双集合卡尔曼滤波LAI同化结合BEPS模型的竹林生态系统碳通量模拟

叶面积指数(LAI)是森林生态系统碳循环研究的重要观测数据,也是驱动森林生态系统模型模拟碳循环的重要参数.本文以毛竹林和雷竹林为研究对象,首先利用双集合卡尔曼滤波,同化两种竹林生态系统观测站点2014—2015年MODIS LAI时间序列数据,然后将同化的高质量毛竹LAI和雷竹LAI作为输入数据驱动BEPS模型,模拟两种竹林生态系统总初级生产力(GPP)、净生态系统碳交换量(NEE)和总生态系统呼吸(TER)等碳循环数据,并用通量站实际观测值评价模拟结果;另外,还对比不同质量LAI对碳循环模拟的影响.结果表明: 双集合卡尔曼滤波同化得到的毛竹林和雷竹林LAI与实测LAI之间的相关关系极为显著,R²分别为0.81和0.91,且均方根误差和绝对偏差均较小,极大地提高了MODIS LAI的产品精度;在同化得到的LAI驱动下,BEPS模型模拟的毛竹林GPP、NEE和TER与实际观测值之间的R²分别为0.66、0.47和0.64,雷竹林分别为0.66、0.45和0.73,模拟结果均好于三次样条帽盖算法平滑LAI模拟得到的GPP、NEE和TER,其中,毛竹林、雷竹林NEE的模拟精度提高幅度最大,分别为11.2%和11.8%.     

亚洲半干旱区碳水通量时空格局及驱动因素

亚洲半干旱区生态系统敏感，环境问题突出，作为全球近30年来碳水通量变化最大的区域，明确其碳水通量的时空分布格局和驱动因素对区域资源管理与可持续发展、全球气候变化等领域具有重要意义。基于植被与土壤湿度的联合同化产品(LPJ-Vegetation and soil moisture Joint Assimilation, LPJ-VSJA),结合研究区植被及气象数据，分析了亚洲半干旱区2010—2018年碳水通量植被总初级生产力(GPP)、蒸散发(ET)和水分利用效率(WUE)的时空变化、年际变化贡献率以及驱动因素。结果表明：(1)2010—2018年亚洲半干旱区年均GPP、ET、WUE空间格局总体呈“双夹型”,中高纬度与低纬度地区的碳水通量值大于中纬度区域。(2)2010—2018年GPP、ET和WUE的年际变化总体都呈现增长趋势，但只有GPP呈现显著增长趋势(P<0.05),增速为7.82 g C m^-2 a^-1。(3)WUE的年际变化表现为总体先增加后减少，正值中农田对WUE年际变化贡献率最大(54.6%),森林生态系统在面积占比仅有...     

基于FORCCHN模型的中国典型森林生态系统碳通量模拟

森林生态系统是陆地碳循环的重要组成部分,其固碳能力显著高于其他陆地生态系统,研究森林生态系统碳通量是认识和理解全球变化对碳循环影响的关键。碳循环模型是研究森林生态系统碳通量有效工具。以长白山温带落叶阔叶林、千烟洲亚热带常绿针叶林、鼎湖山亚热带常绿阔叶林和西双版纳热带雨林等4种中国典型森林生态系统为研究对象,利用涡度相关2003-2012年观测数据,评估FORCCHN模型对生态系统呼吸（ER）,总初级生产力（GPP）,净生态系统生产力（NEP）的模型效果。结果表明：（1） FORCCHN模型能够较好的模拟中国4种典型森林生态系统不同时间尺度的碳通量。落叶阔叶林和常绿针叶林ER和GPP的逐日变化模拟效果较好（ER的相关系数分别为0.94和0.92,GPP的相关系数分别为0.86和0.74）;（2）4种森林生态系统碳通量季节动态模拟值和观测值显著相关（P<0.01）,ER、GPP、NEP的观测值和模拟值的R²分别为0.77-0.93、0.54-0.88和0.15-0.38;模型可以很好地模拟森林生态系统不同季节碳汇（NEP>0）,碳源（NEP<0）的变化规律;（3）4种森林生态系统碳通量模拟值与观测值的年际变化有很好的吻合度,但在数值大小上存在差异,模型高估了常绿阔叶林的ER和GPP,略微低估了其他3种森林生态系统ER和GPP。     

森林生态系统碳循环的基本概念和野外测定方法评述

全球气候变化与森林生态系统碳循环息息相关,定量评估森林碳收支是生态系统与全球变化研究的重要任务。30年来森林生态系统碳循环研究已经取得了长足的进展,但全球和区域森林碳收支仍然存在很大的不确定性。这一方面与森林生态系统本身的复杂性有关,另一方面也与具体研究方法有关。评述了森林生态系统碳循环的基本概念和主要野外测定方法,为我国森林生态系统碳循环研究提供可参考的方法论。从生态系统碳浓度、密度、通量、分配和周转5个方面回顾了碳循环相关概念,指出碳浓度和碳储量是对碳库的静态描述,而碳通量和碳周转是对碳库的动态描述。净初级生产力是测量最普遍的碳通量组分,但大多数情况下因忽略了一些细节而被系统低估。普遍使用的净生态系统生产力,由于没有包含非CO2形式的水文、气象和干扰过程产生的碳通量,通常情况下高于生态系统净碳累积速率。在详细介绍碳通量组分的基础上,改进了森林生态系统碳循环的概念模型。重点讨论了碳通量的3种地面实测方法:测树学方法、箱法和涡度协方差法,并指出了其注意事项和不确定性来源。针对当前碳循环研究的突出问题,建议从4个方面减小碳循环测定的不确定性:(1)恰当运用生物量方程估算乔木生物量;(2)尽可能全面测定生态系统碳组分;(3)给出碳通量估算值的不确定性;(4)多种途径交互验证。     

Biotic effects dominate the inter-annual variability in ecosystem carbon exchange in a Tibetan alpine meadow

青藏高寒草甸生态系统碳交换年际变异主要受生物效应影响 位于西藏的高寒草甸生态系统具有敏感脆弱的特点,在全球气候变化背景下,其碳汇功能的变化受到了广泛的关注。因此,本研究旨在明确高寒草甸碳通量的年际变异特征,并进一步量化各驱动因素对碳通量变异的贡献。本研究基于7年(2012–2018)的碳通量与气象因子和生物因子数据,采用一组查表法(look-up tables,LUTs)对高寒草甸碳通量的年际变异来源进行了拆分和量化,并进一步利用线性扰动分析法量化了各个关键因子对碳通量变异的贡献。2012–2018年,高寒草甸生态系统净生产力(net ecosystem productivity, NEP)、总初级生产力(gross primary productivity, GPP)和生态系统呼吸(ecosystem respiration, Re)多年平均值分别为3.31 ± 26.90、210.18 ± 48.35和206.88 ± 28.45 g C m⁻² y⁻¹,表现出了较大的年际变异。本研究通过区分和量化气象因子和生物因子对碳通量年际变异的贡献,发现了生物因子对年际变异的主控作用。此外,发现了气象因子和生物因子之间的负反馈作用。在气象因子中,只有土壤水分对年际变异的贡献相对较大,并在气象因子和生物因子的相互作用中发挥着调节作用。这些结果表明,在气候变化背景下,若要准确估算碳通量,需考虑生物因子的作用。     

人工高效经营雷竹林CO2通量估算及季节变化特征

利用涡度相关技术观测高效经营雷竹林生态系统的1a碳通量变化过程,初步计算分析了碳收支以及影响的环境因子.数据结果表明,雷竹林系统全年碳收支情况为碳汇,固碳能力小于毛竹林和杉木林,同时也小于水稻田和北方农田.全年净生态系统碳交换量(NEE)为-126.303Cg·m-2·a-1,生态系统呼吸(RE)为1108.845 Cg·m-2·a-1,生态系统总交换量(GEE)为-1235.15Cg·m-2·a-1.其中冬季(12月-2月)覆盖时为碳源,其余月份为碳汇.各月碳吸收量以11月最高,6月次之,呈双峰变化,碳排放量以1月为最高.计算全年平均固碳效率为11％,12-2月为负值,11月最高33％.生态系统呼吸呈单峰变化,以夏季最高,冬季覆盖提高地温后生态系统呼吸随之增加,全年RE受温度影响显著成指数关系.人工经营下温度是影响雷竹林CO2通量过程的主要因素,同时大量有机物覆盖增加了碳排放.     

2000—2015年中国东北森林生产力和碳素利用率的时空变异

中国东北森林生态系统是重要的碳汇功能区,也是对环境变化响应的敏感区,分析其植被生产力和碳素利用效率的变化特征及其对气候变化的响应对于区域碳收支的准确评估和预测具有重要意义.本研究利用MODIS的长期监测数据,结合植被类型分布数据,对中国东北森林生态系统2000—2015年生产力(净初级生产力NPP、总初级生产力GPP)和碳素利用率(NPP/GPP)时空变化特征进行分析.结果表明: 研究期间,东北森林生态系统平均NPP和GPP分别为346.4和773 g C·m^-2·a^-1,平均NPP/GPP为0.45.不同森林类型的NPP和GPP依次为针阔混交林>落叶阔叶林>针叶林,NPP/GPP在不同森林类型间无显著差异.NPP和GPP呈现出东南高、西北低的空间分布特点.2000—2015年间,东北森林生态系统NPP、GPP和NPP/GPP呈波动增加趋势,固碳能力逐步增强.NPP、GPP和NPP/GPP的变化趋势和变化速率表现出空间差异性,在大兴安岭南部地区显著增加,在大兴安岭北部地区显著下降,其余区域呈微弱增加趋势.与气候因子的相关性分析表明,年降水量的增加是驱动东北森林生态系统NPP、GPP和NPP/GPP波动增加的主要因素.     

季节性高温和干旱对亚热带毛竹林碳通量的影响

采用涡度相关技术对安吉亚热带毛竹林生态系统碳通量进行连续观测,选取2011和2013年月尺度净生态系统生产力（NEP）、生态系统呼吸（R_e）和总生态系统生产力（GEP）数据,探讨季节性高温、干旱对毛竹林生态系统碳通量的影响.结果表明： 安吉毛竹林年际间NEP有较大差异;2013年7和8月由于水热不同步而造成的高温干旱使其NEP明显下降,相比于2011年同期分别下降了59.9%和80.0%.对2011和2013年月尺度下NEP、R_e和GEP与环境因子进行相关分析发现,R_e和GEP与温度因子均呈显著相关（P<0.05）,但两者对空气和土壤水分的响应方式和程度有所不同,GEP相比于R_e更易受到土壤水分降低的影响,而饱和水汽压差的升高会在一定程度上促进R_e、同时抑制GEP,这是造成2013年7和8月安吉毛竹林NEP降低的根本原因.     

亚热带毛竹林生态系统能量通量及平衡分析

利用开路涡度相关系统和常规气象观测仪器,对亚热带(浙江省)毛竹林生态系统2011年的净辐射、显热通量、潜热通量、土壤热通量以及气温、地温、降雨量等气象要素进行了连续观测,定量分析了毛竹林生态系统能量通量的变化和各能量分量的分配特征,并计算了能量闭合度以及波文比。结果表明:毛竹林全年净辐射为2628.00 MJ/m2,显热通量为576.80 MJ/m2,潜热通量为1666.77 MJ/m2,土壤热通量为-7.52 MJ/m2,土壤为热源,各能量分量季节变化明显,日变化基本呈单峰型曲线变化。显热通量占净辐射的22.0%,潜热通量占63.4%,毛竹林生态系统潜热通量为能量散失的主要形式。波文比逐月变化规律不明显,波动较大,在0.07—1.77之间变化,能量平衡比率法得出毛竹林年能量闭合度为0.85,月平均闭合度为0.84,能量闭合度高于线性回归法计算结果,但仍有15%的能量不闭合。     

植被覆盖度和物候变化对典型黑沙蒿灌丛生态系统总初级生产力的影响

气候变化和人类活动是植被生产力年际尺度变化的重要驱动因素, 明晰二者对植被生产力的共同影响对于生态系统可持续管理至关重要。气候变化可能导致植被物候变化, 进而影响植被生产力。目前尚不清楚毛乌素沙地典型植被物候如何响应气候变化, 并因此影响生态系统总初级生产力(GPP)。此外, 植被恢复(覆盖度增加)和物候变化对GPP的共同影响有待明确。该研究选取典型黑沙蒿(Artemisia ordosica)灌丛生态系统, 结合MODIS遥感数据与涡度相关数据, 利用植被光合模型(VPM), 模拟并分析了2005-2018年间植被覆盖度和物候变化对GPP的影响。结果表明: (1) VPM模型能够较好地模拟涡度相关法观测的GPP动态(GPP_Flux), 而MODIS遥感产品(MOD17A2H)则显著低估GPP_Flux; (2)研究期内年均归一化差异植被指数(NDVI)、最大NDVI (NDVI_max)和年总GPP均显著增加, 表明植被恢复促进了植被生产力增加; (3)基于NDVI和GPP日序列估算的生长季开始日期显著提前(2.1 d·a^-1), 生长季结束日期显著推迟(1.5 d·a^-1), 二者共同促使生长季长度延长(3.6 d·a^-1); (4)物候期延长促进了GPP增加, 生长季长度每延长1天, 全年GPP显著增加6.44 g C·m^-2·a^-1; (5)植被覆盖度增加和生长季延长分别可以解释79%和57%的GPP增加; (6)尽管植被覆盖度和物候变化均促进GPP增加, 但前者是其增加的主要驱动因素。鉴于植被覆盖度增加和生长季延长也可能导致生态系统呼吸和蒸散发增加, 未来研究仍需探究生态系统碳汇能力、水分利用效率和水分承载力对气候变化和人类活动的响应。此外, 该研究主要探讨GPP在年际尺度的变化趋势及影响因素, 未来需要研究GPP的年际变异规律及驱动因素, 尤其是对降水年际变异和极端干旱事件的响应。     

Effects of seasonal and interannual variations in leaf photosynthesis and canopy leaf area index on gross primary production of a cool-temperate deciduous broadleaf forest in Takayama, Japan

Revealing the seasonal and interannual variations in forest canopy photosynthesis is a critical issue in understanding the ecological mechanisms underlying the dynamics of carbon dioxide exchange between the atmosphere and deciduous forests. This study examined the effects of temporal variations of canopy leaf area index (LAI) and leaf photosynthetic capacity [the maximum velocity of carboxylation (V _cmax)] on gross primary production (GPP) of a cool-temperate deciduous broadleaf forest for 5 years in Takayama AsiaFlux site, central Japan. We made two estimations to examine the effects of canopy properties on GPP; one is to incorporate the in situ observation of V _cmax and LAI throughout the growing season, and another considers seasonality of LAI but constantly high V _cmax. The simulations indicated that variation in V _cmax and LAI, especially in the leaf expansion period, had remarkable effects on GPP, and if V _cmax was assumed constant GPP will be overestimated by 15%. Monthly examination of air temperature, radiation, LAI and GPP suggested that spring temperature could affect canopy phenology, and also that GPP in summer was determined mainly by incoming radiation. However, the consequences among these factors responsible for interannual changes of GPP are not straightforward since leaf expansion and senescence patterns and summer meteorological conditions influence GPP independently. This simulation based on in situ ecophysiological research suggests the importance of intensive consideration and understanding of the phenology of leaf photosynthetic capacity and LAI to analyze and predict carbon fixation in forest ecosystems.     

植被年际变化对蒸散发影响的模拟研究

利用通用陆面模式(CLM3.0)及其植被动力学模式(DGVM)研究植被覆盖度(FC)和叶面积指数(LAI)的年际变化对全球蒸散发的影响。设计两套实验方案,其植被的FC和LAI的气候态相同,但一套实验中植被的FC和LAI有年际变化,而对照实验中则没有。结果表明:(1)在草、灌木、树占优势的地区植被FC年际变化依次减小;LAI年际变化较大的地区集中在草和灌木覆盖的地区,在落叶林地区,春秋两季植被LAI的年际变化也较大。(2)全球树占优势的大部分地区,植被的年际变化使得年平均蒸散发和地表蒸发增加、冠层蒸发和蒸腾减少;而在灌木和草覆盖区,变化则大致相反。(3)低纬度地区蒸散发季节循环变化比较明显,而北半球中纬度地区,蒸散发变化明显区随着纬度增加而在时间上向后推延。(4)FC和LAI年际变化较大时,蒸散发及地表蒸发降低,而蒸腾增加;这些差异随FC和LAI年际变化的增加而增加。单点分析进一步表明植被年际变化不仅改变蒸散发的多年平均值,同时改变其分量间的相对比例。     

2000—2019年中国南方竹林区水分利用效率时空特征及驱动机制

水分利用效率(Water Use Efficiency, WUE)是深入理解生态系统碳、水循环及两者耦合关系的重要指标，然而我国重要森林类型之一的竹林的WUE时空格局及其驱动机制研究不足。通过MODIS净初级生产力(NPP)和蒸散(ET)数据得到竹林区WUE,采用线性趋势法计算WUE年际变化率表征变化趋势，并应用地理加权回归(GWR)模型分析了WUE与气候和地形等10个驱动因子的关系，探究了中国南方竹林区近20年间(2000—2019)WUE驱动机制。结果表明：(1)2000—2019年中国南方竹林区WUE多年均值为0.89 gC m^-2 mm^-1,呈显著下降趋势，下降速率为0.0028 gC m^-2 mm^-1 a^-1,ET上升速度大于NPP上升速度是造成WUE下降的主要原因；WUE呈南高北低的空间分布格局，83.5%区域的WUE呈下降趋势。(2)基于GWR模型的WUE驱动力分析发现，WUE变化最强的驱动因子是CO₂浓度和年降水量，而海拔、坡度等地形因子的...     

Latitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables

Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO₂ based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from ∼29°N to ∼64°N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands.     

Joint structural and physiological control on the interannual variation in productivity in a temperate grassland: A data‐model comparison

Given the important contributions of semiarid region to global land carbon cycle, accurate modeling of the interannual variability (IAV) of terrestrial gross primary productivity (GPP) is important but remains challenging. By decomposing GPP into leaf area index (LAI) and photosynthesis per leaf area (i.e., GPP_leaf), we investigated the IAV of GPP and the mechanisms responsible in a temperate grassland of northwestern China. We further assessed six ecosystem models for their capabilities in reproducing the observed IAV of GPP in a temperate grassland from 2004 to 2011 in China. We observed that the responses to LAI and GPP_leaf to soil water significantly contributed to IAV of GPP at the grassland ecosystem. Two of six models with prescribed LAI simulated of the observed IAV of GPP quite well, but still underestimated the variance of GPP_leaf, therefore the variance of GPP. In comparison, simulated pattern by the other four models with prognostic LAI differed significantly from the observed IAV of GPP. Only some models with prognostic LAI can capture the observed sharp decline of GPP in drought years. Further analysis indicated that accurately representing the responses of GPP_leaf and leaf stomatal conductance to soil moisture are critical for the models to reproduce the observed IAV of GPP_leaf. Our framework also identified that the contributions of LAI and GPP_leaf to the observed IAV of GPP were relatively independent. We conclude that our framework of decomposing GPP into LAI and GPP_leaf has a significant potential for facilitating future model intercomparison, benchmarking and optimization should be adopted for future data‐model comparisons.     

Interannual variability of plant phenology in tussock tundra: modelling interactions of plant productivity, plant phenology, snowmelt and soil thaw

We present a linked model of plant productivity, plant phenology, snowmelt and soil thaw in order to estimate interannual variability of arctic plant phenology and its effects on plant productivity. The model is tested using 8 years of soil temperature data, and three years of bud break data of Betula nana. Because the factors that trigger the end of the growing season of arctic vegetation are less well known than those of the start of the growing season, three hypotheses were formulated and tested for their effects on productivity and its sensitivity to climate change; the hypothesised factors determining the end of the growing season were frost, photoperiod and periodic constraints. The performance of the soil thermal model was good; both the onset of soil thaw in spring and the initiation of freezing in autumn were predicted correctly in most cases. The phenology model predicted the bud break date of Betula nana closely for the three different years. The soil thaw model predicted similar growing season start dates under current climate as the models based on sum of temperatures, but it made significantly different predictions under climate change scenarios, probably because of the non‐linear interactions between snowmelt and soil thaw. The uncertainty about the driving factors for the end of the growing season, in turn, resulted in uncertainty in the interannual variability of the simulated annual gross primary productivity (GPP). The interannual variability ranged from ? 25 to + 26% of the mean annual GPP for the frost hypothesis, from ? 20 to + 20% for the photoperiod hypothesis and only from ? 7 to + 7% for the periodic hypothesis. The different hypotheses also resulted in different sensitivity to climate change, with the frost hypothesis resulting in 30% higher annual GPP values than the periodic hypothesis when air temperatures were increased by 3 °C.     

Heterogeneity of Soils and Vegetation in an Eastern Amazonian Rain Forest: Implications for Scaling Up Biomass and Production

Transferring fine-scale ecological knowledge into an understanding of earth system processes presents a considerable challenge to ecologists. Our objective here was to identify and quantify heterogeneity of, and relationships among, vegetation and soil properties in terra firme rain forest ecosystems in eastern Amazonia and assess implications for generating regional predictions of carbon (C) exchange. Some of these properties showed considerable variation among sites; soil textures varied from 11% to 92% clay. But we did not find any significant correlations between soil characteristics (percentage clay, nitrogen [N], C, organic matter) and vegetation characteristics (leaf area index [LAI], foliar N concentration, basal area, biomass, stem density). We found some evidence for increased drought stress on the sandier sites: There was a significant correlation between soil texture and wood δ¹³C (but not with foliar δ¹³C); volumetric soil moisture was lower at sandier sites; and some canopy foliage had large, negative dawn water potentials (ψ_ld), indicating limited water availability in the rooting zone. However, at every site at least one foliage sample indicated full or nearly full rehydration, suggesting significant interspecific variability in drought vulnerability. There were significant differences in foliar δ¹⁵N among sites, but not in foliar % N, suggesting differences in N cycling but not in plant access to N. We used an ecophysiological model to examine the sensitivity of gross primary production (GPP) to observed inter- and intrasite variation in key driving variables—LAI, foliar N, and ψ_ld. The greatest sensitivity was to foliar N; standard errors on foliar N data translated into uncertainty in GPP predictions up to ±10% on sunny days and ±5% on cloudy days. Local variability in LAI had a minor influence on uncertainty, especially on sunny days. The largest observed reductions in ψ_ld reduced GPP by 4%–6%. If uncertainty in foliar N estimates is propagated into the model, then GPP estimates are not significantly different among sites. Our results suggest that water restrictions in the sandier sites are not enough to reduce production significantly and that texture is not the key control on plant access to N. Received 28 June 2001; accepted 13 March 2002.     

散射辐射对中国东部典型人工林总初级生产力的影响

散射辐射是影响森林碳吸收的重要因子。然而, 有关生态系统总初级生产力(GPP)对散射辐射响应机理的理解仍有限。该研究利用中国东部6个人工林生态系统2019-2020年观测的碳通量数据和气象数据, 估算了散射辐射, 区分了直接辐射和散射辐射条件; 基于直角双曲线方程获取了不同辐射条件下生态系统光响应参数; 量化了GPP对散射辐射和直接辐射变化的响应; 采用偏相关方法分析了光照和环境因子对GPP日变化的贡献, 旨在探究生长季散射辐射对人工林生态系统GPP的影响机理。研究表明: 散射辐射增加可以有效促进冠层光合作用, 初始量子效率(α)和光合有效辐射(PAR)为1 000 μmol·m^-2·s^-1时的GPP (P₁₀₀₀)分别提高了47%-150%和2%-65%。与直接辐射条件相比, 散射辐射条件下的PAR每增加1 μmol·m^-2·s^-1, GPP增加0.86%-1.70%, 森林植被类型和站点物候变化会影响这一过程, 具有较低归一化植被指数(NDVI)的樟子松(Pinus sylvestris var. mongolica)和油松(Pinus tabuliformis)人工林GPP随单位PAR增加的变化量的增量(0.86%-1.00%)明显低于其他人工林站点的增量(1.04%-1.70%), 且植被NDVI与P₁₀₀₀存在显著正相关关系。在低光照时, PAR控制生态系统平均总初级生产力(GPP_a)的变化; 在中等至高光照时, 散射辐射比例(DF)是影响GPP_a的主要因子。在中等光照时, 散射辐射对应的光合作用接近于高光照时太阳辐射对应的光合作用, 且杉木(Cunninghamia lanceolata)、杨树(Populus spp.)、栓皮栎(Quercus variabilis)和华北落叶松(Larix gmelinii)在中高DF (≥0.5)时的GPP_a比低DF (<0.5)高出27%-50%, 油松和樟子松在中高DF时的GPP_a比低DF约高出2%。散射辐射条件下, 散射光合有效辐射(PAR_dif)解释了GPP变化的16%-45%, 气温(T_a)和饱和水汽压差(VPD)解释了杉木、栓皮栎和华北落叶松林GPP变化的10%-19%。在散射辐射条件下, 人工林在T_a为15-25 ℃和VPD为0-1 kPa时P₁₀₀₀最大。