Photosynthesis, N2 fixation and taproot reserves during the cutting regrowth cycle of alfalfa under elevated CO2 and temperature

Abstract

Future climatic conditions, including rising atmospheric CO(2) and temperature may increase photosynthesis and, consequently, plant production. A larger knowledge of legume performance under the predicted growth conditions will be crucial for safeguarding crop management and extending the area under cultivation with these plants in the near future. N(2) fixation is a key process conditioning plant responsiveness to varying growth conditions. Moreover, it is likely to increase under future environments, due to the higher photosynthate availability, as a consequence of the higher growth rate under elevated CO(2). However, as described in the literature, photosynthesis performance is frequently down-regulated (acclimated) under long-term exposure to CO(2), especially when affected by stressful temperature and water availability conditions. As growth responses to elevated CO(2) are dependent on sink-source status, it is generally accepted that down-regulation occurs in situations with insufficient plant C sink capacity. Alfalfa management involves the cutting of shoots, which alters the source-sink relationship and thus the photosynthetic behaviour. As the growth rate decreases at the end of the pre-cut vegetative growth period, nodulated alfalfa plants show photosynthetic down-regulation, but during regrowth following defoliation, acclimation to elevated CO(2) disappears. The shoot harvest also leads to a drop in mineral N uptake and C translocation to the roots, resulting in a reduction in N(2) fixation due to the dependence on photosynthate supply to support nodule function. Therefore, the production of new shoots during the first days following cutting requires the utilization of reduced C and N compounds that have been stored previously in reserve organs. The stored reserves are mediated by phytohormones such as methyl jasmonate and abscisic acid and in situations where water stress reduces shoot production this potentially enables the enhancement of taproot protein levels in nodulated alfalfa, which may lead to these plants being in better condition in the following cut/regrowth cycle. Furthering our knowledge of legume performance under predicted climate change conditions will be crucial for the development of varieties with better adaptation that will achieve greater and more efficient production values. Furthermore, for this purpose it will be necessary to improve existing methodologies and create new ones for phenotype characterization. Such knowledge will provide key information for future plant breeding programs.

Water Relations and Gas Exchange in Alfalfa Leaves under Drought Conditions in Southern Tunisian Oases

“…This change is considered a key factor determining plant productivity under limited water supply [35], and it is mentioned as an adaptive response and a strategy to improve crop performance under limited water conditions [14]. In accordance with our results, many studies have found that WUE p increased with increasing water stress in alfalfa plants [36]. This change keeps being controversial, because improving WUE may confl ict with the high growth rate for many species [37].…”

Nutrient solution composition and growing season affect yield and chemical composition of Cichorium spinosum plants

“…Similar results have been reported by Wang et al (2009) who also observed an increase in dry weight of spinach plants when nitrogen: ammonium nitrogen changed from 1:0 to 0:1, while Szalai et al (2010) have also reported an increase of stem dry matter in purslane when ammonium was the sole nitrogen source. Additionally, uncut plants (H3 treatment) had higher dry weight than cut plants in almost every treatment (apart from treatment F4), which could be attributed to the consumption of more carbohydrate reserves for regrowth, comparing to the uncut plants (Erice et al, 2011; Table 2). …”

Factors Affecting Growth of Perennial Wall Rocket and Annual Garden Rocket

“…Higher leaf dry weights were achieved for the second harvest crop for all cultivars, meaning that differences in plant growth occur between harvests (Figure 1). The higher leaf dry weights for the second harvest crop may have been influenced by the ability of this species to store and utilize carbohydrate reserves in the tap root (Bewley, 2002;Cry et al, 1990;Erice et al, 2011). The perennial nature of the plant indicates that it is adapted to produce new vegetative growth once conditions become favorable.…”