Effects of thinning and understory removal on water use efficiency of Pinus massoniana:evidence from photosynthetic capacity and stable carbon isotope analyses

Understanding the relationship between forest management and water use efficiency(WUE)is important for evaluating forest adaptability to climate change.However,the effects of thinning and understory removal on WUE and its key controlling processes are not well understood,which limits our comprehension of the physiological mechanisms of various management practices.In this study,four forest management measures(no thinning:NT;understory removal:UR;light thinning:LT;and heavy thinning:HT)were carried out in Pinus massoniana plantations in a subtropical region of China.Photosynthetic capacity and needle stable carbon isotope composition(δ^(13)C)were measured to assess instantaneous water use efficiency(WUE_(inst))and long-term water use efficiency(WUE_(i)).Multiple regression models and structural equation modelling(SEM)identified the effects of soil properties and physiological performances on WUE_(inst)and WUE_(i).The results show that WUE_(inst)values among the four treatments were insignificant.However,compared with the NT stand(35.8μmol·mol^(-1)),WUE_(i)values significantly increased to 41.7μmol·mol^(-1)in the UR,50.1μmol·mol^(-1)in the LT and 46.6μmol·mol^(-1)in HT treatments,largely explained by photosynthetic capacity and soil water content.Understory removal did not change physiological performance(needle water potential and photosynthetic capacity).Thinning increased the net photosynthetic rate(A_n)but not stomatal conductance(g_s)or predawn needle water potential(ψ_(pd)),implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability.In general,thinning may be an appropriate management measure to promote P.massoniana WUE to cope with seasonal droughts under future extreme climates.

Carbon sequestration rate,nitrogen use efficiency and rice yield responses to long-term substitution of chemical fertilizer by organic manure in a rice–rice cropping system

Combined application of chemical fertilizers with organic amendments was recommended as a strategy for improving yield,soil carbon storage,and nutrient use efficiency.However,how the long-term substitution of chemical fertilizer with organic manure affects rice yield,carbon sequestration rate(CSR),and nitrogen use efficiency(NUE)while ensuring environmental safety remains unclear.This study assessed the long-term effect of substituting chemical fertilizer with organic manure on rice yield,CSR,and NUE.It also determined the optimum substitution ratio in the acidic soil of southern China.The treatments were:(i)NPK0,unfertilized control;(ii)NPK1,100%chemical nitrogen,phosphorus,and potassium fertilizer;(iii)NPKM1,70%chemical NPK fertilizer and 30%organic manure;(iv)NPKM2,50%chemical NPK fertilizer and 50%organic manure;and(v)NPKM3,30%chemical NPK fertilizer and 70%organic manure.Milk vetch and pig manure were sources of manure for early and late rice seasons,respectively.The result showed that SOC content was higher in NPKM1,NPKM2,and NPKM3 treatments than in NPK0 and NPK1 treatments.The carbon sequestration rate increased by 140,160,and 280%under NPKM1,NPKM2,and NPKM3 treatments,respectively,compared to NPK1 treatment.Grain yield was 86.1,93.1,93.6,and 96.5%higher under NPK1,NPKM1,NPKM2,and NPKM3 treatments,respectively,compared to NPK0 treatment.The NUE in NPKM1,NPKM2,and NPKM3 treatments was higher as compared to NPK1 treatment for both rice seasons.Redundancy analysis revealed close positive relationships of CSR with C input,total N,soil C:N ratio,catalase,and humic acids,whereas NUE was closely related to grain yield,grain N content,and phenol oxidase.Furthermore,CSR and NUE negatively correlated with humin acid and soil C:P and N:P ratios.The technique for order of preference by similarity to ideal solution(TOPSIS)showed that NPKM3 treatment was the optimum strategy for improving CSR and NUE.Therefore,substituting 70%of chemical fertilizer with organic manure could be the best management option for increasing CSR and NUE in the paddy fields of southern China.

Changes in Water Use Efficiency Caused by Climate Change,CO_(2) Fertilization,and Land Use Changes on the Tibetan Plateau

Terrestrial ecosystem water use efficiency(WUE)is an important indicator for coupling plant photosynthesis and transpiration,and is also a key factor linking the carbon and water cycles between the land and atmosphere.However,under the combination of climate change and human intervention,the change in WUE is still unclear,especially on the Tibetan Plateau(TP).Therefore,satellite remote sensing data and process-based terrestrial biosphere models(TBMs)are used in this study to investigate the spatiotemporal variations of WUE over the TP from 2001 to 2010.Then,the effects of land use and land cover change(LULCC)and CO_(2) fertilization on WUE from 1981-2010 are assessed using TBMs.Results show that climate change is the leading contributor to the change in WUE on the TP,and temperature is the most important factor.LULCC makes a negative contribution to WUE(-20.63%),which is greater than the positive contribution of CO_(2) fertilization(11.65%).In addition,CO_(2) fertilization can effectively improve ecosystem resilience on the TP.On the northwest plateau,the effects of LULCC and CO_(2) fertilization on WUE are more pronounced during the driest years than the annual average.These findings can help researchers understand the response of WUE to climate change and human activity and the coupling of the carbon and water cycles over the TP.

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.

Soil Carbon Sequestration,Water Use Efficiency(WUE) and Biological Nitrogen Fixation(BNF) Under Conservation Agriculture in Rain-fed Dry Area of North-west Pakistan

Land degradation,unbalanced nutrition,change in climate and its extreme variability are the factors affecting the sustainability of agriculture and food security.In North-west Pakistan,more than 50%of the cultivated area is rain-fed and the crop productivity is low.Conservation agriculture reduces greenhouse gas emissions by enhancing soil carbon sequestration and then improved soil fertility,WUE and crop productivity.A field experiment

Interaction of Carbon Dioxide Enrichment and Soil Moisture on Photosynthesis, Transpiration, and Water Use Efficiency of Soybean

Soybean (Glycine max (L.) Merrill) is one of the most important oil and protein sources in the world. Interactive effect of elevated carbon dioxide (CO2) and soil water availability potentially impact future food security of the world under climate change. A rhizotron growth chamber experiment was conducted to study soil moisture interactions with elevated CO2 on gaseous exchange parameters of soybean under two CO2 concentrations (380 and 800 μmol·mol-1) with three soil moisture levels. Elevated CO2 decreased photosynthetic rate (11.1% and 10.8%), stomatal conductance (40.5% and 36.0%), intercellular CO2 concentration (16.68% and 12.28%), relative intercellular CO2 concentration (17.4% and 11.2%), and transpiration rate (43.6% and 39%) at 42 and 47 DAP. This down-regulation of photosynthesis was probably caused by low leaf nitrogen content and decrease in uptake of nutrients due to decrease in stomatal conductance and transpiration rate. Water use efficiency (WUE) increased under elevated CO2 because increase in total dry weight of plant was greater than that of water use under high CO2 conditions. Plants under normal and high soil moisture levels had significantly higher photosynthetic rate (7% to 16%) favored by optimum soil moisture content and high specific water content of soybean plants. Total dry matter production was significantly high when plants grown under elevated CO2 with normal (74.3% to 137.3%) soil moisture level. Photosynthetic rate was significantly and positively correlated with leaf conductance and intercellular CO2 concentration but WUE was significantly negatively correlated with leaf conductance, intercellular CO2 concentration and transpiration rate. However, the effect of high CO2 on plants depends on availability of nutrients and soil moisture for positive feedback from CO2 enrichment.

Some Physiological Processes Related to Water Use Efficiency of Higher Plants

Water use efficiency （WUE） of higher plants is of vital importance in the dry-land agricultural ecosystem in terms of the development of water-saving agriculture. Of all the approaches used to improve WUE, the intrinsic water use efficiency （WUET, the ratio of CO2 assimilation rate to transpiration rate） can be a right index, as the variation of WUET is correlated with the physiological and biochemical processes of higher plants. The measurements of leaf gas exchange and carbon isotope discrimination （D^13C） are the two ways to detect the variation in WUEr. This article reviewed some physiological processes related to WUEv, including the relationship between CO2 assimilation and stomatal conductance and WUET and water absorption. The relationship between WUE and aquaporin and the yield are discussed as well.

Paludification reduces black spruce growth rate but does not alter tree water use efficiency in Canadian boreal forested peatlands

Background:Black spruce(Picea mariana(Mill.)BSP)-forested peatlands are widespread ecosystems in boreal North America in which peat accumulation,known as the paludification process,has been shown to induce forest growth decline.The continuously evolving environmental conditions(e.g.,water table rise,increasing peat thickness)in paludified forests may require tree growth mechanism adjustments over time.In this study,we investigate tree ecophysiological mechanisms along a paludification gradient in a boreal forested peatland of eastern Canada by combining peat-based and tree-ring analyses.Carbon and oxygen stable isotopes in tree rings are used to document changes in carbon assimilation rates,stomatal conductance,and water use efficiency.In addition,paleohydrological analyses are performed to evaluate the dynamical ecophysiological adjustments of black spruce trees to site-specific water table variations.Results:Increasing peat accumulation considerably impacts forest growth,but no significant differences in tree water use efficiency(iWUE)are found between the study sites.Tree-ring isotopic analysis indicates no iWUE decrease over the last 100 years,but rather an important increase at each site up to the 1980 s,before iWUE stabilized.Surprisingly,inferred basal area increments do not reflect such trends.Therefore,iWUE variations do not reflect tree ecophysiological adjustments required by changes in growing conditions.Local water table variations induce no changes in ecophysiological mechanisms,but a synchronous shift in iWUE is observed at all sites in the mid-1980 s.Conclusions:Our study shows that paludification induces black spruce growth decline without altering tree water use efficiency in boreal forested peatlands.These findings highlight that failing to account for paludification-related carbon use and allocation could result in the overestimation of aboveground biomass production in paludified sites.Further research on carbon allocation strategies is of utmost importance to understand the carbon sink capacity of these widespread ecosystems in the context of climate change,and to make appropriate forest management decisions in the boreal biome.

Photosynthetic Water Use Efficiency of Heritage and Modern Potatoes under Limited and Unlimited Water Environments

Photosynthetic capacity for heritage (Taewa) and modern potato cultivars were compared at different water and nitrogenregimes in the glasshouse and field. The glasshouse was 2*2*4 factorial design with two irrigation: 100% ET and 60% ET;two applied N: 50 kg N ha-1 and 200 kg N ha-1, two Taewa (Moe Moe, Tutaekuri) and two modern potatoes (Moonlight, Agria). The 2009/2010 field experiment was a split-plot, with irrigation and rain-fed regimes as the main treatments: four potatoes above were sub-treatments. The 2010/2011 field experiment was a split-split-plot, with three water regimes as the main treatments: three cultivars (Moe Moe, Tutaekuri, and Agria) were subplots;two N rates were sub-sub-treatments. Gaseous exchange was measured by CIRAS-2 at different days from emergence. Leaf water potential was measured using pressure chamber method. Taewa achieved high photosynthetic WUE in glasshouse and 2010/2011 experiment by maintaining high An, low gs and low Ci compared to modern cultivars (p The An, gs and T increased with irrigation and N increase while decreasing Ci (p < 0.01). Water stress significantly increased VPD resulting in low An and photosynthetic WUE in Moonlight in the glasshouse. The leaf water potential for Taewa was very tolerant while modern potatoes were weakened by water stress. The study indicated that Taewa can be scheduled at partial irrigation without more detrimental effects on photosynthetic capacity while modern potatoes need full irrigation to avoid detrimental effects on photosynthetic capacity.

近20年中国西南地区植被碳利用率时空变化特征及驱动因素

植被碳利用率作为生物圈与大气圈碳循环的关键参数之一,对了解生态系统碳源和碳汇具有重要作用。本文基于MOD17A2H数据,采用Theil-Sen media趋势分析、空间插值以及偏相关分析法,分析2001~2020年西南地区植被碳利用率(Carbon Use Efficiency,CUE)时空分布格局及变化趋势,根据气象数据和数字高程模型(Digital Elevation Model,DEM)数据,重点研究了西南地区植被CUE对气候变化的响应。结果表明:(1)2001~2020年西南地区不同植被类型年内CUE整体呈上升—下降—再上升—再下降的变化特征,整体上各植被类型CUE呈下降趋势,下降速率依次为:灌木>森林>草地>农作物。(2)近20年西南地区植被CUE多年均值约为0.75,植被固碳能力较强,空间上表现出由南部和东北部向西北部递增的空间分布格局,趋势分析表明西南地区植被CUE整体表现为微弱下降趋势。(3)2001~2020年西南地区植被碳利用率与气温、降水以及日照时长均呈负相关关系,整体上西南地区植被CUE主要受气温和日照时长影响,其次为降水。

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.

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.

2000-2013年中国植被碳利用效率(CUE)时空变化及其与气象因素的关系

植被碳利用效率(CUE)是评估陆地碳循环的重要指标,探讨其动态特征对气候变化的响应对于陆地生态系统碳循环研究具有重要的指示意义。基于MOD17数据计算中国植被CUE,辅以地统计学理论,利用趋势分析、变异系数及相关性分析等方法,研究了2000—2013年中国植被CUE的时空变化特征,并结合气象要素数据剖析植被CUE对气候变化的响应。结果表明:全国植被年CUE在研究年限内总体上表现为轻微的增长趋势,具体表现为在2000—2007年以0.000 6的变化率呈现波动下降的趋势,而2007—2013年植被CUE呈现显著上升的变化趋势,该变化特征可归因于2007年气温及降水格局的改变;植被CUE空间分布具有明显的空间异质性,大体呈现西部高东部低的状态。CUE增加较明显的区域主要分布在内蒙古呼伦贝尔地区,青藏高原大部分地区,东部沿海地区以及台湾岛。而CUE呈减少趋势的区域分布范围较广,其中减少趋势较为明显的地区主要包括东北平原及华北华中的大部分地区,另江南地区及新疆部分地区也有零星分布。草地及森林区域植被CUE波动变化较小,表明该部分地区生态系统处于良性循环。不同植被类型的CUE均值表现为:草地(0.21)>农田(0.14)>森林(0.09)>灌丛(0.06)。全国大多数地区植被CUE与降水呈正相关,而与气温则呈负相关,而这种相关性会随着区域气候格局及植被类型的变化而变化。总体上,全国植被CUE的增加主要归因于降水量的增加,而气温的升高则造成植被CUE的降低。

Seasonal and inter-annual variations in carbon fluxes and evapotranspiration over cotton field under drip irrigation with plastic mulch in an arid region of Northwest China

Xinjiang is the largest semi-arid and arid region in China, and drip irrigation under plastic mulch is widely used in this water-limited area. Quantifying carbon and water fluxes as well as investigating their environ- mental drivers over cotton fields is critical for understanding regional carbon and water budgets in Xinjiang, the largest cotton production basin of China. In this study, an eddy covariance （EC） technique was used to measure the carbon and water fluxes of cotton field under drip irrigation with plastic mulch in the growing seasons of 2009, 2010, 2012 and 2013 at Wulanwusu Agrometeorological Experiment Station, a representative oasis cropland in northern Xinjiang. The diurnal patterns of gross primary production （GPP）, net ecosystem exchange （NEE） and evapotran-spiration （ET） showed obviously sinusoidal variations from June to September, while the diurnal ecosystem respiration （Res） was stable between daytime and nighttime. The daytime hourly GPP and ET displayed asymptotic rela-tionships with net solar radiation （Rnet）, while showed concave patterns with raising vapor pressure deficit （VPD） and air temperature （Ta）. The increases in hourly GPP and ET towards the maximum occurred over half ranges of VPD and Ta. The seasonal variations of GPP, NEE and ET were close to the cotton phenology, which almost reached the peak value in July. The cumulative GPP averaged 816.2±55.0 g C/m^2 in the growing season （from April to October）, and more than half of GPP was partitioned into NEE （mean value of -478.6±41.4 g C/m^2）. The mean seasonal ET was 501.3±13.9 mm, and the mean water use efficiency （WUE） was 1.0＋0.1 （mg C/g H2O）/d. The agro-ecosystem behaved as a carbon sink from squaring to harvest period, while it acted as a carbon source before the squaring time as well as after the harvest time.

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.

Spatio-temporal characteristics and typical patterns of eco-efficiency of cultivated land use in the Yangtze River Economic Belt, China

Identifying the dynamics of the eco-efficiency of cultivated land use(ECLU)is important to balance food security and environmental protection.The Yangtze River Economic Belt(YREB)is a vital region of national strategic development in China.However,the spatio-temporal characteristics and typical patterns of the ECLU in the YREB remain unclear.This study aims to reveal the spatio-temporal characteristics of the ECLU by using the super-efficiency slack-based measure(SBM)and a spatial autocorrelation model.The typical patterns of the ECLU were classified based on a decision tree algorithm.The results indicate that the overall ECLU increased from 0.78 to 0.87 from 2000 to 2019,dropping sharply in 2003 before rising again.Different reaches had similar trends.The local indicators of spatial association(LISA)cluster reflect that the spatial distributions of high-high and low-low agglomeration varied dramatically among these years.The ECLU was divided into three typical patterns considering the restriction of agrochemicals and water resources(RAW),cultivated land and agrochemicals(RCA),as well as technology(RT).Most cities belonged to the low ECLU category in RT pattern.Fully understanding the spatio-temporal characteristics and classification of the ECLU will provide a reference for decision-makers to improve the ECLU in different regions.

Spatiotemporal variations of cultivated land use efficiency in the Yangtze River Economic Belt based on carbon emission constraints

In this study,the carbon emissions(CEs)from cultivated land(CL)were included as an undesirable output in the utilization efficiency of such land.A slack-based model was used to calculate the CL use efficiency(CLUE)for 11 provinces and cities in the Yangtze River Economic Belt(YREB)from 2007 to 2016,and then a kernel density estimation map was drawn to analyze the spatiotemporal variations of CLUE.The Tobit model was also employed to analyze the factors affecting the CLUE.The results show the following.1)In the YREB,the CEs from CL showed a rising and then a slowly decreasing trend.In this paper,we calculate CEs by carbon emission factors and major carbon sources,and the CEs from CL in the YREB totaled 25.2354 million tons in 2007.By 2014,the value had increased gradually to 28.4400 million tons,and by 2016 it had declined to 27.8922 million tons,suggesting that the carbon-emission reduction measures of the government had an impact.2)The CLUE of various provinces and cities in the YREB showed an upward trend in the time dimension,while for the spatial dimension,the kernel density was high in the east and low in the west,and the areas with high kernel density were mainly located in the Yangtze River Delta.3)The per capita gross domestic product,the primary industrial output,and the number of agricultural technicians per 10,000 people had positive effects on the CLUE.The CL area per capita and the electrical power per hectare for agricultural machinery had significant negative impacts on CLUE.In addition,every 1%increase in the number of agricultural technicians increased the CLUE by 0.057%.

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.

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.