Influence of vapor pressure deficit on vegetation growth in China

Vapor pressure deficit(VPD)plays a crucial role in determining plant physiological functions and exerts a substantial influence on vegetation,second only to carbon dioxide(CO_(2)).As a robust indicator of atmospheric water demand,VPD has implications for global water resources,and its significance extends to the structure and functioning of ecosystems.However,the influence of VPD on vegetation growth under climate change remains unclear in China.This study employed empirical equations to estimate the VPD in China from 2000 to 2020 based on meteorological reanalysis data of the Climatic Research Unit(CRU)Time-Series version 4.06(TS4.06)and European Centre for Medium-Range Weather Forecasts(ECMWF)Reanalysis 5(ERA-5).Vegetation growth status was characterized using three vegetation indices,namely gross primary productivity(GPP),leaf area index(LAI),and near-infrared reflectance of vegetation(NIRv).The spatiotemporal dynamics of VPD and vegetation indices were analyzed using the Theil-Sen median trend analysis and Mann-Kendall test.Furthermore,the influence of VPD on vegetation growth and its relative contribution were assessed using a multiple linear regression model.The results indicated an overall negative correlation between VPD and vegetation indices.Three VPD intervals for the correlations between VPD and vegetation indices were identified:a significant positive correlation at VPD below 4.820 hPa,a significant negative correlation at VPD within 4.820–9.000 hPa,and a notable weakening of negative correlation at VPD above 9.000 hPa.VPD exhibited a pronounced negative impact on vegetation growth,surpassing those of temperature,precipitation,and solar radiation in absolute magnitude.CO_(2) contributed most positively to vegetation growth,with VPD offsetting approximately 30.00%of the positive effect of CO_(2).As the rise of VPD decelerated,its relative contribution to vegetation growth diminished.Additionally,the intensification of spatial variations in temperature and precipitation accentuated the spatial heterogeneity in the impact of VPD on vegetation growth in China.This research provides a theoretical foundation for addressing climate change in China,especially regarding the challenges posed by increasing VPD.

Clipping Effect on Growth and Plant Water Use Response to Diurnal Variation of Vapor Pressure Deficit in Cenchrus biflorus Roxb

Cenchrus biflorus called Karangiya in the Hausa language is an annual pastoral grass which is a valuable herbaceous fodder in dry land region in the context of climate change. However, little is known about the plant water use under the effects of cut in West Africa Sahel like Niger where the plant is a multipurpose grass species. Therefore, this study investigated the impact of grazing (simulated by shoot cuts) on biomass production. Cenchrus biflorus Roxb was grown on field plots and in pots and subjected to shoot cuts at different levels (3 cm and 5 cm from soil surface). The effect of shoot cuts on drought tolerance was evaluated by assessing the response of transpiration to the diurnal variation of vapor pressure deficit (VPD). Results showed that the biomass production varied in response to shoot cuts depending on the culture system, and the level or frequency of cuts. The mean biomass production increased significantly especially in field plots for 5 cm cuts compared to those at 3 cm and the control treatment. In addition, transpiration was highly increased in response to the VPD increase. Shoot cuts significantly reduced transpiration, whatever the level, largely because they reduced leaf surface. We concluded that moderate grazing (cuts to 5cm) can improve biomass production and allow better adaptation to water deficit as they significantly reduced water loss through transpiration. The study recommends the cropping of the Cenchrus biflorus as climate solution as it performs better under water deficit for improving grazing resilience in Niger.

Response of stomatal conductance of two tree species to vapor pressure deficit in three climate zones

Stomatal behavior is a central topic of plant ecophysiological research under global environmental change. However, the physiological mechanism controlling the response of stomata to vapor pressure deficit （VPD） or relative humidity （RH） has been inadequately understood till now. In this study, responses of stomatal conduc- tance （gs） to VPD in two species of trees （Fraxinus chinensis Roxb., Populus alba L. var. pyramidalis Bge.）in three different climate zones （Jinan with typical warm humid/semi-humid climate, Urumqi with temperate continental arid climate and Turpan with extreme arid desert climate） were measured. Levels of two phytohormones （abscisic acid, ABA; indole-3-acetic acid, IAA） in the leaves of the two tree species at these three sites were also measured by high performance liquid chromatography. The results showed that the responses of gs to an increasing VPD in these two tree species at the three sites had peak curves which could be fitted with a Log Normal Model （gs=a.exp（-O.5（In（DIc）lb）2）. The VPD/RH values corresponding to the maximum g, can be calculated using the fitting models for the two tree species in the three sites. We found that the calculated g, -VPD correlated nega- tively with relative air humidity in the three sites during the plant growth period （April to October 2010）, which showed the values of g,-max-VPD were related to the climate conditions. The prevailing empirical stomatal model （Leuning model） and optimal stomatal behavior model could not properly simulate our measured data. The water use efficiency in the two tree species did not show obvious differences under three very different climatic conditions, but the highest gs, photosynthetic and transpiration rates occurred in P. alba var. of Turpan. The sensitivity in re- sponse of g~ to VPD in leaves of the two trees showed positive correlations with the concentration of ABA, which implied that ABA level could be used as an indicator of the sensitivity of stomatal response to VPD. Our results confirmed that the prediction of the response of gs to VPD might be incomplete in the two current popular models. Therefore, an improved g, model which is able to integrate the results is needed. Also, the stomatal response mechanism of single peak curves of g~ to VPD should be considered.

Spatio-temporal variation in transpiration responses of maize plants to vapor pressure deficit under an arid climatic condition

The transpiration rate of plant is physically controlled by the magnitude of the vapor pressure deficit（VPD） and stomatal conductance. A limited-transpiration trait has been reported for many crop species in different environments, including Maize（Zea mays L.）. This trait results in restricted transpiration rate under high VPD, and can potentially conserve soil water and thus decrease soil water deficit. However, such a restriction on transpiration rate has never been explored in maize under arid climatic conditions in northwestern China. The objective of this study was to examine the transpiration rate of field-grown maize under well-watered conditions in an arid area at both leaf and whole plant levels, and therefore to investigate how transpiration rate responding to the ambient VPD at different spatial and temporal scales. The transpiration rates of maize at leaf and plant scales were measured independently using a gas exchange system and sapflow instrument, respectively. Results showed significant variations in transpiration responses of maize to VPD among different spatio-temporal scales. A two-phase transpiration response was observed at leaf level with a threshold of 3.5 k Pa while at the whole plant level, the daytime transpiration rate was positively associated with VPD across all measurement data, as was nighttime transpiration response to VPD at both leaf and whole plant level, which showed no definable threshold vapor pressure deficit, above which transpiration rate was restricted. With regard to temporal scale, transpiration was most responsive to VPD at a daily scale, moderately responsive at a half-hourly scale, and least responsive at an instantaneous scale. A similar breakpoint（about 3.0 k Pa） in response of the instantaneous leaf stomatal conductance and hourly canopy bulk conductance to VPD were also observed. At a daily scale, the maximum canopy bulk conductance occurred at a VPD about 1.7 k Pa. Generally, the responsiveness of stomatal conductance to VPD at the canopy scale was lower than that at leaf scale. These results indicate a temporal and spatial heterogeneity in how maize transpiration responses to VPD under arid climatic conditions. This could allow a better assessment of the possible benefits of using the maximum transpiration trait to improve maize drought tolerance in arid environment, and allow a better prediction of plant transpiration which underpin empirical models for stomatal conductance at different spatio-temporal scales in the arid climatic conditions.

VPD modifies CO_(2) fertilization effect on tomato plants via abscisic acid and jasmonic acid signaling pathways

Atmospheric CO_(2)concentration is elevated globally,which has“CO_(2)fertilization effects”and potentially improves plant photosynthesis,yield,and productivity.Despite the beneficial effect of CO_(2)fertilization being modulated by vapor pressure deficit(VPD),the underlying mechanism is highly uncertain.In the present study,the potential roles of hormones in determining CO_(2)fertilization effects under contrasting high and low VPD conditions were investigated by integrated physiological and transcriptomic analyses.Beneficial CO_(2)fertilization effects were offset under high VPD conditions and were constrained by plant water stress and photosynthetic CO_(2)utilization.High VPD induced a large passive water driving force,which disrupted the water balance and consequently caused plant water deficit.Leaf water potential,turgor pressure,and hydraulic conductance declined under high VPD stress.The physiological evidence combined with transcriptomic analyses demonstrated that abscisic acid(ABA)and jasmonic acid(JA)potentially acted as drought-signaling molecules in response to high VPD stress.Increased foliar ABA and JA content triggered stomatal closure to prevent excessive water loss under high VPD stress,which simultaneously increased the diffusion resistance for CO_(2)uptake from atmosphere to leaf intercellular space.High VPD also significantly increased mesophyll resistance for CO_(2)transport from stomatal cavity to fixation site inside chloroplast.The chloroplast“sink”CO_(2)availability was constrained by stomatal and mesophyll resistance under high VPD stress,despite the atmospheric“source”CO_(2)concentration being elevated.Thus,ABA-and JA-mediated drought-resistant mechanisms potentially modified the beneficial effect of CO_(2)fertilization on photosynthesis,plant growth,and yield productivity.This study provides valuable information for improving the utilization efficiency of CO_(2)fertilization and a better understanding of the physiological processes.

4种木瓜新品种光合作用日变化以及气孔导度-VPD响应

研究了4个木瓜Carica papaya Linn新品种的光合作用日变化特性,表明在网室栽培下的4个木瓜品种光合日变化均为“单峰曲线”,而不使用遮荫措施的两个木瓜品种均为“双峰曲线”,气孔导度与蒸汽压差的响应拟合表明,在遮荫条件下,其气孔导度-VPD的负相关趋势不显著,而在不遮荫栽培条件下则呈显著负相关(P≤0.05)。表明遮荫使木瓜避开了午间的高光强、高温以及高湿度的抑制。

Spatial and Temporal Changes in Vapor Pressure Deficit and Their Impacts on Crop Yields in China during 1980–2008

Vapor pressure deficit（VPD） is a widely used measure of atmospheric water demand. It is closely related to crop evapotranspiration and consequently has major impacts on crop growth and yields. Most previous studies have focused on the impacts of temperature, precipitation, and solar radiation on crop yields, but the impact of VPD is poorly understood. Here, we investigated the spatial and temporal changes in VPD and their impacts on yields of major crops in China from 1980 to 2008. The results showed that VPD during the growing period of rice, maize, and soybean increased by more than 0.10kPa（10 yr）^–1 in northeastern and southeastern China, although it increased the least during the wheat growing period. Increases in VPD had different impacts on yields for different crops and in different regions. Crop yields generally decreased due to increased VPD, except for wheat in southeastern China. Maize yield was sensitive to VPD in more counties than other crops. Soybean was the most sensitive and rice was the least sensitive to VPD among the major crops. In the past three decades, due to the rising trend in VPD, wheat, maize, and soybean yields declined by more than 10.0% in parts of northeastern China and the North China Plain, while rice yields were little affected. For China as a whole, the trend in VPD during 1980–2008 increased rice yields by 1.32%,but reduced wheat, maize, and soybean yields by 6.02%, 3.19%, and 7.07%, respectively. Maize and soybean in the arid and semi-arid regions in northern China were more sensitive to the increase in VPD. These findings highlight that climate change can affect crop growth and yield through increasing VPD, and water-saving technologies and agronomic management need to be strongly encouraged to adapt to ongoing climate change.

Interactive response of photosynthetic characteristics in Haloxylon ammodendron and Hedysarum scoparium exposed to soil water and air vapor pressure deficits

C4 plants possess better drought tolerance than C3 plants. However, Hedysarum scoparium, a C3 species, is dominant and widely distributed in the desert areas of northwestern China due to its strong drought tolerance. This study compared it with Haloxylon ammodendron, a C4 species, regarding the interactive effects of drought stress and different leaf–air vapor pressure deficits. Variables of interest included gas exchange, the activity levels of key C4 photosynthetic enzymes, and cellular anatomy. In both species, gas exchange parameters were more sensitive to high vapor pressure deficit than to strong water stress, and the net CO2 assimilation rate（A n） was enhanced as vapor pressure deficits increased. A close relationship between A n and stomatal conductance（g s） suggested that the species shared a similar response mechanism. In H. ammodendron, the activity levels of key C4 enzymes were higher, including those of phosphoenolpyruvate carboxylase（PEPC） and nicotinamide adenine dinucleotide phosphate-malate enzyme（NADP-ME）, whereas in H. scoparium, the activity level of nicotinamide adenine dinucleotide-malate enzyme（NAD-ME） was higher.Meanwhile, H. scoparium utilized adaptive structural features, including a larger relative vessel area and a shorter distance from vein to stomata, which facilitated the movement of water. These findings implied that some C4 biochemical pathways were present in H. scoparium to respond to environmental challenges.

Higher plant photosynthetic capability in autumn responding to low atmospheric vapor pressure deficit

It has been long established that the terrestrial vegetation in spring has stronger photosynthetic capability than in autumn.However,this study challenges this consensus by comparing photosynthetic capability of terrestrial vegetation between the spring and autumn seasons based on measurements of 100 in situ eddy covariance towers over global extratropical ecosystems.At the majority of these sites,photosynthetic capability,indicated by light use efficiency(LUE)and apparent quantum efficiency,is significantly higher in autumn than in spring,due to lower atmosphere vapor pressure deficit(VPD)at the same air temperature.Seasonal VPD differences also substantially explain the interannual variability of the differences in photosynthetic capability between spring and autumn.We further reveal that VPD in autumn is significantly lower than in spring over 74.14% of extratropical areas,based on a global climate dataset.In contrast,LUE derived from a data-driven vegetation production dataset is significantly higher in autumn in over 61.02% of extratropical vegetated areas.Six Earth system models consistently projected continuous larger VPD values in spring compared with autumn,which implies that the impacts on vegetation growth will long exist and should be adequately considered when assessing the seasonal responses of terrestrial ecosystems to future climate conditions.

The decadal abrupt change in the global land vapor pressure deficit

The vapor pressure deficit(VPD) is an important variable used to characterize atmospheric aridity.This paper analyses the spatial and temporal characteristics of the decadal abrupt change(DAC) in the global land VPD after 1980 using monthly scale data from the Climatic Research Unit.The results show that 60.5% of the global land area underwent a significantly increased decadal abrupt change(IDAC) in the VPD,and the persistent IDAC of the VPD was obvious in the middle and low latitudes of Eurasia,Africa and parts of South America but not in central North America or Western Siberia.From 1980 to 2020,most regions experienced no more than two persistent IDACs,while more than two significant increases occurred mainly around the Mediterranean and in eastern South America.The persistent IDAC occurred relatively early in the middle and low latitudes of Eurasia,Africa,and eastern South America and after 2000 in the high latitude regions,Eastern Europe,and near the Qinghai-Tibet Plateau.The regions where the persistent IDAC lasted longer than 10 years mainly included North Africa,West Asia,eastern South America,and parts of East Asia,indicating that the persistent increases in atmospheric aridity in these regions were obvious.In general,the persistent IDAC that began in 1993–2000 was significantly more than that occurred in other periods and lasted longer than that before 1990,suggesting that the land area experiencing an abrupt increase has an expansion after the 1990s and that the role of water limitation in this persistent IDAC in Central Asia and most of China strengthened.In addition,the VPD showed another large-scale persistent IDAC over the global land region in 2009,indicating that global atmospheric aridity intensified over the last decade.At the same time,in a few global regions,the VPD has exhibited decreased decadal abrupt changes(DDACs) with durations shorter than 2 years.

贵州省饱和水汽压差时空变化特征与影响因素

饱和水汽压差(VPD)是表示区域大气干燥程度的重要指标,分析贵州省VPD时空变化特征及其影响机制对明晰气候变化规律和农业生产具有重要意义。研究基于中国气象局提供的CN05.1格点化观测数据集,量化并分析了1961—2022年贵州省喀斯特区域和非喀斯特区域VPD及其时空变化特征,采用多元线性回归方法识别了影响VPD变化的主要气象要素并分析了基于VPD的干旱危险性。结果发现:贵州省年际和季节尺度VPD存在显著的升高趋势,其中喀斯特区域和非喀斯特区域春季和夏季VPD空间分布和变化趋势均呈现相反的格局;以VPD为指标的贵州省干旱危险性显著升高,非喀斯特区域速率更快;气温和相对湿度是贵州省年际和季节尺度上VPD变化的主导气象要素,不同区域年和季节尺度上不同气象要素的贡献率稍有差异。

中国中高纬地区植被物候对干旱的响应特征研究

植被物候直接影响其生物量,调控生态系统碳循环过程。目前,气候变化(尤其干旱)对中国中高纬度植被物候的影响依然不清楚。因此,文章基于GIMMS NDVI3g数据集,提取中国30°N以北地区中多种植被类型生长季的开始日期(Start of the Season,SOS)与结束日期(End of the Season,EOS)两物候参数。然后结合野外观测数据,验证提取物候参数结果可靠性,并结合饱和水汽压差(Vapor Pressure Deficit,VPD)与改进后的标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI)探究植被物候对干旱的响应特征规律。结果表明:(1)不同地区的植被物候变化呈现明显的差异性,单季植被与双季植被第1个生长季的SOS集中在每年的第30~180天,而双季植被第2个生长季的SOS集中在每年的第200~220天。单季植被与双季植被第1个生长季的EOS主要集中在每年的第180~300天,双季植被第2个生长季的EOS主要集中在每年的第260~300天。(2)森林季前VPD的上升导致植被的SOS提前及EOS延迟;草地季前VPD上升导致植被的SOS滞后以及EOS提前。(3)研究区内大部分地区的SPEI与植被的SOS、EOS均呈正相关,即干旱促使该地区植被的SOS、EOS提前。

全球旱地饱和水汽压差和根区土壤水分变化对植被生产力的影响及其成因

旱地约占全球陆地面积的40%,而水分是旱地植被生长的一大限制要素。尽管土壤水分与饱和水汽压差对植被生长的重要性已经得到了广泛证实,然而目前二者对植被生产力影响的空间异质性及其形成因素仍未得到深入研究,这对研究旱地生态系统对气候变化的响应带来了挑战。为了填补这一认知空白,研究收集了多源气象、根区土壤含水率和总初级生产力产品,基于随机森林算法量化了植被总初级生产力对根区土壤含水率和饱和水汽压差的敏感性,结合土地覆盖数据和分档平均方法分析了敏感性空间异质性的形成机制。结果表明:全球旱地饱和水汽压差与植被生产力总体呈显著上升趋势;根区土壤水分对植被生长的影响以正效应主导,饱和水汽压差对植被生长的影响以负效应主导;相较于森林和灌木,饱和水汽压差对植被生长的负效应及根区土壤含水率对植被生长的正效应在农田、草地和苔原及半干旱区更为强烈;植被生产力对饱和水汽压差和根区土壤水分的敏感性在数量上总体呈显著的线性负相关性。综上,植被种类和气候条件是导致全球旱地植被生产力对土壤水分和饱和水汽压差敏感性空间异质性的重要因素。

1981—2023年雅鲁藏布江流域大气饱和水汽压差变化及影响因素

饱和水汽压差(vapor pressure deficit,VPD)可反映大气对水分的需求,厘清VPD时空变化特征有助于了解区域大气干湿程度对气候变化的响应。基于近43年(1981—2023年)雅鲁藏布江流域(简称雅江流域)34个气象站点逐月日照时数、平均气温、平均最高气温、平均最低气温、降水量(P_(r))、相对湿度、水汽压和平均风速等资料,采用线性倾向估计、R/S分析、Mann-Kendall法、Morlet小波分析和逐步回归等方法,分析近43年雅江流域VPD时空变化特征及影响因子。结果表明:(1)雅江流域年、季VPD总体上呈东西部低、中部高分布特征;月际变化呈双峰型,第1、2峰值分别在6、10月,1月最小;VPD夏季最大,春季次之,冬季最小。(2)年VPD以0.030 kPa/(10 a)的速率显著增加,主要表现在夏秋季,尤其近23年(2001—2023年)增速明显。年、季VPD在21世纪前10年中后期发生了突变,且未来持续增大的可能性很高。20世纪80和90年代年、季VPD均偏低,以90年代最明显;21世纪前10年因夏、冬两季VPD偏高,年VPD偏高;21世纪10年代年、季VPD均偏高,主要表现在夏、秋两季。VPD在春、夏、秋3季都存在3~4 a显著周期,冬季有2~3 a周期,年VPD无显著周期。(3)四季和年VPD与地理因子的线性关系不显著,但存在极显著的二次曲线关系。(4)年、季平均气温升高是致使VPD增加的主导因子;2004年以后,年平均气温、水汽压对VPD贡献率有所降低,P_(r)的作用明显增大。

中国土壤水和饱和水汽压差对植被物候始期的影响

在全球变暖气候背景下,由于气温升高而导致的植被春季物候提前已经被熟知。气候变暖的同时加剧了土壤水分(Soil Moisture,SM)和饱和水汽压(Vapor Pressure Deficit,VPD)亏缺,二者作为植被生长必要的水分条件,对植被春季物候的影响尚不明晰。为此,研究基于日光诱导叶绿素荧光数据集通过多项式-导数法、双逻辑-曲率最大值法和Timesat法提取了2001-2018年以来中国植被春季光合物候始期(Start Of Season,SOS)的参数;其次,运用近地面气象驱动数据集和彭曼公式计算了研究期内的VPD值;最后,采用Teil-Sen Median趋势分析和Mann-Kendall检验、敏感性分析法,阐明了SOS、VPD和SM的时空变化规律,揭示了春季SM和VPD对SOS的影响机制。结果表明:①SOS先随着纬度的上升逐渐推迟,在35°N以北开始平稳波动,平均SOS在第130 d;②中国春季SM和VPD呈大面积不显著干旱化趋势,土壤水以0.037 m^(3)(/m^(3)∙10 a)的速度干化,VPD以0.34 hPa/10 a的速度升高,SOS呈大面积不显著提前趋势,以5.1 d/10 a的速度提前;③干旱地区的SOS对春季SM和VPD的变化最敏感,并且随着春季SM梯度的降低,VPD对SOS的重要性逐渐增加,SM的重要性逐渐减少。研究对于理解和预测全球变暖背景下植被生长对水分条件变化的响应,以及对于制定应对气候变化的政策至关重要,可为我国生态环境建设提供科学依据。

猕猴桃树干液流特征及其对环境因子的响应

【目的】探明环境因子对猕猴桃树液流特征的影响,为科学制定猕猴桃树灌溉方案提供依据。【方法】以2023年生长季(4—9月)的6年生猕猴桃树为试材,采用热扩散法对猕猴桃植株液流进行1个生长季的连续测量,结合气象及土壤数据分析环境因素(气温、降水、辐射、蒸汽压亏缺、土壤湿度和温度等)与猕猴桃植株液流的关系。【结果】生长季猕猴桃树干平均液流速率为43.607~355.775 g/h,液流日累积量7月>6月>8月>9月>5月>4月。不同月份猕猴桃树液流特征存在相似性,0:00—24:00呈低-高-低变化趋势。不同天气条件下小时尺度果树液流速率规律相同,但树干液流速率峰值存在差异,表现为晴天>阴天>雨天,且晴天、阴天和雨天条件下树干液流速率与太阳净辐射强度(Rn)、水汽压亏缺(VPD)、20 cm土壤温度(T)均呈正相关关系,与空气相对湿度(H)均呈负相关关系。晴天、阴天、雨天树干液流速率与4个环境因子的多元回归拟合方程分别为F=4894.222+8.078e^(-5)Rn+284.579VPD-256.581T+10.019H(R^(2)=0.866)、F=-5220.102+3.410e^(-5)Rn+288.798VPD+181.098T+9.861H(R^(2)=0.855)、F=-2345.668+9.976e^(-6)Rn-4.915VPD+103.162T-0.482H(R^(2)=0.568)。【结论】猕猴桃树耗水量在不同月份、不同天气条件下存在明显差异,7月、8月晴天猕猴桃树干日蒸腾量最大,可适当蓄水、增加灌溉。

马铃薯水分胁迫指数模型优化研究

【目的】探究马铃薯的叶气温差与环境因子的关系,进一步优化马铃薯水分胁迫指数模型。【方法】在河南农业大学林学院试验基地进行马铃薯盆栽试验,选择晴朗天气测定不同土壤含水率下马铃薯的叶气温差随太阳辐射和大气饱和水汽压差(VPD)的变化规律,确定作物水分胁迫指数(crop water stress index,CWSI)的上下基线,进一步试验后得到优化后的马铃薯CWSI经验模型,并对相关模型进行验证。【结果】马铃薯的叶气温差随着土壤含水率的降低而升高;当土壤含水率较低(7.28%)时,马铃薯的叶气温差随太阳辐射的增大而增大,呈显著线性关系;当土壤含水率较高(15.85%)时,马铃薯的叶气温差随VPD的增大而减小,呈显著线性关系;构建出马铃薯CWSI的上基线为y=0.0098Q-0.68[Q为太阳辐射强度/(W·m^(-2))],下基线为y=-1.67V+3.75(V为大气饱和水汽压差/kPa);将优化的CWSI模型验证后得知,随着土壤含水率的减少,CWSI值增加,且CWSI同土壤含水量呈极显著负相关关系(p<0.01)。【结论】马铃薯的最大叶气温差与太阳辐射的线性关系作为马铃薯水分胁迫指数的上基线是可行的,该研究对传统CWSI经验模型进行改进,进一步优化了CWSI经验模型。

热带常绿阔叶林冠层光合作用光响应特征

【目的】研究云南省典型热带常绿阔叶林的冠层光合作用光响应特征,为理解森林碳汇时空变化特征提供科学依据。【方法】基于云南省景洪市普文热带常绿阔叶林通量塔从2023年3月至2024年2月的观测数据,利用Michaelis-Menten方程,以1个月为时间窗口,拟合生态系统光合作用的3个光响应特征参数(以下简称“光合参数”),并与相应时间尺度的环境因子平均值进行相关分析。【结果】热带常绿阔叶林的表观初始光能利用效率(apparent initial light use efficiency,ɑ)和生态系统暗呼吸速率(dark ecosystem respiration,R_(d))有相似的季节变异特征,均在10月份达到最大值,2月份为最小值;最大光合速率(maximum photosynthesis rate,P_(max))在3至5月较低,其余月份变化不明显。与ɑ、R_(d)和P_(max)的季节变异相关性最大的环境因子分别是风速、空气相对湿度和饱和水汽压差,冠层导度也对Rd和Pmax的季节变异有一定影响。【结论】热带常绿阔叶林的3个冠层光合参数有明显的季节变异特征,风速和水分条件相比光合有效辐射和空气温度对光合参数的季节变异有更大影响。

新疆植被总初级生产力对大气水分亏缺的响应

近几十年来新疆气候变化显著,“暖湿化”转型与“湿干转折”先后出现,势必对地区植被生产力、大气干旱状况以及二者间的响应关系产生影响。以植被总初级生产力(GPP)和大气水分亏缺(VPD)作为评价指标,分析了1982—2018年新疆地区植被GPP、VPD的时空分布与演变规律,并揭示了大气水分胁迫对植被GPP的影响。结果表明:(1)新疆植被GPP整体具有北高南低的分布特征,年均值为256.6 g C·m^(-2)·a^(-1),呈显著上升趋势。GPP增加趋势占植被总面积的82.00%,其中增加显著区约占42.81%,多分布于南疆绿洲和北疆山前农业区;GPP下降趋势占比较小且分布零散。(2)新疆地区VPD具有“山区低、平原/盆地高”的鲜明格局,年均值为0.66 kPa,呈不显著波动上升趋势。全疆大部地区表现出VPD显著性上升,下降趋势零星出现在昆仑山脉高海拔山区。(3)新疆植被GPP对VPD的响应“正负共存”,并具有明显空间异质性。GPP与VPD的负相关占植被区总面积的54.52%,主要出现在山前草地地带;正相关则主要分布在塔里木盆地边缘和天山北坡及其东段,以栽培作物和灌木类型为主。VPD对GPP的影响在不同植被类型间差异鲜明,而在同一植被类型内正、负响应共存。分析认为,虽然大气水分胁迫尚未成为地区植被生产力变化的主导驱动力,但在新疆干旱化急剧增加背景下,仍需加强对GPP与VPD响应关系的跟踪。

青藏高原东缘亚高山针叶林和采伐迹地中藓类生长速率及其影响因子

利用红油漆标记法,对青藏高原东缘地区壤塘林业局二林场亚高山采伐迹地和云杉(Picea)原始林中的6种藓类近一个生长季的生长速率进行了研究。结合原地同时进行的微气候观测,分析了气候因子和藓类生长速率之间的相关度。这6种藓类中,有5种在原始林和采伐迹地都出现,只有绢藓(Entodon conncinus)仅在采伐迹地出现。不同物种和不同生境条件下藓类的生长速率都不相同。塔藓(Hylocomium splendens)的茎生长速率最大,而阿萨姆曲尾藓(Dicranum assamicum)生长速率最小。生境对塔藓、阿萨姆曲尾藓和细叶羽藓(Thuidium lepidoziaceum)的生长速率影响很大,它们在林内比在采伐迹地生长快。锦丝藓(Actinothuidium hookeri)和垂枝藓(Rhytidiadelphus triquetrus)的生长速率中等并且对生境不敏感。据此可以将藓类分成生境敏感型和不敏感型。微气候5～7月分析显示林内比采伐迹地的辐射通量低,并且更为干燥。但是早上林内的蒸汽压亏缺(Vapor pressure deficit,VPD)一直比采伐迹地低。林内较低的蒸汽压亏缺和较低的辐射通量使其成为更有利于藓类的生长场所。对于那些生境类型不敏感的藓类,微地形的效应也许抵消了这种大生境的效应。藓类的生理生态特征如变水(Poikilohydry)特征等对其在严酷气候条件下的生存和生长起着重要的作用。如同积温一样,藓类的生长速率同样可以指示生境的适宜度,因为其生长和蒸汽压亏缺紧密相关,是温度和湿度的函数,而这两个因素对于川西亚高山地区森林人工更新时幼苗的建植极为关键。因此藓类的生长状况可以作为指示适宜植树生境的指标。