Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g(-1) for soluble sugars, 6-533 (mean = 94) mg g-1 for starch and 53-649 (mean = 153) mg g-1 for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R-2 = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g-1 for total NSC, compared with the range of laboratory estimates of 596 mg g-1. Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.

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Non-structural carbohydrates in woody plants compared among laboratories.

Published in Agron. J. 105:735–744 (2013) doi:10.2134/agronj2012.0273 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. A major goal of current agronomic research is to make annual grain crop production more sustainable, with management strategies that supply adequate fertility to meet crop demand while conserving soil and water quality. For temperate humid environments, these management strategies typically strive to minimize soil disturbance (e.g., no-till and conservation tillage strategies), maximize plant cover on the soil (e.g., cover crops and no-till), and manipulate fertilizer strategies and sources to reduce nutrient losses to the environment (e.g., organic amendments and precision agriculture) (Robertson, 1997; Raun and Johnson, 1999; Snapp et al., 2005, 2010; Grandy et al., 2006). The management choices that growers make can have dramatic impacts on local ecosystem services. For example, N fertilizer type, rate, and application in relationship to crop demand are important regulators of N cycling efficiency and loss pathways; this has direct and indirect consequences for water and soil quality (Robertson, 1997; Snapp et al., 2010; Syswerda et al., 2012). Despite the realized environmental benefits of some conservation management strategies, grower adoption of these strategies can be limited for a variety of socioeconomic and biophysical reasons (Snapp et al., 2005; Grandy et al., 2006). Another approach that has received far less attention than management strategies for improving ecosystem services is to “perennialize” annual grain systems via breeding for new perennial grain crops (Glover et al., 2010b). The perceived benefits of this approach are based on inferences from agronomic research that has consistently shown herbaceous perennial systems, such as forages or restored or native grasslands, outperforming annual cropping systems with regard to soil conservation (Montgomery, 2007), primary production and C cycling efficiencies (Buyanovsky et al., 1987; Jenkinson et al., 1994; Silvertown et al., 1994; Glover et al., 2010a; Zeri et al., 2011), N cycling efficiencies (Jenkinson et al., 2004; Glover et al., 2010a; Syswerda et al., 2012), maintenance of soil nutrient stocks and soil C pools (Buyanovsky et al., 1987; Jenkinson et al., 2004; Mikhailova et al., 2000; Culman et al., 2010; Bremer et al., 2011), and maintenance of soil food webs (Ferris et al., 2001; Culman et al., 2010; DuPont et al., 2010). These benefits have been documented in established herbaceous perennial systems, but future perennial grain systems will likely be rotated with other crops and will have to be reestablished with each rotation. The length of time newly planted perennial crops need to improve ecosystem services is very important because there have been some reports of decreased ecosystem services in establishing herbaceous perennials (McLaughlin et al., 2002; Syswerda et al., 2012). One promising perennial grain crop is intermediate wheatgrass, a widely adapted, high-yielding, cool-season forage grass that provides excellent feed for livestock in the Great Plains ABSTRACT

Soil and Water Quality Rapidly Responds to the Perennial Grain Kernza Wheatgrass

Senescence is an age-dependent process, ultimately leading to plant death, that in annual crop plants overlaps with the reproductive stage of development. Research on the molecular and biochemical mechanisms of leaf senescence has revealed a multi-layered regulatory network operating to control age-dependent processes. Abiotic stress-induced senescence challenges source-sink relationships and results in significant reduction in crop yields. Although processes associated with plant senescence are well studied, the mechanisms regulating stress-induced senescence are not well known. Here, we discuss the effects of abiotic stress on crop productivity, mechanisms associated with stress-induced senescence, and the possible use of these mechanisms for the generation of plant stress tolerance. We emphasize the involvement of source strength and stability of the photosynthetic apparatus in this process, and suggest a possible role of a perennial plant life strategy for the amelioration of stress-induced senescence.

Stress-induced senescence and plant tolerance to abiotic stress.

Plant breeders are increasing yields and improving agronomic traits in several perennial grain crops, the first of which is now being incorporated into commercial food products. Integration strategies and management guidelines are needed to optimize production of these new crops, which differ substantially from both annual grain crops and perennial forages. To offset relatively low grain yields, perennial grain cropping systems should be multifunctional. Growing perennial grains for several years to regenerate soil health before rotating to annual crops and growing perennial grains on sloped land and ecologically sensitive areas to reduce soil erosion and nutrient losses are two strategies that can provide ecosystem services and support multifunctionality. Several perennial cereals can be used to produce both grain and forage, and these dual-purpose crops can be intercropped with legumes for additional benefits. Highly diverse perennial grain polycultures can further enhance ecosystem services, but increased management complexity might limit their adoption.

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Managing for Multifunctionality in Perennial Grain Crops

RuBisCO-catalyzed CO2 fixation is the main source of organic carbon in the biosphere. This enzyme is present in all domains of life in different forms (III, II, and I) and its origin goes back to 3500 Mya, when the atmosphere was anoxygenic. However, the RuBisCO active site also catalyzes oxygenation of ribulose 1,5-bisphosphate, therefore, the development of oxygenic photosynthesis and the subsequent oxygen-rich atmosphere promoted the appearance of CO2 concentrating mechanisms (CCMs) and/or the evolution of a more CO2 -specific RuBisCO enzyme. The wide variability in RuBisCO kinetic traits of extant organisms reveals a history of adaptation to the prevailing CO2 /O2 concentrations and the thermal environment throughout evolution. Notable differences in the kinetic parameters are found among the different forms of RuBisCO, but the differences are also associated with the presence and type of CCMs within each form, indicative of co-evolution of RuBisCO and CCMs. Trade-offs between RuBisCO kinetic traits vary among the RuBisCO forms and also among phylogenetic groups within the same form. These results suggest that different biochemical and structural constraints have operated on each type of RuBisCO during evolution, probably reflecting different environmental selective pressures. In a similar way, variations in carbon isotopic fractionation of the enzyme point to significant differences in its relationship to the CO2 specificity among different RuBisCO forms. A deeper knowledge of the natural variability of RuBisCO catalytic traits and the chemical mechanism of RuBisCO carboxylation and oxygenation reactions raises the possibility of finding unrevealed landscapes in RuBisCO evolution.

Evolutionary trends in RuBisCO kinetics and their co-evolution with CO2 concentrating mechanisms.

Perennial wheat (Triticum aestivum L. × Th inopyrum spp.) and perennial rye (Secale cereale L. × S. montanum) are novel hybrid species under development as alternatives to annual cereal crops. We conducted a 2-yr fi eld study with a split plot design to evaluate agronomic performance, including yield, phenology, and biomass production, of perennial accessions of wheat and rye, along with annual analogs. Th is is one of the fi rst studies to rigorously compare agronomic performance of 2-yr-old plants to 1-yr-old plants in perennial cereals. Perennial wheat produced 1.0 to 1.6 Mg ha –1 grain yield, 50% of annual wheat (2.7 Mg ha –1 ), while perennial rye produced 1.3 Mg ha –1 , 73% of annual rye (1.8 Mg ha –1 ). Modest yields from perennials relative to annuals refl ected lower harvest index, lower yield per tiller, and less kernel mass. One-year-old and 2-yr-old perennial plants had similar seed yields, yield components, and biomass production, indicating that plant age had little eff ect on these parameters and older plants maintained yield potential. In contrast, phenology did vary with plant age, and showed a shift toward earlier spring growth and later fl owering dates in older perennial plants. Th is illustrates an expanded vegetative period for regrowing plants of these perennial cereals. Th ere appears to be potential for producing an early season forage crop from these cereals, although biomass yields were not high at this site and regrowth was not always reliable. Overall, performance of perennial rye was consistent with a viable new cereal crop. On the other hand, perennial wheat requires further selection for allocation of biomass to grain and vigorous regrowth.

https://acsess.onlinelibrary.wiley.com/doi/pdf/10.2134/agronj2012.0291

Agronomic Assessment of Perennial Wheat and Perennial Rye as Cereal Crops

Effects of plant age on resource acquisition and stress tolerance processes is a largely unstudied subject in herbaceous perennials. In a field experiment, we compared rates of photosynthesis (A), ribulose-1,5-bisphosphate (RuBP) carboxylation capacity (V Cmax), maximum electron transport rate (J max), and triose phosphate utilization (TPU), as well as concentrations of Rubisco and sucrose-phosphate synthase (SPS) in 5-year-old and 2-year-old intermediate wheatgrass (Thinopyrum intermedium) under both optimal growing conditions and cold stress in early spring and autumn. This species is a relative of wheat undergoing domestication. An additional experiment compared photosynthetic rates in different cohorts at mid-season and under colder conditions. We hypothesized that photosynthetic capacity in older plants would be lower under favorable conditions but higher under cold stress. Our hypothesis was generally supported. Under cold stress, 5-year-old plants exhibited higher A, TPU, and temperature-adjusted V Cmax than younger plants, as well as 50% more SPS and 37% more Rubisco. In contrast, at mid-season, photosynthetic capacities in older plants were lower than in younger plants in one experiment, and similar in the other, independent of differences in water status. Both cohorts increased A, temperature-adjusted TPU and J max, [Rubisco], and [SPS] under cold stress, but changes were greater in older plants. Photosynthetic differences were largest at 1.2 oC in very early spring, where older plants had 200% higher A and maintained up to 17% of their peak photosynthetic capacity. We find evidence of increased cold tolerance in older cohorts of wheatgrass, consistent with a growing body of research in woody perennials.

Older Thinopyrum intermedium (Poaceae) plants exhibit superior photosynthetic tolerance to cold stress and greater increases in two photosynthetic enzymes under freezing stress compared with young plants

Photosynthetic responses in annual rye, perennial wheat, and perennial rye subjected to modest source:sink ratio changes

 Premise of the study: Few previous studies have considered how plant age affects photosynthetic physiology in herbaceous perennials or how photosynthetic capacity in annual cereals compares to perennial relatives. Newly developed perennial cereals offer novel systems for addressing these questions. Our study makes a novel contribution by considering how life history differences affect photosynthetic physiology.  Methods: In two linked fi eld studies, we evaluated effects of life history and plant age on photosynthetic rates ( A ), and related biochemical, morphological, and water-relations traits, comparing 1- and 2-yr-old cohorts of perennial wheat, intermediate wheatgrass, and perennial rye to close annual relatives (wheat and rye).  Key results: Photosynthetic rates ( A ) were 10–50% higher in perennial cereals compared to annuals. In wheatgrass, elevated A was associated with higher carboxylation ( V C ), triose phosphate utilization (TPU) and electron transport rates ( J ), and higher leaf soluble protein and chlorophyll. Younger wheatgrass plants maintained higher A , TPU , J , and V C than older plants did. Perennial wheat and rye differed from annual relatives in some but not all of these parameters. Differences in stomatal limitation were not involved, while differences in stomatal conductance ( g s ) became evident under drier conditions.  Conclusions: This study demonstrates that some perennial cereal species can maintain higher midseason A than their annual crop relatives. These changes are not fully explainable by increased access to soil water and may refl ect trade-offs between allocation to reproduction and to resource acquisition. We also found evidence for age-related changes in photosynthetic physiology in a herbaceous perennial plant.

Life history and resource acquisition: Photosynthetic traits in selected accessions of three perennial cereal species compared with annual wheat and rye

Previous studies have found that maximum quantum yield of CO2 assimilation (Φ CO2,max,app) declines in lower canopies of maize and miscanthus, a maladaptive response to self-shading. These observations were limited to single genotypes, leaving it unclear whether the maladaptive shade response is a general property of this C4 grass tribe, the Andropogoneae. We explored the generality of this maladaptation by testing the hypothesis that erect leaf forms (erectophiles), which allow more light into the lower canopy, suffer less of a decline in photosynthetic efficiency than drooping leaf (planophile) forms. On average, Φ CO2,max,app declined 27% in lower canopy leaves across 35 accessions, but the decline was over twice as great in planophiles than in erectophiles. The loss of photosynthetic efficiency involved a decoupling between electron transport and assimilation. This was not associated with increased bundle sheath leakage, based on 13C measurements. In both planophiles and erectophiles, shaded leaves had greater leaf absorptivity and lower activities of key C4 enzymes than sun leaves. The erectophile form is considered more productive because it allows a more effective distribution of light through the canopy to support photosynthesis. We show that in sorghum, it provides a second benefit, maintenance of higher Φ CO2,max,app to support efficient use of that light resource.

/pdf/can-improved-canopy-light-transmission-ameliorate-loss-of-jrs314t4n8.pdf

Can improved canopy light transmission ameliorate loss of photosynthetic efficiency in the shade? An investigation of natural variation in Sorghum bicolor.

Nikhil S. Jaikumar

Papers

Agronomic Assessment of Perennial Wheat and Perennial Rye as Cereal Crops

Older Thinopyrum intermedium (Poaceae) plants exhibit superior photosynthetic tolerance to cold stress and greater increases in two photosynthetic enzymes under freezing stress compared with young plants

Photosynthetic responses in annual rye, perennial wheat, and perennial rye subjected to modest source:sink ratio changes

Life history and resource acquisition: Photosynthetic traits in selected accessions of three perennial cereal species compared with annual wheat and rye

Can improved canopy light transmission ameliorate loss of photosynthetic efficiency in the shade? An investigation of natural variation in Sorghum bicolor.