The Affecting Factors Of Plants' δ ¹³C Values And Their Ecological Significance In Northwest China

The use of stable isotope techniques in plant ecological research has grown steadily during the past two decades.Carbon isotope composition of plant is a useful index for assessing intrinsic water use efficiency,meanwhile it can provide information on long-term water use efficiency,becauseδ¹³C value integrates photosynthetic activity throughout the period of time when the leaf tissue was synthesized.Most of the arid and semi-arid areas in northwest China are with average annual precipitations under 600 mm,in particular,they are less than 200 mm in arid areas.In such areas,water,which can control the stomata of plant leaves on closing and opening,and influences the Pi/Pa values of plant leaves,will be the main restrictive factor for plants growth.Many studies have shown that theδ¹³C values of leaves and WUE values are related to the stomatic closing,opening and Pi/Pa values. For one thing,δ¹³C valuesof leaves can reflect Pi/Pa values.For another,plants which are with high WUE values,theδ¹³C values of leaves are also high.Above all, WUE values can be reflected byδ¹³C values.According to the distributing characters of plants,we have studied three regions, which are temperate grassland zone,temperate desert zone and plateau,mountain zone.All the samples that we have collected include herbs,shrubs,semi-shrubs and trees.We have studied the distributing characters ofδ¹³C values in various regions, and theδ¹³C values can reflect many affecting factors and WUE values.Our results are as follows:1.After having analyzed the spatial distribution character of plants' in studying areas(arid and semi-arid regions in northwest China),we found that plants'δ¹³C values are in the range of-23.1%o and -32.6%o,within an average of-27.1‰.At the same time,it shows that plants,which are collected this time,are all C₃ species,and the differences ofδ¹³C values are related to environmental and part of biological factors.2.We have analyzed the environmental parameters that could affectδ¹³C values of plants,and found the average annual precipitation would influenceδ¹³C values greatly,furthermore,when the average annual precipitation increases by 100 mm,theδ¹³C values will decrease by about 0.8%,and the change of Pi values is about 12.9ppm.Other environmental factors,such as average annual temperature,light hours in one year,altitude and environmental space parameters(longitude and latitude),are more or less correlation withδ¹³C values,however,they would be interfered by average annual precipitation.Biological factors,such as life forms,plant organs will also influenceδ¹³C values of plants.Theδ¹³C values of evergreen trees are higher than deciduous trees'.Branches'δ¹³C values are higher than leaves'.3.We have discussed the relationship betweenδ¹³C values and WUE values in theoretical and experimental aspects.It is evident that theδ¹³C and WUE values are with positive correlation in theoretics.In order to expore the relationship betweenδ¹³C and WUE values in experimental aspect,we have analyzed the average annual precipitation that affectsδ¹³C values of plants in studying regions.Furthermore,we have obtained the variational average event of Pi/Pa values,and the preliminary estimates showed that the WUE values can vary by about 80%in studying regions.