【作者】 孙杰；

【导师】 陈光水；

【作者基本信息】 福建师范大学 ， 生态学， 2023， 博士

【摘要】 植物水分利用效率反映了植物的固碳能力和水分消耗之间的关系,影响着生态系统生产力及其对环境变化的适应能力。全球变暖引起的水分可利用性降低将加剧生态系统水分的限制,特别是存在季节性干旱的我国亚热带地区。我国亚热带杉木人工林是我国乃至全世界分布面积最大的人工林,在我国木材生产和碳吸存中发挥着巨大的作用。但全球变暖对杉木人工林水分利用效率的影响及其调控机制目前仍不清楚,深入回答该科学问题,对于全球变暖背景下我国杉木人工林生产力和碳汇能力的科学预测和适应性管理具有十分重要的意义。为此,本研究于2016年开始,在福建三明森林生态系统国家野外科学观测研究站陈大观测点开展杉木幼树的大气增温×土壤增温双因子交互控制试验,设有对照（CT）、土壤增温（SW）、大气增温（AW）及土壤和大气同时增温（SW+AW）4个处理,研究增温后杉木幼树水分利用特征(包括树干液流密度、叶δ¹³C)及各营养器官（细根、枝条、叶片）形态特征、CNP化学计量学特征变化,并探讨杉木营养器官形态与化学计量学特征调整对杉木水分利用效率的调控作用。主要研究结果如下:（1）大气增温和土壤增温对杉木年树干液流密度有显著的交互作用:土壤增温和大气增温处理均显著降低年树干液流密度;但土壤和大气同时增温处理则显著提高了年树干液流密度,特别是在夏季和秋季,这可能与高温胁迫导致杉木需要增加蒸腾作用进行降温有关。仅大气增温（AW和SW+AW处理）显著降低了水分利用效率(叶片δ¹³C),可能与大气增温抑制了杉木光合能力有关。各增温方式的年树干液流密度和叶片δ¹³C均与光合有效辐射（PAR）和饱和水汽压亏缺（VPD）呈显著正相关。大气增温和土壤增温主效应均抑制了杉木的胸径生长,表明不同增温方式均不利于杉木的生长。（2）土壤增温显著降低了杉木细根和叶片的P浓度,杉木细根N浓度也显著下降,但枝条和叶片的N浓度均无显著变化。大气增温对杉木细根、枝条、叶片P浓度均具有显著负效应,且以一序级根和一年生枝和叶P浓度的下降更明显;但对N浓度均无显著影响。土壤和大气同时增温仅显著降低了叶片P浓度。不同增温方式均提高了细根和叶片的C:P比、N:P比,表明不同增温方式在一定程度上缓解了N限制,加剧了P限制。这可能与增温促进土壤氮矿化而提高了对氮的吸收,但同时抑制了对P的吸收有关。（3）不同增温处理均提高了细根比根长,降低了根直径（特别是较高序级）;土壤增温处理（包括AW和SW+AW）提高了比根表面积、降低了根组织密度。表明增温后杉木提高了根系养分与水分资源吸收效率。大气增温处理（包括AW和SW+AW）提高了比枝条长度,表明杉木幼树通过增加比枝条长度增强光的捕获能力。所有增温处理均降低了叶片厚度,此形态性状的改变将有利于降低叶片的构建成本;仅大气增温处理（AW）显著降低了叶面积,其原因可能是杉木幼树通过减少蒸腾面积以应对水分供给不足。不同增温方式下杉木各器官间以及器官内的形态性状间之间表现出相关性,表明增温处理下杉木通过协调与权衡各器官间形态性状,提高对水分和养分资源的吸收、储存以及转运能力,从而提高其适应性。（4）杉木年树干液流密度与叶片δ¹³C呈边缘显著正相关关系,表明增温后杉木光合作用的调整速率快于蒸腾作用。年树干液流密度与杉木各营养器官形态性状均无显著相关性,且杉木叶片δ¹³C仅与叶面积呈边缘显著正相关关系,表明杉木营养器官单个构件形态性状的调整对杉木水分利用的影响可能十分有限。杉木幼树根、枝、叶的P浓度与年树干液流密度和叶片δ¹³C均呈显著的正相关关系,表明P元素及其化学计量学对林木水分利用具有重要的调节作用。综上所述,大气增温处理和土壤增温处理降低了杉木树干液流密度;虽然同时大气增温和土壤增温处理显著增加了杉木树干液流密度,但这可能是对高温胁迫的一种逆境响应;同时大气增温降低了水分利用效率,这可能是造成增温后杉木生长下降的重要机制之一。增温后杉木营养器官形态性状的调整对杉木水分利用效率的影响很小,但增温后营养器官P元素浓度下降及化学计量学变化则对杉木水分利用效率有着重要影响。本研究结果为深入揭示杉木人工林对全球变暖的适应机制提供了理论支撑,也为深入认识全球变暖背景下植物化学计量学特征与水力过程之间的联系提供基础。更多还原

【Abstract】 Plant water use efficiency（WUE）reflects the tradeoff between plant C capture and water consumption,which affects the capacity of plants adapting to environmental changes and then,ecosystem production.Globally,the ongoing warming caused decrease in soil water availability has been expected to aggravate water limitation in a series of terrestrial ecosystems,particularly in the subtropics in China where there has a seasonal-drought.The Chinese fir（Cunninghamia lanceolata）plantation in south of China has the largest area globally,and plays an important role in wood production and carbon sequestration in China.However,there remains unclear that to which extent and how global warming affects the WUE in Chinese fir plantation,which is of significance for the scientific prediction of the production and carbon sequestration capacity as well as for the adaptation management of Chinese fir plantation in the context of global warming.In the current study,therefore,we performed a factorial atmospheric and soil warming manipulated experiment with randomized block design in a Chinese fir plantation since2016 at the Chenda observation site of the Sanming Forest Ecosystem National Field Science Observation and Research Station in Fujian Province.This includes four treatments:control without any warming（CT）,soil warming by 4℃（SW）,atmospheric warming by open-top chambers（AW）,and soil plus atmospheric warming（SW+AW）,each with 4replicate plots.We aimed to investigate changes in water use(e.g.,stem sap flux density（SFD）and leafδ¹³C)and morphological and chemical traits of vegetative organs（i.e.,<2mm fine roots,branches,and leaves）of Chinese fir,and,to explore the regulation of adjustment of morphological and chemical（C,N,P concentration and stoichiometries）traits of vegetative organs on WUE.The main results are as follows:（1）There is a significant interaction between atmospheric warming and soil warming on annual SFD.Relative to the control,soil warming and atmospheric warming significantly decreased the annual SFD,whereas soil plus atmospheric warming significantly increased the annual SFD,especially in summer and autumn.The increased SFD might be attributed to an increased demand to cool down by increasing transpiration under high-temperature stress.Leafδ¹³C,indicating WUE,was just significantly reduced by atmospheric warming（AW and SW+AW treatments）,which was possibly due to the inhibited photosynthetic capacity by atmospheric warming.Regardless of warming method（SW or AW）,both the annual SFD and the leafδ¹³C were positively and significantly related to the photosynthetic active radiation（PAR）and the saturated water vapor pressure deficit（VPD）.Both atmospheric warming and soil warming inhibited the growth of DBH,indicating a negative effect of warming on the growth of Chinese fir regardless of warming method.（2）Soil warming significantly reduced the P concentration of fine roots and leaves,significantly decreased the N concentration of fine roots,whereas had no significant effect on the N concentration of branches and leaves.Atmospheric warming significantly reduced the P concentration of fine roots,branches,and leaves,especially the P concentration of the first-order fine roots,and the one-year old branches and leaves.However,it was not the case of N concentration.Soil plus atmospheric warming just significantly decreased the P concentration of leaves,but not the case of fine roots and branches.Additionally,soil plus atmospheric warming had no effect on the N concentration of fine roots,branches,and leaves.Relative to the control,both soil-and atmospheric warming increased the C:P and N:P ratios of fine roots and leaves,indicating an alleviated N limitation but an intensified P limitation.Possibly,it could be explained by that warming enhances nitrogen mineralization and subsequent plant N uptake but simultaneously decreases plant P uptake.（3）Relative to the control,all warming treatments significantly increased the specific root length（SRL）and reduced the root diameter（RD）of fine roots（especially the higher-order roots）.In addition,soil warming treatments（including AW and SW+AW）also increased specific root surface area（SRA）and decreased root tissue density（RTD）.These results suggest an increase in root nutrient and water uptake efficiency under warming.Atmospheric warming treatment（including AW and SW+AW）increased specific branch length（SBL）,suggesting an enhanced light capture capacity.All warming treatments reduced leaf thickness（LT）,which indicates a reduced construction cost of leaves.However,only the atmospheric warming treatment significantly reduced leaf area（LA）,indicating that Chinese fir in the AW treatment responded to the insufficient water supply by reducing the transpiration area.There were some correlations among morphological traits within or among organs,indicating that Chinese fir improves the capacity to absorb,store,and transport water and nutrients by coordinating and trade-offing different morphological traits within or among different organs under warming,and thereby,improves the adaptability to warming.（4）There was a marginal significant positive relationship between annual SFD and leafδ¹³C,indicating a faster adjustment rate of photosynthesis relative to transpiration of Chinese fir after warming.There was no significant correlation between the annual SFD and the morphological traits of all vegetative organs,and the leafδ¹³C was positively correlated with leaf area only,indicating that the adjustment of morphological traits of individual modules of vegetative organs might have a limited impact on water use of Chinese fir.However,the annual SFD,and especially the leafδ¹³C,correlated significantly to the P concentration of fine roots,branches,and leaves,indicating that P and its stoichiometries played an important role in regulating the water use of Chinese fir.Overall,relative to the control,soil and atmospheric warming decreased the annual SFD.While soil plus atmospheric warming significantly increased the annual SFD,it could just be a passive response of Chinese fir to high-temperature stress.Simultaneously,atmospheric warming decreased WUE,which,together,may be an important mechanism responsible for the decreased growth of Chinese fir after warming.Not the adjustment of morphological traits of vegetative organs,but the changes in P concentration and its stoichiometries of various vegetative organs,are of pivotal significance in affecting the WUE of Chinese fir after warming.Thereby,this study provides theoretical support for revealing the adaptation mechanism of Chinese fir plantation to global warming,and also forms a basis for in-depth understanding of the relationship between plant stoichiometry and hydraulic processes in the context of global warming.更多还原