基于地面观测光谱数据的冬小麦冠层叶片氮含量反演模型

冬小麦冠层叶片氮含量是反映其产量与品质的重要指标,构建高普适性、高精准性冬小麦冠层叶片氮含量高光谱反演模型对提高其监测效率具有重要意义。以不同地点、品种、年份、施氮水平、生育期的大田试验数据为基础,基于两波段光谱植被指数NDRE和550 nm光谱反射率组合构建一个三波段植被指数NEW-NDRE,并与11个传统冬小麦冠层叶片氮素光谱指数进行比较。结果表明: NEW-NDRE及传统植被指数中NDRE、NDDA、RI-1dB与冬小麦冠层叶片氮含量的相关性较好;其中,灌浆初期NEW-NDRE与冬小麦冠层叶片氮含量相关性最好,决定系数R²为0.9,均方根误差(RMSE)为0.4;经独立数据检验,以NEW-NDRE为变量建立的冬小麦冠层叶片氮含量反演模型的平均相对误差(RE)为9.3%,明显低于以NDRE、NDDA、RI-1dB为变量的模型RE。总体上,新构建的NEW-NDRE对冬小麦冠层叶片氮含量的模拟能力显著优于传统指数,减弱了试验条件的限制性,可为精准施肥提供新的技术支撑。     

种植密度和施氮水平对小麦吸收利用土壤氮素的影响

2011-2013小麦季,在大田条件下设置2个氮肥水平(180和240kgN· hm-2)和3个种植密度(135、270和405万·hm-2),并将15N-尿素分别标记在20、60和100 cm土层处,研究种植密度-施氮互作对小麦吸收、利用土壤氮素及硝态氮残留量的影响.结果表明:种植密度从135万·hm-2增加至405万·hm-2,小麦在20、60和100 cm土层的15N吸收量分别增加1.86、2.28和2.51 kg·hm-2,地上部氮素积累量和吸收效率分别提高12.6％和12.6％,氮素利用效率降低5.4％;施氮量由240 kg N·hm-2降至180 kg N·hm-2,小麦在20、60 cm土层的15N吸收量分别降低4.11和1.21 kg·hm-2,在100 cm土层的15N吸收量增加1.02 kg·hm-2,地上部氮素积累量平均降低13.5％,氮素吸收效率和利用效率分别提高9.4％和12.2％.施氮180kg N·hm-2+种植密度为405万·hm-2处理与施氮240 kg N·hm-2+种植密度为270或405万·hm-2处理相比,其籽粒产量无显著差异,深层土壤氮素的吸收量显著提高,氮素吸收效率和利用效率分别提高13.4％和11.9％,O～ 200 cm土层的硝态氮积累量及100～ 200 cm土层硝态氮分布比例降低.在适当降低氮肥用量条件下,通过增加种植密度可以促进小麦吸收深层土壤氮素,减少土壤氮素残留,并保持较高的产量水平.     

施氮水平对小麦籽粒发育过程中氨基酸含量的影响

施氮能提高小麦籽粒蛋白质氨基酸的含量,并与施氮水平呈正相关;但对普通小麦必需氨基酸与蛋白质氨基酸的比值没有影响,而硬粒小麦4286随施氮水平的提高,该比值下降。在开花后32d以前,籽粒发育过程中游离氨基酸与施氮水平呈正相关,以后,籽粒中游离氨基酸趋于相近,表明施氮增加了游离氨基酸的库源,不同基因型小麦对施氮水平的反应不同,在同等施氮水平和栽培条件下,籽粒中蛋白质氨基酸和游离氨基酸含量为硬粒小麦4286＞小偃6号＞小偃107,不同施氮水平下,籽粒中氨基酸含量为高氮＞中氮＞低氮。     

基于减量精细采样法估算小麦叶片氮积累量的最佳归一化光谱指数

基于6个小麦品种、5个施氮水平、4年田间试验条件下不同生育时期的小麦叶片高光谱反射率和相应的氮含量及生物量,采用减量精细采样法,系统构建了350～2500 nm范围内所有两两波段组成的归一化光谱指数［NDSI（i, j）］,综合分析了小麦叶片氮积累量(LNA, g N·m^-2)与NDSI（i, j）的定量关系,确定了估算叶片氮积累量的新高光谱特征波段和光谱指数,进而建立了小麦叶片氮积累量监测模型.结果表明：估算小麦叶片氮积累量的敏感波段主要存在于可见光区和近红外区,最佳特征波段组合为720 nm和860 nm;基于NDSI(860,720)的叶片氮积累量监测模型为LNA=26.34×［NDSI(860,720)］^1.887（R²=0.900,SE=1.327）.利用独立试验资料的检验结果表明,基于NDSI(860,720)建立的回归模型对小麦叶片氮积累量的估测精度为0.823,RMSE为0.991 g N·m^-2,模型预测值与观察值之间的符合度较高.可利用新的归一化高光谱参数NDSI(860,720)来估算小麦叶片氮积累量.     

水分胁迫对耐旱性不同小麦小花化发育和氮磷及激素含量的影响

土壤分水分亏缺导致小麦幼穗内氮、磷、异戊烯基腺嘌呤（ｉＰＡｓ）含量降低,脱落酸（ＡＢＡ）含量升高,影响小花的发育,结实粒数减少。在水分充足的条件下,耐旱性不同的品种穗中氮、氮、ｉＰＡｓ含量和ＡＢＡ含量无显著差异;在水分胁迫条件下,旱地品种幼穗中氮,磷、ｉＰＡｓ含量降低的幅度和ＡＢＡ含量升高的幅度低于水浇地品种,这是耐旱品种在土壤水分亏缺时,较水浇地品种小花发育好、成花率和结实率高,穗粒数稳定的生理     

基于最佳波段判别的湿地植物叶片全氮反演研究

利用高光谱遥感技术定量估测湿地植被叶片全氮含量,对于监测和诊断湿地植被的生理状况及生长趋势具有重要意义。但叶片氮素遥感诊断研究多存在反演模型过拟合、入选波段与生化参量间因果关系不明确和入选变量间"多重共线性"等局限。以芦苇(Phragmites australis)和香蒲(Typha angustifolia)叶片全氮含量作为研究对象,通过谱带分区,分区最佳波段选取和偏最小二乘回归相结合的方法构建芦苇和香蒲叶片全氮含量反演模型,并利用交叉验证决定系数(R2cv)和均方根误差(RMSEcv)对模型精度进行检验,尝试克服传统反演方法中的不足。结果表明,不同湿地植物类型相比,利用芦苇反射光谱建立的预测模型精度都高于香蒲。不同回归模型相比,一阶导数光谱-偏最小二乘回归模型(FDS-PLSR)精度远高于原始光谱-偏最小二乘回归模型(OS-PLSR)。芦苇最佳模型交叉验证决定系数(R2cv)达到了0.84,方根误差(RMSEcv)为0.10,香蒲最佳模型交叉验证的决定系数(R2cv)达到了0.66,方根误差(RMSEcv)为0.13,是构建湿地植物芦苇和香蒲光谱与叶片全氮含量关系的最佳模型。在不降低湿地植物叶片氮含量反演精度的基础上,有效地避免了传统地物高光谱模型反演中的局限性,是无损害遥感探测方面的有益尝试。     

一种估测小麦冠层氮含量的新高光谱指数

提出了一种估测小麦冠层氮含量的新高光谱指数--微分归一化氮指数(FD-NDNI)。以FieldSpec Pro FR地物光谱仪采集拔节后至孕穗前小麦的冠层光谱190份,随机抽取142份作为训练集,其余48份作为预测集。将光谱以小波阈值去噪法去噪后,利用其525、570 与730 nm处的一阶导数值,采用差值、比值以及归一化的方法构建了12种光谱指数以实现小麦冠层氮含量的估测,并与mNDVI705、mSR以及NDVI705等22种常用指数进行了比较分析。发现指数FD-NDNI对小麦冠层氮含量的估测结果最佳,其估测模型(指数形式)校正集决定系数(C-R²)与预测集决定系数(P-R²)分别达0.818与0.811,优于mNDVI705等常用指数。进一步分析表明,在各指数中,FD-NDNI对叶面积系数最不敏感,可最有效地避免冠层郁闭度等因素对氮含量估测的影响。为优化结果,采用最小二乘支持向量回归算法(LS-SVR)对模型进行了改进,当模型惩罚系数C与RBF核函数参数g取得最优解6.4与1.6时,其C-R²与P-R²分别提高至0.846与0.838,具有比指数模型更高的精度。结果表明:FD-NDNI是小麦冠层氮含量估测的优选指数,LS-SVR为建模的优选算法。     

Estimating photosynthetic traits from reflectance spectra: A synthesis of spectral indices,numerical inversion,and partial least square regression

The lack of efficient means to accurately infer photosynthetic traits constrains understanding global land carbon fluxes and improving photosynthetic pathways to increase crop yield. Here, we investigated whether a hyperspectral imaging camera mounted on a mobile platform could provide the capability to help resolve these challenges, focusing on three main approaches, that is, reflectance spectra-, spectral indices-, and numerical model inversions-based partial least square regression (PLSR) to estimate photosynthetic traits from canopy hyperspectral reflectance for 11 tobacco cultivars. Results showed that PLSR with inputs of reflectance spectra or spectral indices yielded an R² of ~0.8 for predicting V _cmax and J _max, higher than an R² of ~0.6 provided by PLSR of numerical inversions. Compared with PLSR of reflectance spectra, PLSR with spectral indices exhibited a better performance for predicting V _cmax (R² = 0.84 ± 0.02, RMSE = 33.8 ± 2.2 μmol m⁻² s⁻¹) while a similar performance for J _max (R² = 0.80 ± 0.03, RMSE = 22.6 ± 1.6 μmol m⁻² s⁻¹). Further analysis on spectral resampling revealed that V _cmax and J _max could be predicted with ~10 spectral bands at a spectral resolution of less than 14.7 nm. These results have important implications for improving photosynthetic pathways and mapping of photosynthesis across scales.     

不同种植模式对土壤氮素转化及酶活性的影响

采用两年大田试验,研究了小麦-大豆（A₁）、小麦-甘薯（A₂）、玉米（A₃）、小麦/玉米/大豆（A₄）和小麦/玉米/甘薯（A₅）5种种植模式下,小麦/玉米/大豆套作体系的土壤酶活性变化特征及其对土壤氮素转化的影响.结果表明：与A₁、A₂、A₃和A₅相比,A₄提高了各作物在开花期（或吐丝期）和成熟期的土壤总氮含量及脲酶和蛋白酶活性,处理间表现为套作＞单作、大豆茬口＞甘薯茬口、边行＞中行;降低了小麦、玉米土壤的NO₃^--N、NH₄⁺-N含量及小麦土壤的硝酸还原酶活性.玉米土壤的硝酸还原酶活性在玉米、大豆共生前的拔节期为单作＞套作,在玉米、大豆共生后的吐丝期和成熟期为套作＞单作、大豆茬口＞甘薯茬口;大豆土壤的NO₃^--N、NH₄⁺-N含量及硝酸还原酶活性在分枝期为单作＞套作,在开花期和成熟期为套作＞单作、大豆茬口＞甘薯茬口、中行＞边行.     

不同形态氮素对专用型小麦花后氮代谢关键酶活性及籽粒蛋白质含量的影响

采用盆栽方法研究了氮素形态对不同专用型小麦开花后氮素同化关键酶活性及籽粒蛋白质含量的影响。结果表明:不同专用型小麦氮素同化关键酶硝酸还原酶、谷氨酰胺合成酶和谷氨酸合酶对氮素形态的反应不同。强筋小麦豫麦34施用酰胺态氮对旗叶硝酸还原酶和谷氨酰胺合成酶活性、籽粒谷氨酰胺合成酶和谷氨酸合酶活性具有明显的促进作用,最终籽粒蛋白质含量较高;中筋小麦豫麦4 9在施用铵态氮时,3种氮素同化关键酶活性均有较大增强,籽粒蛋白质含量最高;弱筋小麦豫麦5 0硝酸还原酶活性以铵态氮处理最高,而籽粒和旗叶谷氨酰胺合成酶和谷氨酸合酶活性在酰胺态氮处理下明显增强,酰胺态氮对籽粒中蛋白质含量的增加具有明显的促进作用。相关性分析表明,籽粒蛋白质含量与旗叶GS活性和籽粒GOGAT活性呈显著或极显著正相关,与旗叶NR活性和GS活性、籽粒GOGAT活性相关性不显著     

外源一氧化氮供体硝普钠浸种对盐胁迫下小麦幼苗碳氮代谢及抗氧化系统的影响

预先用0.1mmol/L的SNP(硝普钠,NO供体)浸种,研究NO预处理对120mmol/L NaCl胁迫下两小麦品种(扬麦12和淮麦17)幼苗叶片抗氧化系统、碳氮代谢及蛋白酶活性的影响。结果表明,NO预处理能有效地抑制NaCl胁迫下小麦幼苗叶片超氧阴离子释放(O.2-)和过氧化氢(H2O2)积累,提高超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性,降低丙二醛(MDA)含量,提高叶绿素、类胡萝卜素和可溶性总糖含量。另外,NO预处理显著提高叶片可溶性蛋白质含量,以及内肽酶和羧肽酶活性。分析表明,NO有利于维持盐胁迫下小麦碳氮代谢正常运转,从而促进植株生长,提高小麦幼苗株高、鲜重和干重。试验条件下,NO对淮麦17的促进作用大于扬麦12。     

Comparison of methods for assessing the impact of different disturbances and nutrient conditions upon functional characteristics of grassland communities

Background and Aims

Predicting the response of plant communities to variation in resources and disturbance is still a challenge, because findings depend on how ecological gradients are characterized and how grassland functional composition is assessed. Focusing on leaf dry matter content (LDMC), the efficacy of different methods for evaluating the best response of plant communities to either environmental or disturbance change is examined.

Methods

Data were collected on 69 grasslands located at four sites in the Pyrenees and Massif Central. N-Ellenberg indices and plant nutrient content (Ni) were compared to assess fertility, and either LDMC (meas) measured or calculated from a trait database for which traits were measured under the same environmental conditions (db). Management regime (MR) was characterized in terms of categories (grazing, cutting) and plant height.

Key Results

LDMCdb was positively correlated to LDMCmeas, but depended significantly on site temperature. N-Ellenberg and Ni were significantly correlated, and there was a significant effect of MR and temperature. LDMC responded to fertility, MR and temperature. Replacing MR by plant height in an REML analysis reduced the uncertainty of the LDMC prediction. LDMC was correlated to plant height at community level, whereas the correlation was weak at species level. Differences in LDMC between plant communities under any of the management regimes were significantly correlated to the standing herbage mass.

Conclusion

The N-Ellenberg index is a better indicator of fertility than Ni which is short-term and environment-dependent. LDMC taken from a database allows plant trait variation due to species abundance (excluding variation due to trait plasticity in response to management) to be captured. So the former is better suited for assessing agricultural services that mainly depend on plant phenology and tissue composition. LDMC responded to defoliation regime in addition to fertility because plant height is roughly correlated with LDMC at plant community level.     

Intra-specific hybridization: generator of genetic diversification and heterosis in Andrographis paniculata Nees. A bridge from extinction to survival

Andrographis paniculata (AP) has been stated as a low-diverse, endangered and red-listed plant species. Self-pollinated mating system, being an introduced species and experiencing a bottleneck as well as over exploitation cause such a consequence. Inter and intra-specific hybridizations have been suggested as essential techniques for generating genetic diversity. To test the effect of intra-specific hybridization on diversification and heterosis of AP, seven accessions were outcrossed manually in all 21 possible combinations. Three types of markers including morphological, phytochemical and RAPD markers were employed to evaluate the mentioned hypothesis. The results revealed that hybridization acted as a powerful engine for diversification of AP as it caused heterotic expression of the studied traits, simultaneously. Initially, it seems that additive and non-additive gene effects both can be considered as the genetic basis of heterosis in AP for the investigated traits. Agronomic and morphological traits were differentiated from each other, while positive heterosis was recorded mainly for agronomic traits but not for the morphological traits. Intra-specific hybridization increased the genetic diversity in AP population. Nevertheless, a part of this variation could also be attributed to the negative heterosis. The current exploration demonstrated the first ever conducted manual intra-specific hybridization among AP accessions in a mass scale. However, the 17 RAPD primers produced a monomorph pattern, but perhaps increasing the number of markers can feature a new genetic profile in this plant.