遥感分析中亚地区生态系统水分利用效率对干旱的响应

生态系统水分利用效率(water use efficiency,WUE)是碳水循环中的重要参数。全球干旱在未来几十年将会持续增加,干旱对生态系统WUE的影响研究成为了区域及全球尺度上的研究热点与难点。该文研究中亚地区生态系统WUE对干旱的响应。以中亚5国及中国新疆为研究区,利用基于中分辨率成像光谱仪的总初级生产力产品和蒸散产品计算2000—2014年生态系统尺度上的WUE,使用归一化植被指数和陆地表面温度计算温度植被干旱指数分析干旱区生态系统WUE与干旱的关系。结果表明,WUE对干旱的响应在不同地区和植被类型中表现出一定的差异;当干旱发生时,干旱区生态系统WUE对干旱通常表现出负面响应,同时干旱对生态系统WUE有滞后影响;干旱事件结束后,生态系统WUE与干旱指数呈现正相关关系;另外,干旱区生态系统WUE对干湿环境突变敏感,当环境从干旱转向湿润,郁闭灌木林,农田,森林,草地,稀疏灌木林WUE分别增加了30.03%,49.57%,18.39%,54.71%,49.28%,WUE的快速增长表明了干旱区生态系统有较强的恢复力稳定性。     

北京松山林下典型灌木绣线菊光、水利用效率的季节动态及其对环境因子的响应

[目的]植物资源利用效率是反映植物对环境条件适应性的重要指示指标,是气候变化生态学领域的研究热点,因此对林下灌木物种光能利用效率(LUE)和水分利用效率(WUE)的环境调控机理需进一步明晰。[方法]以北京松山天然阔叶林下典型灌木绣线菊(Spiraea salicifolia)为研究对象,于2019年6月至9月完全展叶期开展原位叶片光合测定和同步环境因子的连续观测,分析了绣线菊LUE和WUE的变化特征及其对环境因子的响应。[结果]LUE和WUE具有较为明显的季节变化特征,其中LUE随着光合有效辐射(PAR)和空气温度(T_a)的变化呈现逐渐增大的趋势,季节平均为0.03 mol/mol; WUE随PAR和空气饱和水汽压差(VPD)的变化呈现先增大后减小的趋势,季节平均为8.32 μmol/mmol。PAR和T_a是影响LUE变化的主要因子,分别为指数和线性负相关; PAR和VPD是影响WUE变化的主要因子,均与WUE呈线性负相关,其中VPD通过影响气孔导度(g_s)限制叶片蒸腾,从而影响WUE; LUE、WUE的季节变化和土壤含水量(SWC)均无显著相关性。LUE与WUE对环境因子存在趋同响应关系。[结论]研究初步确定光合有效辐射、空气温度和空气饱和水汽压差是研究区林下灌木绣线菊资源利用效率的主要限制因子,而非土壤水分; 林下灌木绣线菊在有限资源条件下呈现资源保守策略,具体表现为在光能受限的条件下能够最大限度地使用光能进行光合作用,从而具备较高的光能利用效率。     

植物冠层分析仪测定荆条孤立冠层叶面积指数和透光率的分析

利用LAI-2200植物冠层分析仪(PCA)无损测定分析8株荆条(Vitex negundo L.)冠层叶面积指数LAIPCA(3.5~6.5)和天空开度(DIFN),通过LI-200SA传感器同步测定相应的光强透射率τ;同时利用收获法实测荆条冠层叶面积指数LAI收获法,对比分析LAIPCA与LAI收获法、DIFN与τ的相关性和偏差。结果表明:(1)两种方法所测叶面积指数相关极显著(P0.01);LAIPCA比LAI收获法平均偏高2.57%,表明LAI-2200用于荆条灌丛冠层叶面积指数LAI的测定结果偏差较小。(2)LAI-2200PCA测定DIFN与辐射传感器测定冠层透光率τ相关极显著(P0.01),说明LAI-2200 PCA可以替代收获法无损测定荆条孤立灌丛冠层叶面积指数和透光率。本文实现了用冠层分析仪对植物孤立冠层的分析,为林业生产和研究中较为普遍存在的孤立植物冠层下光照分析和叶面积指数测定提供了简便方法。     

亚热带红壤丘陵区季节性干旱成因及其发生规律研究

结合多年气象资料系统研究亚热带红壤丘陵区季节性干旱成因与发生规律结果表明 ,该区季节性干旱严重 ,“土壤 作物”干旱年发生概率为 85 .7% ,其中≥中等干旱年发生概率为 5 0 .0 % ,7～ 8月份和 11～ 12月份为年内高发期 ,以夏秋干旱危害最大 ;气候性干旱 (Z值法 )年发生概率为 5 9.5 % ,其中≥中等干旱年发生概率为31.0 %。“土壤 作物”干旱明显大于气候性干旱 ,且二者发生概率和危害程度均为 2 0世纪 90年代 >80年代 >70年代 >6 0年代 ,表明红壤丘陵区抵御季节性干旱的能力呈下降趋势 ,农业生态系统抗逆性能仍在不断退化。     

中国典型陆地生态系统水分利用效率及其对气候的响应

水分利用效率(Water Use Efficiency,WUE)是陆地生态系统碳-水耦合的重要指标之一,也是研究陆地生态系统响应全球变化的重要参数。深入了解生态系统WUE的长时序变化特征及其影响因素,对生态系统碳水循环研究以及水资源合理开发具有重要意义。该研究基于2003—2010年中国8个碳通量观测站的通量数据、气象数据分析WUE的年内、年际变化特征及其与关键气候因子之间的响应关系。研究表明:1)处于热带季风气候区的千烟洲、西双版纳、鼎湖山3个站点的WUE全年波动较大,无明显规律,其余5个站点的WUE则表现出明显的季节变化特征,均表现为在4—7月份之间,呈现显著增加的特征,在7—8月份达到最高值,8—10月份,WUE逐渐下降,在11月至次年2月份,植被WUE接近于0;2)2003—2010年间,高寒草甸(当雄)年均WUE值最低(0.18 g/kg),热带雨林(西双版纳)最高(4.20 g/kg)。人工针叶林(千烟洲)、热带雨林(西双版纳)、落叶阔叶林和针叶混合林(长白山)植被WUE呈下降趋势,其余5个生态系统年均WUE呈增加趋势;3)8 d时间尺度上,高寒草甸、农田、草原生态系统WUE分别与气温呈正相关;森林生态系统WUE与气温呈负相关,其中人工针叶林生态系统WUE与气温的负相关系数(r=-0.607,P0.01)明显高于常绿阔叶林和针阔混交林;相比森林和农田生态系统,高寒草甸、草原生态系统WUE与相对湿度和降水具有较高的相关性;4)森林生态系统可通过土壤管理调控、冠层修剪等方式提高水分利用效率;农田生态系统需从灌溉方式、作物育种方面提高水分利用效率;高寒草甸及草原生态系统需采取人工种草、休牧以及划区轮牧等方式增强草原碳汇,从而提高水分利用效率。     

典型年份渭河流域蓝水绿水时空差异分析

以西北地区湿润/干旱过渡地带的渭河流域为例,采用降水距平百分率和标准化降水指数识别湿润年、正常年和干旱年,同时结合SWAT（Soil and Water Assessment Tool）模型的输出结果分析各典型年该流域蓝水绿水的时空分布差异。结果表明：（1）采用降水距平百分率和标准化降水指数两种方法确定1983、1997和2007年分别为湿润年、干旱年和正常年;（2）模型评价的结果表明,SWAT模型的月径流模拟的精度较高,可以准确描述渭河流域的径流变化过程;（3）在流域尺度上,绿水流的变化在湿润年、干旱年和正常年的变化相对稳定,绿水系数在湿润年、干旱年和正常年分别为82.06%、93.47%和87.72%;（4）从空间分布来看,蓝水绿水资源在渭河流域的分布呈现自东南向西北减少的趋势,绿水系数的空间分布表明在湿润年份（1983）或地区（东南部）绿水比重明显低于干旱年份（1997）或地区（北部）。     

播期和播量对冬小麦冠层光合有效辐射和产量的影响

小麦适期播种不仅是达到全苗壮苗的关键, 还有利于小麦健壮生长发育, 是提高小麦单产的重要措施.本试验研究了不同播期和播量条件下小麦冠层底部光合有效辐射(TPAR)、叶面积指数(LAI)、冠层截获的光合有效辐射(IPAR)等的变化及播期对冬小麦产量的影响.结果表明, 叶面积指数和冠层截获的光合有效辐射随小麦播种时间的推迟而降低, 小麦冠层底部的光合有效辐射随小麦播种时间的推迟而增大.小麦冠层截获的光合有效辐射与叶面积指数呈显著正相关, 相关系数为0.756; 冠层底部的光合有效辐射与叶面积呈显著负相关, 相关系数为-0.872.小麦产量虽然随播期的推迟呈递减趋势, 但10月20日之前播种的小麦产量间无显著差异.因此, 在冬小麦和夏玉米一年两熟区, 可相应推迟小麦的播种时间, 尽量延长上茬玉米的生长期, 以实现两茬作物的均衡增产.     

2001—2020年黄河流域水分利用效率时空变化及其对环境因素的响应

[目的] 分析黄河流域生态系统水分利用效率(water utilization efficiency,WUE)的变化情况及其对不同环境因子的敏感度,为认识植被恢复、干旱及气候条和水资源之间的关系,预测未来陆地表面—大气相互作用和陆地生态系统的动态变化提供理论依据。[方法] 基于MODIS GPP和ET数据计算了黄河流域2001—2020年WUE,并结合Theil-Sen趋势法+Mann-Kendall检验法、Hurst指数法、偏相关分析法、结构方程模型和线性回归残差分析法探究了不同土地利用覆盖区域WUE时空动态、未来可能的持续状态以及其对温度植被干旱指数(TVDI)、太阳辐射(RS)和风速(WIN)的响应情况。[结果] ①黄河流域WUE空间分布上呈现出从上游—中游—下游逐渐增加。时间变化上总体以下降趋势为主,且未来一段时期内WUE仍以减弱趋势为主。②上游WUE与WIN,TVDI和RS为正相关性,RS主要通过影响TVDI和WIN来影响WUE;中游TVDI,WIN对WUE负影响较大,RS对WUE的影响不显著;下游WUE主要受到WIN的负影响和RS的正影响,TVDI对WUE的影响不显著。③草地和未利用地区域的WUE与RS呈正相关性,与TVDI和WIN呈负相关性。其他区域WUE与RS,TVDI为正相关性。④黄河流域上游WUE变化主要受到TVDI和WIN的负贡献;中游主要受到RS,TVDI和WIN的正贡献;下游主受到TVDI的正贡献和RS和WIN的负贡献。[结论] 黄河流域WUE未来易受到干旱和气候因素影响,后期研究应在气候因子研究基础上进一步分析月尺度干旱、极端气候等对不同土地利用区WUE的影响。     

基于夏玉米冠层内辐射分布的不同层叶面积指数模拟

为了模拟夏玉米冠层内各层叶面积指数垂直分布,光合有效辐射（photosynthetically active radiation, PAR）是研究作物群体光合作用和长势的重要特征参数,阐明冠层内PAR的垂直分布规律与冠层结构等参数之间的相关关系,可为遥感定量反演冠层结构参数提供模型基础。该文基于PAR在冠层内的辐射传输规律结合冠层结构模拟不同太阳高度角的PAR透过率垂直分布模型,并用地面冠层分析仪测量值进行验证,结果表明模型对封垄前玉米抽雄期冠层内PAR透过率垂直分布模拟精度较高。通过不同太阳高度角PAR透过率的垂直分布模型结合消光系数运用不同算法分别反演层叶面积指数（leaf area index, LAI）,并与不同高度层LAI实测值进行比较。结果显示：Bonhomme& Chartier算法反演不同高度层LAI精度较高,上层均方根误差（root mean square error,RMSE）为0.18,中层RMSE为0.55,下层RMSE为0.09。不同太阳高度角反演结果存在差异,30°和45°高度角均能较好地反演下层LAI,RMSE分别为0.11与0.09;30°高度角反演中层LAI精度较高,RMSE为0.30;45°高度角反演上层LAI精度较高,RMSE为0.18。结果表明基于不同太阳高度角构建的层LAI反演模型更适于实现夏玉米不同高度层LAI的遥感估算。该研究可为模拟垄行结构冠层内LAI垂直分布提供参考。     

基于土壤前期含水量-降雨耦合关系的陕北黄土坡面产流临界降雨值

土壤前期含水量与降雨是坡面产流的主要影响因素。该研究基于超渗产流基本原理,通过引入土壤前期含水量与降雨2个指标,最终推导出基于土壤前期含水量-降雨耦合关系的坡面产流所需临界值公式。通过该公式结合土壤水分实测值对陕北黄土区吴起县典型植被群落干旱年、正常年和湿润年的产流临界降雨值进行模拟计算与分析。结果表明:1)陕北黄土坡面湿润年产流所需临界降雨量与干旱年和正常年存在显著差异,湿润年产流所需降雨量较少且油松湿润年理论产流值最低,仅需5. 60 mm;干旱年与正常年产流所需临界降雨量则不存在显著差异,但干旱年产流所需降雨量较大。2)不同植被类型产流所需最低降雨量不同,其中油松林地产流所需临界降雨量最小,即油松林地较易产流,沙棘纯林产流所需降雨量最大,即沙棘林地较难产流;且2种林地产流所需降雨量存在显著差异。土壤前期含水量与降雨二者耦合关系及其与坡面产流临界阈值的研究,对该区域预防土壤侵蚀带来的危害和水土资源高效利用具有重要意义。     

Responses of net ecosystem CO2 exchange to nitrogen fertilization in experimentally manipulated grassland ecosystems

Nitrogen (N) addition enhances primary productivity of terrestrial ecosystems. However, the effects of N fertilization and/or deposition on net ecosystem CO₂ exchange (NEE) are not fully understood. The effects of N on NEE were investigated in two experimental cheatgrass ecosystems in Ecologically Controlled Enclosed Lysimeter Laboratories (EcoCELLs), Reno, Nevada. In this experiment, no N fertilization was added to the two EcoCELLs in the first year and two different N fertilization regimes were applied in the second year. N fertilizer was applied once to one EcoCELL (pulse fertilization, PF), and the same total amount of N in biweekly increments to the other EcoCell (gradual fertilization, GF). NEE, photosynthetically active radiation (PAR) and canopy green leaf area index (LAI) were continuously measured in the two EcoCELLs during the pretreatment and N-fertilized years. Plant N content and biomass were measured at the end of the growing season in each year. Radiation-use efficiency (RUE_CO2) was calculated as the ratio of gross ecosystem photosynthesis (GEP) to the intercepted photosynthetically active radiation (IPAR). The responses of NEE to IPAR were used to estimate the maximum ecosystem photosynthetic capacity (F_max). N fertilization stimulated canopy LAI, plant N content, F_max, RUE_CO2, NEE and biomass in both methods of N supply applications. PF led to higher LAI, F_max and NEE than GF, but both had a similar RUE_CO2 during the early growing season. GF maintained higher LAI, F_max, RUE_CO2 and NEE than PF during the late growing season. At the ecosystem level, N fertilization stimulated daily NEE directly by increasing canopy LAI, plant N content, shoot/root ratio and the maximum ecosystem photosynthetic capacity, and increased the seasonally accumulated NEE indirectly by extending the growing season. PF differed significantly from GF in its effects on NEE and RUE_CO2, possibly due to differential rates and timing of N availability. Our study suggested that these changes in the canopy RUE_CO2 and growing season under N fertilization or N deposition regimes should be considered in modeling studies of ecosystem C sequestration.     

Measurement variability in soybean water status and soil‐nutrient extraction in a row spacing study in the U.S. southeastern coastal plain

Abstract

Full‐season determinate soybean [Glycine max (L.) Merrill] was grown in the field in a humid climate for three seasons (1979–81). The objective was to examine variability in several methods of determining basic relationships between soil and plant water status in a range of canopy configurations and to examine treatment effects on soil‐nutrient extraction. In each year, two cultivars, “Davis” (group VI) and “Coker 338” (group VIII) were planted in four row spacings. In 1980 and 1981 the experiment was expanded and split for irrigation and row orientation (N—S or E‐W). Post‐harvest soil samples were collected and analyzed to determine if irrigation, row spacing, or cultivar influenced K, Ca, and Mg extraction patterns.

During the growing seasons, parallel leaf diffusive resistance (R_s) was poorly correlated with xylem pressure potential (ψ_x), canopy s x temperature (T_c), canopy minus air temperature (?T), leaf vapor pressure deficit (LVPD), and atmospheric vapor pressure deficit (VPD) in single factor correlations. Xylem pressure potential was highly correlated with T_c , ?T, VPD, and LVPD, but was poorly correlated with soil water potential. Both ψ_x and T_c were significantly affected by the imposition of shade from a 60% shading cloth within as little as 1 minute of shade imposition. The impact of cultivar on seasonal ψ_x was significant and was nearly half the magnitude of the observed difference caused by irrigation. Irrigation raised ψ_x by only 2.2 bars over the two—year observation period, in spite of large differences in soil water potential when irrigation was imposed. The impact of canopy configuration was not measureable in any water relations parameter except infrared‐determined T_c. Correlation of T and ψ_x was significantly more reliable when limited to a single variety, row spacing, and row orientation. Aspect of infrared temperature measurement also significantly affected observed T_c.

Analysis of post‐harvest soil samples indicated that narrow (50 cm) row spacing in 1980 and irrigation in 1981 significantly decreased post—harvest Mehlich No. I extractable K, but none of the cultural practices influenced extractable Ca or Mg at P(0.05). In 1980, ex‐tractable K within soybean rows was significantly greater than between rows. Similar trends were observed for Ca and Mg in 1980 and for all 3 nutrients in 1981, but those differences were not significant at P(0.05). Overall, these measurements quantify the difficulty in relating soil and plant water status and identifying nutrient extraction patterns in sandy soils within the humid U.S. Southeastern Coastal Plain.     

蒸渗仪测定滴灌枣树不同时间尺度下腾发强度特征

为精确测定、准确模拟阿克苏地区滴灌枣树腾发过程,基于大型称重式蒸渗仪测定枣树全生育期逐时及逐日腾发强度（ET）,利用水量平衡方程、PM公式及经典统计原理,分析不同时间尺度下叶面积指数（LAI）、气象因素[温度（I）、风速（V）、净辐射（R_n）]、表层土壤含水率（W）与枣树腾发强度的相关关系并建立预测模型。结果表明：枣树日内腾发强度呈单峰型变化趋势,夜间变化幅度较小且腾发贡献率低。枣树全生育期逐日腾发强度变化呈先增大后减小的趋势,花期的腾发强度最大,为4.42 mm·d^-1;全生育期腾发总量为640.83 mm,其中花期和果实生长发育期耗水量占比较大,分别为38.61%和32.72%。在小时和日时间尺度上,影响腾发强度的主要因素不完全相同,且影响程度有所差异。综合考虑各影响因素,以萌芽期、花期、果实发育期为基础,分别建立以小时、日尺度下估算腾发强度的经验模型ET₁（h）=0.153+0.004T+0.012V+0.176R_n+0.002W+0.067LAI、ET₂（d）=-3.325+0.081T+0.163R_n+0.069W+2.089LAI,拟合度R²均在0.7以上,以果实发育期与成熟期数据对模型进行检验,纳什效率系数分别达0.63、0.80。经偏相关检验,冠层净辐射（R_n）对两种尺度的腾发强度均影响最显著,因此以枣树全生育期数据量为基础,仅建立冠层净辐射（R_n）与腾发强度的回归模型ET₁（h）=-0.063 3R_n²+0.361 2R_n—0.003 7、ET₂（d）=-0.018 3R_n²+0.684 7R_n–1.642 1,R²分别为0.704 7与0.743 6,可满足缺少数据支撑情况下的腾发过程估算。这些模型明确了阿克苏地区滴灌枣树腾发机制及影响程度,可为水分管理精准化提供计算基础。     

重庆缙云山毛竹林次降雨再分配特征及穿透雨的空间异质性

为分析毛竹林的林冠降雨再分配规律及其穿透雨的空间分布特征和影响因素,在重庆缙云山自然保护区内选择的30m×30m毛竹林标准地内,随机布置72个穿透雨监测点,并选取6株标准木观测干流,于2017年5-8月监测毛竹林水文特征。结果表明:18场典型降雨的合计林冠截留量、穿透雨量和树干茎流量分别为32.74,208.09,10.97mm,分别占总降雨量的13.00%,82.64%,4.36%;次穿透雨率随次降雨量增加呈对数函数增长;穿透雨的空间变异系数(CVS)随次降雨量和降雨强度增加呈幂函数递减;当次降雨量小于10mm时,叶面积指数(LAI)与穿透雨率呈显著负相关(p0.05);各监测点不同降雨场次中穿透雨率变异系数(CV_T)为19.2%~47.7%,其空间分布格局与毛竹密度的空间分布较为一致,而与观监测点上方的LAI无显著相关;穿透雨量较大的监测点趋向于分布在毛竹冠区边缘。     

自然条件下半干旱雨养春小麦生育后期旗叶光合的气孔和非气孔限制

为探究半干旱地区雨养春小麦旗叶的光合作用限制因素、不同生育期差异及其适应策略,分析了大田条件下春小麦旗叶在抽穗期和灌浆期光合生理特征的动态变化规律,探讨了自然条件下光合作用的气孔与非气孔限制特征。结果表明:净光合速率日变化趋势在抽穗期和灌浆期分别为单峰型和双峰型,峰值相当,为18.5μmol(CO2)·m-2·s-1左右。气孔导度具有与净光合作用几乎相似的日变化规律,胞间CO2浓度大致为上午下降、下午回升。胞间CO2浓度变化除受光合作用消耗和气孔限制共同作用外,下午时段叶肉导度增大,也影响胞间CO2浓度变化。在抽穗期和灌浆期,春小麦旗叶光合作用速率与气孔导度相关性十分显著,相关系数分别达0.916(P=0.000)和0.945(P=0.000)。并且2个生育期均出现明显的光合气孔限制,抽穗期达0.64,灌浆期为0.53。其中,抽穗期气孔导度对饱和水汽压差响应十分敏感,下午出现较为明显的气孔限制;灌浆期中午出现较为明显的光合"午休"现象,其主要原因是半干旱区较大饱和水汽压差和强烈辐射致使气孔关闭,气孔限制达到极大值,并且非气孔限制因素也较为突出。抽穗期至灌浆期,由于气孔对饱和水汽压差敏感性的下降以及"午休"策略,光合气孔限制逐渐减小,是春小麦在半干旱地区维持较高光合速率和保证产量的重要自适应机制。     

Evaluation of wheat and maize evapotranspiration determination by direct use of the Penman–Monteith equation in a semi-arid region

The Penman–Monteith (PM) equation was introduced as one of the most reliable equations to determine crop ET_c, without using crop coefficient or ET_o values. In this study, the PM equation was evaluated using lysimeters in a semi-arid region for wheat and maize. Different equations for aerodynamic resistance (r _a) and canopy resistance (r _c) were tested in the PM equation and they were ranked using statistical analysis. It was shown that the combined method of r _a and r _c in FAO-56 does not lead to a good prediction of ET_c for wheat and maize in comparison with the lysimeter-measured data. The results indicated that a modified equation for r _c was the most accurate method for both wheat and maize. Using this equation, the suggested model of FAO-56 and another investigation for r _a led to the best results for wheat and maize, respectively. Furthermore, it was shown that the previously modified equation for r _c was newly modified as a function of vapor pressure deficit (VPD) and the results were as accurate as before. Therefore, an equation as a function of VPD can be used when solar radiation (R _n) is not available easily.     

Relationship between wheat yield and foliage temperature: theory and its application to infrared measurements

A theoretical basis is presented for the relationship between crop yield and one time-of-day measurements of the foliage-ambient temperature differential (T_f — T_a). The theory was used to analyse two contrasting relationships between wheat yield and T_f — T_a. The relationships resulted from a range of irrigation treatments and two times of sowing imposed on 26 plots. This caused yields to vary from 8.3 to 1.7 t ha^?1 when the crop was sown in June and from 5.5 to 2.2 t ha^?1 when sown in August. To explain these variations T_f — T_a and associated micrometeorological data were collected around solar noon during the period from jointing to maturity. From these data transpiration and the associated aerodynamic and canopy stomatal resistances to water vapour transport were predicted. The associated canopy conductances for diffusion of CO₂ were derived and used to predict the corresponding CO₂ assimilation rates.The predicted transpiration and CO₂ assimilation rates were closely related to yield within each year but not between years. However if the rates were normalised for the shorter growing season of the late sown crop the yields from the 26 plots formed a common relationship. The transpiration vs. yield relationship was further improved by normalising for differences in foliage vapour pressure deficit. The good agreement between field data and theory was probably due to the dominating effect of stomatal control on both T_f — T_a and CO₂ assimilation rate. If CO₂ assimilation rate is strongly influenced by factors other than soil water stress then the theory may not hold and a different relationship may exist. It was concluded that infrared thermometry is a useful technique for studying yield variations in agronomic experiments where these variations are due to stomatal control.     

Satellite-based estimation of evapotranspiration of an old-growth temperate mixed forest

Evapotranspiration (ET) is a key flux in the water cycle and has strong seasonal dynamics for forest ecosystems. Recently eddy flux covariance measurements are continuously taken at a temperate mixed forest in Northeastern China since 2002. In an effort to better understanding the factors that control the seasonal dynamics of ET, here we (1) calculate ecosystem-level water use efficiency (WUE) from observed water and CO₂ flux data, and (2) relate the resultant WUE with satellite-derived vegetation indices, and (3) develop and evaluate a simple model that uses satellite images and climate data as input data to predict ET on the coupling of photosynthesis and transpiration processes. Ground WUE estimates obtained from eddy covariance tower were correlated with moderate resolution imaging spectroradiometer (MODIS) vegetation indexes (VIs) and ground micrometeorological data over 3 years (2003–2005). The enhanced vegetation index (EVI) was more closely correlated (r = 0.82) with WUE than the normalized difference vegetation index (NDVI; r = 0.64). Air temperature (T_A) measured over the canopy was the meteorological variable that was most closely correlated with WUE (r = 0.74) over years. For the significant correlation between EVI and T_A (r = 0.82, P < 0.05), EVI was selected as the single variable to predict WUE to simplify calculation. We calculated ET by ET = GPP/WUE, gross primary production (GPP) was predicted by vegetation photosynthesis model (VPM) that uses satellite images and meteorological variables. At a temporal resolution of 8 days, the annual curves showed good correspondence between measured and predicted values of WUE and ET in terms of phase and magnitude for each year. Seasonally integrated predicted ET was +4% (in 2003), +2% (in 2004), +0.4% (in 2005) higher than observed values.     

留茬高度对小叶锦鸡儿光合生理和生长特征的影响

[目的] 研究不同留茬高度小叶锦鸡儿生长和光合生理的变化规律,揭示不同留茬高度下小叶锦鸡儿生长和光合能力的强弱,探索其平茬时的最适留茬高度,为寻求合理抚育管理措施、指导小叶锦鸡儿生产实践提供理论依据。[方法] 选择2003年人工种植小叶锦鸡儿为研究材料,设置未平茬（CK）、留茬高度5 cm （T₁）,10 cm （T₂）,15 cm （T₃）,20 cm （T₄）,25 cm （T₅）共6个处理于2018年秋季进行平茬,分别测定次年生长季小叶锦鸡儿生长和光合生理指标。[结果] 平茬能显著提高小叶锦鸡儿株高、冠幅、新稍长的增长;不同留茬高度处理净增长量均不同,留茬高度15 cm处理株高、冠幅长和宽度、新稍长净增长量值最高,分别较未平茬处理增加了203.44%,278.10%,292.59%,385.43%;留茬高度5,10和20 cm处理的净增长量次之,留茬高度25 cm的值最低,较未平茬处理分别增加了25.15%,26.38%,25.93%,88.48%;一定留茬高度平茬能显著提高小叶锦鸡儿净光合速率（P_n）、蒸腾速率（T_r）和水分利用效率（WUE）;不同处理小叶锦鸡儿日变化均有不同程度的光合、蒸腾“午休”现象;留茬高度15 cm处理叶片P_n,T_r,WUE日均值均最高,分别比未平茬处理增加了2.52,0.37和1.52倍;留茬高度5,10和20 cm处理次之,留茬高度25 cm处理值最低,其P_n和WUE值分别比未平茬处理增加了0.45和0.32倍,而T_r值比未平茬处理降低了0.02倍。[结论] 平茬后次年生长季内,留茬高度15 cm的平茬小叶锦鸡儿具有较强的生长补偿和光合能力,留茬5,10和20 cm植株的生长补偿和光合能力次之,留茬25 cm植株的生长补偿和光合能力最弱。     

POTASSIUM SULFATE IMPROVES WATER DEFICIT TOLERANCE IN MELON PLANTS GROWN UNDER GLASSHOUSE CONDITIONS

Interactive effects of water stress and potassium (K) on some physiological attributes and nutritional status of melon (Cucumis melo L. cv. ‘Tempo F1’) plants were assessed in a pot experiment. Treatments used were: (1) control or well-watered (WW) + K1, (2) WW + K2, (3) WW + K3, (4) water stress (WS) + K1, (5) WS + K2, and (6) WS + K3. Water stress (WS) was imposed by maintaining the moisture level equivalent to 50% pot capacity, whereas well-watered (WW) pots (control) were maintained at full pot capacity (100% PC). Hoagland's nutrient solution was modified to supply K as potassium sulfate (K₂SO₄) at 6, 9, and 12 mM for K1, K2, and K3 treatments, respectively. Water stress reduced fruit yield, total dry matter, chlorophyll content and relative water content (RWC), but increased proline accumulation in the melon plants. However, additional supply of K as 3 or 6 mM significantly enhanced all the earlier mentioned physiological parameters, but the values were still not the same as the levels of the control treatment. Water stress also reduced leaf calcium (Ca) and K of the melon plants, but additional supply of K to the root zone increased the levels of both nutrients much higher than those at the control (C) treatment. Our study revealed that additional supply of K improved water stress tolerance in melon plants by enhancing chlorophyll, relative water content and concentrations of some essential nutrients in leaves.