accumulate certain compatible solutes such as proline, soluble sugar, and glycine betaine to deal with drought stress [12]. Under moderate drought conditions, four Karst adapted plants with different growth forms enhanced water use efficiency (WUE), antioxidant enzymes activities, and osmoregulation substances, indicating the essential roles of these defense systems involved in drought resistance [13].Calcium has been approved to ameliorate the adverse effects of water deficit on plants, which might be related to increased antioxidant enzyme activities and reduced membrane lipid peroxidation [1...
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