New progress has been made in the study of plant water use and adaptation mechanism in key zones of karst slope

Karst carbonate rocks undergo strong dissolution in the vertical direction, so that precipitation is dispersed and infiltrated through the fractures of the rock, forming karst landforms dominated by peak clusters. Karst action makes the soil layer of karst slope shallow and poor water holding capacity, coupled with soil erosion along the slope, resulting in great heterogeneity in bottom-up geotechnical structure and water process, resulting in special karst drought phenomenon under humid climate conditions.

The harsh ecological environment with little water and soil makes the ecological restoration project nearly 30 years after the implementation of the ecological restoration project, the natural vegetation community is still in the early stage of succession. Studies have shown that the average transpiration age of karst plants is extremely short. However, how the water changes in the key zones of the slope affect plant transpiration and water adaptation, it is necessary to deeply analyze the water absorption sources and transpiration processes of community communities on the slope, clarify the water use patterns of plants along the slope, and evaluate the sustainability of vegetation restoration.

In response to the above problems, Chen Hongsong’s research group, a researcher at the Institute of Subtropical Agroecology, Chinese Academy of Sciences, relied on the karst key zone platform of the Huanjiang Karst Ecosystem Observation and Research Station to set up two plots uphill and downhill (altitude difference of about 70 meters, horizontal distance of about 100 meters). The team selected the typical early succession community construction group species Saloderma as the research object, which belongs to the succession pioneer tree species, which is widely distributed along the slope, and is a representative of native tree species that have been adapted to the karst environment for a long time.

The team’s preliminary field investigation found that the root system of Salinewood was mainly laterally stretched at a soil depth of 0 to 40 cm, and the longest lateral extension length was 3.5 meters, and the height and breast diameter of the uphill Salogena trees of similar age were significantly lower than those of the downhill. In this study, we monitored the moisture and meteorological factors of the soil-surface karst zone from 0 to 300 cm during the complete growing season, analyzed the water source and transpiration rate of Salinewood wood, and explored the response mechanism of transpiration along the slope to atmospheric evaporation and water supply.

The results show that the average water content of the soil-surface karst zone in the upslope is 0.178m3·m-3, which is only about 60% of the downhill, and there are significant differences in water supply along the slope. Combined with MixSIAR model analysis, it can be seen that the water absorption strategies of salty wood along the slope are similar, and the soil water is mainly used from 0 to 60 cm, not surface karst zone water (groundwater). The transpiration rate and transpiration of the uphill salt skin wood are reduced to about half of the downhill. The downhill soil has sufficient moisture, and plant transpiration changes with the change of atmospheric evaporation demand, and uphill water supply limits the sensitivity of plant transpiration and transpiration to atmospheric evaporation demand.

Conceptual diagram of water use patterns of sloped plants. Photo courtesy of interviewee

According to reports, this study shows that the transpiration of secondary plants naturally restored in karst areas is mostly dependent on soil water, and cannot compensate for the transpiration difference caused by slope effect by absorbing deep water. The study further revealed that soil moisture was still the limiting factor affecting vegetation recovery in the early stage of karst succession in southwest China, and plants adapted to the arid environment by reducing transpiration uphill.

Recently, the above results were published in Science of the Total Environment. The research was supported by the National Natural Science Foundation of China, the Youth Fund, and the outstanding members of the Youth Promotion Association of the Chinese Academy of Sciences. (Source: China Science News, Wang Haohao, Liu Wenna)

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