Nitrogen:phosphorous supply ratio and allometry in five alpine plant species

Abstract

In terrestrial ecosystems, atmospheric nitrogen (N) deposition has greatly increased N availability relative to other elements, particularly phosphorus (P). Alterations in the availability of N relative to P can affect plant growth rate and functional traits, as well as resource allocation to above‐ versus belowground biomass (M A and M B). Biomass allocation among individual plants is broadly size‐dependent, and this can often be described as an allometric relationship between M A and M B, as represented by the equation MnormalA=αMBnormalβ, or log M A = logα + βlog M B. Here, we investigated whether the scaling exponent or regression slope may be affected by the N:P supply ratio. We hypothesized that the regression slope between M A and M B should be steeper under a high N:P supply ratio due to P limitation, and shallower under a low N:P supply ratio due to N limitation. To test these hypotheses, we experimentally altered the levels of N, P, and the N:P supply ratio (from 1.7:1 to 135:1) provided to five alpine species representing two functional groups (grasses and composite forbs) under greenhouse conditions; we then measured the effects of these treatments on plant morphology and tissue content (SLA, leaf area, and leaf and root N/P concentrations) and on the scaling relationship between M A and M B. Unbalanced N:P supply ratios generally negatively affected plant biomass, leaf area, and tissue nutrient concentration in both grasses and composite forbs. High N:P ratios increased tissue N:P ratios in both functional groups, but more in the two composite forbs than in the grasses. The positive regression slopes between log M A and log M B exhibited by plants raised under a N:P supply ratio of 135:1 were significantly steeper than those observed under the N:P ratio of 1.7:1 and 15:1. Synthesis: Plant biomass allocation is highly plastic in response to variation in the N:P supply ratio. Studies of resource allocation of individual plants should focus on the effects of nutrient ratios as well as the availability of individual elements. The two forb species were more sensitive than grasses to unbalanced N:P supplies. To evaluate the adaptive significance of this plasticity, the effects of unbalanced N:P supply ratio on individual lifetime fitness must be measured.

N:P stoichiometric changes via species turnover in arid versus saline desert environments

“…leaves with low leaf N and P concentrations compared with species grown in high fertility soils (Jager et al, 2015). However, our findings are inconsistent with the studies reporting higher plant nutrient concentrations with increasing aridity in grassland systems (Luo et al, 2016(Luo et al, , 2018Sandel et al, 2010). For grassland ecosystems, plant community assembly tends to select species with higher nutrient concentrations to increase their competitive advantage under persistent water stress (Li et al, 2017;Luo et al, 2018;Sardans & Penuelas, 2012).…”

Nitrogen–phosphorus interplay: old story with molecular tale

“…Nitrogen (N) and phosphorus (P) are the two most abundant mineral nutrients for plants, and their coordinated acquisition is vital for plants to achieve nutritional balance and optimal growth under a fluctuating nutritional environment (G€ usewell, 2004;Khan et al, 2014;Luo et al, 2016). Nitrogen (N) and phosphorus (P) are the two most abundant mineral nutrients for plants, and their coordinated acquisition is vital for plants to achieve nutritional balance and optimal growth under a fluctuating nutritional environment (G€ usewell, 2004;Khan et al, 2014;Luo et al, 2016).…”

“…Different mineral elements need to be maintained at relatively stable ratios in plants in order for the development of biological structures or functional macromolecules. Nitrogen (N) and phosphorus (P) are the two most abundant mineral nutrients for plants, and their coordinated acquisition is vital for plants to achieve nutritional balance and optimal growth under a fluctuating nutritional environment (G€ usewell, 2004;Khan et al, 2014;Luo et al, 2016). The uptake of N or P affect each other, indicating the strategy that has evolved for maintaining N-P nutritional balance in plants (G€ usewell, 2005).…”

Effects of body size and root to shoot ratio on foliar nutrient resorption efficiency in Amaranthus mangostanus

“…Plants acquire nutrients mainly from two sources: soil and senescent organs; both acquisition modes are energy consumptive processes. The R/S ratio is closely related to plant nutrient conditions (Marschner, ) and highly plastic in response to changes in nutrient conditions (Ericsson, ; Luo et al., ). Plants can allocate disproportionally more photosynthates to roots to increase nutrient acquisition under some stress conditions (Ericsson, ; Lambers et al., ; Reef et al., ) and vice versa.…”