Barley shoot biomass responds strongly to N:P stoichiometry and intraspecific competition, whereas roots only alter their foraging

Abstract

1 Background and Aims Plants respond to various environmental stimuli, and root systems 2 are highly responsive to the availability and distribution of nutrients in the soil. Root system 3 responses to the limitation of either nitrogen (N) or phosphorus (P) are well documented, 4 but how the early root system responds to (co-) limitation of one (N or P) or both (N and 5 P) in a stoichiometric framework is not well known despite its relevance in agriculture. In 6 addition, how plant-plant competition (here intra-specific) alters plant responses to N:P 7 stoichiometry is understudied. Therefore, we aimed to investigate the effects of N:P 8 stoichiometry and competition on root system responses and overall plant performance. 9  Methods Plants (Hordeum vulgare L.) were grown in rhizoboxes for 24 days in the 10 presence or absence of competition (three vs. one plant per rhizobox), and fertilized with 11 different combinations of N:P (low N+low P, low N+high P, high N+low P, and high 12 N+high P). 13 Key Results Shoot biomass was highest when both N and P were provided in high 14 amounts. In competition, shoot biomass decreased on average by 22%. Interestingly, N:P 15 stoichiometry and competition had no clear effect on root biomass. However, we found 16 distinct root responses in relation to biomass allocation across depths. Specific root length 17 depended on the identity of limiting nutrient (N or P) and presence/absence of competition. 18 Plants rooted deeper when N was the most limiting compared to shallower rooting when P 19 was the most limiting nutrient. 20  Conclusions Overall, our study sheds light on the early plant responses to plant-plant 21 competition and stoichiometric availability of two macronutrients most limiting plant 22 performance. With low N and P availability during early growth, higher investments in 23 root system development can significantly trade off with aboveground productivity, and 24 strong intra-specific competition can further strengthen such effects. 25 Keywords: Root system responses, vertical root distribution, specific root length, nutrient 26 stoichiometry, intraspecific competition 27

Plant intraspecific competition and growth stage alter carbon and nitrogen mineralization in the rhizosphere

“…In view of the root economics spectrum (Ma et al, 2018; Valverde‐Barrantes et al, 2015), the decrease in root diameter may increase the efficiency of root growth and thus enhance root length to explore temporal and spatial available resources (Kuzyakov & Xu, 2013; Ma et al, 2018; Wen, Li, Shen, & Rengel, 2017). Accordingly, specific root length increased with belowground intraspecific competition (RCI of roots) and increasing planting densities (Figure S2b), which is in agreement with previous studies (Kumar et al, 2020; Li et al, 2019). Furthermore, soil C and N turnover were modulated by root morphological traits at higher planting densities, since both SOM‐C and N mineralization increased with specific root length for the double and triple densities (Figure 4).…”

Timing matters: Distinct effects of nitrogen and phosphorus fertilizer application timing on root system architecture responses

“…Root hairs are known to be essential for acquiring P because P is highly immobile in the soil due to adsorption and precipitation, and uptake by bulk flow and diffusion is very low (Gahoonia et al, 1997; Haling et al, 2013). By altering N and P availability in a stoichiometric manner, Kumar et al (2020) showed that barley had greater proportion of root biomass in deeper soil layers when N was the limiting nutrient and the reverse root response was true for P limitation. In our study, we found no effect of N and P fertilization timing on RMF.…”

“…Furthermore, morphological and root system architecture (RSA) responses, such as an increase in lateral root length over the amount of laterals, increase in lateral root elongation steeper and angle of laterals, and an increase in root hair length/density are all common plant responses as a mean to increase P uptake when it is limiting (Haling et al, 2013; Linkohr et al, 2002). In contrast to P‐limited plants, N‐limited plants tend to invest more roots in deeper layers because N (especially in the form of NO 3 − ions) is more mobile in soil than P, and they achieve this by changing root growth angles—a root architectural response (Kumar et al, 2020; Trachsel et al, 2013). Consequently, breeding for these specific adaptations in crops could prove advantageous for productivity in N‐ and P‐deficient soils (Lynch, 2011, 2013).…”

Assembly history modulates vertical root distribution in a grassland experiment

“…Instead, we believe that plastic and species-specific root responses to plant order of arrival are more likely to explain why grasses-first communities rooted more shallowly than the others did. Such plastic root responses affecting root allocation and foraging have been well documented in the past (Mahall and Callaway, 1991;Semchenko et al, 2007;Mommer et al, 2012;Kumar et al, 2020;Lepik et al, 2021) but, to date, there has been little evidence that the order of arrival of plants can affect the root distribution of individual species (Weidlich et al, 2018a). Studying the extent to which the behaviour of the roots of species inhabiting plant communities changes as a function of the order of arrival of plants, as well as studying how these plastic root responses would be reflected at the community level, requires information on the distribution of roots at the species level, which unfortunately was not available in our study.…”