Trade-off Between Beneficial Investment And Support Cost For The Leaves Of Lauraceae Species

As the central place of photosynthesis,transpiration,and gas exchange,leaf plays a vital role in plant growth and development and performs multiple functions.The relationship between plant functional traits is not mutual separation,but there are inextricably related,trade-off relationship is the most common in many functional traits,also known as ecological strategy.Exploring the trade-off between the profitable inputs and the supporting cost of plant leaves can help us understand the differences of biomass investment between plants in various homogeneous and heterogeneous environments,and reveal the adaptive strategies of leaves to the extrinsic environment.The trade-off between photosynthetic returns investment（increasing lamina area）and support cost（petiole,vein,lamina shape）is an important feature.The trade-off of plant biomass investment can be understood by studying the relationship between lamina shape,lamina area,lamina mass,petiole traits,and lamina centroid.In this study,5908 leaves of 17 Lauraceae species belong to the subtropical region Nanjing and belong to the tropical region Xishuangbanna.The leaves of 17 species have two vein patterns:pinnate veins and ternate veins according to vein types.The relationships among lamina shape,lamina area,lamina mass（fresh mass and dry mass）,petiole fresh mass,and lamina centroid were analyzed to explore the trade-off mode of leaves biomass investment in Lauraceae.The phenomenon called“diminishing returns”refers to a scaling relationship between lamina mass（M）and lamina area（A）in many plant species,i.e.,M∝A^α>1,whereαis the scaling exponent exceeding unity.On average,300 of each species were sampled,and the data of lamina mass（fresh mass and dry mass）and petiole mass were measured using a balance;were scanned the leaves with a scanner;the software Photoshop,MATLAB,and R are used to determine the lamina area,lamina perimeter,lamina length,lamina width,and lamina centroid;the bilateral asymmetry standardized index,the ellipticalness index and the ratio of width to length were used to measure the lamina shape;the Montgomery equation was used to verify the relationship between lamina area and the product of lamina length,and lamina width.For each of 5908 leaves from nine Lauraceae species,fresh mass,dry mass,lamina area,and petiole fresh mass were measured,and their scaling relationships were fitted using reduced major axis regression protocols.The bootstrap percentile method was used to test the significance of the difference inα-values between any two species.The relationship between the lamina centroid,the petiole mass,and the lamina mass is analyzed.The main results are as follows:（1）The leaves of 17 Lauraceae species have asymmetries on both sides,the ellipticalness index values were significantly different among different species and the average ratio of width to length of the leaves of 17 Lauraceae species ranged from 0.227 to 0.574.The bilateral symmetry of pinnate veins is better than that of ternate veins,and the ratio of width to length of leaves in tropical regions is greater than that in subtropical regions;（2）The relationship between lamina area and lamina length and lamina width of 17Lauraceae species was verified by the Montgomery equation.The lamina area is proportional to the product of lamina length and lamina width.The parameter estimates of the equation all fall within a certain range（0.60-π/4）;（3）The phenomenon of diminishing returns was verified between fresh mass and lamina area and between dry mass and lamina area.The fresh mass vs.lamina area scaling relationship was statistically more robust than the dry mass vs.lamina area scaling relationship based on bivariate regression r²-values.Diminishing returns were also observed for the petiole fresh mass vs.fresh mass and petiole fresh mass vs.lamina area scaling relationships.The petiole fresh mass vs.fresh mass scaling relationship was statistically more robust than the petiole fresh mass vs.lamina area scaling relationship;（4）The centroid ratio of the leaves of 17 Lauraceae species was significantly different,and the centroid ratio of the leaves in the subtropical region was larger than that in the tropical region,and the centroid ratio for the pinnate vein pattern was larger than that the ternate vein pattern.The size and shape of the lamina reflected by the lamina centroid ratio may adjust the investment allocation between lamina mass and petiole mass,thus affecting the leaf development mode under different environments.In summary,on the condition that external resources are limited,most Lauraceae leaves will make a trade-off between beneficial investment（increasing lamina area to obtain photosynthetic benefits）and support costs（petiole,vein,lamina shape）,and optimize the allocation of resources among different functions to maximize their benefits.The study on the scaling relationships among lamina shape,lamina area,lamina mass,petiole traits,and lamina centroid can help to understand the trade-off between functional and support structure of plants,provide new insights into how the Lauraceae leaves make biomass allocation that maximizes plant benefits,and reveals adaptive strategies of leaves to the extrinsic environment and their investment and costs.