Photosynthetic decline in aging perennial grass is not fully explained by leaf nitrogen

Abstract

Aging in perennial plants is traditionally observed in terms of changes in end-of-season biomass, however, the driving phenological and physiological changes are poorly understood. We found that three-year-old (mature) stands of the perennial grass Miscanthus × giganteus had 19 – 30% lower Anet than one-year-old M. × giganteus (juvenile) stands; 10 – 34% lower maximum carboxylation rates of rubisco (P < 0.05); and 34% lower light saturated Anet (Asat; P < 0.05). These changes could be related to nitrogen (N) limitations as mature plants were larger and had 14-34% lower leaf N on an area basis (Na) than juveniles (P<0.05). However, N fertilization restored Na to juvenile levels but compensated only 50% of the observed decline in leaf photosynthesis with age. Comparison of leaf photosynthesis per unit of leaf N (PNUE) showed that mature stands had at least 26% lower PNUE than juvenile stands across all N fertilization rates, suggesting that other factors, besides N, may be limiting photosynthesis in mature stands. We hypothesize that sink limitations in mature stands could be causing feedback inhibition of photosynthesis which is associated with the age-related decline in photosynthesis.

A 30% reduction in switchgrass rhizome reserves did not decrease biomass yield

“…Because the larger sink demand was distributed between more leaves, each individual leaf would not perceive as large of a change in the sink demand and would not need to readjust its individual photosynthetic rates. Similarly, our results cannot support or deny that sink limitations drive the late season decline in leaf-level photosynthesis (De Souza et al, 2018;McCormick et al, 2006;Tejera et al, 2022;Tejera-Nieves et al, 2023) but confirm that whole-plant photosynthesis is affected by changes in sink strength.…”

“…This implies that during the growing season, perennial grasses allocate carbon to growth, development, and storage organs. The accumulation of storage reserves in storage organs (e.g., rhizomes, crowns, stolons, and ratoons) is crucial for winter maintenance and spring regrowth, (Sarath et al, 2014; Sheikh et al, 2022; Smith, 1975; Zhang et al, 2021) and it is also an important driver of carbon assimilation and growth during the same growing season (De Souza et al, 2018; Palmer et al, 2017; Palmer et al, 2014; Ruiz‐Vera et al, 2021; Tejera‐Nieves et al, 2023; Tejera et al, 2022; Van Heerden et al, 2010), however, it is less understood how changes in the storage reserve affect growth and development during the next season.…”

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.…”

Nitrogen fertilization effects on aged Miscanthus × giganteus stands: Exploring biomass yield, yield components, and biomass prediction using in‐season morphological traits

“…Furthermore, without historical fertilization records, we cannot determine whether the response to N would have been similar had the stand been historically fertilized. Current research, however, indicates biomass increases following N application may still be insufficient to overcome age‐related declines in biomass (Tejera et al., 2022). We recommend that future studies focus on previously fertilized mature stands to evaluate the magnitude of yield response after N re‐application.…”

“…To our knowledge, only Tejera et al (2019Tejera et al ( , 2021Tejera et al ( , 2022) and Yost et al (2017) have conducted multi-site assessments of the effect of N on the performance of miscanthus of different ages. These studies have the advantage of incorporating the between and within-site differences arising from establishment conditions.…”