国际贸易对环境脆弱性的影响

Owing to the harsh natural environment and unsustainable production system,environmental vulnerability differs substantially among and within regions^([1]).Over the past 20 years,the most environmentally vulnerable countries lost over half of their economic growth potential^([2]).International trade is a double-edged sword for environmental vulnerability.On the one hand,production occurs beyond countries’borders while associated environmental impacts are displaced away from the location of consumption.

中国北方温带草原植被恢复的氮限制

围栏禁牧被认为是退化草原植被恢复的有效手段。在植被的恢复过程中,植物需要从土壤中吸收更多的氮。氮素也是中国北方温带草原植被生长的一个主要限制因素。目前尚不清楚该地区的土壤氮素供应是否能够支持长期的植被恢复。本研究在植被的生长季期间对我国北方7个温带草原进行了野外调查。其中,围栏外侧草地保持持续放牧状态,围栏内侧草地保持完全禁牧状态。研究结果表明,禁牧显著提高了草地地上生物量、物种丰富度和香农-维纳多样性指数,其分别提高了126.2%、42.6%和18.8%。禁牧使土壤硝态氮和总无机氮浓度分别降低了51.9%和21.0%,这表明生长季氮素供应与植物需求可能存在错配现象。同时,围封草地地上生物量、物种丰富度和香农-维纳多样性指数与豆科植物群落优势度呈正相关。这些结果表明,温带草原植被恢复受土壤无机氮限制。群落中豆科植物的生物固氮可能缓解植被恢复的氮限制。

Global patterns of the responses of leaf-level photosynthesis and respiration in terrestrial plants to experimental warming

Aims The balance between leaf photosynthesis and respiration of terrestrial plants determines the net carbon(C)gain by vegetation and consequently is important to climate–C cycle feedback.This study is to reveal the global patterns of the responses of leaf-level net photosynthesis and dark respiration to elevated temperature.Methods Data for leaf-level net photosynthesis rate(P_(n))and dark respiration rate(R_(d))in natural terrestrial plant species with standard deviation(or standard error or confidence interval)and sample size were collected from searched literatures on Web of Science.Then a metaanalysis was conducted to estimate the effects of experimental warming on leaf-level P_(n) and R_(d) of terrestrial plants.Important findings Across all the plants included in the analysis,warming enhanced P_(n) and R_(d) significantly by 6.13 and 33.14%,respectively.However,the responses were plant functional type(PFT)specific.Specifically,photosynthesis of C_(4) herbs responded to experimental warming positively but that of C_(3) herbs did not,whereas their respiratory responses were similar,suggesting C_(4) plants would benefit more from warming.The photosynthetic response declined linearly with increasing ambient temperature.The respiratory responses linearly enhanced with the increase in warming magnitude.In addition,a thermal acclimation of R_(d),instead of P_(n),was observed.Although greater proportion of fixed C was consumed(greater R_(d)/P_(n) ratio),warming significantly enhanced the daily net C balance at the leaf level.This provides an important mechanism for the positive responses of plant biomass and net primary productivity to warming.Overall,the findings,including the contrastive responses of different PFTs and the enhancement in daily leaf net C balance,are important for improving model projection of the climate–C cycle feedback.

Priming effect and its regulating factors for fast and slow soil organic carbon pools: A meta-analysis

The priming effect (PE) plays a critical role in the control of soil carbon (C) cycling and influences the alteration of soil organic C (SOC) decomposition by fresh C input.However,drivers of PE for the fast and slow SOC pools remain unclear because of the varying results from individual studies.Using meta-analysis in combination with boosted regression tree (BRT) analysis,we evaluated the relative contribution of multiple drivers of PE with substrate and their patterns across each driver gradient.The results showed that the variability of PE was larger for the fast SOC pool than for the slow SOC pool.Based on the BRT analysis,67%and 34%of the variation in PE were explained for the fast and slow SOC pools,respectively.There were seven determinants of PE for the fast SOC pool,with soil total nitrogen (N) content being the most important,followed by,in a descending order,substrate C:N ratio,soil moisture,soil clay content,soil pH,substrate addition rate,and SOC content.The directions of PE were negative when soil total N content and substrate C:N ratio were below 2 g kg~(-1)and 20,respectively,but the directions changed from negative to positive with increasing levels of this two factors.Soils with optimal water content (50%–70%of the water-holding capacity) or moderately low pH (5–6) were prone to producing a greater PE.For the slow SOC pool,soil p H and soil total N content substantially explained the variation in PE.The magnitude of PE was likely to decrease with increasing soil pH for the slow SOC pool.In addition,the magnitude of PE slightly fluctuated with soil N content for the slow SOC pool.Overall,this meta-analysis provided new insights into the distinctive PEs for different SOC pools and indicated knowledge gaps between PE and its regulating factors for the slow SOC pool.

Country-level land carbon sink and its causing components by the middle of the twenty-first century

Background:Countries have long been making efforts by reducing greenhouse-gas emissions to mitigate climate change.In the agreements of the United Nations Framework Convention on Climate Change,involved countries have committed to reduction targets.However,carbon(C)sink and its involving processes by natural ecosystems remain difficult to quantify.Methods:Using a transient traceability framework,we estimated country-level land C sink and its causing components by 2050 simulated by 12 Earth System Models involved in the Coupled Model Intercomparison Project Phase 5(CMIP5)under RCP8.5.Results:The top 20 countries with highest C sink have the potential to sequester 62 Pg C in total,among which,Russia,Canada,USA,China,and Brazil sequester the most.This C sink consists of four components:productiondriven change,turnover-driven change,change in instantaneous C storage potential,and interaction between production-driven change and turnover-driven change.The four components account for 49.5%,28.1%,14.5%,and 7.9%of the land C sink,respectively.Conclusion:The model-based estimates highlight that land C sink potentially offsets a substantial proportion of greenhouse-gas emissions,especially for countries where net primary production(NPP)likely increases substantially and inherent residence time elongates.

Response to Smith’s comment

A commentary on our recent article on Journal of Plant Ecology(Liang et al.2013)by Smith(2014)argues that it is not appro-priate to lump data from different experiments together to demonstrate the thermal acclimation of leaf dark respiration.We agree that many factors,as listed by Smith(2014),would impact the responses of leaf carbon exchanges to warming and the consequent thermal acclimation.Although not all factors were included,we discussed in the article that light and vapor pressure deficit(VPD)could have affected our conclusions(Liang et al.2013).The“acclimation”in our paper did not exactly accord with the physiological definition(Atkin and Tjoelker 2003;Smith and Dukes 2013).It is hard to make the environ-mental factors as well as warming magnitude coherent in a syn-thesis study because the data were from different experiments.Therefore,the“acclimation”in our meta-analysis was more like an apparent one rather than the physiologically intrinsic one as defined by Atkin et al.