新疆石河子市不同绿地类型下
Under different green space types in Shihezi City, Xinjiang

植物碳收支特征
Characterization of plant carbon balance

张瑞静¹,田晓鸽²,王 利²,宋于洋¹¹*
Ruijing Zhang ¹ ,Xiaoge Tian ² ,Li Wang ² ,Yuyang Song ^{1 1} *

（1.石河子大学，新疆 石河子832000；2.石河子市城市研究所，新疆 石河子832000）
(1. Shihezi University, Shihezi 832000, Xinjiang; 2. Shihezi Urban Research Institute, Shihezi 832000, Xinjiang)

摘要：城市绿地中树木的固碳能力对于中和城市温室气体排放具有重要意义，科学解析其碳收支特征对优化绿地低碳管理策略至关重要。本研究以居住区、公园及道路三类绿地为对象，通过实测12种相同年龄常见树种的生长参数计算单株碳储量，结合生命周期评价法量化碳收支。利用基因型主效应及其与环境互作（GGE）和Pearson分析三种绿地上植物与环境的互作关系。结果表明：（1）公园绿地单株平均碳储量（102.01 kg）显著高于道路（86.53 kg）和居住区绿地（70.15 kg），新疆杨单株碳储量最高（156.32 kg），长枝榆在不同绿地间差异最大（1.6倍）；（2）养护碳排放呈现公园（6.73 kg/株）>道路（5.05 kg/株）>居住区（3.18 kg/株）趋势，灌溉贡献率超70%；（3）GGE双标图显示樟子松在道路绿地碳收支最优，云杉碳收支稳定性最高；（4）碳收支与土壤紧实度、树高呈显著正相关，与修剪强度、栽植密度呈负相关。研究为干旱区城市绿地低碳营建提供了树种选择依据与养护管理优化策略。
Abstract: The carbon sequestration capacity of trees in urban green spaces is important for neutralizing urban greenhouse gas emissions, and scientific analysis of their carbon balance characteristics is crucial for optimizing the low-carbon management strategies of green spaces. In this study, the growth parameters of 12 common tree species of the same age were measured to calculate the carbon stock of individual trees, and the carbon balance was quantified by the life cycle assessment method, using three types of green spaces: residential areas, parks and roads. Genotype main effects and their interactions with the environment (GGE) and Pearson were used to analyze the interactions between plants and the environment on the three types of green spaces. The results showed that: (1) the average carbon stock per plant in park green space (102.01 kg) was significantly higher than that in road (86.53 kg) and residential green space (70.15 kg), Xinjiang poplar had the highest carbon stock per plant (156.32 kg), and long-branch elm had the largest difference between different green spaces (1.6-fold); (2) the conservation carbon emission showed the difference of carbon emission in parks (6.73 kg/plant) > roads ( 5.05 kg/plant) > residential area (3.18 kg/plant), and the contribution of irrigation was more than 70%; (3) GGE double-scaled graphs showed that camphor pine had the best carbon balance in the road green space, and spruce had the highest stability of carbon balance; (4) carbon balance was significantly positively correlated with soil compactness and tree height, and negatively correlated with pruning intensity and planting density. The study provides a basis for tree species selection and maintenance management optimization strategies for low-carbon urban green space construction in arid areas.

关键词：城市绿地；碳储量；碳排放；环境互作；
Keywords: urban green spaces; carbon stocks; carbon emissions; environmental interactions;

中图分类号：S718.55
CCS: S718.55

城市化是社会文明和发展的必然过程，中国和世界上大多数发展中国家一样，正在经历快速的城市化进程，预计到2030年全球城市化水平将超过60% (United Nations, 2018)。作为最大的发展中国家和世界第二大经济体，到2050年，中国的城市化水平将达到70% (Huang et al.,2020)。根据政府官方统计数据，2019年中国建筑面积和绿地面积分别增加到2×10⁴km²和3.15×10⁶ha(Zhang et al.2022)。由于大城市经历两种气候变化机制：全球温室效应和局部热岛效应，他们的变暖速度比附近的农村地区快50%。城市绿地植物被视为冷却城市环境和减少温室气体（GHG）的最有效和最低能耗的方法排放 (Stone 2012)。
Urbanization is an inevitable process of social civilization and development, and China, like most developing countries in the world, is experiencing rapid urbanization, with the global urbanization level expected to exceed 60% by 2030 (United Nations, 2018). As the largest developing country and the world's second largest economy, China's urbanization level will reach 70% by 2050 (Huang et al., 2020). According to official government statistics, China's built-up area and green space increased to 2 × 10 ⁴ km ² and 3.15 × 10 ⁶ ha in 2019 (Zhang et al., 2022). Because large cities experience two climate change mechanisms: the global greenhouse effect and the local heat island effect, they are warming up to 50% faster than nearby rural areas. Urban green space plantings are seen as the most effective and least energy efficient way to cool urban environments and reduce greenhouse gas (GHG) emissions (Stone 2012).

路易斯安那州新奥尔良的城市森林调查结果显示，新奥尔良的城市森林覆盖率达到了24.5%；碳封存量达到了1.3×10⁷吨，年均0.11吨/公顷/年 (McPherson and Simpson, 2003)。这项研究表明，植树对于未来负荷峰值的降低具有重要意义，并且在改善空气质量以及减轻对不断增长的人口的影响方面具有巨大的潜力。然而，与天然林等自然植被不同，城市绿地在提供休闲游憩服务的同时，其建设和维护所消耗的能源与资源会产生持续性碳排放，如果人为经营与管理措施造成的碳排放量高于植物自身碳汇量，那么园林植物非但不能发挥碳汇功能，反而可能成为净碳排放源，由此影响城市植被总体碳汇量乃至城市碳平衡(Kuittinen M,et al.2021)。McPherson 和 Kendall以芝加哥百万树木计划为例，核算了从苗木生产到林木修剪和清除用于覆盖和生物制能 40 年生命周期的碳收支清单(McPherson and Kendall, 2014)。又以美国梧桐为例，核算了50年生命周期内的碳固定量和不同管理方式下的碳消耗量(McPherson and Kendall, 2015)。这些研究清楚地表明,温带半干旱气候条件下城市绿地表现为碳源。Strohbach et al.(2012)等认为地中海气候条件下的德国莱比锡地区每公顷城市绿地在建成后50年间的碳排放总量约为2.6-4.7t/CO₂，其碳固定量为102t/CO₂。Park and Jo(2021)评估的30个韩国中小型公园也大多需要 20-30年实现碳平衡。而我们发现，不同气候条件下，降水量与蒸发量的不同，树木的碳收支量具有显著差异。在干旱半干旱地区，高强度的灌溉需求使得绿地系统碳收支平衡面临更大挑战。科学评估不同绿地类型中树木的碳储量与养护碳排放，制定精准化低碳养护策略，对于提升城市绿地净碳汇能力具有重要意义。
The results of an urban forest survey in New Orleans, Louisiana, showed that New Orleans had 24.5% urban forest cover; carbon sequestration reached 1.3 x 10 ⁷ tons, with an annual average of 0.11 tons/ha/year (McPherson and Simpson, 2003). This study suggests that tree planting is important for future reductions in peak loads and has great potential to improve air quality and mitigate impacts on growing populations. However, unlike natural vegetation such as natural forests, urban green spaces provide recreational services while consuming energy and resources for their construction and maintenance, which will generate continuous carbon emissions. If anthropogenic operation and management measures result in higher carbon emissions than the plants' own carbon sinks, garden plants may become a net source of carbon emissions instead of performing their function as carbon sinks, thus affecting the overall carbon sinks and even the carbon balance of urban vegetation (Kuusen, 2003). McPherson and Kendall used the Chicago Million Tree Program as an example to calculate the carbon balance from seedling production to forest pruning and removal for mulching and biomass energy production over a 40-year life cycle (McPherson and Kendall, 2014). Another example of American sycamore was used to account for carbon fixation over a 50-year life cycle and carbon consumption under different management practices (McPherson and Kendall, 2015). These studies clearly show that urban green space under temperate semi-arid climatic conditions behaves as a carbon source.Strohbach et al. (2012) et al. concluded that the total carbon emissions per hectare of urban green space in the Leipzig region of Germany under Mediterranean climatic conditions were about 2.6-4.7 t/CO ₂ during the 50 years after its establishment, and its carbon fixation was 102 t/CO ₂ .Most of the 30 small and medium-sized Korean parks assessed by Park and Jo (2021) also take 20-30 years to achieve carbon balance. In contrast, we found significant differences in carbon balance of trees under different climatic conditions with different precipitation and evapotranspiration. In arid and semi-arid regions, the high intensity of irrigation demand makes it more challenging to balance the carbon balance of green space systems. It is important to scientifically assess the carbon stocks and maintenance carbon emissions of trees in different green space types, and formulate precise low-carbon maintenance strategies to enhance the net carbon sink capacity of urban green spaces.

本研究通过计算城市中不同绿地条件下的15年的12种树种，基于生命周期评价（LCA）方法，计算各个树木的碳收支特征。旨在解决三大科学问题：（1）15年的树龄的树木，在城市不同绿地中呈现碳源还是碳汇特征？（2）灌溉强度、树种配置等关键因子如何影响碳平衡阈值？
In this study, we calculated the carbon balance characteristics of individual trees based on the Life Cycle Assessment (LCA) method by calculating 12 tree species of 15 years of age in different green space conditions in the city. It aims to address three major scientific questions: (1) Do trees of 15 years of age present carbon source or sink characteristics in different green spaces in the city? (2) How do key factors such as irrigation intensity and tree species configuration affect the carbon balance threshold?

1材料与方法
1 Materials and Methods

1.1研究区域概况
1.1 Overview of the study area

石河子市（43°26′—45°20′N,84°58′—86°24′E）位于新疆维吾尔自治区北部，地势平坦，地处天山北麓中段，辖区总面积约为460 km²是典型的温带大陆性干旱气候。目前石河子市绿地面积已经达到2680 hm²，公共绿地达341 hm²，建成区绿化覆盖率达43%，居全疆城市前列。
Shihezi City (43°26′-45°20′N,84°58′-86°24′E) is located in the northern part of Xinjiang Uygur Autonomous Region, with a flat terrain, located in the middle of the northern foothills of the Tianshan Mountains, and with a total area of about 460 km ² It is a typical temperate continental arid climate. At present, the green area of Shihezi has reached 2,680 hm ² , with 341 hm ² of public green space, and the green coverage rate of the built-up area has reached 43%, which is at the forefront of cities in the whole Xinjiang.

表1 研究区环境条件对比
Table 1 Comparison of environmental conditions in the study area

Table 1 Comparison of environmental conditions in the study area

1.2研究材料
1.2 Research materials

在城市三种不同绿地中选取12种植物，其中包括新疆杨(Populus alba var. pyramidalis)、大叶白蜡(Fraxinus rhynchophylla)、小叶白蜡(Fraxinus chinensis)、长枝榆（Ulmus pumila）、白榆(Ulmus pumila)、垂柳(Salix babylonica)、夏橡(Quercus robur)、樟子松(Pinus sylvestris)、黄金树(Catalpa speciosa)、云杉(Picea koraiensis)、暴马丁香(Syinga reticulata)、海棠(Malus spectabilis)，覆盖了7科，10属，如表1。在三种样地上，分别选取品种一致、年龄相同的植物作为研究对象。
Twelve plant species were selected from three different green spaces in the city, including Xinjiang poplar (Populus alba var. pyramidalis), large-leaved ash (Fraxinus rhynchophylla), small-leaved ash (Fraxinus chinensis), long-branch elm (Ulmus pumila), white elm ( Ulmus pumila), weeping willow (Salix babylonica), summer oak (Quercus robur), sphagnum pine (Pinus sylvestris), golden tree (Catalpa speciosa), spruce (Picea koraiensis), storm horse lilac (Syinga reticulata), and begonia (Malus spectabilis), covering 7 families and 10 genera, as shown in Table 1.On each of the three sample plots, plants of the same species and age were selected for the study.

1.3研究方法
1.3 Research methodology

1.3.1城市绿地植物生物量方程估算
1.3.1 Estimation of plant biomass equations for urban green spaces

城市绿地碳储量计算分为地上和地下两个部分，本研究主要针对乔木层，不计算灌木、 地被层及土壤碳储量。选取了12种树种的30-60棵左右的数据，对树木生物量进行分段式测量，使用林分速测镜测量树干和直径大于5 cm各级枝条的各个节段的直径与长度，将测得的树干和各级枝条的直径及长度，利用已有的原木材积表进行查询，获得树木材积，通过乘以基本木材密度（树干实测重量与树干实测体积的比值）求得生物量(Markwardt, 1930)。将剩余直径小于等于5 cm的枝条进行采伐，每一树种采伐15枝标准枝进行烘干称重，得出一个平均值，使用小枝干重平均值乘以树上的小枝数量，可得出树木小于等于5cm枝条的生物量。地下生物量则按根冠比0.26计算(Nowak et al., 1994)。这样就获取了不同树种全株生物量，为了实用和方便，依据上述方法（Dimobe et al.,2019）获取的生物量建立胸径和树高为自变量的方程。
The calculation of carbon stock in urban green space was divided into two parts: aboveground and belowground, and this study mainly focused on the tree layer, without calculating the carbon stock in shrubs, ground cover layer and soil. The data of about 30-60 trees of 12 species were selected to measure the biomass of the trees in sections, and the diameter and length of the trunks and branches with diameters larger than 5 cm were measured using a forest stand velocimeter, and the measured diameters and lengths of the trunks and branches were queried using the existing log volume table to obtain the volume of the trees, which was multiplied by the basic wood density (the ratio of measured weight of trunks to measured volume) to obtain the biomass (the volume of the trunks). The biomass was obtained by multiplying the basic wood density (the ratio of the measured weight of the trunk to the measured volume of the trunk) (Markwardt, 1930). Remaining branches less than or equal to 5 cm in diameter were harvested, and 15 standard branches of each species were harvested, dried and weighed to obtain an average value, and the biomass of the tree's branches less than or equal to 5 cm in diameter was obtained by multiplying the average dry weight of the branches by the number of branchlets in the tree. Below-ground biomass was then calculated using a root-crown ratio of 0.26 (Nowak et al., 1994). In this way the whole plant biomass of the different tree species was obtained and for practicality and convenience, equations with diameter at breast height (DBH) and tree height as independent variables were established based on the biomass obtained by the above method (Dimobe et al., 2019).

最后建立出各个树种的生物量方程：大叶白蜡为W=0.245(D²H)^0.880、小叶白蜡为W=0.282(D²H)^0.845、长枝榆为W=0.080(D²H)^0.961、夏橡为W=0.245(D²H)^0.879、白榆为W= 0.131(D²H)^0.911、樟子松为W= 0.168(D²H)^0.870、黄金树为W= 0.009(D²H)^1.191、暴马丁香为W= 0.143(D²H)^0.935、新疆杨为W= 0.092(D²H)^0.962、垂柳为W= 0.105(D²H)^0.93、海棠为W= 0.085(D²H)^0.970、云杉为W= 0.169(D²H)^0.826。全株生物量乘以植物的含碳率即为树种碳储量(Leith, 1975)。
Finally, biomass equations were developed for each species: W=0.245(DH for large-leafed ash ^0.880 , W=0.282(DH for small-leafed ash ^0.845 , W=0.080(DH for longbranch elm ^0.961 , W=0.245(DH for summer oak ^0.879 , W=0.131(DH for white elm) ^0.911 , Sphagnum pine for W= 0.168(DH) ^0.870 , Golden tree for W= 0.009(DH) ^1.191 , Storm horse lilac for W= 0.143(DH) ^0.935 , Xinjiang poplar for W= 0.092(DH) ^0.962 , Weeping willow for W= 0.105(DH) ^0.93 , Begonia for W= 0.092(DH) ^0.93 , and Pittosporum for W= 0.105(DH). , W= 0.085(DH) ^0.970 for Begonia, and W= 0.169(DH) ^0.826 for Spruce. Whole-plant biomass multiplied by the plant's carbon content is the carbon stock of the species (Leith, 1975).

1.3.2养护管理碳排放估算
1.3.2 Estimation of carbon emissions from conservation management

研究采用生命周期评价法，聚焦于城市绿地植物群落养护管理阶段的碳排放量计算。关于园林全生命周期中的其他阶段，例如初始材料生产与运输、设计与建造、废弃物处理等活动，则不作为本次研究的核心内容。养护管理基础数据包括灌溉方式及频率、施肥与打药频率、年用灌溉水量、化肥农药使用量、机械设备型号、功率、年燃油电力消耗等。这些数据通过与园林养护工作人员和管理者深入访谈，并查阅公园的养护管理日志得以收集。为了保证数据的准确性和真实性，本研究依据《IPCC 国家温室气体排放清单指南》中推荐的碳排放转换因子，来计算各具体过程的碳排放量。城市绿地植物养护管理的碳投入量计算公式为：
The study adopts the life cycle assessment method, focusing on the calculation of carbon emissions at the stage of maintenance and management of plant communities in urban green spaces. Regarding other phases of the whole life cycle of the garden, such as initial material production and transportation, design and construction, waste disposal and other activities, they are not the core content of this study. The basic data for maintenance and management include irrigation method and frequency, frequency of fertilization and dosing, annual irrigation water use, fertilizer and pesticide use, mechanical equipment model, power, and annual fuel and electricity consumption. These data were collected through in-depth interviews with landscape maintenance staff and managers, and by reviewing the park's maintenance management logs. In order to ensure the accuracy and authenticity of the data, this study calculates the carbon emissions of each specific process based on the carbon emission conversion factors recommended in the IPCC Guidelines for National Greenhouse Gas Emission Inventories. The formula for calculating the carbon input of plant maintenance and management in urban green spaces is:

其中，Ct表示碳投入量，单位为kgCE/（hm²·a）；n表示城市绿地植物养护管理消耗的能源量与物资投入具体种类；m为能源消耗量与物资投入量；β是指第i种能源消耗量与物资投入量的碳排放系数。
Where Ct denotes the carbon input in kgCE/(hm ² -a); n denotes the specific types of energy and material inputs consumed by the maintenance and management of urban green space plants; m is the energy consumption and material inputs; and β is the carbon emission coefficient of the first type of energy consumption and material inputs.

表2 CO₂排放因子系数
Table 2 CO ₂ emission factor coefficients

Table 2 CO₂ emission factor coefficients

1.3.3城市绿地植物碳收支估算
1.3.3 Estimation of plant carbon balance in urban green spaces

城市绿地主要树种养护管理周期的碳收支量为每个植物的固碳量与碳排放量相减，若相减值为正值，则此植物表现为碳汇，反之则为碳源。碳收支量代表该植物的碳平衡状况，碳收支平衡是根据固碳值和碳排值确定的，其确定依据为当固碳值等于碳排值时，即为碳收支相对平衡状态。植物养护管理周期的碳收支计算公式如下：
The carbon balance of the maintenance and management cycle of the main tree species in urban green space is the carbon sequestration of each plant minus the carbon emission, if the value is positive, the plant is a carbon sink, and vice versa, it is a carbon source. Carbon balance represents the carbon balance of the plant, which is determined based on the carbon sequestration value and carbon emission value, based on the fact that when the carbon sequestration value is equal to the carbon emission value, it is a relatively balanced state of carbon balance. The formula for calculating the carbon balance of the plant maintenance and management cycle is as follows:

式中，C 为城市绿地植物养护管理周期的碳收支量；CS为每个植物的年固碳总量；CE为每个植物养护管理阶段的CO₂年排放总量，单位均为kg/株。
In the formula, C is the carbon income and expenditure of the maintenance and management cycle of urban greenland plants; CS is the total annual carbon sequestration of each plant; CE is the total annual emission of CO ₂ during the maintenance and management stage of each plant, and the unit is kg/plant.

1.3.4 GGE双标图
1.3.4 GGE bilabeled maps

GGE双标图数学模型采用环境中心化数据展示植物效应和植物与环境互作效应的结果，是分析多点试验数据的理想工具（Yan,2008），公式为：
The GGE biscotopic graphical mathematical model uses environmentally centered data to show the results of plant effects and plant-environment interaction effects, and is an ideal tool for analyzing data from multi-point experiments (Yan, 2008), with Eq:

式中：为第i个绿地中第j个植物碳收支量均值；u为总体植物碳收支均值；为第i个绿地中所有植物碳收支均值；${''\lambda ''}_{\mathrm{}}$和${''\lambda ''}_{\mathrm{}}$为第1个和第2个主成分的特征值；${''\gamma ''}_{\mathrm{}}$和${''\gamma ''}_{\mathrm{}}$为第j个植物在第1个和第2个主成分的特征向量；${}_{\mathrm{}}$和${}_{\mathrm{}}$为第i个植物在第1个和第2个主成分的特征向量；${''\epsilon ''}_{\mathrm{}}$为剩余残差（Diagnostics,2003）。
Where: is the mean carbon balance of the jth plant in the ith green space; u is the overall mean plant carbon balance; is the mean carbon balance of all plants in the ith green space; ${''\lambda ''}_{\mathrm{}}$ and ${''\lambda ''}_{\mathrm{}}$ are the eigenvectors for the 1st and 2nd principal components; ${''\gamma ''}_{\mathrm{}}$ and ${''\gamma ''}_{\mathrm{}}$ are the eigenvectors for the jth plant in the 1st and 2nd principal components; ${}_{\mathrm{}}$ and ${}_{\mathrm{}}$ are the eigenvectors of the ith plant in the 1st and 2nd principal components; and ${''\epsilon ''}_{\mathrm{}}$ is the residual residual (Diagnostics, 2003).

1.3.5 数据处理
1.3.5 Data processing

采用Pearson法对植物碳收支与影响因子进行相关分析。利用R软件制作GGE双标图，Origin 2022 软件制作相关性热图。
The Pearson method was used to correlate the plant carbon balance with the influencing factors. GGE biscale plots were produced using R software and correlation heat maps were produced using Origin 2022 software.

2结果与分析
2 Results and Analysis

2.1不同绿地类型主要树种的碳储量比较
2.1 Comparison of carbon stocks of major tree species in different green space types

同一树龄的同种乔木以及不同乔木间，在不同绿地环境中碳储量均存在一定差异（图1）。公园绿地中树木平均碳储量最高（102.01kg C/株），显著高于居住区绿地（70.15 kg C/株）和道路绿地（86.53 kg C/株）。三种绿地中，大叶白蜡、黄金树、新疆杨和长枝榆的单株碳储量差异显著，其中，新疆杨的单株平均单株碳储量最高，为156.32kg，最大值与最小值相差1.3倍。长枝榆在不同绿地类型中的单株碳储量相差最大，最大值为最小值的1.6倍。
There were some differences in carbon stocks among trees of the same species of the same age and among trees in different green space environments (Figure 1). The average carbon storage of trees in the park green space was the highest (102.01 kg C/plant), which was significantly higher than that in the residential green space (70.15 kg C/plant) and road green space (86.53 kg C/plant). Among the three kinds of green spaces, the differences in carbon storage per plant were significant among large-leaved ash, golden tree, Xinjiang poplar and long-branch elm, among which, Xinjiang poplar had the highest average carbon storage per plant of 156.32 kg C/plant, and the difference between the maximum value and the minimum value was 1.3 times. The difference between the maximum and minimum values was 1.3 times. The difference between the carbon stocks of the long-branch elm and the long-branch elm was the largest among the different green space types, with the maximum value being 1.6 times of the minimum value.

图1 同一树种在不同类型城市绿地固碳量的差异性
Fig. 1 Differences in carbon sequestration by the same tree species in different types of urban green spaces

Figure 1 Difference of carbon sequestration of the same tree species

in different types of urban green space

2.2不同绿地类型主要树种的碳排放
22 Carbon emissions of major tree species in different green space types

受绿地不同的养护管理水平以及植物生长特征影响，树种的年养护管理碳排放量也不同（表3）。公园绿地树种养护管理年碳排放量变化范围为4.93—7.75kg/株，平均值为6.73kg/株。道路绿地树种养护管理年碳排放量变化范围为3.54—6.77kg/株，平均值为5.05kg/株。居住区绿地树种养护管理年碳排放量变化范围为2.34—4.03kg/株，平均值为3.18kg/株。落叶乔木年周期碳排放量均值(5.14kg/株)高于常绿乔木(4.20/株)。长枝榆是树种中平均年碳排放量最高的树种(6.18kg/株)，其次为夏橡(6.01kg/株)，第三为新疆杨(5.73kg/株)。
The annual carbon emissions from maintenance and management of tree species varied depending on the different levels of maintenance and management of green spaces and plant growth characteristics (Table 3). The annual carbon emissions of tree species in parks varied from 4.93 to 7.75 kg/plant, with an average value of 6.73 kg/plant. The annual carbon emissions of tree species maintenance and management in road green space varied from 3.54 to 6.77 kg/plant, with an average value of 5.05 kg/plant. The annual carbon emissions of tree species maintenance and management in residential green areas varied from 2.34 to 4.03kg/plant, with an average value of 3.18kg/plant. The mean annual cycle carbon emissions were higher for deciduous trees (5.14kg/plant) than evergreen trees (4.20/plant). Long-branch elm had the highest mean annual carbon emissions among the tree species (6.18kg/plant), followed by summer oak (6.01kg/plant), and third by Xinjiang poplar (5.73kg/plant).

表3 不同类型城市绿地各树种养护管理碳排放量的差异
Table 3 Differences in carbon emissions from maintenance and management of tree species in different types of urban green spaces

Table 3 Differences in carbon emissions from conservation and

management of tree species in different types of urban green space

Ⅰ：公园绿地；Ⅱ：道路绿地；Ⅲ：居住区绿地.
Ⅰ: park green space; Ⅱ: road green space; Ⅲ: residential green space.

图2 碳吸收量和碳排放量对比
Figure 2 Comparison of carbon sequestration and carbon emissions

Figure 2 Comparison of carbon absorption and carbon emissions

基于12个树种的碳排放量与碳吸收量计算结果（图2），获得各个树种的15年碳收支量，有4个树种的碳收支值为负值。由此可知，绝大部分树种呈现了正值，即是城市的碳汇。新疆杨和小叶白蜡的碳收支最大，分别为70.47和53.49kg。除此以外，其余树种的碳排放量和碳吸收量的差值基本持平，碳固定量微大于碳排放量，具有较大的碳汇潜力，包括大叶白蜡（35.07kg）、长枝榆（24.57kg）、夏橡（19.37kg）、樟子松（5.86kg）、白榆（24.20kg）、黄金树（7.61kg）。
Based on the results of carbon emissions and carbon sequestration calculations of 12 tree species (Fig. 2), the 15-year carbon balance of each tree species was obtained, and four tree species showed negative values. From this, it can be seen that the vast majority of tree species showed positive values, i.e., they are carbon sinks in the city. The carbon balance of Xinjiang poplar and small-leaved ash was the largest, 70.47 and 53.49 kg, respectively, except for the rest of the tree species where the difference between carbon emissions and carbon sequestration was basically flat, and carbon fixation was slightly larger than carbon emissions, which had a large potential for carbon sinks, including large-leaved ash (35.07 kg), long-branch elm (24.57 kg), summer oak (19.37 kg), camphor pine (5.86 kg), white elm (24.20kg), and golden tree (7.61kg).

2.3基于GGE双标图的碳收支差异
2.3 Differences in carbon balance based on GGE bi-scalar map

2.3.1不同绿地树种间碳收支水平比较
2.3.1 Comparison of carbon sequestration levels among different greenfield tree species

生态适应性分析主要用于确定在不同绿地上碳收支最好的植物。在图3a中，樟子松位于道路绿地环境区间即表示在该环境下碳收支水平最佳。三种绿地上，碳收支水平最好的植物为樟子松，其在道路绿地上的碳收支量更好。大叶白蜡在三种环境上碳收支差异性最大，黄金树碳收支差异性最小。图3b中，边缘图标连线形成的多边形，顶点代表环境中碳收支水平最佳的顶角植物，靠近原点的植物对环境变化不敏感，不具有特殊适应性。三种绿地均对应一个顶角植物，公园绿地、道路绿地和居住区绿地上分别是大叶白蜡、樟子松和垂柳。
The ecological adaptability analysis is mainly used to determine the plants with the best carbon balance on different green spaces. In Figure 3a, camphor pine is located in the environmental zone of the road green space which means that it has the best level of carbon sequestration in this environment. The plant with the best level of carbon sequestration on the three green spaces is camphor pine, which has better carbon sequestration on the road green space. Large-leaved ash had the greatest variability in carbon balance on the three environments, and golden tree had the least variability in carbon balance. In Figure 3b, the polygon formed by the connecting lines of the edge icons, the apex represents the top corner plant with the best carbon balance level in the environment, and the plants close to the origin are not sensitive to the environmental changes and do not have special adaptations. Each of the three green spaces corresponds to an apex corner plant, which is large-leaved ash, camphor pine and weeping willow on park green spaces, road green spaces and residential green spaces, respectively.

图3 不同绿地环境的植物碳收支比较
Fig. 3 Comparison of plant carbon balance in different green space environments

Figure 3 Comparison of plant carbon

budget in different green space environments

2.3.2不同绿地中植物排序
2.3.2 Plant sequencing in different green spaces

用“环境排序”模式鉴别植物稳定性，其中，纵向双标轴代表植物固碳降温效益平均值，位于右侧的植物高于平均值，越靠近中心圆稳定性越好。由图4可以看出，通过与模拟理想树种对比，在三种绿地上分别筛选出 9个碳收支水平高于平均值的植物，作为景观配置优选植物范围，公园绿地上为：大叶白蜡>夏橡>小叶白蜡>长枝榆>黄金树>樟子松>云杉>新疆杨>白榆，道路绿地上为：樟子松>暴马丁香>白榆>云杉>新疆杨>垂柳>黄金树>海棠>夏橡，居住区绿地上为：垂柳>海棠>暴马丁香>白榆>长枝榆>小叶白蜡>大叶白蜡>新疆杨>黄金树。
The plant stability was identified by the "environmental ranking" model, in which the vertical double-scaled axis represents the average value of plant carbon sequestration and cooling benefit, and the plants located on the right side are higher than the average value, and the closer to the center circle, the better the stability is. As can be seen in Figure 4, by comparing with the simulated ideal tree species, nine plants with higher-than-average levels of carbon sequestration were screened out in three kinds of green spaces as the preferred plant range for landscape configuration, including: large-leafed ash>summer oak>small-leafed ash>long-leafed elm>golden tree>camphor pine>spruce>Xinjiang poplar>white elm in the park, and camphor pine>storm lilac>white elm>spruce>Xinjiang poplar>triumph laurel>golden tree>begonias>summer willow>pineapple>spruced wood. On the road green space, it is: weeping willow > golden tree > begonia > summer oak, and on the residential green space, it is: weeping willow > begonia > storm martin > white elm > long-branch elm > small-leafed ash > large-leafed ash > Xinjiang poplar > golden tree.

图3 不同绿地环境的植物碳收支稳定性排序
Fig. 3 Ordering of plant carbon balance stability in different green space environments

Figure 4 Stability ranking of plant

carbon budget in different green space environments

2.4不同树种碳收支的综合评价
2.4 Comprehensive evaluation of carbon balance of different tree species

樟子松是距离中心圆最近的植物，碳收支水平最强且稳定。按图标与同心圆的距离远近，对植物碳收支量进行排序：樟子松>云杉>黄金树>新疆杨>夏橡>白榆>小叶白蜡>大叶白蜡>长枝榆>暴马丁香>海棠>垂柳。理想品种指所有试验环境中平均碳收支量最高且最稳定的品种。理想品种体现净固碳量平均值和环境平均值同等权重时的综合指标，以理想品种所在的点为圆心做同心圆，各个品种到圆心距离越小越好。图5分析结果显示，本组区试理想程度较高的树种为P8、P10和P9。
Camphor pine is the plant closest to the center circle, with the strongest and stable level of carbon balance. Plants were ranked in terms of carbon sequestration according to the distance of the icon from the concentric circles: camphor pine > spruce > golden tree > Xinjiang poplar > summer oak > white elm > small-leafed ash > large-leafed ash > long-branching elm > riotous lilac > begonia > weeping willow. Ideal variety refers to the variety with the highest and most stable average carbon sequestration across all test environments. Ideal varieties reflect the comprehensive index when the average net carbon sequestration and the average environmental value are equally weighted. Concentric circles are made with the point where the ideal varieties are located as the center of the circle, and the smaller the distance from each variety to the center of the circle, the better. The results of the analysis in Figure 5 show that the tree species with a higher degree of ideality in this group of district tests are P8, P10 and P9.

图5 品种的综合排名
Figure 5 Combined ranking of varieties

Figure 5 Comprehensive ranking of varieties

2.5植物碳收支与影响因子的相关性
2.5 Correlation of plant carbon balance with impact factors

为进一步探究植物固碳能力与环境因子的相关性，选择植物土壤紧实度、降温值、年灌溉量、栽植密度、修剪强度、气温、胸径、树高等影响因子，与植物的固碳量与碳排放量进行相关分析。由图6可以看出，城市三种绿地上植物固碳量与土壤紧实度、降温效果、胸径和树高呈极显著正相关关系，与栽植密度呈极显著负相关关系；碳排放量与树高呈极显著正相关关系，与修剪强度呈极显著负相关关系。此外，居住区绿地植物固碳量还与年灌溉量呈极显著负相关关系，降温值与气温呈显著正相关关系。三种绿地上植物与各生理因子和环境因子间的相关性的密切程度不同，道路绿地植物固碳能力受环境因子影响较另外两个绿地更显著。
In order to further explore the correlation between plant carbon sequestration capacity and environmental factors, plant soil compactness, cooling value, annual irrigation, planting density, pruning intensity, air temperature, diameter at breast height, and tree height were selected as the influencing factors to be correlated with plant carbon sequestration and carbon emission. As can be seen from Figure 6, the carbon sequestration of plants on three kinds of urban green spaces was significantly positively correlated with soil compactness, cooling effect, diameter at breast height (DBH) and tree height, and negatively correlated with planting density; the carbon emission was significantly positively correlated with tree height, and negatively correlated with pruning intensity. In addition, carbon sequestration by plants in residential green areas was also significantly negatively correlated with annual irrigation, and the cooling value was significantly positively correlated with air temperature. The closeness of the correlations between plants and various physiological and environmental factors varied among the three types of green spaces, and the carbon sequestration capacity of plants in the road green space was more significantly affected by environmental factors than in the other two green spaces.

图6 植物碳收支与影响因子的相关系数
Fig. 6 Correlation coefficients between plant carbon balance and impact factors

Figure 6 Correlation coefficient between

plant carbon budget and influencing factors

3讨论
3 Discussion

由于气候、土壤、光照、水文条件和人为干扰程度的不同，同年龄树木碳收支水平存在明显差异 (Zhou et al., 2013，He, 2017, Liu et al., 2010)。在城市中良好的植被管理能够有效维持植物的碳封存功能，不当的养护措施会显著削弱植物的生态效益（Gratani et al.,2007）。树种，种植密度和土壤条件影响了UGS的碳封存水平。在芝加哥西北部，研究了两个植被覆盖度不同的居民区，对碳收支进行了评价，结果表明，差异主要表现在维持过程中，这表明覆盖率对城市绿地的影响小于养护管理（Nowak et al.,2002）。本研究对12种15年生乔木的跨绿地类型比较显示，75%的树种在公园绿地的单株碳储量显著高于道路与居住区绿地。以新疆杨为例，其公园绿地碳储量较道路和居住区分别提升18.3%和29.1%。
Due to differences in climate, soil, light, hydrological conditions and the degree of anthropogenic disturbance, there are significant differences in the carbon balance levels of trees of the same age (Zhou et al., 2013, He, 2017, Liu et al., 2010). Good vegetation management in urban areas can effectively maintain the carbon sequestration function of plants, and improper conservation measures can significantly weaken the ecological benefits of plants (Gratani et al., 2007). Tree species, planting density, and soil conditions influence carbon sequestration levels in UGS. In northwest Chicago, two neighborhoods with different levels of vegetation cover were studied to evaluate the carbon balance, and the results showed that the differences were mainly in the maintenance process, suggesting that cover has a lesser impact on urban green spaces than conservation management (Nowak et al.,2002). Comparison of 12 15-year-old trees across green space types in this study showed that 75% of the tree species had significantly higher carbon stocks per plant in park green spaces than in road and residential green spaces. In the case of Xinjiang poplar, for example, its park green space carbon storage was 18.3% and 29.1% higher than that of roads and residential areas, respectively.

树木的碳汇能力不仅受气候约束，更与其寿命、生长速率和成熟体型等内在特性密切相关。寿命长的大型树种，通过缓慢而持续的碳累积策略，其碳汇效益期是短寿命树种的16倍（Nowak et al.,2002）。北美地区研究显示即使在高维护强度下，长寿命树种仍能维持正碳效益至540年，而短寿命树种在相同管理下仅能维持60年。年龄的增长，生长通常会放缓，在大多数城市绿地中，人为干扰较大，生长至一定年份的成熟树木会被抹头处理或移栽再植，加上城市规划的变化，使城市绿地的生命周期小于植物本身的生长周期(Michael et al.,2011)。本研究结果显示，乔木的碳固定量显著大于小乔木，15年的落叶树种相较于同年龄的常绿树种平均单株碳储量高出54%。
The carbon sequestration capacity of trees is not only constrained by climate, but is also closely related to their intrinsic characteristics such as longevity, growth rate and mature size. Large, long-lived tree species, through a slow and continuous carbon accumulation strategy, have a carbon sink benefit period that is 16 times greater than that of short-lived species (Nowak et al., 2002). Studies in North America have shown that even under high maintenance intensity, long-lived trees can maintain positive carbon benefits for up to 540 years, whereas short-lived trees can only maintain them for 60 years under the same management. Growth usually slows down with age, and in most urban green spaces, human disturbance is high, and mature trees that have grown to a certain age are obliterated and treated with a header or transplanted and replanted, which, together with changes in urban planning, results in urban green spaces having a life cycle that is smaller than that of the plants themselves (Michael et al., 2011). The results of this study showed that the carbon fixation of trees was significantly greater than that of small trees, with 15-year deciduous trees storing 54% more carbon per plant on average compared to evergreen trees of the same age.

城市树木为满足景观美学与安全需求，需持续投入能源与资源，进一步扩大了碳排放量。Ingram（2012）的一项研究研究发现，与需要机器处理和种植的较大树苗相比，可以手工处理和种植的较小树木的温室气体排放量更低。在麦克弗森的研究中，二氧化碳排放的最大来源是覆盖物的分解（65.1%）、木材燃烧（14.5%）和灌溉水（9.7%）。他们对不同树木栽培实践的研究表明，灌溉产生的碳排放量最多，其排放量量大于砍伐和种植。分析认为这与研究在评价边界界定、数据获取方法、碳排放因子取值、研究区域降水条件等方面不同有关。这种现象在干旱区尤为突出：为维持植被存活而强化的灌溉与修剪措施，可能使本已受限的碳汇能力被完全抵消(Xiao et al., 2013)。本研究中城市绿地树种均采用中水或自来水灌溉，城市绿地灌溉年碳排放量约为152kg/ha，灌溉所释放的碳排放量占整个养护管理碳排放量的73.4%。相比之下，上海市的城市绿地灌溉碳年排放量仅为0.02kg/ha，上海市的灌溉用水主要来自降水与地表水。因此，种植高生物量的树木和采取节能措施是实现园林可持续发展的必要条件，维护方法需要适应当地条件和植物生长（Jansson et al，2019），在改善人类健康和环境的同时，有很多机会减少碳排放和运营成本。
Urban trees require a continuous investment of energy and resources to meet landscape aesthetics and safety needs, further amplifying carbon emissions.A study by Ingram (2012) found that smaller trees that can be hand-treated and planted have lower GHG emissions than larger saplings that require machine treatment and planting. In McPherson's study, the largest sources of carbon dioxide emissions were decomposition of mulch (65.1%), wood burning (14.5%), and irrigation water (9.7%). Their study of different arboriculture practices showed that irrigation produced the most carbon emissions, with a larger volume of emissions than cutting and planting. The analysis suggests that this is related to the fact that the studies differed in terms of the definition of the evaluation boundaries, the method of data acquisition, the value of the carbon emission factors, and the precipitation conditions in the study area. This phenomenon is particularly prominent in arid zones: intensified irrigation and pruning measures to maintain vegetation survival may completely offset the already limited carbon sink capacity (Xiao et al., 2013). In this study, urban green space tree species were irrigated with either water or tap water, and the annual carbon emissions from urban green space irrigation were about 152 kg/ha, with the carbon emissions released from irrigation accounting for 73.4% of the overall carbon emissions from maintenance and management. In contrast, the annual carbon emissions from urban green space irrigation in Shanghai are only 0.02 kg/ha, and irrigation water in Shanghai is mainly from precipitation and surface water. Therefore, planting high biomass trees and adopting energy saving measures are necessary to achieve sustainable landscape development, and maintenance practices need to be adapted to local conditions and plant growth (Jansson et al, 2019), with many opportunities to reduce carbon emissions and operational costs while improving human health and the environment.

4结论
4 Conclusion

本研究以石河子市不同绿地上12种树种为例，揭示了城市绿地中的树木的碳收支现象，并分析了影响树木碳收支的主要影响因素，主要研究结论如下: (1)乔木层单株碳储量显著高于小乔木，其中新疆杨单株碳储量最高。公园绿地因土壤管理与树种配置优化，其碳汇强度较道路绿地和居住区绿地分别提升17.9%和45.4%。(2)三类绿地中，养护碳排放强度依次为公园>道路>居住区，灌溉贡献率达73.2%。落叶乔木碳排放集中于修剪作业，而常绿乔木以病虫害防治为主，凸显节水灌溉与精准管护对减排的重要性。(3) 石河子市城市绿地养护管理标准下，新疆杨、大叶白蜡等6种乔木表现为碳汇，海棠、暴马丁香等小乔木因高养护需求成为碳源。
This study reveals the carbon balance phenomenon of trees in urban green spaces by taking 12 tree species on different green spaces in Shihezi City as an example, and analyzes the main influencing factors affecting the carbon balance of trees, and the main conclusions of the study are as follows: (1) The carbon stock of single plant of the tree layer is significantly higher than that of the small trees, among which the Xinjiang poplar has the highest carbon stock of single plant. Due to the optimization of soil management and tree species allocation, the carbon sink intensity of the park green space was 17.9% and 45.4% higher than that of the road green space and residential green space, respectively. (2) Among the three types of green spaces, the intensity of carbon emission from conservation is parks > roads > residential areas in the order of parks > roads > residential areas, and the contribution rate of irrigation reaches 73.2%. Carbon emissions from deciduous trees are concentrated in pruning operations, while evergreen trees are dominated by pest and disease control, highlighting the importance of water-saving irrigation and precise care for emission reduction. (3) Under the urban green space maintenance and management standards in Shihezi City, six species of trees, including Xinjiang poplar and large-leaved ash, showed carbon sinks, and small trees, such as begonias and riparian lilacs, became carbon sources due to high maintenance requirements.

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