Growth Analysis of Potted Seedlings of Satsuma Mandarin (<i>Citrus unshiu</i> Marc.) under Different Light Conditions and Air Temperatures

Abstract

To establish cultural practice based on a consecutive growth model for potted 1-year-old seedlings of Satsuma mandarin (Citrus unshiu Marc.), growth analysis by classical and functional approaches was conducted under different light conditions and air temperatures over 2.5 years, and the active growth of potted seedlings in the greenhouse was investigated. Under the classical approach, the general change patterns of relative growth rate (RGR) and net assimilation rate (NAR) were hard to determine because of irregularities including quiescence of vegetative growth. Under the functional approach, plant mass modeled using linear, exponential, power-law, monomolecular, three-parameter logistic, four-parameter logistic (4L), and Gompertz functions showed significant correlations with the observed plant mass. 4L was the best model because it showed the highest r, and the lowest root mean square error and Akaike Information Criterion, so RGR and NAR were estimated by 4L. Analysis of the RGR components showed significant positive correlations between RGR and NAR. Analysis of covariance indicated the NAR costs for increasing RGR were lower in the greenhouse than in open culture; this was explained by differences in specific leaf area (SLA). Therefore, in greenhouse culture, growth was primarily enhanced by NAR as net photosynthesis and underpinned by SLA as a morphological trait improvement for the relatively low light intensity compared with open culture. A multiple regression model for NAR using the pooled data (n = 60) suggested solar radiation had a positive effect (P < 0.0001) and air temperature had a negative effect (P < 0.01) on NAR.

A Generalized Linear Model to Predict the Growth of Potted Seedlings of Satsuma Mandarin (<i>Citrus unshiu</i> Marcow.) under Different Initial Plant Conditions, Environmental Conditions, and Pot Size

“…In addition, NAR is difficult to measure because it requires the dry mass of the tree, including the roots. In the latter relationship, ΣR S was already excluded by the stepwise AIC, and SLA has been shown to be a suitable and precise parameter representing light conditions (Yano et al, 2018). Therefore, three of the short models [Model 2, consisting of Model 1 without NAR; Model 3, consisting of Model 1 without NAR and SLA; and Model 4, consisting of Model 1 without NAR and LMR] were not the best models, but would be useful for predicting growth because the models that included SLA and/or LMR as explanatory variables reduced the AIC as compared with Model 5 (Table 3).…”

“…Under equal pot-size conditions, a previous study indicated that the naturallog-transformed plant mass of Satsuma mandarin seedlings (m P ) fitted a 4-parameter logistic (4L) model on a tt basis (Yano et al, 2018). However, even under equal tt conditions, different environmental conditions (e.g.…”

“…Based on the results of many studies, including interspecific analysis of herbaceous and woody plants, RGR can be classified as SLA-dominant (Gibert et al, 2016;Lambers and Poorter, 1992;Poorter and Remkes, 1990;Rees et al, 2010;Reich et al, 1992Reich et al, , 1998Walters et al, 1993;Westoby, 1999, 2000) or NAR-dominant (Huante and Rincon, 1998;Huante et al, 1995;Poorter, 1999;Ryser and Wahl, 2001;Saverimuttu and Westoby, 1996;Shipley, 2006;Taub, 2002;Yano et al, 2018), while LMR barely contributes to RGR (Shipley, 2006).…”

“…We assumed that the m P of unpruned Satsuma mandarin seedlings would fit 4L functions as growth trajectories on a tt basis (Yano et al, 2018). In the fitting, the initial m P and tt for unpruned 2-year-old Satsuma mandarin seedlings were replaced as follows; tt in greenhouse was estimated by the initial linear relationship between m P (4.2-5.6) and tt (0-5,056 day·°C) of unpruned 1-year-old Satsuma mandarin seedlings (Fig.…”

“…In evaluating the effects of initial plant conditions (age and shoot pruning) on the growth process of potted Satsuma mandarin seedlings, it was assumed that the m P fitted a 4L model on a tt basis (Yano et al, 2018). Both in a greenhouse and an open field, the growth patterns of unpruned potted Satsuma mandarin seedlings, including both 1-year-old Satsuma mandarin seedlings (1y) and 2-year-old Satsuma mandarin seedlings (2y), followed this assumption ( the m P of shoot-pruned 2-year-old Satsuma mandarin seedlings (p2y) showed different growth trajectories, with trends below the 4L line estimated from the unpruned m P (Fig.…”