The Study On Leaf Characters And Spectral Characteristics Of Plantago Asiatica In Swamp Wetland Conversion Succession

The characteristics of biomass allocation strategy,adaptability mechanism and growth-survival balance of plants to the environment require close relationship and regulation among the traits to achieve substitution transformation and build stability between traits,and to form an optimal homeostasis mechanism to ensure survival.With the succession of wetland restoration,species richness in the community increases gradually,niche overlap among species increases gradually,competition among community resources increases gradually.The change of plant community environment and its restrictive regulation are the key factors to determine the balance of plant resources allocation,and promote the adaptability adjustment of plant leaf traits.Plant leaves are the main photosynthetic organs.Environmental changes can trigger the response of reflectance spectra to physiological changes such as leaf structure,pigment transformation and carbon assimilation.Therefore,it is of great significance to study the allometric growth relationships and adaptation strategies among leaf traits,the changes of leaf photosynthetic characteristics,and the response of leaf spectral characteristics to leaf traits,so as to reveal the trade-off mechanism between leaf traits,the process of resource allocation and life history strategies.In view of this,This paper takes Plantago asiatica in the swamp wetland of the middle reaches of Shiyang River as the research object.Four gradients,I?conversion 5a?,II?conversion 15a?,III?conversion 25a?and IV?primary gradient?,are set up according to the length of wetland restoration.The allometric growth relationship between structural characteristics of Cheqian leaves during the process of wetland restoration succession is analyzed,and the change of Photosynthetic Pigments Content in Cheqian leaves is studied.The relationship between the response of spectral characteristics and the inversion of vegetation index was discussed.The results show that:?1?With the succession of wetland conversion,the environment of wetland community tends to be stable gradually,the density,average plant height and aboveground biomass of wetland community show a trend of increasing gradually;the soil water content of community shows a trend of increasing gradually,the content of hydrolytic nitrogen,available phosphorus and organic matter in soil shows a U-shaped trend of decreasing first and then increasing;the coverage and density of population in front of Cheqian increase first and then decrease.Small inverted U-shaped trend,plant height showed a gradual increase trend.?2?With the succession of wetland restoration,there were significant differences?P<0.05?.Leaf area first increased and then decreased,leaf thickness first increased and then decreased,petiole length gradually increased,leaf dry weight and petiole dry weight first decreased and then increased in U-shaped trend.In the 5a?I?and 25a?III?of returning farmland,leaf area and leaf thickness in front of plantation were both increased.There was a very significant negative correlation?P<0.01?.In the 15a?II?and original plots?IV?,there was a significant negative correlation?P<0.05?.There was a very significant negative correlation between the leaf area and the petiole length under each gradient?P<0.01?.In the 5a?I?,15a?II?and 25a?III?,there was a very significant positive correlation between the leaf dry weight and the petiole dry weight?P<0.05?.In the original plot?IV?,there was a significant positive correlation between the dry weight of anterior leaf and petiole?P<0.05?.?4?The photosynthetic active radiation?PAR?of wetland community decreased gradually with the increase of years of wetland conversion.Stomatal conductance?Gs?,intercellular CO₂ concentration?Ci?,net photosynthetic rate?P_n?and transpiration rate?T_r?of plantain front leaves increased first.The water use efficiency?WUE?of leaves showed a U-shaped trend of first decreasing and then increasing,and the chlorophyll and carotenoid contents in front of each gradient were positively correlated with net photosynthetic rate?P<0.01?.?3?With the succession of wetland restoration,the original spectral curve,first-order differential spectrum and red edge position of plantain leaves showed obvious differences;the chlorophyll and carotenoid content of plantain leaves increased gradually,the chlorophyll normalized vegetation index?CNDVI?decreased first and then increased,and the carotenoid reflectance index?CRI1?increased gradually.The correlation of quantity is high,and the fitting R² of each plot is 0.84,0.95,0.97 and 0.97,respectively.It shows that the fitting degree of the relationship equation is good.The correlation between CRI1 index and carotenoid content is high.The fitting R² of each plot is 0.75,0.79,0.97 and 0.97,respectively,which indicates that the fitting accuracy of the relationship equation is different.The growth relationship and restriction law between leaf structural and functional traits are closely related to the acquisition and utilization of plant resources,and can reflect the mechanism of leaf plasticity and adaptation to environmental heterogeneity.Spectroscopic techniques and special spectral responses play an important role in the study of non-damage and physiological mechanism of leaves.With the increase of years of returning farmland,the wetland community environment gradually approached the original sample plot.The fierce competition of resources in the living environment prompted the plantain to choose the large-leaf model for growth.At the same time,the content of photosynthetic pigments was increased and its net photosynthetic rate was increased,which changed the spectral characteristics of its leaves and formed different spectral responses under different gradients.The coordinated growth of leaves ensures the maximum utilization of resources in heterogeneous habitats,and forms the optimal homeostasis mechanism to balance growth and survival.