In this work, we investigated the microphase separation, mechanical, and dynamic mechanical properties of thermoplastic polyurethane elastomers (TPUs) with one‐soft segment (polypropylene glycol, PPG, or hydroxyl‐terminated polybutadiene, HTPB) or bi‐soft segment (PPG and HTPB) using FTIR, XRD, SAXS and amplitude modulated‐frequency modulated viscoelastic mode of AFM (AM‐FM mode AFM) methods. The results showed that the microphase separation process of hard and soft segments (HS and SS) in TPU containing PPG and HTPB soft segments (PPG‐HTPB‐PU) was restricted by randomly alternated bi‐soft segments, which results in formation of a low content of irregular‐shaped hard domain (HD). In addition, the microphase separation of PPG‐HTPB‐PU induced a triple‐phased structure of HD, HTPB rich phase and mesophase. The mesophase of PPG‐HTPB‐PU was formed of HS, PPG and HTPB segments which were excluded out of HD and HPTB rich domains during microphase separation process. The damping temperature range (at tan δ greater than 0.3) of PPG‐HTPB‐PU was from −14.6 to 32.1°C (46.5°C) which was more broad than that of TPU containing HTPB soft segment (HTPB‐PU). The broad damping temperature range of PPG‐HTPB‐PU is mainly attributed to the enhanced energy consumption caused by the frictional motions of mixed segments of mesophase.

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Background and aims Drought is predicted to have a profound impact on soil respiration. This study aimed to assess the effects of long-term precipitation decrease on soil respiration in a tropical rainforest. Methods A precipitation reduction experiment was conducted in a tropical forest in southwest China at the beginning of 2011. Soil respiration and environmental parameters were measured monthly for three years. Results The continuous precipitation reduction treatment did not affect the seasonal patterns of soil respiration, but it significantly increased soil respiration in the study plot during the rainy season, and the relationship between soil respiration and soil moisture differed in the control and reduction treatment in the rainy season. Compared with the net ecosystem exchange of carbon in this system, the increment of annual soil carbon emissions in the reduction treatment was considerable and should not be ignored. ConclusionsOur results indicate that the responses of soil respiration to precipitation decrease may vary seasonally and the variation of volumetric water content in different seasons may be an important factor leading to the seasonal variation. The variation of soil moisture among different ecosystems as well as in different seasons should be taken into consideration when predicting the future response of soil respiration to drought globally.

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To gain the effects of N fertilizer applications on N2O emissions and local climate change in fertilized rubber (Hevea brasiliensis) plantations in the tropics, we measured N2O fluxes from fertilized (75 kg N ha−1 yr−1) and unfertilized rubber plantations at Xishuangbanna in southwest China over a 2-year period. The N2O emissions from the fertilized and unfertilized plots were 4.0 and 2.5 kg N ha−1 yr−1, respectively, and the N2O emission factor was 1.96%. Soil moisture, soil temperature, and the area weighted mean ammoniacal nitrogen (NH4+-N) content controlled the variations in N2O flux from the fertilized and unfertilized rubber plantations. NH4+-N did not influence temporal changes in N2O emissions from the trench, slope, or terrace plots, but controlled spatial variations in N2O emissions among the treatments. On a unit area basis, the 100-year carbon dioxide equivalence of the fertilized rubber plantation N2O offsets 5.8% and 31.5% of carbon sink of the rubber plantation and local tropical rainforest, respectively. When entire land area in Xishuangbanna is considered, N2O emissions from fertilized rubber plantations offset 17.1% of the tropical rainforest’s carbon sink. The results show that if tropical rainforests are converted to fertilized rubber plantations, regional N2O emissions may enhance local climate warming.

Savanna ecosystems play a crucial role in the global carbon cycle. However, there is a gap in our understanding of carbon fluxes in the savanna ecosystems of Southeast Asia. In this study, the eddy covariance technique (EC) and the biometric-based method (BM) were used to determine carbon exchange in a savanna ecosystem in Southwest China. The BM-based net ecosystem production (NEP) was 0.96 tC ha −1 yr −1 . The EC-based estimates of the average annual gross primary productivity (GPP), ecosystem respiration (R eco ), and net ecosystem carbon exchange (NEE) were 6.84, 5.54, and −1.30 tC ha −1 yr −1 , respectively, from May 2013 to December 2015, indicating that this savanna ecosystem acted as an appreciable carbon sink. The ecosystem was more efficient during the wet season than the dry season, so that it represented a small carbon sink of 0.16 tC ha −1 yr −1 in the dry season and a considerable carbon sink of 1.14 tC ha −1 yr −1 in the wet season. However, it is noteworthy that the carbon sink capacity may decline in the future under rising temperatures and decreasing rainfall. Consequently, further studies should assess how environmental factors and climate change will influence carbon-water fluxes.Savanna ecosystems are characterized by distinct wet and dry seasons, the codominance of C3 trees and C4 grasses 1 , and their location mainly in the tropics and subtropics. They cover almost 60%, 50%, and 45% of the areas of Africa, Australia, and South America, respectively, and more than 10% of the area of Southeast Asia 2 . They play an increasing role in the carbon cycle and energy fluxes in the context of climate changes (e.g., decreasing precipitation and increasing temperature), as they cover approximately 20.0% (2.7 billion ha) of the global land surface 1,3-5 and account for ~30% of the net primary production (NPP) of the terrestrial ecosystem 6 . Savannas also have a large and rapidly growing human population: about one-fifth of the global population is supported by savanna ecosystems 3,4,7 . The carbon exchange of savanna ecosystems, therefore, has a significant influence on global carbon cycling. Consequently, research on the spatiotemporal characteristics of carbon exchange and its responses to biotic and abiotic controls on savanna ecosystems is of great importance, not only for improved fundamental ecological understanding of the impact of global change on carbon fluxes but also for the improved protection and management of this vulnerable ecosystem type for sustainable development and provision of better ecosystem services (e.g., the management of resources, water, biodiversity, and climate change).

Canopy temperature is a result of the canopy energy balance and is driven by climate conditions, plant architecture, and plant-controlled transpiration. Here, we evaluated canopy temperature in a rubber plantation (RP) and tropical rainforest (TR) in Xishuangbanna, southwestern China. An infrared temperature sensor was installed at each site to measure canopy temperature. In the dry season, the maximum differences (T - T) between canopy temperature (T) and air temperature (T) in the RP and TR were 2.6 and 0.1 K, respectively. In the rainy season, the maximum (T - T) values in the RP and TR were 1.0 and -1.1 K, respectively. There were consistent differences between the two forests, with the RP having higher (T - T) than the TR throughout the entire year. Infrared measurements of T can be used to calculate canopy stomatal conductance in both forests. The difference in (T - T) at three g levels with increasing direct radiation in the RP was larger than in the TR, indicating that change in (T - T) in the RP was relatively sensitive to the degree of stomatal closure.