Effects of drought treatment on photosystemⅡactivity in the ephemeral plant Erodium oxyrhinchum

Drought is a critical limiting factor affecting the growth and development of plants in arid and semi-arid areas.Photosynthesis,one of the most important physiological processes of plants,can be significantly inhibited by drought.PhotosystemⅡ(PSⅡ)is considered the main attack target when photosynthesis is affected by drought.To clarify how PSⅡcomponents of the ephemeral plant Erodium oxyrhinchum(grown in the Gurbantunggut Desert,China)respond to drought treatment,we evaluated the functional activity of PSII by determining chlorophyll fluorescence and gas exchange parameters under different drought treatment levels(control(400 mL),moderate drought(200 mL),and severe drought(100 m L)).Under moderate drought treatment,significant decreases were found in net photosynthetic rate(Pn),effective quantum yield of PSII(Y(Ⅱ)),relative electron transfer rate of PSII(rETR(Ⅱ)),oxygen-releasing complex,probability of an absorbed exciton moving an electron into the electron transport chain beyond primary quinone receptor Q_(A)-(Φ(E_(o))),probability of a trapped exciton moving an electron into the electron transport chain beyond primary quinone receptor Q_(A)-(ψ(E_(o))),and performance index of PSⅡ(PI_(abs)).Compared to control treatment,marked increases were observed in water use efficiency(WUE),relative variable fluorescence at the J step(V_(J)),initial fluorescence(F_(o)),and dissipated energy per active reaction center(DI_(o)/RC)under moderate drought treatment,but there were no substantial changes in semi-saturated light intensity(I_(K)),active reaction centers per cross-section(RC/CS),and total performance index of PSII and PSI(PI_(total),where PSI is the photosystemⅠ).The changes of the above parameters under severe drought treatment were more significant than those under moderate drought treatment.In addition,severe drought treatment significantly increased the absorbed energy per active reaction center(ABS/RC)and trapping energy per active reaction center(TR_(o)/RC)but decreased the energy transmission connectivity of PSⅡcomponents,RC/CS,and PI_(total),compared to moderate drought and control treatments.Principle component analysis(PCA)revealed similar information according to the grouping of parameters.Moderate drought treatment was obviously characterized by RC/CS parameter,and the values of F_(o),V_(J),ABS/RC,DI_(o)/RC,and TR_(o)/RC showed specific reactions to severe drought treatment.These results demonstrated that moderate drought treatment reduced the photochemical activity of PSII to a certain extent but E.oxyrhinchum still showed strong adaptation against drought treatment,while severe drought treatment seriously damaged the structure of PSⅡ.The results of this study are useful for further understanding the adaptations of ephemeral plants to different water conditions and can provide a reference for the selection of relevant parameters for photosynthesis measurements of large samples in the field.

不同生境/萌发类型尖喙牻牛儿苗生物量分配特征

短命植物是荒漠生态系统重要的植物类群,其具有多样化的生境,且很多种类还具有异时萌发特性。植物生物量积累和分配能体现其对环境的响应与适应性特征,因此,研究不同环境条件下短命植物生物量分配格局有助于进一步了解短命植物的生存策略。以裸沙春萌(Bare Sand-Spring Germination,BS)、藻结皮春萌(Algal-Spring Germination,AS)、地衣结皮春萌(Lichen-Spring Germination,LS)3种自然结皮生境中萌发的尖喙牻牛儿苗春萌株及裸沙区夏季萌发(Summer Germination in Bare Sand,SG)的尖喙牻牛儿苗夏萌株为研究对象,采用全株挖掘法获取地上和地下生物量,系统对比分析了4个类型间植株生物量分配及异速生长关系的差异性,以探究其资源分配策略的变异性和保守型。结果表明:(1)尖喙牻牛儿苗单株地上、地下及总生物量总体表现为BS>AS>LS=SG的格局,其根冠比则呈SG=LS=AS>BS的特征。(2)BS和SG类型植株地上与地下生物量间为等速生长关系,而AS和LS生境为异速生长关系,但4个类型具有共同的异速生长指数(0.8843)。(3)AS和LS生境尖喙牻牛儿苗根冠比随个体增大均呈异速减小趋势,而BS和SG类型植株根冠比则保持相对恒定。可见,尖喙牻牛儿苗生物量分配会受到外界环境及个体发育的影响,并呈现明显的可塑性,在一定程度上反映了其资源分配的保守性与可塑性的权衡。

降水、氮沉降对尖喙牻牛儿苗隔代生理可塑性的影响

隔代可塑性是后代免受环境胁迫的有效方式,通过增加子代与环境匹配的可能性来缓冲环境变化对子代的影响,提高子代对所处环境的适应度。因此,本研究以生长发育快、对环境响应敏感的一年生短命植物优势种尖喙牻牛儿苗(Erodium oxyrhinchum)作为研究材料,结合增水、增氮处理,从短命植物生理生化指标角度分析短命植物代际间对气候因子的响应差异,尝试明确气候因子对荒漠短命植物隔代生理可塑性的影响。结果表明:(1)增水处理显著提高了两代植株的可溶性糖(SS)含量、其余生理指标呈代际差异性,增水处理下可溶性蛋白(SP)、可溶性糖(SS)、过氧化物酶(POD)呈隔代适应性。(2)增氮处理显著抑制亲代植株的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、丙二醛(MDA)含量,对子代植株过氧化氢酶(CAT)、活性氧(ROS)含量呈抑制作用,增氮处理下可溶性蛋白(SP)、超氧化物歧化酶(SOD)、过氧化物酶(POD)呈隔代适应性。(3)水氮互作处理显著促进亲代植株的过氧化物酶(POD)、过氧化氢酶(CAT)、活性氧(ROS)含量,但显著抑制超氧化物歧化酶(SOD)含量。对子代植株超氧化物歧化酶(SOD)、过氧化物酶(POD)含量呈促进作用,过氧化氢酶(CAT)、丙二醛(MDA)、活性氧(ROS)含量呈抑制作用,水氮互作处理下可溶性蛋白(SP)、过氧化物酶(POD)呈隔代适应性。总体而言,降水、氮沉降对尖喙牻牛儿苗隔代生理可塑性具有显著影响,尖喙牻牛儿苗生理生化指标对增水、增氮以及水氮互作处理呈现不同的响应差异。未来降水、氮沉降的增加可能改变尖喙牻牛儿苗后代的生态适应能力和策略,进而改变其种群未来发展趋势。