Relationship Of Pollen And Leaf Stable Carbon Isotopes Of Pinus Yunnanensis To Climate Change

Stable isotope technology is widely used in plant physiology and ecology studies.Its features of tracer,traceability,and indicator are used to study a range of issues such as plant photosynthetic pathways,long-term water use efficiency,climatic and global changes.Pinus yunnanensis is an endemic species in Yunnan.It plays an important role in soil and water conservation in plateau areas,and it also has high economic,ecological,and social values.The relationship between Pinus yunnanensis and climate focused on the macroscopic aspects in ecology to biogeography in the past,no studies of relationship of its stable isotopes and climate are available.Therefore,a study of the relationship between stable carbon isotope of Pinus yunnanensis and climate will provide theoretical basis and technological supports for the maintenance and protection of ecological environments in Yunnan.In this study,pollen and leaf of Pinus yunnanensis were used as study objects to study the relationship between their stable carbon isotopes and climate and altitude,and to explain the differences in fractionation between different plant organs and causes.Following results and conclusions were obtained in this study:(1)Among 71 pairs of pollen and leaf samples from Pinus yunnanensis trees collected in 2018,pollen?¹³C(?¹³C_pollen)values ranged from-32.92 to-26.34‰,with an average value of-30.88±1.14‰,and leaf?¹³C(?¹³C_leaf)values ranged from-33.79to-28.96‰,with an average value of-31.2±0.99‰.In 2019,33 pollen samples and40 leaf samples were collected from Pinus yunnanensis trees.?¹³C_pollen values varied from-30.61 to-26.56‰with an average value of-28.93±1.07‰,while?¹³C_leaf values varied from-29.68 to-22.82‰with an average value of-26.33±1.51‰.Among 83pairs of pollen and leaf samples collected from Pinus yunnanensis trees in 2020,?¹³C_pollen values varied from-30.79 to-22.41‰with an average value of-25.85±1.66‰,and?¹³C_leafvalues ranged in-31.2 to-25.27‰with an average of-28.08±1.16‰.For all pollen and leaf samples collected in the last three years,the average values of?¹³C_pollen and?¹³C_leaf values were-28.30‰and-28.86‰,respectively.Their average values are lighter than the average value of-27‰of global C₃ plant?¹³C.It is also evident that?¹³C_leaf value of Pinus yunnanensis is lighter than?¹³C_pollenbecause of isotope fractionation resulted from the structural difference between pollen and leaf of Pinus yunnanensis.The leaf carries out not only respiration but also photosynthesis,whereas pollen just carries out respiration only.Studies have shown that?¹³C_pollen value of untreated pollen can be directly used as a representative of treated pollen.Compared with leaf,pollen structure is stable and more sensitive to environmental changes.(2)Among 71 pairs of pollen and leaf samples from the south bank of Lugu Lake in northwestern Yunnan,?¹³C_pollen value of Pinus yunnanensis was negatively correlated with altitude,while no significant correlation occurred between?¹³C_leaf value and altitude.However,both?¹³C_pollen and?¹³C_leaf showed a lighter trend with the increase in altitude.It was speculated that the location of Lugu Lake was probably responsible for this fact because Lugu Lake is in a karst landform region with a warm temperate mountain monsoon climate.The sampling time was May in 2018 when local climate was influenced by precipitation,temperature,sunshine,and other parameters,and sampling sites have a 354m vertical gradient,resulting in a series of changes in internal climate factors among sampling sites.Therefore,small vertical span and sample size in the study area may cause uncertainties in this result.Further studies will be needed for the relationship of the stable carbon isotope of pollen and leaf from Pinus yunnanensis to altitude in high altitude areas.(3)The Meteorological parameters in this study include monthly,seasonal(flowering period,growing season,four seasons)and annual temperature,precipitation,humidity,light,wind speed at the sampling sites in the past five years.The correlation between each parameter and?¹³C_pollen and?¹³C_leaf of Pinus yunnanensis was estimated using SPSS.The results revealed that the main meteorological parameters affecting?¹³C_pollen and?¹³C_leaf of Pinus yunnanensis were humidity and precipitation.Both parameters showed a significantly negative correlation with?¹³C of pollen and leaf,i.e.,the greater the precipitation and humidity were,the lighter?¹³C_pollen and?¹³C_leafwere.Despite other parameters also had certain correlations with?¹³C_pollen and?¹³C_leaf,the largest limiting parameter for the growth of Pinus yunnanensis was water in this study.