Spatio-temporal variations of vegetation carbon use efficiency and potential driving meteorological factors in the Yangtze River Basin

Understanding of the vegetation dynamics is essential for addressing the potential threats of terrestrial ecosystem.In recent years,the vegetation coverage of the Yangtze River Basin(YRB)has increased significantly,yet the spatio-temporal variations and potential driving meteorological factors of carbon use efficiency(CUE)under the context of global warming are still not clear.In this study,MODIS-based public-domain data during 2000–2015 was used to analyze these aspects in the YRB,a large river basin with powerful ecological functions in China.Spatio-temporal variations of CUE in different sub-basins and land cover types were investigated and the correlations with potential driving meteorological factors were examined.Results revealed that CUE in the YRB had strong spatiotemporal variability and varied remarkably in different land cover types.For the whole YRB,the average CUE of vegetated land was 0.519,while the long-term change trend of CUE was obscure.Along the rising altitude,CUE generally showed an increasing trend until the altitude of 3900 m and then followed by a decreasing trend.CUE of grasslands was generally higher than that of croplands,and then forest lands.The inter-annual variation of CUE in the YRB is likely to be driven by precipitation as a strong positive partial correlation between the inter-annual variability of CUE and precipitation was observed in most of sub-basins and land cover types in the YRB.The influence of temperature and relative humidity is also outstanding in certain regions and land cover types.Our findings are useful from the view point of carbon cycle and reasonable land cover management under the context of global warming.

Erosion effects on soil microbial carbon use efficiency in the mollisol cropland in northeast China

●Soil erosion decreased soil microbial CUE and increased microbial uptake of carbon.●Soil erosion decreased microbial CUE by decreasing substrate C,N and MBC and increasing soil pH.●Soil microbes had to increase their uptake rate to cope with the loss of substrates with increasing erosion rate.●Soil microbial respiration increased with increasing degree of erosion.●Soil microbial growth rate remained relative stable under different degrees of soil erosion.●Microbial CUE in soil surface was less responsive to erosion than that in deeper soil.Soil microbial carbon use efficiency(CUE)is an important synthetic parameter of microbial community metabolism and is commonly used to quantify the partitioning of carbon(C)between microbial growth and respiration.However,it remains unclear how microbial CUE responds to different degrees of soil erosion in mollisol cropland.Therefore,we investigated the responses of soil erosion on microbial CUE,growth and respiration to different soil erosion rates in a mollisol cropland in northeast China based on a substrate independent method(18O-H2O labeling).Soils were sampled at four positions along a down-slope transect:summit,shoulder,back and foot.We found microbial CUE decreased significantly with increasing soil erosion rate in 5−20 cm soil,but did not change in 0−5 cm.The decrease of microbial CUE in subsoil was because microbes increased C uptake and allocated higher uptake C to microbial basal respiration with increasing soil erosion rate.Microbial respiration increased significantly with soil erosion rate,probably due to the more disturbance and unbalanced stoichiometry.Furthermore,soil microbes in surface soil were able to maintain their growth rates with increasing degree of erosion.Altogether,our results indicated that soil erosion could decrease microbial CUE by affecting soil physical and chemical properties,resulting in more decomposition of soil organic matter and more soil respiration,which had negative feedbacks to soil C sequestration and climate changes in cropland soil.

Responses of soil microbial carbon use efficiency to warming: Review and prospects

Microbial carbon use efficiency(CUE)is an important factor driving soil carbon(C)dynamics.However,microbial CUE could positively,negatively,or neutrally respond to increased temperature,which limits our prediction of soil C storage under future climate warming.Experimental warming affects plant production and microbial communities,which thus can have a significant impact on biogeochemical cycles of terrestrial ecosystems.Here,we reviewed the present research status of methods measuring microbial CUE and the response of microbial CUE to the changes of biotic and abiotic factors induced by warming.Overall,current measurement methods mainly include metabolic flux analysis,calorespirometry,stoichiometric model,13C and 18O labeling.Differences in added substrate types can lead to an overestimation or underestimation on microbial CUE,particularly when using the 13C labeling method.In addition,changes in the dominant microbial community under warming may also affect CUE.However,there is still uncertainty in CUE characteristics of different microorganisms.Microbial CUE is generally decreased under warming conditions as microbes are subjected to water stress or soil labile organic matter is much more depleted compared to ambient conditions.In contrast,considering that warming increases soil nutrient availability,warming may enhance microbial CUE by alleviating nutrient limitations for microbes.In conclusion,the response of microbial CUE to warming is more complex than expected.The microbial growth and physiological adaptation to environmental stress under warming is one of the main reasons for the inconsistence in microbial CUE response.Finally,we propose five aspects where further research could improve the understanding of microbial CUE in a warmer world,including using new technologies,establishing multi-factor interactive experiments,building a network of experimental research platform for warming,and strengthening studies on response of CUE to warming at different soil depths and on different temporal scales.

Effects of soil organism interactions and temperature on carbon use efficiency in three different forest soils

Microbial carbon use efficiency(CUE)affects the soil C cycle to a great extent,but how soil organisms and the abiotic environment combine to influence CUE at a regional scale remains poorly understood.In the current study,microcosms were used to investigate how microbial respiration,biomass,and CUE responded to biotic and abiotic factors in natural tropical,subtropical,and temperate forests.Soil samples from the forests were collected,sterilized,and populated with one or a combination of three types of soil organisms(the fungus Botrytis cinerea,the bacterium Escherichia coli,and the nematode Caenorhabditis elegans).The microcosms were then kept at the mean soil temperatures of the corresponding forests.Microbial respiration,biomass,and CUE were measured over one-month incubation period.The results showed that microbial biomass and CUE were significantly higher,but microbial respiration lower in the subtropical and temperate forest soils than in tropical forest soil.Biotic factors mainly affected CUE by their effect on microbial biomass,while temperature affected CUE by altering respiration.Our results indicate that temperature regulates the interactive effects of soil organisms on microbial biomass,respiration,and CUE,which would provide a basis for understanding the soil C cycle in forest ecosystems.

Effect of climate change on seasonal water use efficiency in subalpine Abies fabri

Abies fabri is a typical subalpine dark coniferous forest in southwestern China. Air temperature increases more at high elevation areas than that at low elevation areas in mountainous regions,and climate change ratio is also uneven in different seasons. Carbon gain and the response of water use efficiency(WUE) to annual and seasonal increases in temperature with or without CO_2 fertilization were simulated in Abies fabri using the atmospheric-vegetation interaction model(AVIM2). Four future climate scenarios(RCP2.6,RCP4.5,RCP6.0 and RCP8.5) from the Coupled Model Intercomparison Project Phase 5(CMIP5) were selectively investigated. The results showed that warmer temperatures have negative effects on gross primary production(GPP) and net primary production(NPP) in growing seasons and positive effects in dormant seasons due to the variation in the leaf area index. Warmer temperatures tend to generate lower canopy WUE and higher ecosystem WUE in Abies fabri. However,warmer temperature together with rising CO_2 concentrations significantlyincrease the GPP and NPP in both growing and dormant seasons and enhance WUE in annual and dormant seasons because of the higher leaf area index(LAI) and soil temperature. The comparison of the simulated results with and without CO_2 fertilization shows that CO_2 has the potential to partially alleviate the adverse effects of climate warming on carbon gain and WUE in subalpine coniferous forests.

The effect of abiotic stresses on plant C:N:P homeostasis and their mitigation by silicon

In crop plants, various environmental stresses affect the balance of carbon, nitrogen, and phosphorus(C:N:P), leading to biochemical and physiological alterations and reductions in yield. Silicon(Si) is a beneficial element that alleviates plant stress. Most studies involving silicon have focused on physiological responses, such as improvements in photosynthetic processes, water use efficiency, and antioxidant defense systems. But recent research suggests that stressed plants facing either limited or excessive resources(water, light, nutrients, and toxic elements), strategically employ Si to maintain C:N:P homeostasis, thereby minimizing biomass losses. Understanding the role of Si in mitigating the impact of abiotic stresses on plants by regulating C:N:P homeostasis holds great potential for advancing sustainable agricultural practices in crop production. This review presents recent advances in characterizing the influence of environmental stresses on C:N:P homeostasis, as well as the role of Si in preserving C:N:P equilibrium and attenuating biological damage associated with abiotic stress. It underscores the beneficial effects of Si in sustaining C:N:P homeostasis and increasing yield via improved nutritional efficiency and stress mitigation.

Manipulated precipitation regulated carbon and phosphorus limitations of microbial metabolisms in a temperate grassland on the Loess Plateau,China

Manipulated precipitation patterns can profoundly influence the metabolism of soil microorganisms.However,the responses of soil organic carbon(SOC)and nutrient turnover to microbial metabolic limitation under changing precipitation conditions remain unclear in semi-arid ecosystems.This study measured the potential activities of enzymes associated with carbon(C:β-1,4-glucosidase(BG)andβ-D-cellobiosidase(CBH)),nitrogen(N:β-1,4-N-acetylglucosaminidase(NAG)and L-leucine aminopeptidase(LAP))and phosphorus(P:alkaline phosphatase(AP))acquisition,to quantify soil microbial metabolic limitations using enzymatic stoichiometry,and then identify the implications for soil microbial metabolic limitations and carbon use efficiency(CUE)under decreased precipitation by 50%(DP)and increased precipitation by 50%(IP)in a temperate grassland.The results showed that soil C and P were the major elements limiting soil microbial metabolism in temperate grasslands.There was a strong positive dependence between microbial C and P limitations under manipulated precipitation.Microbial metabolism limitation was promoted by DP treatment but reversed by IP treatment.Moreover,CUE was inhibited by DP treatment but promoted by IP treatment.Soil microbial metabolism limitation was mainly regulated by soil moisture and soil C,N,and P stoichiometry,followed by available nutrients(i.e.,NO^(-)_(3),NH^(+)_(4),and dissolved organic C)and microbial biomass(i.e.,MBC and MBN).Overall,these findings highlight the potential role of changing precipitation in regulating ecosystem C turnover by limiting microbial metabolism and CUE in temperate grassland ecosystems.

Climate-driven variations in productivity reveal adaptive strategies in Iberian cork oak agroforestry systems

Background:Cork oak agroforestry systems(AFS)have been managed for centuries by humans to produce cork and other goods and services and have recently been recognised as an important reservoir for biodiversity improvement and conservation.However,despite having recently been included as a natural habitat of community-wide interest within the EU Habitats Directive,these systems are in a critical situation of decline.Among other factors,they are strongly threatened by climate change,the effects of which are also expected to be particularly severe in the Mediterranean region.In this study,we aimed to evaluate the influence of climate variability by examining primary production indicators and also to analyse whether the geographical location may have a role in the incidence of the adverse effects of climate.Methods:Cork oak AFS were identified in the Forest Map of Spain and the Land use map of Portugal and categorized on the basis of canopy cover.Seasonal climate data from 2001 to 2020 were used to model relationships with climate predictors and proximity to the coast.Hotspot analysis was conducted to identify significant spatial clusters of high-and low-efficiency areas.Results:The responses to the influence of climatic conditions differed among the various cork oak AFS categories,particularly in the forest category,which was less dependent on climate variations.Relative humidity and water availability were the main drivers of net primary production(NPP).Carbon use efficiency(CUE)was limited by relative humidity and spring temperature in open ecosystems.Proximity to the coast proved beneficial,especially in years with adverse weather conditions,but was not a limiting factor for survival of the ecosystem.Finally,the results of the hotspot analysis supported the other findings,highlighting high-efficiency areas close to the coast and cold spots grouped in specific areas or dispersed inland.Conclusions:Canopy plays a key role in the influence of climatic conditions,particularly in forest categories in which a high density seems to generate microclimate conditions.Water availability,both via the soil and air moisture,is the main driver of primary production,reflecting different adaptive strategies.The oceanic atmosphere may act as a buffer in years of extreme drought.

Soil microbial respiration is regulated by stoichiometric imbalances: Evidence from a humidity gradient case

Humidity not only affects soil microbial respiration(SMR) directly, but, indirectly by regulating the availability of soil water and nutrients. However,the patterns of direct and indirect effects of humidity on SMR over large precipitation gradients remain unclear, limiting our understanding of the effects of precipitation changes on soil C cycle. Here, we investigated the relationships among humidity, soil nutrients, and SMR by identifying stoichiometric imbalances, microbial elemental homeostasis, and microbial C use efficiency along a precipitation gradient at a continental scale. The relationship between SMR and humidity index(HI) corresponded to a Richard’s curve with an inflection point threshold value of approximately 0.7. Soil microbial respiration increased with increasing humidity in drier areas(HI < 0.7), but tended to balance above this threshold. Increasing humidity exacerbated C:P and N:P imbalances across the selected gradient. Severe N and P limitations in soil microbial communities were observed in drier areas, while soil microbes suffered from aggravated P limitation as the humidity increased in wetter areas(HI > 0.7). Soil microbial communities regulated their enzyme production to maintain a strong stoichiometric homeostasis in drier areas;enzyme production, microbial biomass, and threshold elemental ratios were non-homeostatic under P limitation in wetter areas, which further contributed to the increase in SMR. Our results identified a moisture constraint on SMR in drier areas and highlighted the importance of nutrient(especially for P) limitations induced by humidity in regulating SMR in wetter areas. Understanding the modulation of SMR via soil enzyme activity may improve the prediction of soil C budget under future global climate change.

Soil calcium content as the driving factor for vegetative structure and soil microbial function diverging across a fire chronosequence of the boreal forests in northeast China

The role of biophysical variables in constructing community structure changes with the time since fire.The major objective of this study is to verify the transition stage and its underlying variables for the postfire forest and soil microbial function in the boreal forested area of China.A 50-year fire chronosequence was presented,and biomass of forbs,shrubs and woody plants was separately weighted to assess their contribution to the whole community with the year since fire(YSF).Simultaneously,soil biophysical properties were measured for stands in different time periods after fire.Soil microbial functions,i.e.growth efficiency(GE)and carbon use efficiency(CUE),were calculated based on ecoenzymatic and soil nutrient stoichiometry.In terms of vegetative structure,forbs’proportion decreased from 75%to 1.5%,but the proportion of woody plants increased from 0.04%to 70%across this fire chronosequence.GE and CUE of soil microorganisms averaged 0.242 and 0.236 and were significantly higher in 9,15 and 31 YSF than in 2 and 3 YSF.Soil metal content was significantly increased at the late stage of this fire chronosequence,and soil calcium content showed a positive correlation with woody plant biomass and a negative correlation with soil microbial function.Overall,the present work highlights that the time period of 15 and 31 YSF is a hallmark stage for aboveground vegetative structure and soil microbial function to change in different trends and that the calcium content may partly account for these two divergent trajectories.