Effect Of Nitrogen Addition On Plant Photosynthesis:a Meta-analysis

In recent years,atmospheric nitrogen deposition has increased dramatically and has become one of the main factors affecting global climate change.Since nitrogen is one of the limiting nutrients in most terrestrial ecosystems and the main controlling factor for photosynthesis of most terrestrial plants,the intensification of nitrogen deposition will inevitably have a certain impact on plant photosynthesis.At present,many studies have simulated the effects of nitrogen deposition on plant photosynthesis,but most of these studies are limited to a certain experimental site or part of the region,and there is a lack of systematic research on a global scale.In addition,the results of different studies are inconsistent because of the differences in the type of ecosystems,experimental settings and experimental environments.Therefore,in the present study,data from 153 relevant publications were collected,integrated,and statistically analyzed.The aims of this study were to:?1?elucidate the effects of nitrogen addition on soil physical and chemical properties and plant leaf growth;?2?analyze the effects of nitrogen addition on photosynthetic physiological indexes of plants;?3?clarify how environmental factors?e.g.,climate,altitude,and soil properties?affect the response of photosynthetic physiological indexes to nitrogen addition;and?4?preliminarily explore the potential mechanism of nitrogen addition affecting plant photosynthetic rate.This study will help us to clarify the change law of plant photosynthetic rate with nitrogen addition,and to provide a theoretical basis and scientific basis for better response to global climate change.The main results of this study are as follows:?1?Nitrogen addition led to soil acidification,which increased the content of Mg²⁺,Mn²⁺and Al³⁺in the soil solution.In addition,nitrogen addition increased the amount of nitrogen available for plant uptake in the soil solution,inducing a significant increase of plant foliar nitrogen content and leading to an increase of plant leaf area and photosynthetic pigment content.Changes in leaf area and photosynthetic pigment content will have a certain effect on plant photosynthetic rate.?2?Nitrogen addition significantly increased the photosynthetic rate,stomatal conductance,transpiration rate,and water use efficiency of plants.The changes of plant photosynthetic rate varies with the nitrogen application form,nitrogen application rate,nitrogen application duration,plant photosynthetic type,taxonomic feature,family,ecosystem,and experimental environment.?3?There were significant positive correlations between the responses of photosynthetic rate to nitrogen addition and the responses of stomatal conductance and transpiration rate to nitrogen addition.Moreover,there is also a great important positive correlation between the response of stomatal conductance and the transpiration rate to nitrogen addition.?4?Climate,altitude and soil physical and chemical properties can affect the response of photosynthetic physiological indexes to nitrogen addition.This suggests that the effects of local climate,altitude,and soil physical and chemical properties should be fully considered when evaluating the effects of nitrogen addition on plant photosynthesis and proposing reasonable fertilization strategies in agricultural practice.?5?Nitrogen addition resulted in a significant increase in the total nitrogen content of soil,and the nitrogen content of plant leaves increased accordingly,which in turn led to an increase in the chlorophyll content of the plants,thereby increasing the plant photosynthetic rate.In summary,when measuring the response of plant photosynthesis to nitrogen addition,it is necessary to fully consider the effects of plant characteristics,specific nitrogen application plans,local climate,altitude,and soil physical and chemical properties.This conclusion will provide a theoretical basis and scientific basis for coping with the increase of atmospheric nitrogen deposition and global climate change.