Water table drawdown across peatlands increases carbon dioxide (CO 2 ) and reduces methane (CH 4 ) emissions. The net climatic effect remains unclear. Based on observations from 130 sites around the globe, we found a positive (warming) net climate effect of water table drawdown.Using a machine-learning based upscaling approach, we predict that peatland water table drawdown driven by climate drying and human activities will increase CO 2 emissions by 1.13 (95% interval: 0.88 -1.50 ) Gt yr -1 and reduce CH 4 by 0.26 (0.14 -0.52) Gt CO 2 -eq yr -1 , resulting in a net increase of greenhouse gas (GHG) of 0.86 (0.36 -1.36) Gt CO 2 -eq yr -1 by the end of the 21 st century under the RCP8.5 climate scenario. This net source drops to 0.73 (0.2 -1.2) Gt CO 2 -eq yr -1 under RCP2.6. Our results point to an urgent need to preserve pristine and rehabilitate drained peatlands to decelerate the positive (more warming) feedback among water table drawdown, increased GHG emissions and climate warming.

Natural grassland productivity, which is based on an individual plant’s aboveground biomass (AB) and its interaction with herbivores, can obviously affect terrestrial ecosystem services and the grassland’s agricultural production. As plant traits have been linked to both AB and ecosystem success, they may provide a useful approach to understand the changes in individual plants and grassland productivity in response to grazing on a generic level. Unfortunately, the current lack of studies on how plant traits affect AB affected by herbivores leaves a major gap in our understanding of the mechanism of grassland productivity decline. This study, therefore, aims to analyze the paths of overgrazing-induced decline in the individual AB of Leymus chinensis (the dominant species of meadow-steppe grassland in northern China) on a plant functional trait scale. Using a paired-sampling approach, we compared the differences in the functional traits of L. chinensis in long-term grazing-excluded and experimental grazing grassland plots over a continuous period of approximately 20 years (located in meadow steppe lands in Hailar, Inner Mongolia, China). We found a highly significant decline in the individual height and biomass (leaf, stem, and the whole plant) of L. chinensis as a result of overgrazing. Biomass allocation and leaf mass per unit area were significantly affected by the variation in individual size. Grazing clearly enhanced the sensitivity of the leaf-to-stem biomass ratio in response to variation in individual size. Moreover, using a method of standardized major axis estimation, we found that the biomass in the leaves, stems, and the plant as a whole had highly significant allometric scaling with various functional traits. Also, the slopes of the allometric equations of these relationships were significantly altered by grazing. Therefore, a clear implication of this is that grazing promotes an asymmetrical response of different plant functional traits to variation in individual plant size, which influences biomass indirectly. Furthermore, we detected paths of individual AB decline in L. chinensis induced by grazing by fitting to a structural equation model. These results indicate that grazing causes AB decline primarily through a ‘bottom-up’ effect on plant height and stem traits. However, leaf traits, via the process of allometric scaling, affect plant AB indirectly.

Five aromatic plants, Centaurea cyanus, Saturela hortensis, Nepeta cataria, Agerarum houstonianum, and Ocimum basilicum, were assessed as intercrops in a pear orchard, and all significantly reduced the pest population compared with that in the plot natural grasses. The decrease was particularly marked for C. cyanus, S. hortensis, and A. houstonianum, and plots intercropped with these aromatic plants also had significantly higher values of ratios of natural enemies to pests, Simpson's index, the Shannon-Wiener index, and the evenness index of arthropod species at the flowering, immature-fruits, and fruit-growth stages of the pear trees. In none of the plots except that intercropped with C. cyanus, however, were there any significant changes in the abundance of predators and parasitoids. Intercropping with aromatic plants in pear orchards proved beneficial to the main crop by repelling pests and regulating the structure of the arthropod community in the pear orchard ecosystem.