Substrate Dependency and Effect of Xylanase Supplementation on Enzymatic Hydrolysis of Ammonia-Treated Biomass

Pretreatment based on aqueous ammonia was investigated under two different modes of operation: soaking in aqueous ammonia and ammonia recycle percolation. These processes were applied to three different feedstocks with varied composition: corn stover, high lignin (HL), and low lignin (LL) hybrid poplars. One of the important features of ammonia-based pretreatment is that most of the hemicellulose is retained after treatment, which simplifies the overall bioconversion process and enhances the conversion efficiency. The pretreatment processes were optimized for these feedstocks, taking carbohydrate retention as well as sugar yield in consideration. The data indicate that hybrid poplar is more difficult to treat than corn stover, thus, requires more severe conditions. On the other hand, hybrid poplar has a beneficial property that it retains most of the hemicellulose after pretreatment. To enhance the digestibility of ammonia-treated poplars, xylanase was supplemented during enzymatic hydrolysis. Because of high retention of hemicellulose in treated hybrid poplar, xylanase supplementation significantly improved xylan as well as glucan digestibility. Of the three feedstocks, best results and highest improvement by xylanase addition was observed with LL hybrid poplar, showing 90% of overall sugar yield.     

What can be Learned from Silage Breeding Programs?

Improving the quality of cellulosic ethanol feedstocks through breeding and genetic manipulation could significantly impact the economics of this industry. Attaining this will require comprehensive and rapid characterization of large numbers of samples. There are many similarities between improving corn silage quality for dairy production and improving feedstock quality for cellulosic ethanol. It was our objective to provide insight into what is needed for genetic improvement of cellulosic feedstocks by reviewing the development and operation of a corn silage breeding program. We discuss the evolving definition of silage quality and relate what we have learned about silage quality to what is needed for measuring and improving feedstock quality. In addition, repeatability estimates of corn stover traits are reported for a set of hybrids. Repeatability of theoretical ethanol potential measured by near-infrared spectroscopy is high, suggesting that this trait may be easily improved through breeding. Just as cell wall digestibility has been factored into the latest measurements of silage quality, conversion efficiency should be standardized and included in indices of feedstock quality to maximize overall, economical energy availability.     

新型铜胁迫植被指数NCSVI探索铜污染下玉米叶片光谱敏感区间

目前我国土壤重金属污染日趋严重,高光谱遥感因具有光谱分辨率高、图谱合一等特点成为农作物重金属污染研究的热点。农作物受重金属污染后其光谱会发生细微的改变,如何探寻叶片光谱中对重金属污染敏感的波段是目前的一种研究方向。提出了一种新型铜胁迫植被指数（NCSVI）来探索铜胁迫下玉米光谱敏感区间。通过设计不同梯度下的玉米铜胁迫实验,测定每个铜胁迫浓度下玉米叶片的光谱和Cu2+的含量。首先,将玉米叶片光谱分为11个子区间,以每个子区间的中间波长对应的光谱反射率构建各自的NCSVI。然后,计算NCSVI与玉米叶片中Cu2+含量的相关性系数R及均方根误差RMSE,结合水波段指数（WBI）、改进的叶绿素吸收率指数（MCARI）和归一化水指数（NDWI）这三种常规植被指数进行对比。最后,选用其他年份相同实验条件下获取的玉米叶片光谱进行验证,确认NCSVI的稳定性和有效性。结果表明,11个子区间中只有绿峰、红边、近谷和近峰A这四个子区间对应的NCSVI与玉米叶片Cu2+含量相关性系数的绝对值高于0.9,分别为-0.94,-0.97,-0.94和-0.96,均方根误差均低于15,分别为12.57,8.71,12.71和10.06,而WBI,MCARI和NDWI的相关性系数最高的仅达到0.75,均方根误差最小的为24.21,说明四个子区间对应的NCSVI对玉米叶片铜污染有着更好的指示性。利用不同年份相同条件下的玉米实验对以上结果进行验证,发现11个子区间中,R绝对值大于0.9、RMSE小于1.55的只有绿峰、红边、近谷和近峰A这四个子区间,其中R分别为-0.9,-0.97,-0.97和-0.93,RMSE分别为1.50,0.85,0.78和1.29,均优于WBI,MCARI和NDWI,与2016年实验得出的敏感子区间一致,说明NCSVI能探测铜胁迫下玉米光谱的敏感区间,具备效率高、稳定性好的特点。所提出的NCSVI指数可作为监测玉米叶片铜污染的一种方法,并为其他农作物重金属污染研究提供一定的理论支持。     

不同光温环境下玉米苗期叶片的高光谱特性响应分析

光温环境胁迫是影响作物优质高产的一个主要制约因素,传统的作物胁迫监测,敏锐性不足、耗时费力且多为有损检测。近年来随着信息技术的快速发展,高光谱技术能够快速无损的获取作物生理信息,并对逆境胁迫响应进行动态监测,为现代农业的精准化生产和智能化决策提供了数字化支撑,对实现传统农业向精准化、数字化的现代农业转变具有重要意义。以玉米苗期为研究对象,获取不同光温环境下叶片的高光谱数据和生理参数,探究玉米苗期叶片对不同光温环境的响应规律,进行高光谱差异性分析,并构建生理参数的高光谱反演模型。利用相关分析法筛选光谱敏感波段,采用多元散射校正(MSC)、标准正态变量变换(SNV)、Savitzky-Golaay(S-G)平滑相结合的预处理方法,分别与偏最小二乘回归法(PLS)、主成分回归法(PCR)、逐步多元线性回归法(SMLR)三种建模方法组合,以模型相关系数和均方根误差作为模型效果评价指标,探索高光谱反演叶片生理参数模型的最优方法。结果表明：不同光温环境下玉米的高光谱特性在整体上变化趋势一致,但仍存在差异,在500～700 nm波段内,光谱反射率的升高表明光强的增强;在760～900 nm波段内,光谱反射率的升高表明温度的增强;且光温胁迫环境的变化,均可反映在高光谱特性上,波段760～900 nm内光谱的反射率在高温胁迫环境下较高,在弱光胁迫环境下较低,在低温胁迫环境下反射率显著降低;所构建的SPAD和F_v/F_m的反演模型中,建模最优方法为PLS-MSC-SG,模型验证集相关系数分别为0.958和0.976,训练集相关系数分别为0.979和0.995。模型的预测性精度较高,表明利用高光谱技术,可以实现光温环境胁迫下玉米植株的定量监测,提高田间精细化管理水平,为玉米优质高产的智能化管理提供参考依据。     

Ion conducting corn starch biopolymer electrolytes doped with ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Biodegradable corn starch-lithium hexafluorophosphate (LiPF₆) based biopolymer electrolytes were prepared by solution casting technique. Ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF₆) was doped into the polymer matrix. Upon addition of 50 wt.% BmImPF₆, the maximum ionic conductivity of (1.47 ± 0.02) × 10^− 4 Scm^− 1 was achieved due to its higher amorphous region. This result had been further proven in ATR-FTIR study. Frequency dependence of conductivity and dielectric studies reveal the occurrence of polarization at the electrolyte-electrode interface and thus form the electrical double layer, asserting the non-Debye characteristic of polymer electrolytes. This result is in good agreement with dielectric loss tangent study. Based on the changes in shift, changes in intensity, changes in shape and existence of some new peaks, attenuated total reflectance-Fourier Transform Infrared (ATR-FTIR) divulged the complexation between corn starch, LiPF₆ and BmImPF₆, as shown in the spectra.     

The impact of cell wall acetylation on corn stover hydrolysis by cellulolytic and xylanolytic enzymes

Analysis of variously pretreated corn stover samples showed neutral to mildly acidic pretreatments were more effective at removing xylan from corn stover and more likely to maintain the acetyl to xylopyranosyl ratios present in untreated material than were alkaline treatments. Retention of acetyl groups in the residual solids resulted in greater resistance to hydrolysis by endoxylanase alone, although the synergistic combination of endoxylanase and acetyl xylan esterase enzymes permitted higher xylan conversions to be observed. Acetyl xylan esterase alone did little to improve hydrolysis by cellulolytic enzymes, although a direct relationship was observed between the enzymatic removal of acetyl groups and improvements in the enzymatic conversion of xylan present in substrates. In all cases, effective xylan conversions were found to significantly improve glucan conversions achievable by cellulolytic enzymes. Additionally, acetyl and xylan removal not only enhanced the respective initial rates of xylan and glucan conversion, but also the overall extents of conversion. This work emphasizes the necessity for xylanolytic enzymes during saccharification processes and specifically for the optimization of acetyl esterase and xylanase synergies when biomass processes include milder pretreatments, such as hot water or sulfite steam explosion.