Bamboo plants are an essential component of tropical ecosystems, yet their vulnerability to climate extremes, such as drought, is poorly understood due to limited knowledge of their hydraulic properties. Cephalostachyum pergracile, a commonly used tropical bamboo species, exhibited a substantially higher mortality rate than other co-occurring bamboos during a severe drought event in 2019, but the underlying mechanisms remain unclear. This study investigated the leaf and stem hydraulic traits related to drought responses, including leaf-stem embolism resistance (P50leaf; P50stem) estimated using optical and X-ray microtomography methods, leaf pressure-volume and water-releasing curves. Additionally, we investigated the seasonal water potentials, native embolism level (PLC) and xylem water source using stable isotope. We found that C. pergracile exhibited strong resistance to embolism, showing low P50leaf, P50stem, and turgor loss point, despite its rapid leaf water loss. Interestingly, its leaves displayed greater resistance to embolism than its stem, suggesting a lack of effective hydraulic vulnerability segmentation (HVS) to protect the stem from excessive xylem tension. During the dry season, approximately 49% of the water was absorbed from the upper 20-cm-deep soil layer. Consequently, significant diurnal variation in leaf water potentials and an increase in midday PLC from 5.87 ± 2.33% in the wet season to 12.87 ± 4.09% in the dry season were observed. In summary, this study demonstrated that the rapid leaf water loss, high reliance on surface water, and a lack of effective HVS in C. pergracile accelerated water depletion and increased xylem embolism even in the typical dry season, which may explain its high mortality rate during extreme drought events in 2019.
In mountainous areas, rock fragments (RFs) are a common feature on the soil surface and in topsoil. Few studies, however, have investigated the spatial distribution of RFs and the relevant mechanisms underpinning their distribution on steep hillslopes, especially in karst regions. We have collected and measured the RF cover, size, and content at the soil surface and within the topsoil of secondary forest, man-made forest, and non-forest land hillslopes in a karst region in Yunnan Province, southwest China. The results revealed no significant relationships between slope position and mean total RF coverage, median diameter (D50), and mean total volumetric RF in topsoil within the three karst hillslopes covered by different types of vegetation. A limited effect of vegetation on the spatial distribution of RFs on the hillslopes was identified. However, the variation in RFs in the topsoil between the top and bottom slopes was greater than that at the surface between the top and bottom slopes, implying that underground leakage was greater than surface runoff.
Forests , Geology/methods , Soil , China , Soil/chemistry
This study explored the capsule formation and fiber development process of kapok which is a tree in Yuanjiang dry-hot valleys (DHV) using the methods of paraffin section and scanning electron microscopy. The result showed that formation process of kapok capsule can be divided into four stages: the capsule formation within 5 days after anthesis (DAA), the capsule mass period from 5 to 35 DAA, the capsule dehydration period from 35 to 50 DAA, and the capsule bursting period after 50 DAA. The kapok fiber was developed via endocarp cells differentiation (0-2 DAA), swelling (2-5 DAA), bulging (5-10 DAA), fiber elongating (10-40 DAA), and divorcing from pericarp (40-50 DAA). During the development, the length and projection width of fiber increased as a power function, and their daily average growth rates reached .the maximums at 20 DAA. Fiber fresh mass substantially increased and then reduced, and the daily average growth rate reached the maximum in the period from 25 to 30 DAA. Fiber dry mass gradually increased and reached the maximum growth rate in the period from 20 to 25 DAA. The seed and fiber continually increased their mass after 30 DAA, but the pericarp mass declined with its dehydration and aging. Compared with cotton, it was easy to separate fiber from kapok capsule inner wall because of small adhesion power between kapok fiber and capsule inner wall. The period from 5 to 35 DAA was critical for the fiber development and growth. Therefore, water and fertilizer management should be concentrated at this stage. The capsule should be harvested at 50 DAA because the fiber began to divorce from the pericarp.
Malvaceae , Seeds/ultrastructure , Microscopy, Electron, Scanning , Trees , Water
