Abstract Drylands are home to more than 38% of the world's population and are one of the most sensitive areas to climate change and human activities. This review describes recent progress in dryland climate change research. Recent findings indicate that the long‐term trend of the aridity index (AI) is mainly attributable to increased greenhouse gas emissions, while anthropogenic aerosols exert small effects but alter its attributions. Atmosphere‐land interactions determine the intensity of regional response. The largest warming during the last 100 years was observed over drylands and accounted for more than half of the continental warming. The global pattern and interdecadal variability of aridity changes are modulated by oceanic oscillations. The different phases of those oceanic oscillations induce significant changes in land‐sea and north‐south thermal contrasts, which affect the intensity of the westerlies and planetary waves and the blocking frequency, thereby altering global changes in temperature and precipitation. During 1948–2008, the drylands in the Americas became wetter due to enhanced westerlies, whereas the drylands in the Eastern Hemisphere became drier because of the weakened East Asian summer monsoon. Drylands as defined by the AI have expanded over the last 60 years and are projected to expand in the 21st century. The largest expansion of drylands has occurred in semiarid regions since the early 1960s. Dryland expansion will lead to reduced carbon sequestration and enhanced regional warming. The increasing aridity, enhanced warming, and rapidly growing population will exacerbate the risk of land degradation and desertification in the near future in developing countries.
Simultaneous and accurate measurements of whole-plant instantaneous carbon-use efficiency (ICUE) and annual total carbon-use efficiency (TCUE) are difficult to make, especially for trees. One usually estimates ICUE based on the net photosynthetic rate or the assumed proportional relationship between growth efficiency and ICUE. However, thus far, protocols for easily estimating annual TCUE remain problematic. Here, we present a theoretical framework (based on the metabolic scaling theory) to predict whole-plant annual TCUE by directly measuring instantaneous net photosynthetic and respiratory rates. This framework makes four predictions, which were evaluated empirically using seedlings of nine Picea taxa: (i) the flux rates of CO2 and energy will scale isometrically as a function of plant size, (ii) whole-plant net and gross photosynthetic rates and the net primary productivity will scale isometrically with respect to total leaf mass, (iii) these scaling relationships will be independent of ambient temperature and humidity fluctuations (as measured within an experimental chamber) regardless of the instantaneous net photosynthetic rate or dark respiratory rate, or overall growth rate and (iv) TCUE will scale isometrically with respect to instantaneous efficiency of carbon use (i.e., the latter can be used to predict the former) across diverse species. These predictions were experimentally verified. We also found that the ranking of the nine taxa based on net photosynthetic rates differed from ranking based on either ICUE or TCUE. In addition, the absolute values of ICUE and TCUE significantly differed among the nine taxa, with both ICUE and temperature-corrected ICUE being highest for Picea abies and lowest for Picea schrenkiana. Nevertheless, the data are consistent with the predictions of our general theoretical framework, which can be used to access annual carbon-use efficiency of different species at the level of an individual plant based on simple, direct measurements. Moreover, we believe that our approach provides a way to cope with the complexities of different ecosystems, provided that sufficient measurements are taken to calibrate our approach to that of the system being studied.
The variation of mutual-inductance is the essential reason for fluctuation of transmission power and efficiency during wireless power transfer (WPT) misalign. To maintain output power stability, current methods, such as primary regulation, secondary conversion, magnetic coupling mechanism (MCM) optimization, and compensation topology design, have not changed the characteristic of mutual-inductance changing with misalignment. A strong misalignment tolerance WPT system based on the influence of high permeability magnetic materials on equivalent electrical parameters of MCM is proposed. When the primary and secondary sides of MCM shift, the relative distance between magnetic shielding and coil (RDMSC) is adjusted to maintain the stability of mutual-inductance. The transmission efficiency and power are not affected by misalignment. Alternatively, RDMSC can be actively adjusted to meet the various needs of diverse loads at different times. Simulations and experiments are conducted. The effectiveness of the proposed scheme that RDMSC is actively adjusted to overcome misalignment is verified. This is a new method based on active adjustment of spatial electromagnetic coupling, which provides a new idea for WPT to overcome the influence of misalignment and maintain stable output.
Morphological traits of co- nifer species are known to vary adaptively with the geographic and climatic variables, but little is known about intra- and inter-population varia- tion and impact of associated climate factors on the morphological variation. Chinese hard pine (Pinus tabulaeformis Carr) is a major and wide- spread component of coniferous forests in the temperate and semi-humid zone in northern China. Here we investigated 12 life history traits involving cone length (Cl), width (Cw ) and dry weight (CD w), cone length to width ratio (Clw), seed length (sl), width (Cw ) and total weight (stw ), seed length to width ratio (slw ), seed wing length (swl), width (sww ) and total weight (swtw ), seed wing length to width ration (swlw) at 12 sites between longitudes (102oe to 122oe) and latitudes (32oN to 43oN) covering an altitude range of 125-2581 m. our results showed that each morphological character presented a large variation both within and among popula- tions. Moreover, we found that proportion of phe- notypic variation (i.e. st , %) of the all cone traits except for the cone width was over 50% among populations, indicating that the variation of these traits was mainly controlled by the environmen- tal variables. although the mean proportion of phenotypic variation of all measured traits was only about 28% among populations of this spe- cies, it was much higher than those of other co- nifers, which further suggested that this species held the higher adaptive phenotypic variation or stress-tolerance ability under varying environ- mental conditions. Furthermore, the phenotypic variation presented a general pattern that almost all measured traits were negatively correlated with the potential evapotranspiration which reflected the synthetic effects of multiple factors such as the temperature and rainfall, rather than a single environmental or climatic factor. In conclusion, according to the relationship between phenotypic variation and climate factors, it will undoubtedly provide important information for the reforesta- tion and genetic conservation for this species in the changing climate.
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