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121.
Rodrigo Hakamada Carmeni Giunti Neto Cristiane CZ de Lemos Sérgio R Silva Marina SG Otto Kevin B Hall 《Southern Forests》2016,78(4):275-281
Leaf area index (LAI) is a key ecophysiological parameter in forest stands because it characterises the interface between atmospheric processes and plant physiology. Several indirect methods for estimating LAI have been developed. However, these methods have limitations that can affect the estimates. This study aimed to evaluate the accuracy and applicability of a visual method for estimating LAI in clonal Eucalyptus grandis × E. urophylla plantations and to compare it with hemispherical photography, ceptometer and LAI-2000® estimates. Destructive sampling for direct determination of the actual LAI was performed in 22 plots at two geographical locations in Brazil. Actual LAI values were then used to develop a field guide with photographic images representing an LAI range of 1.0–5.0 m2 m?2 (leaf area/ground area). The visual LAI estimation guide was evaluated with 17 observers in the field. The average difference between actual LAI and visual LAI estimation was 12% and the absolute difference between the two methods was less than or equal to 0.5 m2 m?2 in 77% of plots. Pearson’s correlation coefficients were high between actual LAI and hemispherical photographs (0.8), visual estimation (0.93) and LAI-2000® (0.99) and low for the ceptometer (0.18). However, absolute values differed among methods, with the average difference between the actual and estimated LAI of [12]% for visual estimation, 28% for the LAI-2000®, 37% for the ceptometer and ?43% for hemispherical photographs. The LAI-2000® and ceptometer overestimated LAI in all plots, whereas hemispherical photographs underestimated the values in all measurements, showing that these methods need calibration to be used. No differences were observed between actual LAI and visual estimates across stand ages of 2–8 years and LAI of 1.5–5.3 m2 m?2 (P > 0.05). The results show that visual estimation of LAI in Eucalyptus stands is a practical method that is unaffected by atmospheric characteristics and can be used on an operational scale. 相似文献
122.
枣棉间作条件下棉花密度对棉花光合特性及产量影响 总被引:3,自引:0,他引:3
在枣棉间作条件下,通过设置不同的棉花种植密度(13.5万、18.0万和22.5万株·hm-2),研究了密度对棉花光合作用及产量的影响。结果表明,间作棉花形态、荧光参数和光合特性受到枣树的显著不利影响,表现出明显的边行负效应。随着枣棉间距离的增加,不利影响减小,SPAD值、光系统II的实际光化学效率(ΦPSII)和净光合速率(Pn)显著增加;随着密度增加,间作棉花LAI和干物质质量显著增加。密度为18万株·hm-2的间作棉花的光系统II的实际光化学效率(ΦPSII)、净光合速率(Pn)、蒸腾速率(Tr)和产量显著高于13.5万株·hm-2和22.5万株·hm-2。在枣棉间作复合系统中,适当增加枣棉间距可以减轻枣树对棉花的不利影响,而较高的棉花密度也有利于棉花高产。 相似文献
123.
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125.
植被指数与作物叶面积指数的相关关系研究 总被引:1,自引:0,他引:1
作物长势参数是精细农业遥感监测的重要对象,叶面积指数(LAI)是作物长势最重要的参数之一,利用遥感手段快速获取作物的LAI具有重要的意义。为此,考虑到波段组合方式对LAI的反演效果的不可忽略性,采用4种不同的波段组合,结合PROSPECT和SAIL的模拟数据、地面实测数据和高光谱影像数据,从植被指数的饱和性和模型拟合精度两个角度对6个植被指数展开了评价。结果表明:TVI、MSAVI和MCARI23个植被指数在以上3个方面均表现较优,750~680 nm波段组合更加适合于LAI的反演。 相似文献
126.
为确定江苏地区水稻田块信息提取的适宜尺度,选取拔节期30m×30m空间分辨率HJ1A/CCD2影像和16m×16m空间分辨率GF1/WFV4近红外波段影像,采用高通滤波(HPF)算法构建4种空间尺度融合影像。利用定量指标评价和植被指数反演评价分析4种融合影像筛选适宜尺度,最后通过多类光谱指标构建决策树提取水稻面积与PROSAIL冠层光谱模型反演叶面积指数(LAI),验证融合影像适宜尺度相较原始影像尺度的优越性。结果表明:(1)综合定量指标评价和植被指数反演评价,20m×20m尺度和15m×15m尺度均可保证光谱继承性,反演水稻田块信息,而结合尺度优势,适宜尺度筛选为15m×15m;(2)与原始影像尺度相比,15m×15m尺度空间分辨率提高,同时水稻面积提取精度增大,面积精度93.33%,样方精度94.71%,标准误差0.25hm2,且能理想反演LAI,精度达94.69%,标准误差0.893。结论表明,研究区水稻田块信息反演的适宜尺度为15m×15m。 相似文献
127.
128.
密植对不同玉米品种产量性能的影响及其耐密性分析 总被引:48,自引:2,他引:46
提高种植密度是玉米高产的重要措施之一,并且群体密度对冠层光合特性与产量有重要影响,为阐明不同基因型玉米品种的耐密性,本研究以先玉335、郑单958、吉单209为供试品种,设置60 000株 hm-2、75 000株 hm-2、90 000株 hm-2、105 000株 hm-2 4种密度处理,测定并计算6个生育期的叶面积指数(LAI)、光合势(LAD)、净同化率(NAR)以及产量性能参数平均叶面积指数(MLAI)、平均净同化率(MNAR)、收获指数(HI)、单位面积穗数(EN)、单穗粒数(GN)、千粒重(GW),并结合产量性能参数的变化对各品种进行耐密性分析。结果表明,不同品种产量性能参数对密度胁迫的反应相同,MLAI、EN与密度呈显著正相关,MNAR、HI、GN、GW与密度呈显著负相关;各品种产量对密度的响应呈一元二次方程关系,并具有良好的相关性;在试验密度范围内,品种耐密性表现以先玉335最好、郑单958次之,吉单209较差,其中,先玉335的适宜密度范围为90 000~105 000株 hm-2,郑单958与吉单209的适宜密度范围为75 000~90 000株 hm-2。 相似文献
129.
Tanaka Kenzo Tomoaki Ichie Daisuke Hattori Joseph Jawa Kendawang Katsutoshi Sakurai Ikuo Ninomiya 《Forest Ecology and Management》2010
Uncertainties in the rate of biomass variation with forest ageing in tropical secondary forests, particularly in belowground components, limit the accuracy of carbon pool estimates in tropical regions. We monitored changes in above- and belowground biomass, leaf area index (LAI), and biomass allocation to the leaf component to determine the variation in carbon accumulation rate with forest age after shifting cultivation in Sarawak, Malaysia. Nine plots in a 4-year-old forest and fourteen plots in a 10-year-old forest were monitored for 5 and 7 years, respectively. Forest and plant part biomass were calculated from an allometric equation obtained from the same forest stands. Both above- and belowground biomass increased rapidly during the initial decade after abandonment. In contrast, a much slower rate of biomass accumulation was observed after the initial decade. LAI also increased by approximately double from the 4-year-old to 10-year-old forest, and then gently increased to the 17-year-old forest. We also found that allocation variation in leaf biomass and nitrogen was closely related to the rate of biomass accumulation as a forest aged. During the first decade after abandonment, a high biomass and nitrogen allocation to the leaf component may have allowed for a high rate of biomass accumulation. However, reduction in those allocations to leaf component after the initial decade may have helped to suppress the biomass accumulation rate in older secondary forests. Roots accounted for 14.0–16.1% of total biomass in the 4–17-year-old abandoned secondary forests. We also verified the model predicted values for belowground biomass by Cairns et al. (1997) and Mokany et al. (2006), although both models overestimated the values throughout our data sets by 45–50% in the 10-year-old forest. The low root:shoot ratio in the secondary forests may have caused this overestimation. Therefore, our results suggest that we should modify the models to estimate belowground biomass considering the low root:shoot ratio in tropical secondary forests. 相似文献
130.
Tomonori Kume Yuka Onozawa Hikaru Komatsu Kenji Tsuruta Yoshinori Shinohara Toshihiro Umebayashi Kyoichi Otsuki 《Forest Ecology and Management》2010
The applicability of sap flux (Fd) measurements to bamboo forests has not been studied. This study was undertaken to establish an optimal and effective design for stand-scale transpiration (E) estimates in a Moso bamboo forest. To this aim, we validated Fd measurements in Moso bamboos in a cut bamboo experiment. In addition, we analyzed how sample sizes affect the reliability of E estimates calculated from Fd and conducting culm area (AS_b). In the cut bamboo experiments, we found that Fd measurement using a 10 mm probe was a valid means of determining the water-use behavior of a Moso bamboo, although a specific correction was needed. Furthermore, we calculated E from stand AS_b (AS_stand) and mean stand Fd (JS). Employing Monte Carlo analysis, we examined potential errors associated with sample size in E, AS_stand, and JS using an original dataset with AS_b and Fd measured for 40 and 16 individuals, respectively. Consequently, we determined the optimal sample size for both AS_stand and JS estimates as 11. The optimal sample sizes for JS were almost the same under different vapor pressure deficit and soil moisture conditions. The optimal sample size for JS at the study site was less than that of a coniferous plantation in the same region probably owing to small individual-to-individual variations in sap flux in the Moso bamboo forest. Our study concludes that sap flux measurements are an applicable technique for assessing water use in Moso bamboo forests. 相似文献