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Tree transpiration is an important part of the global water cycle, and it is frequently represented by sap flow measurements at the individual plant scale. The thermal dissipation probes (TDPs) are commonly employed to measure and calculate sap flows, for which Granier equation is generally used. However, the original Granier equation has been found to underestimate sap flow rates. Calibration methods using different materials (i.e., whole trees or stem segments) have been proposed to recalibrate TDPs; however, these methods are often either expensive or complicated. This study proposes a new device that uses the gravimetric measurement method (GMM) to recalibrate TDPs. The GMM is relatively simple and easy to conduct. The proposed device uses a tube and siphon to maintain a constant pressure; an electronic balance is used to measure the actual sap flow. Four plant species with different stem porosity types, Pyrus pyrifolia (diffuse‐porous), Quercus fabri (ring‐porous), Platycarya strobilacea (ring‐porous) and Kalopanax septemlobus (ring‐porous), were selected to examine the performance of the GMM. The results showed that: (1) good correlations were obtained between the actual sap flow (from gravimetric measurements) and sap flow estimates obtained using the original TDP technique; (2) the results of the GMM‐recalibrated TDP measurement equation greatly differed from those of the original Granier calibration equation; and (3) the recalibration equation derived from the GMM outperformed the original Granier equation. This study suggests that the developed GMM can be used to recalibrate TDPs, and that using this method can help to improve sap flow measurements, thereby improving estimates of tree water consumption and transpiration. [ABSTRACT FROM AUTHOR]

• The 10-year flooding process in subtropical karst depressions was studied. • Napier grass can tolerates 10.2 days of flooding. • Maize can survive when the Maize plant protruded 1.5 m above the water level. • Safe planting heights: Napier grass 3.09 m, Maize 6.21 m, relative to lowest point. Understanding the characteristics of flood resistance within agricultural ecosystems is essential for the planning of agricultural structures within karst depressions against floods. However, the responses of crops to flooding were rarely investigated under natural precipitation extremes in karst depressions. This study investigates the influence of flooding on agricultural ecosystems (Maize and Napier grass) in a typical karst peak-cluster depression in Southwest China after an extreme rainfall event in 2016. Results showed that this rainfall event was once every 10 years, and caused 78.6 % of Maize and 20.4 % of Napier grass in death. Napier grass performed better than Maize when submerged, due to higher fine root biomass and the stable photosynthetic capacity of the leaves. The submergence critical tolerance time of flooding to Napier grass was 10.2 days; only when the Maize plant protruded 1.5 m above the water level can it survive. In response to this extreme event in 2016, the safe planting height for Napier grass and Maize was 3.09 m and 6.21 m, respectively, relative to the lowest point of the depression elevation (set at 0.00 m). This study implicated that it is necessary to rationally arrange the layout of agroecosystems at the karst depression according to the ability of plants to withstand flooding to cope with future climate change. [ABSTRACT FROM AUTHOR]

Soil hydrologic functions are important for karst landscapes where soil water loss is significant. The largest global ecological restoration engineering project, namely the “Grain for Green” program, is being implemented since 2000 in karst landscapes across southwestern China. However, its effects on soil hydrologic functions are still unknown. Using data acquired in field investigations and a generalized linear model (GLM), this study examines the effects of different vegetation restoration types on soil field saturated-hydraulic conductivity ( K fs ) in karst landscapes of southwest China. The results indicate that the K fs of artificial grassland (napiergrass) was higher than in other vegetation restoration types (zenia insignis, toona sinensis, orchard, and natural restoration shrubland) and cropland at both the surface and 10 cm depths. The K fs of vegetation restoration lands was lower than that of Mulun nature reserve (primary forest) at both the surface and 30 cm depths. We found significant differences of K fs in different depths of vegetation restoration lands but not significant for primary forest. The GLM model explains 64.75% of the total variation in K fs . Among the input variables, vegetation type explained the largest proportion (11.29%) of the variation, followed by bulk density (BD), soil organic carbon, and BD and vegetation type interactions. The factors above were significantly related to K fs . This study suggests that the implementation of different vegetation restoration types can alter soil hydrologic functions and provides useful knowledge for ecological restoration practices and management in karst landscapes. [ABSTRACT FROM AUTHOR]