Nutrient Dynamics in Switchgrass as a Function of Time

Abstract

<jats:p>There are wide variations in fertilizer recommendations for switchgrass (Panicum virgatum L.) as biofuel feedstock or forage. Inconsistent yield responses to fertilization are common. Nutrient translocation, from aboveground leaves and stems to belowground roots, is a contributor to variable, and sometimes the absence of, fertilizer response. A field study evaluated how major nutrients are cycled within switchgrass during the growing season. Aboveground (AG) and belowground (BG) biomasses were harvested and analyzed separately for yield (AG) and nutrient concentrations (AG and BG). Maximum yields were 26.3 (2008), 17.5 (2009) and 29.3 (2010) Mg ha−1 until senescence. In all years, the N concentration of the AG biomass decreased as the season progressed (p &lt; 0.0001). The belowground biomass N concentration increased over time in 2008 and 2010 (p &lt; 0.05). Phosphorus (P) and potassium (K) displayed similar trends to nitrogen concentration. Temporal changes of other nutrients in the AG and BG biomass concentrations were inconsistent and varied compared with N. The dynamics of the macronutrients suggested translocation from AG to BG as the switchgrass matured. Nutrients stored in roots can be beneficial for regrowth in the following growing season, which may reduce response to fertilizers. A greater understanding of nutrient cycling and harvest timing is needed to better manage different switchgrass production systems.</jats:p>

Seasonal decline in leaf photosynthesis in perennial switchgrass explained by sink limitations and water deficit

“…Autumnal senescence is characterized by a decrease in chlorophyll content and an up-regulation of genes associated with protein degradation (Palmer et al, 2015;Palmer et al, 2019). During this process, light-harvesting pigments of the photosynthetic system are degraded (Moy et al, 2015), leading to N retranslocation from aboveground to belowground organs (Yang et al, 2009;Yang et al, 2016;Yang and Udvardi, 2018;Massey et al, 2020), and a concomitant decrease in photosynthetic capacity (Tang et al, 2005;Galvagno et al, 2013;Donnelly et al, 2020). Therefore, the decline in leaf photosynthesis may not be driven solely by sink limitations but also a decrease in photochemical efficiency of photosynthesis resulting from senescence.…”

“…This dynamic occurs in many genera of grasses including the bioenergy crops Panicum, Miscanthus, and Saccharum spp., and even in some evergreen and deciduous trees (Eggemeyer et al, 2006;Kosugi and Matsuo, 2006;Inman-Bamber et al, 2011;De Souza et al, 2013;Boersma et al, 2015;Gao et al, 2015;Yan et al, 2015;De Souza et al, 2018;Endres et al, 2019;Rusinowski et al, 2019;Stavridou et al, 2020). This seasonal decline in photosynthesis could be partially adaptative as it is associated with the remobilization of nutrients from leaves to belowground perennating organs, which allows the plant to recycle nutrients that otherwise would be lost to leaf drop (Yang et al, 2009;Yang et al, 2016;Yang and Udvardi, 2018;Massey et al, 2020). Beyond this putative adaptive role in nutrient retranslocation, additional physiological and environmental drivers of this decrease in photosynthesis are unknown but could have large effects on end-of-season biomass and long-term yield dynamics.…”

“…Specifically, physiological signals like carbohydrate buildup and sink strength are known to limit development and leaf photosynthesis in certain perennial grasses ( McCormick et al, 2009 ; Van Heerden et al., 2010 ; De Souza et al., 2018 ; Ruiz-Vera et al., 2021 ; Tejera et al., 2021 ; Tejera et al., 2022 ) . For example, when the photoassimilate source-sink balance was perturbed by shading some leaves of sugarcane plants, photosynthesis in the unshaded leaves increased by 32%, indicating source-sink coordination at the level of the entire plant to match supply (source) with demand (sinks) ( McCormick et al, 2006 ). Similarly, when sink strength was reduced by cold-girdling leaves or by placing leaves in sucrose solution, photosynthesis decreased by 30 – 45%, probably inhibited by foliar sucrose and hexose concentrations that increased 2 – 3 fold ( McCormick et al, 2008 ).…”

Patterns of changes in photosynthetic parameters of switchgrass grown on marginal lands of the Right Bank Forest Steppe of Ukraine

“…Сезонні зміни інтенсивності фотосинтезу можуть бути пов'язані з ремобілізацією поживних речовин із листя до підземних багаторічних органів, що дає рослині змогу переробляти поживні речовини, які інакше були б втрачені через опадання листя. Тобто значна частина поживних речовин, синтезованих фотосинтетичним апаратом рослин, накопичується саме в підземній їх частині й у традиційних обрахунках ефективності фотосинтезу не задіяна [26][27][28].…”

Soil phosphorus drawdown by perennial bioenergy cropping systems in the Midwestern US

“…The rate of P removal by crop harvest depends on initial soil P stocks, crop productivity, and the P content of harvested biomass, the latter affected by the degree of P retranslocation to belowground root systems prior to harvest (Massey et al, 2020). Phosphorus budgets (comparisons of inputs to outputs) for specific cropping systems or entire agricultural watersheds are useful to identify whether the systems show a net P surplus or deficit over time.…”